Journal articles on the topic 'Unconformably'
To see the other types of publications on this topic, follow the link: Unconformably.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Unconformably.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
El-Arnauti, A., and M. Shelmani. "Stratigraphic and Structural Setting." Journal of Micropalaeontology 4, no. 1 (March 1, 1985): 1–10. http://dx.doi.org/10.1144/jm.4.1.1.
Full textAbstract:
Abstract. INTRODUCTIONThe material which forms the basis of this project was obtained from a number of wells in the study area in Cyrenaica, the northeastern part of Libya. The study area, which is located between latitudes 25° and 33°N and between longitudes 20° and 25° E, covers some 365,750 square kilometres (see Fig. 1). The area extends from the Egyptian border in the east to the eastern flank of the Sirte Basin in the west and is part of the stable Saharan Shield.Since Precambrian time several phases of epeirogenic movements have produced troughs, horst blocks or platforms which have in turn influenced the subsequent sedimentological history of the area. In the southern and southeastern part of the study area, the basement is unconformably overlain by a thick, partially marine Palaeozoic sequence which is in turn unconformably overlain by sediments of Jurassic or younger age. The basement in the central and southwestern parts of the area is unconformably overlain by non-marine clastics of Late Jurassic and Early Cretaceous age or by marine sediments of Late Cretaceous and Tertiary age. In the eastern and northeastern section the basement is overlain by a wedge of eastward thickening marine Palaeozoic rocks which are in turn unconformably overlain by marine sediments of Late Cretaceous and Tertiary age. In the most northerly part of the northeastern region of the study area, a thick paralic sequence of Triassic, Jurassic and Early Cretaceous deposits is unconformably overlain by Late Cretaceous and Tertiary sediments.PALAEOZOICRocks of Cambro-Ordovician . . .
2
Cope, J. C. W., and A. W. A. Rushton. "Cambrian and early Tremadoc rocks of the Llangynog Inlier, Dyfed, South Wales." Geological Magazine 129, no. 5 (September 1992): 543–52. http://dx.doi.org/10.1017/s0016756800021701.
Full textAbstract:
AbstractUntil recently no Cambrian rocks were known in the Llangynog area. Detailed mapping has now revealed a succession of ?Lower and Upper Cambrian rocks overlain by Tremadoc rocks. The Allt y Shed Sandstones (new) rest unconformably on the Precambrian, but have yielded no diagnostic fossils and are tentatively assigned to the Comley Series. Succeeding with faulted or unconformable contact is an Upper Cambrian Merioneth Series succession which includes in ascending order: conglomerates, sandstones and siltstones with olenid trilobites and resembling the Treffgarne Bridge Beds of the Haverfordwest area; micaceous shales and siltstones referred to the Ffestiniog Flags Formation; and black mudstones with calcareous concretions and a rich olenid fauna referred to the Dolgellau Formation. Succeeding the latter with possible disconformity is a succession belonging to the lower part of the Tremadoc Series and earlier than any rocks of that series hitherto recorded from the area.
3
Malak, Zaid A. "Stratigraphic and Microfacies Study of Kometan Formation (Upper Turonian-Lower Campanian), in the Dokan area, Northern Iraq." Iraqi Geological Journal 54, no. 1F (June 30, 2021): 51–68. http://dx.doi.org/10.46717/igj.54.1f.6ms-2021-06-26.
Full textAbstract:
The Kometan Formation is widely distributed in the northern (Kurdistan region) and central Iraq. The studied area is located near the Dokan Dam, about 58 km., to the Northwest of the Sulaymaniyah city, Northeastern Iraq. The Kometan Formation is exposed on the southwest flank of the Sarah anticline. The formation consists of limestone and dolomitic limestone, which have cherts nodules throughout the formation. The Gulneri Formation is recorded below the Kometan Formation with unconformable contact, while at the top is bounded by the Shiranish Formation unconformably too. Three microfacies are identified, these are lime mudstone, planktic foraminiferal lime wackestone-packstone, keeld planktonic foraminiferal lime wackestone-packstone microfacies. All the sedimentary and fossil evidence refer that the sedimentary environment of the formation is the outer shelf to upper bathyal at the lower and upper parts of formation and its extension to the middle bathyal in the middle part of the formation. Based on the stratigraphic ranges of the recorded Calcareous nannofossils biozones, the age of the Kometan Formation at Dokan area is Late Turonian-Early Campanian.
4
Schwennicke, Tobias, Diana María Santisteban-Mendívil, José Antonio Pérez-Venzor, Mara Yadira Cortés-Martínez, and Elvia Plata-Hernández. "Evolución estratigráfica de la cuenca Los Barriles, Baja California Sur, México." Revista Mexicana de Ciencias Geológicas 34, no. 3 (November 29, 2017): 212. http://dx.doi.org/10.22201/cgeo.20072902e.2017.3.476.
Full textAbstract:
The Los Barriles basin, located north of the San José del Cabo basin, is part of the Gulf Extensional Province. It is a half graben bounded by the Los Barriles fault system on its western side. Our study confirms that this system is not part of the San José del Cabo fault but an independent structure. The basin fill includes three stratigraphic sequences: SE 1, SE 2, and SE 3. Los Barriles and Trinidad Formations constitute SE 1. The Los Barriles Formation is in contact with the marginal fault and on the eastern margin it rests unconformably upon the plutonic and meta- morphic basement. The unit is composed of conglomerate and sandstone formed in alluvial fans. The marine Trinidad Formation is composed of sandstone and mudstone. Both formations interfinger and constitute fan deltas without foresets, suggesting rapid subsidence along the Los Barriles fault. Calcareous nannofossils in SE 1 point toward an age in the nannofossil zone NN11 (Late Tortonian-Messinian). Thus, faulting and subsidence occurred since the late Miocene, indicating that the Los Barriles fault system is older than the San José del Cabo fault, which had been activated during the Pliocene. The Refugio Formation (SE 2) rests unconformably on the Trinidad Formation; it consists of fossiliferous sandstone and conglomerate originated in a shallow marine coastal set- ting. Laterally, it interfingers with younger portions of the Los Barriles Formation, forming a fan delta setting of probable Pliocene age. The El Chorro Formation unconformably covers all older units and, locally, even Los Barriles fault system. It comprises sandstone and conglomer- ate formed in an alluvial fan depositional environment. These deposits interfinger towards the present coastline with fossiliferous sandstone and conglomerate formed during the last interglacial period, representing SE 3.
5
Zhou, Jian-Bo, Jie Han, Guo-Chun Zhao, Xing-Zhou Zhang, Jia-Lin Cao, Bin Wang, and Sheng-Hui Pei. "The emplacement time of the Hegenshan ophiolite: Constraints from the unconformably overlying Paleozoic strata." Tectonophysics 662 (November 2015): 398–415. http://dx.doi.org/10.1016/j.tecto.2015.03.008.
Full text
6
Jefferson, C. W., and R. R. Parrish. "Late Proterozoic stratigraphy, U–Pb zircon ages, and rift tectonics, Mackenzie Mountains, northwestern Canada." Canadian Journal of Earth Sciences 26, no. 9 (September 1, 1989): 1784–801. http://dx.doi.org/10.1139/e89-151.
Full textAbstract:
Stratigraphic evidence suggests sporadic rifting began during deposition of the mainly platformal Mackenzie Mountains Supergroup: minor magnetite iron-formation in shale basins, lead–zinc in karsted and brecciated carbonates, red-bed and evaporite wedges, and basalts at the top. In the unconformably overlying Coates Lake Group similar climates and definite rifting are recorded by thin orthoconglomerates with thick red-bed and evaporite wedges containing stratiform copper deposits in paleovalleys. Unconformably above this, basal Windermere Supergroup records major climatic change and more emphatic rifting, with thick orthoconglomerates next to fault scarps overlain by glaciomarine deposits with volcanics and hydrothermal iron-formation.A quartz diorite plug, here dated by the U–Pb zircon method at [Formula: see text], is bounded by faults but is contained in a thrust panel together with Mackenzie Mountains Supergroup and is chemically similar to diabase sills previously dated at 766–769 ± 27 Ma (Rb–Sr). A diatreme intruding Coates Lake Group contains clasts of granite and gneiss from inferred basement. U–Pb systematics from a granite clast indicate inherited zircons about 1.6 ± 0.25 Ga in age and crystallization between 1100 and 1175 Ma, a maximum age for Mackenzie Mountains Supergroup.
7
Strank, A. R. E. "Foraminiferal biostratigraphy of the Woo Dale Borehole, Derbyshire and the age of the Dinantian-Basement unconformity." Journal of Micropalaeontology 5, no. 1 (April 1, 1986): 1–4. http://dx.doi.org/10.1144/jm.5.1.1.
Full textAbstract:
Abstract. Detailed micropalaeontological analysis of the Woo Dale Borehole shows that Dinantian strata of Holkerian and Arundian age lie unconformably on top of the pre-Carboniferous basement beds. The Chadian and Tournaisian are missing. The chronostratigraphy here recognised is compared with that proposed by Cope (1973) and the differences in the two interpretations explained in the light of recent palaeontological and Midlands regional research.
8
Lenhardt, N., W. Altermann, F. Humbert, and M. de Kock. "Lithostratigraphy of the Palaeoproterozoic Hekpoort Formation (Pretoria Group, Transvaal Supergroup), South Africa." South African Journal of Geology 123, no. 4 (December 1, 2020): 655–68. http://dx.doi.org/10.25131/sajg.123.0043.
Full textAbstract:
Abstract The Palaeoproterozoic Hekpoort Formation of the Pretoria Group is a lava-dominated unit that has a basin-wide extent throughout the Transvaal sub-basin of South Africa. Additional correlative units may be present in the Kanye sub-basin of Botswana. The key characteristic of the formation is its general geochemical uniformity. Volcaniclastic and other sedimentary rocks are relatively rare throughout the succession but may be dominant in some locations. Hekpoort Formation outcrops are sporadic throughout the basin and mostly occur in the form of gentle hills and valleys, mainly encircling Archaean domes and the Palaeoproterozoic Bushveld Complex (BC). The unit is exposed in the western Pretoria Group basin, sitting unconformably either on the Timeball Hill Formation or Boshoek Formation, which is lenticular there, and on top of the Boshoek Formation in the east of the basin. The unit is unconformably overlain by the Dwaalheuwel Formation. The type-locality for the Hekpoort Formation is the Hekpoort farm (504 IQ Hekpoort), ca. 60 km to the west-southwest of Pretoria. However, no stratotype has ever been proposed. A lectostratotype, i.e., the Mooikloof area in Pretoria East, that can be enhanced by two reference stratotypes are proposed herein. The Hekpoort Formation was deposited in a cratonic subaerial setting, forming a large igneous province (LIP) in which short-termed localised ponds and small braided river systems existed. It therefore forms one of the major Palaeoproterozoic magmatic events on the Kaapvaal Craton.
