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1.
In the Getic of the Carpatho-Balcanides (eastern Serbia) and the Tirgan Formation of the Kopet-Dagh Basin (northeast Iran), platform carbonates were deposited during the Barremian/Early Aptian in environments in the domain of the northern Alpine Tethys and deformed during the Alpine orogeny. In this study, Urgonian carbonate platform deposits are discussed in detail with regard to depositional facies, microfacies, biostratigraphy, palaeoenvironments and palaeoecology. Detailed sedimentological and palaeontological investigations have been carried out on five sections in eastern Serbia and three sections in northeast Iran supported by an analysis of 392 thin-sections. Petrographic analysis of thin-sections led to the recognition of eight microfacies types grouped into four facies zones. A supratidal–intertidal (restricted)–intertidal (open-lagoon)–platform-margin sand-shoal transition was recorded in both areas. Supratidal facies are characterized by bioclastic mudstones and fenestral and peloidal wackestones and packstones; intertidal (restricted) facies are represented by bioclastic wackestones, whereas intertidal (open-lagoon) facies are indicated by bioclastic packstones/grainstones and oncoid grainstones. High-energy sand-shoal facies are dominated by ooid grainstones/rudstones followed by orbitolinid packstones. Benthic foraminifera are especially abundant and along with calcareous algae are the most important fossils used for age determination of shallow-marine carbonate deposits. Thirty-two benthic foraminiferal genera were identified from eastern Serbia with an additional 38 genera from northeast Iran dominated by agglutinated forms. Identified calcareous algae provide significant data for depositional environments and palaeoecology. The microfossil associations in the two regions are very similar and share a number of common characteristics, but also some differences and show a strong affinity to those of the northern margins of Tethys. In both study areas shallow-marine environments of the Barremian/Early Aptian were replaced by deep-marine conditions during the Late Cretaceous. 相似文献
2.
Detailed study of marine shales (the Ostracod zone) within a Cretaceous, third-order transgressive-regressive sequence in the Alberta Foreland Basin reveals a systematic association between shell beds and parasequence-scale flooding surfaces, including surfaces of maximum flooding. The Ostracod zone (a subsurface lithostratigraphic unit known as the Calcareous Member in outcrop) consists of 10-20 m of black shale and bioturbated sandstones with many thin, fossiliferous limestones. Parasequences (shallowing-up cycles 2–3 m thick) were delineated within this transgressive unit based on lithology, sedimentary structures, degree of bioturbation, dinoflagellate diversity, total organic carbon and carbon/sulphur ratios; many flooding surfaces are firmgrounds or hardgrounds. Shell-rich limestones occur in three different positions relative to these flooding surfaces, and each has a distinctive bioclastic fabric and origin. (i) Base-of-parasequence shell beds (BOPs) lie on or just above flooding surfaces in the deepest water part of a parasequence; they are thin (up to a few centimetres), graded or amalgamated skeletal packstones/wackestones composed of well-sorted granular shell, and are interpreted as hydraulic event concentrations of exotic shell debris. (ii) Top-of-parasequence shell beds (TOPs) are capped by flooding surfaces at the top, shallowest water part of a parasequence; they typically are several decimetres thick, are physically amalgamated packstones/grainstones or bioturbated wackestones, and contain abundant whole as well as comminuted shells; these are composite, multiple-event concentrations of local shells. (iii) Mid-sequence shell beds rest on as well as are capped by firmgrounds or hardgrounds, and are intercalated between parasequences in the deepest water part of the larger sequence; they are laterally extensive lime mudstones a few decimetres thick, with sparse shells in various states of dissolution, recrystallization and replacement; these beds are terrigenous-starved hiatal concentrations and record maximum flooding within the Ostracod zone. Offshore sections of the Ostracod zone typically contain several starved mid-sequence shell beds, underscoring the difficulty of identifying a single‘maximum flooding surface’ within a third-order sequence. 相似文献
3.
