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1.
The 380 m thick fine-grained Vischkuil Formation comprises laterally extensive hemipelagic mudstones, separated by packages of graded sandstone and siltstone turbidites, and volcanic ash beds, and is an argillaceous precursor to a 1 km thick sand-prone basin floor fan to shelf succession. The Vischkuil Formation provides an insight into the process by which regional sand supply is initiated and for testing sequence stratigraphic principles in a basin plain setting. Regionally mapped 1–2 m thick hemipelagic mudstone units are interpreted as condensed drapes that represent the starved basin plain equivalents of transgressive systems tracts and maximum flooding surface on the coeval shelf (now removed during later uplift). The section above each mudstone drape comprises siltstone turbidites interpreted as highstand systems tract deposits and a surface of regional extent, marked by an abrupt grain size shift to fine sandstone. These surfaces are interpreted as sequence boundaries, related to abrupt increases in flow volume and delivery of sand grade material to the basin-plain. The interpreted lowstand systems tract comprises sandstone-dominated turbidites and is overlain by another hemipelagic mudstone drape. The upper Vischkuil Formation is marked by three 20–45 m thick debrites, with intraformational sandstone clasts up to 20 cm in diameter that can be mapped over 3000 km2. In each case, debrite emplacement resulted in widespread deformation of the immediately underlying 3–10 m of silty turbidites. A sequence boundary is interpreted at the base of each deformation/debrite package. Six depositional sequences are recognised and the interfered energy shift across each successive sequence boundary and LSTs include a larger volume of sandstone increases up section. The lower two sequences thin to the NW and show NW-directed palaeocurrents. The four overlying sequences show a polarity switch in palaeocurrent directions and thinning, to the E and SE. Sequence 6 is overlain sharply by the 300 m thick sandstone dominated Fan A of the Laingsburg Formation. The LST debrites may indicate gradual development of major routing conduits that subsequently fed Fan A. The polarity shift from westward flowing turbidity currents to an eastward prograding deepwater to shelf system represents establishment of a long term feeder system from the west. Sand supply to the Karoo basin floor was established in an incremental, stepwise manner. Given the early post-glacial setting in an icehouse climate, glacio-eustatic sea-level changes are considered to have been the main control on sequence development. 相似文献
2.
This work discusses the synsedimentary structural control affecting the turbidites of the Marnoso-arenacea Formation (MAF) deposited in an elongate, NW-stretched foredeep basin formed in front of the growing Northern Apennines orogenic wedge. The stratigraphic succession of the MAF (about 4000 m thick) records the progressive closure of the Apennine foredeep basin due to the NE propagation of thrust fronts. In this setting, Langhian to Serravallian turbidites are overlain by Tortonian mixed turbidite deposits, i.e. sandstone-rich low-efficiency turbidites. The high-resolution stratigraphic framework of basin-plain turbidites has made it possible to identify five informal stratigraphic units (I, II, III, IV, V) mainly on the basis of the structural control highlighted by: 1) the presence of topographic highs and relative depocentres detected through a progressive flattening approach, and 2) the presence of thrust-related mass-transport complexes and the progressive appearance and disappearance of five bed types (Types 1, 2, 3, 4, 5) considered important to understand the interaction between flow efficiency and basin morphology. By contrast, the upper part of the MAF succession (Tortonian in age) is formed by more sandstone-rich systems characterized by beds whose origin is likely to depend, at least in part, upon flow decelerations related to topographic confinement due to the progressive closure of the foredeep. The vertical and lateral distribution of these types of beds is, therefore, useful for the reconstruction of the morphological evolution of structurally controlled basins; in the MAF example, this is mainly due to the progressive narrowing of the foredeep caused by the propagation of the main thrust fronts toward the foreland. 相似文献
3.