9
Al-Husseini, Moujahed, and Robley K. Matthews. "Devonian Jauf Formation, Saudi Arabia: Orbital Second-order Depositional Sequence 28." GeoArabia 11, no. 2 (April 1, 2006): 53–70. http://dx.doi.org/10.2113/geoarabia110253.
Full textAbstract:
ABSTRACT The Devonian Jauf Formation (Huj Group) froms part of a regional transgressive-regressive depositional sequence that extends more than 1,500 km across the Arabian Platform from the Al Jawf outcrops in northwest Saudi Arabia, to the subsurface of eastern Saudi Arabia and Oman (Misfar Group). The formation ranges in thickness from 200–335 m in eastern Saudi Arabia to about 300–330 m in northwest Saudi Arabia. It disconformably (?unconformably) overlies the continental to shallow-marine Tawil Formation, and is unconformably overlain by the continental Jubah Formation. The Jauf Formation consists of five members that are apparently conformable; from base-up: Sha’iba Shale, Qasr Limestone, Subbat Shale, Hammamiyat Limestone and Murayr. In the Al-Qalibah reference section, it is divided into 21 informal units. The Early Devonian Emsian Hammamiyat Member represents the main marine flooding event; it consists of Hammamiyat units 1–6 each characterized by a clastic section that is capped by limestone. The Jauf Formation is interpreted as an orbital second-order depositional sequence (denoted DS2 28), which is bounded by two second-order sequence boundaries: SB2 28 = Jauf/Tawil (c. 407.6 Ma) and SB2 27 = Jubah/Jauf (c. 393.0 Ma). The Jauf Formation appears to consist of six third-order depositional sequences (DS3 28.1 to 28.6) that were deposited in the Early Devonian, ?Pragian and Emsian stages The Hammamiyat Member (DS3 28.4) is interpreted to consist of six fourth-order orbital cycles (DS4 28.4.1 to 28.4.6) each deposited in 0.405 million years.
10
Lavoie, Denis, and Esther Asselin. "A new stratigraphic framework for the Gaspé Belt in southern Quebec: implications for the pre-Acadian Appalachians of eastern Canada." Canadian Journal of Earth Sciences 41, no. 5 (May 1, 2004): 507–25. http://dx.doi.org/10.1139/e03-099.
Full textAbstract:
The post-Taconian units in the Quebec and northern New Brunswick Appalachians constitute the Gaspé Belt and geological studies have mostly focussed on its eastern Quebec segment. Biostratigraphic data indicate that the succession in southern Quebec is no older than Late Silurian and extends into the Early Devonian. Two distinct stratigraphic assemblages are present. The first assemblage (Saint-Luc, Cranbourne, and Lac Aylmer formations, and Glenbrooke Group) unconformably overlies the Humber and Dunnage zones. The units show a basal alluvial conglomerate that passes progressively to deeper marine facies upsection, which have recorded a post-Late Silurian transgressive event. The second assemblage (Saint-Francis Group and Frontenac Formation) is faulted against either Dunnage units or autochthonous post-Taconian units. It locally unconformably overlies units of the Dunnage Zone; the succession shows progressively deeper marine conditions upsection and also has recorded a post-Late Silurian transgressive event. The biostratigraphic framework suggests that some of the units that were assumed to be vertically stacked are rather laterally equivalent. Independant evidence supports the hypothesis that the Gaspé Belt in southern Quebec formed after the collapse of the Taconian orogen in Late Silurian time. This event is ascribed to the Salinian Orogeny. The framework from southern Quebec is incorporated in a regional scenario. The Gaspé Belt experienced a PridolianLochkovian sea-level rise. In Pragian time, shallower marine conditions were established in southern Quebec, whereas in the Gaspé Peninsula, the shallower conditions only occurred in early Emsian time.
11
Jutras, Pierre, and Gilbert Prichonnet. "Record of Late Mississippian tectonics in the new Percé Group (Viséan) of eastern Gaspésie, Quebec." Canadian Journal of Earth Sciences 42, no. 5 (May 1, 2005): 815–32. http://dx.doi.org/10.1139/e05-024.
Full textAbstract:
Viséan clastic units and structures at the northwest margin of the upper Paleozoic Maritimes Basin provide information on tectonic events that are only poorly recorded in more central parts of the basin. These continental units are time equivalent to marine sediments of the Windsor Group of Nova Scotia. They are herein assigned to the new Percé Group, which includes the La Coulée and Bonaventure formations, as well as a new unit, the Cap d'Espoir Formation. The latter unit unconformably underlies the Bonaventure Formation in a small but thick sub-basin of the Ristigouche Basin in eastern Quebec. It is characterized by a succession of sandstone and mudstone rhythmites that contrast with the coarse alluvial fan deposits of the overlying Bonaventure Formation. The Cap d'Espoir Formation was sourced from a broad area of subdued topography occupied by the Viséan La Coulée Formation and underlying units. Erosional remnants of the La Coulée Formation are unconformably overlain by the Bonaventure Formation in marginal parts of the Ristigouche Basin, whereas these units are separated by the Cap d'Espoir Formation in more central areas of the basin. The La Coulée and Cap d'Espoir formations underwent tilting and erosion during a normal faulting event that preceded deposition of the fault-controlled Bonaventure Formation. This series of events is interpreted to represent different steps in the reactivation of a pre-Carboniferous dextral strike-slip system in response to northwestsoutheast compression during the Viséan in Gaspésie.
12
Thusu, B., and J. O. Vigran. "Middle – Late Jurassic (Late Bathonian – Tithonian) Palynomorphs." Journal of Micropalaeontology 4, no. 1 (March 1, 1985): 113–29. http://dx.doi.org/10.1144/jm.4.1.113.
Full textAbstract:
Abstract. INTRODUCTIONJurassic palynomorph assemblages have been recovered in numerous wells in northeast Libya. Jurassic rocks reflect changing sedimentary environments which have greatly influenced the composition of the palynological assemblages.In the northernmost area, Jurassic sediments unconformably overlie the Palaeozoic or Triassic and show a mixed marine and continental influence. In the northeastern part of the area thicker and deeper water marine sediments are known, while shallow marine sediments overlie the platform facies immediately to the south. Pollen and miospores are fairly well preserved and are dominant in most samples. Dinoflagellate cysts are richly represented especially in the deposits of the north and northeast. Most samples contain abundant variably sorted cuticular debris and structured wood fragments. This significant influx of terrestrial debris together with the associated palynomorph assemblages indicate deposition in a shallow marine environment in close proximity to the shoreline for most of the Jurassic deposits in the northern area.In the central and southern region, sandstone, silt stone and red shale deposited in non-marine fluvial to lacustrine or lagoonal environment, unconformably overlie the metamorphic or igneous Precambrian Basement. These sediments show a general lack of well preserved palynomorphs. Miospores, though present are generally long ranging and terrestially derived detrital kerogen dominate the assemblages.MICROFLORAL SUCCESSIONMiospore assemblages present in most of the samples investigated are dominated by small gymnosperm pollen. Classopollis spp., Exesipollenites spp., Sphaeripollenites spp., and nonaperturate pollen assigned to Araucariacites spp. Saccate pollen assigned to Concentrisporites spp., Perinopollenites spp., Callialasporites spp., and Inaperturopollenites spp., are often common . . .
13
Sivan, Dorit, Gedaliahu Gvirtzman, and Eytan Sass. "Quaternary Stratigraphy and Paleogeography of the Galilee Coastal Plain, Israel." Quaternary Research 51, no. 3 (May 1999): 280–94. http://dx.doi.org/10.1006/qres.1999.2044.
Full textAbstract:
AbstractThe Quaternary deposits in the Galilee coastal plain comprise alternating calcareous sandstone, red loam, dark clay, and uncemented sand. The calcareous sandstone in the lower part of the sequence represents a Pliocene to early Pleistocene marine transgression, and is covered unconformably by the late Quaternary sequence. The base of this sequence has an estimated age of ∼500,000 yr. It is covered unconformably by marine calcareous sandstone in the west, which represents the global high sea-level stand of isotope stage 7.1, and is known as one of the “Tyrrhenian” events in the Mediterranean area. The overlying members represent the low sea-level stand of stage 6, the first a red paleosol indicating a relatively wet phase and the second an eolianite unit representing a drier phase. The eolianite forms longitudinal, subparallel ridges that formed contemporaneously. The overlying marine sandstone, which contains one of the diagnostic fossils of the “Tyrrhenian” events, the gastropodStrombus buboniusLMK, accumulated during the global high stand of stage 5.5. The last glacial period left no sedimentary record. The Holocene is represented by a marine clay unit that is covered by sand. The present study establishes a complete and detailed chronostratigraphic sequence for an eastern Mediterranean beach, which contains the gastropodS. buboniusLMK.S. buboniuson the Galilee coast is attributed to stage 5.5 and therefore, establishes an east–west Mediterranean correlation, which can be used for linking Mediterranean events to paleo-sea levels and global climate changes.
14
Friderichsen, J. D., R. E. Holdsworth, H. F. Jepsen, and R. A. Strachan. "Caledonian and pre-Caledonian geology of Dronning Louise Land, North-East Greenland." Rapport Grønlands Geologiske Undersøgelse 148 (January 1, 1990): 133–41. http://dx.doi.org/10.34194/rapggu.v148.8133.
Full textAbstract:
The western border of the East Greenland Caledonides is exposed in Dronning Louise Land, where it is marked by a N–S trending thrust Imbricate Zone. The autochthonous crystalline basement to the west of the Imbricate Zone is dominated by orthogneisses, and unconformably overlain by two metasedimentary sequences (Zebra Series and Trekant Series). These metasedimentary units can be recognised in the Caledonian thrust slices of the Imbricate Zone and also as folded inliers in the gneiss complexes to the east, and witness to a progressive increase in Caledonian deformation and metamorphism.
15
Anderton, R., W. Gibbons, and P. G. Nicholson. "Precambrian." Geological Society, London, Memoirs 13, no. 1 (1992): 5–12. http://dx.doi.org/10.1144/gsl.mem.1992.013.01.04.
