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1.
Compaction-induced subsidence in the margin of a carbonate platform   总被引：1，自引：0，他引：1  
Abstract The Late Carnian Raibl Formation of the Sella Group (Dolomites, N Italy) forms a sedimentary wedge which thins progressively toward the core of a stratigraphically underlying Middle Carnian carbonate platform (Cassian Dolomite). The platform is composed largely of megabreccia clinoforms displaying progradation above the coeval basinal sequence (San Cassiano Formation). These basinal sediments thin from a maximum in a basinward direction to a pinchout towards the central core of the Sella buildup. The progradational foreslopes thin in an antithetic fashion, from a maximum immediately adjacent to the central core of the Sella to a minimum in a basinward direction. The wedge geometry and onlap of the Raibl Formation atop the Sella platform margin is interpreted as the result of compaction-induced differential subsidence and tilting of the platform top. Basinward increase in subsidence of the platform top resulted from a basinward increase in compaction of basinal San Cassiano sediments. Decompaction calculations and stratigraphic/geometric restoration of Carnian strata support this conclusion.  相似文献   

2.
Seismic-reflection data show that most deepwater (>200 m water depth) basins are filled by sand and mud dispersed across clinoformal geometries characterized by gently dipping topsets, steeper foresets and gently dipping bottomsets. However, the entire geometry of these ubiquitous clinoforms is not always recognized in outcrops. Sometimes the infill is erroneously interpreted as “layer cake” or “ramp” stratigraphy because the topset-foreset-bottomset clinoforms are not well exposed. Regional 2-D seismic lines show clinoforms in the Lower to Middle Jurassic Challaco, Lajas, and Los Molles formations in S. Neuquén Basin in Argentina. Time equivalent shelf, slope and basin-floor segments of clinoforms are exposed, and can be walked out in hundreds of metres thick and kilometres-wide outcrops. The studied margin-scale clinoforms are not representing a continental-margin but a deepwater shelf margin that built out in a back-arc basin. Lajas-Los Molles clinoforms have been outcrop-mapped by tracing mudstones interpreted as flooding surfaces on the shelf and abandonment surfaces (low sedimentation rate) in the deepwater basin. The downslope and lateral facies variability in the outcrops is also consistent with a clinoform interpretation. The Lajas topset (shelf) is dominated by fluvial and tidal deposits. The shelf-edge rollover zone is occasionally occupied by a 40–50-m-thick coarse-grained shelf-edge delta, sometimes incising into the underlying slope mudstones, producing oblique clinoforms expressing toplap erosion on seismic. A muddy transgressive phase capping the shelf-edge deltas contains tidal sandbodies. Shelf-edge deltas transition downslope into turbidite- and debris flow-filled channels that penetrate down the mud-prone Los Molles slope. At the base-of-slope, some 300m below the shelf edge, there are basin-floor fan deposits (>200 m thick) composed of sandy submarine-fan lobes separated by muddy abandonment intervals. The large-scale outcrop correlation between topset–foreset–bottomset allows facies and depositional interpretation and sets outcrop criteria recognition for each clinoform segment.  相似文献   

3.
Two nested clinoform set types of different scales and steepness are mapped and analysed from high-resolution seismic data. Restoration of post-depositional faulting reveals a persistent pattern of small-scale, high-angle clinoforms contained within platform-scale, low-angle clinothems, showing a combined overall progradational depositional system. The large clinoforms lack a well-defined platform edge, and show a gradual increase in dip from topset to foreset. A consistent recurring stratal pattern is evident from the architecture, and is considered a result of interplay between relative sea-level change and autocyclic switching of sediment delivery focal points that brought sediment to the platform edge. This un-interrupted succession records how intra-shelf platforms prograde. Quantitative clinoform analysis may assist in determining the most influential depositional factors. Post-depositional uplift and erosion requires restoration with re-burial to maximum burial depth. Backstripping, decompaction and isostatic correction was performed assuming a range of lithologic compositions, as no wells test the lithology. Nearby wells penetrate strata basinward of the clinoforms, proving mudstone content above 50%, which in turn guide restoration values. Typical restored platform heights are 250–300 m, with correspondingly sized platform-scale clinoform heights. Typical large-scale clinoform foreset dip values are 1.3°–2.4°. Small-scale clinothems are typically 100 m thick, with restored foreset dip angles at 4.4° - > 10°. The results suggest that intrashelf platform growth occurs in pulses interrupted by draping of strata over its clinoform profile. The resultant architecture comprises small-scale clinoforms nested within platform-scale clinothems.  相似文献   