The role of wave reworking on the architecture of storm sandstone facies, Bell Island Group (Lower Ordovician), eastern Newfoundland 总被引：2，自引：0，他引：2
Stacked shallow marine cycles in the Lower Ordovician, Bell Island Group, of Bell Island, Newfoundland, show upward thickening and upward coarsening sequences which were deposited on a storm-affected shelf. In the Beach Formation each cycle has a facies sequence comprised, from base to top, of dark grey mudstones, light grey mudstones, tabular sandstones and mudstones, lenticular sandstones and mudstones, and thick bedded lenticular sandstones, reflecting a progressive increase of wave orbital velocities at the sediment surface. The mudstones and tabular sandstones reflect an environment in which the sea floor lay in the lower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents. The lenticular sandstones in the succeeding facies are wave reworked sands, commonly lying in erosional hollows and having erosional tops and internal hummocky cross-stratification. Planar lamination is relatively uncommon and sole marks are mainly absent. In this facies oscillatory currents were dominant and accumulated sand in patches generally 10–30 m in diameter. The facies formed on the inner shelf where the oscillatory currents generated by storm waves had powerful erosional effects and also determined the depositional bedforms. Mud partings and second-order set boundaries within sandstone beds are believed to separate the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds. This interpretation has important implications for attempts to estimate event frequency by counting sandstone beds within a sequence and for estimates of sand budgets during storm events. The thick bedded lenticular facies appears to have been formed by erosion of the mud beds between the lenticular sands, leading to nearly complete amalgamation of several lenticular sand bodies except for residual mud partings. In the overlying Redmans Formation the process of amalgamation progressed even further so that nearly all the mud partings were removed, resulting in the formation of thick bedded tabular sandstones. Sequence stratigraphic analysis of the cyclical sequence suggests that the cycles were eustatically controlled. The rising limb of the sea level curve produced only the dark grey mudstone part of the cycle while the remainder of the cycle was deposited on the falling limb. There is a gradational but rapid facies transition from the tabular to the lenticular sandstone facies which is interpreted as occurring at the inflexion point on the falling limb. The thick bedded facies of the Beach Formation and the thick bedded tabular facies of the Redmans Formation represent periods of maximum sea level fall. The stacked cycles in the Beach Formation are interpreted as an aggradational, high frequency sequence or parasequence set bounded at the top by a sequence boundary and succeeded by the three aggradational parasequences of the Redmans Formation. The recognition of storm facies with sandstone beds of very different bed length has important implications for the reservoir modelling of such facies. 相似文献
4.
Mud-mound complexes identified within the early to middle Ashgill Cystoid Limestone Formation of northeastern Spain are the first fossil build-ups to be described in the high latitude north-facing margin of Gondwana. Mud-mound complexes comprise individual lenticular mounds (composed of floatstones, cephalopod-rich mudstones and cementstones), flanks and intermound deposits (including pelmatozoan packstones and floatstones). The small mounds are mainly composed of bryozoans, cystoids and crinoids, and were developed on outer ramp environments. Mound initiation depended upon the stabilization and colonization of densely packed lenses of pelmatozoan-rich sediments. In a mid-ramp setting, pelmatozoan–bryozoan meadows were episodically degraded by common wave- and storm-induced processes, the development of semi-consolidated substrates, and the periodic influx of terrigenous material. Finally, during the Hirnantian regression, the Iberian mixed (carbonate–siliciclastic) platform was exposed to subaerial conditions sufficiently for erosion and karstification to occur. From a palaeogeographical point of view, the pattern of the Ashgill Iberian platform deposition is characterized by episodic exclusion of carbonates from most nearshore environments by a shoreline source of siliciclastic sediments. A similar interpretation to that made on the Iberian Cystoid Limestone Formation, in terms of gradual proximality–distality changes, is proposed for comparable facies types in Ashgill limestones described in southwestern Europe. © 1998 John Wiley & Sons, Ltd. 相似文献
5.
WOLFGANG BLENDINGER 《Sedimentology》1991,38(2):223-242
Norian crinoidal/brachiopod limestones and cephalopod limestones of the Hallstatt-type occur as blocks in a Hettangian(?) calcareous breccia of the Haliw Formation in the Oman Mountains. Crinoidal and brachiopod packstones, up to 12 m thick, prevail in the lower part of the sequence and were deposited on a substrate of Norian forereef breccia. The overlying cephalopod wackestones, up to 4.9 m thick, have a basal white bed followed by red limestones with abundant planar and scalloped, corroded surfaces and local stromatolites. Upward, red, nodular wackestones and, finally, slumped grey wackestones follow. The analysis of geopetal fabrics in orientated samples shows that bedding of these facies is, in fact, inclined bedding. Inclinations varied between 15 and 29°. In addition, the restored dip directions demonstrate rotation, indicating deposition on a gliding block. The preferred orientation of orthoconic cephalopods and imbrication of discoidal ammonoids coincide with the dip direction measured from geopetal fabrics. Such features, generally interpreted as current-induced, are here interpreted as gravity-induced. The overall mud-supported rock fabric thus indicates deposition under very low-energy conditions. The common mud-supported texture of the rocks contrasts with evidence for current activity found in the scalloped surfaces and shell lags, particularly in the crinoidal/brachiopod facies and the lower, stratigraphically condensed, cephalopod limestones. This indicates that deposition of lime mud alternated with periods of elevated current strength. A comparison of the Hallstatt-type limestones and current-influenced sediments on the northern slope of the Little Bahama Bank suggests that condensed sequences of the Hallstatt-type are restricted to relatively shallow depths with strong fluctuation of contour-following currents undersaturated with respect to aragonite along carbonate shelf margins facing the open ocean. On steep slopes, sediment bypassing may be an additional factor for stratigraphic condensation. 相似文献
6.
