Integration of High and Very High-resolution Seismic Reflection Profiles to Study Upper Quaternary Deposits of a Coastal Area in the Western Gulf of Lions, SW France

High resolution (HR – sparker) and very high resolution (VHR – boomer) seismic reflection data acquired in shallow water environments of the Roussillon coastal area are integrated to provide an accurate image of the stratigraphic architecture of the Quaternary deposits. The complementary use of the two systems is shown to be of benefit for studies of shallow water environments. The HR sparker data improved the landward part of a general model of Quaternary stratigraphy previously established offshore. They document an incised valley complex interpreted as the record of successive late Quaternary relative sea-level cycles. The complex is capped by a polygenetic erosional surface developed during the last glacial period (>18 ky) and variably reworked by wave ravinement during the subsequent post-glacial transgression. The overlying transgressive systems tract is partly preserved and presents a varying configuration along the Roussillon coastal plain. The VHR boomer data provide information on the architecture of the uppermost deposits, both in the near-shore area and in the lagoon. These deposits overlie a maximum flooding surface at the top of the transgressive systems tract and constitute a highstand systems tract composed of two different architectural elements. In the near-shore area, a sandy coastal wedge is subdivided into a lower unit and an upper unit in equilibrium with present day dynamics. In the Salses-Leucate lagoon area, the sedimentary architecture is highly complex due to the closure of a former embayment and the formation of the present beach barrier.     

Seismic and sequence stratigraphy of the central western continental margin of India: late-Quaternary evolution

Seismic and sequence stratigraphic architecture of the central western continental margin of India (between Coondapur and south of Mangalore) has been investigated with shallow seismic data. Seismic stratigraphic analysis defined nine seismic units, that are configured in a major type-1 depositional sequence possibly related to fourth-order eustatic sea-level changes, comprising regressive, lowstand, transgressive and highstand systems tracts. The late-Quaternary evolution of the continental margin took place under the influence of an asymmetric relative fourth-order sea-level cycle punctuated by higher frequency cycles. These cycles of minor order were characterised by rapid sea-level rises and gradual sea-level falls that generated depositional sequences spanning different time scales. During the regressive periods, dipping strata were developed, while erosional surfaces and incised valleys were formed during the lowstands of sea level. Terraces, v-shaped depressions, lagoon-like structures observed on the outer continental shelf are the result of the transgressive period. In the study area we have recognised a complex erosional surface that records a long time span during the relative sea-level fall (regressive period) and the following sea-level lowstand and has been reworked during the last transgression. We also infer that sedimentation processes changed from siliciclastic sedimentation to carbonate sedimentation and again to siliciclastic sedimentation, marking an important phase in the late-Quaternary evolution of the western continental shelf of India. We attribute this to an abrupt climate change at the end of the oxygen isotope stage 2, between the Last Glacial Maximum and the Bølling-Allerod event (14?000 yr BP). This sensitive climate change (warming) favoured the formation of reefs at various depths on the shelf, besides the development of Fifty Fathom Flat, a carbonate platform on the outer shelf off Bombay developed prior to 8300 yr BP. The highstand systems tracts were deposited after the sea level reached its present position.     

Stratigraphic framework of gas accumulations in the Ría de Pontevedra (NW Spain)

Knowledge of marine geological environments in which shallow gas is accumulating is becoming increasingly important in global studies of climate change because a measurable proportion of the total methane source comes from continental margins. Previous studies have revealed that coastal environments represent important geological environments where microbial methane is being generated, is accumulating, and is being released. In the Ría de Pontevedra, at least 4.5 km² of seafloor in the innermost part of the ría is underlain by sediments containing natural gas. Seismic interpretation contributes new findings for the definition of periods and geological environments in which the gas could have been generated, and is accumulating and released in the Ría de Pontevedra. Groundtruthing the seismic data (facies, environments) makes it possible to identify favourable geological environments for gas generation in the sedimentary infill of the Ría de Pontevedra. Sequence stratigraphy based on high-resolution seismic profiles and post-Last Glacial Maximum sea-level records makes it possible to establish the stratigraphic architecture of the ría and to define the periods in which gas could have been generated. The results of this study show that the sedimentary infill is composed of a fifth-order sequence developed since the Last Glacial Maximum. Within this sequence, gas appears to have accumulated in the Holocene deposits associated with the latest transgressive and highstand system tracts. Seismic analysis shows that gas could have been generated in different geological environments in the Ría de Pontevedra. If coastal environments at times of lower sea level were similar to those of the present, organic-rich mud deposits (deposited mainly in lakes, estuaries and floodplains) could have survived transgression and remained buried as potential gas sources in the inner part of the ría.     

The application of geostatistical inversion in shale lithofacies prediction: a case study of the Lower Silurian Longmaxi marine shale in Fuling area in the southeast Sichuan Basin,China

Based on cores, well logs and seismic data, we established the isochronous sequence stratigraphic framework of the Lower Silurian Longmaxi Formation and predicted the shale lithofacies distribution within the sequence stratigraphic framework using geostatistical inversion. The results of our study show that the Lower Member of the Longmaxi Formation is a third order sequence that includes a transgressive systems tract (TST), an early highstand systems tract (EHST) and a late highstand systems tract (LHST). Four lithofacies units have been recognized, specifically siliceous shale, argillaceous shale, calcareous shale and mixed shale. The results of geostatistical inversion reveal that the TST is characterized by flaky siliceous shale and some sparsely distributed calcareous shale. The EHST is dominated by mixed shale with minor amounts of siliceous shale, which occurs in only a small area. Moreover, in the LHST, argillaceous shale occupies almost the entire study region. Comparing to traditional geological research with geophysical research, the vertical resolution of the predictive results of geostatistical inversion could reach 1–2 m. Geostatistical inversion effectively solves the problem of precisely identifying the lithofacies in the Fuling shale gas field and predicting their spatial distribution. This successful study showcases the potential of this method for carrying out marine shale lithofacies prediction in China and other locations with similar geological backgrounds.     