4.
This article presents a new numerical inversion method to estimate progradation rates in ancient shallow‐marine clinoform sets, which is then used to refine the tectono‐stratigraphic and depositional model for the Upper Jurassic Sognefjord Formation reservoir in the super‐giant Troll Field, offshore Norway. The Sognefjord Formation is a 10–200‐m thick, coarse‐grained clastic wedge, that was deposited in ca. 6 Myr by a fully marine, westward‐prograding, subaqueous delta system sourced from the Norwegian mainland. The formation comprises four, 10–60‐m thick, westerly dipping, regressive clinoform sets, which are mapped for several tens of kilometres along strike. Near‐horizontal trajectories are observed in each clinoform set, and the sets are stacked vertically. Clinoform age and progradation rates are constrained by: (i) regionally correlatable bioevents, tied to seismically mapped clinoforms and clinoform set boundaries that intersect wells, (ii) exponential age–depth interpolations between bioevent‐dated surfaces and a distinctive foreset‐to‐bottomset facies transition within each well, and (iii) distances between wells along seismic transects that are oriented perpendicular to the clinoform strike and tied to well‐based stratigraphic correlations. Our results indicate a fall in progradation rate (from 170–500 to 10–65 km Myr?1) and net sediment flux (from 6–14 to ≤1 km2 Myr?1) westwards towards the basin, which is synchronous with an overall rise in sediment accumulation rate (from 7–16 to 26–102 m Myr?1). These variations are attributed to progradation of the subaqueous delta into progressively deeper waters, and a concomitant increase in the strength of alongshore currents that transported sediment out of the study area. Local spatial and temporal deviations from these overall trends are interpreted to reflect a subtle structural control on sedimentation. This method provides a tool to improve the predictive potential of sequence stratigraphic and clinoform trajectory analyses and offers a greater chronostratigraphic resolution than traditional approaches.  相似文献   

5.
Two-dimensional seismic modelling has been undertaken on an overall progradational succession of sloping mudstone and sandstone units from the Palaeogene of Spitsbergen. The modelling shows that the main geometric features of the section would be resolved at 1500 m depth (with frequencies below 60 Hz, which is common in seismic data at these depths). However, interference between the base and top of lithological units gives lateral amplitude variations and discrepancies between the seismic image and the geometrical model. This is particularly prominent in low-frequency models. Terminations of reflectors, resembling toplap and onlap, may be interpreted, but are artefacts of the general convergence of lithological units present in the geometrical model. The geological section causes a seismic pattern resembling sigmoid progradational seismic facies. Two-dimensional seismic modelling is an efficient tool in bridging the gap between outcrop observations and subsurface data. Hence, modelled outcrop sections are important as reference points' for improved seismic stratigraphic interpretation.  相似文献   

6.
《Basin Research》2018,30(4):671-687
The Mesozoic shelf margin in the Mahajanga Basin, northwest Madagascar, provides an example where inherited palaeobathymetry, coupled with sea‐level changes, high sediment supply and fluctuations in accommodation influenced the stacking patterns and geometry of clinoforms that accreted onto a passive rifted margin. Two‐dimensional (2D) seismic profiles are integrated with existing field data and geological maps to study the evolution of the margin. The basin contains complete records of transgression, highstand, regression and lowstand phases that took place from Jurassic to Cretaceous. Of particular interest is the Cretaceous, Albian to Turonian (ca. 113‐93 Ma), siliciclastic shelf margin that prograded above a drowned Middle Jurassic carbonate platform. The siliciclastic phase of the shelf margin advanced ca. 70 km within ca. 20 My, and contains 10 distinct clinoforms mapped along a 2D seismic reflection data set. The clinoforms show a progressive decrease in height and slope length, and a fairly constant slope gradient through time. The successive shelf edges begin with a persistent flat to slightly downward‐directed shelf‐edge trajectory that changes to an ascending trajectory at the end of clinoform progradation. The progressive decrease in clinoform height and slope length is attributed to a decrease in accommodation. The prograding margin is interpreted to have formed when siliciclastic input increased as eastern Madagascar was uplifted. This work highlights the importance of sediment supply and inherited palaeobathymetry as controls on the evolution of shelf margins and it provides a new understanding of the evolution of the Mahajanga Basin during the Mesozoic.  相似文献   

