Journal articles on the topic 'Late cambrian depositional environment'
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Maslov, A. V., D. V. Grazhdankin, and V. N. Podkovyrov. "Late Vendian kotlinian crisis on the East European Platform: lithogeochemical indicators of depositional environment." Литология и полезные ископаемые 1, no. 1 (February 16, 2019): 2–30. http://dx.doi.org/10.31857/s0024-497x201912-30.
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Sharp changes in the biodiversity of fossil organisms in the Upper Vendian of the East European Platform are considered as the manifestation of global crisis immediately prior to the “Cambrian Explosion.” However, they could be caused by local environmental perturbations. Variations of some lithogeochemical indicators of depositional environment (indicators of paleoclimate, exhalation activity, redox settings, and paleobioproductivity) were analyzed in order to establish the possible influence of sedimentary systems on evolutionary processes in the Late Vendian and at the boundary with the Cambrian. The applied algorithm of lithogeochemical studies revealed no significant perturbations in physical properties of the environment on a scale of sedimentary basins. The obtained data suggest that local factors did not affect the evolution of Ediacaran biota on the East European Platform and confirm the global nature of transitions between the Redkinian, Belomorian, and Kotlinian biotas.
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Huang, Jing, Yali Chen, Xuelei Chu, and Tao Sun. "The geochemistry of the late Cambrian carbonate in North China: the Steptoean Positive Carbon Isotope Excursion (SPICE) record suppressed in a coastal condition?" Geological Magazine 156, no. 10 (March 8, 2019): 1805–19. http://dx.doi.org/10.1017/s0016756819000025.
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AbstractThe Steptoean Positive Carbon Isotope Excursion (SPICE) is globally distributed in late Cambrian sedimentary records but controversially heterogeneous in its magnitudes. Here we use multiple geochemical proxies to investigate the late Cambrian carbonates from the Tangwangzhai section in North China, which were deposited in a shallow coastal environment with three depositional sequences (S1–S3). Each sequence comprises a transgressive systems tract (TST) and a highstand systems tract (HST). The REE + Y and trace element records are consistent with the depositional condition and indicate that terrigenous influence was more significant in the TST than HST. δ13Ccarb and δ34SCAS are low in the TST relative to HST, consistent with the scenario that terrigenous inputs were profoundly aggressive to seawater by introducing 13C-depleted and 34S-depleted materials. Within the TST of S2, the SPICE excursion shows a scaled-down δ13Ccarb positive shift (∼1.7 ‰) relative to its general records (∼4–6 ‰); the corresponding δ34SCAS show no positive excursion. This ‘atypical’ SPICE record is attributed to enhanced 13C-depleted and 34S-depleted terrigenous influence during the TST, which would reduce the amplitude of δ13Ccarb excursion, and even obscure δ34SCAS excursion. Meanwhile the subaerial unconformity at the base of TST would also cause a partially missing and a ‘snapshot’ preservation. Our study confirms significant local influence to the SPICE records, and further supports the heterogeneity and low sulphate concentrations of the late Cambrian seawater, because of which the SPICE records may be vulnerable to specific depositional conditions (e.g. sea-level, terrigenous input).
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Curtis, Michael L., and Simon A. Lomas. "Late Cambrian stratigraphy of the Heritage Range, Ellsworth Mountains: implications for basin evolution." Antarctic Science 11, no. 1 (March 1999): 63–77. http://dx.doi.org/10.1017/s0954102099000103.
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Deposition of the Upper Cambrian succession of the Ellsworth Mountains was influenced by major, episodic tectonically-driven changes to the depositional basin geometry. We subdivide the succession into four stratigraphical sequences based on the recognition of three sequence-bounding unconformities. The upper part of Sequence 1 is composed of the laterally equivalent Liberty Hills, Springer Peak and Frazier Ridge formations, a siliciclastic fluvial to marine deltaic association displaying NW-directed palaeocurrents. A switch in the position of the Late Cambrian depocentre from the north-west to the south coincided with cessation of terrigenous clastic deposition and accumulation of Sequence 2, the limestones of the Minaret Formation. Previously unreported talus breccias from the Independence Hills provide important clues to basin configuration at this time. A brief period of emergence of the Minaret Formation is inferred, prior to rapid subsidence and disconformable deposition of Sequence 3 (the ‘transition beds’) in outer-inner shelf environments. Localized intra-basinal uplift occurred prior to the deposition of Sequence 4 (the lower Crashsite Group), the base of which is locally an erosive unconformity, with a correlative conformity exposed elsewhere. We interpret the Upper Cambrian succession as representing the ‘rift-drift’ transition from initial rifting (preceded by Middle Cambrian volcanism) to thermal subsidence along the South African sector of the palaeo-Pacific margin of Gondwana.
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Surlyk, F., and J. R. Ineson. "Aspects of Franklinian shelf, slope and trough evolution and stratigraphy in North Greenland." Rapport Grønlands Geologiske Undersøgelse 133 (December 31, 1987): 41–58. http://dx.doi.org/10.34194/rapggu.v133.7974.
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The Early Palaeozoic Franklinian basin of North Greenland was initiated in early Cambrian times with the onset of siliciclastic and mixed carbonate shelf deposition on a substratum of Proterozoic sediments and Precambrian crystalline basement. The basin rapidly differentiated into shelf, slope, and trough environments. The boundary between these major depositional regimes follows major roughly east-west trending lineaments. The inner-outer shelf transition fluetuated widely in position and was controlled by the interplay between sea-level changes and periodic northwards downwarping. In Ordovician-Silurian times the margin of the carbonate platform migrated northwards to coincide with the shelf-slope break and had a steep scarp configuration with an abrupt transition to the shales and turbidites of the deep-water basin. In this paper we pay special attention to the initial basin sequence (Skagen Group), the collapsed and broken platform carbonates of the Lower Cambrian Portfjeld Formation, the Middle - Late Cambrian inner-outer shelf transition and to the nature of the Silurian platform margin scarp.
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Fahad Al-Ajmi, Hussain, Martin Keller, Matthias Hinderer, and Claudio Miro Filomena. "Lithofacies, depositional environments and stratigraphic architecture of the Wajid Group outcrops in southern Saudi Arabia." GeoArabia 20, no. 1 (January 1, 2015): 49–94. http://dx.doi.org/10.2113/geoarabia200149.
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ABSTRACT The Wajid Group is a Palaeozoic siliciclastic succession of southern Saudi Arabia. In the outcrop belt it is ca. 500 m thick, whereas in the subsurface, the thickness increases to more than 4,500 m. The siliciclastic sediments have great reservoir potential for hydrocarbons and for groundwater. Although they represent one of the most important aquifers of the Arabian Peninsula, neither their sedimentologic, lithostratigraphic, nor their reservoir characteristics are satisfactorily known. In this study, a detailed description of lithology and sedimentology is given and the Wajid Group sediments are interpreted in terms of depositional environment and facies architecture. Thirteen lithofacies (LF 1 to LF 13) have been recognised, most of them composed of different subfacies. These lithofacies are grouped into 9 lithofacies associations (LF-A1 through LF-A9). LF-A1 through LF-A3 and LF-A7 represent shallow-marine siliciclastic environments. The remaining lithofacies associations describe periglacial environments of the Hirnantian (Late Ordovician) and Permian Gondwana glaciations. Except for a few pro-glacial fluvial deposits, fluvial successions and aeolian sediments are absent in the outcrops of the Wajid Sandstone. Five formations are recognised in the Wajid Group: the Dibsiyah, Sanamah, Qalibah, Khusayyayn, and Juwayl formations. They are all separated by major unconformities. The Dibsiyah Formation represents a vast sand-sheet complex with core and margin facies formed under shallow-marine conditions. These marine conditions enabled an abundant fauna to proliferate and leave its traces in the form of Skolithos piperock and Cruziana sp. A late Cambrian to Early Ordovician age is inferred for these deposits from regional considerations. The Sanamah Formation records the Late Ordovician Hirnantian glaciation with coarse sandstones and conglomerates. A variety of glacier-induced sedimentary structures are present. The internal succession is composed of three major sediment packages reflecting three ice advance-retreat cycles. The latest of these cycles is overlain by a few metres of marginal-marine sediments of the Qalibah Formation. The Khusayyayn Formation was deposited probably during Early Devonian times. It also represents a sand-sheet environment characterised by the dominance of mega-scale and giant cross beds and bed sets. A marine depositional environment is assumed from scarce Skolithos sp., and because nearly all indicators of a braided river system are absent. The Juwayl Formation of Permian age was deposited at the interface of the Late Palaeozoic Gondwana ice shield with a large lake that may have covered most of southern Arabia and adjacent areas. Proglacial sandstones and conglomerates were deposited close to the glaciers, whereas fine-grained sediment with dropstones, boulder pavements and a wide spectrum of soft-sediment deformation are characteristic of the lake environment. While the two glacial successions and the Khusayyayn Formation can rather confidently be attributed to the geological time scale, either through seismic correlation or biostratigraphically, the Dibsiyah Formation has not yet been biostratigraphically well dated.
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GEYER, G. "The Fish River Subgroup in Namibia: stratigraphy, depositional environments and the Proterozoic–Cambrian boundary problem revisited." Geological Magazine 142, no. 5 (September 2005): 465–98. http://dx.doi.org/10.1017/s0016756805000956.
