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1.
《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   

2.
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   

3.
Late Miocene lacustrine clinoforms of up to 400 m high are mapped using a 1700 km2 3‐D seismic data set in the Dacian foreland basin, Romania. Eight Meotian clinoforms, constructed by sediment from the South Carpathians, prograded around 25 km towards southwest. The individual clinothems show thin (10–60 m thick), if any, topsets, disrupted foresets and highly aggradational bottomsets. Basin‐margin accretion occurred in three stages with changing of clinoform heights and foreset gradients. The deltaic system prograded into an early‐stage deep depocenter and contributed to high gradient clinoforms whose foresets were dominated by closely (100–200 m) spaced 1.5–2 km wide V‐shaped sub‐lacustrine canyons. During intermediate‐stage growth, 2–4 km wide canyons were dominant on the clinoform foresets. From the early to intermediate stages, the lacustrine shelf edges were consistently indented. The late‐stage outbuilding was characterised by smaller clinoforms with smoother foresets and less indentation along the shelf edge. Truncated and thin topsets persisted through all three stages of clinoform evolution. Nevertheless, the resulting long‐term flat trajectory shows alternating segments of forced and low‐amplitude normal regressions. The relatively flat trajectory implies a constant base level over time and was due to the presence of the Dacian–Black Sea barrier that limited water level rise by spilling to the Black Sea. Besides the characteristic shelf‐edge incision of the thin clinoform topsets and the resultant sediment bypass at the shelf edge, the prolonged regressions of the shelf margin promoted steady sediment supply to the basin. The high sediment supply at the shelf edges generated long‐lived slope sediment conduits that provided sustained sediment transport to the basin floor. Clinothem isochore maps show that large volumes of sediment were partitioned into the clinoform foresets, and especially the bottomsets. Sediment predominantly derived from frequent hyperpycnal flows contributed to very thick, ca. 300–400 m in total, bottomsets. Decreasing subsidence over time from the foredeep resulted in diminishing accommodation and clinoform height, reduced slope channelization and smoother slope morphology.  相似文献   

4.
Exhumed basin margin‐scale clinothems provide important archives for understanding process interactions and reconstructing the physiography of sedimentary basins. However, studies of coeval shelf through slope to basin‐floor deposits are rarely documented, mainly due to outcrop or subsurface dataset limitations. Unit G from the Laingsburg depocentre (Karoo Basin, South Africa) is a rare example of a complete basin margin scale clinothem (>60 km long, 200 m‐high), with >10 km of depositional strike control, which allows a quasi‐3D study of a preserved shelf‐slope‐basin floor transition over a ca. 1,200 km2 area. Sand‐prone, wave‐influenced topset deposits close to the shelf‐edge rollover zone can be physically mapped down dip for ca. 10 km as they thicken and transition into heterolithic foreset/slope deposits. These deposits progressively fine and thin over tens of km farther down dip into sand‐starved bottomset/basin‐floor deposits. Only a few km along strike, the coeval foreset/slope deposits are bypass‐dominated with incisional features interpreted as minor slope conduits/gullies. The margin here is steeper, more channelized and records a stepped profile with evidence of sand‐filled intraslope topography, a preserved base‐of‐slope transition zone and sand‐rich bottomset/basin‐floor deposits. Unit G is interpreted as part of a composite depositional sequence that records a change in basin margin style from an underlying incised slope with large sand‐rich basin‐floor fans to an overlying accretion‐dominated shelf with limited sand supply to the slope and basin floor. The change in margin style is accompanied with decreased clinoform height/slope and increased shelf width. This is interpreted to reflect a transition in subsidence style from regional sag, driven by dynamic topography/inherited basement configuration, to early foreland basin flexural loading. Results of this study caution against reconstructing basin margin successions from partial datasets without accounting for temporal and spatial physiographic changes, with potential implications on predictive basin evolution models.  相似文献   

