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41.
42.
Stratigraphic grade is the similarity of the morphology of successive slope-to-basin profiles in a genetically related depositional system. In this article we use data collected from regional cross-sections of six depositional systems, stratal architecture derived from outcrops of the Lewis Shale (Wyoming, USA), and the Ross Sandstone (Ireland), and supplementary outcrop and subsurface data from other depositional systems to determine how stratigraphic grade relates to stratal (reservoir) architecture in deepwater systems.Four methods are developed that collectively define stratigraphic grade: (1) regional stacking patterns of fourth-order stratigraphic surfaces, (2) the relationship between the trajectory of the shelf edge (Tse) and the trajectory of the depocenter (Td) for fourth-order stratigraphic units, (3) morphology of the slope-to-basin profiles of fourth-order stratigraphic surfaces, and (4) the similarity of the morphologies of slope-to-basin profiles of fourth-order surfaces in a system (σs, σr). Several characteristics of stratigraphic (reservoir) architecture of fourth-order stratigraphic cycles are related to stratigraphic grade: (1) longitudinal distribution of sandstone in fourth-order cycles, (2) location of maximum sandstone relative to the depocenter of fourth-order cycles, (3) lengths of fourth-order submarine fans, and (4) longitudinal and vertical distribution of architectural elements. Stratigraphic grade is thus a predictor of reservoir architecture and can thereby be used to reduce the uncertainty in the interpretation of subsurface data.The concept of stratigraphic grade is useful in understanding the stratigraphic evolution of deepwater systems. Most deepwater systems analyzed in this study initiated as out-of-grade and temporally evolved to graded systems over a time span of millions of years. Systems rarely evolve from graded to out-of-grade. First-order controls on stratigraphic grade are determined to be angle of slope, tectonically forced changes in angle of slope during deposition, and sediment supply. 相似文献
43.
In southern India the older Precambrian is overlain unconformably in the Cuddapah Basin by the Cuddapah and Kurnool Systems. The former is tilted and unmetamorphosed in the west but eastwards becomes strongly folded and metamorphosed. It contains lavas and sills, particularly in the lower two groups, is intruded by dolerites and at Chelima by diatremes of kimberlitic affinities related to those intruding the older gneisses west of the Cuddapah Basin in the Wajrakarur area. The Kurnool System lacks any igneous rocks; its basal conglomerate is diamondi‐ferous. Rb‐Sr dating of lava samples from the lowest group of the Cuddapah System shows that the age of the base of the system may be as great as 1,700 m.y. Together with data for a granite which intrudes probable Cuddapah rocks near the disturbed eastern margin of the basin the data imply that the base is unlikely to be younger than 1,555 m.y. Metamorphism affected some lavas at about 1,360 m.y. The diatremes have two ages of intrusion, about 1,225 m.y. and 1,140 m.y., the latter being the age of the Majhgawan pipe near Panna in northern India. Pre‐Kurnool dolerites have an age of 980 ±110 m.y. The lavas and dolerites show a range of initial 87Sr/86Rb ratios from about 0.704 to 0.708 and possibly 0.712. The age data suggest that no simple correlation can be made with other Precambrian sequences in northern peninsular India. Deposition of the Cuddapah System appears to have started well before the start of the deposition of the Vindhyan System, while the Kurnool System is coeval with only part of the Upper Vindhyan. The data also suggest that present interpretations of the structural development of the Cuddapah Basin may need some revision. 相似文献
44.
Lithofacies in the mid‐Permian Nowra Sandstone indicate a middle/upper shoreface to foreshore environment of deposition under the influence of storm‐generated waves and north‐northeasterly directed longshore currents. Palaeogeographic reconstruction for the Nowra Sandstone portrays a sand‐dominated high energy shelf and offshore shoal forming a sequence thickening seaward away from the western shore of the Sydney Basin. The shoal‐crest at the outer edge of the shelf trends north‐northeast. It is characterized by fine‐ to medium‐grained sandstone with upper flow regime structures and a high proportion of conglomerate, whereas coarser sandstone with lower energy bedforms occurs along the seaward side of the shoal. In the deeper water to the east, the lower Nowra Sandstone becomes rapidly thinner as it passes seaward, via bioturbated storm redeposited sandstone beds, into the shelf deposits of the Wandrawandian Siltstone. This sequence accumulated during a regressive event and the base of the formation becomes progressively younger eastward. The sand may have been supplied by rivers along the western coast but the major source was south of the study area. The lower Nowra Sandstone is separated from the upper part of the formation by an extensive ravinement surface overlain by the Purnoo Conglomerate Member. In contrast to the lower unit, the upper Nowra Sandstone forms a westward thickening wedge that represents a backstepping nearshore sand facies that accumulated during a transgression. The upper Nowra Sandstone passes vertically and laterally eastward into the Berry Siltstone. Thus both boundaries of the Nowra Sandstone are diachronous, first younging eastward and then westward as a response to a regressive‐transgressive episode. 相似文献
45.
