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1.
The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest non-marine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analyses of 25 cores from the Upper Freeport Limestone in western Pennsylvania (Armstrong and Indiana Counties) identified four facies associations containing thirteen separate facies: rudstone-limestone (Association A), rudstone-laminated limestone (Association B), laminated limestone (Association C), and coal — siliciclastics (Association D). We interpreted them, respectively, as shallow, high energy lacustrine margin (A); littoral to sublittoral lacustrine (B); offshore lake (C); and vegetated swamp and marsh (D). The depositional environment is envisaged as an anastomosed channel system surrounded by extensive wetlands containing adjacent densely vegetated swamp and marsh areas and freshwater, carbonate-producing lakes.Lakes developed in the topographic lows of the alluvial plain, protected and filtered from siliciclastic deposition by vegetated swamps. These lakes were small in size (several square km), shallow, and stratified, as indicated by the abundance of laminated facies. They were hydrologically open, and interconnected by surface and ground waters. Carbonate production in this lacustrine system was not triggered by evaporative concentration but by biogenic algal production. Carbonates were continually being recycled, both physicochemically and biologically, within the depositional system. Various early diagenetic processes, including brecciation, pedogenesis and recrystallization, masked original evidence for transport mode. The Upper Freeport Limestone contains numerous features of palustrine carbonates, and provides a case study for one end-member of freshwater carbonate models, characterized by a very short period of subaerial exposure. Small-scale climatic changes or autocyclic processes such as small topographic differences, changes in local drainage patterns, and fluvial dynamics may have controlled Upper Freeport lake level changes.Facies analysis does not support a climate forcing as a control for cyclothem development of non-marine sequences during the Pennsylvanian. Tectonic and autocyclic processes better explain the evolution of these wetland (lacustrine/alluvial) systems with its associated coal formation.This is the seventh paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.  相似文献   

2.
The Middle to Upper Triassic Tanzhuang Formation represents part of the infill of the early Mesozoic Jiyuan-Yima Basin. The upper part of this stratigraphic unit records deposition within prevailing shallow lake conditions. Well-developed sequences crop out near Jiyuan, western Henan Province, central China. Six sedimentary facies clustered into two facies assemblages were recognized in the lacustrine section. Facies assemblage 1 consists of stacked coarsening-upward sequences composed, from base to top, of organic-rich shales (facies E, type I), laminated siltstones (facies A) and current-rippled laminated sandstones (facies B). Units of assemblage 1 record progradation of small mouth-bar deltas within a perennial open lacustrine system under temperate and humid conditions. Facies assemblage 2 lacks a clear vertical pattern and consists of interbedded fine-grained carbonates and siltstones (facies C); deformed and wave-reworked sandstones (facies D); organic-rich shales (facies E, type II) and clayey mudstones (facies F). The assemblage also represents a perennial, hydrologically-open, shallow lacustrine system, but characterized by strong seasonal climatic control. Water stratification probably occurred in several periods of the lake history. Pangaean megamonsoonal influence is envisaged to explain the strong seasonality imprint evidenced toward the upper part of the Tanzhuang lacustrine column.This is the fourth paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.  相似文献   

3.
In the western part of the Canadian Prairies, there are thousands of small, closed-basin saline lakes. Most of these lakes are ephemeral, filling with water during the spring and drying completely by late summer. Ceylon Lake, located in southern Saskatchewan, is typical of many of these shallow ephemeral lacustrine basins. The stratigraphic sequence recovered from this salt playa can be subdivided into six distinct facies types: (a) icelaid gravelly clay loam diamicton; (b) fluvial massive bedded to laminated sand; (c) lacustrine laminated calcareous clay and silt; (d) lacustrine laminated gypsiferous clay and silt; (e) lacustrine black, anoxic, nonlaminated, organic-rich mud; and (f) lacustrine salt. The crystalline salt facies, which can be up to 9 meters thick, is comprised mainly of sodium and sodium + magnesium sulfates, with smaller and more variable proportions of other sulfates, halides, carbonates, and insoluble clastic detritus.Although a variety of postdepositional processes have significantly altered the nature and stratigraphic relationships in the basin, the sediment fill does record, in a general way, the fluctuating depositional, hydrological, and geochemical conditions that existed in the basin since deglaciation. The Ceylon Lake basin originated about 15 000 years ago as meltwater from the retreating glacial ice cut a major spillway system in the drift and bedrock. The initial (early Holocene) phases of lacustrine sedimentation in Ceylon Lake occurred in a relatively deep freshwater lake. By about 6000 years B.P., the lake had become much shallower with numerous episodes of complete drying and subaerial exposure. The most recent 5000 years of deposition in the basin have been dominated by evaporite sedimentation. The composition of the soluble salts deposited during this time indicates some degree of cyclic sedimentation superimposed on an overall gradual shift from a sodium dominated brine to one of mixed sodium and magnesium.  相似文献   

