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1
Phillips, Bruce J., Alan W. James e Graeme M. Philip. "THE GEOLOGY AND HYDROCARBON POTENTIAL OF THE NORTH-WESTERN OFFICER BASIN". APPEA Journal 25, n. 1 (1985): 52. http://dx.doi.org/10.1071/aj84004.
Testo completoAbstract (sommario):
Recent petroleum exploration in EP 186 and EP 187 in the north-western Officer Basin has greatly increased knowledge of the regional stratigraphy, structure and petroleum prospectivity of the region. This exploration programme has involved the drilling of two deep stratigraphic wells (Dragoon 1 and Hussar 1) and the acquisition of 1438 km of seismic data. Integration of regional gravity and aeromagnetic data with regional seismic and well data reveals that the Gibson Sub-basin primarily contains a Proterozoic evaporitic sequence. In contrast, the Herbert Sub-basin contains a Late Proterozoic to Cambrian clastic and carbonate sequence above the evaporites. This sequence, which was intersected in Hussar 1, is identified as the primary exploration target in the Western Officer Basin. The sequence contains excellent reservoir and seal rocks in association with mature source rocks. Major structuring of the basin has also been caused by compressive movements associated with the Alice Springs Orogeny. The northwestern Officer Basin thus has all of the ingredients for the discovery of commercial hydrocarbons.
2
Martins-Neto, Marcelo A. "Sequence stratigraphic framework of Proterozoic successions in eastern Brazil". Marine and Petroleum Geology 26, n. 2 (febbraio 2009): 163–76. http://dx.doi.org/10.1016/j.marpetgeo.2007.10.001.
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Cosgrove, G. I. E., L. Colombera e N. P. Mountney. "Eolian stratigraphic record of environmental change through geological time". Geology 50, n. 3 (22 novembre 2021): 289–94. http://dx.doi.org/10.1130/g49474.1.
Testo completoAbstract (sommario):
Abstract The terrestrial sedimentary record provides a valuable archive of how ancient depositional systems responded to and recorded changes in Earth's atmosphere, biosphere, and geosphere. However, the record of these environmental changes in eolian sedimentary successions is poorly constrained and largely unquantified. Our study presents the first global-scale, quantitative investigation of the architecture of eolian systems through geological time via analysis of 55 case studies of eolian successions. Eolian deposits accumulating (1) under greenhouse conditions, (2) in the presence of vascular plants and grasses, and (3) in rapidly subsiding basins associated with the rifting of supercontinents are represented by significantly thicker eolian dune-set, sand-sheet, and interdune architectural elements. Pre-vegetation eolian systems are also associated with more frequent interactions with non-eolian environments. The interplay of these forcings has resulted in dune-set thicknesses that tend to be smallest and largest in Proterozoic and Mesozoic successions, respectively. In the Proterozoic, the absence of sediment-binding plant roots rendered eolian deposits susceptible to post-depositional wind deflation and reworking by fluvial systems, whereby highly mobile channels reworked contiguous eolian deposits. During the Mesozoic, humid greenhouse conditions (associated with relatively elevated water tables) and high rates of basin subsidence (associated with the breakup of Pangea) favored the rapid transfer of eolian sediment beneath the erosional baseline. The common presence of vegetation promoted accumulation of stabilizing eolian systems. These factors acted to limit post-depositional reworking. Eolian sedimentary deposits record a fingerprint of major environmental changes in Earth history: climate, continental configuration, tectonics, and land-plant evolution.
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Alsop, G. I. "The geometry and structural evolution of a crustal-scale Caledonian fold complex: the Ballybofey Nappe, northwest Ireland". Geological Magazine 131, n. 4 (luglio 1994): 519–37. http://dx.doi.org/10.1017/s0016756800012139.
Testo completoAbstract (sommario):
AbstractThe gross geometries exhibited by crustal-scale fold nappes are considered a consequence of both original stratigraphic relationships associated with sub-basin configuration, coupled with the nature of the structural regime and tectonic processes involved in the generation of the nappe pile. The Neo-Proterozoic Dalradian metasediments of northwestern Ireland provide a well-constrained and correlatable stratigraphy which defines a sequence of sub-reclined, tight-isoclinal Caledonian (c. 460 Ma) fold nappes. Within this fold complex, the dominant structure is the crustal-scale Ballybofey Nappe, which may be traced for 40 km along strike and is responsible for a regional (500 km2) stratigraphie inversion. The gentle, NE-plunging attitude of this fold results in a complete spectrum of tectonic levels and deformation gradients being exposed. Relatively low strains in the upper fold limb gradually increase down through the nappe, resulting in the generation of composite foliations and lineations and the development of a 10 km thick shear zone which culminates in a high strain basal detachment with underlying pre-Caledonian basement. The Ballybofey Nappe nucleated and propagated along a major zone of lateral sedimentary facies variation, coincident with the margin of a major Dalradian sub-basin. The large amplitude of the nappe is strongly influenced by the lateral heterogeneity within the metasedimentary sequence, and is associated with a minimum of 25–30 km ESE-directed translation concentrated within the overturned limb. Additional significant displacement is also focused along the basal décollement. Generation of the nappe complex resulted in significant crustal thickening and amphibolite facies metamorphism consistent with 15–18 km of burial, induced by a sequence of nappes propagating in the direction of overshear. The ESE-directed translation of the major fold nappes is away from the Caledonian foreland and a gravity-driven mechanism of nappe emplacement is suggested. Rigorous structural analysis within the cohesive stratigraphie framework enables relationships between the tectonic evolution and stratigraphic patterns to be distinguished, thus allowing models of fold nappe generation and mid-crustal deformation to be evaluated.
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GEHLING, JAMES G., SÖREN JENSEN, MARY L. DROSER, PAUL M. MYROW e GUY M. NARBONNE. "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine 138, n. 2 (marzo 2001): 213–18. http://dx.doi.org/10.1017/s001675680100509x.
Testo completoAbstract (sommario):
The range of Treptichnus pedum, the index trace fossil for the Treptichnus pedum Zone, extends some 4 m below the Global Standard Stratotype-section and Point for the base of the Cambrian Period at Fortune Head on the Burin Peninsula in southeastern Newfoundland. The identification of zigzag traces of Treptichnus isp., even further below the GSSP than T. pedum in the Fortune Head section, and in other terminal Proterozoic successions around the globe, supports the concept of a gradational onset of three-dimensional burrowing across the Proterozoic–Cambrian boundary. Although T. pedum remains a reasonable indicator for the base of the Cambrian Period, greater precision in the stratotype section can be achieved by a detailed re-evaluation of the stratigraphic ranges and the morphological variation of ichnotaxa included in the T. pedum Zone.
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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, n. 5 (settembre 2005): 465–98. http://dx.doi.org/10.1017/s0016756805000956.
Testo completoAbstract (sommario):
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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Kulikov, V. S., V. V. Kulikova e A. K. Polin. "NEW CHRONOSTRATIC SCHEME OF SOUTH-EASTERN FENNOSCANDIA AND ITS USE IN THE PREPARATION OF SMALL-SCALE GEOLOGICAL MAPS OF THE PRECAMBRIAN REGIONS". Proceedings of higher educational establishments. Geology and Exploration, n. 5 (28 ottobre 2017): 5–12. http://dx.doi.org/10.32454/0016-7762-2017-5-5-12.
Testo completoAbstract (sommario):
A new chronostratic scheme of South-East (SE) Fennoscandia has been developed, based on the International Stratigraphie Scale, taking into account some elements of the Common Stratigraphic Scale of Russia and the regional stratigraphic scheme of the North-West (NW) of Russian Federation. A rank of Archean and Proterozoic stratons has been determined (including supersystems for Riphean and Archean geonotems), compatable in dutation to the Phanerozoic systems (Mesozoic and Paleozoic ones). An original coloring for the geological maps of the newly allocated systems and their analogues in the Precambrian, as well as the digital indexing of all stratons of the rank of systems instead of the traditional alphabetic one, have been proposed. Based on the extensive geological materials of the Institute of Geology of Karelian Research Centre of the Russian Academy of Sciences, in view of the new approaches and reliable geochronological data, an areal geological map of SE Fennoscandia in scale 1: 750 000 has been created, which includes the territory of Karelia and adjacent areas of the Russian Federation and eastern Finland. The proposed chronostratic scheme can serve as a basis for developing legends of small-scale state geological maps of the new generation, especially in the regions of the Precambrian development.
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Jackson, J., I. P. Sweet e T. G. Powell. "STUDIES ON PETROLEUM GEOLOGY AND GEOCHEMISTRY, MIDDLE PROTEROZOIC, McARTHUR BASIN NORTHERN AUSTRALIA I: PETROLEUM POTENTIAL". APPEA Journal 28, n. 1 (1988): 283. http://dx.doi.org/10.1071/aj87022.
Testo completoAbstract (sommario):
Mature, rich, potential source beds and adjacent potential reservoir beds exist in the Middle Proterozoic sequence (1400-1800 Ma) of the McArthur Basin. The McArthur and Nathan Groups consist mainly of evaporitic and stromatolitic cherty dolostones interbedded with dolomitic siltstone and shale. They were deposited in interfingering marginal marine, lacustrine and fluvial environments. Lacustrine dolomitic siltstones form potential source beds, while potential reservoirs include vuggy brecciated carbonates associated with penecontemporaneous faulting and rare coarse-grained clastics. In contrast, the younger Roper Group consists of quartz arenite, siltstone and shale that occur in more uniform facies deposited in a stable marine setting. Both source and reservoir units are laterally extensive (over 200 km).Five potential source rocks at various stages of maturity have been discovered. Two of these source rocks, the lacustrine Barney Creek Formation in the McArthur Group and the marine Velkerri Formation in the Roper Group, compare favourably in thickness and potential with rich demonstrated source rocks in major oil-producing provinces. There is abundant evidence of migration of hydrocarbons at many stratigraphic levels. The geology and reservoir characteristics of the sediments in combination with the distribution of potential source beds, timing of hydrocarbon generation, evidence for migration and chances of preservation have been used to rank the prospectivity of the various stratigraphic units in different parts of the basin.