5.
We developed a seismic geomorphology-based procedure to enhance traditional trajectory analysis with the ability to visualize and quantify lateral variability along carbonate prograding-margin types (ramps and rimmed shelves) in 3D and 4D. This quantitative approach analysed the shelf break geometric evolution of the Oligo-Miocene carbonate clinoform system in the Browse Basin and delineated the feedback between antecedent topography and carbonate system response as controlling factor on shelf break rugosity. Our geometrical analysis identified a systematic shift in the large-scale average shelf break strike direction over a transect of 10 km from 62° to 55° in the Oligo-Miocene interval of the Browse Basin, which is likely controlled by far-field allogenic forcing from the Timor Trough collision zone. Plotting of 3D shelf break trajectories represents a convenient way to visualize the lateral variability in shelf break evolution. Shelf break trajectories that indicate contemporaneous along-strike progradation and retrogradation correlate with phases of autogenic slope system re-organization and may be a proxy for morphological stability of the shelf break. Shelf break rugosity and shelf break trajectory rugosity are not inherited parameters and antecedent topography does not dictate long-term differential movement of the shelf margin through successive depositional sequences. The autogenic carbonate system response to antecedent topography smooths high-rugosity areas by filling accommodation and maintains a relatively constant shelf break rugosity of ~150 m. Color-coding of the vertical component in the shelf break trajectory captures the creation and filling of accommodation, and highlights areas of the transect that are likely to yield inconsistent 2D sequence stratigraphic interpretations.  相似文献   

6.
The application of high‐resolution seismic geomorphology, integrated with lithological data from the continental margin offshore The Gambia, northwest Africa, documents a complex tectono‐stratigraphic history through the Cretaceous. This reveals the spatial‐temporal evolution of submarine canyons by quantifying the related basin depositional elements and providing an estimate of intra‐ versus extra‐basinal sediment budget. The margin developed from the Jurassic to Aptian as a carbonate escarpment. Followed by, an Albian‐aged wave‐dominated delta system that prograded to the palaeo‐shelf edge. This is the first major delivery of siliciclastic sediment into the basin during the evolution of the continental margin, with increased sediment input linked to exhumation events of the hinterland. Subaqueous channel systems (up to 320 m wide) meandered through the pro‐delta region reaching the palaeo‐shelf edge, where it is postulated they initiated early submarine canyonisation of the margin. The canyonisation was long‐lived (ca. 28 Myr) dissecting the inherited seascape topography. Thirteen submarine canyons can be mapped, associated with a Late Cretaceous‐aged regional composite unconformity (RCU), classified as shelf incised or slope confined. Major knickpoints within the canyons and the sharp inflection point along the margin are controlled by the lithological contrast between carbonate and siliciclastic subcrop lithologies. Analysis of the base‐of‐slope deposits at the terminus of the canyons identifies two end‐member lobe styles, debris‐rich and debris‐poor, reflecting the amount of carbonate detritus eroded and redeposited from the escarpment margin (blocks up to ca. 1 km3). The vast majority of canyon‐derived sediment (97%) in the base‐of‐slope is interpreted as locally derived intra‐basinal material. The average volume of sediment bypassed through shelf‐incised canyons is an order of magnitude higher than the slope‐confined systems. These results document a complex mixed‐margin evolution, with seascape evolution, sedimentation style and volume controlled by shelf‐margin collapse, far‐field tectonic activity and the effects of hinterland rejuvenation of the siliciclastic source.  相似文献   

7.
A synthesis has been undertaken based on regionally compiled data from the post early Eocene foreland basin succession of Svalbard. The aim has been to generate an updated depositional model and link this to controlling factors. The more than kilometer thick progradational succession includes the offshore shales of the Gilsonryggen Member of the Frysjaodden Formation, the shallow marine sandstones of the Battfjellet Formation and the predominantly heterolithic Aspelintoppen Formation, together recording the progressive eastwards infill of the foredeep flanking the West Spitsbergen fold‐and‐thrust belt. Here we present a summary of the paleo‐environmental depositional systems across the basin, their facies and regional distribution and link these together in an updated depositional model. The basin‐margin system prograded with an ascending shelf‐edge trajectory in the order of 1°. The basin fill was bipartite, with offset stacked shelf and shelf‐edge deltas, slope clinothems and basin floor fans in the western and deepest part and a simpler architecture of stacked shelf‐deltas in the shallower eastern part. We suggest a foredeep setting governed by flexural loading, likely influenced by buckling, and potentially developing into a wedge top basin in the mature stage of basin filling. High‐subsidence rates probably counteracted eustatic falls with the result that relative sea‐level falls were uncommon. Distance to the source terrain was small and sedimentation rates was temporarily high. Time‐equivalent deposits can be found outbound of Stappen High in the Vestbakken Volcanic Province and the Sørvestsnaget Basin 300 km further south on the Barents Shelf margin. We cannot see any direct evidence of coupling between these more southerly systems and the studied one; southerly diversion of the sediment‐routing, if any, may have taken place beyond the limit of the preserved deposits.  相似文献   

