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1.
The Andean Orogen is the type‐example of an active Cordilleran style margin with a long‐lived retroarc fold‐and‐thrust belt and foreland basin. Timing of initial shortening and foreland basin development in Argentina is diachronous along‐strike, with ages varying by 20–30 Myr. The Neuquén Basin (32°S to 40°S) contains a thick sedimentary sequence ranging in age from late Triassic to Cenozoic, which preserves a record of rift, back arc and foreland basin environments. As much of the primary evidence for initial uplift has been overprinted or covered by younger shortening and volcanic activity, basin strata provide the most complete record of early mountain building. Detailed sedimentology and new maximum depositional ages obtained from detrital zircon U–Pb analyses from the Malargüe fold‐and‐thrust belt (35°S) record a facies change between the marine evaporites of the Huitrín Formation (ca. 122 Ma) and the fluvial sandstones and conglomerates of the Diamante Formation (ca. 95 Ma). A 25–30 Myr unconformity between the Huitrín and Diamante formations represents the transition from post‐rift thermal subsidence to forebulge erosion during initial flexural loading related to crustal shortening and uplift along the magmatic arc to the west by at least 97 ± 2 Ma. This change in basin style is not marked by any significant difference in provenance and detrital zircon signature. A distinct change in detrital zircons, sandstone composition and palaeocurrent direction from west‐directed to east‐directed occurs instead in the middle Diamante Formation and may reflect the Late Cretaceous transition from forebulge derived sediment in the distal foredeep to proximal foredeep material derived from the thrust belt to the west. This change in palaeoflow represents the migration of the forebulge, and therefore, of the foreland basin system between 80 and 90 Ma in the Malargüe area.  相似文献   

2.
The Upper Ordovician in the Tarim Basin contains 5000–7000 m of siliciclastic and calciclastic deep‐water, gravity‐flow deposits. Their depositional architecture and palaeogeographical setting are documented in this investigation based on an integrated analysis of seismic, borehole and outcrop data. Six gravity‐flow depositional–palaeogeomorphological elements have been identified as follows: submarine canyon or deeply incised channels, broad and shallow erosional channels, erosional–depositional channel and levee–overbank complexes, frontal splays‐lobes and nonchannelized sheets, calciclastic lower slope fans and channel lobes or sheets, and debris‐flow complexes. Gravity‐flow deposits of the Sangtamu and Tierekeawati formations comprise a regional transgressive‐regressive megacycle, which can be further classified into six sequences bounded by unconformities and their correlative conformities. A series of incised valleys or canyons and erosional–depositional channels are identifiable along the major sequence boundaries which might have been formed as the result of global sea‐level falls. The depositional architecture of sequences varies from the upper slope to abyssal basin plain. Palaeogeographical patterns and distribution of the gravity‐flow deposits in the basin can be related to the change in tectonic setting from a passive continental margin in the Cambrian and Early to Middle Ordovician to a retroarc foreland setting in the Late Ordovician. More than 3000 m of siliciclastic submarine‐fan deposits accumulated in south‐eastern Tangguzibasi and north‐eastern Manjiaer depressions. Sedimentary units thin onto intrabasinal palaeotopographical highs of forebulge origin and thicken into backbulge depocentres. Sediments were sourced predominantly from arc terranes in the south‐east and the north‐east. Slide and mass‐transport complexes and a series of debris‐flow and turbidite deposits developed along the toes of unstable slopes on the margins of the deep‐water basins. Turbidite sandstones of channel‐fill and frontal‐splay origin and turbidite lobes comprise potential stratigraphic hydrocarbon reservoirs in the basin.  相似文献   