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The Fish River Subgroup of the Nama Group, southern Namibia, is restudied in terms of lithostratigraphy and depositional environment. The study is based on partly fine-scaled sections, particularly of the Nababis and Gross Aub Formation. The results are generally in accordance with earlier studies. However, braided river deposits appear to be less widely distributed in the studied area, and a considerable part of the formations of the middle and upper subgroup apparently were deposited under shallowest marine conditions including upper shore-face. Evidence comes partly from sedimentary features and facies distribution, and partly from trace fossils, particularly Skolithos and the characteristic Trichophycus pedum. Environmental conditions represented by layers with T. pedum suggest that the producer favoured shallow marine habitats and transgressive regimes. The successions represent two deepening-upward sequences, both starting as fluvial (braided river) systems and ending as shallow marine tidally dominated environments. The first sequence includes the traditional Stockdale, Breckhorn and lower Nababis formations (Zamnarib Member). The second sequence includes the upper Nababis (Haribes Member) and Gross Aub formations. As a result, the Nababis and Gross Aub formations require emendation: a new formation including the Haribes and Rosenhof and possibly also the Deurstamp members. In addition, four distinct sequence stratigraphic units are deter-minable for the Fish River Subgroup in the southern part of the basin. The Proterozoic–Cambrian transition in southern Namibia is most probably located as low as the middle Schwarzrand Subgroup. The environmentally controlled occurrence of Trichophycus pedum undermines the local stratigraphic significance of this trace fossil which is eponymous with the lowest Cambrian and Phanerozoic trace fossil assemblage on a global scale. However, occurrences of such trace fossils have to be regarded as positive evidence for Phanerozoic age regardless of co-occurring body fossils. Other suggestions strongly dispute the concept of the formal Proterozoic–Cambrian and Precambrian–Phanerozoic boundary. Carbon isotope excursions and radiometric datings for the Nama Group do not help to calibrate precisely the temporal extent of the Fish River Subgroup. Fossil content, sequence stratigraphy and inferred depositional developments suggest that this subgroup represents only a short period of late orogenic molasse sedimentation during the early sub-trilobitic Early Cambrian.
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Strauss, Harald, Stefan Bengtson, Paul M. Myrow, and Gonzalo Vidal. "Stable isotope geochemistry and palynology of the late Precambrian to Early Cambrian sequence in Newfoundland." Canadian Journal of Earth Sciences 29, no. 8 (August 1, 1992): 1662–73. http://dx.doi.org/10.1139/e92-131.
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A sequence of clastic sediments in southeastern Newfoundland straddling the Precambrian–Cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid-resistant organic-walled microfossils. A detailed study of the Chapel Island Formation, which includes the boundary interval, has revealed fluctuations in the isotopic composition of organic carbon. These are largely interpreted as caused by differences in the depositional environments. Highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite-forming process, sometimes under sulfate-limited conditions. Palynological results are quite limited with respect to diagnostic microfossils.
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Post, Ryan T., and Darrel G. F. Long. "The Middle Cambrian Mount Roosevelt Formation (new) of northeastern British Columbia: evidence for rifting and development of the Kechika Graben System." Canadian Journal of Earth Sciences 45, no. 4 (April 2008): 483–98. http://dx.doi.org/10.1139/e08-014.
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The eastern margin of the Kechika Graben in the vicinity of Muncho and Moose lakes, northeastern British Columbia, contains Middle Cambrian rift-related strata herein named the Mount Roosevelt Formation. The formation conformably overlies a quartzite package equivalent to the uppermost clastic unit of the informal late Early Cambrian Gataga group ( Bonnia – Olenellus zone) and is conformably overlain by a thick, unnamed carbonate sequence of Middle Cambrian age ( Plagiura – Poliella zone). The Mount Roosevelt Formation is subdivided into three members. The lowermost member is characterized by oöid-bearing siltstone and sandstone, interbedded with dolostone, limestone, and hematitic conglomerate. Conformably above this, the middle member is a thick sequence of polymict cobbly pebble conglomerate. The upper member includes karstified dolostone, calcareous-cemented conglomerate and sandstone, and limestone. Collectively the Mount Roosevelt Formation reflects alluvial fan delta progradation into a transgressive marine environment. Deposition occurred in an active fault-controlled basin, located on the eastern margin of the Kechika Graben adjacent to the Muskwa High. Basin initiation in the late Early Cambrian coincided with the reactivation of pre-existing regional faults. High rates of subsidence during the initial phase of extension were accommodated on these faults, which provided a locus for fan delta deposition. Continuing high rates of subsidence limited basinward fan delta development. Deposition of the formation ended with base-level transgression in the early Middle Cambrian that drowned the fan deltas and the adjacent Muskwa High and allowed development of the Kechika Trough above the older graben system.
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Ji, Tianyu, Wei Yang, Renhai Pu, and Xueqiong Wu. "Research on the lithofacies and paleogeography of the lower Cambrian Xiaoerbulake Formation in the northern Tarim Basin, northwestern China." Canadian Journal of Earth Sciences 57, no. 12 (December 2020): 1463–77. http://dx.doi.org/10.1139/cjes-2019-0214.
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Based on the study of cores, thin sections, and outcrops, the sedimentary facies of the lower Cambrian carbonate rocks in the northern Tarim Basin can be divided into four types: restricted platform, open platform, ramp, and basin. Based on the lithologic analysis of thin sections, two-dimensional seismic data interpretation, and an isopach map of the lower Cambrian Xiaoerbulake Formation in the study area, seven sedimentary facies of carbonate rocks were identified, including inner platform depression, shoal, intershoal sea, platform margin, gypsum salt lake, ramp, and basin. The depositional model of the lower Cambrian Xiaoerbulake Formation in the northern Tarim Basin is constructed based on this integrated research. The topset, foreset, and bottomset of oblique progradational reflections are interpreted as the platform margin beach, ramp, and basin environments, respectively. The thicker area with micritic dolomite as the dominant lithology is interpreted as a platform depression. The low-amplitude hummocky reflections are interpreted as shoals that consist of a variety of granular dolomite and algal dolomite. The thinner uplifted area with gypsum and dolomite present in cores is interpreted as a restricted platform with a gypsiferous dolomite tidal flat or lake environment. Well LT1, which was drilled recently in the platform margin and ramp region, as indicated by seismic progradational clinoform reflections, has produced high yields of oil and gas. Supported by the above research results, the map of the lithofacies and paleogeography of the Xiaoerbulake Formation in the northern Tarim Basin was recompiled.
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Li, Xing, and Mary Droser. "The development of Early Paleozoic shell concentrations: evidence from the Cambrian and Ordovician of the Great Basin." Paleontological Society Special Publications 6 (1992): 183. http://dx.doi.org/10.1017/s2475262200007437.
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Shell concentrations have constituted an important and conspicuous part of the stratigraphic record since the Early Cambrian. The paleontological and stratigraphic significance of shell beds is well understood, primarily from Mesozoic and Cenozoic examples. Lower Paleozoic fossil concentrations, however, have not received much attention. The Cambrian and Ordovician evolutionary radiations were two of the most significant events in the history of life and established the Cambrian and Paleozoic faunas respectively. In order to determine the effect of these radiations on the development of fossil accumulations, a systematic study of early Paleozoic shell beds was conducted in the Great Basin areas of California, Nevada, and Utah.In order to minimize taphonomic variations in original chemical and physical conditions, shell beds were compared from strata deposited in similar depositional environments from similar tectonic settings. Preliminary analysis of the shell beds from relatively pure carbonate facies and mixed carbonate and siliciclastic facies shows: 1) that shell concentrations became a significant stratigraphic feature in the later Early Cambrian; 2) the thickness and lateral extent of the shell beds increase from Early Cambrian to Middle Ordovician; 3) the abundance and internal complexity of the shell beds increase from Early Cambrian to Middle Ordovician; and 4) the Cambrian and Early Ordovician shell beds are primarily, if not exclusively, dominated by trilobites whereas the Middle Ordovician shell beds are dominated by brachiopods and ostracodes.These data show a temporal trend in the development of the early Paleozoic shell beds. The nature of the Cambrian and Ordovician shell beds differs qualitatively and quantitatively. There is an increase in physical scale, abundance, and internal complexity through time. The thickness and abundance of the trilobite beds increase through the Cambrian. Interestingly, although trilobites were still diverse and abundant, they did not commonly generate thick trilobite beds after the Late Cambrian. The early Middle Ordovician is a critical time in the development of early Paleozoic shell beds. A variety of monotaxic and polytaxic shell beds, including 6m thick composite beds, first appeared at this time. While the brachiopods and ostracodes generate laterally extensive, commonly monotaxic, shell beds, the gastropods and bryozoans only formed lenticular concentrations.
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Pedersen, Gunver Krarup,. "The sedimentology of Lower Palaeozoic black shales from the shallow wells Skelbro 1 and Billegrav 1, Bomholm, Denmark." Bulletin of the Geological Society of Denmark 37 (April 10, 1989): 151–73. http://dx.doi.org/10.37570/bgsd-1988-37-13.
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Previous studies of the Lower Palaeozoic shales on Bornholm have mainly been based on the outcrops along the streams. The outcrops provide data on the lateral continuity of the facies while the selection of (2-3 cm wide) cores for the present study focused the attention on the vertical sequence of facies. Cores of high quality were obtained and have been found to provide an excellent basis for a study of structures, sediment composition and diagenesis. In the outcrops of shale fossils are locally present in high numbers and such levels are also recognized in the cores. Seven sedimentary facies, ranging from black mudshale to greyish mudstone and silt-streaked shale, are distinguished in the Middle Cambrian to lowermost Silurian shales. Gamma-ray logs were run in the two wells and a convincing correlation to the cored sequence can be demonstrated. Gamma-ray logs provide thus a good means of correlation to wells where no cores have been cut. The shales are all interpreted as deposited in an epicontinental sea due to their geological setting i.e. the association with shallow water carbonates (Andrarum Limestone and Komstad Limestone) and their stratigraphical position above the shelf to shoreface sandstones of the Lresa formation. Three facies associations are distinguished: The mudshale association comprises black organic-rich shales which represent a low-energy anoxic depositional environment which prevailed in the Middle Cambrian to Lower Ordovician. The mudstone association is typical of the Middle and Upper Ordovician and represents a continuation of low-energy environments though mottling indicates that ventilation improved in certain periods. The siltshale association represents higher energy environments which were dominant in the lowermost Silurian. A well defined Upper Ordovician CU sequence probably reflects the global eustatic fall in sea level caused by the extensive glaciation in Gondwanaland. In the late Silurian the average rate of deposition increased in response to the approaching Caledonian orogeny.
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Landing, Ed, Gerd Geyer, and Kenneth E. Bartowski. "Latest Early Cambrian small shelly fossils, trilobites, and Hatch Hill dysaerobic interval on the Québec continental slope." Journal of Paleontology 76, no. 2 (March 2002): 287–305. http://dx.doi.org/10.1017/s0022336000041718.