8.
Located on the southern margin of the Lhasa terrane in southern Tibet, the Xigaze forearc basin records Cretaceous to lower Eocene sedimentation along the southern margin of Asia, prior to and during the initial stages of continental collision with the Tethyan Himalaya in the Early Eocene. We present new measured stratigraphic sections, totalling 4.5 km stratigraphic thickness, from a 60 km E–W segment of the western portion of the Xigaze forearc basin, northeast of the Lopu Kangri Range (29.8007° N, 84.91827° E). In addition, we apply U–Pb detrital zircon geochronology to constrain the provenance and maximum depositional ages of investigated strata. Stratigraphic ages range between ca. 88 and ca. 54 Ma and sedimentary facies indicate a shoaling‐upward trend from deep‐marine turbidites to fluvial deposits. Depositional environments of coeval Cretaceous strata along strike include deep‐marine distal turbidites, slope‐apron debris‐flow deposits and marginal marine carbonates. This along‐strike variability in facies suggests an irregular paleogeography of the Asian margin prior to collision. Paleocene–Eocene strata are composed of shallow marine carbonates with abundant foraminifera such as Nummulites‐Discocyclina and Miscellanea‐Daviesina and transition into fluvial deposits dated at ca. 54 Ma. Sandstone modal analyses, conglomerate clast compositions and detrital zircon U–Pb geochronology indicate that forearc detritus in this region was derived solely from the Gangdese magmatic arc to the north. In addition, U–Pb detrital zircon age spectra within the upper Xigaze forearc stratigraphy are similar to those from Eocene foreland basin strata south of the Indus‐Yarlung suture near Sangdanlin, suggesting that the Xigaze forearc was a possible source of Sangdanlin detritus by ca. 55 Ma. We propose a model in which the Xigaze forearc prograded south over the accretionary prism and onto the advancing Tethyan Himalayan passive margin between 58 and 54 Ma, during late stage evolution of the forearc basin and the beginning of collision with the Tethyan Himalaya. The lack of documented forearc strata younger than ca. 51 Ma suggests that sedimentation in the forearc basin ceased at this time owing to uplift resulting from continued continental collision.  相似文献   

9.
Interplays among diachronous tectonism, uneven sediment supply, and local marine hydraulic processes make the northern margin of the South China Sea (SCS) an ideal location to investigate the complexity of along‐strike variability in shelf margins. This study examines shelf‐margin morphology, stratigraphy, and sedimentation from the northern SCS using multichannel seismic reflection profiles complemented with the data from commercial and ocean drilling sites. Analysis of seismic reflection profiles reveals three categories of shelf‐margin cross‐sectional profiles, the concave‐up, linear, and sigmoidal, according to which five margin sectors were recognized. Results show that these margin segments differ in relief, shelf‐edge trajectory, submarine canyon development, and long‐term accretion pattern. The westernmost margin sector, or the Yinggehai (YGH)‐western Qiongdongnan (QDN) margin, has appeared to be supply dominated since its commencement at ca. 10.5 Ma, which is characterized by well‐developed prograding clinoforms, low‐angle shelf‐edge trajectories, and an absence of canyons. Presence of concave‐up profiles is also suggestive of high sediment influx. In contrast, the eastern QDN margin was primarily regulated by local subsidence and faulting, leading to a stationary shelf‐edge migrating pattern and linear upper‐slope morphology. Densely distributed slope‐confined gullies indicate the margin’s disequilibrium and erosive nature. Further east, the Pearl River Mouth (PRM) margin formed much earlier (ca. 30 Ma) and experienced a more complicated accretion history, including three phases which were dominated by sequential marginal faulting (before ca. 30 Ma), basement structure (ca. 30–23 Ma), and sediment supply (ca. 23 Ma to the present). The overall sigmoidal morphology and truncated stratigraphy of this margin probably resulted from the sculpting of local marine processes, especially ocean currents and internal waves. The exception of the central PRM margin where concave‐up profiles develop is mainly related to canyon erosion. Overall, this study highlights the vital role of local forcing factors in controlling along‐margin variations and determining the final fates of different margin segments. A comparison between the northern SCS and other well‐established examples reveals that concave‐upward shelf‐margin shapes, which are usually associated with high sediment supply, little influence from hydraulic regimes, or sometimes, high degree of canyon development, may be an indicator of good reservoir potential beyond the shelf edge.  相似文献   