3.
Deposition and subsidence analysis, coupled with previous structural studies of the Sevier thrust belt, provide a means of reconstructing the detailed kinematic history of depositional response to episodic thrusting in the Cordilleran foreland basin of southern Wyoming, western interior USA. The Upper Cretaceous basin fill is divided into five megasequences bounded by unconformities. The Sevier thrust belt in northern Utah and southwestern Wyoming deformed in an eastward progression of episodic thrusting. Three major episodes of displacement on the Willard‐Meade, Crawford and ‘early’ Absaroka thrusts occurred from Aptian to early Campanian, and the thrust wedge gradually became supercritically tapered. The Frontier Formation conglomerate, Echo Canyon and Weber Canyon Conglomerates and Little Muddy Creek Conglomerate were deposited in response to these major thrusting events. Corresponding to these proximal conglomerates within the thrust belt, Megasequences 1, 2 and 3 were developed in the distal foreland of southern Wyoming. Two‐dimensional (2‐D) subsidence analyses show that the basin was divided into foredeep, forebulge and backbulge depozones. Foredeep subsidence in Megasequences 1, 2 and 3, resulting from Willard‐Meade, Crawford and ‘early’ Absaroka thrust loading, were confined to a narrow zone in the western part of the basin. Subsidence in the broad region east of the forebulge was dominantly controlled by sediment loading and inferred dynamic subsidence. Individual subsidence curves are characterized by three stages from rapid to slow. Controlled by relationships between accommodation and sediment supply, the basin was filled with retrogradational shales during periods of rapid subsidence, followed by progradational coarse clastic wedges during periods of slow subsidence. During middle Campanian time (ca. 78.5–73.4 Ma), the thrust wedge was stalled because of wedge‐top erosion and became subcritical, and the foredeep zone eroded and rebounded because of isostasy. The eroded sediments were transported far from the thrust belt, and constitute Megasequence 4 that was mostly composed of fluvial and coastal plain depositional systems. Subsidence rates were very slow, because of post‐thrusting rebound, and the resulting 2‐D subsidence was lenticular in an east–west direction. During late Campanian to early Maastrichtian time, widespread deposits of coarse sediment (the Hams Fork Conglomerate) aggraded the top of the thrust wedge after it stalled, prior to initiation of ‘late’ Absaroka thrusting. Meanwhile Megasequence 5 was deposited in the Wyoming foreland under the influence of both the intraforeland Wind River basement uplift and the Sevier thrust belt.  相似文献   

4.
Abstract The Mesozoic stratigraphy of the westernmost part of the Western Canada Basin is used to estimate sedimentation and relative crustal subsidence rates in the region between 49oN and 60oN, immediately to the east of the disturbed belt. Average rates of subsidence varied from zero to 120 m/Myr, with prominent maxima occurring three times during the Mesozoic. The first occurred during the Tithonian, when rates rose to 100 m/Myr; the second during the Albian to early Santonian, when rates rose to 120 m/Myr in the north and to 70 m/Myr in the south, with subsidence occurring earlier in the north than in the south. The third period of rapid subsidence occurred during the Campanian and Maastrichtian, with rates rising to 120 m/Myr in the southern part of the basin. During non-peak periods, average rates of subsidence ranged from 3.5 m/Myr to 35 m/Myr in the Triassic, from zero to 20 m/Myr in the Jurassic and from zero to 30 m/Myr in the Cretaceous.
Tectonic loading of the lithosphere is considered to be the most probable cause for all three of these periods of rapid subsidence. The three separate episodes are correlated with the separate arrivals of accreted terranes; the first in north-east Oregon and central west Idaho during the Late Jurassic, the second in the central Yukon during the late Early Cretaceous and the third in south-east British Columbia during the Late Cretaceous.  相似文献   