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HARLAND, W. BRIAN. "Origins and assessment of snowball Earth hypotheses". Geological Magazine 144, n. 4 (6 giugno 2007): 633–42. http://dx.doi.org/10.1017/s0016756807003391.
Testo completoAbstract (sommario):
Brian Harland was for many years an editor of this journal. He was also a seminal figure in the origins of the current ‘snowball Earth’ debate, having recognized in 1964 the significance of coupling emerging palaeomagnetic data on palaeolatitude with his interpretations of diamictites. Harland worked extensively in the Arctic and knew well many of the workers involved in the arguments surrounding the origin of diamictites. He thus had a unique perspective on the evidence and the disputes surrounding it. This was his last paper but he was not able to complete it before he died. However, with the help of Professor Ian Fairchild to whom we are indebted, the editors have lightly revised this work which is presented as the personal view of one of the key figures with a very broad stratigraphic appreciation of the problems of ‘snowball Earth’.Records of Precambrian glaciation onwards from the late nineteenth century led to the concept of one or more major ice ages. This concept was becoming well advanced by the mid 1930s, particularly through the compilation of Kulling in 1934. Even so tillite stratigraphy shows that glaciation was exceptional rather than typical of Earth history. Some Proterozoic tillites, sandwiched between warm marine facies, indicate low, even equatorial palaeolatitudes as determined magnetically, and more recently led to ideas of a snow- and ice-covered ‘snowball Earth’. However, interbedded non-glacial facies as well as thick tillite successions requiring abundant snowfall both militate against the hypothesis of extreme prolonged freezing temperatures referred to here as an ‘iceball Earth’ in which all oceans and seas were sealed in continuous ice cover. On the other hand tropical environments were interrupted by glaciation several times in the Proterozoic, something that did not recur in the Phanerozoic. The term ‘snowball Earth’ is consistent with the established view of extremely widespread Proterozoic glaciation, but the ‘iceball Earth’ version of this is not compatible with the geological record.
10
Green, J. W., A. H. Knoll e K. Swett. "Microfossils from silicified stromatolitic carbonates of the Upper Proterozoic Limestone-Dolomite 'Series', central East Greenland". Geological Magazine 126, n. 5 (1 settembre 1989): 567–85. http://dx.doi.org/10.1017/s0016756800022858.
Testo completoAbstract (sommario):
AbstractSilicified flake conglomerates andin situstratiform stromatolites of the Upper Proterozoic (c.700–800 Ma) Limestone-Dolomite ‘Series’, central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages isSiphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder,Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively bySiphonophycus kestron.Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new:Myxococcoides stragulescensn.sp. andScissilisphaera gradatan. sp.
11
Myrow, P. M., N. C. Hughes e N. R. McKenzie. "Reconstructing the Himalayan margin prior to collision with Asia: Proterozoic and lower Paleozoic geology and its implications for Cenozoic tectonics". Geological Society, London, Special Publications 483, n. 1 (21 novembre 2018): 39–64. http://dx.doi.org/10.1144/sp483.10.
Testo completoAbstract (sommario):
AbstractReconstructing the stratigraphic architecture of deposits prior to Cenozoic Himalayan uplift is critical for unravelling the structural, metamorphic, depositional and erosional history of the orogen. The nature and distribution of Proterozoic and lower Paleozoic strata have helped elucidate the relationship between lithotectonic zones, as well as the geometries of major bounding faults. Stratigraphic and geochronological work has revealed a uniform and widespread pattern of Paleoproterozoic strata >1.6 Ga that are unconformably overlain by <1.1 Ga rocks. The overlying Neoproterozoic strata record marine sedimentation, including a Cryogenian diamictite, a well-developed carbonate platform succession and condensed fossiliferous Precambrian–Cambrian boundary strata. Palaeontological study of Cambrian units permits correlation from the Indian craton through three Himalayan lithotectonic zones to a precision of within a few million years. Detailed sedimentological and stratigraphic analysis shows the differentiation of a proximal realm of relatively condensed, nearshore, evaporite-rich units to the south and a distal realm of thick, deltaic deposits to the north. Thus, Neoproterozoic and Cambrian strata blanketed the northern Indian craton with an extensive, northward-deepening, succession. Today, these rocks are absent from parts of the inner Lesser Himalaya, and the uplift and erosion of these proximal facies explains a marked change in global seawater isotopic chemistry at 16 Ma.
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Nagovitsin, K. E., A. M. Stanevich e T. A. Kornilova. "Stratigraphic setting and age of the complex Tappania-bearing Proterozoic fossil biota of Siberia". Russian Geology and Geophysics 51, n. 11 (novembre 2010): 1192–98. http://dx.doi.org/10.1016/j.rgg.2010.10.004.
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SAYLOR, BEVERLY Z., JANICE M. POLING e WARREN D. HUFF. "Stratigraphic and chemical correlation of volcanic ash beds in the terminal Proterozoic Nama Group, Namibia". Geological Magazine 142, n. 5 (settembre 2005): 519–38. http://dx.doi.org/10.1017/s0016756805000932.
Testo completoAbstract (sommario):
At least twenty silicified volcanic ash beds have been identified in the Kuibis and Schwarzrand subgroups of the terminal Proterozoic Nama Group of Namibia. Nineteen of the Nama ash beds are in the Schwarzrand Subgroup in the Witputs subbasin. Two of these are in the siliciclastic-dominated lower part of the subgroup, which consists of the Nudaus Formation and Nasep Member of the Urusis Formation and comprises two depositional sequences. Identification and correlation of these ash beds are very well known based on stratigraphic position. Sixteen ash beds are contained within the carbonate-dominated strata of the Huns, Feldschuhhorn and Spitskop members of the Urusis Formation. These strata comprise four large-scale sequences and eighteen medium-scale sequences. Ash beds have been found in three of the large-scale sequences and seven of the medium-scale sequences. Correlations are proposed for these ash beds that extend over large changes in facies and stratal thickness and across transitions between the seaward margin, depocentre and landward margin of the Huns-Spitskop carbonate shelf. A study of whole rock and in situ phenocryst compositions was conducted to evaluate the feasibility of independently testing sequence stratigraphic correlations by geochemically identifying individual ash beds. Whole rock abundances of Al, Fe, Mg, K and Ti vary inversely with Si, reflecting variations in phenocryst concentration due to air fall and hydrodynamic sorting. These sorting processes did not substantially fractionate whole rock rare earth element abundances (REE), which vary more widely with Si. REE abundances are higher in samples of the Nudaus ash bed than in samples of the Nasep ash bed, independent of position in bed, phenocryst abundance, or grainsize, providing a geochemical means for discriminating between the two beds. Variations in the position of chondrite-normalized whole rock REE plots similarly support suspected correlations of ash beds between widely separated sections of the Spitskop Member. Abundances of Fe, Mg and Mn in apatite plot in distinct clusters for Spitskop ash beds that are known to be different and in clusters that overlap for ash beds suspected of correlating between sections. Abundances of REE in monazites differ for the Nudaus, Nasep and Spitskop ash beds in which these phenocrysts were identified. Multivariate statistical analysis provided a quantitative analysis of the discriminating power of different elements and found that whole rock abundances of Ge, Nb, Cs, Ba and La discriminate among the whole rock compositions of the Nudaus and Nasep ash beds and the Spitskop ash beds that are thought to correlate between sections. Each of the above geochemical signatures, by itself, is not definitive because the differences between beds are comparable to the variability within beds and because some signatures are shared by beds known to be different. Taken together, however, weight-of-evidence arguments based on multiple components and phases can successfully discriminate among Nama ash beds. Results from this study support sequence stratigraphic correlations of Spitskop ash beds that document stratal truncations and gaps in the record related to onlap and erosion.
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Evans, James E., Joshua T. Maurer e Christopher S. Holm-Denoma. "Recognition and significance of Upper Devonian fluvial, estuarine, and mixed siliciclastic-carbonate nearshore marine facies in the San Juan Mountains (southwestern Colorado, USA): Multiple incised valleys backfilled by lowstand and transgressive systems tracts". Geosphere 15, n. 5 (9 agosto 2019): 1479–507. http://dx.doi.org/10.1130/ges02085.1.
Testo completoAbstract (sommario):
Abstract The Upper Devonian Ignacio Formation (as stratigraphically revised) comprises a transgressive, tide-dominated estuarine depositional system in the San Juan Mountains (Colorado, USA). The unit backfills at least three bedrock paleovalleys (10–30 km wide and ≥42 m deep) with a consistent stratigraphy of tidally influenced fluvial, bayhead-delta, central estuarine-basin, mixed tidal-flat, and estuarine-mouth tidal sandbar deposits. Paleovalleys were oriented northwest while longshore transport was to the north. The deposits represent Upper Devonian lowstand and transgressive systems tracts. The overlying Upper Devonian Elbert Formation (upper member) consists of geographically extensive tidal-flat deposits and is interpreted as mixed siliciclastic-carbonate bay-fill facies that represents an early highstand systems tract. Stratigraphic revision of the Ignacio Formation includes reassigning the basal conglomerate to the East Lime Creek Conglomerate, recognizing an unconformity separating these two units, and incorporating strata previously mapped as the McCracken Sandstone Member (Elbert Formation) into the Ignacio Formation. The Ignacio Formation was previously interpreted as Cambrian, but evidence that it is Devonian includes reexamined fossil data and detrital zircon U-Pb geochronology. The Ignacio Formation has a stratigraphic trend of detrital zircon ages shifting from a single ca. 1.7 Ga age peak to bimodal ca. 1.4 Ga and ca. 1.7 Ga age peaks, which represents local source-area unroofing history. Specifically, the upper plate of a Proterozoic thrust system (ca. 1.7 Ga Twilight Gneiss) was eroded prior to exposure of the lower plate (ca. 1.4 Ga Uncompahgre Formation). These results are a significant alternative interpretation of the geologic history of the southern Rocky Mountains.