四川江油-广元地区上石炭统碳酸盐岩发育良好,厚度不大,化石丰富,含多层紫红色砾屑生物碎屑灰岩和泥岩韵律层,在整个华南同期沉积中颇具特色。根据野外观察和室内显微分析,共识别出15种微相类型。根据这些微相类型在纵向和横向上的组合与分布特点,参考Wilson的标准微相和镶边碳酸盐岩台地沉积模式,利用微相组合分析将这些微相组合划分到4个相带,即蒸发台地、局限台地、开阔台地和台地边缘浅滩。沉积相带的变化特征表明研究区晚石炭世存在着多期海侵-海退旋回,其中在黄龙组上段沉积中期海侵达到最大值,使得川西北大部分地区和川东地区广泛接受碳酸盐岩沉积。江油-广元地区上石炭统特殊岩层的研究表明:黄龙组下部4套红层具有浅海陆棚上部近积风暴岩的特征;船山组核形石灰岩粒序层及其地球化学特征表明核形石的形成可能与晚石炭世晚期全球冰期事件有密切的关系。 相似文献
7.
The carbonatic sequence of the Calabozo Formation (Lower Callovian) developed in southwestern Gondwana, within the northern area of the Neuquén basin, and is widespread in thin isolated outcrops in southwestern Mendoza province, Argentina. This paper describes the facies, microfacies and geochemical-isotopic analysis carried out in five studied localities, which allowed to define the paleoenvironmental conditions of a homoclinal shallow ramp model, highly influenced by sea level fluctuations, where outer, mid and inner ramp subenvironments were identified. The outer ramp subenvironment was only recognized in the south of the depocenter and is characterized by proximal outer ramp facies with shale levels and interbedded mudstone and packstone layers. The mid ramp subenvironment is formed by low energy facies (wackestone) affected by storms (packstones, grainstones and floatstones). The inner ramp subenvironment is the most predominant and is characterized by tidal flat facies (wackestones, packstones and grainstones) over which a complex of shoals (grainstones and packstones) dissected by tidal channels (packstone, grainstones and floatstones) developed. In the north area, protected environment facies were recorded (bioturbated wackestones and packstones). The vertical distribution of facies indicates that the paleoenvironmental evolution of the Calabozo Formation results from a highstand stage in the depocenter, culminating in a supratidal environment, with stromatolitic levels interbedded with anhydrite originated under restricted water circulation conditions due to a progressive isolation of the basin. δ13C and δ18O values of the carbonates of the Calabozo Formation suggest an isotopic signature influenced by local palaeoenvironmental parameters and diagenetic overprints. The δ13C and δ18O oscillations between the carbonates of the different studied sections are related with lateral facies variations within the carbonate ramp accompanied with dissimilar reactivities in relation to diagenetic fluids. The δ18O values of all sections exhibit a rather broad scatter which may be attributed to diagenesis and recrystallisation while the carbon isotopic composition has been less affected by those processes. Carbon isotope system has best retained the primary isotopic signal and δ13C values (0–3.9‰) are within the Callovian isotope range. The 87Sr/86Sr ratios of the bulk carbonates of El Plomo creek, La Vaina creek and Potimalal River sections are in agreement with the Callovian seawater Sr-isotope curve. 相似文献
8.