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Latest Early Cambrian continental slope deposition of the early Hatch Hill dysaerobic interval (new name, latest Early Cambrian—earliest Ordovician) is recorded by dark grey shales and turbidite limestones in the Bacchus slice at Ville Guay, Québec. Platform-derived microfaunas of the Bicella bicensis trilobite assemblage were transported into a dysoxic environment of the upper “Anse Maranda Formation,” and many organisms were buried alive. Phosphatization preserved a diverse skeletal fossil assemblage that includes four agnostid trilobites, echinoderm debris, and twenty small shelly fossil taxa. The latter include five helcionellids; Pelagiella Matthew, 1895b, classified herein as a gastropod; a bivalve (Fordilla Barrande, 1881); the brachiopod Linnarssonia taconica Walcott, 1887; two conodontomorphs; four hyoliths; and such phosphatic and calcareous problematica as Coleoloides Walcott, 1889, emend. Most small shelly fossil taxa, including Discinella micans Billings, 1872, range through much of the Olenellus Zone and Elliptocephala asaphoides assemblage interval. Trilobites allow a more resolved correlation into the uppermost Olenellus Zone. A comparable stratigraphy occurs in Cambrian—Ordovician slope facies of the Bacchus slice and the Giddings Brook slice in eastern New York. The “Anse Maranda Formation” correlates with the West Granville—Browns Pond—lower Hatch Hill formations in eastern New York and brackets two dysaerobic intervals (Browns Pond and early Hatch Hill). Sea-level change associated with the Hawke Bay regression between the Browns Pond and Hatch Hill onlap/dysaerobic intervals led to the longest period of oxygenated green shale and sandstone deposition on the east Laurentian slope in the late Early Cambrian-earliest Ordovician.
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HUGHES, NIGEL C., PAUL M. MYROW, N. RYAN MCKENZIE, D. A. T. HARPER, O. N. BHARGAVA, S. K. TANGRI, K. S. GHALLEY, and C. M. FANNING. "Cambrian rocks and faunas of the Wachi La, Black Mountains, Bhutan." Geological Magazine 148, no. 3 (September 14, 2010): 351–79. http://dx.doi.org/10.1017/s0016756810000750.
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AbstractThe Pele La Group in the Wachi La section in the Black Mountains of central Bhutan represents the easternmost exposure of Cambrian strata known in the Himalaya. The group contains a succession of siliciclastic rocks with minor amounts of carbonate, the uppermost unit of which, the Quartzite Formation, bears age-diagnostic trilobite body fossils that are approximately 493 Ma old. Trilobite species includeKaolishania granulosa, Taipaikia glabraand the new speciesLingyuanaspis sangae.A billingsellid brachiopod,Billingsellacf.tonkiniana, is co-occurrent. This fauna is precisely correlated with that of a specific stratigraphic horizon within the upper part of theKaolishaniaZone, Stage 9 of the Cambrian System, Furongian Epoch of the North China block, and thus represents the youngest Cambrian sedimentary rocks yet known from the Himalaya. The faunal similarity suggests proximity between North China and the Himalayan margin at this time. This unit was deposited in a predominantly storm-influenced shelf and shoreface environment. U–Pb geochronological data from detrital zircon grains from the fossil-bearing beds of the Quartzite Formation and strata of the underlying Deshichiling Formation show grain age spectra consistent with those from Cambrian rocks of the Lesser and Tethyan Himalaya in Tibet, India and Pakistan. These data support continuity of the northern Gondwanan margin across the Himalaya. Prominent peaks of approximately 500 Ma zircons in both the Quartzite and Deshichiling formations are consistent with the Furongian (late Cambrian) age assignment for these strata. The presence of these relatively young zircon populations implies rapid post-cooling erosion of igneous bodies and subsequent deposition which may reflect the influence of a widespread Cambro-Ordovician orogenic event evident in the western Himalaya.
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Algeo, T. J., G. M. Luo, H. Y. Song, T. W. Lyons, and D. E. Canfield. "Reconstruction of secular variation in seawater sulfate concentrations." Biogeosciences 12, no. 7 (April 10, 2015): 2131–51. http://dx.doi.org/10.5194/bg-12-2131-2015.
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Abstract. Long-term secular variation in seawater sulfate concentrations ([SO42−]SW) is of interest owing to its relationship to the oxygenation history of Earth's surface environment. In this study, we develop two complementary approaches for quantification of sulfate concentrations in ancient seawater and test their application to late Neoproterozoic (635 Ma) to Recent marine units. The "rate method" is based on two measurable parameters of paleomarine systems: (1) the S-isotope fractionation associated with microbial sulfate reduction (MSR), as proxied by Δ34SCAS-PY, and (2) the maximum rate of change in seawater sulfate, as proxied by &partial; δ 34SCAS/∂ t(max). The "MSR-trend method" is based on the empirical relationship of Δ34SCAS-PY to aqueous sulfate concentrations in 81 modern depositional systems. For a given paleomarine system, the rate method yields an estimate of maximum possible [SO42−]SW (although results are dependent on assumptions regarding the pyrite burial flux, FPY), and the MSR-trend method yields an estimate of mean [SO42−]SW. An analysis of seawater sulfate concentrations since 635 Ma suggests that [SO42−]SW was low during the late Neoproterozoic (<5 mM), rose sharply across the Ediacaran–Cambrian boundary (~5–10 mM), and rose again during the Permian (~10–30 mM) to levels that have varied only slightly since 250 Ma. However, Phanerozoic seawater sulfate concentrations may have been drawn down to much lower levels (~1–4 mM) during short (
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VOLDMAN, GUSTAVO G., JUAN L. ALONSO, LUIS P. FERNÁNDEZ, ALDO L. BANCHIG, GUILLERMO L. ALBANESI, GLADYS ORTEGA, and RAÚL CARDÓ. "Cambrian–Ordovician conodonts from slump deposits of the Argentine Precordillera: new insights into its passive margin development." Geological Magazine 155, no. 1 (October 18, 2016): 85–97. http://dx.doi.org/10.1017/s0016756816000832.
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AbstractThe Los Sombreros Formation represents the western continental margin slope deposits of the Argentine Precordillera, a sub-terrane accreted to Gondwana as part of the Cuyania Terrane in early Palaeozoic times. The age of these gravity-driven deposits is controversial and, therefore, a precise biostratigraphic scheme is essential to reveal the evolution of the continental margin. New conodont samplings along with sedimentological and structural analysis carried out in the Los Sombreros Formation in the La Invernada Range provide clues to its depositional framework. The sedimentary succession is made up of dominantly calciturbidites, carbonate breccias and conglomerates, along with mudstones that represent the pelagic/hemipelagic background sedimentation. It displays hectometric to outcrop-scale slump folds with variable hinge-line orientations and pinch-and-swell structures, evidencing soft-sediment deformation, consistent with a slope to base-of-slope setting. Three limestone samples from this succession include conodonts referable to the pandemicHirsutodontus simplexSubzone of theCordylodus intermediusZone (upper Furongian, Cambrian) and from theMacerodus dianaeZone (upper Tremadocian, Ordovician), implying that a slope connected the shallow-water shelf with a deep-water (oceanic) basin at least since late Cambrian times. The conodont faunas show affinities to coeval assemblages from outer shelf and slope environments around Laurentia yet they are not conclusive to postulate a geographic origin for the Precordillera. The thermal alteration of the conodonts is consistent with sedimentary burial and nappe stacking in this sector of the Precordillera.
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Repetski, J. E., M. E. Taylor, D. S. Collins, A. R. Palmer, G. D. Wood, and R. C. Tobin. "Integrating paleontology, geothermometry, and sedimentology in determining the history of the Reelfoot Basin, southern midcontinent, U.S.A." Paleontological Society Special Publications 6 (1992): 243. http://dx.doi.org/10.1017/s2475262200008030.
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The northeast-trending Reelfoot basin, extending from northeast Arkansas and westernmost Tennessee into southeastern Missouri, southernmost Illinois, and westernmost Kentucky, is geologically, and socioeconomically, significant because it is co-extensive with the New Madrid Seismic Zone, one of the most seismically active areas of the central and eastern United States. The basin has been periodically active from its inception as a rift basin in the Proterozoic to the present and has accumulated up to at least 5,000 m of sediment, including up to at least 1 km of Cretaceous and Tertiary sedimentary strata near the head of the Mississippi Embayment. Structural and stratigraphic interpretations within the subsurface pre-Mesozoic part of the basin have been based almost entirely on geophysical and physical stratigraphic criteria; these interpretations have been loosely constrained due to an extreme sparsity of drillhole data through the Paleozoic sequence. Recent analysis of Cambrian and Ordovician fossils (conodonts, palynomorphs, brachiopods, and trilobites) from cuttings and core from a very few drillholes allows establishment of the beginnings of a verifiable stratigraphy for this part of the sequence. The paleontological data also provide (1) biofacies evidence for interpretations of the depositional setting during part of the Late Cambrian and Early Ordovician interval and (2) thermal maturation data pertaining to the post-depositional geothermal history of these strata.Upper Cambrian phosphatic brachiopods and trilobites provide improved correlations between strata in the basin, the Ozark shelf to the northwest, and the Upper Mississippi River Valley. Cold-water-realm palynomorphs and trilobites from siliciclastic rocks of turbiditic origin in the central part of the Reelfoot basin support an interpretation, based on sedimentary structures in a short interval of core, of a deep-water basinal origin for these strata.Lower Ordovician conodonts provide a biostratigraphy for the carbonate rocks of this part of the sequence; correlations can be made with the shallow-water sequences of the Knox, Prairie du Chien, and Arbuckle Groups, and the Ozark sequence of the adjacent shelf areas to the east, north, and west. The uppermost Lower Ordovician strata in the basin record a short-term incursion of cooler water environments, reflected by the character of both the conodont fauna and the lithofacies. The youngest Paleozoic dates known from the basin south of the Pascola arch are latest Ibexian (Early Ordovician).Thermal alteration indices of both the Cambrian palynomorphs (organic-walled microphytoplankton) and Ordovician conodonts in the deeper parts of the basin, corroborated by fluid inclusion thermometry, vitrinite reflectance, and other geochemical techniques, are of higher values than predicted using any published estimates of overburden burial. These maturation values most likely reflect burial enhanced by the passage of hydrothermal fluids on a regional scale; they place constraints on interpretations of the tectonothermal evolution of the basin.