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Gubin, Igor A., e Vladimir A. Kontorovich. "Seismogeological structure model of the Anabar-Olenek region". Georesursy 23, n. 1 (30 marzo 2021): 70–77. http://dx.doi.org/10.18599/grs.2021.1.7.
Testo completoAbstract (sommario):
The velocity characteristics of the Upper Proterozoic-Phanerozoic sedimentary cover of the Anabar-Olenek region were studied, in particular, the bimodal character of the distribution interval P-wave velocities was established. Taking into account modern ideas about the chronostratigraphy of sediments encountered by the Charchykskaya-1, Burskaya-3410 and Khastakhskaya-930 deep boreholes, stratification of reflecting horizons was carried out and time sections from previous years were reinterpreted. From the perspective of seismic stratigraphic and seismic facies analysis, the Cambrian, Vendian, and Riphean intervals of the section were examined in detail. In the course of the analysis, adjustments to the stratigraphic breakdown of the Burskaya-3410 and Charchykskaya-1 boreholes are proposed. The study shows that the Lapar Formation, which underwent Prepermian erosion, increase in the thickness multiple in an eastward direction. The distribution areas of the Tuessal Formation, the Lower and Middle Cambrian clinoform complex, as well as the areas of the Upper Riphean Formations reaching the Prevendian erosion surface are contoured. An Intrariphean tectonic disagreement between the Kulady Formation and older deposits was established.
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Singh, Rajinder Kumar, Surendra Kumar e Ratikant Sikdar. "Geology and Mineral Potential of Copper-Silver mineralization in Kulu district of Himachal Pradesh, India." Journal of Geoscience, Engineering, Environment, and Technology 4, n. 2-2 (25 luglio 2019): 39. http://dx.doi.org/10.25299/jgeet.2019.4.2-2.2127.
Testo completoAbstract (sommario):
Naraul Formation of the Larji Group in Kulu district of Himachal Pradesh contains the major strata bound Copper mineralization at many places as observed through old working near Naraul, Danala and Kanda in Sainj Valley of Kulu district exposing the Proterozoic Northwestern Himalayan belt. The same structural belt is also known for Silver mineralisation around Manikaran. At Naraul, a regional stratigraphic and mineralogical framework of the Naraul Formation for mineralogical resource assessment was viewed. The old workings within 4-5 km long and 200-300m wide along the NW- SE trending structural trend cover the main ore potential zones. The ore mineralisation seems to be alike the copper silver deposit of the Revett Formation of Montana and Idaho, USA. The deposit in Naraul needs further more drilling investigation and exploration for actual reserve assessment.
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Liu, Deng, e Dai Yong Cao. "Regional Geology Background and Minerogenetic Series in Ongniud Banner of Inner Mongolia". Advanced Materials Research 734-737 (agosto 2013): 408–17. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.408.
Testo completoAbstract (sommario):
Ongniud Banner is located in the northern margin of the North China platform, possessing binary attribute of the greenville period orogenic belt and North China block. The authors reclassify geological unit through the rock stratigraphic correlation and isotope chronology. Achaean strata is mainly composed of quartz schist, chlorite schist, amphibole schist, and the rocks have been highly metamorphosed into the green schist facies, and its single particle zircon U-Pb age is 2645 ±86Ma, so it is assigned to North China block. Proterozoic strata is mainly composed of metamorphic complex including chlorite schist, marble, basalt, amphibolite, plagiogranite and olivine pyroxenolite, and its single particle zircon U-Pb age is 1620±160Ma, so it is assigned to Greenville period orogenic belt. According to 1:50000 stream sediment geochemical elementary assemblage characteristics, the authors discuss the metallogenic endowment and minerogenetic series of geological unit in research area.
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Jinbiao, Chen. "An explanatory note on proterozoic stratigraphic nomenclature used in the People's Republic of China". Precambrian Research 29, n. 1-3 (giugno 1985): 3–4. http://dx.doi.org/10.1016/0301-9268(85)90054-3.
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Alvan, Aldo A., Yacory F. Bustamante, Elvis A. Sánchez e Mirian I. Mamani. "Arquitectura estratigráfica, paleogeografía y proveniencia sedimentaria de las rocas cenozoicas del sur de Perú (Tacna, 18° S)". Andean Geology 47, n. 2 (29 maggio 2020): 351. http://dx.doi.org/10.5027/andgeov47n2-3168.
Testo completoAbstract (sommario):
The Cenozoic rocks lying in the Province of Tacna (18° S), southern Perú, represent approximately 600 m of stratigraphic thickness. This stacking groups the Sotillo (Paleocene), Moquegua Inferior (Eocene), Moquegua Superior (Oligocene), Huaylillas (Miocene) and Millo formations (Pliocene), and these are the sedimentary fill of the Moquegua Basin. The sediments of the three latter formations are organized into nine sedimentary facies and five architectural elements. Their facies associations suggest the existence of an ancient highly channelized multi-lateral fluvial braided system, with upward increase of pyroclastic and conglomeratic depositions. The heavy mineral spectra make each lithostratigraphic unit unique and distinguishable, being the sediments of the Moquegua Superior Formation rich in garnets, titanites and zircons; while the sediments of the Huaylillas and Millo formations in clinopyroxenes. This mineral arrangement becomes an excellent tool for stratigraphic correlations between outcrops and subsurface stratigraphy (by means of well cores studies) and allow to sketch out a new stratigraphic framework and a complex of rocky blocks bounded by normal faults, often tilted. The sediment mineralogy also suggests that the rocks conforming the Western Cordillera were the main source of sediments for the Moquegua Basin in Tacna. In this context, the detritus of the Moquegua Superior Formation derives mainly from the erosion of the rocks forming the Coastal Basal Complex (Proterozoic), the Ambo Group (Carboniferous) and the Junerata/Chocolate Formation (Early Jurassic). The Huaylillas Formation is a pyroclastic and sedimentary unit which components derived mainly from the Huaylillas volcanism (Miocene) and partly from the denudation of the Toquepala Group (Late Cretaceous). The Huaylillas Formation widely contrasts to the underlying Moquegua Superior Formation due its mineralogy and facies. Finally, the detritus of the Millo Formation derived mostly from the rocks forming the Barroso Formation (Pliocene), and their facies represent a higher contrast in relation to the underlying units due its notorious conglomerate facies.
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Clarke, G. L., J. P. Burg e C. J. L. Wilson. "Stratigraphic and structural constraints on the proterozoic tectonic history of the Olary Block, South Australia". Precambrian Research 34, n. 2 (dicembre 1986): 107–37. http://dx.doi.org/10.1016/0301-9268(86)90053-7.
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Chandler, Val W., e Kelley Carlson Malek. "Moving‐window Poisson analysis of gravity and magnetic data from the Penokean orogen, east‐central Minnesota". GEOPHYSICS 56, n. 1 (gennaio 1991): 123–32. http://dx.doi.org/10.1190/1.1442948.
Testo completoAbstract (sommario):
Analytical correlation of gravity and magnetic data through moving‐window application of Poisson's theorem is useful in studying the complex Precambrian geology of central Minnesota. Linear regression between the two data sets at each window position yields correlation, intercept, and slope parameters that quantitatively describe the relationship between the gravity and magnetic data and, in the case of the slope parameter, are often accurate estimates of magnetizatons‐to‐density ratios (MDR) of anomalous sources. In this study, gridded gravity and magnetic data from a 217.6 × 217.6 km area in central Minnesota were analyzed using a 8.5 × 8.5 km window. The study area includes part of the Early Proterozoic Penokean orogen and an Archean greenstone‐granite terrane of the Superior Province. The parameters derived by the moving‐window analysis show striking relationships to many geologic features, and many of the MDR estimates agree with rock property data. Inversely related gravity and magnetic anomalies are a characteristic trait of the Superior Province, but moving‐window analysis reveals that direct relationships occur locally. In the Penokean fold‐and‐thrust belt, gravity and magnetic highs over the Cuyuna range produce a prominent belt of large MDR estimates, which reflect highly deformed troughs of iron‐formation and other supracrustal rocks. This belt can be traced northeastward to sources that are buried by 3–5 km of Early Proterozoic strata in the Animikie basin. This configuration, in conjunction with recent geologic studies, indicates that the Animikie strata, which may represent foreland basin deposits associated with the Penokean orogen, unconformably overlie parts of the fold‐and‐thrust belt, and that earlier stratigraphic correlations between Cuyuna and Animikie strata are wrong. The results of this study indicate that moving‐window Poisson analysis is useful in the study of Precambrian terranes.
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Delpomdor, Franck R. A., Xavier Devleeschouwer, Simo Spassov e Alain R. Préat. "Stratigraphic correlations in mid- to late-Proterozoic carbonates of the Democratic Republic of Congo using magnetic susceptibility". Sedimentary Geology 351 (aprile 2017): 80–101. http://dx.doi.org/10.1016/j.sedgeo.2017.02.007.
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Neogi, Susobhan, Apoorve Bhardwaj e Amitava Kundu. "Evolution of Neoproterozoic Shillong Basin, Meghalaya, NE India: implications of supercontinent break-up and amalgamation". Geological Magazine 159, n. 4 (9 dicembre 2021): 628–44. http://dx.doi.org/10.1017/s0016756821001230.
