Study Of Sedimentary Facies Research Articles

Application of Integrative Geophysical Methods To Predicting Sedimentary Facies of Marine Residual Basins in Middle Guangxi Province, China

AbstractThe sedimentary facies study is one of the key procedures in exploration of subtle reservoirs in basins, of which a prerequisite is effective identification of its structural, lithologic or lithofacies differences through integrated usage of geophysical methods. Based on geophysical data, including gravity, aeromagnetic and seismic data, this paper describes the density distribution characteristics of marine strata in middle Guangxi province, South China, and predicts the regularities of lithofacies and sedimentary facies changes in terms of potential field forward stripping and profile forward/inverse fitting. It is revealed that transversal lithologic and lithofacies changes exist in the marine strata of mid‐ and lower‐Devonian series of the area. The platform zones in the northwest and southeast of the area have high gravity anomalies and high fitting rock density. The “X”‐shaped platform‐marginal facies zone in the middle is characterized by irregular gravity anomalies and a large variation range of fitted rock density. And the platform‐trough facies zone in the east exhibits low gravity anomalies as well as low fitted rock density. Predicting sedimentary facies through integrative geophysical methods offers a new approach for exploration of lithologic trap reservoirs and bioherm reservoirs in basins. This method has been preliminarily proved, and needs further improvements and applications.

La plate-forme carbonatée oxfordienne de Lorraine : arguments pour une ouverture vers la mer Germanique

The Oxfordian carbonate platform of Lorraine: evidences for an opening toward the Germanic Sea. The study of sedimentary facies in the quarry of Dompcevrin (Middle Oxfordian) located northwestward of St-Mihiel (Meuse department) provides evidences of high-energy depositional conditions. The occurrence of beaches associated with hurricane coral breccias containing megaclasts is characteristic of platform edge environments. The open sea was located northeastward, in the direction of Germany, as it is indicated by the direction of progradation of beaches. It is concluded that the Oxfordian carbonate platform of Lorraine was opened to the northeast toward the Germanic Sea during the Middle Oxfordian. To cite this article:

Successions of sea-level changes during the Pleistocene in Mauritania and Senegal distinguished by sedimentary facies study and U/Th dating

Abstract The marine Quaternary Basin in Mauritania corresponds to a large gulf covering a 600×200 km area. The progressive reduction in size of marine gulfs from the early Pleistocene to Holocene (Nouakchottian), suggests that the gulf size has been affected by successive positive epirogenic episodes. However, recent studies have indicated that the oldest and largest concentric outcrops (Tafaritian) seem to have been deposited in various continental and unstable environments (lakes, sebkhas). In this study, we verified first the absence of recrystallization in fossil mollusc shells, and then U/Th measurements were carried out on seven of these. Most deposits (sandstones more or less cemented or coquina) belong to the interglacial Eemian sea-level high-stand (isotopic stage 5). On the basis of 14C radiometric measurements, the deposits were initially attributed to the relative warming during isotopic stage 3, and were named Inchirian. In view of our recent dating results, this attribution needs to be re-examined. Two other U/Th dates performed on shells from the section where isotopic stage 5 was obtained or from a neighbouring area, indicated deposition during isotopic stage 7. These observations and dating would imply an improbable uplift of the shorelines that controlled decreasing widespread transgressions. The morphostructure of shoreline outcrops, previously described as aureoles, has to be revised: the extent of the Quaternary marine plain has to be restricted and does not exceed a maximum of 100 km in width at the latitude of Nouakchott. It was invaded by marine transgressions whose deposits are: (1) extremely condensed by deep cuts and/or by aeolian deflation during regression episodes; (2) often restricted to layers of cemented shore-sands or to upper parts of ferruginous crusts with ferric iron encrustation; and (3) sometimes fossilised shelly beds of different ages in the same sediment column. On the basis of these observations, the uplift rising above the present zero of Pleistocene shoreline deposits or subsidence processes are even more unlikely at the scale of the Mauritanian Quaternary Basin. Post sedimentary alteration of these deposits, especially dissolution has been negligible, which explains the exceptional preservation of such Pleistocene outliers. In the neighbouring Senegalian Basin, outcrops of marine Pleistocene deposits are usually restricted to a very narrow coastal band. They disappear about 40 km south of Dakar with the progression of tropical weathering. In this area, the sediment column is about 1 m thick and indicates the superposition of shelly layers of isotopic stages 5 and 7.