7.
Utilizing two outcrop data sets with dip direction exposures of shallow-water (tens of meters) deltaic clinoforms, this paper quantifies sedimentary facies proportions and clinoform lengths and gradients, and links process regimes to delta clinoform dimensions. Both data sets are from foreland basins, the Cretaceous Chimney Rock Sandstone of the Rock Springs Formation from the US Western Interior, and the Eocene Brogniartfjellet Clinoform Complex 8 of the Battfjellet Formation from the Central Basin of Spitsbergen. Sedimentary facies indicate presence of both river- and wave-dominated clinothems in each data set. Facies characteristics and distribution implies that river-dominated clinothem progradation was primarily driven by deposition from weak hyperpycnal flow turbidity currents across the clinoforms, and minor slumps. Wave-dominated clinothems were constructed by wave processes rather than alongshore currents, and are also progradational subaerial clinoforms, with one exception, where the formation of a compound subaqueous clinoform set indicates erosion and sediment bypass above the wave base. Sediment distribution and lithological heterogeneity in the river-dominated clinothems is controlled by individual hyperpycnal flow events or mouth-bar collapse events, and thus by self-organization and minimal reworking that results in a heterogeneity that is difficult to predict (high entropy). The efficient reworking of river-derived sediments in wave-dominated clinothems results in predictable lithological sediment partitioning (low entropy). Clinoform dimension analyses show that although of similar sediment caliber, river-dominated clinoforms in both data sets are on average 3–4 times steeper and 3–4 times shorter than the wave-dominated clinoforms, with mean gradients of ca 4 degrees and ca 1 degree, respectively, and mean lengths of 150–230 m and 640–760 m. These results require corroboration from additional data sets, but do suggest that river- and wave-dominated delta clinoforms are likely to have distinct downdip extents (lengths) and gradients for given clinoform heights. Clinoform shape can thus be a method for differentiating ancient river- vs. wave-dominated deltaic clinoforms, in addition to their sedimentary facies, biogenic features and sandstone maturity, and helpful when incorporated into reservoir models.  相似文献   

8.
Although the trajectory and geometry of clinoforms in different types of basins have been described in many studies, few studies discuss the influence of halokinesis on clinoforms in salt-related basins. In this study, we analyse the Lower Cretaceous clinoforms in the Tiddlybanken Basin, Norwegian Barents Sea to evaluate the impact of salt mobilization on the geometry and trajectory of clinoforms as well as its implications on sediment partitioning. To accomplish this objective, we use a multidisciplinary approach consisting of seismic and well-interpretation, 3D structural restoration, and forward stratigraphic modelling. The results show that salt mobilization affects prograding clinoforms by: (a) causing lateral variations in progradation rates, resulting in complex palaeogeography, (b) increasing slope angles, which affect the equilibrium of the clinoform profile and can trigger slope-readjustment processes and (c) producing lateral and temporal variations in accommodation space, leading to different clinoform trajectories, stacking patterns and reservoir distribution along the basin. Forward stratigraphic modelling shows that in salt-related basins and other tectonically active basins, the isolated use of conventional methods for clinoform analysis might lead to potential interpretation pitfalls such as misinterpretation of trajectories and overestimation of foreset angles, which can have negative consequences for exploration models.  相似文献   

9.
Most slope-channel outcrop studies have been conducted at continental margin-scale on seismic data. However, in foreland and back-arc deepwater settings, sub-seismic scale slope channels hold equally important information on deepwater sediment delivery, often in hydrocarbon-bearing provinces. One such slope-channel system is examined in Lower Jurassic prograding shelf-margin clinoforms in Bey Malec Estancia, La Jardinera area, southern Neuquén Basin, Argentina. In a 4 km wide, 300 m tall, slightly oblique- to depositional-dip section of Jurassic Los Molles Formation deepwater slope deposits, seven clinoform timelines were identified by isolated slope-channel fills with thicknesses less than 50 m. Sedimentary logs, satellite images, a digital elevation model and drone photogrammetry were used to map variations in downslope channel geometry and infill facies. The slope channels are filled with sediment density flow deposits: poorly sorted conglomeratic debrites, structureless sandy high-density turbidites and well-sorted, fine-grained, graded low-density turbidites. The debrite portion decreases downslope, whereas high- and low-density turbidites increase. A grain-size analysis reveals a broad downslope fining trend of turbidite and debrite beds within slope channels with increasing water depth, and some notable bypass of conglomeratic facies to the lowermost slope channels and basin floor fans. The architecture of the slope channels changes from lateral to aggradational infill downstream. The Bey Malec clinoforms and its slope channels add new knowledge on downslope changes for sediment delivery in relatively shallow (<500 m water depth), prograding-dominant deepwater basins. They also highlight one of very few outcropping examples of oblique-type clinoforms.  相似文献   

