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Flow Deposits (flow + deposit)
Selected AbstractsTURBIDITE, SLUMP AND DEBRIS FLOW DEPOSITS AT THE KALCHINSKOE AND ZIMNEE OILFIELDS, WEST SIBERIAN BASINJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2005S. F. Khafizov This paper discusses specific facies associated with Cretaceous deep-water slumps and sandstone intrusions in the West Siberian Basin. The slumps were formed during sea-level falls when storms caused sediment masses to be discharged into deep-water areas where they imposed a significant load on the underlying semi-consolidated black shales, deforming and partially destroying them. Multiple slump / avalanche events are observed at the boundary between the Lower Cretaceous (Neocomian) and Upper Jurassic (Tithonian) sequences and form potential targets for oil exploration. High-resolution sequence stratigraphic analyses show that both slump and distal fans are genetically related to lower slope/basin floor sediments and were deposited during regressions and subsequent lowstands. Two key depositional environments are recognized: the proximal parts of fans, where the most prospective potential reservoirs are found; and the more distal parts of slumps, which are principally composed of deformed shale clasts in a silt-mudstone matrix. A third facies ("slump head") is only observed on seismic profiles and is probably related to horizontally displaced "shingled" semi-consolidated black shales. [source] K,Ar ages of the Ohmine Granitic Rocks, south-west JapanISLAND ARC, Issue 4 2003Tomoaki Sumii Abstract The Ohmine Granitic Rocks are a series of granitic rocks that are distributed in a chain stretching along the central axis of the Kii Peninsula. Their precise ages have not been determined, although precise ages have been reported for other geological units of the early to middle Miocene distributed over the peninsula. In this study, biotite K,Ar ages were obtained for the six major granitic plutons of the Ohmine Granitic Rocks: Dorogawa, Shirakura, Kose, Asahi, Tenguyama and Shiratani. Most are aged from 14.8 to 14.6 Ma. Although one pluton is older (15.4 ± 0.2 Ma) and two are younger (14.0 ± 0.2 Ma and 13.4 ± 0.1 Ma), these ages are excluded from the discussion of the mutual correlation among the plutons because some ambiguities exist in their ages. The age of the southernmost unit, the Katago,Mukuro Dykes, was not determined because of its intense alteration, but stratigraphic constraints suggest that it is younger than 16.1 Ma. The majority of the Ohmine Granitic Rocks concentrate within a narrow age window of approximately 14.8,14.6 Ma, although their geochemical/petrographical characteristics suggest that they were generated by multiple magma batches. The results of this study also reveal the simultaneous occurrence of the major activities of the Ohmine Granitic Rocks and the gigantic felsic igneous activities in the Kii Peninsula, such as the Kumano Acidic Rocks and the Muro Pyroclastic Flow Deposit. [source] Human and climatic impact on late Quaternary deposition in the Sparta Basin Piedmont: Evidence from alluvial fan systemsGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2003Richard J. J. Pope The evolution of four alluvial fans in the Evrotas Valley, southern Greece, was examined using a combination of geomorphological and sedimentological techniques. Source material for the fans is derived largely from the Taygetos Mountains, and thus the fan deposits provide proxy evidence for erosion of upland landscapes. Stratigraphic sequences exposed in the fanhead trenches suggest a progressive change in depositional style down-fan. Within the St. Johns, North Anogia, and North Xilocambi fans, debris flow deposits are gradually replaced by gravel-dominated hyperconcentrated flow deposits and then fine-grained hyperconcentrated flow deposits. Within the Kalivia Sokas fan, gravel-dominated hyperconcentrated flow deposits give way to fine-grained hyperconcentrated flow deposits, and finally to fluvial gravels. Mineral magnetic studies combined with thermoluminescence dating suggest that sedimentation also occurred over a similar time scale. Deposition cycles during the late Pleistocene appear to be climatically driven, with proximal and medial fan segments developing during stadial phases of the Riss/Würm and Würm, respectively. Distal segments aggraded during the Holocene. During interstadial episodes of the late Pleistocene, fan entrenchment occurred. Holocene accretion is likely to be related to human activity and appears to be concentrated in the early/middle Helladic and the Hellenistic periods, when population levels, indicated by increased numbers of archaeological sites, were rising. © 2003 Wiley Periodicals, Inc. [source] A NEW SPINICAUDATAN GENUS (CRUSTACEA: ,CONCHOSTRACA') FROM THE LATE CRETACEOUS OF MADAGASCARPALAEONTOLOGY, Issue 5 2008ALYCIA L. STIGALL Abstract:, A new spinicaudatan genus and species, Ethmosestheria mahajangaensis gen. et sp. nov., is described from the Anembalemba Member (Upper Cretaceous, Maastrichtian) of the Maevarano Formation, Mahajanga Basin, Madagascar. This is the first spinicaudatan reported from the post-Triassic Mesozoic of Madagascar. The new species is assigned to the family Antronestheriidae based on the cavernous or sievelike ornamentation on the carapace. Of well-documented Mesozoic spinicaudatan genera, Ethmosestheria mahajangaensis is most closely related to Antronestheria Chen and Hudson from the Great Estuarine Group (Jurassic) of Scotland. However, relatively poor documentation of the ornamentation of most Gondwanan Mesozoic spinicaudatan species precludes detailed comparison among taxa. Ethmosestheria mahajangaensis exhibits ontogenetic trends in carapace growth: a change in carapace outline from subcircular/subelliptical to elliptical, and from very wide juvenile growth bands to narrow adult growth bands. Ornamentation style, however, does not vary with ontogeny. Ethmosestheria mahajangaensis individuals lived in temporary pools in a broad channel-belt system within a semiarid environment; preserved desiccation structures on carapaces indicate seasonal drying out of pools within the river system. Specimens of Ethmosestheria mahajangaensis are preserved with exquisite detail in debris flow deposits; these are the first spinicaudatans reported from debris flow deposits. These deposits also contain a varied vertebrate fauna, including dinosaurs, crocodyliforms, turtles, and frogs. Rapid entombment of the spinicaudatan carapaces likely promoted early fossil diagenesis leading to highly detailed preservation. [source] | ||||||||||