Full textAbstract:
AbstractFor much of Precambrian time, it is not possible to reconstruct any sort of meaningful palaeogeographies. For this Atlas, therefore, the earliest reconstructions are for Proterozoic intervals and are, of necessity, limited geographically.The term 'Torridonian' has long since been used to refer to the entire Upper Proterozoic succession of predominantly fluvial clastic sediments situated along the northwest coast of Scotland. These rocks rest unconformably on Archaean to Lower Proterozoic Lewisian Gneiss, are overlain unconformably by Cambro-Ordovician marine sediments, and constitute the best sedimentary exposures in the British Isles. Stratigraphically, 'Torridonian' deposits are subdivided into the Stoer, Sleat and Torridon groups. The Stoer and Torridon groups are separated by an angular unconformity (Lawson 1965; Stewart 1969) and have been dated at 968 and 777 Ma respectively (Moorbath 1969; Stewart 1982), although these ages may be up to 100 Ma too young (see discussion in Stewart 1988a, p. 98). Sedimentation dates of c. 1050 (Stoer Group) and c. 850 (Torridon Group) are, therefore, likely to be more realistic.The lowest of the three groups consists of a diverse suite of red bed deposits up to 2 km thick representing fluvial, aeolian and ephemeral lacustrine environments, suggesting a semi-arid climate (Stewart 1988a). Deposition occurred at an approximate palaeolatitude of 15°N (Torsvik & Sturt 1987). Stoer Group sediments have been divided by Stewart (1988a) into seven constituent facies. The illustrated palaeogeographical time interval encompasses the end of Bay of Stoer facies deposition, theThe Bay .of Stoer facies consists of roughly 200 m
16
Utting, John, and Peter S. Giles. "Palynostratigraphy and lithostratigraphy of Carboniferous Upper Codroy Group and Barachois Group, southwestern Newfoundland." Canadian Journal of Earth Sciences 45, no. 1 (January 1, 2008): 45–67. http://dx.doi.org/10.1139/e07-066.
Full textAbstract:
A new zone, the Reticulatisporites carnosus Assemblage Zone of late Pendleian to Arnsbergian age, is proposed for miospore assemblages in the Searston Formation of the Barachois Group and in unnamed coal-bearing strata in higher portions of the group. The beds containing the zone can be correlated with those in other parts of the Euramerican floral province in western Europe (including the North Sea), where the climate was semi-humid. Temporal relationships suggested by these new biostratigraphic data indicate that a reassessment of the regional lithostratigraphy of southwestern Newfoundland is required. The Overfall Brook Member of the Robinsons River Formation, formerly assigned with its correlative, the Brow Pond Lentil, to the Codroy Group, is here identified as a basal unit of the Searston Formation. It lies unconformably on Codroy Group beds of Brigantian age. Elsewhere, the basal beds of the Barachois Group lie unconformably on pre-Carboniferous rocks. The Barachois Group in the Codroy and St. George’s Bay lowlands correlates with the Humber Falls and Howley formations of the Deer Lake Subbasin of western Newfoundland and with the Pomquet Formation of the Mabou Group, Nova Scotia. The Pendleian–Arnsbergian coal-bearing strata high in the undivided Barachois Group predate the post-Arnsbergian major floral crisis and, with their correlatives, represent the youngest known rock units of Mississippian age in Atlantic Canada. They are significantly older than the Pennsylvanian coal measures of Moscovian (Bolsovian) age in a small outlier near Stephenville, and we recommend the latter be removed from the Barachois Group.
17
LANDING, ED, STEPHEN R. WESTROP, and SAMUEL A. BOWRING. "Reconstructing the Avalonia palaeocontinent in the Cambrian: A 519 Ma caliche in South Wales and transcontinental middle Terreneuvian sandstones." Geological Magazine 150, no. 6 (May 20, 2013): 1022–46. http://dx.doi.org/10.1017/s0016756813000228.
Full textAbstract:
AbstractAn Early Cambrian caliche on the St Non's Formation (emended) is the base of the Caerfai Bay Formation (unit-term changed) at Caerfai Bay, South Wales. Subaerial exposure and the caliche mean the two formations were not genetically related units. The St Non's is an older sand sheet (likely tidalitic, not delta-related) referred to Avalonian depositional sequence (ADS) 2, and the Caerfai Bay is a shallow mud basin unit refered to ADS 4A. The similar Random Formation (upper ADS 2) in North American Avalonia has a basal age ofc. 528 Ma and is unconformably overlain by red mudstones or sandstones in fault-bounded basins on the Avalonian inner platform. Coeval British sandstones (lower Hartshill, Wrekin, St Non's, Brand Hills?) are unconformably overlain by latest Terreneuvian (ADS 3) or Epoch 2 (ADS 4A) units. Dates of 519 Ma on Caerfai Bay ashes give an upper bracket on the late appearance of Avalonian trilobites and suggest an ADS 2–4A hiatus of several million years. Post-St Non's and post-Random basin reorganization led to abundant Caerfai Bay Formation volcanic ashes and sparse Brigus Formation ashes in Newfoundland. The broad extent of erosional sequence boundaries that bracket lithologically similar to identical units emphasize that ‘east’ and ‘west’ Avalonia formed one palaeocontinent. The inner platform in southern Britain was larger than the Midlands craton, a tectonically defined later Palaeozoic area unrelated to terminal Ediacaran – Early Palaeozoic depositional belts. The cool-water successions of Early Palaeozoic Avalonia were distant from coeval West Gondwanan carbonate platforms.
18
Durling, P. W., J. S. Bell, and G. B. J. Fader. "The geological structure and distribution of Paleozoic rocks on the Avalon Platform, offshore Newfoundland." Canadian Journal of Earth Sciences 24, no. 7 (July 1, 1987): 1412–20. http://dx.doi.org/10.1139/e87-133.
Full textAbstract:
Single-channel seismic reflection profiles obtained across the Avalon Platform, offshore Avalon Peninsula, Newfoundland, have been studied for seismic reflections and interpreted in conjunction with lithologic and biostratigraphic data. Formline structural mapping revealed a 4000 m thick Ordovician–Silurian marine shale sequence that is gently folded about north-northwest–south-southeast axes and is unconformably overlain by a synclinal outlier of Devonian(?) redbeds approximately 700 m thick.The Avalon Platform on the Grand Banks may represent a mildly deformed Acadian terrane, which is contiguous with onshore Avalonian sequences, or it may be part of a foreland zone adjacent to an overthrust belt, or both.
19
Bjergager, Morten, Peter Alsen, Jussi Hovikoski, Sofie Lindström, Anders Pilgaard, Lars Stemmerik, and Jens Therkelsen. "Triassic lithostratigraphy of the Wandel Sea Basin, North Greenland." Bulletin of the Geological Society of Denmark 67 (October 11, 2019): 83–105. http://dx.doi.org/10.37570/bgsd-2019-67-06.
Full textAbstract:
The Wandel Sea Basin in eastern North Greenland forms the northern continuation of the offshore Danmarkshavn Basin and the conjugate margin to the western Barents Shelf south of Spitsbergen. The Triassic succession of eastern North Greenland, up to 700 m thick, spans the Induan (Dienerian) – Norian. The Triassic sediments rest unconformably on Upper Carboniferous and Upper Permian sediments, and are unconformably overlain by Upper Jurassic – Lower Cretaceous deposits. Based on recent fieldwork in the Wandel Sea Basin, five new and revised Triassic formations are described and included in the Trolle Land Group (revised). The Lower Triassic (Induan) Parish Bjerg Formation (revised) consists of marine sandstones, fluvial conglomerates and sandstones, and muddy flood-plain deposits. It is conformably overlain by Lower Triassic (Dienerian – lower Spathian) offshore mudstones with minor sand-dominated intervals of the Ugleungernes Dal Formation (new). The upper Spathian to Ladinian Dunken Formation (revised) is represented mainly by marine sandstones. A marked erosional unconformity characterises the base of the overlying Upper Triassic (Carnian – Norian) Storekløft Formation (new) composed of marginal marine to marine, massive sandstones and conglomerates as well as cross-bedded and biomottled marine sandstones and minor mudstone units. The Isrand Formation (mainly Middle Triassic) consists of laminated mudstones with minor thin sandstone units that were deposited in slope and basin floor settings in the eastern deeper part of the Wandel Sea Basin in Kronprins Christian Land. The Triassic succession of the Wandel Sea Basin represents a well-constrained shallow shelf to deep shelf / basin floor transect and thus forms an excellent outcrop analogue to the time-equivalent intervals in the western Barents Sea basins and the Danmarkshavn Basin offshore North-East Greenland.
20
Tuncer, Alaettin, and Cemal Tunoglu. "Early Pleistocene (Calabrian) Ostracoda assemblage and paleoenvironmental characteristics of the Fevzipasa Formation,Western Anatolia." Micropaleontology 61, no. 1-2 (2015): 69–83. http://dx.doi.org/10.47894/mpal.61.1.06.
Full textAbstract:
The study area is located about 40km west ofAydin city in western Turkey and includesNeogene to Quaternary sediments of the Fevzipasa Formation, which unconformably overlies the Miocene rock units. The Fevzipasa Formation is composed of conglomerates, sandstones, mudstones, marls, limestones and tuff layers and is unconformably overlain by recent deposits of the Söke-Milet Basin. The lower part of the Fevzipasa Formation is represented by coarse clastics and lacustrine carbonates followed by fine to coarse-grained sandstones bearing mollusc shells. Prominent tuff layers (lower and upper tuff layers) of this dominantly sandstone succession were radiometrically dated between roughly 2 and 1Ma. Based on small mammal fauna the age of the upper part of the formation is Early to Late Pleistocene. To investigate the paleoenvironmental evolution of the succession, forty-two samples were collected along two stratigraphic sections. Ostracoda assemblages together with Chara flora, Gastropoda and Pelecypoda and fish remains were recovered from only twenty-nine samples. Ostracoda assemblages include Candona neglecta, Cyclocypris ovum, Ilyocypris gibba, I. bradyi, Heterocypris salina and Scottia cf. S. pseudobrowniana. Additionally, fish remains belonging to the Cyprinidae family (Tinca sp., Leuciscus sp. and Leuciscus etilius) and Characeae gyrogonites referable to Nitellopsis obtusa, Chara sp., C. aspera, C. globularis, C. hispida, C. vulgaris, Lychnothamnus sp. and Sphaerochara sp. occurred in the samples. The ostracod, fish, and gyrogonite records all indicate that the Fevzipasa Formation was deposited in a paleoenvironmental setting characterized by permanent and shallow water bodies. According to the identified Ostracoda assemblages and combining all available stratigraphic data, the age of middle part of the Fevzipasa Formation is suggested as Early Pleistocene (Calabrian).
21
Anderson, Arlene V., and Kristian E. Meisling. "Ulungarat Basin: Record of a major Middle Devonian to Mississippian syn-rift to post-rift tectonic transition, eastern Brooks Range, Arctic Alaska." Geosphere 17, no. 6 (October 12, 2021): 1972–96. http://dx.doi.org/10.1130/ges02272.1.