5.
Isopach and sedimentary facies maps of Upper Devonian (upper Frasnian and lower Famennian) strata deposited in a part of the central Appalachian foreland basin (eastern United States) during the Acadian orogeny show a significant change in depositional style over time. Maps of two successive upper Frasnian intervals show steady thickening to the east towards the hinterland. Coarser‐grained sediment was deposited in distinct tongues in front of the Augusta lobe, a previously recognized locus of sediment input in the central Appalachian basin. Maps of two subsequent lower Famennian stratigraphic intervals show distinct depocentres in the study area. Famennian strata thin eastward (by about 50%) over a distance of about 90 km from these depocentres to the limit of mapping at the Allegheny structural front. This is towards the Acadian sediment source and in contrast to general Upper Devonian thickening in that direction. The axes of these lower Famennian depocentres are stacked on top of each other. Also, coarser‐grained lower Famennian sediment is concentrated in strike trends just east of the axes of the depocentres, and no coarser tongues exist in front of the Augusta lobe, in contrast to the underlying (upper Frasnian) strata. The duration of each of the four study intervals is estimated to be between 0.5 and 3.0 Myr. The early Famennian depocentres may be in a back‐bulge basin, with a forebulge uplifted to the east of the study area. Earlier deposition may have occurred in a basin with a subtle, subdued, and longer wavelength forebulge (perhaps located west of the study area). Previously published regional isopachs of Upper Devonian strata suggest that the main axis of subsidence of the Acadian foreland basin (foredeep depozone) at this time was over 350 km east of the study area. Examination of published quantitative flexural models of other foreland basins with flexural rigidities close to published rigidities calculated for the Appalachian basin suggests that the proposed back‐bulge basin is in the correct location, relative to the suggested position of the foredeep at that time. Several previously recognized structural features of the northern Appalachian basin support the interpretations presented herein. Much of the Acadian foreland basin may be eroded in the central Appalachian basin. The present study demonstrates the difficulties in recognizing foreland basin depozones in partially preserved orogens.  相似文献   

6.
Investigation of a >6-km-thick succession of Cretaceous to Cenozoic sedimentary rocks in the Tajik Basin reveals that this depocentre consists of three stacked basin systems that are interpreted to reflect different mechanisms of subsidence associated with tectonics in the Pamir Mountains: a Lower to mid-Cretaceous succession, an Upper Cretaceous–Lower Eocene succession and an Eocene–Neogene succession. The Lower to mid-Cretaceous succession consists of fluvial deposits that were primarily derived from the Triassic Karakul–Mazar subduction–accretion complex in the northern Pamir. This succession is characterized by a convex-up (accelerating) subsidence curve, thickens towards the Pamir and is interpreted as a retroarc foreland basin system associated with northward subduction of Tethyan oceanic lithosphere. The Upper Cretaceous to early Eocene succession consists of fine-grained, marginal marine and sabkha deposits. The succession is characterized by a concave-up subsidence curve. Regionally extensive limestone beds in the succession are consistent with late stage thermal relaxation and relative sea-level rise following lithospheric extension, potentially in response to Tethyan slab rollback/foundering. The Upper Cretaceous–early Eocene succession is capped by a middle Eocene to early Oligocene (ca. 50–30 Ma) disconformity, which is interpreted to record the passage of a flexural forebulge. The disconformity is represented by a depositional hiatus, which is 10–30 Myr younger than estimates for the initiation of India–Asia collision and overlaps in age with the start of prograde metamorphism recorded in the Pamir gneiss domes. Overlying the disconformity, a >4-km-thick upper Eocene–Neogene succession displays a classic, coarsening upward unroofing sequence characterized by accelerating subsidence, which is interpreted as a retro-foreland basin associated with crustal thickening of the Pamir during India–Asia collision. Thus, the Tajik Basin provides an example of a long-lived composite basin in a retrowedge position that displays a sensitivity to plate margin processes. Subsidence, sediment accumulation and basin-forming mechanisms are influenced by subduction dynamics, including periods of slab-shallowing and retreat.  相似文献   