In order to assess the controlling factors on the evolution of a shelf margin and the timing of sediment transfer to deep waters, a seismic stratigraphic investigation was carried out in the Eocene interval of northern Santos Basin, offshore Brazil. The studied succession configures a complex of prograding slope clinoforms formed in a passive margin and encompasses five seismic facies and their respective depositional settings: shelf-margin deltas/shorefaces, oblique slope clinoforms, sigmoidal slope clinoforms, continental to shelfal deposits and mass-transport deposits. These are stratigraphically arranged as seven depositional sequences recording a total shelf-edge progradation of about 35 km and a progradation rate of 1,75 km/My. Two main types of sequences can be recognized, the first one (type A) being dominated by oblique slope clinoforms and shelf-margin deltas/shorefaces in which shelf-edge trajectories were essentially flat to descending and extensive sandy turbidites were deposited on the foreset to bottomset zones. Sequences of this type are dominated by forced-regressive units deposited during extensive periods of relative sea-level fall. Type B comprises an upper part represented by aggradational shelfal deposits and a lower part composed of mass-transport deposits and high-relief sigmoidal clinoforms with descending shelf-edge trajectory. Steep slump scars deeply cut the shelfal strata and constitutes the boundary between the two intervals observed in type B sequences. Sandy turbidites occur at the same frequency in both forced- and normal-regressive units but are more voluminous within forced-regressive clinoforms associated with shelf-margin deltas/shorefaces. Major slope failures and mass-transport deposits, by the other hand, occurred exclusively in type B sequences during the onset of sea-level fall and their volume are directly related to the thickness of the shelfal sediments formed during the pre-failure normal regressions. 相似文献
4.
The sequence stratigraphic architecture of the Neogene section from the subsurface Nile Delta is resolved based on exceptionally well-preserved microfossils from the offshore NDOB-1 borehole. The architecture is configured on bathymetry variations and statistical parameters as deduced from the relative abundance of foraminiferal associations. The statistical parameters include ratios of planktic versus benthic foraminifera, and cluster and correspondence analysis of the twelve most commonly used benthic foraminiferal genera as proxies of water depths. The combination of cluster and correspondence analysis was employed to decipher the evolution and dynamics of the basin and the mechanisms that controlled the deposition of Neogene sequences in the Nile Delta region. Four basic environmental settings were recognized: 1.) a middle to outer neritic eutrophic setting, 2.) a middle to outer neritic mesotrophic setting, 3.) an outer neritic to upper bathyal mesotrophic setting and 4.) an upper bathyal mesotrophic setting.Eight stratigraphic sequences were identified in the Neogene Nile Delta section. Three sequence in the Miocene (MSeq1, MSeq2 and MSeq3), three in the Pliocene (PSeq1, PSeq2 and PSeq3) and two in the Pleistocene (PtSeq1 and PtSeq2). These sequences are systematically measured and described in terms of time, space and water bathymetry. The sequence boundaries and flooding surfaces were dated using high-resolution microfossil biochronology and stratigraphic index markers. Individual sequences and boundaries were correlated with international and local sequence stratigraphic models. The new sequence stratigraphic model established here provides age calibrated surfaces for inter-basinal correlations and opens new avenues for hydrocarbon reservoir exploration. 相似文献
5.
The post-Calabrian sedimentary column of the northwestern Alboran Sea comprises three depositional sequences. The two older depositional sequences are defined by lowstand systems tracts (shelf-margin deltas, slope, base-of-slope, and basin deposits, and the Guadiaro channel-levee complex). In contrast, the most recent depositional sequence also includes transgressive (relict shelf facies) and high-stand (the Guadalmedina-Guadalhorce prodelta and hemipelagic facies) systems tracts. The stratigraphic architecture of these depositional sequences is controlled by the synchronism between high frequency sea-level changes, variations in sediment supply, and sedimentary processes. The configuration of the depositional sequences is variable and their distribution is complex, as a result of the relative importance played by sea-level changes and tectonism through the area.
The sequence boundaries are represented by polygenetic surfaces in the proximal margin, and by monogenetic surfaces in the distal margin and basin. Each polygenetic surface results from the interaction between the sequence boundary with the lowstand erosional truncation surface and the transgressive surface, both developed during the previous sea-level cycle. The monogenetic surfaces correspond to unconformities and their correlative conformities, formed during sea-level lowstands. This pattern of depositional sequences developed in the margin and basin of the northwestern Alboran Sea shows differences with the Exxon Sequence Stratigraphy Model as traditionally applied: sea-level change control is essentially recognized through lowstand systems tracts, and sequence boundary coincides with lowstand erosional truncation surface and transgressive surface, both developed during the previous sea-level cycle. 相似文献
6.
