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1.
The study area is located in the east Tabas Block in Central Iran. Facies analysis of the Qal’eh Dokhtar Formation (middle Callovian to late Oxfordian) was carried out on two stratigraphic sections and applied to depositional environment and sequence stratigraphy interpretation. This formation conformably overlies and underlies the marly-silty Baghamshah and the calcareous Esfandiar formations, respectively. Lateral and vertical facies changes documents low- to high energy environments, including tidal-flat, beach to intertidal, lagoon, barrier, and open-marine. According to these facies associations and absence of resedimentation deposits a depositional model of a mixed carbonate–siliciclastic ramp was proposed for the Qal’eh Dokhtar Formation. Seven third-order depositional sequences were identified in each two measured stratigraphic sections. Transgressive systems tracts (TSTs) show deepening upward trends, i.e. shallow water beach to intertidal and lagoonal facies, while highstand systems tracts (HST) show shallowing upward trends in which deep water facies are overlain by shallow water facies. All sequence boundaries (except at the base of the stratigraphic column) are of the no erosional (SB2) types. We conclude eustatic rather than tectonic factors played a dominant role in controlling carbonate depositional environments in the study area.  相似文献   

2.
The Neoarchean Carawine Formation, Hamersley Group, Western Australia is a carbonate ramp that preserves diverse microbial structures which are characteristic of specific depositional environments. These distinctive structures are distributed in five shallow subtidal and two deeper‐water facies in the Oakover area of the Carawine Formation. The shallow subtidal facies are composed of biohermal and bedded stromatolites, centimetre‐scale ridge‐shaped microbialites and wavy‐laminated microbialites. The deeper‐water facies are composed of fenestrate microbialites, planar laminated dolostone and dolostone with rolled‐up microbial laminae. Microbialites in the Carawine Formation lie within a continuum of Archean to Proterozoic microbial facies. Some shallow‐water microbial facies in the Carawine Formation are similar to Proterozoic facies, such as large bioherms internally composed of a variety of stromatolite morphologies. In contrast, fenestrate microbialites grew in quiet subtidal environments and are common in Archean rocks but have not been documented in similar Proterozoic environments. The similarity of shallow‐water facies across the Archean–Proterozoic transition, before and after the oxidation of the atmosphere and surface oceans, indicates that stromatolite growth in shallow subtidal environments was not strongly affected by the chemical changes associated with oxidation of the oceans or by biological responses to those chemical changes. Rather, stromatolite morphology was controlled mostly by the physical environment and the corresponding biological responses to that environment. In contrast, the absence of fenestrate microbialites from Proterozoic deep subtidal environments suggests that the morphology of deep subtidal microbial structures was influenced by chemical or biological changes that occurred in association with oxidation of the surface oceans.  相似文献   

3.
This paper reports on the structural and sedimentary evolution of the middle to late Eocene of the Prepyrenean External Sierras (southern Pyrenees, Spain). The initiation, duration and kinematics of a set of growth structures that developed in a shallow marine depositional setting is documented. The detailed analysis of the syntectonic marine sediments not only confirms the already known east to west progression of deformation, but also reveals the continued growth of the early formed structures as later ones propagate towards the foreland. The sedimentary units coevally deposited with these growth structures are arranged in four depositional sequences. Their boundaries correspond to flooding surfaces which grade basinwards into correlative conformities. They are also indicated by the presence of both angular unconformities and onlap geometries. Each depositional sequence generally consists of two systems tracts. The lower one, or transgressive systems tract, is formed by up to 400 m of azoic marls deposited in outer ramp areas. The upper one, or highstand systems tract, mainly consists of shallow siliciclastic and carbonate facies, up to 200 m thick, deposited in middle to inner ramp areas. These depositional sequences are interpreted to be controlled by regional tectonic pulses. An increase of tectonic activity resulted in the flooding of the basin and in the subsequent deposition of a thick succession of nearly azoic blue marls (i.e. transgressive systems tract). The overlying highstand systems tract developed following periods of diminished tectonism, with the consequent growth and progradation of shallow carbonate platform facies.  相似文献   