4.
S.Liu  S.Yang 《Basin Research》2000,12(1):1-18
Upper Triassic, Lower–Middle Jurassic and Upper Jurassic strata in the western Ordos Basin of North China are interpreted as three unconformity-bounded basin phases, BP-4, BP-5 and BP-6, respectively. The three basin phases were deposited in three kinds of predominantly continental basin: (1) a Late Triassic composite basin with a south-western foreland subbasin and a north-western rift subbasin, (2) an Early–Middle Jurassic sag basin and (3) a Late Jurassic foreland molasse wedge. Within the Late Triassic composite basin BP-4 includes three sequences, S4-1, S4-2 and S4-3. In the south-western foreland subbasin, the three sequences are the depositional response to three episodes of thrust load subsidence, and are mainly composed of alluvial fan, steep-sloped lacustrine delta and fluvial systems in front of a thrust fault-bounded basin flank. In the north-western rift subbasin, the three sequences are the depositional response to three episodes of rift subsidence, and consist of alluvial fan – braid plain and fan delta systems basinward of a normal fault-bounded basin margin. In the sag basin BP-5 includes four sequences, S5-1, S5-2, S5-3 and S5-4, which reflect four episodes of intracratonic sagging events and mainly consist of fluvial, gentle-gradient lacustrine delta and lacustrine systems sourced from peripheral uplifted flanks. BP-6, deposited in the foreland-type basin, includes one sequence, S6-1, which is the depositional response to thrust load subsidence and is composed of alluvial fan systems. The formation and development of these three kinds of basins was controlled by Late Triassic and Jurassic multi-episode tectonism of basin-bounding orogenic belts, which were mainly driven by collision of the North China and South China blocks and subduction of the western Pacific plate.  相似文献   

5.
This paper presents an overview of some of the most significant, recent to ancient, littoral morpho-sedimentary structures and deposits from the Lake Turkana Basin. We highlight the importance of wave-related sedimentary processes in lakes, and more specifically in rift lakes. In the published literature, references to wave-dominated shorelines are mainly in regards to coastal marine environments. However, numerous modern lakes exhibit typical wave-dominated littoral landforms, and related sedimentary deposits are known from several paleolake successions in the geological record. Wave-related processes are often of relatively minor importance in depositional models for lacustrine environments. Classical models emphasize clastics transported by rivers, which are then distributed by fan-deltas and/or deltas into a water body of fluctuating depth, where reworking of clastics is limited in the littoral domain, and episodic in deep waters. Modern processes in Lake Turkana and the exposed paleolake deposits of the Turkana Basin demonstrate that this view is incomplete. Wave-dominated shorelines are evident (1) for modern Lake Turkana based on prominent and active littoral landforms (e.g., beach ridges, sand spits, washover fans, and arcuate-cuspate deltas); (2) for the Holocene (African Humid Period) climate-driven highstand of Megalake Turkana and its subsequent forced regression based on conspicuous raised beach ridges and spits; and (3) for the Pliocene–Pleistocene (Omo Group, Nachukui Formation) from typical nearshore sedimentary facies and stratigraphic architectures associated with paleolake Turkana. These examples from the Turkana Basin coupled with examples from other lacustrine settings, suggest that wave-dominated clastic shorelines represent significant portions of existing and ancient lake-shores. As this view contrasts with classic depositional models for lakes, notably for those found in rift setting, we also present examples of wave-influenced littoral landforms from other lakes of the East African Rift System. Identifying lacustrine paleoshorelines from typical clastic landforms and deposits is the key to the spatial reconstruction of lakes over time, and to determine transgressive–regressive cycles. Waves action is an important agent in lakes for the erosion, transport, and deposition of clastics at the basin-scale, an aspect that needs to be integrated in sedimentary models.  相似文献   