7.
The Upper Muschelkalk sedimentary record constitutes a major transgressive pulse of north‐eastern Iberia during the Ladinian. This record is arranged in two transgressive–regressive (T–R) sequences formed by two stepped microbial‐dominated carbonate ramp systems where accommodation was mainly controlled by extensional faults. This study seeks to gain new insights into how the evolution of syn‐rift subsidence controls the creation of accommodation space, the depositional styles and, especially, the palaeogeographical domains where specific microbialites developed (thrombolites and stromatolites). Thrombolite bodies (at least 40 m thick) display two types of architecture, biostromal and mud‐mounded and stromatolite bodies (at least 7 m thick) consist of tabular and domed, head‐shaped morphologies. Domed and mounded forms are usually developed during stages of increasing accommodation rates, low‐to flat‐nelief forms tend to grow in association with periods of low accommodation rates. A sea‐level fall of at least 50 m occurred at the end of the Early Ladinian leaving the platform subaerially exposed. As a result, a prominent karst with significant erosional incisions and profuse collapse breccia fillings was formed in the inner and middle ramp settings. The resultant subaerial unconformity bounds T–R sequences 1 and 2. Subsidence curves display two stages of rapid/decelerated total subsidence, constituting two discrete rift/post‐rift pulses in the large Triassic rifting period: (i) Buntsandstein – Middle Muschelkalk, and (ii) Late Muschelkalk – Imon Formation (Rhaetian). The second pulse is characterized by a rapid syn‐rift subsidence during the Late Muschelkalk, and a decelerated post‐rift subsidence throughout the deposition of Keuper facies and Imon Formation. The Late Muschelkalk rapid syn‐rift pulse of total subsidence produces gains in accommodation, which controls the development of the stromatolites and thrombolites (biostromes and mud‐mounds).  相似文献   

8.
OLA EIKEN 《Polar research》1985,3(2):167-176
The status of seismic exploration work mapping the post-Caledonian strata in the Svalbard area is presented. Compressional wave velocities are very high throughout the area, around 4km/s in the Tertiary and Mesozoic layers. In the Permian section velocities exceed 5 km/s, with refraction velocities > 6 km/s in the calcareous rocks of the Gipsdalen Group (early Permian/Late Carboniferous). Apart from correlation with carbonate and chert lithology, high velocities reflect the high degree of consolidation and the low porosities of shales and sandstones in the post-Caledonian strata in Svalbard. In van Mijenfjorden seismic reflection events are observed down to 3–4 km depth and associated with Carboniferous and younger strata. The thickness of the Mesozoic layers in this part of the central Spitsbergen syncline seems to be greater than previously suggested, and there is an apparent eastward divergence between the Jurassic and the Triassic reflectors. In south-western Storfjorden, reflections interpreted to originate from Carboniferous and Permian strata might represent the seaward extension of the central Spitsbergen syncline. In the northern part of Storfjorden, carbonate layers within the Gipsdalen Group are interpreted to lie about one kilometre below the sea floor. A prominent fault zone in this area trends NNW-SSE, like the main structural elements on Spitsbergen. It shows block-faulting, presumably caused by extensional movement in late Devonian-Carboniferous time.  相似文献   

9.
ABSTRACT This study combines stratigraphic evidence with geodynamic modelling to demonstrate that a forebulge played an identifiable role in Cenomanian–Turonian erosion and sediment accumulation in the North American Western Interior basin. The early to middle Turonian forebulge migrated progressively eastwards, and by the upper middle Turonian acted as a 'backstop' against which barrier islands formed in the axial basin.
This paper focuses on the progressive migration of an unconformity on the forebulge. The lengthwise orogen-parallel orientation and time-transgressive orogen-normal migration of the forebulge unconformity are characteristics that differentiate it from unconformities developed on reactivated basement structures. We present a conceptual model in which the unconformity formed as the seafloor was uplifted by forebulge-related flexure to a water depth at which submarine bypass and erosion occurred. A numerical model that describes forebulge migration in response to load dispersal by erosion of the orogenic front and sedimentation into the foredeep indicates that the distance from the thrust front to the forebulge is within reasonable bounds established using a flexural rigidity of 3×1024 Nm.
We identify architecturally similar, coeval unconformities from Montana to New Mexico, and interpret the similar distance from the thrust front to a point where each unconformity dissipates as indicative of a uniform lithospheric flexural response along the orogenic front. Here we ascribe cratonward (west-to-east) forebulge migration to erosional load redistribution, whereas orogen-parallel (north–south) stratigraphic climb of the forebulge unconformities developed in response to depocentre migration. Inherited lithospheric inhomogeneities may have allowed the forebulge in central Colorado to crest farther from the orogen than to the north and south.  相似文献   