Westphalian B (Duckmantian) alluvial Coal Measures along the Northumberland coast, NE England, comprise coal-capped coarsening-upward crevasse-splay sequences of shale, siltstone and sandstone, interbedded with a number of major distributary channel sandbodies, including the Table Rocks Sandstone. Lithofacies, architectural analysis and outcrop geometries divide the Table Rocks Sandstone into flaggy sandstone, massive sandstone, heterolithic, and mudstone facies associations, each comprising up to 7 lithofacies types. The three sandy facies associations are characterised by lenticular bed geometries on different scales producing a hierarchy of lensoid packages and associated bounding surfaces, all showing typical offset stacking patterns: (1) lenses, represent individual lenticular cross-bed sets, bounded by 1st order surfaces; (2) packages of lenses, called lens clusters are bounded by 2nd order surfaces, and are the basic architectural building block of the sandy facies associations; and (3) vertically stacked lens clusters called amalgamated lens clusters, bounded by 3rd order surfaces. The Table Rocks sandbody has a laterally extensive, irregular, lobate subsurface plan geometry, it displays a radial palaeocurrent pattern with 180° dispersion, and it forms part of a 14-m thick coarsening-upward regressive sequence. It is interpreted as a composite, lobate crevasse-splay delta system that prograded into a shallow interdistributary fresh to brackish water lake up to 14 m deep. The shallow lake water, fluvial input, and extensive development of traction structures such as cross-bedding and ripple cross-lamination suggests a friction-dominated delta, in which the four facies associations can be interpreted in terms of discrete elements of the mouth bar environment. The flaggy sandstone facies association represents the main, axial part of the mouth bar system, the erosively based massive sandstone facies association major subaqeous distributary channels, the lithologically more variable heterolithic facies association the medial mouth bar, and the mudstone facies association the distal mouth bar fringe and prodelta. Within this environmental setting amalgamated lens clusters are interpreted as small, discrete mouth bar sand lobes, whose offset, imbricate stacking pattern reflects channel spacing and bifurcation, the rate of channel shifting, or shallow depths and lack of accommodation space. Thus, lens clusters are interpreted as discrete growth elements of the mouth bar sand lobes, and lenses as individual bedforms making up these growth elements. Because of the high rate of channel shifting, lack of extensive erosion of the mouth bar lobes, and deposition of low discharge fines, the lobes retained much of their original depositional geometry, thereby providing advantageous gradients for offset deposition and stacking of adjacent sand lobes. Although the delta complex was maintained by frequent crevassing from the feeder channel, and by subsidence due to contemporaneous compaction and/or local tectonism, it was deeply incised on two occasions by subaqeous channels in response to high magnitude floods or falling lake level. 相似文献
9.
《Sedimentology》2018,65(4):1331-1353
The Faxe Quarry in south‐east Denmark offers excellent exposures of Early Palaeocene, Danian deep‐water intercalated coral and bryozoan mounds that form complexes at least 40 m thick and a few kilometres wide along and over submarine highs. The coexisting coral and bryozoan mounds represent two different biogenic carbonate factories with a highly dynamic interplay during growth. The sedimentary facies, mound geometries and the density, diversity and palaeoecology of the associated benthic invertebrates and nannofossils allow recognition of six successive growth units. Unit 1 represents an outer shelf bryozoan mound belt characterized by an oligotrophic cool‐water nannofossil assemblage. Unit 2 comprises a mixed faunal assemblage of bryozoans and octocorals with an initial sparse colonization of hexacorals. The nannofossil assemblage records a decrease in diversity and an increase in warm water forms. Unit 3 marks the onset of dense colonization of the scleractinian coral Dendrophyllia candelabrum with associated low‐diversity macrofauna and nannofossil assemblages. Unit 4 represents the main coral build‐up phase with frame‐building hexacorals of Dendrophyllia and Faxephyllia associated with a high‐diversity invertebrate fauna, and relatively low‐diversity nannofossil assemblages. Unit 5 represents the late coral mound phase showing extensive lateral distribution and finally death and erosion of the coral mounds. This event was contemporaneous with a warming trend in the pelagic environment. The succeeding Unit 6 marks the burial and overgrowth of the coral mound complex by bryozoan‐rich sediments. The coral mound complex in the Faxe Quarry initiated and terminated in global nannofossil zone NP 3 and regional nannofossil zones NNT p2G–3 suggesting a mound growth duration of ca 300 kyr and a mean vertical accretion of the coral mound of 13 cm kyr−1. The mound complex probably serves as the best‐exposed analogue to modern deep and cold‐water coral mounds in the North Atlantic. 相似文献
10.