Testo completoAbstract (sommario):
AbstractFragmentation and amalgamation of supercontinents play an important role in shaping our planet. The break-up of such a widely studied supercontinent, Rodinia, has been well documented from several parts of India, especially the northwestern and eastern sector. Interestingly, being located very close to the Proterozoic tectonic margin, northeastern India is expected to have had a significant role in Neoproterozoic geodynamics, but this aspect has still not been thoroughly studied. We therefore investigate a poorly studied NE–SW-trending Shillong Basin of Meghalaya from NE India, which preserves the stratigraphic record and structural evolution spanning the Neoproterozoic Era. The low-grade metasedimentary rocks of Shillong Basin unconformably overlie the high-grade Archean–Proterozoic basement and comprise a c. 4000-m-thick platform sedimentary rock succession. In this study, we divide this succession into three formations: lower Tarso, middle Ingsaw and upper Umlapher. A NW–SE-aligned compression event later caused the thrusting of these sedimentary rocks over the basement with a tectonic contact in the western margin, resulting in NE–SW-trending fold belts. The rift-controlled Shillong Basin shows a comparable Neoproterozoic evolution with the equivalent basins of peninsular India and eastern Gondwana. The recorded Neoproterozoic rift tectonics are likely associated with Rodinia’s break-up and continent dispersion, which finally ended with the oblique collision of India with Australia and the intrusion of Cambrian granitoids during the Pan-African Orogeny, contributing to the assembly of Gondwana. This contribution is the first to present a complete litho-structural evolution of the Shillong Basin in relation to regional and global geodynamic settings.
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Lindsay, Mark D., Sandra Occhipinti, Crystal Laflamme, Alan Aitken e Lara Ramos. "Mapping undercover: integrated geoscientific interpretation and 3D modelling of a Proterozoic basin". Solid Earth 11, n. 3 (24 giugno 2020): 1053–77. http://dx.doi.org/10.5194/se-11-1053-2020.
Testo completoAbstract (sommario):
Abstract. Gravity and 3D modelling combined with geochemical analysis examine the subsurface within and below the poorly exposed Palaeoproterozoic Yerrida Basin in central Western Australia. Understanding the structure of a region is important as key features indicating past geodynamic processes and tectonic activity can be revealed. However, in stable, post-depositional tectonic settings only the younger sedimentary units tend to be widely exposed, rendering direct observation of basement and intrusive rocks impossible. Geophysical imaging and modelling can reveal the structure of a region undercover. High-magnitude density anomalies around the basin cannot be reconciled with current geological knowledge in the case presented here. The gravity anomalies infer an abundance of buried and high-density material not indicated by the surface geology. A hypothetical causative source for the high-magnitude gravity anomalies is mafic rocks that were intruded and extruded during basin rifting. The simplest and plausible stratigraphic attribution of these interpreted mafic rocks is to the Killara Formation within the Mooloogool Group. However, geochemistry reveals that the Killara Formation is not the only host to mafic rocks within the region. The mafic rocks present in the Juderina Formation are largely ignored in descriptions of Yerrida Basin magmatism, and results indicate that they may be far more substantial than once thought. Sulfur isotopic data indicate no Archean signature to these mafic rocks, a somewhat surprising result given the basement to the basin is the Archean Yilgarn Craton. We propose the source of mafic rocks is vents located to the north along the Goodin Fault or under the Bryah sub-basin and Padbury Basin. The conclusion is that the formation of the Yerrida Basin involves a geodynamic history more complex than previously thought. This result highlights the value in geophysics and geochemistry in revealing the complexity of the earlier geodynamic evolution of the basin that may be indiscernible from surface geology but may have high importance for the tectonic development of the region and its mineral resources.
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Kuznetsov, A. B., M. A. Semikhatov e I. M. Gorokhov. "The Sr isotope chemostratigraphy as a tool for solving stratigraphic problems of the Upper Proterozoic (Riphean and Vendian)". Stratigraphy and Geological Correlation 22, n. 6 (novembre 2014): 553–75. http://dx.doi.org/10.1134/s0869593814060033.
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Li, Shuang-Qing, Song He e Fukun Chen. "Provenance changes across the mid-Cretaceous unconformity in basins of northeastern China: Evidence for an integrated paleolake system and tectonic transformation". GSA Bulletin 133, n. 1-2 (1 giugno 2020): 185–98. http://dx.doi.org/10.1130/b35660.1.
Testo completoAbstract (sommario):
Abstract Detrital zircon U-Pb dating and whole-rock Nd isotopic analyses were carried out on selected stratigraphic horizons across a major unconformity between synrift and postrift stages in the Songliao Basin and Dasanjiang basin group of NE China to constrain the crustal evolution of the source area providing detritus into these basins. The strata underlying the mid-Cretaceous unconformity in the Songliao Basin show regionally distinct detrital zircon age populations and Nd isotopic compositions, which generally are characterized by Phanerozoic age peaks and relatively depleted Nd isotopic compositions, indicating derivation from nearby highlands. In contrast, the overlying strata are dominated by Proterozoic zircon ages and enriched Nd isotopic compositions, which imply that the provenance source region shifted to the northern part of the North China craton. A coeval provenance change also affected the sedimentary architecture in the eastern Dasanjiang basin group, marking the migration of erosion centers from west to east. The contribution from Lesser Xing’an–Zhangguangcai ranges was pronounced during deposition of synrift strata but became negligible afterward in the Songliao and Dasanjiang areas, which is consistent with both basin complexes temporarily forming an extensive lake system during the early Late Cretaceous. This paleolake was likely responsible for transgressive events recorded in the Late Cretaceous strata of basins in NE China. Combining observations from seismic reflection profiles and the stratigraphic record of neighboring intracontinental sedimentary basins as well as widespread contemporaneous exhumation and denudation events, we suggest that the provenance variation in basin strata was controlled by large-scale tectonic transitions in East Asia. The switch from extension to contraction during the mid-Cretaceous is attributed to the docking of the Okhotomorsk block along the East Asian continental margin. The resulting lithospheric buckling might have been responsible for reshaping the basin-and-range configuration in NE Asia.
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Young, Grant M. "Stratigraphic and tectonic settings of Proterozoic glaciogenic rocks and banded iron-formations: relevance to the snowball Earth debate". Journal of African Earth Sciences 35, n. 4 (novembre 2002): 451–66. http://dx.doi.org/10.1016/s0899-5362(02)00158-6.
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Al-Hadidy, Aboosh H. "Paleozoic stratigraphic lexicon and hydrocarbon habitat of Iraq". GeoArabia 12, n. 1 (1 gennaio 2007): 63–130. http://dx.doi.org/10.2113/geoarabia120163.
Testo completoAbstract (sommario):
ABSTRACT The crystalline Proterozoic Basement does not crop out in Iraq, but is interpreted from seismic and geophysical potential data to range in depth from about 6–10 km in western Iraq, to 12–15 km in the Zagros Mountains, in eastern Iraq. The Cambrian and Lower Ordovician sedimentary successions of Jordan and Saudi Arabia (including the Middle Cambrian Burj carbonates) are interpreted to extend into Iraq based on seismic data and regional correlations. The entire Paleozoic succssion is about 3–4 km thick. The Ordovician-Permian succession in Iraq consists of ten formations that are here described in a lexicon format. For each formation, the type and reference sections in outcrop or/and subsurface are reviewed (as defined by the original authors or herein), and further documented by including subsurface data (electrical logs and biostratigraphic studies). The Ordovician-Permian formations (and their members) are here placed chronostratigraphically according to the “Geological Time Scale GTS 2004” (and standard global Ordovician stages) and the Arabian Plate sequence stratigraphic framework. The ten formations are: (1) the Early?, Middle and Late Ordovician Khabour Formation (with from base-up seven informal members K7 to K1); (2) the Silurian Akkas Formation (with the proposed lower Hoseiba and upper Qaim members); (3 and 4) the Late Devonian Pirispiki Red Beds Formation and enclosed Chalki Volcanics; (5) the Late Devonian (Famennian) and early Carboniferous (early Tournaisian) Kaista Formation; (6) the Carboniferous (Tournaisian) Ora Formation; (7) the Carboniferous (Tournaisian-Visean) Harur Limestone Formation; (8) the Visean-Serpukhovian Raha Formation (proposed here); (9) the late Carboniferous-early Middle Permian Ga’ara Formation; and (10) the late Middle and Late Permian Chia Zairi Formation (in outcrop consisting from base-up of the informal Dariri, Satina Anhydrite and Zinnar members). The Late Devonian-early Carboniferous succession, comprising the Pirispiki, Chalki, Kaista, Ora, Harur and Raha formations, is here proposed to comprise the Khleisia Group. The Paleozoic succession of Iraq is hydrocarbon-prospective in the western part of the country, and particularly in the Western Desert near Jordan, Saudi Arabia and Syria. The source-rock component of the petroleum system consists of several potential organic-rich shales including the regionally widespread Silurian Akkas “hot shale”. In the Akkas-1 well, two hot shale units have a combined thickness of 61 m (210 ft) and total organic carbon (TOC) values that reach 16.6%. Several reservoirs and seals present exploration targets in the Western Desert of Iraq. In the Akkas field, light (specific gravity of 42° API), sweet oil and gas (no H2S) were discovered in 1993 in the Akkas and Khabour formations, respectively. The Akkas reservoir occurs in the upper Qaim Member of the Silurian Akkas Formation and consists of sandstones that have a porosity of 6.5% and permeability of 0.2 mD. The Khabour reservoir occurs in the Upper Ordovician K1–K4 members and consists of sandstones with a fracture porosity of up to 7.6% and permeability of 0.13 mD. In North Iraq the carbonates of the Permian Chia Zairi and Triassic Mirga Mir formations correlate to gas reservoirs in the Khuff Formation of Arabia and the Dalan and Kangan formations of Iran, and may therefore be prospective. Southern Iraq, along the Kuwait and Saudi Arabian border, may also be prospective; however, no wells have been drilled into the deep Paleozoic succession in this vast region.