Full textAbstract:
Abstract The Ulungarat Basin of Arctic Alaska is a unique exposed stratigraphic record of the mid-Paleozoic transition from the Romanzof orogeny to post-orogenic rifting and Ellesmerian passive margin subsidence. The Ulungarat Basin succession is composed of both syn-rift and post-rift deposits recording this mid-Paleozoic transition. The syn-rift deposits unconformably overlie highly deformed Romanzof orogenic basement on the mid-Paleozoic regional angular unconformity and are unconformably overlain by post-rift Endicott Group deposits of the Ellesmerian passive margin. Shallow marine strata of Eifelian age at the base of the Ulungarat Formation record onset of rifting and limit age of the Romanzof orogeny to late Early Devonian. Abrupt thickness and facies changes within the Ulungarat Formation and disconformably overlying syn-rift Mangaqtaaq Formation suggest active normal faulting during deposition. The Mangaqtaaq Formation records lacustrine deposition in a restricted down-faulted structural low. The unconformity between syn-rift deposits and overlying post-rift Endicott Group is interpreted to be the result of sediment bypass during deposition of the outboard allochthonous Endicott Group. Within Ulungarat Basin, transgressive post-rift Lower Mississippian Kekiktuk Conglomerate and Kayak Shale (Endicott Group) are older and thicker than equivalents to the north. North of Ulungarat Basin, deformed pre-Middle Devonian rocks were exposed to erosion at the mid-Paleozoic regional unconformity for ∼50 m.y., supplying sediments to the rift basin and broader Arctic Alaska rifted margin beyond. Although Middle Devonian to Lower Mississippian chert- and quartz-pebble conglomerates and sandstones across Arctic Alaska share a common provenance from the eroding ancestral Romanzof highlands, they were deposited in different tectonic settings.
22
Bozkaya, Ömer, Hüseyin Yalçın, and Mehmet Cemal Göncüoğlu. "Mineralogic evidences of a mid-Paleozoic tectono-thermal event in the Zonguldak terrane, northwest Turkey: implications for the dynamics of some Gondwana-derived terranes during the closure of the Rheic Ocean." Canadian Journal of Earth Sciences 49, no. 4 (April 2012): 559–75. http://dx.doi.org/10.1139/e11-076.
Full textAbstract:
The Zonguldak terrane is a Gondwana-derived continental microplate along the Black Sea coast in northwest Anatolia. It includes a Cadomian basement, with oceanic- and island-arc sequences, unconformably overlain by siliciclastic rocks of Ordovician to Middle Silurian age. After a period of deformation and erosion, late Lower Devonian (Emsian) quartzites and shallow-marine limestones unconformably cover Middle Silurian (Wenlock) graptolitic shales. Along several cross sections across the unconformity plane, the mineralogical characteristics of the Paleozoic sedimentary rocks in the Zonguldak terrane are studied to check whether this regional unconformity is only of epeirogenic nature or the result of a thermal event. In addition to the appearance of kaolinite in Devonian units, crystal-chemical data of illites show a sudden jump at the unconformity plane. The b cell dimension values of illites of Ordovician–Silurian units are somewhat higher than those of Devonian–Carboniferous units and show a drastic drop between the Silurian and Devonian units. The new mineralogic data indicate that the pre-Emsian rocks in the Zonguldak terrane experienced a thermodynamo event, prior to the Emsian transgression. This Caledonian-time event is also reported in east Moesian terrane but not noticed in the neighboring Istanbul–Zonguldak and in the west Moesian – Balkan – Kreishte terranes. By this, it is suggested that Zonguldak and east Moesian terranes behaved independently from the Istanbul–Balkan terranes during the closure of the Rheic Ocean. They very likely docked to Laurussia during Emsian by strike-slip faults and remained thereon at its platform margin, where the Middle–Late Devonian shallow-platform conditions were followed by fluvial (lagoon and delta) conditions and deposition of coal during Late Carboniferous.
23
Natal’in, Boris A., Gürsel Sunal, Erkan Gün, Bo Wang, and Yang Zhiqing. "Precambrian to Early Cretaceous rocks of the Strandja Massif (northwestern Turkey): evolution of a long lasting magmatic arc." Canadian Journal of Earth Sciences 53, no. 11 (November 2016): 1312–35. http://dx.doi.org/10.1139/cjes-2016-0026.
Full textAbstract:
The Strandja Massif, northwestern Turkey, forms a link between the Balkan Zone of Bulgaria, which is correlated with the Variscan orogen in Europe, and the Pontides, where Cimmerian structures are prominent. Five fault-bounded tectonic units form the massif structure. (1) The Kırklareli Unit consists of the Paleozoic basement intruded by the Carboniferous to Triassic Kırklareli metagranites. It is unconformably overlain by Permian and Triassic metasediments. (2) The Vize Unit that is made of Neoproterozoic metasediments, which are intruded by Cambrian metagranites, and overlain by the pre-Ordovician molasse. Unconformably laying the Ordovician quartzites pass upward into quartz schists and then to alternating marble and chert of, possibly, latest Devonian age. Rocks of the Vize Unit are intruded by the late Carboniferous metagranites. The Vize Unit may be correlated with the passive continental margin of the Istanbul Zone. (3) The Mahya accretionary complex and (4) the paired Yavuzdere magmatic arc were formed in the Carboniferous. (5) Nappes consisting of the Jurassic dolomites and marbles thrust to the north in late Jurassic – early Cretaceous time. They occupy the highest structural position on all above-mentioned tectonic units. Tectonic subdivision of the Strandja Massif is supported by new 18 ages of magmatic and detrital zircons. The long duration of subduction-related magmatism in the region and its continuity in the Triassic contradicts with the widely accepted ideas about the dominance of the passive continental margin settings in the tectonic evolution of the Strandja Massif. The massif is interpreted as a fragment of the long-lived, Cambrian to Triassic Silk Road magmatic arc. At least since the late Paleozoic this arc evolved on the northern side of Paleo-Tethys.
24
Landing, Ed. "Upper Precambrian through Lower Cambrian of Cape Breton Island: faunas, paleoenvironments, and stratigraphic revision." Journal of Paleontology 65, no. 4 (July 1991): 570–95. http://dx.doi.org/10.1017/s0022336000030675.
Full textAbstract:
Latest Precambrian through Early Cambrian tectonic history and stratigraphy are comparable in southeastern Cape Breton Island and the western Placentia–Bonavista axis, southeastern Newfoundland. The lithostratigraphic nomenclature of southeastern Newfoundland is used for this interval in Cape Breton Island. Upper Precambrian volcanic rocks of the Forchu Group (=“Giant Lake Complex,’ designation abandoned) are unconformably overlain by uppermost Precambrian through lowest Cambrian strata termed the “Morrison River Formation’ (designation abandoned). This depositional sequence consists of three formations: 1) red beds through tidalites of the Rencontre Formation (to 279+ m; =“Kelvin Lake Formation,’ designation abandoned); 2) prodeltaic clastics of the Chapel Island Formation (to 260 m); and 3) macrotidal quartzites of the Random Formation (to 71 + m). Post-Random block faulting and 300 m of local erosion took place prior to onlap of the “MacCodrum Formation’ (abandoned). Siliciclastic mudstones of the lower “MacCodrum’ are re-assigned to the middle Lower Cambrian Bonavista Group. Sub-trilobitic faunas from the Bonavista Group include “Ladatheca’ cylindrica from the West Centre Cove Formation(?) and higher diversity faunas (23 species) in the Camenella baltica Zone of the Cuslett and Fosters Point Formations. Trilobite-bearing, upper Lower Cambrian (Branchian Series) strata (Brigus Formation, =upper “MacCodrum’ and overlying “Canoe Brook’ Formations) unconformably overlie the Placentian Series in Cape Breton Island, southeastern Newfoundland, Shropshire, and, probably, eastern Massachusetts. Correlations based on small shelly fossils indicate an earlier appearance of trilobites in Avalon than on the South China Platform. Twenty-six species are illustrated. Halkieria fordi n. sp., the conodont(?) “Rushtonites’ asiatica n. sp., and the zhijinitid(?) Samsanoffoclavus matthewi n. gen. and sp. are described. Ischyrinia? sp. may be the oldest ischyrinoid rostroconch.
25
Over, D. Jeffrey. "Conodonts and the Devonian–Carboniferous boundary in the upper Woodford Shale, Arbuckle Mountains, south-central Oklahoma." Journal of Paleontology 66, no. 2 (March 1992): 293–311. http://dx.doi.org/10.1017/s0022336000033801.
Full textAbstract:
The Woodford Shale of south-central Oklahoma was deposited in an offshore, quiet-water, oxygen-poor setting on the southern margin of North America in assocation with other dark organic-rich shales of the Upper Devonian–Lower Carboniferous black-shale facies. The basal Woodford was deposited unconformably over lower Paleozoic carbonate strata as a south-to-north transgressive unit during the Frasnian and early Famennian. Black shales and cherts lie directly above the basal beds.Phosphatic shales in the upper Woodford contain a conodont succession characterized by three distinct environmentally controlled faunas. The lower fauna is characterized by Palmatolepis gracilis ssp., Branmehla inornata, Bispathodus stabilis, and Pseudopolygnathus marburgensis trigonicus, indicative of the Late Devonian Lower expansa Zone to Upper praesulcata Zone. The middle fauna, which spans the Devonian–Carboniferous (D/C) boundary, is characterized by Polygnathus communis communis and species of Protognathodus. On the Lawrence uplift the D/C boundary is disconformable, as indicated by the absence of Protognathodus kockeli before the first occurrence of Siphonodella sulcata. Light-colored phosphate laminae and beds, indicative of erosion and nondeposition, and a change in biofacies from an offshore palmatolepid–bispathodid fauna to a more nearshore, palmatolepid–polygnathid–protognathodid fauna indicate higher energy conditions and a lowering of sea level associated with the boundary interval. In the eastern Arbuckle Mountains the D/C boundary is apparently conformable, marked by a green shale interval containing a Protognathodus fauna. Species of Siphonodella, indicative of an offshore setting, characterize the third and youngest fauna. The Early Carboniferous sulcata, Lower duplicata, and Upper duplicata Zones are recognized in the upper Woodford. The Woodford Shale is conformably overlain by the “pre-Welden Shale’ and its equivalents, or unconformably overlain by the lower Caney Shale (Osagean?–Meramecian) in the northern outcrop regions and the Sycamore Formation (late Osagean?–Meramecian) in the southern Arbuckle Mountains.
26
Sanz de Galdeano, C., and M. D. Ruiz Cruz. "Late Palaeozoic to Triassic formations unconformably deposited over the Ronda peridotites (Betic Cordilleras): Evidence for their Variscan time of crustal emplacement." Estudios Geológicos 72, no. 1 (March 3, 2016): e043. http://dx.doi.org/10.3989/egeol.42046.368.
Full text
27
Dean, W. T., O. Monod, and Yilmaz Günay. "Lower Palaeozoic stratigraphy in the southern and central Amanos Mountains, south central Turkey." Geological Magazine 123, no. 3 (May 1986): 215–26. http://dx.doi.org/10.1017/s0016756800034713.