10.
ABSTRACT There is continued interest in how the rate of relative sea‐level rise [A ( > 0)] and the rate of sediment supply [S] function during the growth and evolution of deltaic shorelines. The theory of shoreline autoretreat, recently corroborated in flume experiments, claims that (1) A( > 0) and S can never be in equilibrium, and (2) shoreline or shelf‐edge progradation inevitably turns to retrogradation, when relative sea level is rising even modestly and even if A/S = const (> 0). Autoretreat arises because the area of the clinoform surface of the delta (or shelf edge) per kilometer of shoreline must increase as the relative sea level rises, and the delta (or shelf edge) progrades into deeper water. A finite sediment supply rate is thus liable to become inadequate to sustain progradation. The problem increases further as a rising sea level also greatly increases the delta‐plain volume that needs to be filled, further limiting the progradation of the system. The fundamental trajectory of shoreline migration is thus one characterized by a concave‐landward shape, even under the steady forcing of the basin. The magnitudes of A (> 0) and S, or A/S do not determine whether the landward turnaround of the shoreline is realized or not, but affect merely the length and height of the fundamental trajectory curve. Thus, any attempt to detect and interpret temporal changes in A and S from the observed stratigraphic record of shoreline trajectory needs first to take full account of the inbuilt autoretreat mechanism. We develop here a simple, semi‐quantitative method of reconstructing the basin conditions (A and S) from the stratigraphic record of prograding deltaic shorelines (or prograding shelf‐margin clinoforms) on the basis of the theory of shoreline autoretreat. The deterministic nature of the autoretreat theory is advantageous in managing this latter issue, because any expected or unexpected change emerges as some discrepancy from a trajectory that was predicted for the initial conditions. The autoretreat theory also provides a convenient graphical method of dealing with the uncertainty of the field data, and with evaluating the accuracy of any reconstruction. Our methodology has been developed to deal with the behaviour of deltaic shorelines, but is basically applicable to any clinoform system, the development of which is affected by relative sea level. The suggested method is applied to an Early Eocene (Ypresian) regressive shoreline succession in the Central Tertiary Basin on Spitsbergen. The studied regressive wedge developed as a delta‐driven, progradational shelf‐margin system under a regime of overall (i.e. long‐term) rise of relative sea level, but also suffered short‐term sea‐level falls associated with valley incisions on the coastal plain and shelf. On the assumption that S was constant or was steadily decreasing, the analysis of field data obtained from three sites within the basin suggests that the initial water depth in the basin was around 0.45 km, and that the overall relative sea‐level rise (c. 0.80 km) happened largely during an early time period and was followed by a longer period of much lower rate of rise. This pattern of relative sea‐level rise is consistent with the Palaeogene tectonic subsidence trend of the basin which was determined independently through a geohistory analysis. The uncertainty of the field data does not negate our reconstruction. The combined effects of autoretreat and A/S changes on a deltaic shoreline trajectory are confirmed through the development of an autoretreat‐based methodology. Conventional sequence stratigraphic models that assume a possible equilibrium condition between A and S are both conceptually misleading and insufficient to analyse basin conditions quantitatively. Sequence stratigraphic analyses of shorelines need to incorporate the autoretreat concept.  相似文献   