10.
Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region.  相似文献   

11.
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12.
Understanding how sedimentary rocks represent time is one of the significant challenges in sedimentology. Sedimentation rates retrieved from vertical sections are strongly timescale dependent, which means that we cannot use empirical rate data derived from vertical sections in modern environments to interpret the temporal structure of ancient sedimentary deposits. We use the Lower to Middle Campanian Blackhawk Formation deposits in eastern Utah and western Colorado as a natural laboratory to test a source-to-sink methodology circumventing this timescale dependence by relating modern progradation rates to the deltaic shoreline progradation of ancient siliciclastic rocks. Our objective is to quantify how much time is needed to account for the observed cumulative deltaic shoreline progradation recorded by the shallow-marine sandstone bodies of the Blackhawk Formation in terms of progradation rates derived from comparable modern deltaic systems. By making the simplifying assumption that the Blackhawk Formation rocks were deposited along a linear coastline that only grew by aggradation and progradation, it is possible to argue that the stratigraphic completeness of two-dimensional dip-oriented stratigraphic cross-sections through these deposits should be high. Furthermore, we hypothesise that delta progradation estimates capture a significant portion of the biostratigraphically and radiometrically constrained duration of the succession. By comparing the recorded progradation with modern progradation rates, we estimate that we need ca. 20% (median value, with minimum and maximum estimates of 2% and 300%) of the time available from biostratigraphic and radiometric dating to account for the progradation recorded by the sedimentary deposits. This indicates that long-term progradation rates averaged over the entire duration of the Blackhawk Formation were only a factor of five times slower than the modern progradation rates derived from observations over periods that are five to six orders of magnitude shorter. We conclude that a significant amount of time is represented by prograding deltaic shoreline deposits and that by considering the cumulative shoreline progradation, we could limit the effects of timescale dependence on the rate estimates used in our analysis.  相似文献   

13.
Sandy clinothems are of interest as hydrocarbon reservoirs but there is no proven, economic, clinothem reservoir in the Norwegian Barents Sea. We used high-resolution, 2D and 3D seismic, including proprietary data, to identify a previously untested, Barremian, clinoform wedge in the Fingerdjupet Subbasin (FSB). Data from recent well 7322/7-1 plus seismic have been used to characterize this wedge and older Lower Cretaceous clinoforms in the FSB. In the latest Hauterivian – early Barremian, during post-rift tectonic quiescence, shelf-edge clinoforms (foreset height > 150 m) prograded into an under-filled basin. Increased sediment input was related to regional uplift of the hinterland (northern Barents Shelf). Early Barremian erosion in the north-western FSB and mass wasting towards the SE were followed by deposition of delta-scale (<80 m high), high-angle (c. 8°) clinoform sets seaward of older shelf-edge clinoforms. This may be the local expression of a regional, early Barremian, regressive event. By the close of the Barremian, clinoforms had prograded, within a narrow, elongate basin, across the FSB and towards the uplifted Loppa High. A seismic wedge of high-angle (10–12°), low-relief, delta-scale (25–80 m) clinoform sets occurs between shelf-edge clinoforms to the NW and the uplifted area to the SE. Well 7322/7-1, positioned on a direct hydrocarbon indicator, <1 km NNW of the high-angle, low-relief, delta-scale clinoforms, found upward coarsening siltstone-cycles linked to relative sea-level fluctuations on a marine shelf. Sand may have accumulated, offshore from the well, in high-angle, low-relief foresets of the delta-scale clinothems (which are typical geometries elsewhere interpreted as ‘delta-scale, sand-prone subaqueous clinoforms’). Deposition was controlled by the paleosurface, storms and longshore currents on an otherwise mud-dominated shelf. The study highlights challenges associated with exploration for sandstone reservoirs in seismic wedges on an outer shelf.  相似文献   