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Savage, Jeni E., Margaret A. Bradshaw, and Kari N. Bassett. "Marginal marine depositional setting and correlation of the Devonian Sperm Bluff Formation (Taylor Group), southern Victoria Land, Antarctica." Antarctic Science 25, no. 6 (April 16, 2013): 767–90. http://dx.doi.org/10.1017/s0954102013000205.
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AbstractAnalysis of conglomerates and sandstones of the Sperm Bluff Formation at the base of the Taylor Group (Devonian) between the Mackay Glacier and Bull Pass provides new insights into the nature of initial coarse-grained deposition on basement along the northern side of the McMurdo sedimentary basin. Six lithofacies are recognized in the Sperm Bluff Formation: conglomerate lithofacies, pebbly sandstone lithofacies, cross-bedded sandstone lithofacies, low-angle cross-stratified sandstone lithofacies, bioturbated sandstone lithofacies and interbedded siltstone/sandstone lithofacies. Sedimentary environments ranged from wave-dominated delta, estuary or lagoon to shoreface and inner shelf. The assemblage is thought to reflect changes in sea level. Rhyolite is the most abundant clast type in the coarse lithofacies, but is unknown in outcrop in southern Victoria Land. The rhyolites correlate in age and geochemistry with Cambrian granites in the basement. Coarse beds also contain numerous quartzite clasts, probably derived from the late Precambrian Skelton Group. Palaeocurrents on Mount Suess indicate a strong unimodal flow to the west, but other sites show polymodal palaeoflow. The Sperm Bluff Formation is correlated with Terra Cotta Siltstone, New Mountain Sandstone and Altar Mountain formations based on the lithology of sandstones and their ichnology. A northward onlap during the Early Devonian is indicated.
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Finnegan, Seth, and Mary L. Droser. "Body size, energetics, and the Ordovician restructuring of marine ecosystems." Paleobiology 34, no. 3 (2008): 342–59. http://dx.doi.org/10.1666/07074.1.
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Major shifts in ecological dominance are one of the most conspicuous but poorly understood features of the fossil record. Here we examine one of the most prominent such shifts, the Ordovician shift from trilobite to brachiopod dominance of benthic ecosystems. Using an integrated database of high-resolution paleoecological samples and body size data, we show that while the average local richness and relative abundance of trilobites declined significantly through the Ordovician, the estimated standing biomass of trilobites, and by implication the amount of energy that they used, remained relatively invariant. This is attributable to an increase in the average body size of trilobite species in our data set, and especially to the widespread occurrence of the exceptionally large Middle-Late Ordovician trilobite genus Isotelus. Brachiopods increase in both mean body size and relative abundance throughout the Ordovician, so that estimates of brachiopod biomass and energetic use increase substantially between the Early and Late Ordovician. Although the data set includes a range of depositional environments, similar trends are observed in both shallow subtidal and deep subtidal settings. These results suggest that diversification of the Paleozoic Fauna did not come at the energetic expense of the Cambrian Fauna. The declining relative abundance of trilobites may reflect a combination of numerical dilution and the necessary energetic trade-offs between body size and abundance.
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McDougall, N., P. J. Brenchley, J. A. Rebelo, and M. Romano. "Fans and fan deltas – precursors to the Armorican Quartzite (Ordovician) in western Iberia." Geological Magazine 124, no. 4 (July 1987): 347–59. http://dx.doi.org/10.1017/s0016756800016678.
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AbstractThe Armorican Quartzite (Lower Ordovician) is a very extensive sandstone body found throughout a large part of Iberia and Brittany; similar quartzites are present in north Africa and elsewhere. In Iberia it generally lies unconformably on a thick, folded, late Precambrian to Cambrian turbidite sequence (the Complexo Xisto-Grauváquico (CXG)), but there are some places where the quartzite has a conformable relationship with the underlying CXG. Where conformable the whole succession shows varied facies sequences including: (i) a regressive mud–sand sequence as a precursor to the main quartzite development, (ii) submarine fan sediments of the CXG passing up into slope and then shallow marine facies, or (iii) fluvially influenced breccio-conglomerates of a marginal fan delta passing up into shallow marine sediments.The inferred development of alluvial fans associated with fan deltas prograding into shallow marine environments implies steep slopes and the likelihood that faulting controlled some of the uplift. The mozaic pattern of differential uplift and subsidence throughout the region suggests that the CXG was affected by local block movements rather than by regional folding.The presence of upstanding blocks during the initial sedimentation of the Armorican Quartzite suggests that the quartz sand might have been derived from multiple sources dispersed throughout the area rather than from sources along a single shoreline at the margin of the depositional area.
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Shaller, Philip J., Macan Doroudian, and Michael W. Hart. "The Eureka Valley Landslide: Evidence of a Dual Failure Mechanism for a Long-Runout Landslide." Lithosphere 2020, no. 1 (December 2, 2020): 1–26. http://dx.doi.org/10.2113/2020/8860819.
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Abstract Long-runout landslides are well-known and notorious geologic hazards in many mountainous parts of the world. Commonly encompassing enormous volumes of debris, these rapid mass movements place populations at risk through both direct impacts and indirect hazards, such as downstream flooding. Despite their evident risks, the mechanics of these large-scale landslides remain both enigmatic and controversial. In this work, we illuminate the inner workings of one exceptionally well-exposed and well-preserved long-runout landslide of late Pleistocene age located in Eureka Valley, east-central California, Death Valley National Park. The landslide originated in the detachment of more than 5 million m3 of Cambrian bedrock from a rugged northwest-facing outcrop in the northern Last Chance Range. Its relatively compact scale, well-preserved morphology, varied lithologic composition, and strategic dissection by erosional processes render it an exceptional laboratory for the study of the long-runout phenomenon in a dry environment. The landslide in Eureka Valley resembles, in miniature, morphologically similar “Blackhawk-like” landslides on Earth, Mars, and minor planet Ceres, including the well-known but much larger Blackhawk landslide of southern California. Like these other landslides, the landslide in Eureka Valley consists of a lobate, distally raised main lobe bounded by raised lateral levees. Like other terrestrial examples, it is principally composed of pervasively fractured, clast-supported breccia. Based on the geologic characteristics of the landslide and its inferred kinematics, a two-part emplacement mechanism is advanced: (1) a clast-breakage mechanism (cataclasis) active in the bedrock canyon areas and (2) sliding on a substrate of saturated sediments encountered and liquefied by the main lobe of the landslide as it exited the main source canyon. Mechanisms previously hypothesized to explain the high-speed runout and morphology of the landslide and its Blackhawk-like analogs are demonstrably inconsistent with the geology, geomorphology, and mineralogy of the subject deposit and its depositional environment.
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King, Lewis H., Gordon B. J. Fader, W. A. M. Jenkins, and Edward L. King. "Occurrence and regional geological setting of Paleozoic rocks on the Grand Banks of Newfoundland." Canadian Journal of Earth Sciences 23, no. 4 (April 1, 1986): 504–26. http://dx.doi.org/10.1139/e86-052.
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Analyses of seismic reflection profiles supported by lithological and palynological studies of core samples from submarine outcrops indicate that the lower Paleozoic succession of the Avalon Terrane, southeast Newfoundland, is continuous offshore. The succession crops out over an area greater than 30 000 km2 and is approximately 8 km thick. The sequence is dominantly siltstone and is of Late Cambrian to ?Devonian or younger age. It is relatively unmetamorphosed, underlain by Hadrynian acoustic basement, and overlain along its eastern and southern margins by a Mesozoic–Cenozoic succession that is economically important from an oil and gas perspective.Lithofacies studies indicate that in Early Ordovician time restricted shallow-marine conditions probably prevailed over a vast area of the Avalon Terrane. Upper Ordovician and Silurian siltstones show evidence of deposition under more-dynamic and well-oxygenated conditions and probably represent a normal shallow-marine environment. Redbeds of possible Devonian or younger age are interpreted to be of continental origin. Black shales of Ordovician age are potential source rocks for the generation of hydrocarbons.
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Rousseau, Mathieu, Gilles Dromart, Henk Droste, and Peter Homewood. "Stratigraphic organisation of the Jurassic sequence in Interior Oman, Arabian Peninsula." GeoArabia 11, no. 1 (January 1, 2006): 17–50. http://dx.doi.org/10.2113/geoarabia110117.
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ABSTRACT A Stratigraphic model is proposed for the Jurassic sequence in Interior Oman. The model is based on regional well-log correlations, outcrop analysis and integration of Biostratigraphy. Large-scale architectures are restored using a well-to-well correlation technique, after the well-log markers of the relevant surfaces of sequence stratigraphy are identified. This identification is achieved by comparing well-log signatures to lithological and sedimentological columns of nearby exposed sections. The subsurface dataset consists of 19 wells arranged in two east-west profiles, 341 km and 332 km long. The Jurassic sequence in Interior Oman shows a general easterly thinning wedge and includes two hiatuses with marked age-gaps. Three major depositional episodes are identified: (1) a Pliensbachian-Toarcian coastal encroachment in a southward direction, represented by the dominantly clastic deposition of the Lower Mafraq Formation upon the Permian carbonates; (2) a general late Bajocian marine flooding (hybrid facies of marginal-marine environments of the Upper Mafraq Formation), followed through the Bathonian-Callovian by the carbonate Dhruma-Tuwaiq System which evolved through time from a low-angle, homoclinal ramp dipping in a (north) westwards direction, to a purely aggradational, flat-topped platform (upper Dhruma and Tuwaiq Mountain formations); (3) a Kimmeridgian-Tithonian onlap in an eastwards direction of finegrained limestones (Jubaila-Rayda) upon the post-Tuwaiq unconformity. Depositional hiatuses in the early Liassic and at the Early-Middle Jurassic transition are likely to reflect major eustatic sea-level lowstands. In contrast, subsurface correlations of the MFSs through the Dhruma-Tuwaiq indicate that the post-Tuwaiq unconformity is a low-angle (0.001 degrees) angular unconformity associated with tilting and truncation of the underlying sequences. Oxfordian sequences were probably never deposited in Interior Oman because of a lack of accommodation space and prolonged subaerial exposure. It is here proposed that the Upper/Middle Jurassic angular unconformity in Interior Oman was planed-off by subaerial carbonate dissolution during a steady, tectonically-driven uplift of the whole eastern Arabian shelf edge. The proposed geological model has several implications for the petroleum systems of Interior Oman. The geometric model predicts the distribution of the sedimentary facies, including source rocks, clastic and carbonate reservoirs, and seal facies. The occurrence of isolated Upper Mafraq-producing reservoir sands (i.e. Sayh Rawl field) are believed to be restricted to central and eastern Interior Oman. There are two other reservoir/seal combinations, both related to the Upper/Middle Jurassic unconformity: (1) truncation traps of the Dhruma-Tuwaiq below the unconformity (i.e. Hadriya and Uwainat reservoirs); (2) updip pinch-out trap of the Hanifa above the unconformity. Finally, it is believed that the early Late Jurassic general uplift and truncation of eastern Oman may have caused local remobilisation, updip migration, and loss to the surface of oil in reservoirs, initially generated from the prolific Al Huqf source rocks of Late Precambrian-Early Cambrian age.