4.
The Lower Cretaceous sections in northern Sinai are composed of the Risan Aneiza (upper Barremian-middle Albian) and the Halal (middle Albian-lower Cenomanian) formations. The facies reflect subtle paleobathymetry from inner to outer ramp facies. The inner ramp facies are peritidal, protected to open marine lagoons, shoals and rudist biostrome facies. The inner ramp facies grade northward into outer ramp deposits. The upper Barremian-lower Cenomanian succession is subdivided into nine depositional sequences correlated with those recognized in the neighbouring Tethyan areas. These sequences are subdivided into 19 medium-scale sequences based on the facies evolution, the recorded hardgrounds and flooding surfaces, interpreted as the result of eustatic sea level changes and local tectonic activities of the early Syrian Arc rifting stage. Each sequence contains a lower retrogradational parasequence set that constituted the transgressive systems tracts and an upper progradational parasequence set that formed the highstand systems tracts. Nine rudist levels are recorded in the upper Barremian through lower Cenomanian succession at Gabal Raghawi. At Gabal Yelleg two rudist levels are found in the Albian. The rudist levels are associated with the highstand systems tract deposits because of the suitability of the trophic conditions in the rudist-dominated ramp.  相似文献   

5.
A major shift from Urgonian oligotrophic carbonate accumulation to orbitolinid‐rich mixed siliciclastic–carbonate deposition is observed near the Barremian–Aptian boundary in many sections both within and outside the shallow‐marine Tethyan Realm. This important facies change in the Swiss Helvetic Alps is documented here and interpreted in the context of general palaeoenvironmental change. To achieve this, a detailed micropalaeontological, sedimentological, mineralogical and geochemical study has been carried out on six sections across the upper part of the lower Schrattenkalk Member (Late Barremian), the Rawil Member (formerly ‘Lower Orbitolina Beds’, earliest Aptian) and the lowermost part of the upper Schrattenkalk Member (Early Aptian). The sediments of the Rawil Member exhibit inner‐platform facies with rudists, miliolids, orbitolinids and dasycladals to outer‐platform facies characterized by small benthic foraminifera, orbitolinids, crinoids and bryozoans. Stratigraphic trends in microfacies environments and the composition of microfossil assemblages, indicate that the Rawil Member includes a transgressive systems tract and the base of a highstand systems tract which are composed of an increasing number of parasequences in distal directions (five to nine in the sections studied here). The sea‐level rise discerned in the Rawil Member is coeval with increased detrital input and phosphorus burial, with maximum values up to 80 times and 21 times the background values in the subjacent part of the lower Schrattenkalk Member, respectively. Furthermore, the Rawil Member records the appearance of kaolinite, indicating a change towards tropical and more humid climate conditions. This change may have led to an increase in continental weathering rates and an associated increase in detrital and nutrient fluxes towards the ocean. The phase of climate change observed near the Barremian–Aptian boundary may have been triggered by a phase of intensified volcanic activity linked with the onset of the Ontong Java large igneous province and the Rawil Member may be the expression of a precursor episode to Oceanic Anoxic Event 1a in the shallow‐marine environment.  相似文献   

6.
This study, based in the Haushi‐Huqf area of central east Oman, aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of Lower Cretaceous tidal flat facies within the Tethyan epeiric platform. Field, petrographic and geochemical data were acquired from the Barremian–Aptian Jurf and Qishn formations that crop out in a 500 × 1000 m2 butte, thus allowing for pseudo three‐dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies. The interpretation presented here suggests that the main processes impacting sedimentation in the Lower Cretaceous peritidal environment of the Haushi‐Huqf were transport and erosion processes related to storm waves and currents. The vertical evolution of the carbonate system is organized into six types of metre‐scale depositional sequences, from subtidal dominated sequences to supratidal‐capped sequences, which are bounded by regional discontinuity surfaces. At subaerial exposure and submarine erosion surfaces associated with a base level shift, sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events. Chemostratigraphy allows correlation between the Haushi‐Huqf and the age‐equivalent sections logged in the interior of the platform in Oman. The correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf. This study is the first to discuss the controls on Lower Cretaceous peritidal carbonate cyclicity of the Arabian epeiric platform. The results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context.  相似文献   