14.
The Pennsylvanian marine foreland basin of the Cantabrian Zone (NW Spain) is characterized by the unique development of kilometre‐size and hundred‐metre‐thick carbonate platforms adjacent to deltaic systems. During Moscovian time, progradational clastic wedges fed by the orogen comprised proximal alluvial conglomerates and coal‐bearing deltaic sequences to distal shelfal marine deposits associated with carbonate platforms (Escalada Fm.) and distal clay‐rich submarine slopes. A first phase of carbonate platform development (Escalada I, upper Kashirian‐lower Podolskian) reached a thickness of 400 m, nearly 50 km in width and developed a distal high‐relief margin facing a starved basin, nearly 1000‐m deep. Carbonate slope clinoforms dipped up to 30° and consisted of in situ microbial boundstone, pinching out downslope into calciturbidites, argillaceous spiculites and breccias. The second carbonate platform (Escalada II, upper Podolskian‐lower Myachkovian) developed beyond the previous platform margin, following the basinward progradation of siliciclastic deposits. Both carbonate platforms include: (1) a lower part composed of siliciclastic‐carbonate cyclothems characterized by coated‐grain and ooid grainstones; and (2) a carbonate‐dominated upper part, composed of tabular and mound‐shaped wackestone and algal‐microbial boundstone strata alternating at the decametre scale with skeletal and coated‐grain grainstone beds. Carbonate platforms initiated in distal sectors of the foreland marine shelf during transgressions, when terrigenous sediments were stored in the proximal part, and developed further during highstands of 3rd‐order sequences in a high‐subsidence context. During the falling stage and lowstand systems tracts, deltaic systems prograded across the shelf burying the carbonate platforms. Key factors involved in the development of these unique carbonate platforms in an active foreland basin are: (1) the large size of the marine shelf (approaching 200 km in width); (2) the subsidence distribution pattern across the marine shelf, decreasing from proximal shoreline to distal sectors; (3) Pennsylvanian glacio‐eustacy affecting carbonate lithofacies architecture; and (4) the environmental conditions optimal for fostering microbial and algal carbonate factories.  相似文献   

15.
Reconstructions of ancient delta systems rely typically on a two-dimensional (2D) view of prograding clinothems but may miss their three-dimensional (3D) stratigraphic complexity which can, instead, be best documented on modern delta systems by integrating high-resolution geophysical data, historical cartography, core data and geomorphological reconstructions offshore. We quantitatively compare three precisely positioned, high-resolution multi-beam bathymetry maps in the delta front and pro delta sectors (0.3 to 10 m water depth) of Po di Pila, the most active of the modern Po Delta five branches. By investigating the detailed morphology of the prograding modern Po Delta, we shed new light on the mechanisms that control the topset to foreset transition in clinothems and show the temporal and spatial complexity of a delta and its pro delta slope, under the impact of oceanographic processes. This study documents the ephemeral nature of the rollover point at the transition between sandy topset (fluvial, delta plain to mouth-bar) and muddy seaward-dipping foreset deposits advancing, in this case, in >20 m of water depth. Three multibeam surveys, acquired between 2013 and 2016, document the complexity in space and time of the topset and foreset regions and their related morphology, a diagnostic feature that could not be appreciated using solely 2D, even very high-resolution, seismic profiles. In addition, the comparison of bathymetric surveys gathered with one-year lapses shows the migration of subaqueous sand dunes on the clinothem topset, the formation of ephemeral cut-and-fill features at the rollover point (few m below mean sea level), the presence of collapse depressions derived by sagging of sediments and fluid expulsion (possibly induced by storm waves) on the foreset, and splays of sand likely reflecting gravity flows on the lower foreset. Though the modern Po Delta is anthropogenic in many respects, its subaqueous clinothem can be studied as a scale model for ancient clinothems that are less resolved geometrically and far less constrained chronologically.  相似文献   