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Nesbitt, Bruce E., and Walter Prochaska. "Solute chemistry of inclusion fluids from sparry dolomites and magnesites in Middle Cambrian carbonate rocks of the southern Canadian Rocky Mountains." Canadian Journal of Earth Sciences 35, no. 5 (May 1, 1998): 546–55. http://dx.doi.org/10.1139/e98-006.
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Middle Cambrian carbonate rocks of the southern Canadian Rocky Mountains are host to widespread units of white, sparry, hydrothermal, replacement, and open-space filling dolomite. Contained within the dolomites are occurrences of talc and Mississippi Valley type Pb-Zn (the former Kicking Horse and Monarch mines) mineralization and economic concentrations of magnesite (Mount Brussilof mine). Results of studies of solute chemistry of saline (18-25 equivalent wt.% NaCl) inclusion fluids reveal distinctly low Na/Br (55-220) and Cl/Br (95-340) values. These values indicate that the brines which formed the dolomite originated from seawater that had deposited large amounts of halite in an evaporitic environment. Low I/Br ratios for the dolomite-magnesite inclusion fluids are consistent with their derivation from seawater and contrast sharply with the high I/Br ratios of Laramide-age fluids, which formed veins throughout the Rocky Mountains. Variations in F/Br ratios between texturally early and late magnesites indicate the involvement of a second fluid in the formation of the late magnesites. Results of the study of solute chemistry of inclusion fluids from hydrothermal dolomites, magnesites, and associated mineralization are consistent with a model of the pre-Laramide formation of these materials from seawater that had undergone extensive evaporation and halite deposition. Distinct differences in I/Br, total salinity, and delta D values between the dolomite-magnesite depositing fluids and Laramide-age vein-forming fluids clearly indicate the lack of the involvement of Laramide-age fluids in the genesis of the dolomites, magnesites, and associated mineralization.
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Krainer, Karl, Peter Tropper, Kurt Krenn, and Spencer G. Lucas. "Occurrence and origin of glauconite in the Cambro-Ordovician Bliss Formation of southern New Mexico and West Texas (U.S.A.)." Journal of Sedimentary Research 92, no. 4 (April 13, 2022): 353–70. http://dx.doi.org/10.2110/jsr.2021.102.
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ABSTRACT In southern New Mexico and West Texas, USA, the Late Cambrian–Early Ordovician Bliss Formation is a relatively thin and dominantly siliciclastic succession that was deposited on the Proterozoic basement during a major global transgression. The Bliss Formation can be divided into two members: 1) a lower, coarser-grained member composed mostly of sandstone (quartz arenite and subarkose) that lacks glauconite and calcite cement, and 2) an upper, finer-grained member that includes glauconitic sandstone, arkosic sandstone, and mixed siliciclastic–carbonate siltstone to fine-grained sandstone, intercalated with thin carbonate beds of grainstone, packstone, and rudstone. Iron oolite and oolitic sandstone are locally exposed at the base of the upper member. Sandstone of the lower member represents upper-shoreface to foreshore deposits, whereas sedimentary structures in the upper member indicate deposition in a middle- to lower-shoreface setting, and locally in a tidal-flat environment. Intercalated carbonate beds are storm layers (tempestites). Glauconite grains are abundant in the upper member as mostly rounded to well-rounded, spheroidal to ovoidal pellets. Two types of glauconite grains are present: homogeneous, dark green grains with high K2O contents (> 8 wt.%; stage 4) and mottled pellets composed of a mixture of glauconite and apatite. Glauconite of the Bliss Formation is not autochthonous as proposed by earlier workers, but of allochthonous (parautochthonous) origin. Thus, the glauconite grains were reworked from deeper shelf environments in northern Mexico to the south and were transported and deposited under regressive–transgressive conditions. Mottled glauconite grains formed by the reworking of phosphatized and glauconitized micritic sediments during regression and were transported and deposited by storm-induced currents, particularly in storm layers during transgressive events. Homogeneous, mature glauconite grains probably were derived from the reworking of glauconitized fecal pellets or completely glauconitized micritic sediments during regressive–transgressive cycles. The world-wide occurrence of glauconite in Cambrian–Early Ordovician sediments indicates that glauconite formation during that period can be considered as a “global event.”
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van Loon, A. J. (Tom), Zuozhen Han, and Yu Han. "Slide origin of breccia lenses in the Cambrian of the North China Platform: new insight into mass transport in an epeiric sea." Geologos 18, no. 4 (December 30, 2012): 223–35. http://dx.doi.org/10.2478/v10118-012-0011-3.
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Abstract An oolite in the Furongian (Late Cambrian) Chaomidian Formation in Shandong Province, China, which was deposited on the North China Platform in an epeiric sea, contains several limestone breccia lenses of various dimensions (centimetres to decimetres thick and decimetres to more than 10 metres in length) in an E-trending section. The oolite, which is approximately 40 cm thick, was originally thicker, as indicated by a planar truncation surface that formed by wave abrasion. The breccia lenses in this oolite are generally mound-shaped with a flat base and a convex top. The western margin of the lenses is commonly rounded whereas the eastern margin commonly has a tail (consisting of a rapidly eastwards thinning breccia horizon that gradually ends in a horizon of isolated clasts). Some of the breccia lenses are underlain by a shear zone. The formation of the breccia lenses cannot be easily explained by normal depositional or deformational processes. It is concluded that the lenses represent fragments of a partly consolidated layer, consisting of both rounded and angular platy clasts, which slid down over a very gently inclined sedimentary surface which acted – possibly together with a water film – as a lubricant layer. During transport, the layer broke up into several discrete bodies that formed small ‘highs’ at the sedimentary surface of the shallow epeiric sea. Subsequently, waves partially eroded the lenses, mostly at their margins, producing their mound-shaped form. Sliding of blocks is known from a wide variety of environments in the sedimentary record; however, this is the first description of the sliding of blocks in an epeiric sea. This indicates that such a low-relief submarine carbonate setting is, like its siliciclastic counterparts, susceptible to this process.
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Zagorchev, Ivan. "Introduction to the geology of SW Bulgaria." Geologica Balcanica 31, no. 1-2 (June 30, 2001): 3–52. http://dx.doi.org/10.52321/geolbalc.31.1-2.3.
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The geologic structure of Southwest Bulgaria is characterized by a complex Mid Cretaceous pile of thrust sheets, a complex system of horsts and grabens of Palaeogene age, and a neotectonic (Neogene - Quaternary) pattern dominated by the Strouma rift system and the Serbo-Macedonian neotectonic swell. Amphibolite-facies metamorphic rocks belong to the Ograzhdenian (Prerhodopian) and Rhodopian Supergroup and the Osogovo “Formation”. The last intensive metamorphic event is proven to be of Cadomian age, and later superimposed metamorphic and deformation events have had a local occurrence. The greenschist-facies Frolosh Formation (Vendian - Lower Cambrian) has a diabasephyllitoid composition and is typical for the Strouma tectonic superunit. The basement of the latter Ograzhdenian Supergroup, Osogovo “Formation”, Frolosh Formation) is covered with a major depositional unconformable contact by sedimentary complexes of Ordovician (only in the Bosilegrad District in Yugoslavia) and Permian and Triassic age. Palaeozoic formations of Ordovician to Devonian age are present only in the thrust sheets of the Morava superunit, and in parts of the southern edge of the Srednogorie zone. Permian formations (mostly continental red beds) have a restricted occurrence. The Triassic (only in the Strouma superunit and parts of the Srednogorie) consists of the Petrohan Terrigenous Group (continental red beds), the Iskur Carbonate Group (marine) and the Moesian Group (marine red beds). After folding, uplift and erosion, the transgressive Jurassic formations have been formed in several different environments, in latest Jurassic - earliest Cretaceous times represented by the carbonate platform to the North, and the Nish-Troyan flysch trough. The principal orogenesis occurred in Mid Cretaceous times, and Upper Cretaceous sedimentary formations are present only in parts of the Srednogorie zone. Late Cretaceous intrusive rocks are known from the Srednogorie (of mantle origin) and in Pirin (crustal granitoids). The Late Cretaceous orogenesis formed the Srednogorie superunit (to the North) and the Morava-Rhodope superunit (to the South). Thus, the Alpine structure consists of the following principal tectonic units: Late Cretaceous Srednogorie superunit (with fragments from the Mid-Cretaceous Lyubash, Golo-burdo, Melovete, Radomir and Verila units) and Morava-Rhodope superunit with the Mid-Cretaceous Morava superunit and Ograzhden unit (allochthonous), Strouma superunit (Louzhnitsa-Trun and Osogovo-Vlahina unit), Rhodope and Pirin-Pangaion superunit. The Palaeogene and Neogene formations have the character of a neoautochthone that is controlled by the Late Alpine and neotectonic block movements.
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Lindström, M., T. Flodén, Y. Grahn, and B. Kathol. "Post-impact deposits in Tvären, a marine Middle Ordovician crater south of Stockholm, Sweden." Geological Magazine 131, no. 1 (January 1994): 91–103. http://dx.doi.org/10.1017/s0016756800010529.