Modern Pearl River Delta and Permian Huainan coalfield, China: a comparative sedimentary facies study

Sedimentary facies types of the Pleistocene deposits of the Modern Pearl River Delta in Guangdong Province, China and Permian Member D deposits in Huainan coalfield in Anhui Province are exemplified by depositional facies of anastomosing fluvial systems. In both study areas, sand/sandstone and mud/mudstone-dominated facies types formed in diverging and converging, coeval fluvial channels laterally juxtaposed with floodplains containing ponds, lakes, and topogenous mires. The mires accumulated thin to thick peat/coal deposits that vary in vertical and lateral distribution between the two study areas. This difference is probably due to attendant sedimentary processes that affected the floodplain environments. The ancestral floodplains of the Modern Pearl River Delta were reworked by combined fluvial and tidal and estuarine processes. In contrast, the floodplains of the Permian Member D were mainly influenced by freshwater fluvial processes. In addition, the thick, laterally extensive coal zones of the Permian Member D may have formed in topogenous mires that developed on abandoned courses of anastomosing fluvial systems. This is typified by Seam 13-1, which is a blanket-like body that thickens to as much as 8 m but also splits into thinner beds. This seam overlies deposits of diverging and converging, coeval fluvial channels of the Sandstone D 3 and associated overbank-floodplain deposits. The limited areal extent of lenticular Pleistocene peat deposits of the Modern Pearl River Delta is due to their primary accumulation in topogenous mires in the central floodplains that were restricted by contemporaneous anastomosing channels.

Authigenic Chlorite as a Controlling Factor in the Exploration of Turonian/Coniacian Turbidites in the Santos Basin: ABSTRACT

Upper Turonian/Coniacian and Campanian turbidites are major targets for petroleum exploration in the Santos Basin, southeastern Brazil. They occur between 140 and 1000 m of present water depth, are buried at about 4500 m, and reach thickness of up to 60 m. The main reservoir facies is composed of unstratified, fine to very fine grained, poorly sorted sandstones, which framework is compositionally immature, including a high proportion of feldspars and volcanic rock fragments. Early coating of grains by authigenic chlorite inhibited pressure solution and quartz cementation in the reservoir. This diagenetic characteristic allowed important preservation of primary porosity (>20%) in the reservoir; nevertheless its permeability never exceeds 30 ml. The study of sedimentary facies and related depositional processes has been conducted to predict the distribution of petroleum-bearing turbidites throughout the Santos Basin; this comprises a major challenge for the petroleum exploration in this important Brazilian exploration frontier.

Sedimentary dynamics and structural control of Neogene tropical biofacies during the formation of the Central American Isthmus

The central evolutionary, ecological and paleoceanographic questions of the American tropical Neogene relate to how and during what time the Central American Isthmus formed. Geographically, closure was located between the southern edge of the Chortis Block in southern Nicaragua and the Atrato Valley in Colombia. In this region we describe, on the Caribbean side, five Neogene sedimentary basins. They are the Atrato, Chucunaque, Gatun, Bocas del Toro, and Limon Basins. On the Pacific side the Neogene sediments formed as part of the Central American Trench and are well exposed in a series of uplifted blocks on the Nicoya, Osa and Burica Peninsulas. Our analysis allows 1) a construction of the sequence of contrasting sedimentary environments which characterize the different basins, giving a composite geological history of the isthmus for the Late Neogene and 2) identifies the comparable biofacies from the different basins which allow and constrain the evolutionary and ecological questions to be posed concerning the effect of the isthmus as a biogeographic barrier. Temporally, from it's partial emergence in the Middle Miocene, the isthmus shallows by the Early Pliocene (3.5–3.4 Ma) to less than 50 m (Duque-Caro, 1990) when there is a marked differentiation of shelf marine macrobenthic species between the Caribbean and the Pacific. The evidence from reliably dated, large, diverse exchanges of North and South American vertebrates on land constrains the final closure date to not later than 2.8–2.5 Ma (Marshall, 1988). Given that no conclusive evidence for final closure can come exclusively from a study of sedimentary facies, when depths of less than 50 m are involved, the present window of almost 1 Ma, during which final closure must have occurred, will only be narrowed further by the detailed study of very shallow-water fossil clades and complementary molecular data. Present studies indicate that such clades are abundantly preserved.