10.
The adequate documentation and interpretation of regional‐scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. However, this is often challenged by the amalgamated nature of low‐accommodation settings and control of backwater hydraulics on fluvio‐deltaic stratigraphy. Exhumed examples of full‐transect depositional profiles across river‐to‐delta systems are key to improve our understanding about interacting controlling factors and resultant stratigraphy. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which allows mapping of down‐dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio‐deltaic deposition in the Tucumcari sub‐basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down‐dip into single‐story channel sandstones and eventually into contemporaneous distributary channels and delta‐front strata. Down‐dip changes reflect accommodation decrease towards the paleoshoreline at the Tucumcari basin rim, and subsequent expansion into the basin. Additionally, multi‐storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised‐valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta‐front geometries. This opposes criteria offered to differentiate incised valleys from flood‐induced backwater scours. As the incised valleys evidence relative sea‐level fall and flood‐induced backwater scours do not, the interpretation of incised valleys impacts sequence stratigraphic interpretations. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS). The RCS’ diachronous nature demonstrates that its down‐dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea‐level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low‐accommodation settings to dominantly promote bypass, especially during forced regressions. Source‐to‐sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea‐level cycle.  相似文献   

11.
《Basin Research》2018,30(4):746-765
This study of Eocene carbonate succession in the Dinaric Foreland Basin of northern Dalmatia, Croatia, integrates palaeontological and sedimentological data to document a range of carbonate ramps formed intermittently during the basin tectonic development. The end‐Cretaceous basal erosional unconformity records the coupling of Adria and Eurasia crustal plates, with an antiformal uplift along their suture zone. The overlying late Ypresian carbonate ramp, spanning biozones SBZ 11–12, developed on the forebulge flank of a shallow‐marine early synclinal basin. Basal grainstone/packstone facies, dominated by encrusting foraminifers with alveolinids and miliolids, pass upwards into packstones dominated by miliolids and rotaliids with bryozoan and echinoid fragments, indicating an increased bathymetry of the retreating forebulge flank. Deposition of grainstone facies preceded an end‐Ypresian (SBZ 12/13 transition) subaerial exposure due to post‐subductional isostatic uplift. The younger, middle to late Eocene carbonate ramps (SBZ 13–19) formed episodically as perched isolated features on blind‐thrust anticlines in a bathymetrically diversified wedge‐top basin, where phases of clastic and skeletal biogenic sedimentation alternated due to disharmonic thrusting and relative sea‐level changes. Clastic sedimentation reflects anticline crest erosion and a forced‐regressive progradation of gravelly foreshore and sandy shoreface facies over heterolithic offshore‐transition and muddy offshore facies on the anticline flank. Biogenic sedimentation represents inner‐ to middle‐ramp environments, with the latter terminating bluntly in muddy offshore environment. An outer‐ramp environment, known from classic ramp models, was lacking due to bathymetric threshold. Analysis of larger benthic foraminifers (LBF), as biostratigraphic age indicators and palaeobathymetric proxies, helped distinguish systems tracts and determine their time span. A comparison of local and global sea‐level changes allowed the interplay of tectonic and eustatic forcing to be deciphered for the study area.  相似文献   