11.
The siliciclastic topset of a continental margin, or a shelf-margin prism in subsiding nonplate-margin deepwater basins, is the flat-lying upper part of the margin succession; it is coeval basinwards with deepwater slope clinoforms. Topsets develop by the aggradation of repeated, cross-shelf, shoreline regressions and transgressions, thereby hosting the shelf portion of stacked, fourth-order stratigraphic sequences. Sediment spreading downdip and along strike during the cross-shelf transit of the sediment delivery system, as well as process regime changes of deltas and shorefaces (regressive) and of estuaries, barrier–lagoon systems and shelf ridges (transgressive) are highly variable over short distances, so that correlation within a single stratigraphic sequence is far more difficult than correlation of the cross-shelf maximum flooding surface boundaries. Thickness of individual regressive–transgressive, fourth-order sequences is given by shelf accommodation, typically <10 m in embayment or on the inner shelf and up to 200 m on outer shelf. Tectonic subsidence and compaction will enhance this thickness only if rates are very high compared to shelf-transit time. In very high subsidence rate settings, the transgressive tracts are well preserved and often thickly developed. Topset sequences in an Icehouse climate setting tend to have a high proportion and greater landward development of marine vs nonmarine deposits, compared to Greenhouse sequences, because of the importance of eustatic rise of sea level in the former. Previous numerical experiments show that even for very wide shelves and irrespective of Icehouse or Greenhouse conditions, deltas rarely take more than 10 s of ky to reach their shelf edge, suggesting that it is fourth-order (or higher) sequences that are the fundamental ones in sequence stratigraphy.  相似文献   

12.
Shelf-margin clinoforms and prediction of deepwater sands   总被引：1，自引：1，他引：1  
Early Eocene successions from Spitsbergen and offshore Ireland, showing well‐developed shelf‐margin clinoforms and a variety of deepwater sands, are used to develop models to predict the presence or absence of turbidite sands in clinoform strata without significant slope disturbance/ponding by salt or mud diapers. The studied clinoforms formed in front of narrow to moderate width (10–60 km) shelves and have slopes, 2–4°, that are typical of accreting shelf margins. The clinoforms are evaluated in terms of both shelf‐transiting sediment‐delivery systems and the resultant partitioning of the sand and mud budget along their different segments. Although this sediment‐budget partitioning is controlled by sediment type and flux, shelf width and gradient, process regime on the shelf and relative sea‐level behaviour, the most tell‐tale or predictive signs in the stratigraphic record appear to be (1) sediment‐delivery system type, (2) degree of shelf‐edge channelling and (3) character of shelf‐edge trajectory through time. The clinoform data sets from the Porcupine Basin (wells and 3‐D seismic) and from the Central Basin on Spitsbergen (outcrops) suggest that river‐dominated deltas are the most efficient delivery systems for dispersing sand into deep water beyond the shelf‐slope break. In addition, low‐angle or flat, channelled shelf‐edge trajectories associate with co‐eval deepwater slope and basin‐floor sands, whereas rising trajectories tend to associate with muddy slopes and basin floors. Characteristic features of the shelf‐edge, slope and basin‐floor segments of clinoforms for these trajectory types are documented. Seismic lines along the slope to basin‐floor transects tend to show apparent up‐dip sandstone pinchouts, but most of these are likely to be simply sidelap features. Dip lines aligned along the axes of sandy fairways show that stratigraphic traps are unlikely, unless slope channels become mud‐filled or are structurally partitioned. Another feature that is prominent in the data sets examined is the lack of slope onlap. During the relative rise of sea level back up to the shelf, the clinoform slopes are generally mud‐prone and they are characteristically aggradational.  相似文献   

13.
Constraining the thermal and denudational evolution of continental margins from extensional episodes to early orogenic stages is critical in the objective to better understand the sediment routing during the growth of orogenic topography. Here, we report 160 detrital zircon U/Pb ages and 73 (U‐Th)/He ages from Albian, Upper Cretaceous and Eocene sandstones from the south‐central Pyrenees. All samples show dominant zircon U/Pb age peaks at 310–320 Ma, indicating a primary contribution from Variscan granites of the central Pyrenean Axial Zone. A secondary population at 450–600 Ma documents zircon grains sourced from the eastern Pyrenees. Zircon (U‐Th)/He ages recovered from older samples document, a Triassic age peak at ca. 241 Ma, corresponding to denudation coeval with the initiation of Atlantic rifting. An Early Cretaceous cooling event at ca. 133 Ma appears consistent with rift‐related exhumation and thermal overprint on the Iberian margin. The (U‐Th)/He age peaks from ca. 80 Ma to ca. 68 Ma with decreasing depositional ages are interpreted to reflect the southward‐migrating thrust‐related exhumation on the pro‐wedge side of the Pyrenean orogen. The increase in lag times, from ca. 15 Ma in the Tremp Formation (ca. 65 Ma) to 28 Ma in the Escanilla Formation (ca. 40 Ma), suggests decreasing exhumation rates from 0.4 km Myr–1 to 0.2 km Myr–1. The apparent inconsistency with convergence rates is used to infer that rocks cooled at 68 Ma may have resided in the crust before final exhumation to the surface. Finally, the cooling event observed at 68 Ma provides support to the inferred acceleration of convergence, shortening and exhumation during Late Cretaceous times.  相似文献   