Cenozoic limestones in New Zealand are mainly skeletal grainstones and packstones formed under non-tropical climatic conditions in open marine shelf or ramp environments. Following petrographic analysis of the nature and abundance of the skeletal components in nearly 500 samples of these limestones, a complete linkage cluster analysis identified seven major skeletal assemblages that may be regarded as subdivisions of the single foramol skeletal association defined by Lees and Buller (1972) for temperate-region carbonate deposits. The seven assemblages are given contracted names, as follows: (a) BARNAMOL = barnacle/bivalve-dominated; (b) BIMOL = bivalve-dominated; (c) BRYOMOL = bryozoan/bivalve-dominated; (d) ECHINOFOR = echinoderm/benthic foraminiferal-dominated; (e) NANNOFOR = nannofossil/planktonic foraminiferal-dominated; (f) RHODALGAL = calcareous red algal-dominated; and (g) RHODECHFOR = calcareous red algal/echinoderm/benthic foraminiferal-dominated. A composite triangular classification diagram has been devised for naming the skeletal assemblage of an unknown sample on the basis of its three main skeletal components. The diagram successfully characterises more than 85% of the New Zealand Cenozoic limestone samples and also appears to be applicable for the skeletal assemblage designation of many overseas examples of non-tropical carbonate deposits. Limitations relate mainly to locally common skeletal types (e.g. serpulids, brachiopods) that are presently not incorporated into the New Zealand-based scheme. The general ecological preferences of the main skeletal contributors in each of the seven skeletal assemblages form a basis for relating the assemblages to broad shelf habitats. Consequently, as well as the benefits of providing a more consistent skeletal assemblage terminology for comparative studies between different workers, the scheme can assist with the paleoenvironmental interpretation of non-tropical skeletal carbonate facies. 相似文献
11.
四川会理 会东及邻区中元古界昆阳群 ,由下而上可分为力马河组、凤山营组和天宝山组 ,与古元古界河口群为不整合接触 ,其代表年龄值为 1 70 0± 1 0 0Ma～ 1 2 0 0± 1 0 0Ma。对这套地层的沉积学研究 ,前人涉及甚少。笔者在野外考察和室内分析的基础上 ,对其沉积相和沉积环境进行了详细的研究。初步认为研究区的中元古界昆阳群可分为 7种沉积相 ,进而探讨了该区的沉积演化历史。 相似文献
12.
On the Boso Peninsula, southeast of Tokyo, individual turbidite layers have been traced over about 38 km with the aid of tuff marker-beds. Sandstones are generally much more variable in thickness than the interbedded mudstones, showing lenticular shapes with great lateral continuities up to 30 km or more. But the latter have greater extents than the former, forming extensive sheets with a slight upslope thickening. Most sandstones show vertical and lateral grading, while mudstones gradually coarsen upslope. Sandstones have a variety of sedimentary structures typical of turbidites, whereas mudstones are virtually devoid of them throughout. Sandstones contain intensely abraded shallow-water fauna in contrast with mudstones with well-preserved deep-water fauna. Thus, mudstones are mostly of hemipelagic origin, and turbiditic mudstones, if present, are of negligible amounts. In general, individual sandstone beds are much more variable in thickness on the upstream side than on the downstream side. This is probably because of the existence of some minor channels and the adjacent levee-like embankments on the upslope side. At the base of thicker sandstone beds local penecontemporaneous erosion has usually taken place, giving rise to a few minor channels bordered by small levee-like embankments on both sides. The downslope side of the largest channel is commonly flanked by the greatest embankment that is coincident with the thickest part of each sandstone layer. Sandstones in the minor channels and levee-like embankments contain a lot of mud lumps torn out of the substratum, which decrease in size and amount and improve in roundness with increasing distance from the channels. In general, thicker sandstones show Bouma abcde sequences around the thickest part. Bouma d-division and convolution are developed preferentially on the downstream side of the thickest part. With decreasing bed thickness laterally, the complete depositional sequences arc successively replaced by Bouma bcde, then cde, and de sequences downslope, while by Bouma bc/c and then c/e sequences upslope. The facies transition of the horizon studied probably represents a section extending from the downslope end of the channelized portion of a suprafan to the outer portion with a smooth surface. 相似文献
13.
中韩第五次《东北亚地壳演化》学术研讨会在北京举行 总被引：2，自引：0，他引：2
新疆天山东部广泛发育晚石炭世碳酸盐岩隆。这些岩隆主要为生物丘,少数为生物滩及与岩隆有关的生物层,其中生物丘含大量灰泥和内碎屑。基本岩石类型为泥粒状灰岩、粒泥状灰岩、粒泥状－泥粒状灰岩,少量岩石类型包括颗粒岩、骨架岩和障积岩。成岩作用是碳酸盐岩隆发展演化的重要阶段和过程,在生物丘内,已经识别出四种重要的胶结物,即球粒泥晶、纤状方解石、放射轴状方解石和粒状方解石。尽管缺失典型的造礁生物,但通过岩石类型研究和微相分析,认为碳酸盐岩隆的形成主要取决于生物作用及古环境格局。本区碳酸盐岩隆可以同欧洲瓦尔索坦的岩隆对比 相似文献
14.