7.
Long‐term relative sea‐level cycles (0·5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault‐controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea‐level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea‐level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea‐level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea‐level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre‐contractional attitude, was >2 km wide and cut ≥115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was backfilled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea‐level drops identified fall within the glacio‐eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long‐term sea‐level trends that are often only recognizable on larger scales (i.e. seismic), such as for the Arabian Plate.  相似文献   

8.
In the Late Cambrian, the North China Platform was a typical carbonate ramp platform. The Upper Cambrian of the northern part of the North China Platform is famous for the development of bioherm limestones and storm calcirudites and can be divided from bottom to top into the Gushan, Changshan and Fengshan formations. In this set of strata, the deep-ramp mudstone and marls and the shallow-ramp packstones and grainstones constitute many carbonate meter-scale cycles of subtidal type. More tidal-flat dolomites axe developed in the Upper Cambrian of the southern margin of the North China platform, in which limestone and dolomite beds also constitute many carbonate meter-scale cycles of the peritidal type. These cycles are marked by a variety of litho-facies successions. There are regularly vertical stacking patterns of meter-scale cycles in long-term third-order sequences, which is the key to discerning such sequences. Third-order sequence is marked by a particular sedimentary-facies succession that is the result of the environment-changing process of deepening and shoaling, which is genetically related to third-order sea level changes. Furthermore, four third-order sequences can be grouped in the Upper Cambrian of the North China Platform. The main features of these four third-order sequences in the northern part of the platform can be summarized as follows: firstly, sequence-boundaries are characterized by drowning unconformities; secondly, the sedimentary-facies succession is generally constituted by one from deep-ramp facies to shallow-ramp facies; thirdly, a succession of “CS (?) HST” (i.e., “condensed section and highstand system”) forms these four third-order sequences. The chief features for the third-order sequences in the southern part of the North China Platform comprises: more dolomites are developed in the HSTs of third-order sequences and also developed more carbonate meter-scale cycles of peritidal types; the sedimentary-facies succession of the third-order sequences is marked by “shallow ramp-tidal flat”; the sequence boundaries are characterized by exposure punctuated surfaces. According to the changes for the third-order sequences from the north to the south, a regular sequence-stratigraphic framework can be established. From cycles to sequences, the study of sequence stratigraphy from litho-facies successions to sedimentary-facies successions exposes that as follows: meter-scale cycles that are used as the basic working unit actually are litho-facies successions formed by the mechanism of a punctuated aggradational cycle, and third-order sequences that are constituted by regularly vertical stacking patterns of meter-scale cycles are marked by sedimentary-facies successions. On the basis of the changing curve of water depth at each section, the curve of the relative third-order sea level changes in the late Cambrian of the North China Platform can be integrated qualitatively from changing curve of water depth. The correlation of Late Cambrian long-term sea level changes between North China and North America demonstrates that there are not only similarities but also differences, reflecting control of long-term sea level changes both by global eustacy and by regional factors.  相似文献   