Full textAbstract:
AbstractFormations of Cambrian and Ordovician age originally identified by the letters A to E in the southern Amanos Mountains are reviewed using lithostratigraphic units known from the western Taurus Mountains and south-eastern Turkey. The youngest Cambrian rocks in the southern Amanos belong to the Sosink Formation and their age, based on trilobite evidence, ranges from the Badulesia Zone to the Solenopleuropsis Zone of the Middle Cambrian; they are overlain unconformably by conglomerates dated as Triassic? by means of plant fossils. Ordovician rocks – Seydişehir Formation (approx. Arenig) and Bedinan Formation (Caradoc in part) – are exposed further north, in the central Amanos. The unusual position of the allochthonous ophiolites, which rest in part directly upon Lower Palaeozoic rocks, is discussed.
28
Williams, J. P., and V. J. S. Grauch. "Comparison of magnetic and gravity terrain models." Exploration Geophysics 20, no. 2 (1989): 201. http://dx.doi.org/10.1071/eg989201.
Full textAbstract:
Modelling of magnetic terrain and comparison with actual data is an efficient method for assessing large sets when residual anomalies are important. The technique of Blakely (1981) which utilises a rapidly converging series of Fast Fourier Transforms is an efficient and sufficiently accurate method for this assessment.The technique has been applied to a data set at Kilkivan, south eastern Queensland. Here the magnetic sources are near horizontal Triassic volcanic flows unconformably overlying a non- magnetic Palaeozoic basement.Geological control is good so that it is possible to model the bottom of the flow. It is postulated that the difference between the calculated and actual data represents paleochannels in the basement. Similar techniques applied to gravity data have not been as successful.
29
Peybernès, Bernard, Marie-José Fondecave-Wallez, and Pierre-Jean Combes. "Evidences of Palaeocene marine breccias unconformably overlying the Cretaceous orogenic axis of the Pyrenees, between Garonne and Gave de Pau." Bulletin de la Société Géologique de France 173, no. 6 (November 1, 2002): 523–32. http://dx.doi.org/10.2113/173.6.523.
Full textAbstract:
Abstract Recently, have been evidenced in central/eastern French Pyrenees sub-marine polygenic breccias (Comus/Baixas Breccias), assigned to Upper Danian-Lower Selandian (P1c-P3) by means of planktonic foraminifera found either within their matrix, or within associated microrhythmic hemipelagites. These ante-Upper Eocene breccias, which are posterior to the HT-LP « Pyrenean » metamorphism (Mid.-Cretaceous in age and characterized by dipyre-bearing marbles and hornfelses) and to the Upper to Uppermost Cretaceous foldings, are only restricted to the Cretaceous orogenic axis of the range [Internal Metamorphic Zone (IMZ) and North-Pyrenean Zone (NPZ)]. They are dated in about 20 layers known from Mediterranean coast to Garonne valley. The breccias define in this part of Pyrenees a wide and long (more than 200 km) W-E trough (subdivided into several meridian palaeocanyons) inherited from former karstic topographies and separated by mountains with a steep topography, flanked to the South and the North of continental areas (covered by « Vitrollian » fluvio-lacustrine deposits). It was important to evidence if this marine breccia-filled « trough », Palaeocene in age, could extend westwards, West of Garonne, in Comminges/Barousse and Bigorre, where, laterally, the « Vitrollian » continental areas are replaced by outer-shelf marine sediments (clinoform carbonates), both covering the Sub-Pyrenean Zone (SPZ) and the High Primary Range (HPR) (Gavarnie-Mont-Perdu thrust sheet). In fact, the presence of those breccias has been already suggested (but without micropalaeontologic arguments) by Mattauer [in Choukroune, 1969 and 1976] in the Lourdes area (Bigorre). The topic of this paper is to characterize and to assign to the lower part of Palaeocene (63-59 Ma interval) several significant outcrops (St-Béat, Bramevaque/Troubat/Gembrié, Lortet, Medous/Bagnères-de-Bigorre and Lourdes/Pibeste) of these marine breccias (some of them previously used as black/yellow marbles called « Brèche romaine de St-Béat », « Portor des Pyrénées » or « Marbres de Medous ») recently identified from Garonne to Gave-de-Pau (fig. 1). Although quite poor in argillaceous hemipelagites, most of the breccias (which contain Mesozoic clasts) are now well dated by sections of « globigerinids » (= superfamily of Globerinacea) observed within their matrix. Other marine Palaeocene breccias also exist, more to the South (col de Gembre) along segments of the North-Pyrenean Fault, but they only rework Palaeozoic clasts. The « globigerinid » assemblage checked within all the Palaeocene breccias of Comminges/Bigorre includes, as more to the east, the following taxa: Globanomalina compressa, Gl. ehrenbergi, Gl. imitata, Parasubbotina varianta, P. variospira, Igorina pusilla, Morozovella angulata, M. praeangulata, Praemurica spiralis, Pr. inconstans and Woodringina hornestownensis. This assemblage is also laterally present within the marine carbonate sequences of the SPZ – HCR cover (« Lasseube Limestones » from the Nay/Pont Labau area, « Globigerinid-bearing Limestones » from the Gavarnie-Mont-Perdu thrust sheet), regions which are peripheric to the Pyrenean Lower/Mid. Cretaceous orogen (IMZ, NPZ) because exempt of major angular unconformity between Maastrichtian and Danian marine deposits (only a short gap of Lower/Lowermost Danian underlines the K/T boundary). On the contrary, the herein studied regions, belonging to this orogen, are characterized by a clear unconformity (both angular and cartographic) along a well-marked ravining surface inherited from erosional processes and karstification. The substratum of these breccias is strongly folded, cleaved and sometimes metamorphic and its younger formation seems to be Mid.– Cretaceous in age at least. Thus, it is very probable that the ante-Palaeocene unconformity seals compressional/transpressional structures (followed by emersions) assigned to the Uppermost Cretaceous phase (palinspastic transect, fig. 5). Danian/Selandian marine breccias and their already folded Mesozoic substratum are later tectonically reactived together by the « Pyrenean » compressions, Upper Eocene in age. If the elements of these breccias sometimes correspond to marbles induced by the Mid.-Cretaceous thermometamorphism (as around the famous « Etang de Lherz », more to the East, where lherzolites are also reworked in similar Danian/Selandian breccias), their matrix locally contain neogenic phyllites (never dipyre !) which could be related to a light (hydrothermal ?) post-breccia metamorphism. The clasts are generally angular, showing a very short transport from emerged steep topographies separating the different elementary canyons of the trough. The last problem is to determine the eventual westwards extension in the Bearn and Basque Pyrenees (fig. 6), particularly in the « Chaînons Béarnais » Zone which belonged to the North-Iberian palaeomargin (Iberian Plate) of the future range during Lower/Mid.-Cretaceous times. At this first level of micropalaeontologic investigations, it seems that several breccias (Lauriolle, Etchebar, Bosmendiette etc …), previously interpreted by several authors (synthesis in James and Canerot [1999]) as Aptian and « diapiric » (collapse) breccias, should be assigned to marine Palaeocene deposits because containing (in their matrix and associated hemipelagites) Danian-Selandian planktonic foraminifera similar to the Comminges/Bigorre ones.
30
Gasparo Morticelli, Maurizio, Vera Valenti, Raimondo Catalano, Attilio Sulli, Mauro Agate, Giuseppe Avellone, Cinzia Albanese, Luca Basilone, and Calogero Gugliotta. "Deep controls on foreland basin system evolution along the Sicilian fold and thrust belt." Bulletin de la Société Géologique de France 186, no. 4-5 (July 1, 2015): 273–90. http://dx.doi.org/10.2113/gssgfbull.186.4-5.273.
Full textAbstract:
Abstract Neogene-Quaternary wedge-top-basins arose during the Sicilian fold and thrust belt (FTB) build-up. The infilling sedimentary successions are: i) middle-upper Miocene silicoclastics succession, accommodated on top of the accreted Sicilide and Numidian flysch nappes; ii) upper Miocene-lower Pliocene deepening-upwards sediments unconformably overlying the inner Meso-Cenozoic deep-water, Imerese and Sicanian thrust units; iii) Upper Pliocene-Quaternary coastal-open shelf deposits unconformably covering (in the outer sector of the FTB) a tectonic stack (Gela thrust system). These successions are characterized by a basal unconformity on the deformed substrate believed to be the depositional interface common both to the coeval wedge-top and foredeep basins. The tectono-sedimentary evolution of the syn-tectonic basins was controlled by the progressive deepening of the structural levels, which were active during the growing of the FTB. The palinspastic restoration of a crustal geological transect in central Sicily points to: i) the occurrence of two subsequent, basal main thrusts (MT1 and MT2) active during the Neogene-middle Pleistocene tectonic evolution, as well as ii) a decrease in slip- and shortening-rate, estimated for the later MT2 as compared to earlier MT1 basal main thrust. The foreland-basin system evolution recorded during these two steps suggests: – the regional lithofacies distribution, during late Tortonian-early Pliocene, accounted for a wide depozone including the Iblean plateau and its offshore;– a crucial change was recorded by the late Pliocene-Pleistocene wedge-top depozone, when the deeper basal main thrust (MT2) involved and thickened (in the inner sector of the FTB) the crystalline basement (thin- to thick-skinned thrust tectonics); this change influenced the depozones, progressively narrowing up to the present-day setting. As regards this general evolutionary framework, thin-skinned and thick-skinned thrust tectonics can be recognized in the Sicilian FTB evolution. The late Tortonian-early Pliocene, thin-skinned thrust tectonics include two main tectonic events, a “shallow-seated” Event 1 and a “deep-seated” Event 2, with the Pliocene-Pleistocene thick-skinned thrust tectonics representing a third tectonic event (Event 3).
31
Melis, M. I., and R. I. Acworth. "An aeolian component in Pleistocene and Holocene valley aggradation: evidence from Dicks Creek catchment, Yass, New South Wales." Soil Research 39, no. 1 (2001): 13. http://dx.doi.org/10.1071/sr99099.
Full textAbstract:
Four late Quaternary depositional units are identified overlying sub-vertically dipping Ordovician bedrock in the upper reaches of the Dicks Creek catchment, near Yass in the Southern Highlands of New South Wales. The units are spatially discontinuous and separated from each other by erosional unconformities. They are found only on the lower slopes and in the valley floors, often exposed by recent gully erosion. The oldest unit (Unit 4) is a competent consolidated well-sorted fine to medium silt that unconformably overlies bedrock. It often forms the base to erosion gullies. Unit 3 is strongly dispersible and frequently has the characteristics of a debris flow. Unit 3 is particularly prone to sheet erosion and exhibits a high risk of dryland salinity development. Unit 2 is light to dark grey, poorly sorted, and often contains irregularly dispersed charcoal. Unit 2 is unconformably overlain by a predominantly pale yellow sand (Unit 1) that shows clear evidence of very recent deposition. Physical and chemical characteristics of Units 2, 3, and 4 suggest an aeolian component. The silt size (4–8 on phi scale) fraction of Unit 4 is often >70% of the total mass, with grain sizes consistent with an origin as aeolian dust. Unit 3 is yellow brown in colour and often has the characteristics of a diamict with a major grain size component similar in size to Unit 4. Unit 2 is typically uniform in appearance and contains a predominantly kaolinite and illite clay mineralogy that contrasts strongly with a predominance of quartz in the underlying bedrock. A simple sediment budget indicates that the volume of Unit 2 could be accounted for by a combination of sheet and rill erosion within the catchment and additional aeolian deposition in the order of 4–8 t/km 2 year. Radiocarbon dates for charcoal recovered from Unit 2 indicate that some deposition was associated with cooler, drier conditions of the late Holocene ‘Little Ice Age’, approximately 200–600 years ago.