6.
During the Early Triassic the Jameson Land Basin (Central East Greenland) was located around 30° N, in the Northern arid belt, but by the Early Jurassic was positioned at a latitude of approximately 50° N. This study examines the record of this transition through a largely continental succession using clay mineralogy, sedimentology, petrography and heavy mineralogy. The Jameson Land Basin is aligned north–south and is 280 km long and 80 km wide. Following an Early Triassic marine phase the basin was filled by predominantly continental sediments. The Early‐to‐Late Triassic succession comprises coarse alluvial clastics (Pingo Dal Formation) overlain by a succession of fine‐grained evaporite‐rich playa/lacustrine sediments (Gipsdalen Formation), indicative of arid climatic conditions. The overlying buff, dolomitic and then red lacustrine mudstones with subordinate sandstones (Fleming Fjord Formation) record reduced aridity. The uppermost Triassic grades into dark organic‐rich, and in places coaly, mudstones and buff coarse‐grained sandstones of lacustrine origin that belong to the Kap Stewart Group, which spans the Triassic–Jurassic boundary, and appear to record more humid climatic conditions. Clay mineralogy analyses highlight significant variations in the kaolinite/illite ratio, from both mudstone and sandstone samples, through the Triassic and into the earliest Jurassic. Complementary heavy mineral analyses demonstrate that the variations recognised in clay mineralogy and sandstone maturity through the Triassic–Early Jurassic succession are not a product of major provenance change or the effect of significant diagenetic alteration. The observed variations are consistent with sedimentological evidence for a long‐term trend towards more humid conditions through the Late Triassic to Early Jurassic, and the suggestion of a significant pluvial episode in the mid‐Carnian.  相似文献   

7.
The Triassic–Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break‐up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre‐Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian–Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian–Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian–Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian–Toarcian boundary. This younger rift bridges the gap between the Hettangian–Sinemurian diffuse rifting and the Callovian–Bathonian break‐up. The late Pliensbachian–Toarcian rift, which eventually lead to continental break‐up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins.  相似文献   

8.
Sub-bottom profiling was conducted at eight sub-basins within the lower French River area, Ontario, to investigate deposits preserved within the ancient North Bay outlet. Ten cores were collected that targeted the four depositional acoustic facies identified in the sub-bottom profiling records. The rhythmically laminated/bedded glaciolacustrine deposits of facies I are interpreted to have aggraded within glacial Lake Algonquin and its associated recessional lakes that persisted between 13,000 and 11,300 cal BP (~11,100 and 9,900 BP). The majority of the facies II, III and IV lacustrine deposits accumulated between about 9,500 cal BP (~8,500 BP) and the mid-Holocene, based on radiocarbon-dated organic materials. These deposits represent sedimentation within a ‘large’ lake during the late portion of the Mattawa-Stanley phase, and the Nipissing transgression, Nipissing Great Lakes and post-Nipissing recession phases of lake levels. Two sets of organic-rich sand beds are preserved within facies II deposits and reveal that the large lake lacustrine depositional environment was interrupted during the late Mattawa-Stanley phase between 9,500–9,300 and 9,000–8,400 cal BP (~8,500–8,300 and ~8,000–7,600 BP), when the water surface of Lake Hough fell below the outlet threshold and the lake basin became hydrologically closed. Pre-9,500 cal BP (~8,500 BP), the early and middle portions of the Mattawa-Stanley phase were dominated by erosion, as reflected by an unconformity at the base of facies II that occurs widely in the sub-basins and the general lack of preserved deposits for these intervals in the cores. This erosion is attributed to wave action and fluvial scouring within the outlet mouth during the early and mid-Stanley-Hough low stages and relates specifically to the period when the flowing portion of the North Bay outlet was situated over the lower French River area. This study reveals that the majority of the post-glacial deposits accumulated after the outlet threshold had shifted permanently eastwards and the lower French River area was inundated under the multiple phases of the large lake occupying the Nipissing Lowlands and Georgian-Huron basins, extending well into the mid-Holocene. The occurrence of deposits marking two closed-basin intervals during the late Stanley-Hough stage are well preserved locally within the lacustrine depositional sequence, but identifying earlier closed-basin intervals from the French River stratigraphy is hindered by the lack of preserved pre-9,500 cal BP (~8,500 BP) post-glacial deposits.  相似文献   