9.
The Late Cenomanian–Mid Turonian succession in central Spain is composed of siliciclastic and carbonate rocks deposited in a variety of coastal and marine shelf environments (alluvial plain–estuarine, lagoon, shoreface, offshore‐hemipelagic and carbonate ramp). Three depositional sequences (third order) are recognized: the Atienza, Patones and El Molar sequences. The Patones sequence contains five fourth‐order parasequence sets, while a single parasequence set is recognized in the Atienza and El Molar sequences. Systems tracts can be recognized both in the sequences and parasequence sets. The lowstand systems tracts (only recognized for Atienza and Patones sequences) are related to erosion and sequence boundary formation. Transgressive systems tracts are related to marine transgression and shoreface retreat. The highstand systems tracts are related to shoreface extension and progradation, and to carbonate production and ramp progradation. Sequences are bounded by erosion or emergence surfaces, whose locations are supported by mineralogical analyses and suggest source area reactivation probably due to a fall in relative sea‐level. Transgressive surfaces are subordinate erosion and/or omission surfaces with a landward facies shift, interpreted as parasequence set boundaries. The co‐existence of siliciclastic and carbonate sediments and environments occurred as facies mixing or as distinct facies belts along the basin. Mixed facies of coastal areas are composed of detrital quartz and clays derived from the hinterland, and dolomite probably derived from bioclastic material. Siliciclastic flux to coastal areas is highly variable, the maximum flux postdates relative sea‐level falls. Carbonate production in these areas may be constant, but the final content is a function of changing inputs in terrigenous sediments and carbonate content diminishes through a dilution effect. Carbonate ramps were detached from the coastal system and separated by a fringe of offshore, fine‐grained muds and silts as distinct facies belts. The growth of carbonate ramp deposits was related to the highstand systems tracts of the fourth‐order parasequence sets. During the growth of these ramps, some sediment starvation occurred basinwards. Progradation and retrogradation of the different belts occur simultaneously, suggesting a sea‐level control on sedimentation. In the study area, the co‐existence of carbonate and siliciclastic facies belts depended on the superimposition of different orders of relative sea‐level cycles, and occurred mainly when the second‐order, third‐order and fourth‐order cycles showed highstand conditions.  相似文献   

10.
An integrated sequence stratigraphic study based on outcrop, core and wireline log data documents the combined impact of Cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern Gulf of Mexico. The diverse facies and abundant data of the Comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting Cretaceous platform development. Regional cross‐sections across the shoreline to shelf‐margin profile provide a detailed record of mixed carbonate–siliciclastic strata for the Hauterivian to lower Campanian stages (ca 136 to 80 Ma). The study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes. Three second‐order supersequences comprised of eight composite sequences are recognized in the Valanginian–Barremian, the Aptian–Albian and the Cenomanian–Campanian. The Valanginian–Barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting, as well as variable rates of mid‐ocean ridge volcanism. The Aptian–Albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b. The Cenomanian–Campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d, after which the platform evolved to a deep‐subtidal system consisting of anoxic/dysoxic shale and chalk in the time surrounding oceanic anoxic event 2. Each period of oceanic anoxia is associated with composite sequence maximum flooding, termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles. Composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain‐dominated facies and shallow‐subtidal to intertidal environments. Because they are products of eustacy and global oceanographic processes, the three supersequences and most composite sequences defined in the south Texas passive margin are recognizable in other carbonate platforms and published eustatic sea‐level curves.  相似文献   

