Facies-succession and architecture of the third-order sequences and their stratigraphic framework of the Devonian in Yunnan-Guizhou-Guangxi area, South China
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Abstract The Caledonian orogeny at the end of the Silurian resulted in great changes in the palaeogeography in the Yunnan-Guizhou-Guangxi area of South China; the continental area of the Early Paleozoic evolved into the extensive Dian-Qian-Gui Sea in the Late Paleozoic. Early in the Devonian, as a result of a major transgression, seawater encroached gradually from the south to the north and clastic facies were deposited. Carbonate deposition was then established in the Yunnan-Guizhou-Guangxi area, with a palaeogeography marked by attached platforms, isolated platforms and narrow basins. As a result of the Ziyun movement towards the end of the Devonian, the Upper Devonian strata are regressive and thin out from the open-sea to the land areas. A study of the nature and distribution of sedimentary facies in space and time recognises 13 third-order sequences in the Devonian strata in Yunnan-Guizhou-Guangxi area, and these form two second-order sequences. The strata of the Lower Devonian comprise 5 third-order sequences (SQ 1 to SQ 5 ), which are dominated by transgressive clastics. 4 third-order sequences (SQ 6 to SQ 9 ) in the Middle Devonian are characterized by alternations of transgressive clastics and highstand carbonates. In the Upper Devonian, carbonates constitute 4 third-order sequences (SQ 10 to SQ 13 ), which are generally marked by the transgressive limestones and highstand dolomites. On the basis of earlier biostratigraphic studies, sea-level changes represented by the third-order sequences with their different facies successions are explored, and the sequence stratigraphic framework is established. Therefore, the Devonian strata in the study area provide an example for further understanding of depositional trends within the sequence-stratigraphic framework.Keywords:
Devonian
Transgressive
Marine transgression
Palaeogeography
Late Devonian extinction
Orogeny
Carbonate platform
Sequence (biology)
Theropod and sauropod footprints in the Early Cretaceous (Aptian) Apenninic Carbonate Platform (Esperia, Lazio, Central Italy): a further constraint on the palaeogeography of the Central-Mediterranean area About eighty dinosaur tracks were recently discovered near the village of Esperia, in the Western Aurunci Mountains (Latium, Central Italy). The footprints are distributed on a bedding plane belonging to a shallow water limestone succession. Tridactyl footprints attributed to small-sized theropods and round to elliptical footprints tentatively ascribed to medium-sized sauropods have been recognized on the trampled layer. This ichnoassemblage reveals the contemporaneous occurrence of carnivores/piscivores (theropods) together with plant-eaters (sauropods) dinosaurs. The Esperia outcrop is the second ichnosite discovered in southern Latium and dates the dinosaur occurrences in the Apenninic carbonate Platform to the Aptian, adding a strong constraint on the Early Cretaceous palaeogeography of the Central-Mediterranean area.
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Palaeogeography
Carbonate platform
Outcrop
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Palaeogeography
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Passive margin
Carbonate platform
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Passive seismic
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Carbonate platform
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Carbonate platform
Paleogene
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Abstract Carbonate slope sediments of the Sumeini Group mark the northeastern margin of the Arabian carbonate platform. Most slope sediments exposed in the Oman Mountains are of Jurassic or Cretaceous age. Older slope deposits at Jebel Sumeini indicate establishment of the Oman continental margin and subsidence accompanied by faulting in the Early Triassic (Dienerian), Middle Triassic (Ladinian) and possibly earlier (Permian). Widespread Jurassic slope deposits indicate significant variations in declivity and facing direction of the continental margin slope in Oman. At Jebel Sumeini, a gullied bypass slope formed an apron along the NNW-trending slope, previously established as a Triassic block-faulted escarpment. In the Dibba Zone, a steep bypass slope formed along an inactive, NE-trending, transform lineament. Farther south near Wadi Qumayrah, a Middle to Late Jurassic base-of-slope apron containing megabreccias formed along a possible NNW-trending fault scarp. East of Wadi Qumayrah, an open-end embayment in the margin separated this area from coarse-grained slope apron deposits at Jebel Sham. Carbonate slope deposits at Saih Hatat indicate a complex history of subsidence culminating in Jurassic platform drowning and development of a long-lived submerged plateau bounded by gently inclined ramp slopes. This general geometry of the Oman passive continental margin was maintained through Jurassic and Early Cretaceous time. Major changes in platform margin sedimentation occurred in the Late Cretaceous (Cenomanian to Coniacian), as recorded by the upper Mayhah Formation and overlying siliceous Qumayrah Formation. Thick Cenomanian(?) to Coniacian syn-orogenic megabreccias associated with pelagic sediments formed due to collapse of oversteepened slopes, possibly resulting from tectonic downbowing of the Oman margin toward a northward-dipping oceanic subduction zone. Later, the geometry of the passive continental margin may have had a significant effect on the emplacement of nappes and formation of the Sumeini culminations during the structural development of the Oman mountain belt.
Palaeogeography
Carbonate platform
Margin (machine learning)
Morphology
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