9.
Ephemeral playa lakes on the Southern High Plains northeast of Amarillo, Texas, are underlain by more than 10 m of Quaternary lake deposits. Sediments beneath 12 lakes were examined in 76 hollow-stem auger cores and in excavations. Stacked depositional cycles recognized in lake sediments record repeated phases of (1) initial highstand, (2) ephemeral lake, and (3) lake shrinkage and prolonged exposure. Sedimentary and soil structures show that during all phases the lakes were ephemeral, but that the duration and frequency of flooding varied, which caused variation in the relative amounts of accumulation, deflation, and soil formation. The highstand phase is documented by wave-cut benches and lake sediments that extend beyond present lake margins. Mud transported as suspended load was deposited from ponded water. Desiccation resulted in mudcracks and allowed deposition of eolian sand, but exposure episodes were relatively short or infrequent, and vertic soil formation, oxidation of organic material, and deflation of sand were minimal. Decreased frequency and duration of flooding resulting in increased pedogenic modification under conditions similar to those under which modern playa lake sediments accumulate. Eolian silt deposited on dry lake beds and clays deposited in flooded lakes were mixed by vertic soil processes during repeated wetting and drying. Organic material was partly oxidized and partly translocated down roots and cracks, and interbedded upland facies were gleyed. Episodes of lake shrinkage and more frequent exposure are recorded by reddening and formation of calcic horizons within lake muds. Red-brown eolian loam prograded across lake sediments, and calcic soils developed on it. These grassland slope facies record decrease in the size of the playa lakes.  相似文献   

10.
In this paper, a literature‐based compilation of the timing and history of salt tectonics in the Southern Permian Basin (Central Europe) is presented. The tectono‐stratigraphic evolution of the Southern Permian Basin is influenced by salt movement and the structural development of various types of salt structures. The compilation presented here was used to characterize the following syndepositional growth stages of the salt structures: (a) “phase of initiation”; (b) phase of fastest growth (“main activity”); and (c) phase of burial’. We have also mapped the spatial pattern of potential mechanisms that triggered the initiation of salt structures over the area studied and summarized them for distinct regions (sub‐basins, platforms, etc.). The data base compiled and the set of maps produced from it provide a detailed overview of the spatial and temporal distribution of salt tectonic activity enabling the correlation of tectonic phases between specific regions of the entire Southern Permian Basin. Accordingly, salt movements were initiated in deeply subsided graben structures and fault zones during the Early and Middle Triassic. In these areas, salt structures reached their phase of main activity already during the Late Triassic or the Jurassic and were mostly buried during the Early Cretaceous. Salt structures in less subsided sub‐basins and platform regions of the Southern Permian Basin mostly started to grow during the Late Triassic. The subsequent phase of main activity of these salt structures took place from the Late Cretaceous to the Cenozoic. The analysis of the trigger mechanisms revealed that most salt structures were initiated by large‐offset normal faults in the sub‐salt basement in the large graben structures and minor normal faulting associated with thin‐skinned extension in the less subsided basin parts.  相似文献   

11.
Seismic reflection and well stratigraphic data are used to investigate the post‐Jurassic evolution of the Northern Lusitanian Basin, offshore west Iberia. Stratigraphic correlations between 11 exploration wells were attained in order to characterize the variations in depositional facies associated with salt tectonics. Latest Triassic–Hettangian salt, which generated multiple salt pillows during the Jurassic rifting, was reactivated after the early Aptian in two main phases. The first phase stretches from the late Turonian to the Maastrichtian. The second relates to Miocene tectonic inversion. The compression of the post‐salt overburden caused the amplification of Jurassic detachment folds, forming barriers to the westward progradation of sediment into distinct salt‐withdrawal sub‐basins. Particularly during the Miocene, thin‐skinned overburden shortening was accommodated by growing salt structures that suffered thrusting and extrusion. This structural style contrasts with that of salt‐scarce areas where a simple westerly tilted, fault‐bounded monocline was generated.  相似文献   