11.
Cenomanian–Turonian strata of the south‐central Pyrenees in northern Spain contain three prograding carbonate sequences that record interactions among tectonics, sea level, environment and sediment fabric in controlling sequence development. Sequence UK‐1 (Lower to Upper Cenomanian) contains distinct lagoonal, back‐margin, margin, slope and basin facies, and was deposited on a broad, flat shelf adjacent to a deep basin. The lack of reef‐constructing organisms resulted in a gently dipping ramp morphology for the margin and slope. Sequence UK‐2 (Upper Cenomanian) contains similar shallow‐water facies belts, but syndepositional tectonic modification of the margin resulted in a steep slope and deposition of carbonate megabreccias. Sequence UK‐3 (Lower to Middle Turonian) records a shift from benthic to pelagic deposition, as the shallow platform was drowned in response to a eustatic sea‐level rise, coupled with increased organic productivity. Sequences UK‐1 to UK‐3 are subdivided into lowstand, transgressive and highstand systems tracts based on stratal geometries and facies distribution patterns. The same lithologies (e.g. megabreccias) commonly occur in more than one systems tract, indicating that: (1) the depositional system responded to more than just sea‐level fluctuations; and (2) similar processes occurred during different times throughout sequence development. These sequences illustrate the complexity of carbonate platform dynamics that influence sequence architecture. Rift tectonics and flexural subsidence played a major role in controlling the location of the platform margin, maintaining a steep slope gradient through syndepositional faulting, enhancing slope instability and erosion, and influencing depositional processes, stratal relationships and lithofacies distribution on the slope. Sea‐level variations (eustatic and relative) strongly influenced the timing of sequence and parasequence boundary formation, controlled changes in accommodation and promoted platform drowning (in conjunction with other factors). Physico‐chemical and climatic conditions were responsible for reducing carbonate production rates and inducing platform drowning. Finally, a mud‐rich sediment fabric affected platform morphology, growth geometries (aggradation vs. progradation) and facies distribution patterns.  相似文献   

12.
Gamma‐ray curves from surface outcrops together with U–Pb SHRIMP zircon dating are used to redefine the evolution of a Palaeoproterozoic sandy dolostone succession from northern Australia. This case history indicates that gamma‐ray logging of surface sections should accompany lithostratigraphic logging or an inadequate interpretation of stratigraphic evolution is a likely outcome. The 1200 m‐thick Nathan Group from the McArthur River area had previously been interpreted as a more‐or‐less continuous package of carbonates deposited in lacustrine and associated shallow‐water environments. Now it is seen to comprise the preserved remnants of three truncated, second‐order supersequences—the Lawn, Wide and Doom Supersequences—each a few hundred metres thick and each deposited over a time period of a few million years. These supersequences are separated by major stratigraphic breaks each approaching probably 10 million years duration. Each supersequence comprises several third‐order sequences which themselves contain higher‐order cycles. These were deposited in a series of continental, shoreline, and inner to outer carbonate platform environments. Transgressive, high‐energy, fluvial to marginal marine, mixed clastic‐carbonate facies dominate most of the sequences. The middle, Wide Supersequence, however, preserves deeper water (mostly sub‐storm‐wave‐base) stromatolitic facies in one sequence, and storm‐reworked clastics in another. These are interpreted as condensed intervals deposited around their respective maximum flooding surfaces and are succeeded by regressive facies that probably represent highstand systems tracts. New correlations between these 1615–1575 Ma sandy carbonate successions of the McArthur Basin (Amos, Balbirini and Dungaminnie Formations) and time‐equivalent largely clastic successions in the Lawn Hill area (Lawn Hill and Doomadgee Formations), some 400 km to the southeast, are proposed.  相似文献   

13.
The Upper Cretaceous succession of the Leonese Area (NW Spain) comprises mixed clastic and carbonate sediments. This succession is divided into two lithostratigraphic units, the Voznuevo Member and the Boñar Formation, which represent fluvial, shoreface, intertidal, subtidal and open‐shelf sedimentary environments. Regional seismic interpretation and sequence stratigraphic analysis have allowed the study of lateral and vertical changes in the sedimentary record and the definition of third‐order levels of stratigraphic cyclicity. On the basis of these data, the succession can be divided into two second‐order depositional sequences (DS‐1 and DS‐2), incorporating three system tracts in a lowstand to transgressive to highstand system tract succession (LST–TST–HST). These sequences are composed of fluvial systems at the base with palaeocurrents that flowed westward and south‐westward. The upper part of DS‐1 (Late Albian–Middle Turonian) shows evidence of intertidal to subtidal and offshore deposits. DS‐2 (Late Turonian–Campanian) comprises intertidal to subtidal, tidal flat, shallow marine and lacustrine deposits and interbedded fluvial deposits. Two regressive–transgressive cycles occurred in the area related to eustatic controls. The evolution of the basin can be explained by base‐level changes and associated shifts in depositional trends of successive retrogradational episodes. By using isobath and isopach maps, the main palaeogeographic features of DS‐1 and DS‐2 were constrained, namely coastline positions, the existence and orientation of corridors through which fluvial networks were channelled and the location of the main depocentres of the basin. Sedimentation on the Upper Cretaceous marine platform was mainly controlled by (i) oscillations of sea level and (ii) the orientation of Mesozoic faults, which induced sedimentation along depocentres. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