Cyclic sequences occur worldwide in nearly every stratigraphic sequence; they are particularly well developed in marine deposits
associated with large river systems. Superimposed on those cycles attributed to shifting sites of deposition are those related
to high-frequency sea level changes. The large data base for this study (including 471 deep foundation borings, thousands
of line kilometers of high-resolution seismic, and sedimentological and dating analyses) represents the most complete information
on high-resolution chronostratigraphy and lithostratigraphy that is available on any modern continental shelf/upper slope.
These data are used to document sedimentological characteristics and spatial depositional patterns during three complete sea
level cycles over the entire continental shelf/upper slope of offshore Louisiana.
Sedimentation during periods of high sea level is characterized by: 1) thin, slowly accumulated depositional sequences, referred
to as condensed sections, 2) calcareous-rich deposits, including hemipelagic sediments and shell hashes, and 3) wide lateral
continuity. Sedimentation during periods of low sea level is characterized by; 1) variable-thickness, rapidly accumulated
sequences referred to as expanded sections, 2) coarse-grained elastic deposits, including abundant sands and gravels, and
3) well-defined depositional trends.
Even though the data set covers only a short period of geologic time (240 000 yrs), these high frequency events are responsible
for the deposition of excellent reservoir-quality facies in well-defined and predictable trends. 相似文献
7.
The paper deals with original stratigraphic, petrographic and structural data concerning the evolution of the southern Apennines chain (Italy). The main Langhian to Pliocene deposits cropping out in the northern sector of the southern Apennines foreland basin system (Sannio-Irpinia area) have been studied and correlated in order to document the effects of tectonic changes on the evolution of sandstone detrital modes and stratigraphic architecture. The studied sandstone units can be grouped in five key intervals: a) Numidian Flysch, mostly formed by Langhian mature quartzarenitic deposits and conformable Serravallian post-Numidian successions, formed by arkosic and calciclastic arenaceous-pelitic beds (foreland depozones); b) Langhian to Tortonian San Giorgio Fm., mostly composed of quartzofeldspatic sandstones (foredeep depozone); c) Tortonian to Early Messinian, quartz-feldspatic and partly sedimentary-carbonatoclastic petrofacies, thrust-top successions (Vallone Ponticello, Villanova del Battista and San Bartolomeo fms.); d) Late Messinian quartzolithic to quartzofeldspatic sandstones (Torrente Fiumarella, Anzano Molasse and Tufo-Altavilla unit), which can be referred to infilled thrust-top basins; e) unconformity-bounded Pliocene quartzofeldspatic sandstone strata (wedge-top depozones), characterized by synsedimentary tectonic activity.Detrital modes of the Serravallian through Middle Pliocene sandstones of the southern Apennines foreland basin system testify clear provenance relations from the accreted terranes forming the southern Apennine thrust-belt. The studied clastics show almost the same blended (quartz-feldspatic) composition; this condition could be related to the tectonic transport over thrust ramp of source rocks, as suggested by the tectonic evolutionary model. This study, dealing with sedimentary provenance analysis and tectonostratigraphic evolution, provides an example of the close relations between clastic compositions and foreland basin system development in southern Apennines. 相似文献
8.