12.
Recent studies of natural, multiphase rifts suggest that the presence of pre‐existing faults may strongly influence fault growth during later rift phases. These findings compare well with predictions from recent scaled analogue experiments that simulate multiphase, non‐coaxial extension. However, in natural rifts we only get to see the final result of multiphase rifting. We therefore do not get the chance to compare the effects of the same rift phase with and without pre‐existing structural heterogeneity, as we may in the controlled environment of a laboratory experiment. Here, we present a case study from the Lofoten Margin that provides a unique opportunity to compare normal fault growth with and without pre‐existing structural heterogeneity. Using seismic reflection and wellbore data, we demonstrate that the Ribban Basin formed during Late Jurassic to Early Cretaceous rifting. We also show that the rift fault network of the Ribban Basin lacks a pre‐existing (Permian‐Triassic) structural grain that underlies the neighbouring North Træna Basin that also formed during the Late Jurassic to Early Cretaceous. Being able to compare adjacent basins with similar histories but contrasting underlying structure allows us to study how pre‐existing normal faults influence rift geometry. We demonstrate that in Lofoten, the absence of pre‐existing normal faults produced collinear fault zones. Conversely, where pre‐existing faults are present, normal fault zones develop strong “zigzag” plan‐view geometries.  相似文献   

13.
新疆主要尾闾湖演变的构造环境   总被引：5，自引：1，他引：5  
亚洲中部大地构造格局及地貌轮廓均以山盆体系为特征，所有封闭性盆地中都发育有尾闾湖。晚第三纪以来印度大陆与欧亚大陆强烈碰撞和右旋挤压，将板内构造激活并以冲断、走滑方式将早第三纪晚期准平原化的大部分山地和相关地段再次抬升，形成了现代亚洲中部的山盆体系，同时导致了湖盆的形成演化和湖泊的变迁。湖盆演化包括湖盆联合、分解、迁移和变形等。湖泊不仅随湖盆的构造演化而变迁，而且构造对水系的调控也直接影响湖泊的物理、化学、水文和生态特性。亚洲中部尾闾湖在新构造作用下的演变具有区域同步性和地域差异性。许多尾闾湖，如艾丁湖、艾比湖、玛纳斯湖等都明显受活动构造的影响。  相似文献   

14.
Lacustrine basins of Neogene age in Serbia were formed either in intramountain valleys-graben and half-graben structures or in the marginal part of the Pannonian sea during Oligocene or at the beginning of Miocene, lasted and ended at the end of Miocene or Pliocene. The formation of the numerous depressions of the Balkan Peninsula, due to tectonic activity, gave lake basins with alluvial, swamp and lacustrine facies. The cycle with these facies was repeated several times. The lakes are mostly meromictic, often permanently stratified (oil-shale). A high rate of sedimentation with thickness up to 2000 m is characteristic for many of these basins. In many lakes phytogenic sedimentation occurs, giving facies with coal and with oil-shales. In this paper only some basins with oil-shales will be discussed, e.g. Valjevo-Mionica, Jadar and Pranjani basin. The characteristics of Vranje and Aleksinac basin will be discussed only in general. The organic rich sequences (oil shales) are characterized by the thin lamination, preservations of fish remains and plant leaves and absence of bioturbation, which needed permanent stratification of water body and anoxic conditions. Paleoclimatic regimes at the time of deposition and diagenesis were warm, subtropic with the changes of humid and dry periods.  相似文献   

15.
The lower Nanaimo Group was deposited in the (forearc) Georgia Basin, Canada and records the basin's initiation and early depositional evolution. Nanaimo Group strata are subdivided into 11 lithostratigraphic units, which are identified based on lithology, paleontology, texture and position relative to both the basal nonconformity and to each other. Significant topography on the basal nonconformity, however, has resulted in assignment of lithostratigraphic units that are not time correlative, and hence, cannot reliably be used to accurately reconstruct basin evolution. Herein, we present a sequence stratigraphic framework for lower Nanaimo Group strata in the Comox Sub-Basin (northern Georgia Basin) that integrates both facies analysis and maximum depositional ages (MDAs) derived from detrital zircon. This stratigraphic framework is used to define significant sub-basin-wide surfaces that bound depositional units and record the evolution of the basin during its early stages of development. Seven distinct depositional phases are identified in the lower 700 m of the lower Nanaimo Group. Depositional phases are separated by marine flooding surfaces, regressive surfaces, or disconformities. The overall stratigraphy reflects net transgression manifested as an upwards transition from braided fluvial conglomerates to marine mudstones. Transgression was interrupted by periods of shoreline progradation, and both facies analysis and MDAs reveal a disconformity in the lowermost part of the Nanaimo Group in the Comox Sub-Basin. Stratigraphic reconstruction of the Comox Sub-Basin reveals two dominant depocenters (along depositional strike) for coarse clastics (sandstones and conglomerates) during early development of the Georgia Basin. The development and position of these depocenters is attributed to subduction/tectonism driving both subsidence in the north-northwest and uplift in the central Comox Sub-Basin. Our work confirms that in its earliest stages of development, the Georgia Basin evolved from an underfilled, ridged forearc basin that experienced slow and stepwise drowning to a shoal-water ridged forearc basin that experienced rapid subsidence. We also propose that the Georgia Basin is a reasonable analogue for ridged forearc basins globally, as many ridged forearcs record similar depositional histories during their early evolution.  相似文献   