14.
A thick Maastrichtian‐Ypresian succession, dominated by marine siliciclastic and carbonate deposits of the regionally recognized Nile Valley and Garra El‐Arbain facies associations, is exposed along the eastern escarpment face of Kharga Oasis, located in the Western Desert of Egypt. The main objectives of the present study are: (i) to establish a detailed biostratigraphic framework; (ii) to interpret the depositional environments; and (iii) to propose a sequence stratigraphic framework in order to constrain the palaeogeographic evolution of the Kharga sub‐basin during the Maastrichtian‐Ypresian time interval. The biostratigraphic analysis suggests the occurrence of 10 planktonic zones; two in the Early Maastrichtian (CF8b and CF7), four in the Palaeocene (P2, P3, P4c and P5) and four in the Early Eocene (E1, E2, E3 and E4). Recorded zonal boundaries and biostratigraphic zones generally match with those proposed elsewhere in the region. The stratigraphic succession comprises seven third‐order depositional sequences which are bounded by unconformities and their correlative conformities which can be correlated within and outside Egypt. These depositional sequences are interpreted as the result of eustatic sea‐level changes coupled with local tectonic activities. Each sequence contains a lower retrogradational parasequence set bounded above by a marine‐flooding surface and an upper progradational parasequence set bounded above by a sequence boundary. Parasequences within parasequence sets are stacked in landward‐stepping and seaward‐stepping patterns indicative of transgressive and highstand systems tracts, respectively. Lowstand systems tracts were not developed in the studied sections, presumably due to the low‐relief ramp setting. The irregular palaeotopography of the Dakhla Basin, which was caused by north‐east to south‐west trending submerged palaeo‐highs and lows, together with the eustatic sea‐level fluctuations, controlled the development and location of the two facies associations in the Kharga Oasis, the Nile Valley (open marine) and Garra El‐Arbain (marginal marine).  相似文献   

15.
Well‐cuttings, wireline logs and limited core and outcrop data were used to generate a regional, three‐dimensional sequence framework for Upper Mississippian (Chesterian), Greenbrier Group carbonates in the Appalachian foreland basin, West Virginia, USA. The resulting maps were used to document the stratigraphic response of the basin to tectonics and to glacio‐eustasy during the transition into ice‐house conditions. The ramp facies include inner ramp red beds and aeolianites, lagoonal muddy carbonates, mid‐ramp ooid and skeletal grainstone shoal complexes, and outer ramp wackestone–mudstone, that grades downslope into laminated silty lime mudstone. The facies make up fourth‐order sequences, a few metres to over 90 m (300 ft) thick. The sequences are bounded along the ramp margin by lowstand sandstones and calcareous siltstones. On the ramp, sequence boundaries are overlain by thin transgressive siliciclastics and aeolianites, and only a few are calichified. Maximum flooding surfaces on the outer ramp lie beneath deeper water facies that overlie lowstand to transgressive siliciclastic or carbonate units. On the shallow ramp, maximum flooding surfaces overlie siliciclastic‐prone transgressive systems tracts, that are overlain by highstand carbonates with significant grainstone units interlayered with lagoonal lime mudstones. The fourth‐order sequences are the major mappable subsurface units; they are bundled into weak composite sequences which are bounded by red beds. In spite of differential subsidence rates across the foreland basin (1 to 3 cm/k.y. up to 25 cm/k.y.), eustatic sea‐level changes controlled regional sequence development. Thrust‐load induced differential subsidence of fault‐blocks, coupled with in‐plane stress, controlled the rapid basinward thickening of the depositional wedge, whose thickness and facies were influenced by subtle structures such as arches trending at high angles as well as parallel to the margin.  相似文献   