12.
Abstract The Jurassic-Cretaceous subsidence history of the Eromanga Basin, a large intracratonic sedimentary basin in central eastern Australia, has been examined using standard backstripping techniques, allowing for porosity reduction by compaction and cementation. Interpretation of the results suggests that during the Jurassic the basin was subsiding in a manner consistent with the exponentially decreasing form predicted by simple thermally based tectonic models. By the Early Cretaceous, the rate of subsidence was considerably higher than that expected from such models and nearly half of the total sediment thickness was deposited over the final 20 Myr of the basin's 95 Myr Mesozoic depositional history. The Early Cretaceous also marks the first marine incursion into the basin, consistent with global sea-level curves. Subsequently, however, the sediments alternate between marine and non-marine, with up to 1200 m of fluvial sediments being deposited, and this was followed by a depositional hiatus of about 50 Myr in the Late Cretaceous. This occurred at a time when global sea-level was rising to its peak. A model is presented which is consistent with the rapid increase in tectonic subsidence rate and the transgressive-regressive nature of the sediments. The model incorporates a sediment influx which is greater than that predicted by the thermally based tectonic models implied by the Jurassic subsidence history. The excess sedimentation results in the basin region attaining an elevation which exceeds that of the contemporary sea-level, and thereby giving the appearance of a regression. The present day elevation of the region predicted by the model is about 100–200 m above that observed. This discrepancy may arise because the primary tectonic subsidence is better represented by a linear function of time rather than an exponentially decreasing form.  相似文献   

13.
The Janusfjellet Subgroup is a marine shelf to prodeltaic succession dominated by shales with subordinate siltstones and sandstones. The subgroup comprises a lower Agardhf jellet (Upper Bathonian - Berriasian) and an upper Rurikf jellet (Berriasian - Hauterivian) formation. Based on field work in central Spitsbergen the following subdivisions of the formations are proposed (units listed in ascending order).
The Agardhf jellet Formation (up to 290 m thick) contains four members: Oppdalen - a fining upwards succession from conglomerates to shales; Lardyfjellet - black paper shales; Oppdalsata - grey shales with siltstones and sandstones; and Slottsmøya - grey shales and black paper shales. Within the Oppdalen Member three beds are recognised: Brentskardhaugen - phosphoritic conglomerate; Marhøgda - glauconitic sandstones', and Drønbreen - siltstones and shales.
The Rurikfjellet Formation (thickness up to 226 m) is composed of two members: Wimanfjellet - grey and partly silty shale sequence, containing the Myklegardfjellet Bed (of plastic clays) at its base; and Ullaberget - silty and sandy shales with siltstones and sandstones.  相似文献   

14.
The previous literature on the occurrence of Tertiary strata at Renardodden provides contradictory information about the primary versus tectonic boundary with the Precambrian basement. Tertiary sandstones and shales overlie unconformably the basement rocks, which have been resedimented as boulder conglomerates prior to Caledonian metamorphism and weathered prior to the deposition of the Tertiary strata. The boundary relations are complicated by a repeatedly active fault system that may form part of the Inner Hornsund Fault Zone.  相似文献   

15.
The Western Irish Namurian Basin reassessed   总被引：1，自引：0，他引：1  
ABSTRACT Current basin models for the Western Irish Namurian Basin (WINB) envisage an elongate trough along the line of the present‐day Shannon Estuary that was infilled with clastic sediments derived from a hinterland that lay to the W or NW. This paper argues for an alternative basin configuration with source areas to the SW supplying sediment to a basin where deepest water conditions were in northern County Clare. Rapid subsidence along the present‐day Shannon Estuary ponded sediment in this area throughout the early Namurian and, only with the rapid increase of sedimentation rates within the mid‐Namurian (Kinderscoutian Stage), were substantial amounts of sediment able to prograde to the NE of the basin. This alternative model better explains the overwhelming predominance of NE‐directed palaeocurrents in the Namurian infill, but requires fundamental revisions to most aspects of current depositional models. Deep‐water black shales (Clare Shale Formation) initially accumulated throughout the region and were progressively downlapped by an unconfined turbidite system (Ross Formation) prograding to the NE. This in turn was succeeded by an unstable, siltstone‐dominated slope system (Gull Island Formation) characterized by large‐scale soft‐sediment deformation, which also prograded to the NE. In the northern‐most basin outcrops, in northern County Clare, this early phase of basin infill was developed as a condensed succession of radiolarian‐rich black shales, minor turbiditic sandstones and undisturbed siltstones. The new basin model envisages the northern exposures of County Clare to be a distal, basin floor succession whereas the traditional model considers it a relatively shallow, winnowed, basin margin succession. Later stages of basin infill consist of a series of deltaic cycles that culminate in major, erosive‐based sandstone bodies (e.g. Tullig Sandstone) interpreted either as axial, deltaic feeder channels or incised valley fills genetically unrelated to the underlying deltaic facies. Within the context of the new basin model the former alternative is most likely and estimated channel depths within the Tullig Sandstone indicate that the basal erosive surface could have been generated by intrinsic fluvial scour without recourse to base‐level fall. The northerly flowing Tullig channels pass down‐dip into isolated channel sandbodies interbedded with wave‐dominated strata that suggest the deltas of the WINB were considerably more wave‐influenced than hitherto proposed. The retreat of the Tullig delta during sea‐level rise saw the rapid southerly retrogradation of parasequences, as may be expected if the basin margin lay to the SW of the present‐day outcrops.  相似文献   