16.
Clinoforms are basinward-dipping and accreting palaeo-bathymetric profiles that record palaeo-environmental conditions and processes; thus, clinothems represent natural palaeo-archives. Here, we document shelf-edge scale clinoform sets which prograded through the entire width of an epicontinental marine basin (ca. 400 km), eventually encroaching onto the opposite basin flank, where they started to prograde upslope and landward, in defiance of gravity (“upslope-climbing clinoforms”). The giant westward-prograding Eridanos muddy shelf-edge clinothem originated from the Baltic hinterland in the Oligocene and achieved maximum regression in the Early Pleistocene, on the UK Central Graben (CG) and Mid North Sea High (MNSH), after crossing the whole North Sea mesopelagic depocentre and causing near complete basin infill. Here we integrate well and seismic data through the MNSH and CG and examine the Eridanos final heyday and demise, identifying five clinothem complexes (A1, A2, A3, B and C) and six depositional sequence boundaries (SB1 to SB6) in the Miocene-Recent section. Tectonic and climatic events drove the recent evolution of this system. Early Pleistocene climate cooling, in particular, resulted in a stepwise increase in sediment supply. This climaxed in the earliest Calabrian, following a likely Eburonian eustatic fall (=SB3) when the Eridanos clastic wedge was restructured from a 100–300 m thick compound shelf-edge and delta system to a “hybrid” shelf-edge delta at sequence boundary SB3 (ca. 1.75 Ma). In the ca. 40 kyr that followed SB3, a progradation rate peak (>1,000 m/kyr) is associated with clinoforms starting to accrete upslope, onto the east-dipping slope between CG and MNSH. This “upslope-climbing clinoform” phase was quickly followed by the maximum regression and final retreat of the Eridanos system in the Early Calabrian (=SB4), likely as the result of climate-driven changes in the Baltic hinterland and/or delta auto-retreat. To our knowledge, this contributions represents the first documentation of “upslope-climbing clinoforms” recorded in the stratigraphic record.  相似文献   

17.
Clinoforms with a range of scales are essential elements of prograding continental margins. Different types of clinoforms develop during margin growth, depending on combined changes in relative sea level, sediment supply and oceanographic processes. In studies of continental margin stratigraphy, trajectories of clinoform ‘rollover’ points are often used as proxies for relative sea-level variation and as predictors of the character of deposits beyond the shelf-break. The analysis of clinoform dynamics and rollover trajectory often suffers from the low resolution of geophysical data, the small scale of outcrops with respect to the dimensions of clinoform packages and low chronostratigraphic resolution. Here, through high-resolution seismic reflection data and sediment cores, we show how compound clinoforms were the most common architectural style of margin progradation of the late Pleistocene lowstand in the Adriatic Sea. During compound clinoform development, the shoreline was located landward of the shelf-break. It comprised a wave-dominated delta to the west and a barrier and back-barrier depositional system in the central and eastern area. Storm-enhanced hyperpycnal flows were responsible for the deposition of a sandy lobe in the river mouth, whereas a heterolithic succession formed elsewhere on the shelf. The storm-enhanced hyperpycnal flows built an apron of sand on the slope that interrupted an otherwise homogeneous progradational mudbelt. Locally, the late lowstand compound clinoforms have a flat to falling shelf-break trajectory. However, the main phase of shelf-break bypass and basin deposition coincides with a younger steeply rising shelf-break trajectory. We interpret divergence from standard models, linking shelf-break trajectory to deep-sea sand deposition, as resulting from a great efficiency of oceanographic processes in reworking sediment in the shelf, and from a high sediment supply. The slope foresets had a large progradational attitude during the late lowstand sea-level rise, showing that oceanographic processes can inhibit coastal systems to reach the shelf-edge. In general, our study suggests that where the shoreline does not coincide with the shelf-break, trajectory analysis can lead to inaccurate reconstruction of the depositional history of a margin.  相似文献   

