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Carboniferous Sequence Stratigraphy and Oil and Gas in Tarim Basin, Northwest China
Published in Wang Naiwen, J. Remane, Stratigraphy, 2020
Lowstand system trace of the three sequence is only distributed on Wushi section and it does not exist inside the basin. The characteristics of lowstand system tract of sequence I is that sediment of basin bottom fan and dark marginal mudatone, which is mainly composed of pebbled sandstone and sand-stone, deposit on the erosion surface. Sediment inside the basin is thin and the main sedimentary types are fluvial lag deposit and fill deposit.. Shelf slope fan, which is composed of sandstone interbeded by shale or sandy conglomerate, is impotent in the lowstand system tract of sequence II and III, where slump, corrugition, involution sturctures which are resulted from gravity are well developed (Fig. 2) Transgressive system tract has widespread occurrence in Tarim Basin and the sediment is thick. Sediment change regularly from west to east due to transgressing from west to east.
The genesis of world-class, high-grade iron ore deposits – the South African experience
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
J. Gutzmer, N.J. Beukes, S. Netshiozwi, A. Szabo
The giant Sishen and somewhat smaller Beeshoek high-grade hematite ore deposits are located immediately to the North and South of the Maremane Dome in the Griquatown West region of may South Africa (Figure 1). The Maremane Dome is a product of regional buckling of the Transvaal strata into wide open folds that took place before or during peneplenation along the Late Paleoproterozoic Wolhaarkop-Hekpoort erosion surface (Beukes et al., submitted). Lateritic paleoweathering profiles are developed in a variety of rock types immediately below this erosion surface. Two types of paleoweathering profiles are preserved on the Maremane Dome, namely ferruginous saprolite and karst latentes. The latter is developed where the erosion surface transects the manganiferous dolomites of the Campbellrand Subgroup and comprises ancient manganese wad deposits (Gutzmer & Beukes, 1997) but also the oldest true karst latentes (Gutzmer & Beukes, 1998).
Silurian and Lower Devonian
Published in W. A. Peck, J.L. Neilson, R.J. Olds, K.D. Seddon, Engineering Geology of Melbourne, 2018
The Silurian-Lower Ordovician rocks of the Melbourne Region were subjected to several cycles of prolonged weathering and erosion from the Middle Devonian to the Quaternary. Extensive weathering and erosion occurred between the mid-Devonian and Triassic periods, (VandenBerg, 1971). An extensive peneplain had developed which according to Hills (1934) was completed during the Triassic. The newly formed peneplain was subjected to further uplift in the Triassic Period and was then subjected to further cycles of deep chemical weathering and erosion. A maturely dissected topography was developed by the Tertiary Eocene Epoch. Extensive subsidence occurred across Victoria during the late Eocene and early Miocene, and it was during this time that the sedimentation (marine and terrestrial) of many of the Tertiary rocks occurred in the low-lying areas. Inland, north of the structure known as the Melbourne Warp, an erosion surface (peneplain) of low relief and gently sloping towards the sea (VandenBerg 1971) had formed during the early Tertiary cycles of uplift and erosion. Jutson (1911) called this the Nillumbik Peneplain. It is now generally called the Nillumbik Terrain (Hills, 1934; Neilson, 1967, 1970). The Nillumbik Terrain was uplifted during the late Pliocene-early Pleistocene periods and, once again, subjected to further cycles of weathering and erosion. The Nillumbik Terrain, where exposed, including areas where the Tertiary sediments have been stripped, experienced an extensive period of lateritic weathering during the Miocene and early Pliocene. Where the Nillumbik Terrain is preserved under the cover of Tertiary soils, weathering under reducing conditions arose.
Sequence subdivision and development characteristics of low-accommodation non-marine basins: a case study of the Yanchang Formation in the Ordos Basin
Published in Australian Journal of Earth Sciences, 2018
S. Fu, Z. Liu, Y.-Z. Li, Y.-R. Guo, X.-M. Xu, J.-J. Liu, X. D. Hu
The sequence boundary characteristics of the Yanchang Formation are clear in outcrop. The top boundary of the Yanchang Formation is an erosion unconformity between the Triassic and Jurassic strata with complex paleogeomorphology, including free ditches and valleys, stacked terraces, rolling monadnock and far-flung slopes and hollows (Guo, Zhang, Chu, & Huang, 2008). The erosion surface is marked by abrupt changes in sediment grainsize and fluvial sediment structures, from meandering river and lacustrine delta deposits, which are mainly characterised by high curvature, suspension load and fine-grained deposition, to braided river deposits, which are mainly characterised by low curvature, riverbed load and coarse-grained deposition. The abrupt changes in the fluvial sedimentary system reveals sudden changes in accommodation caused by relative changes in base-level or changes in the sediment source. At the bottom of the Jurassic strata, apparent river-valley chippings differ markedly in different wells with the greatest height difference approximately 200 m (Luo et al., 2001). The abrupt changes from the Upper Triassic meandering-river sediment to the Lower Jurassic (Fuxian Group) and Middle Jurassic (Chang 10 Member) braided-river sedimentary system demonstrate an increase in alluvial plain gradient, which is caused by the continuous decrease in relative base-level (Luo et al., 2001). Thus, the erosion surface incising the bottom of the river valley can be regarded as a sequence boundary (Figure 3a, b).