16.
During the early Middle Devonian in South China, an extensive carbonate platform was broken up through extension to create a complex pattern of platforms, and interplatform basins. In Givetian and Frasnian carbonate successions, five depositional facies, including peritidal, restricted shallow subtidal, semi‐restricted subtidal, intermediate subtidal and deep subtidal facies, and 18 lithofacies units are recognized from measured sections on three isolated platforms. These deposits are arranged into metre‐scale, upward‐shallowing peritidal and subtidal cycles. Nine third‐order sequences are identified from changes in cycle stacking patterns, vertical facies changes and the stratigraphic distribution of subaerial exposure indicators. These sequences mostly consist of a lower transgressive part and an upper regressive part. Transgressive packages are dominated by thicker‐than‐average subtidal cycles, and regressive packages by thinner‐than‐average peritidal cycles. Sequence boundaries are transitional zones composed of stacked, high‐frequency, thinner‐than‐average cycles with upward‐increasing intensity of subaerial exposure, rather than individual, laterally traceable surfaces. These sequences can be further grouped into catch‐up and keep‐up sequence sets from the long‐term (second‐order) changes in accommodation and vertical facies changes. Catch‐up sequences are characterized by relatively thick cycle packages with a high percentage of intermediate to shallow subtidal facies, and even deep subtidal facies locally within some individual sequences, recording long‐term accommodation gain. Keep‐up sequences are characterized by relatively thin cycle packages with a high percentage of peritidal facies within sequences, recording long‐term accommodation loss. Correlation of long‐term accommodation changes expressed by Fischer plots reveals that during the late Givetian to early Frasnian increased accommodation loss on platforms coincided with increased accommodation gain in interplatform basins. This suggests that movement on faults resulted in the relative uplift of platforms and subsidence of interplatform basins. In the early Frasnian, extensive siliceous deposits in most interplatform basins and megabreccias at basin margins correspond to exposure disconformities on platforms.  相似文献   

17.
The Al‐Jawf area of northern Saudi Arabia provides spectacular outcrops of Early Devonian carbonate bioherms in the Wadi Murayr and Dumat Al‐Jandal areas. These carbonate bioherms belong to the Qasr Member of the Late Pragian–Early Emsian Jauf Formation (~405 Ma) and are surrounded by a bioclastic carbonate succession. The Qasr Member is the first major carbonate unit of the Palaeozoic succession in Saudi Arabia that mainly consists of microbialite carbonates and metazoan reefs exhibiting distinct mound features. These bioherm complexes and their associated carbonate facies are pervasively dolomitized. Stratigraphic, petrographic and geochemical analyses were conducted to determine the facies distribution and interpret their depositional and diagenetic processes. A total of 11 facies are identified from a range of depositional environments within a carbonate platform system, ranging from tidal flats, lagoon, shoal, patch reefs to reef front. The main diagenetic processes are carbonate cementation and dolomitization. Dolomitization occurred as both fabric preserved (mostly in grain‐dominated facies) and fabric destructive (mud‐dominated facies). The microbialites and coralline sponges facies show poor reservoir with visual porosity less than 5%, but this succession may have a potential to serve as a good source for the underlying and overlying facies. Ooid and peloidal grainstone facies show fair to good visual porosity that locally exceeds 10% with intergranular porosity as the dominant type. However, in the most studied samples, vuggy and intraparticle porosities are observed as the dominant type. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