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Farooqui, Mohammed Y., Khamis Farhoud, Dia Mahmoud e Ahmed N. El-Barkooky. "Petroleum potential of the interpreted Paleozoic geoseismic sequences in the South Diyur Block, Western Desert of Egypt". GeoArabia 17, n. 3 (1 luglio 2012): 133–76. http://dx.doi.org/10.2113/geoarabia1703133.
Testo completoAbstract (sommario):
ABSTRACT The South Diyur exploration block of nearly 38,000 sq km is located in the Farafra Oasis region in the Western Desert of Egypt. It is a frontier exploration area, the nearest well being Ammonite-1, a dry hole drilled by Conoco in 1979 immediately outside the southwestern corner of the block. The South Diyur Block is located on the probable northeast extension of the Kufra Basin in southeast Libya. Although prolific reserves of oil and gas occur in Paleozoic basins in North Africa and throughout the Middle East, to date, the targets for petroleum exploration in the northern Western Desert have been in Jurassic and Cretaceous rocks. The regional structural surface features in the South Diyur Block are the NE-trending Bahariya and Farafra anticlines interpreted as a deeply eroded and inverted Late Cretaceous structure on the southern extension of the Syrian Arc system. The oldest exposed rocks are a Cretaceous sequence of sublittoral sediments (the Campanian Wadi Hennis Formation) in the core of the anticline. The interpretation of the subsurface is based on 1,175 line-km of reprocessed 1970s-vintage 2-D seismic. Four sequence boundaries have been identified from the seismic data. SB-1 correlates with the Jurassic/Cretaceous boundary in Ammonite-1. SB-2 is regionally correlated with the Late Devonian to Early Carboniferous Hercynian unconformity that overlies deeply eroded and truncated Paleozoic sequences and possibly marks the regionally extensive Late Paleozoic basin inversion. SB-3 near the base of the interpreted Silurian sequence coincides with the ‘hot shale’ petroleum source rock that is present throughout North Africa and the Middle East. SB-4 is interpreted as a major unconformity at the top of an Upper Proterozoic sedimentary section that was misinterpreted as the Precambrian acoustic basement in Ammonite-1. Five seismic sequences relate to the seismic boundaries. SS-1, from the surface to SB-1 is characterized by subparallel seismic stratification and is composed mainly of sandstone with shale interbeds in Ammonite-1. SS-2, bounded by SB-1 and SB-2, is distinguished by parallel to subparallel seismic stratification. In Ammonite-1, the sequence of interbedded sandstone and shale is fresh-water bearing and lacking in top seals, thus reducing its prospectivity. The underlying SS-3 (SB-2 to SB-3) directly underlies the Hercynian unconformity and is characterized by semi-transparent seismic facies that may correspond to a thick Silurian shale sequence. SS-4 (SB-3 to SB-4) of probable Cambrian–Ordovician age has parallel seismic stratification. Deep channels are interpreted as evidence of a Late Ordovician–Early Silurian glacial phase that is present throughout North Africa and the Middle East. SS-5 (below SB-4) is marked by partial subparallel seismic stratification and block faulting. It probably belongs to the Late Proterozoic (Pan-African) phase of block faulting and pull-apart basins. Similar seismic geometries and facies occur in the Kufra Basin in southeast Libya and in many parts of the Arabian Plate, including the prolific petroleum systems of Oman. Exploration plays in the South Diyur Block are a combination of Paleozoic structural and stratigraphic traps associated with prospective fairways, and possible stratigraphic traps in the Late Ordovician–Early Silurian glacial channels. In addition, the interpreted Late Proterozoic sequences (SS-5) warrant further evaluation. In order to identify future exploration plays and drill targets, additional 2-D seismic (4,490 line-km), aeromagnetic and airborne gravity surveys will be integrated with the present seismic data and drilling results from Ammonite-1. This will allow a proper assessment of the magnetic basement, basin configuration and prospective fairways.
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GROTZINGER, J., E. W. ADAMS e S. SCHRÖDER. "Microbial–metazoan reefs of the terminal Proterozoic Nama Group (c. 550–543 Ma), Namibia". Geological Magazine 142, n. 5 (settembre 2005): 499–517. http://dx.doi.org/10.1017/s0016756805000907.
Testo completoAbstract (sommario):
Thrombolite and stromatolite reefs occur at several stratigraphic levels within the terminal Proterozoic Nama Group (c. 550–543 Ma) of central and southern Namibia. The reefs form integral parts of several carbonate platforms within the Nama Group, including the Kuibis platform of the northern Nama Basin (Zaris subbasin), and Huns platform (Witputs subbasin) of the southern Nama Basin. The reefs are composed of both thrombolites and stromatolites that form laterally continuous biostromes, isolated patch reefs, and isolated pinnacle reefs ranging in scale from a metre to several kilometres in width. In the majority of cases, the reefs occur stratigraphically as an integral facies within the transgressive systems tracts of sequences making up the Kuibis and Huns platforms. This suggests that a regime of increasing accommodation was required to form well-developed reefs, though reefs also occur sporadically in highstand systems tract settings. Within a given transgressive systems tract, a regime of increasing accommodation through time favours the transition from sheet-like biostromal geometries to more isolated patch and pinnacle biohermal geometries. Similarly, increasing accommodation in space, such as a transect down depositional dip, shows a similar transition from more sheet-like geometries in updip positions to more isolated geometries in downdip positions. Reefal facies consist of thrombolitic domes, columns and mounds with well-developed internal clotted textures, in addition to stromatolitic domes, columns and mounds, with crudely to moderately well-developed internal lamination. Stromatolites are better developed in conditions of relatively low accommodation, and updip locations, under conditions of higher current velocities and greater sediment influx. Thrombolites are better developed in conditions of relatively high accommodation and low sediment influx. Both types of microbialites are intimately associated with the first calcifying metazoan organisms, which may have attached themselves to the sediment surface or otherwise lived within sheltered depressions within the rough topography created by ecologically complex mats. The appearance of thrombolitic textures during terminal Proterozoic time is consistent with colonization of cyanobacterial mats by higher algae and metazoans, which would have been an important process in generating clotted textures. Fabrics in the Nama thrombolites are well preserved and show evidence of thrombolitic mesoclots being overgrown by fibrous marine carbonate, interpreted as former aragonite. This was followed by emplacement of geopetal micrite fills, and precipitation of dolomite as an isopachous rim cement, followed by occlusion of remaining porosity by blocky calcite spar.
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Schieber, Juergen. "Stratigraphic control of rare-earth pattern types in Mid-Proterozoic sediments of the Belt Supergroup, Montana, U.S.A.: Implications for basin analysis". Chemical Geology 54, n. 1-2 (gennaio 1986): 135–48. http://dx.doi.org/10.1016/0009-2541(86)90077-x.
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JACKSON, M. J., E. L. SIMPSON e K. A. ERIKSSON. "Facies and sequence stratigraphic analysis in an intracratonic, thermal-relaxation basin: the Early Proterozoic, Lower Quilalar Formation and Ballara Quartzite, Mount Isa Inlier, Australia". Sedimentology 37, n. 6 (dicembre 1990): 1053–78. http://dx.doi.org/10.1111/j.1365-3091.1990.tb01846.x.
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Kaufman, Alan J., J. M. Hayes, Andrew H. Knoll e Gerard J. B. Germs. "Isotopic compositions of carbonates and organic carbon from upper Proterozoic successions in Namibia: stratigraphic variation and the effects of diagenesis and metamorphism". Precambrian Research 49, n. 3-4 (febbraio 1991): 301–27. http://dx.doi.org/10.1016/0301-9268(91)90039-d.
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Al-Husseini, Moujahed I. "MIDDLE EAST GEOLOGIC TIME SCALE 2010: Early Cambrian Asfar Sequence". GeoArabia 15, n. 1 (1 gennaio 2010): 137–60. http://dx.doi.org/10.2113/geoarabia1501137.
Testo completoAbstract (sommario):
ABSTRACT This paper is the first in a series dedicated to the Phanerozoic Cambrian Period, and Neoproterozoic Ediacaran and Cryogenian periods, as represented in the Middle East Geologic Time Scale (ME GTS, see enclosed Chart). It introduces the term Asfar Sequence to represent a regional Early Cambrian time-rock unit, consisting mainly of continental quartz-rich arkosic sandstone, shale and siltstone, which attain a thickness of at least 750 m in Jordan and more than 700 m in Oman. The term “Asfar”, meaning yellow in Arabic, was chosen because it is the standard color for sandstone in ME GTS. To describe its stratigraphy, four representative formations are reviewed in lexicon format: Salib Arkosic Sandstone of Jordan, Siq Sandstone of Saudi Arabia, Amin Formation of Oman and Lalun Sandstone of Iran. The stratigraphic geometry of the lower boundary of the Sequence varies considerably by locality. In some regions in Iran it is conformable above the shales of the Zaigun Formation. In other regions, such as western Jordan, it is an onlap surface over Proterozoic and/or Lower and Middle Cambrian paleohighs, or a pronounced angular unconformity (e.g. central and southern Saudi Arabia). The paleo-relief represented by the unconformity surface, in many regions, forms a regional peneplain (e.g. central and eastern Jordan) implying erosion; in other paleohigh regions, the Sequence is absent by non-deposition. The age of the base Asfar Sequence is estimated at ca. 530 Ma, based on radiometric data and depositional rates in basinal areas. The top boundary of the Sequence, in Iran, Jordan, and northern and northeastern Saudi Arabia, is represented by a sequence boundary (or its correlative unconformity), above which marine, fine-grained siliciclastics and carbonates of late Early to early Mid-Cambrian age were deposited: Mila Formation in Iran, and Burj Formation in Jordan and Saudi Arabia, implying an age older than ca. 510 Ma in GTS 2004. In Oman, however, continental rather than marine deposition (Miqrat and coeval Mahwis formations) continued above the unconformity in ?Middle Cambrian. For the purpose of regional correlations it is proposed that the Angudan Unconformity of Oman be taken as the name for the basal boundary of the Sequence and the Burj Sequence Boundary for its top.