16.
Integration of extensive fieldwork, remote sensing mapping and 3D models from high-quality drone photographs relates tectonics and sedimentation to define the Jurassic–early Albian diapiric evolution of the N–S Miravete anticline, the NW-SE Castel de Cabra anticline and the NW-SE Cañada Vellida ridge in the Maestrat Basin (Iberian Ranges, Spain). The pre shortening diapiric structures are defined by well-exposed and unambiguous halokinetic geometries such as hooks and flaps, salt walls and collapse normal faults. These were developed on Triassic salt-bearing deposits, previously misinterpreted because they were hidden and overprinted by the Alpine shortening. The Miravete anticline grew during the Jurassic and Early Cretaceous and was rejuvenated during Cenozoic shortening. Its evolution is separated into four halokinetic stages, including the latest Alpine compression. Regionally, the well-exposed Castel de Cabra salt anticline and Cañada Vellida salt wall confirm the widespread Jurassic and Early Cretaceous diapiric evolution of the Maestrat Basin. The NE flank of the Cañada Vellida salt wall is characterized by hook patterns and by a 500-m-long thin Upper Jurassic carbonates defining an upturned flap, inferred as the roof of the salt wall before NE-directed salt extrusion. A regional E-W cross section through the Ababuj, Miravete and Cañada-Benatanduz anticlines shows typical geometries of salt-related rift basins, partly decoupled from basement faults. These structures could form a broader diapiric region still to be investigated. In this section, the Camarillas and Fortanete minibasins displayed well-developed bowl geometries at the onset of shortening. The most active period of diapiric growth in the Maestrat Basin occurred during the Early Cretaceous, which is also recorded in the Eastern Betics, Asturias and Basque-Cantabrian basins. This period coincides with the peak of eastward drift of the Iberian microplate, with speeds of 20 mm/year. The transtensional regime is interpreted to have played a role in diapiric development.  相似文献   

17.
The northern Paradox Basin evolved during the Late Pennsylvanian–Permian as an immobile foreland basin, the result of flexural subsidence in the footwall of the growing Uncompahgre Ancestral Rocky Mountain thick‐skinned uplift. During the Atokan‐Desmoinesian (～313–306 Ma) fluctuating glacio‐eustatic sea levels deposited an ～2500 m thick sequence of evaporites (Paradox Formation) in the foreland basin, interfingering with coarse clastics in the foredeep and carbonates around the basin margins. The cyclic deposition of the evaporites produced a repetitive sequence of primarily halite, with minor clastics, organic shales and anhydrite. Sediment loading of the evaporites subsequently produced a series of salt walls and minibasins, through the process of passive diapirism or downbuilding. Faults at the top Mississippian level localised the development of linear salt walls (up to 4500 m high) along a NW–SE trend. A crosscutting NE–SW structural trend was also important in controlling the evaporite facies and the abrupt termination of the salt walls. Seismic, well and field data define the proximal Cutler Group (Permian) as a basinward prograding sequence derived from the growing Uncompahgre uplift that drove salt basinwards (towards the southwest), triggering the growth of the salt walls. Sequential structural restorations indicate that the most proximal salt walls evolved earlier than the more distal ones. The successive development of salt‐withdrawal minibasins associated with each growing salt wall implies that parts of the Cutler Group in one minibasin may have no chronostratigraphic equivalent in other minibasins. Localised changes in along‐strike salt wall growth and evolution were critical in the development of facies and thickness variations in the late Pennsylvanian to Triassic stratigraphic sequences in the flanking minibasins. Salt was probably at or very close to the surface during the downbuilding process leading to localised thinning, deposition of diapir‐derived detritus and rapid facies changes in sequences adjacent to the salt wall structures.  相似文献   