18.
The Middle Triassic–Lower Cretaceous (pre-Late Albian) succession of Arif El-Naga anticline comprises various distinctive facies and environments that are connected with eustatic relative sea-level changes, local/regional tectonism, variable sediment influx and base-level changes. It displays six unconformity-bounded depositional sequences. The Triassic deposits are divided into a lower clastic facies (early Middle Triassic sequence) and an upper carbonate unit (late Middle- and latest Middle/early Late Triassic sequences). The early Middle Triassic sequence consists of sandstone with shale/mudstone interbeds that formed under variable regimes, ranging from braided fluvial, lower shoreface to beach foreshore. The marine part of this sequence marks retrogradational and progradational parasequences of transgressive- and highstand systems tract deposits respectively. Deposition has taken place under warm semi-arid climate and a steady supply of clastics. The late Middle- and latest Middle/early Late Triassic sequences are carbonate facies developed on an extensive shallow marine shelf under dry-warm climate. The late Middle Triassic sequence includes retrogradational shallow subtidal oyster rudstone and progradational lower intertidal lime-mudstone parasequences that define the transgressive- and highstand systems tracts respectively. It terminates with upper intertidal oncolitic packstone with bored upper surface. The next latest Middle/early Late Triassic sequence is marked by lime-mudstone, packstone/grainstone and algal stromatolitic bindstone with minor shale/mudstone. These lower intertidal/shallow subtidal deposits of a transgressive-systems tract are followed upward by progradational highstand lower intertidal lime-mudstone deposits. The overlying Jurassic deposits encompass two different sequences. The Lower Jurassic sequence is made up of intercalating lower intertidal lime-mudstone and wave-dominated beach foreshore sandstone which formed during a short period of rising sea-level with a relative increase in clastic supply. The Middle-Upper Jurassic sequence is represented by cycles of cross-bedded sandstone topped with thin mudstone that accumulated by northerly flowing braided-streams accompanying regional uplift of the Arabo–Nubian shield. It is succeeded by another regressive fluvial sequence of Early Cretaceous age due to a major eustatic sea-level fall. The Lower Cretaceous sequence is dominated by sandy braided-river deposits with minor overbank fines and basal debris flow conglomerate.  相似文献   

19.
Sequence stratigraphical analysis was applied to the Upper Carboniferous–Lower Permian sedimentary succession of the northeastern Ordos Basin, north China based on data acquired from ten entire logging curves and eight outcrops. The facies framework of the lithostratigraphical unit, the Taiyuan Formation comprises seven facies in two facies associations, varying from fluvio-delta to shelf-barrier islands. The facies are presented within a chronostratigraphical framework, linked by systems tract, which in turn are limited by flooding surfaces and sequence boundaries. Six third-order depositional sequences are recognised, bounded by six type 2 unconformities. An upwards-shallowing epicontinental sea sedimentary model is created, which consists of a sandstone, coal seam and carbonate succession.  相似文献   

20.
通常认为黔西南和黔南地区二叠纪栖霞组之下的一套陆缘碎屑岩地层,是石炭纪-二叠纪冈瓦纳大陆冰盖发育鼎盛时期大幅度海平面下降期间的沉积。最新研究表明,石炭纪-二叠纪冈瓦纳冰川是由多次不连续的冰川事件构成的。因此恢复该套以陆源碎屑岩为主地层的形成环境和堆积过程,探讨其成因与冈瓦纳冰川发育的关系,具有非常重要的科学意义。本研究查明了黔西南地区该套陆源碎屑岩的地层厚度和砂泥比值空间变化规律。在此基础上,选取碎屑岩发育最好的普安龙吟剖面开展沉积体系与成因研究。结果表明,沙子塘组主要是碳酸盐沉积体系,龙吟组和包磨山组主要为浅海陆棚三角洲沉积体系,梁山组以滨岸陆源碎屑沉积体系为主;二叠纪早期黔西南地区的陆棚相泥岩形成于冰川消融导致的海平面快速上升期间,三角洲沉积体系形成于海平面晚期高位域期间,而不是形成于冈瓦纳冰川增长期间的低位域沉积。冈瓦纳冰川的推进和消融是龙吟剖面二叠纪早期地层发育样式的主控因素。  相似文献   

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