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Harland, W. Brian, e Nicholas J. Butterfield. "Chapter 12 Pre-Vendian history". Geological Society, London, Memoirs 17, n. 1 (1997): 227–43. http://dx.doi.org/10.1144/gsl.mem.1997.017.01.12.
Testo completoAbstract (sommario):
It so happens that rocks of Vendian age are extensive and are well exposed in Svalbard. This applies especially to early Vendian, i.e. Varanger, with two distinctive glacial horizons as are treated in the Chapter 13. The Early Varanger (Smalfjord) episode can be correlated in most sections and so provides a reference horizon which serves approximately to identify pre-Varanger rocks. The pre-Vendian rocks have yet to show such good correlation characters. Therefore in Svalbard it is convenient to consider pre-Vendian successions together. Their distribution is shown in the map (Fig. 12.1).Some pre-Vendian sequences are punctuated by unconformities. Moreover, the sequences contain both high-grade metamorphosed and highly deformed rocks as well as undeformed fossiliferous strata. Therefore it is of interest to determine any Preeambrian diastroph-ism and even tectonothermal events. The term proto-basement was introduced (Harland 1997) to distinguish a Preeambrian basement, that formed in (say) Proterozoic time, from the ubiquitous basement formed by Early to mid Paleozoic tectogenesis, but made largely of Preeambrian rocks. It is to distinguish proto-basement within the basement underlying Devonian and Carboniferous strata. Proto-basement from such a study (structural, stratigraphic, isotopic) is shown in darker ornament in Fig. 12.1 and discussed in Section 12.3.Were the spatial relationships between these localities originally as now, intense tectonism, metamorphism and magmatism would suggest a division of Preeambrian history in Svalbard by such events. But Svalbard, small though it is on a global scale, comprises three or more distinct provinces which in Preeambrian and early Paleozoic times may have
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Gibson, Timothy M., Sarah Wörndle, Peter W. Crockford, T. Hao Bui, Robert A. Creaser e Galen P. Halverson. "Radiogenic isotope chemostratigraphy reveals marine and nonmarine depositional environments in the late Mesoproterozoic Borden Basin, Arctic Canada". GSA Bulletin 131, n. 11-12 (24 aprile 2019): 1965–78. http://dx.doi.org/10.1130/b35060.1.
Testo completoAbstract (sommario):
Abstract The ca. 1050 Ma Bylot Supergroup in Arctic Canada is one of the best-preserved archives of late Mesoproterozoic geochemistry and biology and offers evidence that this period of Earth history may have been more biogeochemically dynamic than previously appreciated. The Bylot Supergroup was deposited in the Borden Basin and is the most thoroughly studied stratigraphic succession from a series of broadly contemporaneous late Mesoproterozoic intracratonic basins known as the Bylot basins. This ∼6-km-thick mixed carbonate-siliciclastic succession has undergone minimal postdepositional deformation and is now exposed on Baffin and Bylot Islands, Nunavut, Canada. Deep-water and tidally influenced carbonate facies, traditionally interpreted as marine, have yielded important insights into the evolution of Proterozoic seawater chemistry; however, more recent studies indicate that the Borden Basin was restricted marine or lacustrine for portions of its depositional history. Here, we present new multiproxy radiogenic isotope chemostratigraphic data spanning the Bylot Supergroup. A comparison of stratigraphic trends in radiogenic isotope data from hydrogenous (black shale 187Os/188Os and limestone 87Sr/86Sr) and detrital (whole-rock mudstone 143Nd/144Nd) sedimentary phases elucidates the complex hydrologic history of the Borden Basin and reconciles these disparate interpretations. Episodic coupling and decoupling between the composition of basin waters (from Os and Sr isotopes) and the local weathering input to the basin (from Nd isotopes) indicate that depositional environments within the Borden Basin fluctuated between marine and nonmarine (i.e., lacustrine). Variations in basin hydrology controlled secular sedimentation patterns through changes in basin water chemistry. These interpretations help to characterize the environment in which the early red algal fossil Bangiomorpha pubescens evolved. Episodically restricted epeiric seaways, such as within the Borden Basin, were relatively widespread within Rodinia and may have exerted unique selective pressures on eukaryotic evolution in the Mesoproterozoic Era. Hydrogenous and detrital radiogenic isotope chemostratigraphy, as implemented in this study, may provide a useful paleoenvironmental framework for future paleontological studies aimed at testing the role of freshwater environments in eukaryotic evolution. In addition, 87Sr/86Sr compositions from 81 new middle Bylot Supergroup marine limestone samples, calibrated by recent Re-Os geochronology, contribute to the terminal Mesoproterozoic marine 87Sr/86Sr curve. These data display a rise from ∼0.705 to 0.706 that reflects weathering of the active Grenville orogenic belt and demonstrates a global increase in chemical weathering during the amalgamation of Rodinia.
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Sahoo, Janmejaya, Prabodha Ranjan Sahoo, Israil Khan e Akella Satya Venkatesh. "Insights into the Metallogenesis of the Felsic Volcanic Hosted Mundiyawas-Khera Cu Deposit, Alwar Basin, Western India". Minerals 12, n. 3 (17 marzo 2022): 370. http://dx.doi.org/10.3390/min12030370.
Testo completoAbstract (sommario):
Copper and associated gold mineralization in the Mundiyawas-Khera area of western India is hosted by the Proterozoic felsic volcanic rocks of rhyo-dacite composition. Signatures of hydrothermal alteration represented by sericite, epidote, scapolite and carbonates are well observed around the ore mineralization zone. The felsic volcanic rocks with gently to flat sloping REE pattern, variable negative Eu anomaly, intermediate abundances of HFSE and moderate to low Zr/Y anomalies are suggested to be FII, FIIIa and FIV type rhyolite. The felsic volcanic host rock for copper mineralization has a depleted and flat HREE pattern and indicates the crustal source, which is garnet free. Negative Eu anomaly in the rock is probably because of the intracrustal partial melting formed in a rift related environment. The high temperature magmatic activities are probably evolved due to the partial melting of crust at shallow to moderate depths, suggesting an evolved continental crust. The δ13C values of the mineralized carbonate veins range between −10.4‰ and −0.9 ‰ (min = −10.6‰, n = 27), whereas the δ18O values show a range of 16.35‰ to 25.23‰ (min = 21.49‰, n = 27), ideally suggesting a mixed source for the ore bearing fluid. Geological, geochemical and stable isotope data of the Mundiyawas-Khera copper deposit suggest it to be a VMS/VHMS setup and these insights will lead to finding new deposits in the nearby areas, having same stratigraphic horizons and similar lithogeochemical assemblages.
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Semikhatov, M. A., A. B. Kuznetsov e N. M. Chumakov. "Isotope age of boundaries between the general stratigraphic subdivisions of the Upper Proterozoic (Riphean and Vendian) in Russia: The evolution of opinions and the current estimate". Stratigraphy and Geological Correlation 23, n. 6 (novembre 2015): 568–79. http://dx.doi.org/10.1134/s0869593815060088.
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Hughes, G. Wyn, David J. Grainger, Abdul-Jaleel Abu-Bshait e M. Jarad Abdul-Rahman. "Lithostratigraphy and Depositional History of Part of the Midyan Region, Northwestern Saudi Arabia". GeoArabia 4, n. 4 (1 ottobre 1999): 503–42. http://dx.doi.org/10.2113/geoarabia0404503.
Testo completoAbstract (sommario):
ABSTRACT The Midyan region provides a unique opportunity in which to examine exposures of the Upper Cretaceous and Neogene sedimentary succession. Recent investigations have yielded new interpretations of its depositional environments, stratigraphic relationships, and structure. In this paper, all the lithostratigraphic units of the Midyan succession are considered to be informal in advance of an on-going process of formalization. The region is bounded to the north and northeast by mountains of Proterozoic rocks and to the west and south by the Gulf of Aqaba and the Red Sea, respectively. The Wadi Ifal plain occupies most of the eastern half of the region, beneath which is a thick sedimentary succession within the Ifal basin. The oldest sedimentary rocks are the fluviatile Upper Cretaceous Adaffa formation and marine siliciclastics and carbonates of the lower Miocene Tayran group, unconformable on the Proterozoic basement. The Tayran group is unconformably overlain by the deep-marine lower Miocene Burqan formation that, in turn, is overlain by marine mudstones, carbonates, and evaporites of the middle Miocene Maqna group. The poorly exposed middle Miocene Mansiyah and middle to upper Miocene Ghawwas formations consist of marine evaporites and shallow to marginal marine sediments, respectively. The youngest rocks are alluvial sands and gravels of the Pliocene Lisan formation. A complex structural history is due to Red Sea Oligocene-Miocene extension tectonics, and Pliocene-Recent anti-clockwise rotation of the Arabian Plate relative to Africa on the Dead Sea Transform Fault. The Upper Cretaceous succession is a probable pre-rift unit. The Oligocene?-Miocene syn-rift 1 phase of continental extension caused slow subsidence (Tayran group). Syn-rift 2 was an early Miocene phase of rapid subsidence (Burqan formation) whereas syn-rift 3 (early to middle Miocene) was another phase of slow deposition (Maqna group). The middle to late Miocene syn-rift 4 phase coincided with the deposition of the Mansiyah and Ghawwas formations. The Lower Pliocene to Recent succession is related to the drift (post-rift) phase during which about 45 kilometers of sinistral movement occurred on the Dead Sea Fault. The structural control on sedimentation is evident: the Ifal basin was formed by east-west lithospheric extension; pull-apart basins occur along major left-lateral faults on the eastern coast of the Gulf of Aqaba; and basin-bounding faults controlled deposition of the Burqan, Ghawwas, and Lisan formations. Pliocene to Recent earth movements may be responsible for activating salt diapirism in the Ifal basin. Extensive Quaternary faulting and regional uplift caused the uplift of coral reefs to at least 6 to 8 meters above sea level.