The sedimentology and cyclic stratigraphy of palaeokarst structures in Aptian peritidal carbonate successions are interpreted using field and laboratory microfacies analyses of closely spaced samples from measured outcrop stratigraphic sections in southwest Turkey. Cycles displaying shallowing-upward metre-scale cyclicity are generally composed of lime mudstones/wackestones/packestones at the bottom and stromatolites or lime mudstones with charophytes and ostracods at the top. Subaerial exposure structures such as in situ karst breccias, dissolution vugs/pipes, mud cracks and sheet cracks are encountered at the top of the cycles. The presence of limestone layers between the successive karst breccia levels indicates that they are in situ palaeokarst structures, not recent karstifications or deep penetration from the upper palaeokarst surface down to the older strata. Palaeokarst breccia deposits are interpreted as mantling breccia formed as a result of epikarstification. Three main palaeokarst levels are recorded in nearly all sections. The sedimentology of the palaeokarst breccias, their position in cyclic peritidal carbonates and the biostratigraphic framework are used to trace the record of the global mid-Aptian sea-level fall in the southwest Taurides. The successive occurrences of three karst breccia levels close to the mid-Aptian sea-level fall correspond to falling periods of high-amplitude sea-level fluctuation within a late high-stand or early fall condition of a third-order sea level. 相似文献
15.
Hammad Tariq JANJUHAH Josep SANJUAN Mohammad ALQUDAH Mohamed K. SALAH 《《地质学报》英文版》2021,95(5):1668-1683
Carbonate rocks contain prolific hydrocarbon reserves all over the world, particularly in the Middle East. For exploration and production strategies, it is essential to understand carbonate reservoirs in terms of their internal characteristics, depositional environment, relative age, diagenetic processes and impact on petrophysical properties. This study has been performed on exposed Cretaceous, Paleocene and Miocene marine carbonate sedimentary sequences in two localities (Maghdoucheh and Qennarit) near the city of Sidon (Southern Lebanon). It represents the first comprehensive study that takes into consideration the carbonate reservoir facies, diagenetic history and reservoir quality in the area. Rocks at Maghdoucheh are mainly dominated by limestone beds showing sedimentary structures and erosive bases alternating with microfossil-rich silty marls, related to a shallowing upward sequence in a restricted marine platform environment. Shells of benthic foraminifera and mollusks dominate the fossil assemblage extracted from the studied rocks. The microfossil and nannofossil assemblage detected in the Maghdoucheh sections indicates a middle Miocene age. Rocks at Qennarit are composed of mudstone/wackestone limestone beds rich in planktonic foraminifera and nannofossils related to open marine conditions. Based on the nannofossil content, rocks from Qennarit 1 and 2 are Paleocene and Cretaceous in age, respectively. Four main types of microfacies have been identified, i.e. (1) microbioclastic peloidal calcisiltite, (2) pelagic lime mudstone and wackestone with planktonic microfossils, (3) grainstone/packstone with abundant foraminifera and (4) fenestral bindstones, mudstones and packstones with porostromate microstructures. The porosity-permeability (poro-perm) analysis of representative samples reveals moderate to good porosity but very low permeability. This is mainly due to the presence of large moldic pores that are isolated in nature. The diagenetic features are dominated by micritization and dissolution (both fabric selective and non-fabric selective). Among all diagenetic features, dissolution in both localities contributes to porosity enhancement, while micritization, cementation, compaction and the filled fractures have negative impacts on permeability; hence the overall reservoir quality. 相似文献
16.
A geological event that happened at the end of the Middle Permian resulted in different levels of erosion in a shallow-water platform of South China, which led to diverse geological records in different sections. The Lianziya section in western Hubei Province of South China has a well-exposed stratigraphic sequence of the late Middle Permian rocks with abundant fossils and sedimentary facies types, providing new evidences for understanding the evolution of marine biota and environment in the late Middle Permian. Our study shows that four fossil communities can be recognized with the change of sedimentary facies in the late Middle Permian: Foraminiferal-algal community, phylloid algal community, bryozoan community and Ungdarella community. The foraminiferal-algal community is dominated by fusulinids and calcareous algae, but was soon replaced by the phylloid algal community. With an increase of terrestrial input, the phylloid algal community was again replaced by the bryozoan community. Near the end of the Middle Permian, with a decrease of terrestrial input, the bryozoan fossil community disappeared while the Ungdarella community became dominant. A 10 cm-thick weathered crust occurred at the top of the Middle Permian limestone, marking a large amplitude fall in sea-level and the beginning of a terrestrial erosion stage. The sedimentary facies and fossil community changes in the Lianziya section indicates that the Middle Permian crisis was a gradual process while the sea-level fall mainly occurred in the latest Middle Permian. 相似文献
17.