32
ROBERTSON, ALASTAIR H. F., KEMAL TASLI, and NURDAN İNAN. "Evidence from the Kyrenia Range, Cyprus, of the northerly active margin of the Southern Neotethys during Late Cretaceous–Early Cenozoic time." Geological Magazine 149, no. 2 (August 31, 2011): 264–90. http://dx.doi.org/10.1017/s0016756811000677.
Full textAbstract:
AbstractSedimentary geology and planktonic foraminiferal biostratigraphy have shed light on the geological development of the northern, active continental margin of the Southern Neotethys in the Kyrenia Range. Following regional Triassic rifting, a carbonate platform developed during Jurassic–Cretaceous time, followed by its regional burial, deformation and greenschist-facies metamorphism. The platform was exhumed by Late Maastrichtian time and unconformably overlain by locally derived carbonate breccias, passing upwards into Upper Maastrichtian pelagic carbonates. In places, the pelagic carbonates are interbedded with sandstone turbidites derived from mixed continental, basic volcanic, neritic carbonate and pelagic lithologies. In addition, two contrasting volcanogenic sequences are exposed in the western-central Kyrenia Range, separated by a low-angle tectonic contact. The first is a thickening-upward sequence of Campanian–Lower Maastrichtian(?) pelagic carbonates, silicic tuffs, silicic lava debris flows and thick-bedded to massive rhyolitic lava flows. The second sequence comprises two intervals of basaltic extrusive rocks interbedded with pelagic carbonates. The basaltic rocks unconformably overlie the metamorphosed carbonate platform whereas no base to the silicic volcanic rocks is exposed. Additional basaltic lavas are exposed throughout the Kyrenia Range where they are dated as Late Maastrichtian and Late Paleocene–Middle Eocene in age. In our proposed tectonic model, related to northward subduction of the Southern Neotethys, the Kyrenia platform was thrust beneath a larger Tauride microcontinental unit to the north and then was rapidly exhumed prior to Late Maastrichtian time. Pelagic carbonates and sandstone turbidites of mixed, largely continental provenance then accumulated along a deeply submerged continental borderland during Late Maastrichtian time. The silicic and basaltic volcanogenic rocks erupted in adjacent areas and were later tectonically juxtaposed. The Campanian–Early Maastrichtian(?) silicic volcanism reflects continental margin-type arc magmatism. In contrast, the Upper Maastrichtian and Paleocene–Middle Eocene basaltic volcanic rocks erupted in an extensional (or transtensional) setting likely to relate to the anticlockwise rotation of the Troodos microplate.
33
Therkelsen, Jens, and Finn Surlyk. "The fluviatile Bristol Elv Formation, a new Middle Jurassic lithostratigraphic unit from TraillØ, North-East Greenland." Geological Survey of Denmark and Greenland (GEUS) Bulletin 5 (November 1, 2004): 19–29. http://dx.doi.org/10.34194/geusb.v5.4801.
Full textAbstract:
A new lithostratigraphic unit, the Bristol Elv Formation, is erected in this paper. It is only known from Traill Ø, East Greenland, where it unconformably overlies Triassic redbeds of the Fleming Fjord Formation and is overlain by lithologically similar shallow marine Upper Bajocian sandstones of the Pelion Formation. The age of the formation is not well constrained but is probably Early Bajocian. The Bristol Elv Formation is at least 155 m thick and consists of conglomerates, coarse-grained pebbly sandstones and subordinate mudstones, deposited in braided rivers. A finer-grained lacustrine/floodplain unit, c. 37 m thick, is interbedded with the fluvial sandstones at one locality.Depositionofthefluvio-lacustrineBristolElvFormationmarksa major change in basin configuration and drainage patterns, reflecting the onset of the important, protracted Middle–Late Jurassic rift event in East Greenland.
34
Kar, R. K. "Palynostratigraphy of the tertiary sediments in north-east India with comments on the terminal eocene events." Journal of Palaeosciences 49, no. (1-3) (December 31, 2000): 281–92. http://dx.doi.org/10.54991/jop.2000.148.
Full textAbstract:
The Tertiary rocks in North-East India rest unconformably on the granitic basement. They represent more or less a continuous sequence except a post Barail unconformity. The palynological assemblage is more or less known from all the formations. The assemblage by and large is dominated by the pteridophytic spores in all the formations followed by the angiospermic pollen. The gymnospermic pollen are rare in Palaeocene-Middle Eocene and are found in Late Eocene onwards and occur in good numbers in Miocene-Pliocene rocks. The index fossils for each formation have been marked. The Terminal Eocene events have been analysed. It has been observed that during that time India was enjoying a tropical climate and there was no cooling effect as has been advocated from the other parts of the world.
35
Pulvertaft, T. C. R. "The development of thin thrust sheets and basement-cover sandwiches in the southern part of the Rinkian belt, Umanak district, West Greenland." Rapport Grønlands Geologiske Undersøgelse 128 (December 31, 1986): 75–87. http://dx.doi.org/10.34194/rapggu.v128.7926.
Full textAbstract:
At the southern margin of the Rinkian belt, West Greenland, it can be demonstrated that the Lower Proterozoic Marmorilik Marble Formation, which was deposited unconformably on a gneiss basement, has been squeezed and stretched into a thin recumbent syneline and overridden by the basement over an area of more than 1000 km2. Aseeond supracrustal cover unit, seen now as a thin mylonitic biotite schist horizon, occurs at a slightly higher structural level, and marks the site of another thrust along which the gneiss basement has overridden its supracrustal cover. The demonstration that a superficially simple sequence consisting of concordant layers of different gneiss types and supracrustal rocks is in faet a pile ofthrust sheets, has important implications for the interpretation of both West Greenland and other Precambrian areas.
36
Young, Keith. "Emil Böse's Search For an Ancient Landmass." Earth Sciences History 13, no. 1 (January 1, 1994): 58–66. http://dx.doi.org/10.17704/eshi.13.1.8202puv5m2604002.
Full textAbstract:
In 1923 Emil Böse reported on the "Vestiges of an Ancient Continent in northeast Mexico". In searching for evidence for this ancient landmass (the Coahuila Peninsula) in 1920 Böse had traversed parts of Coahuila under most difficult circumstances. His first trip to Las Delicias from the south, although he reached Las Delicias, was geologically unsuccessful. His second, longer trip took him west 185 km from Cuatro Cienegas and then 150 km to the southeast, the latter 100 km with no water. He travelled with mules. On the second trip he was able to obtain the evidence of Aptian rocks overlying unconformably Permian rocks. This evidence he needed to define the ancient landmass from which sediments were supplied to the Tithonian and Neocomian rocks of the La Mula Basin and other parts of northeastern Mexico.
37
Dean, W. T., and O. Monod. "Revised stratigraphy and relationships of Lower Palaeozoic rocks, eastern Taurus Mountains, south central Turkey." Geological Magazine 127, no. 4 (July 1990): 333–47. http://dx.doi.org/10.1017/s0016756800014898.
Full textAbstract:
AbstractLithostratigraphic terminology is revised for rocks of Ordovician age in the eastern Taurus. The Seydişehir Formation, of late middle Cambrian to early Ordovician age, is shown to be applicable in the eastern and western Taurus as well as in south-eastern Turkey. Near Degˇirmentaş, northeast of Adana, the Seydişehir Formation is overlain, with inferred unconformity, by clastic strata of Ashgill age referred to the Şort Tepe Formation, first defined south of Hakkâri, in the Border Folds of southeastern Turkey. Palaeontological evidence is cited for the early Silurian (Llandovery) age of the unconformably overlying Halityayla Formation farther south, on the coast near Ovacik, where the Şort Tepe Formation is as yet unrecorded. A general model is proposed showing relationships of Cambrian and Ordovician rocks and faunas in southern and southeastern Turkey.
38
Montgomery, David R., and Alan Gillespie. "Formation of Martian outflow channels by catastrophic dewatering of evaporite deposits." Geology 33, no. 8 (August 1, 2005): 625–28. http://dx.doi.org/10.1130/g21270ar.1.
Full textAbstract:
Abstract Geological mapping based on topographic analysis of Mars Orbiter Laser Altimeter (MOLA) data, together with photointerpretation of Mars Orbiter Camera (MOC) images and thermodynamic and heat-flow considerations, frame a new hypothesis for the formation of Martian outflow channels through catastrophic dewatering of evaporite deposits. MOLA transects across Valles Marineris show that the valley is located at the crest of a 3-km-high topographic bulge on the flank of the much larger Tharsis Rise. Interpretation of MOC images showing layered deposits within Valles Marineris as unconformably underlying Hesperian-age lava flows means that these thick deposits, thought to contain hydrous sulfates, were heated by an increased geothermal gradient due to development of Tharis. Increased temperatures adequate to dehydrate hydrous evaporites would trigger significant volumetric expansion and catastrophically release tremendous amounts of overpressured water.
39
Vosgerau, Henrik, Michael Larsen, Stefan Piasecki, and Jens Therkelsen. "A new Middle–Upper Jurassic succession on Hold with Hope, North-East Greenland." Geological Survey of Denmark and Greenland (GEUS) Bulletin 5 (November 1, 2004): 51–71. http://dx.doi.org/10.34194/geusb.v5.4807.