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Al-Husseini, Moujahed. "Late Ediacaran to early Cambrian (Infracambrian) Jibalah Group of Saudi Arabia". GeoArabia 16, n. 3 (1 luglio 2011): 69–90. http://dx.doi.org/10.2113/geoarabia160369.
Testo completoAbstract (sommario):
ABSTRACT This paper is one of a series that document the Neoproterozoic – Cambrian rock units in the Middle East Geologic Time Scale. It is focused on the oldest sedimentary succession in Saudi Arabia, the late Ediacaran – early Cambrian (Infracambrian) Jibalah Group (ca. 585 to 530–520 Ma). The group crops out in disconnected, pull-apart basins (ca. 10–100 km long and up to 20 km wide) along the NW-trending, strike-slip Najd Fault System in the Arabian Shield. It was described and mapped in the 1960s to 1980s, and several formations were defined and named in two areas separated by ca. 400 km. The stratigraphic successions in these two areas have not been correlated, nor has their relationship to the subsurface been resolved. This paper reviews the nomenclature, type sections, lithologies and ages of the formations and members (sometimes units and/or facies) of the Jibalah Group. The Jibalah Group unconformably overlies the Ediacaran Shammar Group (ca. 620–585 Ma, consisting mainly of rhyolite or granitic plutons), or older Proterozoic rocks. The age of the intervening Sub-Jibalah Unconformity is here estimated at ca. 585 Ma based on radiometric data and regional correlations. The lower part of the Jibalah Group is defined in the northern Arabian Shield in the Mashhad area, where it consists of three formations, in ascending order: (1) undated Rubtayn Formation, divided informally into the “Volcanic Conglomerate Member” (up to ca. 700 m thick), “Polymictic Conglomerate Member” (up to ca. 1,500 m thick) and “Sandstone Member” (up to ca. 1,000 m thick); (2) poorly dated Badayi Formation consisting of andesite-basalt flows (ca. 150 m thick); (3) undated Muraykhah Formation (330–370 m thick) consisting of the informal “Cherty Limestone Member” (ca. 135 m thick), “Siltstone and Mudstone Member” (ca. 20 m thick) and “Dolomitic Limestone Member” (ca. 135–175 m thick). The Rubtayn, Badayi and Muraykhah formations in the northern Arabian Shield, by stratigraphic position and lithology, correspond to the Umm Al ‘Aisah Formation in the Najd pull-apart basins of the central Arabian Shield. In particular, the Cherty Limestone unit (300–500 m thick) of the Umm Al ‘Aisah Formation is correlated to the Muraykhah Formation, which represents a marine flooding event. Above the Muraykhah Formation, the uppermost part of the group is defined in the central Arabian Shield by the undated Jifn Formation (up to ca. 2,500 m thick). The Jibalah Group is unconformably overlain by the lower Cambrian Siq Sandstone Formation (Asfar Sequence), and the intervening Sub-Siq Unconformity (Angudan Unconformity) has an estimated age between ca. 530–520 Ma.
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Wu, Chen, Changfeng Liu, Suoya Fan, Andrew V. Zuza, Lin Ding, Wencan Liu, Baoying Ye, Shijie Yang e Zhiguang Zhou. "Structural analysis and tectonic evolution of the western domain of the Eastern Kunlun Range, northwest Tibet". GSA Bulletin 132, n. 5-6 (30 ottobre 2019): 1291–315. http://dx.doi.org/10.1130/b35388.1.
Testo completoAbstract (sommario):
Abstract The Tibetan Plateau, the largest highland on Earth, formed due to the collision of India-Asia over the past 50–60 m.y., and the evolution of the Tibetan Plateau impacts our knowledge of continental tectonics. Examination of the northernmost margin of the Tibetan Plateau is key to unravelling the deformation mechanisms acting in northern Tibet. The left-slip Altyn Tagh fault system defines the northwest margin of the Tibetan Plateau, separating the Western and Eastern Kunlun Ranges in the southwest. Both Cenozoic and pre-Cenozoic crustal deformation events at this junction between the Altyn Tagh and Kunlun Ranges were responsible for the construction of northwestern Tibet, yet the relative contribution of each phase remains unconstrained. The western domain of the Eastern Kunlun Range is marked by active NE-trending, left-slip deformation of the Altyn Tagh fault and an E-striking Cenozoic thrust system developed in response India-Asia collision. To better constrain the Paleozoic Altyn Tagh and Kunlun orogens and establish the Cenozoic structural framework, we conducted an integrated investigation involving detailed geologic mapping (∼1:50,000 scale), U-Pb zircon geochronology, and synthesis of existing data sets across northwestern Tibet. Our new zircon analyses from Paleoproterozoic–Cretaceous strata constrain stratigraphic age and sediment provenance and highlight Proterozoic–Paleozoic arc activity. We propose a tectonic model for the Neoproterozoic–Mesozoic evolution of northwestern Tibet wherein restoration of an ∼56-km-long balanced cross section across the western domain of the Eastern Kunlun suggests that Cenozoic minimum shortening strain was ∼30% (∼24 km shortening). Field evidence suggests this shortening commenced after ca. 25–20 Ma, which yields an average long-term shortening rate of 1.2–0.9 mm yr–1 and strain rates of 4.7 × 10–16 s–1 to 2.3 × 10–16 s–1. Geometric considerations demonstrate that this contractional deformation did not significantly contribute to left-slip offset on the Altyn Tagh fault, which has ∼10 mm/yr slip rates.
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Couëffé, Renaud, e Marco Vecoli. "New sedimentological and biostratigraphic data in the Kwahu Group (Meso- to Neo-Proterozoic), southern margin of the Volta Basin, Ghana: Stratigraphic constraints and implications on regional lithostratigraphic correlations". Precambrian Research 189, n. 1-2 (agosto 2011): 155–75. http://dx.doi.org/10.1016/j.precamres.2011.05.009.
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Higgins, A. K. "Geology of central and eastern North Greenland". Rapport Grønlands Geologiske Undersøgelse 128 (31 dicembre 1986): 37–54. http://dx.doi.org/10.34194/rapggu.v128.7923.
Testo completoAbstract (sommario):
A historical review of geological research in North Greenland is followed by a summary of the main results of the 1978-80 GGU expeditions to the region. New outcrops of Archaean and early Proterozoic crystalline rocks are recorded only as xenoliths in dykes and volcanic centres. A revised stratigraphy is applied to the middle Proterozoic Independence Fjord Group sandstones, while petrographic and isotopic studies have been made of the cross-cutting Midsommersø dolerites and the overlying Zig-Zag Dal Basalt Formation. No convincing evidence has been found of a Carolinidian orogenic episode separating these units from succeeding late Proterozoic sedimentary sequences. Lower Palaeozoic sediments dominate North Greenland and are divided into southern shelf and northern trough successions; new or revised stratigraphies are now applied in both settings. The shelf-trough boundary can be shown to have moved south with time, and a major early Silurian expansion of the trough is related to shelf subsidence and a new phase of turbidite deposition derived from the rising East Greenland Caledonian mountains. Devonian - Middle Carboniferous (Ellesmerian) deformation brought deposition to a close and created the North Greenland fold belt, in which deformation intensity and metamorphic grade increase northwards. Thin-skinned thrusting in association with west or south-facing folds is important in southern areas; this is one of the main differences in interpretation compared to earlier work in the fold belt. New outcrops of post-ElIesmerian sediments (Wandel Sea Basin) have mainly been recorded as fault or thrust bounded sequences; a new stratigraphy is applied to the Wandel Sea Basin succession. Cretaceous - Tertiary events include a suite of volcanic centres, dyke swarms, the Kap Washington Group volcanics, and faults and thrusts of Tertiary (Eurekan) age; all have been studied anew, as have the Quaternary deposits.
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Zuza, Andrew V., Christopher D. Henry, Seth Dee, Charles H. Thorman e Matthew T. Heizler. "Jurassic–Cenozoic tectonics of the Pequop Mountains, NE Nevada, in the North American Cordillera hinterland". Geosphere 17, n. 6 (27 ottobre 2021): 2078–122. http://dx.doi.org/10.1130/ges02307.1.