S.S. Flint D.M. HodgsonA.R. Sprague R.L. BruntW.C. Van der Merwe J. FigueiredoA. Prélat D. BoxC. Di Celma J.P. Kavanagh 《Marine and Petroleum Geology》2011,28(3):658-674
The Laingsburg depocentre of the SW Karoo Basin, South Africa preserves a well-exposed 1200 m thick succession of upper Permian strata that record the early filling of a basin during an icehouse climate. Uniformly fine-grained sandstones were derived from far-field granitic sources, possibly in Patagonia, although the coeval staging and delivery systems are not preserved. Early condensed shallow marine deposits are overlain by distal basin plain siltstone-prone turbidites and volcanic ashes. An order of magnitude increase in siliciclastic input to the basin plain is represented by up to 270 m of siltstone with thin sandstone turbidites (Vischkuil Formation). The upper Vischkuil Formation comprises three depositional sequences, each bounded by a regionally developed zone of soft sediment deformation and associated 20-45 m thick debrite that represent the initiation of a major sand delivery system. The overlying 300 m thick sandy basin-floor fan system (Unit A) is divisible into three composite sequences arranged in a progradational-aggradational-retrogradational stacking pattern, followed by up to 40 m of basin-wide hemipelagic claystone. This claystone contains Interfan A/B, a distributive lobe system that lies 10 m beneath Unit B, a sandstone-dominated succession that averages 150 m thickness and is interpreted to represent a toe of slope channelized lobe system. Unit B and the A/B interfan together comprise 4 depositional sequences in a composite sequence with an overall basinward-stepping stacking pattern, overlain by 30 m of hemipelagic claystone. The overlying 400 m thick submarine slope succession (Fort Brown Formation) is characterized by 10-120 m thick sand-prone to heterolithic packages separated by 30-70 m thick claystone units. On the largest scale the slope stratigraphy is defined by two major cycles interpreted as composite sequence sets. The lower cycle comprises lithostratigraphic Units B/C, C and D while the upper cycle includes lithostratigraphic Units D/E, E and F. In each case a sandy basal composite sequence is represented by an intraslope lobe (Units B/C and D/E respectively). The second composite sequence in each cycle (Units C and E respectively) is characterized by slope channel-levee systems with distributive lobes 20-30 km down dip. The uppermost composite sequence in each cycle (Units D and F respectively) are characterised by deeply entrenched slope valley systems. Most composite sequences comprise three sequences separated by thin (<5 m thick) claystones. Architectural style is similar at individual sequence scale for comparable positions within each composite sequence set and each composite sequence. The main control on stratigraphic development is interpreted as late icehouse glacio-eustasy but along-strike changes associated with changing shelf edge delivery systems and variable bathymetry due to differential substrate compaction complicate the resultant stratigraphy. 相似文献
9.
Aggeliki Georgiopoulou Russell B. Wynn Douglas G. Masson Michael Frenz 《Marine and Petroleum Geology》2009,26(10):2021-2031
The northwest African margin has been affected by numerous large-scale landslides during the late Quaternary. This study focuses on a recent collapse of the Sahara Slide headwall and characterises the resulting flow deposit. Core and seismic data from the base of the upper headwall reveal the presence of blocky slide debris, comprising heavily deformed hemipelagic slope sediments. The blocky slide debris spilled over a lower headwall 60 km downslope and formed a thick transparent debris flow unit. Cores recovered 200–250 km farther downslope contain a surficial turbidite that is interpreted to be linked to the headwall collapse event based on timing and composition. One core located approximately 200 km from the headwall scar (C13) contains debrite encased in turbidite. The debrite comprises sheared and contorted hemipelagic mudstone clasts similar as those seen in the vicinity of the Sahara Slide headwall, and lacks matrix. This debrite pinches out laterally within 25 km of C13, whereas the accompanying turbidite can be correlated across 700 km of the northwest African margin. The linked turbidite–debrite bed is interpreted to have formed through recent failure of the steep Sahara Slide headwall that either 1) generated both a debris flow and a turbidity current almost simultaneously, or 2) generated a debris flow which with entrainment of water and progressive dilution led to formation of an accompanying turbidity current. 相似文献
10.
