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Highstand Systems Tracts (highstand + system_tract)
Selected AbstractsDepositional environment and sequence architecture of the Silurian Coralliferous Group, Southern Pembrokeshire, UKGEOLOGICAL JOURNAL, Issue 3 2002Robert D. Hillier Abstract The Lower Silurian siliciclastic Coralliferous Group is shown to have been deposited in an intra-shelf position 10,15,km south of the palaeogeographic shelf-break of the Welsh Basin. After a phase of thermal subsidence related to the development of the predominantly Llandovery Skomer Volcanic Group, the shelf basin was transgressed. This transgression was punctuated by an episode of tectonic uplift in southern Pembrokeshire, resulting in subaerial exposure of the shelf and a significant basinward shift in sedimentary environments. Erosion and sediment bypass ensued, with coarse-grained low-sinuosity fluvial channels transporting sediment to the northerly Welsh Basin, where significant submarine fans developed. During the early Telychian, renewed transgression took place, with lowstand gravels being ravined and reworked into parasequences of the transgressive systems tract. These thin, coarse-grained parasequences record deposition within high-energy wave-dominated shoreface/inner shelf environments. Further coastal onlap resulted in the closing down of significant coarse-grained sediment supply, with the remaining Coralliferous Group being dominated by wave-influenced silts, mud-shales and thin sandstones comprising the highstand systems tract. Copyright © 2002 John Wiley & Sons, Ltd. [source] Clinoform migration patterns of a Late Miocene delta complex in the Danish Central Graben; implications for relative sea-level changesBASIN RESEARCH, Issue 5 2009L. K. Møller ABSTRACT A Late Miocene delta complex is located in the Danish Central Graben. The delta complex provides the opportunity to study the spatial development of a wave-fluvial dominated delta complex in three dimensions. Based on 3D seismic data (seismic sections and amplitude maps) and well data the complex has been investigated. The delta was developed during an initial rise and then a significant fall (approximately 90 m) in relative sea-level. The prograding clinoformal package of the delta complex has clinoform dips of 2,3° and a thickness of maximum 115 m. The sediments are deposited in five elongated depositional units with the long axis parallel to the delta slope, and progradation occurred in a south-westerly direction. The grain size of the units vary from muddy to coarse-grained sand. Incised canyons running parallel to the depositional direction tend to be straight or have low sinuosity and incise approximately 90 m into the top of the delta. The delta complex has been subdivided into two systems tracts based on a study of clinoform migration patterns: (1) Rising trajectory in Unit 1,4 of the complex, the sea-level was rising as documents a highstand systems tract (HST). (2) Descending trajectory in Unit 5 documenting a forced regression wedge systems tract (FRWST) as the sea-level was falling, creating incised canyons. [source] The Tendaguru Formation (Late Jurassic to Early Cretaceous, southern Tanzania): definition, palaeoenvironments, and sequence stratigraphyFOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 2 2009Robert Bussert Abstract The well-known Late Jurassic to Early Cretaceous Tendaguru Beds of southern Tanzania have yielded fossil plant remains, invertebrates and vertebrates, notably dinosaurs, of exceptional scientific importance. Based on data of the German-Tanzanian Tendaguru Expedition 2000 and previous studies, and in accordance with the international stratigraphic guide, we raise the Tendaguru Beds to formational rank and recognise six members (from bottom to top): Lower Dinosaur Member, Nerinella Member, Middle Dinosaur Member, Indotrigonia africana Member, Upper Dinosaur Member, and Rutitrigonia bornhardti-schwarzi Member. We characterise and discuss each member in detail in terms of derivation of name, definition of a type section, distribution, thickness, lithofacies, boundaries, palaeontology, and age. The age of the whole formation apparently ranges at least from the middle Oxfordian to the Valanginian through Hauterivian or possibly Aptian. The Tendaguru Formation constitutes a cyclic sedimentary succession, consisting of three marginal marine, sandstone-dominated depositional units and three predominantly coastal to tidal plain, fine-grained depositional units with dinosaur remains. It represents four third-order sequences, which are composed of transgressive and highstand systems tracts. Sequence boundaries are represented by transgressive ravinement surfaces and maximum flooding surfaces. In a more simple way, the depositional sequences can be subdivided into transgressive and regressive sequences/systems tracts. Whereas the transgressive systems tracts are mainly represented by shallow marine shoreface, tidal channel and sand bar sandstones, the regressive systems tracts predominantly consist of shallow tidal channel, tidal flat, and marginal lagoonal to supratidal deposits. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sequence stratigraphy of the upper Millstone Grit (Yeadonian, Namurian), North WalesGEOLOGICAL JOURNAL, Issue 5 2007Rhodri M. Jerrett Abstract The upper Millstone Grit strata (Yeadonian, Namurian) of North Wales have been studied using sedimentological facies analysis and sequence stratigraphy. These strata comprise two cyclothems, each containing prodelta shales (Holywell Shale) that pass gradationally upwards into delta-front and delta-plain deposits (Gwespyr Sandstone Formation). The deltas formed in shallow water (<100,m), were fluvial-dominated, had elongate and/or sheet geometries and are assigned to highstand systems tracts. Two delta complexes with distinctive sandstone petrographies are identified: (1) a southerly derived, quartzose delta complex sourced locally from the Wales-Brabant Massif, and (2) a feldspathic delta complex fed by a regional source(s) to the north and/or west. The feldspathic delta complex extended further south in the younger cyclothem. A multistorey braided-fluvial complex (Aqueduct Grit, c. 25,m thick) is assigned to a lowstand systems tract, and occupies an incised valley that was eroded into the highstand feldspathic delta complex in the younger cyclothem. A candidate incised valley cut into the highstand feldspathic delta complex in the older cyclothem is also tentatively identified. Transgressive systems tracts are thin (<5,m) and contain condensed fossiliferous shales (marine bands). The high-resolution sequence stratigraphic framework interpreted for North Wales can be readily traced northwards into the Central Province Basin (,Pennine Basin'), supporting the notion that high-frequency, high-magnitude sea-level changes were the dominant control on stratigraphic architecture. Copyright © 2007 John Wiley & Sons, Ltd. [source] ROSS AND BUDE FORMATIONS (CARBONIFEROUS, IRELAND AND ENGLAND): REINTERPRETED AS LAKE-SHELF TURBIDITESJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2004R. Higgs The Ross Formation (Namurian, Ireland) and the near-identical Bude Formation (Westphalian, England), both amply described in the literature, are used by oil companies as deep-sea-fan reservoir analogues. However, the Ross Formation is reinterpreted here, like the Bude Formation in recent publications, to be composed of river-fed turbidites deposited on the wave-influenced northern shelf of a Variscan foreland-basin lake, which also had a southern flysch trough. Key features of these formations are: (i) two classes of thin (, 0.4m) sandstone "event bed" in shale comprising (a) structureless turbidite-like beds, and (b) rippled beds with combined-flow ripples and/or hummocky cross-stratification, neither structure having previously been reported from the Ross Formation; (ii) "trademark" tabular packets (1,10 m) of amalgamated event beds which interfinger laterally with mudstones; (iii) sharp packet bases and tops; (iv) rare sinuous channel fills; and (v) rare thick (1,10m) shale units, each containing a thin (cm-dm) fossiliferous band. The fossil bands are interpreted here as maximum flooding surfaces, reflecting glacioeustatic marine incursions over the lake spill point (sill), forcing the lake to rise and to turn marine or strongly brackish; these bands define Galloway-type depositional sequences 50,100 m thick. During eustatic falls, the lake was forced down to sill level, where it perched and turned fresh (desalination). Intervals containing sandstone packets are attributed to the falling-stage and lowstand systems tracts, each packet representing a higher-order lowstand systems tract. Packets are interpreted as tongue shaped, supplied by river-fed underflows. Packet bases (sharp) represent the storm-wave-graded equilibrium shelf profile, glacioeustatically forced to its lowstand position. On this erosion surface were deposited underflow turbidites produced by floods in the catchment. Occasional catastrophic storms on the lake shaved these turbidites and interfingering fair-weather muds back down to the equilibrium level, leaving behind a subsidence-accommodated increment whose surface was sculpted by storm wind and wave currents, forming hummocks, combined-flow ripples and erosional megaflutes. Whenever a river-fed underflow accompanied one of these storms, the resulting highly erosive combined flow carved a sinuous channel on the wave-sculpted equilibrium surface. Sandstone-shale intervals separating the sandstone packets are interpreted as transgressive- and highstand systems tracts. They contain both turbidites and wave-modified turbidites (rippled beds), deposited on the out-of-equilibrium drowned shelf. A gradual rotation in sole-mark direction with time in both formations is attributed to a reversal of Coriolis deflection as the plate drifted north across the equator, causing underflows (deflected along-shelf geostrophically) to flow first NEwards and then SWwards on an inferred SE-facing shelf. The lack of evidence for emergence in the Ross and Bude Formations, in spite of the great thicknesses (460m and 1,290m, respectively) of these shallow-water deposits, is attributed to regulation of minimum water depth firstly by the lake sill blocking eustatically-forced exposure, and secondly by storm grading, preventing emergence by sedimentation. [source] | ||||||||||