14.
Magallanes–Austral Basin (MAB) fill is preserved along a >1000 km north–south trending outcrop belt in the southern Patagonia region of Argentina and Chile. Although the stratigraphic evolution of the MAB has been well documented in the Chilean sector (referred to as the Magallanes Basin), its northern terminus in southern Argentina (Austral Basin) is poorly constrained. We present new stratigraphic and geochronologic analyses of the early basin fill (Aptian–Turonian) from the Argentine sector (49–51°S) of the MAB to document spatial variability in stratigraphy and timing of deposition during the initial stages of basin evolution. The initiation of the retroarc foreland basin fill is marked by the transition from mudstone to coarse‐clastic deposition, which is characterised by the consistent presence of sandstone beds > ca. 20 cm thick interpreted to represent sediment gravity flows deposited in a submarine fan system. Depositional environments within the early fill of the basin range from lower to upper deep‐water fan settings as well as previously undocumented slope deposits. These facies are present as far north as El Chalten, Argentina (ca. 49°S), indicating that facies‐equivalent rocks can be traced along‐strike for at least 5 degrees of latitude, based on correlation with strata as far south as the Cordillera Darwin (ca. 54°S). Eight new U‐Pb zircon ages from ash beds reveal an overall southward younging trend in the initiation of coarse clastic deposition. Inferred depositional ages range from ca. 115 ± 1.9 Ma in the northernmost study area to not older than 92 ± 1 Ma and 89 ± 1.5 Ma in the central and southern sectors respectively. The apparent diachronous delivery of coarse detritus into the basin may reflect (1) gradual southward progradation of a deep‐water fan system from a northerly point source and/or (2) orogen‐parallel variations in the timing and magnitude of thrust‐belt deformation and erosion that provided more local sources for sediment delivery.  相似文献   

15.
The details of how narrow, orogen‐parallel ocean basins are filled with sediment by large axial submarine channels is important to understand because these depositional systems commonly form in through‐like basins in various tectonic settings. The Magallanes foreland basin is an excellent location to study an orogen‐parallel deep‐marine system. Conglomerate lenses of the Upper Cretaceous Cerro Toro Formation have been previously interpreted to represent the fill of a single submarine channel (4–8 km wide, >100 km long) that funneled coarse detritus southward along the basin axis. This interpretation was based on lithologic correlations. New U/Pb dating of zircons from volcanic ashes and sandstones, coupled with strontium isotope stratigraphy, refine the controls on depositional ages and provenance. Results demonstrate that north‐south oriented conglomerate lenses are contemporaneous within error limits (ca. 84–82 Ma) supporting that they represent parts of an axial channel belt. Channel deposits 20 km west of the axial location are 87–82 Ma in age. These channels are partly contemporaneous with the ones within the axial channel belt, making it likely that they represent feeders to the axial channel system. The northern Cerro Toro Formation spans a Turonian to Campanian interval (ca. 90–82 Ma) whereas the formation top, 70 km to the south, is as young as ca. 76 Ma. Kolmogorov–Smirnoff statistical analysis on detrital zircon age distributions shows that the northern uppermost Cerro Toro Formation yields a statistically different age distribution than other samples from the same formation but shows no difference relative to the overlying Tres Pasos Formation. These results suggest the partly coeval deposition of both formations. Integration of previously acquired geochronologic and stratigraphic data with new data show a pronounced southward younging pattern in all four marine formations in the Magallanes Basin. Highly diachronous infilling may be an important depositional pattern for narrow, orogen‐parallel ocean basins.  相似文献   