The Neogene and Quaternary sediments of the Faeroe-Shetland Channel and West Shetland shelf and slope rest upon a major regional unconformity, the Latest Oligocene Unconformity (LOU), and have been deposited through the interaction of downslope and parallel-to-slope depositional processes. The upper to middle continental slope is dominated by mass-transport deposits (debris flows), which progressively diminish downslope, and were largely generated and deposited during glacial cycles when ice sheets supplied large quantities of terrigeneous sediment to the upper slope and icebergs scoured sea-floor sediments on the outer shelf and uppermost slope. Large-scale sediment failures have also occurred on the upper slope and resulted in deposition of thick, regionally extensive mass-transport deposits on portions of the lower slope and channel floor. In contrast, large fields of migrating sediment waves and drift deposits dominate most of the middle to lower slope below 700 m water depth and represent deposition by strong contour currents of the various water masses moving northeastward and southwestward through the channel. These migrating sediment waves indicate strong northeastward current flow at water depths shallower than 700 m and strong southwestward current flow at water depths from 700 to >1,400 m. These flow directions are consistent with present-day water-mass flow through the Faeroe-Shetland Channel. The Faeroe-Shetland Channel floor is underlain by thin conformable sediments that appear to be predominantly glacial marine and hemipelagic with less common turbidites and debris flows. No evidence is observed in seismic or core data that indicates strong contour-current erosion or redistribution of sediments along the channel floor. 相似文献
11.
The siliciclastic Gadvan Formation from Abadan Plain, southwestern Iran, is highly bioturbated and allows relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high-resolution sequence stratigraphic framework. Relying on the sedimentary and ichnological characteristics, the siliciclastic succession is divided into two facies associations: a wave-dominated offshore-shoreface complex and a tide-river influenced delta. The first includes facies that have been deposited in shelf-offshore, upper offshore, lower shoreface and upper/middle shoreface environments, the latter includes facies that have been deposited in prodelta and delta front. Integrated ichnologic and sedimentologic studies of the Gadvan Formation, allow distinction between prodelta and delta front and open marine deposits. With the identification of maximum flooding and ravinement surfaces as bounding surfaces of the stratal units, detailed analysis on systematic changes in the stacking pattern (cycle thickness, cycle type, and facies proportion) are made. Eight ichnocoenoses could be differentiated in the studied sections. The positions of the ichnocoenoses within genetically related stratal units (genetically related ichnocoenoses), indicate three large-scale cycles (DS1 to DS3, from oldest to youngest). The cyclical nature of the Gadvan Formation is attributed to low-amplitude eustasy in greenhouse conditions formed under interaction of eustatic high-frequency cycles and longer term tectonically driven sea-level variations during the long-term transgressive sea-level trend of the early Cretaceous. Stratigraphic architectural style of sequences DS1 to DS3 (which includes scarce evidence of lowstand deposits, partial or total truncation of the HST, and predominance of thick transgressive deposits), is remarkably similar to long-term transgressive sea-level trend of the Early Cretaceous across the Arabian Plate. This study suggests a more relatively seaward position of the siliciclastic successions of the Gadvan Formation of Abadan Plain than the Mesopotamian Basin (upper Zubair Formation equivalent in western Iraq and Kuwait), which would be concordant with the prevailing view of an easterly prograding coastline across the Arabian Plate.This study reveals important sedimentological and ichnological features and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical significance of trace fossil assemblages that can be readily compared or translated to analogous depositional systems worldwide. The ichnological analysis is based on cores and can be especially applied to evaluate the applicability of current ichnological models to the study of Cretaceous reservoirs of western Iraq, Kuwait and western Saudi Arabia. 相似文献
12.
济阳坳陷博兴洼陷西部沙三段层序地层 总被引：1，自引：0，他引：1
选取以基准面为参照面的高分辨率层序地层学的理论与分析技术,对博兴洼陷西部沙三段开展层序地层分析工作。在博兴洼陷沙三段识别出5个层序界面和4个较大规模的洪泛面,由此将研究层段划分为4个长期基准面旋回(相当于3级层序),并通过长期旋回内部次级转换面的识别,细分出8个中期旋回(大致相当于4级层序)。通过对比建立了研究区的高分辨率层序地层格架,并分析了各层序的地层发育特征。以层序格架为基础,探讨了研究区各层序的沉积演化特征,建立了辫状三角洲—浊积扇层序发育模式,认为研究区辫状三角洲和浊积扇均具有加积作用特点;斜坡区为辫状三角洲发育区,而洼陷区为浊积扇发育区;中期基准面旋回下降期辫状三角洲发育,上升期浊积扇发育;浊积扇体的发育规模与湖泛规模相关。综合分析认为,浊积扇是形成岩性圈闭的主要储集砂体类型,其发育的有利层位是MSC8、MSC7、MSC6、MSC5旋回的上升半旋回,岩性圈闭发育的有利区是博兴南部斜坡坡折带之下的洼陷区。 相似文献
13.