We have investigated the petrography, geochemistry, and detrital zircon U–Pb LA-ICPMS dating of sandstone from the Gorkhi Formation of the Khangai–Khentei belt in the Ulaanbaatar area, central Mongolia. These data are used to constrain the provenance and source rock composition of the accretionary complex, which is linked to subduction of the Paleo-Asian Ocean within the Central Asian Orogenic Belt during the Middle Devonian to Early Carboniferous. Field and microscopic observations of the modal composition of sandstone and constituent mineral chemistry indicate that the sandstone of the Gorkhi Formation is feldspathic arenite, enriched in saussuritized plagioclase. Geochemical data show that most of the sandstone and shale were derived from a continental margin to continental island arc setting, with plutonic rocks being the source rocks. Detrital zircon 206Pb/238U ages of two sandstones yields age peaks of 322 ± 3 and 346 ± 3 Ma. The zircon 206Pb/238U age of a quartz–pumpellyite vein that cuts sandstone has a weighted mean age of 339 ± 3 Ma. Based on these zircon ages, we infer that the depositional age of sandstone within the Gorkhi Formation ranges from 320 to 340 Ma (i.e., Early Carboniferous). The provenance and depositional age of the Gorkhi Formation suggest that the evolution of the accretionary complex was influenced by the intrusion and erosion of plutonic rocks during the Early Carboniferous. We also suggest that spatial and temporal changes in the provenance of the accretionary complex in the Khangai–Khentei belt, which developed aound the southern continental margin of the Siberian Craton in relation to island arc activity, were influenced by northward subduction of the Paleo-Asian Ocean plate. 相似文献
46.
47.
新疆布尔津盆地砂岩型铀矿成矿水文地质条件初探 总被引:7,自引:1,他引:6
本文在简要介绍布尔津盆地地下水赋存条件与分布的基础上,论述了该盆地的构造-水文地质层特征,进而着重阐明区内地下水初、径、排等水动力条件以及水文地球化学特征,总结有利的铀矿成水文地质条件。 相似文献
48.
东濮凹陷低渗致密储层的沉积-成岩特征表现为砂层薄、粒度细、沉积非均质性显著;埋藏深度大于3700m,压实作用、晚期自生伊利石-绿泥石和二氧化硅胶结作用强。储层具有小孔极细喉孔隙结构,表面积大,渗透率对围压的敏感性强,地下真实孔隙度和渗透率分别介于10% -< 5% 、0.1×10-3-< 0.001×10-3μm 2.研究认为,东濮凹陷致密砂岩气藏大多产出于盆地次级深洼陷中,具有高压水溶气的成因机制,这是由储层的低渗性、较高的毛细管准数、高束缚水饱和度和高温-高压以及充足-近源的天然气供给等条件所决定的。 相似文献
49.
中国海相油气田勘探实例之十三 塔里木盆地东河塘海相砂岩油田勘探与发现 总被引:2,自引:1,他引:2
东河塘油田位于新疆库车县,构造上隶属于塔里木盆地塔北隆起轮台凸起东河塘断裂构造带,是我国发现的第一个高产高丰度海相砂岩油田,它的发现是中国海相砂岩油气勘探理论和实践的一次重大突破。油田发现于1990年7月,至1994年探明石油地质储量3323.13×104t,天然气地质储量15.5×108m3,至2009年底累计产原油825.75×104t。石炭系东河砂岩油藏是东河塘油田的主体,其储层东河砂岩段是一套滨岸相砂体,具有厚度巨大、埋深大、储集性能好的特点;其油藏类型为块状底水背斜油藏,产能高,储量丰度高。论述了东河塘油田勘探与发现的历程,剖析了取得勘探成功的实践认识与意义。 相似文献
50.