16.
《Basin Research》2018,30(3):448-479
The onshore central Corinth rift contains a syn‐rift succession >3 km thick deposited in 5–15 km‐wide tilt blocks, all now inactive, uplifted and deeply incised. This part of the rift records upward deepening from fluviatile to lake‐margin conditions and finally to sub‐lacustrine turbidite channel and lobe complexes, and deep‐water lacustrine conditions (Lake Corinth) were established over most of the rift by 3.6 Ma. This succession represents the first of two phases of rift development – Rift 1 from 5.0–3.6 to 2.2–1.8 Ma and Rift 2 from 2.2–1.8 Ma to present. Rift 1 developed as a 30 km‐wide zone of distributed normal faulting. The lake was fed by four major N‐ to NE‐flowing antecedent drainages along the southern rift flank. These sourced an axial fluvial system, Gilbert fan deltas and deep lacustrine turbidite channel and lobe complexes. The onset of Rift 2 and abandonment of Rift 1 involved a 30 km northward shift in the locus of rifting. In the west, giant Gilbert deltas built into a deepening lake depocentre in the hanging wall of the newly developing southern border fault system. Footwall and regional uplift progressively destroyed Lake Corinth in the central and eastern parts of the rift, producing a staircase of deltaic and, following drainage reversal, shallow marine terraces descending from >1000 m to present‐day sea level. The growth, linkage and death of normal faults during the two phases of rifting are interpreted to reflect self‐organization and strain localization along co‐linear border faults. In the west, interaction with the Patras rift occurred along the major Patras dextral strike‐slip fault. This led to enhanced migration of fault activity, uplift and incision of some early Rift 2 fan deltas, and opening of the Rion Straits at ca. 400–600 ka. The landscape and stratigraphic evolution of the rift was strongly influenced by regional palaeotopographic variations and local antecedent drainage, both inherited from the Hellenide fold and thrust belt.  相似文献   

17.
《Basin Research》2018,30(1):75-96
The Xichang Basin in southeastern Tibet provides crucial information about formation and tectonic processes affecting the eastern Tibetan Plateau. To determine when and how the uplift developed, we conducted detailed studies of structures and obtained thermochronology data from the Xichang Basin and its periphery. The Xichang Basin is characterized by gentle deformation of the strata, segmented by an E‐vergent boundary thrust fault. Two stages of deformation, strike‐slip followed by an E‐W oriented shortening resulted in oblique shortening between the southeastern Tibetan Plateau and the Sichuan Basin. New apatite fission‐track data interpreted together with (U‐Th)/He data confirm a simple burial/heating and exhumation/cooling history across the Xichang Basin and its periphery. Subsidence and burial of the Xichang Basin peaked between 80–30 Ma, followed by mountain building with a protracted cooling starting at around 40–20 Ma, with rates of ca. 2.0–8.0 °C Myr−1 (i.e. 0.1–0.3 mm year−1). Our data indicate that the Xichang Basin has experienced ca. 2.5–5 km of exhumation, much more intensive than the ca. 1–2 km of exhumation inferred for the southwestern Sichuan Basin. Restored balanced cross‐sections of post‐Late‐Triassic strata along a ca. 250 km traverse indicate ca. 10–20% east‐west shortening strain (i.e. ca. 20–30 km) at the southeastern Tibetan Plateau during Cenozoic time. Study of crustal thickening and erosion supports a tectonic shortening mechanism to account for the uplift of the Xichang Basin on the southeastern Tibetan Plateau.  相似文献   

18.
《Basin Research》2018,30(Z1):568-595
The continental slopes of the South China Sea (SCS), the largest marginal sea on the continental shelf of Southeast Asia, are among the most significant shelf‐margin basins in the world because of their abundant petroleum resources and a developmental history related to sea floor spreading since Late Oligocene time. Based on integrated analyses of seismic, well‐logging and core data, we systematically document the sequence architecture and depositional evolution of the northern continental slope of the SCS and reveal its responses to tectonism, sea‐level change and sediment supply. The infill of this shelf‐margin basin can be divided into seven composite sequences (CS1–CS7) that are bounded by regional unconformities. Composite sequences CS3 to CS7 have formed since Late Oligocene time, and each of them generally reflects a regional transgressive–regressive cycle. These large cycles can be further divided into 20 sequences that are defined by local unconformities or transgressive–regressive boundaries. Depositional–geomorphological systems represented on the continental slope mainly include shelf‐edge deltas, prodelta‐slope fans, clinoforms of the shelf‐margin slope, unidirectionally migrating slope channels, incised slope valleys, muddy slope fans, slope slump‐debris‐flow complexes and large‐scale soft‐sediment deformation of bedding. Changing sea levels, reflected by evidence from sequence architecture in the study area, are generally comparable with those of the Haq (1987) global sea level curve, whereas the regional transgressions and regressions were apparently controlled by tectonic uplift and subsidence. Composite sequences CS3 and CS4 formed from Late Oligocene to Middle Miocene time and represent continental‐slope deposition during a time of northwest‐northeast seafloor spreading and subsequent development of sub‐basins in the southwest‐central SCS. The development of composite sequences CS5 to CS7 after Middle Miocene time was obviously influenced by the Dongsha Movement during convergence between the SCS and Philippine Sea plates. Climatic variations and monsoon intensification may have enhanced sediment supply during Late Oligocene‒Early Miocene (25–21 Ma) and Late Pliocene‒Pleistocene (3–0.8 Ma) times. This study indicates that shelf‐edge delta and associated slope fan systems are the most important oil/gas‐bearing reservoirs in the SCS continental‐slope area.  相似文献   