The Plio-Pleistocene stratigraphic record of the Peri-Adriatic basin (eastern central Italy) is well exposed along the uplifted western margin of the basin and consists of a series of coarse-grained slope canyon fills encased in a thick succession of hemipelagic mudstones. This study deals with the detailed sedimentology, stratal architecture, and sequence-stratigraphic interpretation of two of these submarine canyon-fills (namely CMC1 and CMC2) exposed at Colle Montarone. These strata contain widespread evidence of gravity-driven sedimentation processes, with high- and low-density turbidity currents, slumps and cohesive debris flows being responsible for most of the sediment transport and deposition. Beds are organised into four recurrent lithofacies, each corresponding to a specific deep-water depositional element: (i) clast-supported conglomerates (channel complexes); (ii) thin-bedded sandstones and mudstones (levee-overbank); (iii) very thinly-bedded mudstones (tributary channels); (iv) pebbly mudstones and chaotically bedded mudstones (mass-transport complexes). 相似文献
14.
Christopher A.-L. Jackson A. Adli Zakaria Howard D. Johnson Felix Tongkul Paul D. Crevello 《Marine and Petroleum Geology》2009,26(10):1957
The West Crocker Formation (Oligocene–Early Miocene), NW Borneo, consists of a large (>20 000 km2) submarine fan deposited as part of an accretionary complex. A range of gravity-flow deposits are observed, the most significant of which are mud-poor, massive sandstones interpreted as turbidites and clast-rich, muddy sandstones and sandy mudstones interpreted as debrites. An upward transition from turbidite to debrite is commonly observed, with the contact being either gradational and planar, or sharp and highly erosive. Based on their repeated vertical relationship and the nature of the contact between them, these intervals are interpreted as being deposited from one flow event which consisted of two distinct flow phases: fully turbulent turbidity current and weakly turbulent to laminar debris flow. The associated bed is called a co-genetic turbidite–debrite, with the upper debrite interval termed a linked debrite. Linked debrites are best developed in the non-channellised parts of the fan system, and are absent to poorly-developed in the proximal channel-levee and distal basin floor environments. Due to outcrop limitations, the genesis of linked debrites within the West Crocker Formation is unclear. Based on clast size and type, it seems likely that a weakly turbulent to laminar debris-flow flow phase was present when the flow event entered the basin. A change in flow behaviour may have led to deposition of a sand-rich unit with ‘turbidite’ characteristics, which was subsequently overlain by a mud-rich unit with ‘debrite’ characteristics. Flow transformation may have been enhanced by the disintegration and incorporation into the flow of muddy clasts derived from the upstream channel floor, channel mouth or from channel-levee collapse. Lack of preservation of this debrite in proximal areas may indicate either bypass of this flow phase or that the available outcrops fail to capture the debris flow entry point. Establishing robust sedimentological criteria from a variety of datasets may lead to the increasing recognition of co-genetic turbidite-debrite beds, and an increased appreciation of the importance of bipartite flows in the transport and deposition of sediments in deepwater environments. 相似文献
15.