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AbstractThe well-preserved Tvären crater is noteworthy for being one of a small number of Early and Middle Ordovician impact structures formed in a marine environment. It is demonstrated to be an impact structure by the presence of a breccia lens, consisting of crystalline basement rocks, and shocked quartz. The breccia lens formed under dry-hot conditions after expulsion of sea-water by the impact. Resurging sea-water thereupon deposited a positively graded, 60 m thick turbidite-like unit. This graded resurge deposit is a previously unknown feature, to be expected in open-sea impacts. Breccia in the lower part of this graded deposit contains fragments of a remarkably complete orthoceratite limestone succession that existed at the site of impact, resting on non-lithified sand of probably Early to earliest Middle Cambrian age. A sedimentary succession was deposited inside the crater at depths decreasing from more than 200 m in the initial stages to some 100 m at the time of deposition of the youngest preserved beds. The environment within the crater thus favoured deposition of an essentially complete stratigraphic succession with depth-controlled palaeoecology for a significant time interval after the impact. Whereas planktonic members, like graptolites and chitinozoa, are present throughout the post-impact succession, and asaphids, almost as persistent, became established at an early date, burrowers were somewhat reluctant to enter and remopleuridids and small strophomenids came in at a late stage. We suggest as a result of this study that structures formed by impact may offer unique information about the palaeogeology and palaeoenvironment of the region hit by the impact.
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Mikhailova, Vasileva, Fedorov, Ershova, Vereshchagin, Rogov, and Pokrovsky. "Glendonite-Like Carbonate Aggregates from the Lower Ordovician Koporye Formation (Russian Part of the Baltic Klint): Detailed Mineralogical and Geochemical Data and Paleogeographic Implications." Minerals 9, no. 9 (August 29, 2019): 524. http://dx.doi.org/10.3390/min9090524.
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Stellate and plate-like carbonate bodies, traditionally called anthraconites, are found throughout the Baltic-Ladoga Klint in bituminous shale of the Koporye Formation (Tremadocian, Lower Ordovician). Although this time interval is usually considered as a greenhouse, there is some evidence for the existence of at least temporary cold conditions during the Cambrian–Ordovician. However, the origin of anthraconites is still strongly debated. We studied the mineralogical, petrographic, cathodoluminescence, geochemical, and isotopic characteristics of anthraconites from five sections of the Russian part of the Baltic paleobasin. A close similarity between the morphological, petrographic, cathodoluminescence, and isotopic characteristics of the studied anthraconites with those of glendonites allow us to suggest that these bodies formed in a similar paleo-environment and should be considered as pseudomorphs of the mineral ikaite. The oxygen and carbon isotope ratios reveal that ikaite precipitation occurred in low-temperature conditions on the seafloor. The carbon isotopic values reveal influence of inorganic seawater carbon along with organic matter decomposition and/or methane oxidation during ikaite-glendonite transformations. The oxygen isotopic composition significantly changed after deposition due to meteoric diagenesis. We propose that the studied Tremadocian anthraconites formed under a region of upwelling, where cold phosphate-rich deep waters rose to the relatively shallow part of the Baltic paleobasin, providing favorable conditions for ikaite precipitation. Based on our cathodoluminescence study, we suggest that ikaite was transformed to calcite over several stages during diagenesis. Mineralogical studies also reveal that primary calcite was transformed to sulfate (gypsum) or dolomite during late superimposed processes.
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Landing, Ed, Stephen R. Westrop, and Linda Van Aller Hernick. "Uppermost Cambrian-lower Ordovician faunas and Laurentian platform sequence stratigraphy, eastern New York and Vermont." Journal of Paleontology 77, no. 1 (January 2003): 78–98. http://dx.doi.org/10.1017/s0022336000043444.
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The Cambrian–Ordovician boundary is a type 1 depositional sequence boundary with dramatic local erosional incision in restricted marine facies on the easternmost New York Promontory. The systemic boundary is bracketed below by Late Cambrian, upper Cordylodus proavus Zone (s.s). conodonts from carbonates of the upper Little Falls Formation (=Whitehall Formation, abandoned). Presumed Lower Ordovician ellesmeraceratoid cephalopods from the upper Little Falls are uppermost Cambrian and among the oldest known in North America. The overlying deepening–shoaling cycle of the Tribes Hill Formation (=Cutting and Great Meadows Formations, abandoned) is the local expression of a lowermost Ordovician (Rossodus manitouensis Zone) depositional sequence recognizable across Laurentia. Complete replacement of conodonts takes place in the late Tremadocian or Tremadocian–Arenigian boundary interval with onlap of the “Fort Ann Formation” across the paleokarst cap of the Tribes Hill. The trilobites Hystricurus sp. and Symphysurina myopia Westrop new species occur in less restricted, thrombolitic facies of the middle Tribes Hill that have the highest conodont diversity. Ulrichodina Furnish, 1938, emend. is regarded as the senior synonym of the conodont Colaptoconus Kennedy, 1994 (=Glyptoconus Kennedy, 1980).
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Idrissi, Assia, Mohamed Saadi, Yassir Astati, Ali Bouayachi, and Kawtar Benyas. "Mapping of Genetic Sequences of the Cambrian Series in the Jbel Saghro Massif, Eastern Anti-Atlas, Morocco: Implications for Eustatic and Tectonic Controls." Iraqi Geological Journal 55, no. 1D (April 30, 2022): 1–20. http://dx.doi.org/10.46717/igj.55.1d.1ms-2022-04-17.
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In this paper, a sedimentological and sequence stratigraphy analysis was performed on Lower and Middle Cambrian deposits of Jbel Saghro, Eastern Anti-Atlas. The field data analysis and the application of sequence stratigraphy concepts were used to classify sedimentary processes and depositional environment, and to define the Lower to Middle Cambrian basin’s detailed geometry. The Cambrian sedimentation of northeastern Saghro indicates a deltaic environment, which is composed of two depositional sequences. These sequences are made of a transgressive system-tract with retrograding sediments and a highstand system tract with prograding sediments. In response to sea-level change, these system-tracts were formed by several genetic units, and limited by various stratigraphic surfaces. The genetic unit stacking-patterns combined with the study of synsedimentary tectonics enabled to follow the sedimentary record’s Spatio-temporal evolution and its three-dimensional geometry. The study area deposits display significant dissimilarities in thickness. The western part shows a Lower Cambrian hiatus and an important reduction of the thickness in the Middle Cambrian deposits. However, the marine trend (progradation/retrogradation) remains similar in the study area. This suggests the same eustatic origin of all genetic sequences and variations in their preservation rate. This configuration is the result of differential subsidence that affected the Anti-Atlas during the Cambrian.
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Lavoie, Denis, Elliott Burden, and Daniel Lebel. "Stratigraphic framework for the CambrianOrdovician rift and passive margin successions from southern Quebec to western Newfoundland." Canadian Journal of Earth Sciences 40, no. 2 (February 1, 2003): 177–205. http://dx.doi.org/10.1139/e02-078.
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The Taconian Humber Zone stretches from western Newfoundland to southern Quebec. The Early Cambrian slope succession in Newfoundland is found in the Curling Group, whereas in Quebec, various units were deposited during that first time slice. Biostratigraphic data allow correlation of the Curling Group with the Labrador Group in Newfoundland and with the newly time-constrained slope succession in Quebec. The end of the riftdrift transition is marked by a sea-level lowstand at the end of the Early Cambrian. The Middle Cambrian to latest Early Ordovician passive margin history recorded five cyclic sea-level fluctuations. Three of these cycles are recorded in the shallow-marine Middle to Late Cambrian platform (Port au Port Group) and slope sediments preserved in the Cow Head and Northern Head groups in Newfoundland. The biostratigraphic information assists correlation with Cambrian passive margin units in Quebec. Major sea-level lowstands are recognized along the continental margin in earlymiddle Late Cambrian (Steptoan) and in late Late Cambrian (Sunwaptan). Even if the Quebec succession can be tied with its Newfoundland correlative, some significant differences in the nature of Upper Cambrian slope conglomerates argue for a tectonic control on the depth of erosion of the Cambrian continental margin. The Lower Ordovician record of the passive margin consists of two depositional cycles (TremadocianArenigian) separated by a sea-level lowstand. This last event is well expressed in platform succession and is also recognized in conglomerate units found in the slope succession.
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Murphy, J. Brendan, Michael A. Hamilton, and Bryan LeBlanc. "Tectonic significance of Late Ordovician silicic magmatism, Avalon terrane, northern Antigonish Highlands, Nova Scotia 1 This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.2 Contribution to International Geological Correlation Programme (IGCP) Project 497." Canadian Journal of Earth Sciences 49, no. 1 (January 2012): 346–58. http://dx.doi.org/10.1139/e11-012.
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Avalonia was a microcontinent during most of the Ordovician, separating the Iapetus Ocean to the north from the Rheic Ocean to the south. In the northern Antigonish Highlands, Nova Scotia, volcanic rocks (Dunn Point and McGillivray Brook formations) underlie Early Silurian – Early Devonian strata (Arisaig Group) and were thought to represent extension that heralded the development of the basin into which Arisaig Group strata were deposited. However, recent U–Pb (zircon, thermal ionization mass spectrometry) data from rhyolite in the Dunn Point Formation (DPF) yielded an age of 460.0 ± 3.4 Ma, and, here, we report a concordant age of 454.5 ± 0.7 Ma for an ignimbrite in the overlying McGillivray Brook Formation (MBF). These data confirm a ca. 10 million year gap between volcanism and onset of Arisaig Group deposition, which occurred after accretion of Avalonia to Baltica. The DPF and MBF both resemble A-type SiO2-rich magmas. The MBF has very high concentrations of Zr (745–1965 ppm), Y (65–213 ppm), Nb (57 to 185 ppm), and high Ga/Al. Several MBF samples exhibit strong LREE depletion, consistent with fractionation of LREE-bearing accessory phases. εNdt values for MBF (t = 455 Ma) range from +1.5 to +3.9, and overlap with DPF rhyolites that range from +2.9 to +3.7. Depleted mantle model ages for MBF and DPF samples unaffected by accessory phase fractionation are between 0.9 and 1.2 Ga and are similar to TDM values in older (Neoproterozoic, Cambrian) crustally derived felsic rocks, suggesting derivation from the lower crustal basement beneath the Antigonish Highlands. DPF and MBF rocks were probably erupted in a local extensional environment within an ensialic arc, perhaps analogous to the modern Taupo Volcanic Zone in northern New Zealand.