19.
Miocene strata in the southern Taranaki Basin (STB), up to 3 km thick, provide a distal record of erosion associated with plate boundary deformation in New Zealand. 2D and 3D seismic reflection data tied to drillhole stratigraphy have been used to constrain four main phases of basin development. These are: (a) Early Miocene (22–19 Ma) subsidence, dominantly bathyal water depths and deposition of minor submarine fans along the eastern basin margin. (b) Middle Miocene (19–14 Ma) widespread submarine fan deposition on a bathyal basin floor in the central STB. (c) Rapid Middle–Late Miocene (14–7 Ma) progradation of the shelf break northwards across the STB. (d) Widespread uplift and erosion of the STB during the latest Miocene–Pliocene (7–4.5 Ma). Bathyal water depths and fan deposition in the Early Miocene were influenced by vertical motions on major reverse faults and regional subsidence produced by subduction of the Pacific plate beneath northern New Zealand. Subsequent submarine fan deposition and northward shelf‐break progradation reflect increasing input of terrigenous material, primarily eroded from an uplifting region to the south of the STB. Sedimentation patterns in the STB are consistent with the age and locations of conglomerates deposited in onshore West Coast basins, related to this uplift and erosion. Sediment transport in the West Coast region was mainly parallel to NNE trending active reverse faults, and in the STB was perpendicular to the NE‐SW orientated shelf break, especially from ca. 14–7 Ma, when sedimentation rates exceeded fault‐displacement rates. Increases in sedimentation rates in the STB coincide with regional increases in the rates of shortening that appear to reflect plate boundary‐wide events and have been attributed to, or correlated with, increases in the plate convergence rate. Miocene sedimentation patterns in the STB thus reflect both intra‐basinal deformation and tectonic signals from the wider developing New Zealand plate boundary.  相似文献   

20.
The Adana Basin of southern Turkey, located at the SE margin of the Central Anatolian Plateau in the vicinity of the Arabia‐Eurasia collision zone, is ideally suited to record Neogene and Quaternary topographic and tectonic changes in the easternmost Mediterranean realm. On the basis of our correlation of 34 seismic reflection profiles with corresponding exposed units along the margins of the Adana Basin, we identify and characterize the seismic facies that corresponds to the upper part of the Messinian Handere Formation (ca. 5.45 to 5.33 Ma), which consists mainly of fluvial conglomerates and marls. The seismic reflection profiles indicate that ca. 1100 km3 of the Handere Formation upper sub‐unit is distributed over ca. 3000 km2, reflecting local sedimentation rates of up to 12.5 mm year?1. This indicates a major increase in both sediment supply and subsidence rates at ca. 5.45 Ma. Our provenance analysis of the Handere Formation upper sub‐unit based on clast counting and palaeocurrent measurements reveals that most of the sediment is derived from the Taurus Mountains at the SE margin of the Central Anatolian Plateau and regions farther north. A comparison of these results with the composition of recent fluvial conglomerates and the present‐day drainage basins indicates major changes between late Messinian and present‐day source areas. We suggest that these changes in drainage patterns and lithological characteristics result from uplift and ensuing erosion of the SE margin of the plateau. We interpret the tectonic evolution of the southern flank of the Anatolian Plateau and the coeval subsidence and sedimentation in the Adana Basin to be related to deep lithospheric processes, particularly lithospheric delamination and slab break‐off.  相似文献   

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