Full textAbstract:
A succession of marine, Jurassic sediments was recently discovered on Hold with Hope, NorthEast Greenland. The discovery shows that the area was covered by the sea during Middle–Late Jurassic transgressive events and thus adds to the understanding of the palaeogeography of the area. The Jurassic succession on northern Hold with Hope is exposed in the hangingwalls of small fault blocks formed by rifting in Late Jurassic – Early Cretaceous times. It unconformably overlies Lower Triassic siltstones and sandstones and is overlain by Lower Cretaceous coarsegrained sandstones with an angular unconformity. The succession is up to 360 m thick and includes sandstones of the Lower–Upper Callovian Pelion and Middle–Upper Oxfordian Payer Dal Formations (Vardekløft Group) and heteroliths and mudstones of the Upper Oxfordian – Lower Kimmeridgian Bernbjerg Formation (Hall Bredning Group). The Pelion Formation includes the new Spath Plateau Member (defined herein). The palaeogeographic setting was a narrow rift-controlled embayment along the western margin of the rifted Jurassic seaway between Greenland and Norway. It was open to marine circulation to the south as indicated by the distribution and lateral facies variations and a dominant south-westwards marine palaeocurrent direction. The Pelion and Payer Dal Formations represent upper shoreface and tidally influenced delta deposits formed by the migration of dunes in distributary channels and mouthbars over the delta front. The boundary between the two formations is unconformable and represents a Late Callovian – Middle Oxfordian hiatus. It is interpreted to have formed by subaerial erosion related to a sea-level fall combined with minor tilting of fault blocks and erosion of uplifted block crests. In Late Jurassic time, the sand-rich depositional systems of the Pelion and Payer Dal Formations drowned and offshore transition – lower shoreface heteroliths and offshore mudstones of the Bernbjerg Formation accumulated. The fault block crest forming the eastern basin margin was inundated by a rise in relative sea level. Major fault activity probably occurred in latest Jurassic – Early Cretaceous times when the major fault block originally defining the Hold with Hope basin was split into smaller blocks.
40
Youssef, Abdulkader. "Early – Middle Miocene Suez Syn-rift-Basin, Egypt: A sequence stratigraphy framework." GeoArabia 16, no. 1 (January 1, 2011): 113–34. http://dx.doi.org/10.2113/geoarabia1601113.
Full textAbstract:
ABSTRACT The analyses of thirteen planktonic and benthonic biozones, paleobathymetry and electric log data were used to interpret the sequence stratigraphy of the Early to early Middle Miocene syn-rift section in the Gulf of Suez. The study area is located in the central province of the Gulf and includes six boreholes located in two half grabens and the October Field. The new framework proposes the Suez Supersequence and Suez Depositional Sequence DS 50 instead of the five paleontological sequences commonly cited in the literature (S10 to S50). The Supersequence starts above the regional unconformity that separates the pre-and syn-rift rocks, commonly referred to as Terrace T00. The shallow-marine deposits of the Aquitanian Nukhul Formation form the lowstand systems tract. The Burdigalian Mheiherrat Formation starts with the Uvigerina costata flooding event and forms the transgressive systems tract deposited in outer-neritic to upper-bathyal settings. The overlying Langhian Hawara Formation was deposited in upper to middle bathyal settings and represents the maximum flooding interval. The Langhian Asl Formation (early falling stage systems tract, upper bathyal to outer neritic) and overlying Langhian Lagia Member of the Ayun Musa Formation (late falling stage systems tract) closed the Supersequence. Suez Depositional Sequence DS 50 lies unconformably on the Supersequence, and represents a major transgression starting with the Praeorbulina glomerosa s.l. flooding event. DS 50 corresponds to the Ras Budran Member of the Ayun Musa Formation (paleontological sequence S50). Its setting is outer neritic and its upper sequence boundary is an unconformable with the Belayim Formation. The Suez Supersequence is interpreted in terms of 35 genetic parasequences and DS 50 by 10 more. The parasequences are interpreted by the coincidence of quantitative paleontological faunal and paleobathymetric breaks with the electric log shifts. The sequences and parasequences are correlated between the six wells to show the evolution of the half-grabens and October Field at different times.
41
Al-Banna, Nabil Y., Majid M. Al-Mutwali, and Nawzat R. Ismail. "Oligocene stratigraphy in the Sinjar Basin, northwestern Iraq." GeoArabia 15, no. 4 (October 1, 2010): 17–44. http://dx.doi.org/10.2113/geoarabia150417.
Full textAbstract:
ABSTRACT The distribution of the Oligocene succession (basinal and reef–back-reef deposits) in Iraq closely follows the pattern set in Middle to Late Eocene times. Reef–back-reef limestone has a linear outcrop across northern Iraq from northwest (the eastern part of the studied area) to southeast. In the Sinjar Basin, the Oligocene succession is unconformable on the Middle Eocene Jaddala Formation and unconformably to relative conformably underlies the Lower Miocene Anah or Ibrahim formations. Two surface sections on the Sinjar Anticline and one cored borehole in the Butmah Anticline formed the basis for our study. Biostratigraphic analysis indicated four planktonic and three benthonic foraminiferal biozones. The planktonic biozones are Pseudohastigerina micra and Globigerina ampliapertura Partial-Range zones, Globorotalia opima opima Total-Range Zone and Globigerina ciperonesis ciperoensis Partial-Range Zone; the three benthonic biozones are Nummulites fichteli-Nummulites intermedius Assemblage Zone, Borelis pygmaeus Total-Range Zone, and Praerhapydionina delicata-Austrotrillina howchini-Peneroplis evolutus Assemblage Zone. Three depositional sequences are present in the sections and borehole and comprise two third-order sedimentary cycles. The first consists of the Palani, Sheikh Alas and Shurau formations and the lower part of the Tarjil Formation deposited in upper-bathyal to intertidal environments; the second is the upper Tarjil Formation and Bajwan Formation. The Baba Formation (a barrier deposit) was not seen in the studied sections, but probably reflects lateral stacking development of the barrier to the west. The upper Tarjil Formation was deposited in upper-bathyal to middle-shelf environments whereas the Bajwan Formation consists of subtidal to tidal-flat deposits. Sequence-stratigraphic analysis, as calibrated by sedimentary facies and biostratigraphy, delineated the two third-order depositional cycles as the Oligocene First Cycle of Rupelian age and the Chattian Oligocene Second Cycle. This suggests that the studied Oligocene succession was deposited over a period of about 9 million years and shows good correlation of the northeastern Arabian Platform with other parts of the Platform and with European Oligocene sequences.
42
Devlin, William J., and Gerard C. Bond. "The initiation of the early Paleozoic Cordilleran miogeocline: evidence from the uppermost Proterozoic – Lower Cambrian Hamill Group of southeastern British Columbia." Canadian Journal of Earth Sciences 25, no. 1 (January 1, 1988): 1–19. http://dx.doi.org/10.1139/e88-001.
Full textAbstract:
The uppermost Proterozoic–Lower Cambrian Hamill Group of southeastern British Columbia contains geologic evidence for a phase of extensional tectonism that led directly to the onset of thermally controlled subsidence in the Cordilleran miogeocline. Moreover, the Hamill Group contains the sedimentological record of the passage of the ancient passive margin from unstable tectonic conditions associated with rifting and (or) the earliest phases of thermal subsidence to post-rift conditions characterized by stabilization of the margin and dissipation of the thermal anomaly generated during the rift phase (the rift to post-rift transition). Widespread uplift that occurred prior to and during the deposition of the lower Hamill Group is indicated by an unconformable relation with the underlying Windermere Supergroup and by stratigraphic relations between Middle and Upper Proterozoic strata and unconformably overlying upper Lower Cambrian quartz arenites (upper Hamill Group) in the southern borderlands of the Hamill basin. In addition, the coarse grain size, the feldspar content, the depositional setting, and the inferred provenance of the lower Hamill Group are all indicative of the activation of basement sources along the margins of the Hamill basin. Geologic relations within the Hamill Group that provide direct evidence for extensional tectonism include the occurrence of thick sequences of mafic metavolcanics and rapid vertical facies changes that are suggestive of syndepositional tectonism.Evidence of extensional tectonism in the Hamill Group directly supports inferences derived from tectonic subsidence analyses that indicate the rift phase that immediately preceded early Paleozoic post-rift cooling could not have occurred more than 10–20 Ma prior to 575 ± 25 Ma. These data, together with recently reported isotopic data that suggest deposition of the Windermere Supergroup began ~730–770 Ma, indicate that the rift-like deposits of the Windermere Supergroup are too old to represent the rifting that led directly to the deposition of the Cambro-Ordovician post-rift strata. Instead, Windermere sedimentation was apparently initiated by an earlier rift event, probably of regional extent, that was part of a protracted, episodic rift history that culminated with continental breakup in the latest Proterozoic – Early Cambrian.
43
Strachan, R. A., J. D. Friderichsen, R. E. Holdsworth, and H. F. Jepsen. "Regional geology and Caledonian structure, Dronning Louise Land, North-East Greenland." Rapport Grønlands Geologiske Undersøgelse 162 (January 1, 1994): 71–76. http://dx.doi.org/10.34194/rapggu.v162.8249.
Full textAbstract:
A major N-S trending thrust zone exposed in Dronning Louise Land marks the western limit of intense Caledonian deformation in East Greenland. Foreland basement to the west of the thrust zone is dominated by orthogneisses which are overlain unconformably by two sedimentary sequences (Trekant Series and Zebra Series). The Zebra Series contains Skolithos trace fossils which indicate that it is no older than latest Proterozoic. Metamorphosed correlatives of the Trekant Series and the Zebra Series can be recognised as tectonic slices within the thrust zone, and also as infoIds within the allochthonous gneisses which overlie the thrust zone. The dominant Caledonian structures are thought to have resulted from sinistral transpression, which involved partitioning of regional deformation between sinistral strike-slip movements in the east of the region, and generally NW-directed oblique thrusting and folding further to the west.
44
DEAN, W. T., T. T. UYENO, and R. B. RICKARDS. "Ordovician and Silurian stratigraphy and trilobites, Taurus Mountains near Kemer, southwestern Turkey." Geological Magazine 136, no. 4 (July 1999): 373–93. http://dx.doi.org/10.1017/s0016756899002848.
Full textAbstract:
Lower Palaeozoic outcrops near Kemer comprise only Ordovician and Silurian strata in the Upper Antalya Nappes, and are described in detail for the first time. The oldest rocks, Seydişehir Formation (lower Arenig), resemble those of the central Taurides. A disconformity is probable, though unexposed, below the succeeding Şort Tepe Formation (Ashgill), a unit seen elsewhere only in south central and southeastern Turkey; sparse trilobites include Cyclopyge, Cyphoniscus, Panderia, Symphysops, Ulugtella, and one new species Placoparia (Hawleia) marcouxi. Silurian rocks (Sapandere Formation) differ from those further east in the Taurides, and are of Llandovery (Telychian), Wenlock and ?Ludlow age, based on conodonts, graptolites and trilobites (Cerauroides, Otarion (Aulacopleura), Sphaerexochus) the affinities of which lie with the Carnic Alps and western Europe. The Sapandere Formation is unconformably overlain by red sandstones at the base of the Armutlugözlek Formation (Devonian).
45
McDougall, I., and R. T. Watkins. "Potassium–argon ages of volcanic rocks from northeast of Lake Turkana, northern Kenya." Geological Magazine 125, no. 1 (January 1988): 15–23. http://dx.doi.org/10.1017/s001675680000933x.