Testo completoAbstract (sommario):
Abstract The Ruby Mountains–East Humboldt Range–Wood Hills–Pequop Mountains (REWP) metamorphic core complex, northeast Nevada, exposes a record of Mesozoic contraction and Cenozoic extension in the hinterland of the North American Cordillera. The timing, magnitude, and style of crustal thickening and succeeding crustal thinning have long been debated. The Pequop Mountains, comprising Neoproterozoic through Triassic strata, are the least deformed part of this composite metamorphic core complex, compared to the migmatitic and mylonitized ranges to the west, and provide the clearest field relationships for the Mesozoic–Cenozoic tectonic evolution. New field, structural, geochronologic, and thermochronological observations based on 1:24,000-scale geologic mapping of the northern Pequop Mountains provide insights into the multi-stage tectonic history of the REWP. Polyphase cooling and reheating of the middle-upper crust was tracked over the range of <100 °C to 450 °C via novel 40Ar/39Ar multi-diffusion domain modeling of muscovite and K-feldspar and apatite fission-track dating. Important new observations and interpretations include: (1) crosscutting field relationships show that most of the contractional deformation in this region occurred just prior to, or during, the Middle-Late Jurassic Elko orogeny (ca. 170–157 Ma), with negligible Cretaceous shortening; (2) temperature-depth data rule out deep burial of Paleozoic stratigraphy, thus refuting models that incorporate large cryptic overthrust sheets; (3) Jurassic, Cretaceous, and Eocene intrusions and associated thermal pulses metamorphosed the lower Paleozoic–Proterozoic rocks, and various thermochronometers record conductive cooling near original stratigraphic depths; (4) east-draining paleovalleys with ∼1–1.5 km relief incised the region before ca. 41 Ma and were filled by 41–39.5 Ma volcanic rocks; and (5) low-angle normal faulting initiated after the Eocene, possibly as early as the late Oligocene, although basin-generating extension from high-angle normal faulting began in the middle Miocene. Observed Jurassic shortening is coeval with structures in the Luning-Fencemaker thrust belt to the west, and other strain documented across central-east Nevada and Utah, suggesting ∼100 km Middle-Late Jurassic shortening across the Sierra Nevada retroarc. This phase of deformation correlates with terrane accretion in the Sierran forearc, increased North American–Farallon convergence rates, and enhanced Jurassic Sierran arc magmatism. Although spatially variable, the Cordilleran hinterland and the high plateau that developed across it (i.e., the hypothesized Nevadaplano) involved a dynamic pulsed evolution with significant phases of both Middle-Late Jurassic and Late Cretaceous contractional deformation. Collapse long postdated all of this contraction. This complex geologic history set the stage for the Carlin-type gold deposit at Long Canyon, located along the eastern flank of the Pequop Mountains, and may provide important clues for future exploration.
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JASTRZĘBSKI, MIROSŁAW, ANDRZEJ ŻELAŹNIEWICZ, IZABELLA NOWAK, MENTOR MURTEZI e ALEXANDER N. LARIONOV. "Protolith age and provenance of metasedimentary rocks in Variscan allochthon units: U–Pb SHRIMP zircon data from the Orlica–Śnieżnik Dome, West Sudetes". Geological Magazine 147, n. 3 (2 novembre 2009): 416–33. http://dx.doi.org/10.1017/s0016756809990501.
Testo completoAbstract (sommario):
AbstractNew U–Pb sensitive high-mass resolution ion microprobe (SHRIMP) data from detrital zircons within the Orlica–Śnieżnik Dome provide new insights into the stratigraphic and palaeogeographic position of assumed relict Precambrian basement preserved in the Variscan collisional orogen of the West Sudetes, SW Poland. Hitherto, the Młynowiec Formation and the Stronie Formation within the Orlica–Śnieżnik Dome were assumed to represent two metavolcano-sedimentary successions of Proterozoic and early Palaeozoic age, respectively. However, when previous U–Pb data and mapping data from the Orlica–Śnieżnik Dome are combined with the new detrital zircon isotopic ages both from paragneisses within the Młynowiec Formation and from light-coloured quartzites and mica schists within the Stronie Formation, the result strongly suggests that the protoliths of these two formations actually form a continuous succession. This continuous succession is herein designated the Młynowiec–Stronie Group. The rocks of this group were deposited during middle Cambrian–early Ordovician times (c.520–470 Ma), presumably at the northern edge of West Gondwana after the 10–20 Ma period of tectonic quiescence that followed the terminal stage of the Cadomian collisions. Monotonous Młynowiec metagreywackes form the lower part of the succession, and the lithologically diverse schistose Stronie Formation forms its upper part. The change from greywacke (Młynowiec) to volcano-sedimentary (Stronie) facies coincided with the onset of rather short-lived volcanic activity which climaxed around 505–495 Ma and which supplied the volcanogenic components to the Stronie Formation. No ‘Cadomian unconformity’ has been observed in the region. Xenocrystic zircons from the Młynowiec–Stronie Group retain records of Archaean (3.0–2.3 Ga), Palaeoproterozoic (2.1–1.8 Ga) and Neoproterozoic to early Cambrian (660–530 Ma) zircon-forming events. These zircon ages, together with the lack of 1.7–1.2 Ga zircon ages, suggest that the source areas for the metasedimentary rocks may have been the West Africa craton, which therefore differs from the Amazonian affinity of the adjacent Brunovistulia Terrane. Nevertheless, two zircons,c.1.0 and 1.1 Ga old, respectively, indicate that the Młynowiec–Stronie Group sedimentary basin must have still been within the delivery reach of detritus ultimately derived from the Grenvillian-age belt(s). The detrital components of the supracrustal formations of the Orlica–Śnieżnik Dome were mainly derived from Neoproterozoic zircon-bearing crystalline rocks that were accreted to, and included in, the Cadomian basement in several intrusive pulses that culminated at 660–640 Ma, 620 Ma and 570–530 Ma.
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Henriksen, N., J. D. Friderichsen, R. A. Strachan, N. J. Soper e A. K. Higgins. "Caledonian and pre-Caledonian geology of the region between Grandjean Fjord and Bessel Fjord (75°–76°N), North-East Greenland". Rapport Grønlands Geologiske Undersøgelse 145 (31 dicembre 1989): 90–97. http://dx.doi.org/10.34194/rapggu.v145.8084.
Testo completoAbstract (sommario):
The area between Grandjean Fjord and Bessel Fjord was the focus in 1988 of regional geological investigations and 1:500000 mapping during the North-East Greenland project (Henriksen, 1989). The greater part of the area forms part of the East Greenland Caledonides and can be divided into three distinct rock groups: infracrustal gneisses and granites of possibie Archaean or early Proterozoic origin; a metasedimentary sequence which has probably suffered both mid-Proterozoic and Caledonian migmatisation and metamorphism; and the late Proterozoic Eleonore Bay Group, a thick sedimentary sequence which has undergone amphibolite facies Caledonian metamorphism in its lower parts and is intruded by Caledonian granites. Aspects of the stratigraphy and sedimentology of the Eleonore Bay Group are described by Sønderholm et al. (1989); only the structures affecting the sequence are described here.
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Jenkins, Richard J. F., David M. McKirdy, Clinton B. Foster, Teresa O'Leary e Stephen D. Pell. "The record and stratigraphie implications of organic-walled microfossils from the Ediacaran (terminal Proterozoic) of South Australia". Geological Magazine 129, n. 4 (luglio 1992): 401–10. http://dx.doi.org/10.1017/s001675680001949x.
Testo completoAbstract (sommario):
AbstractTwo assemblages of organic-walled microfossils have been recognized in drillcore samples from the late Proterozoic Rodda Beds in theeastern Officer Basin, South Australia. The fossils include tube-like remains and large, simple and sculptured acritarchs. Lithostratigraphic studies and seismic information, in conjunction with previous (albeit limited) acritarch finds, allow local correlation of the Rodda Beds with Ediacaran or terminal Proterozoic sequences in the northern Adelaide Fold Belt (site of the nominated Ediacaran stratotype). The new palynofloras are comparable withacritarch assemblages in the Amadeus Basin of central Australia, and suggest tentative correlations with sequences in China and the U.S.S.R. The presence of isotopically heavy marine carbonate in the lower fossiliferous horizons of the Rodda Beds (σ13CPDB = +3 to +6%0) is consistent with isotopic data from the equivalent interval in China. In contrast, the upper fossiliferous strata occur higher in the Rodda Beds where carbonate is significantly lighter (σ13CPDB = -1 to + 3%0).
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HOFMANN, HANS J., e GARTH D. JACKSON. "Proterozoic ministromatolites with radial-fibrous fabric". Sedimentology 34, n. 6 (dicembre 1987): 963–71. http://dx.doi.org/10.1111/j.1365-3091.1987.tb00586.x.
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Cole, Devon B., Brennan O'Connell e Noah J. Planavsky. "Authigenic chromium enrichments in Proterozoic ironstones". Sedimentary Geology 372 (ottobre 2018): 25–43. http://dx.doi.org/10.1016/j.sedgeo.2018.05.002.
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Meyers, Stephen R., e Alberto Malinverno. "Proterozoic Milankovitch cycles and the history of the solar system". Proceedings of the National Academy of Sciences 115, n. 25 (4 giugno 2018): 6363–68. http://dx.doi.org/10.1073/pnas.1717689115.
Testo completoAbstract (sommario):
The geologic record of Milankovitch climate cycles provides a rich conceptual and temporal framework for evaluating Earth system evolution, bestowing a sharp lens through which to view our planet’s history. However, the utility of these cycles for constraining the early Earth system is hindered by seemingly insurmountable uncertainties in our knowledge of solar system behavior (including Earth–Moon history), and poor temporal control for validation of cycle periods (e.g., from radioisotopic dates). Here we address these problems using a Bayesian inversion approach to quantitatively link astronomical theory with geologic observation, allowing a reconstruction of Proterozoic astronomical cycles, fundamental frequencies of the solar system, the precession constant, and the underlying geologic timescale, directly from stratigraphic data. Application of the approach to 1.4-billion-year-old rhythmites indicates a precession constant of 85.79 ± 2.72 arcsec/year (2σ), an Earth–Moon distance of 340,900 ± 2,600 km (2σ), and length of day of 18.68 ± 0.25 hours (2σ), with dominant climatic precession cycles of ∼14 ky and eccentricity cycles of ∼131 ky. The results confirm reduced tidal dissipation in the Proterozoic. A complementary analysis of Eocene rhythmites (∼55 Ma) illustrates how the approach offers a means to map out ancient solar system behavior and Earth–Moon history using the geologic archive. The method also provides robust quantitative uncertainties on the eccentricity and climatic precession periods, and derived astronomical timescales. As a consequence, the temporal resolution of ancient Earth system processes is enhanced, and our knowledge of early solar system dynamics is greatly improved.