The 2-km deep Athboy Borehole (1439/2) together with the lower part of boreholes EP30 and N915 form a standard type section for strata of Dinantian (Courceyan to Asbian) age in west Co. Meath. Above a thin basal red-bed siliciclastic sequence, the marine Courceyan shelf succession is almost 600 m thick. It comprises the Liscartan, Meath, and Moathill Formations of the Navan Group and the Slane Castle Formation of the succeeding Boyne Group. The shallow-water limestones include micrites, oolites, and sandy bioclastic packstones and grainstones with subordinate skeletal wackestones and shales. Lateral facies changes from north to south in the Navan area suggest deepening across a shelf towards a depocentre further to the south around Trim. The deeper-water Waulsortian Limestones of late Courceyan to Chadian age (Feltrim Formation, ca. 213 m thick) form a series of five sheet-like mudbanks, interbedded with generally thin units of nodular crinoidal limestones and shales. The mudbanks are formed of bryozoan-rich peloidal wackestones and lime-mudstones with phase C and D components. Rare soft-sediment breccias occur at the bottom and top of banks. The succeeding Fingal Group commences with a thin interval (3–20 m) of black shales, laminated packstones, and micritic limestones of Chadian age, the Tober Colleen Formation. This is followed by the Lucan Formation (Chadian to Asbian) predominantly of laminated and graded calciturbidites, laminated sandstones, cherts, and black shales, which is over 1300 m thick. Ten sedimentary units have been informally defined, based on lithofacies and facies associations. The oldest unit, the Tara Member, is characterized by proximal debris-flow breccia deposits and nodular mudstones. A thick bioturbated micrite and shale unit (Ardmulchan Member) in the middle of the formation is overlain directly by a coarse oolitic and crinoidal grainstone unit (Beauparc Member). Near the top of the formation is a distinctive unit of coarse-grained laminated sandstones and shales (Athboy Member). The highest rocks in the Borehole are clean thickly-bedded limestones of the Asbian Naul Formation (>90 m thick). The youngest Dinantian strata in the area, the Brigantian Loughshinny Formation, marks a return to shale-dominant basin sedimentation. The significance of this work lies in the fact that the Athboy borehole is the longest continuously cored borehole in the Carboniferous of Ireland and provides a continuous sedimentary and biostratigraphic record for the northern part of the Dublin Basin. Foraminiferal biozones (Cf2–Cf6) have been recognized in this and in borehole N915, and Stage boundaries identified, which can be applied throughout the Basin. The sedimentary record for the Lucan Formation indicates four tectonic pulses during the Viséan, in the late Chadian/early Arundian, mid-Arundian, Holkerian, and late Holkerian/early Asbian. 相似文献
18.
《Proceedings of the Geologists' Association. Geologists' Association》2017,128(4):564-598
Ground investigations for the A303 Stonehenge Tunnels revealed a unique and complex Chalk geology including the presence of the thickest (>20 m thick), and previously unknown phosphatic chalks in England, partly filling fault controlled erosional channels. The use of natural gamma-ray borehole logs to determine the presence and thickness of the phosphatic deposits is of particular value and combined with the lithostratigraphy, macrofossil and nannofossil biostratigraphy from cores has, for the first time, accurately constrained the Coniacian to Santonian age and the lenticular geometry of such deposits. Four phosphatic chalk events between 88.5–86.5 Ma are recognised associated with synsedimentary faulting. We suggest a causal link between tectonics, subsidence and channel-formation, phosphatisation events, pulses of oceanic upwelling on a frequency of about 0.5 million years to mantle-controlled plate tectonic episodes. The implications of this geology for construction of the A303 and the archaeology of the area are discussed. 相似文献
19.