Full textAbstract:
AbstractThe Asille Group, a 1500 m succession comprising dominantly basaltic lavas but with interbedded sediments and silicic volcanics, lies unconformably upon metamorphosed basement northeast of Lake Turkana. Concordant K–Ar ages on alkali feldspars from pantelleritic units in the succession show that the Langaria Formation erupted 26.9±0.3 Ma ago in late Oligocene time, that Gum Dura Formation volcanism occurred at 15.8±0.2 Ma (early Miocene), and that there was widespread middle Miocene silicic volcanism at 13.0±0.3 Ma. Younger basaltic volcanism producing the flood lavas of the Gombe Group commenced at least 6.16±0.09 Ma ago in late Miocene time. These results, based upon 20 K–Ar age determinations, provide good numerical age control for much of the sequence developed within a little known sector of the Eastern Rift of Africa between the Ethiopian and Kenyan domes.
46
Gibson, DL. "Post-early cretaceous landform evolution along the western margin of the Bancannia trough, western NSW." Rangeland Journal 22, no. 1 (2000): 32. http://dx.doi.org/10.1071/rj0000032.
Full textAbstract:
Previously undated post-Devonian sediments outcropping north of Fowlers Gap station near the western margin of the Bancannia Trough are shown by plant macro- and microfossil determinations to be of Early Cretaceous (most likely Neocomian and/or Aptian) age, and thus part of the Eromanga Basin. They are assigned to the previously defined Teleplione Creek Formation. Study of the structural configuration of this unit and the unconformably underlying Devonian rocks suggests that the gross landscape architecture of the area results from post-Early Cretaceous monoclinal folding along blind faults at the western margin of the trough, combined with the effects of differential erosion. This study shows that. while landscape evolution in the area has been dynamic, the major changes that have occurred are on a geological rather than human timescale. Key words: geology, landscape evolution, Eromanga Basin, folding
47
Mao, Qigui, Jingbin Wang, Wenjiao Xiao, Brian F. Windley, Karel Schulmann, Songjian Ao, Mingjing Yu, Ji’en Zhang, and Tonghui Fang. "From Ordovician nascent to early Permian mature arc in the southern Altaids: Insights from the Kalatage inlier in the Eastern Tianshan, NW China." Geosphere 17, no. 2 (February 5, 2021): 647–83. http://dx.doi.org/10.1130/ges02232.1.
Full textAbstract:
Abstract The Kalatage inlier in the Dananhu-Haerlik arc is one of the most important arcs in the Eastern Tianshan, southern Altaids (or Central Asian orogenic belt). Based on outcrop maps and core logs, we report 16 new U-Pb dates in order to reconstruct the stratigraphic framework of the Dananhu-Haerlik arc. The new U-Pb ages reveal that the volcanic and intrusive rocks formed in the interval from the Ordovician to early Permian (445–299 Ma), with the oldest diorite dike at 445 ± 3 Ma and the youngest rhyolite at 299 ± 2 Ma. These results constrain the ages of the oldest basaltic and volcaniclastic rocks of the Ordovician Huangchaopo Group, which were intruded by granite-granodiorite-diorite plutons in the Late Ordovician to middle Silurian (445–426 Ma). The second oldest components are intermediate volcanic and volcaniclastic rocks of the early Silurian Hongliuxia Formation (S1h), which lies unconformably on the Huangchaopo Group and is unconformably overlain by Early Devonian volcanic rocks (416 Ma). From the mid- to late Silurian (S2-3), all the rocks were exhumed, eroded, and overlain by polymictic pyroclastic deposits. Following subaerial to shallow subaqueous burial at 416–300 Ma by intermediate to felsic volcanic and volcaniclastics rocks, the succession was intruded by diorites, granodiorites, and granites (390–314 Ma). The arc volcanic and intrusive rocks are characterized by potassium enrichment, when they evolved from mafic to felsic and from tholeiitic via transitional and calc-alkaline to final high-K calc-alkaline compositions with relatively low initial Sr values, (87Sr/86Sr)i = 0.70391–0.70567, and positive εNd(t) values, +4.1 to +9.2. These new data suggest that the Dananhu-Haerlik arc is a long-lived arc that consequently requires a new evolutionary model. It began as a nascent (immature) intra-oceanic arc in the Ordovician to early Silurian, and it evolved into a mature island arc in the middle Silurian to early Permian. The results suggest that the construction of a juvenile-to-mature arc, in combination with its lateral attachment to an incoming arc or continent, was an important crustal growth mechanism in the southern Altaids.
48
Patranabis-Deb, Sarbani, and Asru K. Chaudhuri. "Sequence evolution in the eastern Chhattisgarh Basin: constraints on correlation and stratigraphic analysis." Journal of Palaeosciences 57, no. (1-3) (December 31, 2008): 15–32. http://dx.doi.org/10.54991/jop.2008.225.
Full textAbstract:
The Proterozoic succession in the eastern part of the Mesoproterozoic Chhattisgarh Basin comprises two unconformity-bounded sequences. Sequence I represents the Chhattisgarh Supergroup of earlier workers. It overlies rocks of the basement complex with a profound unconformity. Sequence II unconformably overlies Sequnce I, and represents the closing phase of basin evolution during the early Neoproterozoic time. It is unconformably overlain by rocks of the Gondwana Supergroup.
The Lohardi and Gomarda formations at the lower part of the Chandarpur Group of Sequence I comprise an immature succession of conglomerate, sandstone and shale deposited in fan-delta - pro-delta environments, marked by rapid facies changes, variable rates of sediment influx, and uneven rates of subsidence and creation of accommodation space. The Kansapathar Sandstone in the upper part of the Chandarpur Group, by contrast, comprises a sheet of mature arenite deposited in a macrotidal shelf. The immature assemblage is best developed in the eastern part of the basin, and rapidly thins out towards west, where the Kansapathar arenite directly overlies the basement. The Raipur Group provides an excellent example of cyclic sedimentation of red shale and limestone. It comprises three shale-dominated intervals and two carbonate-dominated intervals, organized into multiple shallowing-up cycles. The lower carbonate succession, the Sarangarh Limestone, developed as a shallow water un-rimmed platform and evolved into a deep water ramp, with an extensive thin sheet of black limestone facies. Stromatolites are conspicuously absent in the Sarangarh Limestone. Small stromatolite bioherms appear in the Gunderdehi Shale which overlies the ramp succession, and abundant growth of stromatolite is noted in the upper carbonate succession which evolved as a rimmed platform. A thick ignimbrite horizon in the Churtela Shale attests to major felsic volcanism and termination of the Sequence at ~1000 Ma.
The Kansapathar Sandstone, the black limestone facies of the Sarangarh Limestone, and the Gunderdehi Shale embedded with small stromatolite bioherms can be used as key marker horizons to overcome the problem of intrabasinal correlation. The marker horizons can be traced from the western part to the eastern part of the basin. The stromatolites in the Gunderdehi Shale and in the Saradih Limestone further provide a biostratigraphic frame, subject to detailed morphologic and microstructural analysis, for possible chronostratigraphic classification.
49
ZAGORCHEV, IVAN S. "Pre-Priabonian Palaeogene formations in southwestern Bulgaria and northern Greece: stratigraphy and tectonic implications." Geological Magazine 135, no. 1 (January 1998): 101–19. http://dx.doi.org/10.1017/s0016756897008285.
Full textAbstract:
The Paril Formation (South Pirin and Slavyanka Mountains, southwestern Bulgaria) and the Prodromos Formation (Orvilos and Menikion Mountains, northern Greece) consist of breccia and olistostrome built up predominantly of marble fragments from the Precambrian Dobrostan Marble Formation (Bulgaria) and its equivalent Bos-Dag Marble Formation (Greece). The breccia and olistostrome are interbedded with thin layers of calcarenites (with occasional marble pebbles), siltstones, sandstones and limestones. The Paril and Prodromos formations unconformably cover the Precambrian marbles, and are themselves covered unconformably by Miocene and Pliocene sediments (Nevrokop Formation). The rocks of the Paril Formation are intruded by the Palaeogene (Late Eocene–Early Oligocene) Teshovo granitoid pluton, and are deformed and preserved in the two limbs of a Palaeogene anticline cored by the Teshovo pluton (Teshovo anticline). The Palaeocene–Middle Eocene age of the formations is based on these contact relations, and on occasional finds of Tertiary pollen, as well as on correlations with similar formations of the Laki (Kroumovgrad) Group throughout the Rhodope region.The presence of Palaeogene sediments within the pre-Palaeogene Pirin–Pangaion structural zone invalidates the concept of a ‘Rhodope metamorphic core complex’ that supposedly has undergone Palaeogene amphibolite-facies regional metamorphism, and afterwards has been exhumed by rapid crustal extension in Late Oligocene–Miocene times along a regional detachment surface. Other Palaeogene formations of pre-Priabonian (Middle Eocene and/or Bartonian) or earliest Priabonian age occur at the base of the Palaeogene sections in the Mesta graben complex (Dobrinishka Formation) and the Padesh basin (Souhostrel and Komatinitsa formations). The deposition of coarse continental sediments grading into marine formations (Laki or Kroumovgrad Group) in the Rhodope region at the beginning of the Palaeogene Period marks the first intense fragmentation of the mid- to late Cretaceous orogen, in particular, of the thickened body of the Morava-Rhodope structural zone situated to the south of the Srednogorie zone. The Srednogorie zone itself was folded and uplifted in Late Cretaceous time, thus dividing Palaeocene–Middle Eocene flysch of the Louda Kamchiya trough to the north, from the newly formed East Rhodope–West Thrace depression to the south.
50
Zaid, Mohammad, Mujeebul Hasan, and Dr Abdullah Khan. "Provenance, tectonic setting and palaeoclimate of Proterozoic Jiran Sandstone, Southeastern Rajasthan, India: A petrographic approach." Journal of The Indian Association of Sedimentologists 39, no. 1 (June 30, 2022): 43–51. http://dx.doi.org/10.51710/jias.v39i1.205.
Full textAbstract:
Proterozoic Jiran Sandstone rests unconformably on Binota Shale and Khori-Malan Conglomerate. The Jiran Sandstone is comprised mainly of fine to medium-grained, varicolored, thickly bedded sandstones, showing diverse primary sedimentary structures such as ripple marks, planar, and trough cross-bedding. Petrographically, Jiran Sandstone is of mainly quartzarenite which is composed of varieties of quartz with ultra-scarcity of feldspar, lithic fragments, micas, and heavy minerals. Quartz is more abundant mineral shown by X-ray Diffraction Analysis. The provenance, tectonic setting, and paleoclimatic condition of the Jiran sandstone were evaluated using integrated petrographic studies. Analysis pursuant, monocrystalline and polycrystalline quartz grains and heavy minerals are driven primarily from metamorphic and plutonic Precambrian basement source rocks of a craton interior setting with a minor quartzose recycled sedimentary source material. Intensive chemical weathering in warm and humid paleoclimate is indicated by lack of feldspar and rock fragments.