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Nielsen, Arne Thorshøj, and Niels Hemmingsen Schovsbo. "The Lower Cambrian of Scandinavia: Depositional environment, sequence stratigraphy and palaeogeography." Earth-Science Reviews 107, no. 3-4 (August 2011): 207–310. http://dx.doi.org/10.1016/j.earscirev.2010.12.004.
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Gao, Lingfeng, Shan Xu, Xiangyun Hu, Shuang Liu, Qi Zhou, and Bingnan Yang. "Sedimentary Setting and Ore-Forming Model in the Songtao Manganese Deposit, Southwestern China: Evidence from Audio-Frequency Magnetotelluric and Gravity Data." Minerals 11, no. 11 (November 17, 2021): 1273. http://dx.doi.org/10.3390/min11111273.
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The break-up of the supercontinent Rodinia in the late Neoproterozoic led to the formation of the Nanhua rift basin within the South China Block. The Datangpo-type manganese deposit, which developed in the Nanhua rift basin, is one of the most important types of manganese deposits in South China. Although it is widely accepted that deep sedimentary structures significantly affect the manganese ore system, the relationship between the manganese deposits in South China and the Nanhua rifting process is still unclear. The origin of the manganese ore layer remains controversial. In this paper, we integrated the audio-frequency magnetotelluric (AMT) data, gravity data, and comprehensive geological and borehole data analysis to characterize the structure of the Datangpo-type manganese deposit in Songtao, Guizhou Province. The resistivity and density models produced an inclined layered structure, which correlated well with the coeval sediment strata of the Nanhua rift basin. A high-resistivity cap was observed from the surface to a depth of 800 m, corresponding to the Cambrian Loushanguan (ϵ3−4ls) and Palang dolomite formation (ϵ2p), which has helped the storage of the manganese ore. The most significant low-resistivity anomaly (25–40 Ω·m) resides at a depth of 1400 m in the Nantuo (Nh3n) gravel sandstone and Datangpo (Nh2d) silty and carbonaceous shale, corresponding to the ore-forming layer. This distinct low-resistivity layer was possibly produced by aqueous fluids and pyrite in the syn-sedimentary fault and alteration zone. The accumulations of sulfide minerals in the rock samples suggest a possible anoxic-euxinic deposition environment during the manganese mineralization and precipitation. The fault revealed in the resistivity models is perhaps a previous fault zone produced by extension in the Nanhua rifting process, which provided migration and upwelling channels for ore-forming minerals. Based on our resistivity models, density models, and geological survey, the manganese ore-forming model was derived, which can help to provide geophysical evidence for the origin of the Datangpo-type manganese deposit.
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Barr, Sandra M., Deanne Van Rooyen, Brent V. Miller, Chris E. White, and Susan C. Johnson. "Detrital zircon signatures in Precambrian and Paleozoic sedimentary units in southern New Brunswick – more pieces of the puzzle." Atlantic Geology 55 (October 2, 2019): 275–322. http://dx.doi.org/10.4138/atlgeol.2019.010.
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Southern New Brunswick consists of a complex collage of fault-bounded belts of Late Neoproterozoic igneous and metamorphic rocks, Early Paleozoic sedimentary, metamorphic and igneous units, and overlying Carboniferous sedimentary rocks. The area also contains the boundary between the Avalonian and Ganderian terranes as interpreted in the northern Appalachian orogen. New detrital zircon ages reported here provide improved understanding of depositional ages and provenance of diverse Neoproterozoic to Carboniferous rocks in this complex area. Detrital zircon data from samples with Neoproterozoic maximum depositional ages indicate a dominantly Gondwanan provenance with a strong influence from the Amazonian craton. However, quartzite from The Thoroughfare Formation on Grand Manan Island contains dominanly 2 Ga zircon grains, consistent with derivation from the West African Craton. The age spectrum is similar to that from the Hutchins Island Quartzite in the Isleboro block in Penobscot Bay, Maine, strengthening the previously proposed correlation between the two areas. Cambrian samples also show prominent peri-Gondwanan provenance with strong influence from Ediacaran to Early Cambrian arc magmatism. The maximum depositional ages of these samples are consistent with previous interpretations of Cambrian ages based on fossil correlations and field data. A Carboniferous sample from Avalonia shows a significant contribution from Devonian magmatism as the youngest detrital component, although its depositional age based on field relationships is Carboniferous. The results exemplify the need to integrate multiple datasets in making interpretations from detrital zircon data.
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Liu, Hao, Chan Wang, Yong Li, Jianghong Deng, Bin Deng, Yuexing Feng, Hui Chen, Yunlong Xu, and Shaoze Zhao. "Geochemistry of the black rock series of lower Cambrian Qiongzhusi Formation, SW Yangtze Block, China: Reconstruction of sedimentary and tectonic environments." Open Geosciences 13, no. 1 (January 1, 2021): 166–87. http://dx.doi.org/10.1515/geo-2020-0228.
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Abstract The black rock series in the Qiongzhusi Formation contains important geochemical information about the early Cambrian tectonic and ecological environment of the southwestern Yangtze Block. In this paper, major, trace, and rare earth element data are presented in an attempt to reveal the sediment source during the deposition of the early Cambrian Qiongzhusi Formation and to reconstruct the sedimentary tectonic environment and weathering intensity during that time. The basin primarily received continental clastic material with neutral-acidic igneous rocks from a stable source and with a moderate level of maturity during the depositional period of the Qiongzhusi Formation. Furthermore, the strata were weakly influenced by submarine hydrothermal fluids during diagenesis. The reconstruction of the sedimentary environment and weathering intensity shows that P2O5 enrichment and water body stratification occurred due to the effects of upwelling ocean currents during the depositional period of the Qiongzhusi Formation. The combination of upwelling and bottom-water hydrothermal fluids led to environmental changes in the study area, from dry and hot to moist and warm. Last, the reconstruction of the tectonic environment of the Qiongzhusi Formation indicates that deposition occurred in continental slope and marginal marine environments associated with a continental arc tectonic system. These findings provide an essential basis for the comprehensive reconstruction of the early Cambrian sedimentary environment of the Yangtze Block.
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Xiao, Zong Lin, Qing Qing Hao, and Zhong Min Shen. "Maturity Evolution of the Cambrian Source Rocks in the Tarim Basin." Advanced Materials Research 622-623 (December 2012): 1642–45. http://dx.doi.org/10.4028/www.scientific.net/amr.622-623.1642.
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The Tarim basin is an important petroleum basin in China, and the Cambrian strata are the major source rock successions in the basin. Integrated the source rock depositional and structural history with its geochemical and thermal parameters, this paper simulates the evolution of the Cambrian source rocks with the software Basinview. The simulation result shows that the main hydrocarbon-generation centers of the Manjiaer sag in the Tabei depression and the Tangguzibasi sag in the Southwest depression are characterized by their early hydrocarbon generation, and in the late Ordovician depositional age, they reached dry gas stage. The Kuqa and Southwest depressions developed in the Cenozoic foreland basins made the Cambrian source rocks mature rapidly in the Cenozoic period. The source rock maturity in the Tarim basin now is characterized by high in the east and west and low in the middle, and most of the area is in the over-mature stage in the present. This study can provide available maturity data for the next petroleum exploration work.
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THIEDE, JÖRN. "The Late Quaternary Skagerrak and its depositional environment." Boreas 16, no. 4 (January 16, 2008): 425–32. http://dx.doi.org/10.1111/j.1502-3885.1987.tb00116.x.
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Palma, Ricardo M. "Lithofacies and depositional environment of Middle Cambrian San Isidro Formation, Mendoza, Argentina." Carbonates and Evaporites 10, no. 2 (September 1995): 234–44. http://dx.doi.org/10.1007/bf03175408.
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Chen, Feiyang, Glenn A. Brock, Zhiliang Zhang, Brittany Laing, Xinyi Ren, and Zhifei Zhang. "Brachiopod-dominated communities and depositional environment of the Guanshan Konservat-Lagerstätte, eastern Yunnan, China." Journal of the Geological Society 178, no. 1 (August 5, 2020): jgs2020–043. http://dx.doi.org/10.1144/jgs2020-043.
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The Guanshan Biota is an unusual early Cambrian Konservat-Lagerstätte from China and is distinguished from all other exceptionally preserved Cambrian biotas by the dominance of brachiopods and a relatively shallow depositional environment. However, the faunal composition, overturn and sedimentology associated with the Guanshan Biota are poorly understood. This study, based on collections through the best-exposed succession of the basal Wulongqing Formation at the Shijiangjun section, Wuding County, eastern Yunnan, China recovered six major animal groups with soft tissue preservation; brachiopods vastly outnumbered all other groups. Brachiopods quickly replace arthropods as the dominant fauna following a transgression at the base of the Wulongqing Formation. A transition from a botsfordiid-, eoobolid- and acrotretid- to an acrotheloid-dominated brachiopod assemblage occurs up-section. Four episodically repeated lithofacies reveal a relatively low-energy, offshore to lower shoreface sedimentary environment at the Shijiangjun section, which is very different from the Wulongqing Formation in the Malong and Kunming areas. Multiple event flows and rapid obrution are responsible for faunal overturn and fluctuation through the section. A detailed lithofacies and palaeontological investigation of this section provides a better understanding of the processes and drivers of faunal overturn during the later phase of the Cambrian Explosion.Supplementary material: Composition and comparison of the Malong Fauna and the Guanshan Biota is are available at: https://doi.org/10.6084/m9.figshare.c.5080799
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Ineson, Jon R., and John S. Peel. "Geological and depositional setting of the Sirius Passet Lagerstätte (Early Cambrian), North Greenland." Canadian Journal of Earth Sciences 48, no. 8 (August 2011): 1259–81. http://dx.doi.org/10.1139/e11-018.