16.
We analyzed the latest Early Cretaceous to Miocene sections (～110–7 Ma) in 11 New Jersey and Delaware onshore coreholes (Ocean Drilling Program Legs 150X and 174AX). Fifteen to seventeen Late Cretaceous and 39–40 Cenozoic sequence boundaries were identified on the basis of physical and temporal breaks. Within‐sequence changes follow predictable patterns with thin transgressive and thick regressive highstand systems tracts. The few lowstands encountered provide critical constraints on the range of sea‐level fall. We estimated paleowater depths by integrating lithofacies and biofacies analyses and determined ages using integrated biostratigraphy and strontium isotopic stratigraphy. These datasets were backstripped to provide a sea‐level estimate for the past ～100 Myr. Large river systems affected New Jersey during the Cretaceous and latest Oligocene–Miocene. Facies evolved through eight depositional phases controlled by changes in accommodation, long‐term sea level, and sediment supply: (1) the Barremian–earliest Cenomanian consisted of anastomosing riverine environments associated with warm climates, high sediment supply, and high accommodation; (2) the Cenomanian–early Turonian was dominated by marine sediments with minor deltaic influence associated with long‐term (107 year) sea‐level rise; (3) the late Turonian through Coniacian was dominated by alluvial and delta plain systems associated with long‐term sea‐level fall; (4) the Santonian–Campanian consisted of marine deposition under the influence of a wave‐dominated delta associated with a long‐term sea‐level rise and increased sediment supply; (5) Maastrichtian–Eocene deposition consisted primarily of starved siliciclastic, carbonate ramp shelf environments associated with very high long‐term sea level and low sediment supply; (6) the late Eocene–Oligocene was a starved siliciclastic shelf associated with moderately high sea‐level and low sediment supply; (7) late early–middle Miocene consisted of a prograding shelf under a strong wave‐dominated deltaic influence associated with major increase in sediment supply and accommodation due to local sediment loading; and (8) over the past 10 Myr, low accommodation and eroded coastal systems were associated with low long‐term sea level and low rates of sediment supply due to bypassing.  相似文献   

17.
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   

18.
Studies of normal fault systems in modern extensional regimes (e.g. Basin and Range), and in exhumed, ancient rift basins (e.g. Gulf of Suez Rift) have shown a link between the evolution of fault‐related footwall topography and associated erosional drainage systems. In this study, we use 3D seismic reflection data to image the footwall crest of a gravity‐driven fault system developed during late Middle Jurassic to Early Cretaceous rifting on the Halten Terrace, offshore Mid‐Norway. This 22‐km‐long fault system lacks significant footwall uplift, with hangingwall subsidence accommodating throw accumulation on the fault system. Significant erosion has occurred along the length of the footwall crest and is defined by 96 catchments characterized by erosional channels. These erosional channels consist of small, linear systems up to 750 m long located along the front of the fault footwall. Larger, dendritic channel systems extend further back (up to 3 km normal to fault strike) into the footwall. These channels are up to 7 km long, up to 50 m deep and up to 1 km wide. Fault throw varies along strike, with greatest throw in the centre of the fault decreasing towards the fault tips; localized throw minima are interpreted to represent segment linkage points, which were breached as the fault grew. Comparison of the catchment location to the throw distribution shows that the largest catchments are in the centre of the fault and decrease in size to the fault tips. There is no link between the location of the breached segment linkage points and the location and size of the footwall catchments, suggesting that the first‐order control on footwall erosion patterns is the overall fault‐throw distribution.  相似文献   