18.
Depositional models of ancient lakes in thin‐skinned retroarc foreland basins rarely benefit from appropriate Quaternary analogues. To address this, we present new stratigraphic, sedimentological and geochemical analyses of four radiocarbon‐dated sediment cores from the Pozuelos Basin (PB; northwest Argentina) that capture the evolution of this low‐accommodation Puna basin over the past ca. 43 cal kyr. Strata from the PB are interpreted as accumulations of a highly variable, underfilled lake system represented by lake‐plain/littoral, profundal, palustrine, saline lake and playa facies associations. The vertical stacking of facies is asymmetric, with transgressive and thin organic‐rich highstand deposits underlying thicker, organic‐poor regressive deposits. The major controls on depositional architecture and basin palaeogeography are tectonics and climate. Accommodation space was derived from piggyback basin‐forming flexural subsidence and Miocene‐Quaternary normal faulting associated with incorporation of the basin into the Andean hinterland. Sediment and water supply was modulated by variability in the South American summer monsoon, and perennial lake deposits correlate in time with several well‐known late Pleistocene wet periods on the Altiplano/Puna plateau. Our results shed new light on lake expansion–contraction dynamics in the PB in particular and provide a deeper understanding of Puna basin lakes in general.  相似文献   

19.
In this study, we integrate 3D seismic reflection, wireline log, biostratigraphic and core data from the Egersund Basin, Norwegian North Sea to determine the impact of syn‐depositional salt movement and associated growth faulting on the sedimentology and stratigraphic architecture of the Middle‐to‐Upper Jurassic, net‐transgressive, syn‐rift succession. Borehole data indicate that Middle‐to‐Upper Jurassic strata consist of low‐energy, wave‐dominated offshore and shoreface deposits and coal‐bearing coastal‐plain deposits. These deposits are arranged in four parasequences that are aggradationally to retrogradationally stacked to form a net‐transgressive succession that is up to 150‐m thick, at least 20 km in depositional strike (SW‐NE) extent, and >70 km in depositional dip (NW‐SE) extent. In this rift‐margin location, changes in thickness but not facies are noted across active salt structures. Abrupt facies changes, from shoreface sandstones to offshore mudstones, only occur across large displacement, basement‐involved normal faults. Comparisons to other tectonically active salt‐influenced basins suggest that facies changes across syn‐depositional salt structures are observed only where expansion indices are >2. Subsidence between salt walls resulted in local preservation of coastal‐plain deposits that cap shoreface parasequences, which were locally removed by transgressive erosion in adjacent areas of lower subsidence. The depositional dip that characterizes the Egersund Basin is unusual and likely resulted from its marginal location within the evolving North Sea rift and an extra‐basinal sediment supply from the Norwegian mainland.  相似文献   

20.
This study summarizes the results of micropaleontological, sedimentological, and isotope geochemical analyses of cuttings from five deep wells drilled in the Great Salt Lake (Utah, USA). Spanning the last 5.0 million yrs, our environmental history of the Great Salt Lake distinguishes four intervals based on paleobiological and sedimentological characteristics, using a previously developed tephrochronology for age control. For most of its history, the Great Salt Lake Basin has been occupied by a mixture of marsh, shallow lacustrine and sand flat conditions. In contrast, open lake conditions, typical of the Bonneville cycles and the modern Great Salt Lake apparently have only dominated the basin for the past 0.6-0.8 Ma. The two main structural basins in the study area (the North and South Basins) experienced different lacustrine histories. Large but frequently saline lakes occupied the North Basin after about 0.6 Ma. In the South Basin, ephemeral, saline lacustrine conditions started at 2.1 Ma and developed to full lacustrine conditions at 0.3 Ma. Our paleoenvironmental interpretations are broadly consistent with the aquatic palynological records from the same wells, as well as with the prior core- and outcrop-based lines of evidence. However, the differences in lake history between the North and South Basin have not been previously recognized.  相似文献   

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