Jiuquan Basin--a Highly Explored (Mature) Area and Its Exploration Future: ABSTRACT

Jiuquan basin is one of the piedmont basins of the Qilian Mountain range in northwestern China. The basin has an area of about 2,700 km2 (1,042 mi2) and trends WNW-ESE. Cenozoic to Mesozoic deposits, with a total thickness of 4,500 m (14,764 ft) overlie lower Paleozoic rocks. Some Carboniferous, Permian, and Triassic outcrops are exposed near the margin of the basin. Jurassic and Cretaceous formations, characterized mainly by marsh-lake sedimentary facies, are the source beds within this area. The thickness changes of these formations are related to the effect of crustal movement during deposition. On the uplifted parts of this area, Jurassic and Cretaceous deposits are very thin or absent; otherwise, they generally developed to a thickness of about 2,500 m (8,200 ft). The Tertiary formations have a thickness of about 2,000 m (6,560 ft) and consist chiefly of river or lake to alluvial sediments deposited under arid climatic conditions. In the lower part of these formations, the river-delta sand bodies are the regional reservoir beds. Between the Mesozoic and Cenozoic systems, a large depositional interruption exists. Upper Cretaceous to Paleocene deposits are all absent. There are three structural belts in this area. From south to north, they are the southern anticline belt, the center depression belt, and the northern monocline belt. The first field (Laojunmiao oil field) was discovered in 1939. Since the founding of the People's Republic about 33 years ago, six oil fields (comprising 14 oil pools) have been sequentially discovered within this basin. The discovery history of the oil fields can be divided into three stages. During the first stage (1939-59), shallow reservoirs in the Tertiary were explored, based primarily on oil seepage and surface structure drilling. Fields discovered during this period were the Laojunmiao, Yarxia, Beiyanghe, and Shiyougou. From 1960 to 1974, the second exploration phase drilled to the deeper formations. As a result, a buried basement hill was discovered under the shallow Yarxia reservoir, and a new Cretaceous reservoir was found in the direction of the source area. After 1975, exploration entered a new stage with the search for pre-Tertiary nontectonic-type reservoirs. With improved seismic apparatus and data processing, the study of sedimentary facies using seismic stratigraphy is being applied o exploration efforts. The improved seismic and data processing, in combination with advances in drilling techniques, have led to the discovery of new nontectonic-type oil fields in places that had been previously drilled. The number of nontectonic reservoirs and their reserves are growing. End_of_Article - Last_Page 573------------

Anticipating Coal Mining Problems in Hartshorne Formation, East-Central Oklahoma, Using Sedimentary Facies Analysis: ABSTRACT

A study of sedimentary facies associated with the Hartshorne coal beds of east-central Oklahoma provides an opportunity for preventive planning to minimize mining problems. Sedimentary facies within the Hartshorne formation End_Page 724------------------------------ include delta distributary sandstones and interdistributary bar-fill shales, siltstones, and sandstones. One distributary channel sandstone body displays a shoestring geometry, over 12 mi (19.2 km) long and 1 mi (1.6 km) wide, with an average maximum thickness of 200 ft (61 m). This sandstone rests directly on and locally replaces the Lower Hartshorne coal bed. Three major mining problems are related to this sandstone body: (1) the Hartshorne sandstone in this area is a natural gas reservoir which might emit gas into adjacent coal mines; (2) the sandstone body is directly related to local discontinuities and rolls in the Lower Hartshorne coal bed; and (3) an unstable roof may be locally associated with trough cross-bedding and jointing near the base of the sandstone, and with facies changes and slickensides along the lateral margins of the sandstone body. In contrast to this sandstone body, interdistributary bay deposits, because of their relative homogeneity and lateral persistence, do not present potential facies-related mining problems. Potential mining problems associated with these facies are local and are directly related to structural and stress-release features which are difficult to predict in advance of mining. To insure safe and economic coal production from the Hartshorne formation, the distribution of major sandstone bodies overlying the coal beds must be considered when planning degasification programs and shaft, slope, and main entry locations. End_of_Article - Last_Page 725------------