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The Early Cambrian Sirius Passet Lagerstätte of North Greenland occurs in marine mudstones (Buen Formation) deposited in a slope environment along the eroded scarp of a pre-existing carbonate platform. The shallow-water platform is represented by dolostones of the Portfjeld Formation (Neoproterozoic – earliest Cambrian), which record a belt of tide-swept subtidal ooid shoals and microbial patch reefs at the outer edge of the platform. Solution features and meteoric cements attest to exposure of the platform, accompanied by fracturing, mass wastage and erosional retreat of the escarpment producing slope talus, and extensive debris sheets and olistoliths in basinal deposits. The marine mud-dominated siliciclastics of the Buen Formation, deposited in slope and shelf environments, record the transgression and onlap of the degraded platform in the Early Cambrian. The Sirius Passet Lagerstätte has yielded an arthropod-dominated fossil assemblage of over 40 species, many showing exceptional preservation of soft tissues; the finely laminated mudstones hosting this fauna accumulated from suspension in a poorly oxygenated slope sub-environment, such as an erosional embayment or abandoned slope gully. Although taphonomic features suggest that the fauna is mainly parautochthonous, some components (e.g., sponges, worms, the halkieriids and certain sightless arthropods) may be truly autochthonous. Comparison of the Sirius Passet locality with the renowned Middle Cambrian Burgess Shale of western Canada reveals similarities in overall depositional and tectonic setting: both accumulated in deep water adjacent to the steep, eroded margins of carbonate platforms — settings that subsequently sheltered the faunas from tectonic and metamorphic obliteration.
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Ershova, Victoria B., Andrei V. Prokopiev, Andrey K. Khudoley, Tom Andersen, Kåre Kullerud, and Daniil A. Kolchanov. "U–Pb Age and Hf Isotope Geochemistry of Detrital Zircons from Cambrian Sandstones of the Severnaya Zemlya Archipelago and Northern Taimyr (Russian High Arctic)." Minerals 10, no. 1 (December 30, 2019): 36. http://dx.doi.org/10.3390/min10010036.
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U–Pb and Lu–Hf isotope analyses of detrital zircons collected from metasedimentary rocks from the southern part of Kara Terrane (northern Taimyr and Severnaya Zemlya archipelago) provide vital information about the paleogeographic and tectonic evolution of the Russian High Arctic. The detrital zircon signatures of the seven dated samples are very similar, suggesting a common provenance for the clastic detritus. The majority of the dated grains belong to the late Neoproterozoic to Cambrian ages, which suggests the maximum depositional age of the enclosing sedimentary units to be Cambrian. The εHf(t) values indicate that juvenile magma mixed with evolved continental crust and the zircons crystallized within a continental magmatic arc setting. Our data strongly suggest that the main provenance for the studied clastics was located within the Timanian Orogen. A review of the available detrital zircon ages from late Neoproterozoic to Cambrian strata across the wider Arctic strongly suggests that Kara Terrane, Novaya Zemlya, Seward Peninsula (Arctic Alaska), Alexander Terrane, De Long Islands, and Scandinavian Caledonides all formed a single tectonic domain during the Cambrian age, with clastics predominantly sourced from the Timanian Orogen.
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Thiede, Järn. "Late Cenozoic depositional environment of the eastern Arctic Basin." Polar Research 5, no. 3 (January 12, 1987): 323–24. http://dx.doi.org/10.3402/polar.v5i3.6903.
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THIEDE, JORN. "Late Cenozoic depositional environment of the eastern Arctic Basin." Polar Research 5, no. 3 (December 1987): 323–24. http://dx.doi.org/10.1111/j.1751-8369.1987.tb00565.x.
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SANTOSH, M., A. S. COLLINS, T. MORIMOTO, and K. YOKOYAMA. "Depositional constraints and age of metamorphism in southern India: U–Pb chemical (EMPA) and isotopic (SIMS) ages from the Trivandrum Block." Geological Magazine 142, no. 3 (May 2005): 255–68. http://dx.doi.org/10.1017/s0016756805000506.
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We report U–Pb electron microprobe (zircon and monazite) and Secondary Ion Mass Spectrometry (SIMS) U–Pb (zircon) ages from a granulite-facies metapelite and a garnet–biotite gniess from Chittikara, a classic locality within the Trivandrum Block of southern India. The majority of the electron-microprobe data on zircons from the metapelite define apparent ages between 1500 and 2500 Ma with a prominent peak at 2109±22 Ma, although some of the cores are as old as 3070 Ma. Zircon grains with multiple age zoning are also detected with 2500–3700 Ma cores, 1380–1520 mantles and 530–600 Ma outer rims. Some homogeneous and rounded zircon cores yielded late Neoproterozoic ages that suggest that deposition within the Trivandrum Block belt was younger than 610 Ma. The outermost rims of these grains are characterized by early Cambrian ages suggesting metamorphic overgrowth at this time. The apparent ages of monazite grains from this locality reveal multiple provenance and polyphase metamorphic history, similar to those of the zircons. In a typical case, Palaeoproterozoic cores (1759–1967 Ma) are enveloped by late Neoproterozoic rims (562–563 Ma), which in turn are mantled by an outermost thin Cambrian rim (∼515 Ma). PbO v. ThO*2 plots for monazites define broad isochrons, with cores indicating a rather imprecise age of 1913±260 Ma (MSWD=0.80) and late Neoproterozoic/Cambrian cores as well as thin rims yielding a well-defined isochron with an age of 557±19 Ma (MSWD=0.82). SIMS U–Pb isotopic data on zircons from the garnet–biotite gneiss yield a combined core/rim imprecise discordia line between 2106±37 Ma and 524±150 Ma. The data indicate Palaeoproterozoic zircon formation with later partial or non-uniform Pb loss during the late Neoproterozoic/Cambrian tectonothermal event. The combined electron probe and SIMS data from the metapelite and garnet–biotite gneiss at Chittikara indicate that the older zircons preserved in the finer-grained metapelite protolith have heterogeneous detrital sources, whereas the more arenaceous protolith of the garnet–biotite gniess was sourced from a single-aged terrane. Our data suggest that the metasedimentary belts in southern India may have formed part of an extensive late Neoproterozoic sedimentary basin during the final amalgamation of the Gondwana supercontinent.
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Long, D. G. F. "Kennedy Channel Formation: key to the early history of the Franklinian continental margin, central eastern Ellesmere Island, Arctic Canada." Canadian Journal of Earth Sciences 26, no. 6 (June 1, 1989): 1147–59. http://dx.doi.org/10.1139/e89-098.
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The Franklinian sequence in the Canadian Arctic Islands may have been initiated by rifting in Late Proterozoic or Early Cambrian times. Unfortunately, no record of this early phase of basin evolution is exposed; the oldest known strata are weakly metamorphosed mudstones, limestones, and sandstones of the Kennedy Channel Formation. Although these have previously been considered late Precambrian in age, the presence of minor trilobite and brachiopod debris indicates an Early Cambrian age, possibly corresponding to a pre-Olenellus trilobite zone. Strata of the Kennedy Channel Formation reflect repeated progradation of shallow-water facies into a slowly subsiding basin that developed in response to subsidence at a late stage of rift development along the Franklinian shelf margin. The first two cycles involve storm- and tide-influenced clastics derived from the Precambrian Shield to the southeast, whereas the third and fourth cycles involve progradation of carbonate ramp and rimmed platform facies. The contact with overlying dolostones of the Ella Bay Formation represents a depositional and diagenetic facies boundary and not an unconformity.
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Eklöf, Johan, Jens Rydell, Jemima Fröjmark, Maria Johansson, and Adolf Seilacher. "Orientation of agnostid shields in Alum Shale (Upper Cambrian): Implications for the depositional environment." GFF 121, no. 4 (December 1999): 301–6. http://dx.doi.org/10.1080/11035899901214301.
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LEGG, DAVID A., and THOMAS W. HEARING. "A late surviving xenopod (Arthropoda) from the Ordovican Period, Wales." Geological Magazine 152, no. 5 (June 19, 2015): 942–48. http://dx.doi.org/10.1017/s001675681400065x.
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AbstractThe Middle Ordovician Llanfallteg Formation has yielded remains of soft-bodied organisms previously known only from Cambrian Burgess Shale-type deposits. A new arthropod Etania howellsorum gen. et sp. nov. is described here, characterized by a semi-circular cephalon, clusters of spinose endites on the endopod and exopods with ovoid distal lobes. These characters are consistent with xenopod affinities, a clade otherwise known exclusively from the Cambrian Period. The discovery of E. howellsorum demonstrates that a number of Burgess Shale-type taxa, including xenopods, survived past the Cambrian Period (albeit within a restricted environment) and may have been outcompeted during the Great Ordovician Biodiversification Event (GOBE).
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Busch, James F., Alan D. Rooney, Edward E. Meyer, Caleb F. Town, David P. Moynihan, and Justin V. Strauss. "Late Neoproterozoic – early Paleozoic basin evolution in the Coal Creek inlier of Yukon, Canada: implications for the tectonic evolution of northwestern Laurentia." Canadian Journal of Earth Sciences 58, no. 4 (April 2021): 355–77. http://dx.doi.org/10.1139/cjes-2020-0132.
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The age and nature of the Neoproterozoic – early Paleozoic rift–drift transition has been interpreted differently along the length of the North American Cordillera. The Ediacaran “upper” group (herein elevated to the Rackla Group) of the Coal Creek inlier, Yukon, Canada, represents a key succession to reconstruct the sedimentation history of northwestern Laurentia across the Precambrian–Cambrian boundary and elucidate the timing of active tectonism during the protracted breakup of the supercontinent Rodinia. These previously undifferentiated late Neoproterozoic – early Paleozoic map units in the Coal Creek inlier are herein formally defined as the Lone, Cliff Creek, Mount Ina, Last Chance, Shade, and Shell Creek formations. New sedimentological and stratigraphic data from these units is used to reconstruct the depositional setting. In the Last Chance Formation, chemostratigraphic observations indicate a ca. 5‰ δ13Ccarb gradient coincident with the globally recognized ca. 574–567 Ma Shuram carbon isotope excursion. Map and stratigraphic relationships in the overlying Shell Creek Formation provide evidence for latest Ediacaran – middle Cambrian tilting and rift-related sedimentation. This provides evidence for active extension through the Cambrian Miaolingian Series in northwestern Canada, supporting arguments for a multiphase and protracted breakup of Rodinia.
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SOUTHGATE, P. N., I. B. LAMBERT, T. H. DONNELLY, R. HENRY, H. ETMINAN, and G. WESTE. "Depositional environments and diagenesis in Lake Parakeelya: a Cambrian alkaline playa from the Officer Basin, South Australia." Sedimentology 36, no. 6 (December 1989): 1091–112. http://dx.doi.org/10.1111/j.1365-3091.1989.tb01544.x.
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