19.
The <1.5‐km thick Fiq Member of the Ghadir Manqil Formation, Huqf Supergroup, Oman, contains a succession of Marinoan‐age glacially and non‐glacially influenced deposits overlain by a transgressive, 13C‐depleted, deep‐water dolostone (Hadash Formation) that deepens up into the marine shales and siltstones of the Masirah Bay Formation. The Fiq Member and Hadash–Masirah Bay Formations are well exposed in the core of the Jebel Akhdar of northern Oman and provide a valuable insight into the processes operating during a Neoproterozoic glacial epoch and its aftermath. The Fiq Member comprises seven stratigraphic units (F1–F7) of proximal and distal glacimarine, non‐glacial sediment gravity flow, and non‐glacial shallow marine facies associations. These units can be correlated over almost the entire Neoproterozoic outcrop belt (ca. 80 km) of the Jebel Akhdar. Four units contain glacimarine rainout diamictites, commonly at the top of cycles beneath strong lithofacies dislocations suggesting flooding. The units are thought to have been generated by combined glacio‐isostatic and glacio‐eustatic forcing caused by changing volumes of terrestrial glacier ice. The lateral persistence and thickness of massive diamictite units increase upwards in the stratigraphy, the youngest (F7) diamictite being abruptly overlain by the Hadash Formation. Correlation of lithofacies associations across the rift basin and palaeocurrents indicate that siliciclastic sediment and glacially entrained debris were derived from both basin margins. Open‐water conditions existed during interglacials, attested to by the presence of wave‐rippled sandstones in the western part of the basin. The Hadash carbonate also exhibits variations between east and west, showing that despite an overall deep‐water depositional setting, rift margin and intrabasinal structure continued to exert a control on facies development during the post‐glacial aftermath. Onlap of basin margins continued through the deposition of the Masirah Bay Formation. The sedimentology and stratigraphy of the Fiq Member and Hadash–Masirah Bay Formations have a number of implications for the Snowball Earth hypothesis. The overall stratigraphic evolution of the Fiq Member suggests a dynamic, temperate/polythermal style of glaciation, perhaps nucleated on uplifted continental or rift margin topography, with marine‐terminating glaciers. Some transgressions coupled to deglaciations within the Fiq glacial epoch were accompanied by minor deposition of carbonate. However, final deglaciation triggered the deposition of a <8‐m thick, deep‐water dolomite contaminated with siliciclastics, with a lithofacies assemblage still reflecting the underlying bathymetric template, followed by relatively deep marine shales and siltstones. The preservation of relatively deep marine Masirah Bay sediments above the Fiq basin margin suggests either tectonic collapse of the rift shoulder or, more likely, rapid eustatic rise accompanying deglaciation.  相似文献   

20.
Our understanding of continental rifting is, in large parts, derived from the stratigraphic record. This record is, however, incomplete as it does not often capture the geomorphic and erosional signal of rifting. New 3D seismic reflection data reveal a Late Permian-Early Triassic landscape incised into the pre-rift basement of the northern North Sea. This landscape, which covers at least 542 km2, preserves a drainage system bound by two major tectonic faults. A quantitative geomorphic analysis of the drainage system reveals 68 catchments, with channel steepness and knickpoint analysis of catchment-hosted palaeo-rivers showing that the landscape preserved a >2 Myr long period of transient tectonics. We interpret that this landscape records a punctuated uplift of the footwall of a major rift-related normal fault (Vette Fault) at the onset of rifting. The landscape was preserved by a combination of relatively rapid subsidence in the hangingwall of a younger fault (Øygarden Fault) and burial by post-incision sediments. As such, we show how and why erosional landscapes are preserved in the stratigraphic record, and how they can help us understand the tectono-stratigraphic evolution of ancient continental rifts.  相似文献   

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