The Lower Freshwater Molasse (Untere Susswasser Molasse) crops out over a wide area of the Swiss Molasse Basin. Coarse grained alluvial fan conglomerates dominate in proximal basin areas along the Alpine front. These conglomerates pass northwards into sandstones and mudstones of an extensive northeastward draining meandering river system which ran parallel to the basin axis. Sedimentological study of outcrops, quarry exposures and boreholes in the basal Miocene (‘Aquitanian‘) has permitted detailed facies analysis of this distal alluvial sequence. The distal Aquitanian is made up of distinct ‘architectural elements’characterized by their geometries and sedimentary structures. Each may be assigned to a particular depositional setting: meander belt, levees, crevasse channels and splays, overbank fines and palaeosols, and lacustrine. Meander belt sandstones were deposited in mixed load channels with a dominant bedload component. Sandstones commonly comprise amalgamated and locally stacked ribbon bodies 2–15 m thick and 150–1500 m wide. Interbedded rippled, laminated and mottled fine grained levee sandstones and siltstones form lenticular packages up to 3 m thick and 30–100 m across. Small scale crevasse channel sandstones 2–4 m thick and 5–10 m across pass laterally into metre scale, medium to fine grained crevasse sandstone sheets. Rare laminated lacustrine siltstones occur only in the north-east part of the basin. Floodplain mudstones and marls make up the remainder of the succession. These display a variety of pedogenic features recording cyclical palaeosol development. Palaeosols show strong variations in morphology and maturity both laterally across the floodplain and downstream along the basin axis, reflecting local variation in aggradation rate associated with proximity to alluvial channel courses as well as regional variation in subsidence and floodplain drainage. Analysis of the organization and distribution of the various sediment bodies permits reconstruction of the fluvial system and allows development of a model for the sedimentary architecture of the Lower Freshwater Molasse in the study area. Integration of palaeosol studies into a well defined architectural framework assists recognition of areal facies belts and may aid location of sand-prone sequences in the subsurface. 相似文献
20.
Large scale sedimentary structures present in the Upper Turonian to Santonian chalks of Haute Normandie (northern France) represent the remains of a carbonate bank complex which formerly extended over an area of at least 1500 km2. Cliff exposures along the Channel coast from St Valéry-en-Caux to Cauville and along the Seine from Sandouville to Lillebonne show sections of banks up to 50 m high and 1500 m across, their internal structures picked out by hardgrounds, nodular chalks and horizons of burrow flint. Associated with banks are slump sheets up to 20 m thick, slump scars, sedimentary breccias, injection phenomena and faults contemporaneous with sedimentation. Later diagenetic features include extensive dolomitization and silicification. These structures compare closely with the Waulsortian banks of the Palaeozoic, and bryozoan bioherms known from the Upper Cretaceous and Palaeocene of Denmark. Frame-building, sediment trapping and stabilizing organisms are absent, and bank development and stabilization was probably due to a plant covering, either algal or of marine angiosperms. Banks generated much of their own sediment, whilst a pelagic constituent (calcareous nannofossils and Foraminiferida) is also present. The distribution of the bank complex is related to a basement controlled swell area, whilst the life of the complex was limited to a relatively shallow water, regressive episode in the predominantly transgressive Upper Cretaceous history of the region. Les falaises littorales du Pays de Caux comprises entre Antifer et St Valèry-enCaux, et les affleurements de la basse vallée de la Seine permettent d'observer des formations du Turonien supérieur-Sénonien inférieur qui présentent des stratifications irrégulières soulignées par de nombreux hardgrounds, des horizons de craie noduleuse et des cordons de silex. Ces structures sont identifiées à des accumulations de calcilutite et calcarénite sous forme de bancs sous-marins dont la hauteur peut atteindre 50 m et qui couvrent une surface supérieure à 1500 km2; ils apparaissent au-dessus de hardgrounds subhorizontaux qui indiquent un haut-fond régional stable. Des glissements sous-marins sont associés à ces bancs et engendrent des niveaux avec des déformations souples atteignant 20 m d'épaisseur. Des brèches apparaissent localement et contiennent des blocs basculés de hardgrounds fragmentés lors du glissement; on y observe aussi de petites failles intrasédimentaires et des phénomènes d'injection. Aucun organisme constructeur ou capable de piéger et retenir le sédiment n'a été observé. La stabilisation de ces bancs serait due à une couverture végétale (algues ou angiospermes marines) dont on sait qu'elle peut disparâitre sans laisser de trace lors de la fossilisation. La croissance de ces bancs serait réalisée par un apport de sédiment comprenant une part de nourrissage autochtone comme cela existe pour les bancs récents en eau peu profonde, associée au dépôt d'une fraction pélagique. 相似文献