Turbidites deposited on Southern Central Chilean seamounts: Evidence for energetic turbidity currents 总被引：2，自引：0，他引：2
Gravity cores obtained from isolated seamounts located within, and rising up to 300 m from the sediment-filled Peru–Chile Trench off Southern Central Chile (36°S–39°S) contain numerous turbidite layers which are much coarser than the hemipelagic background sedimentation. The mineralogical composition of some of the beds indicates a mixed origin from various source terrains while the faunal assemblage of benthic foraminifera in one of the turbidite layers shows a mixed origin from upper shelfal to middle-lower bathyal depths which could indicate a multi-source origin and therefore indicate an earthquake triggering of the causing turbidity currents. The bathymetric setting and the grain size distribution of the sampled layers, together with swath echosounder and sediment echosounder data which monitor the distribution of turbidites on the elevated Nazca Plate allow some estimates on the flow direction, flow velocity and height of the causing turbidity currents. We discuss two alternative models of deposition, both of which imply high (175–450 m) turbidity currents and we suggest a channelized transport process as the general mode of turbidite deposition. Whether these turbidites are suspension fallout products of thick turbiditic flows or bedload deposits from sheet-like turbidity currents overwhelming elevated structures cannot be decided upon using our sedimentological data, but the specific morphology of the seamounts rather argues for the first option. Oxygen isotope stratigraphy of one of the cores indicates that the turbiditic sequences were deposited during the last Glacial period and during the following transition period and turbiditic deposition stopped during the Holocene. This climatic coupling seems to be dominant, while the occurrence of megathrust earthquakes provides a trigger mechanism. This seismic triggering takes effect only during times of very high sediment supply to the shelf and slope. 相似文献
16.
《Marine Geology》1999,153(1-4):147-160
Magnetostratigraphic and biostratigraphic results are presented from Neogene deposits in the Taza–Guercif Basin, located at the southern margin of the Rifian Corridor in Morocco. This corridor was the main marine passageway which connected the Mediterranean with the Atlantic during Messinian times. Correlation of the biostratigraphy and polarity sequence of the Taza–Guercif composite section to the astronomical time scale, allows an accurate dating of three subsequent events in the Rifian Corridor. (1) The oldest marine sediments marking the opening of the Rifian Corridor were deposited at 8 Ma. At this age, a deep (600 m) marine basin developed in the Taza–Guercif area, marked by deposition of precession-controlled turbidite–marl cycles. (2) Paleodepth reconstructions indicate that a rapid (5 m/ka) shallowing of the marine corridor took place at the Tortonian/Messinian boundary, at an age of 7.2 Ma. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. (3) The Taza–Guercif Basin was emergent at an age of 6.0 Ma and, subsequently, continental sedimentation continued well into the Early Pliocene. We suggest that shallowing and restricting the marine passageway through the Rifian Corridor actually initiated the Messinian salinity crisis, well before the deposition of the Messinian evaporites in the Mediterranean. 相似文献
17.
《Marine and Petroleum Geology》2003,20(6-8):587-600
A regional study of the Veracruz Basin provided an excellent view of long-term deepwater sedimentation patterns from an evolving foreland-type basin. The regional seismic and well-log data set allows for an accurate reconstruction of slope and basin-floor depositional patterns, lithologic compositions, and paleogradients from a continuous succession of bathyal strata that span the Miocene to the lower Pliocene. Variations in Miocene and Pliocene deepwater reservoirs can be linked to prevailing slope characteristics. The Miocene basin had a high-gradient, tectonically generated slope, and the Pliocene basin had a low-gradient constructional slope. The Miocene basin owes its steep margin to the tectonic stacking of early Tertiary, Laramide-age thrust sheets. The Miocene margin shed a mixture of coarse elastic sediments (sands, gravels, and cobbles) and fines (silts and clays) that were transported into the deep basin via turbidity currents and debris flows. Channelized deposits dominate the Miocene slope, and reservoirs occur in long-lasting basement-confined canyons and shorter-lived shallower erosional gulleys. Thick and areally-extensive basin-floor fans exist outboard of the strongly channelized Miocene slope. Fan distribution is strongly controlled by synsedimentary contractional anticlines and synclines. In contrast, the latest Miocene to early Pliocene basin development was dominated by a strongly prograding wedge of shelf and slope deposits that was induced by volcanogenic uplift and increased sediment supply. During this phase, turbidite reservoirs are limited to narrow and sinuous deepwater channels that reside at the toe of the constructional clinoforms and areally limited, thinner basinal fans. 相似文献
18.