18.
The Miocene marine basins of Central and Southeast Europe, once comprising the Paratethys Sea, were gradually filled with sediments during the Neogene and turned to be the catchment area of the proto-Danube and finally that of the modern Danube. Seismic data from various parts of the large Danube catchment area show that these several hundred meter deep basins were filled by lateral accretion of river-transported sediments, appearing as shelf edge scale clinoform sets in seismic profiles. The direction of shelf edge progradation is NW to SE (N to S, W to E) in each basin, except for the Dacian basin where NE to SW direction prevails. The age of the clinoform sets is generally younging downstream: 19–18 Ma in the North Alpine Foreland basin, 14–13 Ma in the Vienna basin, 10–9 Ma in the Danube (Kisalföld) basin, 8.6–4 Ma in the Central Pannonian basin (Alföld), ?9–5 Ma in the Dacian basin, and 6–0 Ma in the Euxinian (Black Sea) basin. In spite of this geographical and temporal pattern, only the Danube (Kisalföld) and the western and central part of the Central Pannonian basin were filled by the proto-Danube shelf accretion. Formation of the Danube, as a longitudinal river of the Alpine foreland that gradually elongated to the east and followed the retreating shoreline of the Paratethys, most probably took place at the beginning of the Late Miocene, ca. 11 Ma ago, thus the Early and Middle Miocene shelf advance in the North Alpine Foreland and Vienna basins, respectively, cannot be attributed to a „paleo-Danube”. The clinoform systems of the Dacian basin are coeval with those of the upstream Central Pannonian basin, indicating that by the time the Danube sedimentary system reached the Dacian basin, it was already a shallow basin. The vast clinoforms of the northwestern Euxinian shelf also significantly overlap in age with the Pannonian basin ones; only the <4 Ma part of the shelf accretion can be attributed to the Danube sensu stricto.  相似文献   

19.
The South China Sea continental margin in the Qiongdongnan Basin (QDNB) area has incrementally prograded since 10.5 Ma generating a margin sediment prism more than 4km-thick and 150–200 km wide above the well-dated T40 stratigraphic surface. Core and well log data, as well as clinoform morphology and growth patterns along 28 2D seismic reflection lines, illustrate the evolving architecture and margin morphology; through five main seismic-stratigraphic surfaces (T40, T30, T27, T20 and T0) frame 15 clinothems in the southwest that reduce over some 200 km to 8 clinoforms in the northeast. The overall margin geometry shows a remarkable change from sigmoidal, strongly progradational and aggradational in the west to weakly progradational in the east. Vertical sediment accumulation rate increased significantly across the entire margin after 2.4 Ma, with a marked increase in mud content in the succession. Furthermore, an estimate of sediment flux across successive clinoforms on each of the three selected seismic cross sections indicate an overall decrease in sediment discharge west to east, away from the Red River depocenter, as well as a decrease in the percentage of total discharge crossing the shelf break in this same direction. The QDNB Late Cenozoic continental margin growth, with its overall increased sediment flux, responded to the climate-induced, gradual cooling and falling global sea level during this icehouse period.  相似文献   

20.
Middle Miocene to Pliocene siliciclastics of the Bare Formation represent a long‐lived (ca. 11 Myr) break in the otherwise carbonate‐dominated shelf of the Northern Carnarvon Basin, Northwest Shelf of Australia. The quartz‐sandstone interval is correlated with the appearance of spectacular clinoform sets mapped on 3D and dense 2D seismic data. Twenty‐seven clinoform sets are interpreted as delta lobes primarily based on their plan‐view morphology (strike‐elongate to lobate features) and their 40–100‐m‐high clinoform amplitudes. The delta lobes were deposited on outer‐shelf to shelf‐edge positions, and the older deltas show evidence of a higher degree wave reworking than the younger deltas. Measurements of the along‐strike (migration) and down‐dip (progradation) movement of these deltas are compared with relative sea‐level behaviour inferred from shelf‐edge trajectory analysis. Delta lobes exhibit greater lateral shifting during relative sea‐level rise, whereas delta lobes are more restricted to dip‐oriented fairways during sea‐level fall, although no major incised valleys have been identified. Long‐term (cumulative) progradation of this delta system and subsequent backstepping correlates with long‐term sea‐level fall and rise during the late middle and late Miocene. In addition, a long‐term northeastward migration trend for these delta lobes was likely a result of localized uplift of an inversion anticline in the Rosemary–Legendre Trend; the growth of this anticline probably steered the fluvial source for the delta system towards the northeast. The Bare Formation siliciclastic influx correlates with other middle Miocene increases in siliciclastic sediment supply worldwide. Global cooling and a shift to more arid conditions, negatively influencing vegetation cover, may have combined with more seasonally variable rainfall to generate the high sediment supply that built the deltas. Retreat of the siliciclastics could correlate with ice‐sheet growth in the Northern Hemisphere and/or increase in the Indonesian Throughflow and Leeuwin Current (ca. 1.6 Ma), which might have modified climate regionally.  相似文献   

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