M. Felix S. Leszczy&#x;ski A.
l&#x;czka A. Uchman L. Amy J. Peakall 《Marine and Petroleum Geology》2009,26(10):2011-2020
Various transformation mechanisms can generate turbidity currents from subaqueous debris flows. Different transformation mechanisms have been described and interpreted in the past from laboratory experiments and from deposits, but the two approaches have not generally been linked. This has made the genetic interpretation and comparison of deposits difficult. In this paper a generic classification scheme of debrite–turbidite couplets is proposed based on transformation mechanisms inferred from laboratory experiments. Five different flow types (called A–E herein) and their resulting deposits are detailed, but they are all part of a continuous spectrum, and a mixture of types is likely to be found in the field. Type A flows are strong, dense debris flows that undergo little transformation. Their deposit will be a debrite overlain by a thin turbidite, which is separated from it by a clear grain size break. Type B flows are weaker and can develop waves at the debris flow-turbidity current interface. The deposit will be a debrite with a wavy top overlain by a turbidite that is thicker than for type A flows. For type C flows, the interfacial waves will grow so much that the debris flow disintegrates into separate parts. The deposit will consist of debrite lenses encased in a turbidite. Type D flows will undergo even more mixing than type C flows so that the debrite parts will be mixed. Their deposit will be a turbidite with laterally varying areas of debrite characteristics near the bed. Type E flows will be so transformed that the debris flow character has disappeared and the flow is a turbidity current with high sediment concentration. The deposit will be largely turbiditic. The flow types and deposits will be illustrated with some examples from two field areas: the Polish Carpathians and the French Maritime Alps. 相似文献
19.
《Marine and Petroleum Geology》2003,20(6-8):733-755
The marine fill of ancient foreland basins is primarily recorded by depositional systems consisting of facies and facies associations deposited by a variety of sediment gravity flows in shallow-marine, slope and basinal settings. Tectonism and climate were apparently the main factors controlling the sediment supply, accommodation and depositional style of these systems. In marginal deltaic systems, sedimentation is dominated by flood-generated hyperpycnal flows that build up impressive accumulations of graded sandstone beds in front of relatively small high-gradient fan-deltas and river deltas. During periods of tectonically forced lowstands of sealevel, these systems may commonly shift basinward to shelfal and slope regions. Instability along the edges of these lowstand deltas and sand-laden hyperpycnal flows generate immature and coarse-grained turbidite systems commonly confined within structural depressions and generally encased in distal delta-front and prodeltaic deposits. Because of the close vertical and lateral stratigraphic relations between deltaic and turbidite-like facies, these marginal systems are herein termed ‘mixed depositional systems’. They are very common in the fill of foreland basins and represent the natural link between deltaic and basinal turbidite sedimentation.Basinal turbidite systems form in deeper water elongate highly subsiding troughs (foredeeps) that developed in front of advancing thrust systems. The impressive volumes of sheet-sandstones that form the fill of these troughs suggest that basinal turbidite systems are likely to form following periods of dramatic tectonic uplift of adjacent orogenic wedges and related high-amplitude tectonically-forced sealevel lowstands. In such deep basinal settings, sediment flux to the sea is dramatically increased by newly formed sediment in fluvial drainage basins and the subaerial and submarine erosion of falling-sealevel deltaic deposits generated during the uplift. Turbidity currents are very likely to be mainly triggered by floods, via hyperpycnal flows and related sediment failures, but can fully develop only in large-scale erosional conduits after a phase of catastrophic acceleration and ensuing bulking produced by bed erosion. This process leads to deepening and widening of the conduits and the formation of large-volume highly efficient bipartite currents whose energy dissipation is substantially reduced by the narrow and elongate basin geometry. These currents can thus carry their sediment load over considerable distances down the basin axis. 相似文献
20.
The Quaternary sections of the Nile Cone in the eastern Mediterranean are formed by regionally extensive repetitions of sediment sequences (cyclothems s.l.) showing a successive, orderly arrangement of sediment types. Detailed lithofacies analysis reveals the recurrence of three basic terms in many cores: a basal olive-gray hemipelagic mud and turbidite sequence; a middle sapropel sequence; and an upper yellowish-orange hemipelagic sequence, including calcareous ooze, and a turbiditic sequence. This cyclic sedimentation closely reflects the Quaternary dynamics. The development of the Nile submarine fan in an enclosed, silled basin has resulted in a particularly close relation between biogenic-terrigenous depositional patterns and climatic and oceanographic factors affecting the Mediterranean. 相似文献