Holocene stratigraphy and depositional architecture of eastern Pozzuoli Bay (eastern Tyrrhenian Sea margin,Italy): the influence of tectonics and wave-induced currents

Pozzuoli Bay is located in the eastern Tyrrhenian Sea and is an area characterized by active tectonics and volcanism. On the basis of high-resolution seismic reflection profiles, it was possible to reconstruct the stratigraphy and three-dimensional stratal architecture of the Holocene succession. Two volcanic units and three sedimentary ones were recognized. The basal unit NC consists of volcanic deposits and dates at 10.0-8.0 ka B.P. It is followed by unit D, deposited between 8.0 and 5.5 ka B.P., which displays a backstepping configuration in the central area and a forestepping configuration in the northern area. Unit D is covered by the progradational unit B which is elongated in a SE-NW direction. Unit C is interbedded between unit B and is interpreted as the volcanic products of the Agnano-Monte Spina eruption which occurred 4.4 B.P. Unit A, the youngest unit, shows a progradational configuration and is elongated in a E-W direction. The sedimentary units record the transgressive and highstand of the eustatic sea level. They show vertical and lateral variations in the depositional architecture. Changes in the stacking pattern record variations in tectonic subsidence and hydrodynamic regimes.     

辽东湾晚第四纪层序地层

通过对辽东湾高分辨率浅地层剖面声学地层与典型钻孔沉积地层的对比分析,揭示了研究区晚第四纪MIS5以来的地层层序。辽东湾高分辨率浅地层剖面自下而上划定的6个声学地层单元(SU5、SU4、SU3、SU2、SU12、SU11)与钻孔岩芯划分的6个沉积地层单元(DU5、DU4、DU3、DU2、DU12、DU11)具有良好的对应关系。分别与MIS4期、MIS2期低海面时期的沉积间断密切相关的两个层序界面R5、R3,将辽东湾识别出的地层单元自下而上划分为3个层序(SQ3、SQ2、SQ1)。其中SQ3仅识别出上部的海侵体系域与高水位体系域,对应MIS5期海平面相对较高时期的滨浅海相沉积(DU5);SQ2自下而上由低水位体系域(MIS4期的河流相与河道充填相沉积(DU4))与海侵体系域(MIS3期早中期滨海相沉积(DU3))组成;SQ1自下而上包括低水位体系域(MIS2期的河流相与河道充填相沉积(DU2))、海侵体系域(全新世早中期滨海相沉积(DU12))高水位体系域(全新世高海面以来的浅海相沉积(DU11))。研究区的海侵体系域厚度较薄且变化较小,分布广泛,而低水位体系域厚度与横向分布均变化较大。     

Late Quaternary evolution of the Çanakkale Strait region (Dardanelles, NW Turkey): implications of a major erosional event for the postglacial Mediterranean-Marmara Sea connection

Seismic and bathymetric data from the Çanakkale Strait and its extensions onto the shelves of the Marmara and Aegean seas indicate that the strait was formed mainly by an erosional event. Four seismic units are observed on seismic profiles. The lower two of these (units 4 and 3) constitute the basement of a regionally widespread erosional unconformity (ravinement), which developed during marine isotope stage 2 (MIS 2). The two upper units (units 2 and 1), which overlie the ravinement surface, form a higher-order sequence. Sequence stratigraphic analysis indicates that units 2 and 1 deposited as lowstand and highstand systems tracts respectively, since the end of MIS 2. The transgressive systems tract is represented by a major erosional event which occurred throughout the Çanakkale sill area when the Mediterranean-Marmara Sea connection and, hence, the Çanakkale Strait was formed. The existence of the erosive ?arköy Canyon along the shelf edge of the southern Marmara Sea demonstrates that the flow direction causing the erosion was from south to north, thus proving that it was produced by Mediterranean water flowing over the sill into the Marmara Sea basin.     

Stratigraphy of Quaternary inner-shelf sediments in Tai O Bay, Hong Kong, based on ground-truthed seismic profiles

High-resolution boomer profiles from Tai O Bay, Hong Kong SAR, were ground-truthed using ten discontinuously sampled boreholes penetrating bedrock with a maximum length of 82.1 m. The relationship between depth below seabed and seismic profiles was established through the measurement of two borehole compressional-wave velocity profiles. In departure from previous interpretations, nine Quaternary seismic units were identified, which can be divided into eight systems tracts formed by cycles of fourth-order sea-level fluctuations dating back at least to marine isotope stage (MIS) 7 (ca. 190–245 ka). These consist of two lowstand systems tracts, two transgressive systems tracts, and four highstand systems tracts. Secondary unconformities within the highstand deposits are interpreted to document fifth-order sea-level fluctuations. Lowstand deposits are less common because, as soon as the sea level drops by a few metres, Tai O Bay becomes sub-aerially exposed, leading to widespread non-deposition or erosion. At the same time, extensive fluvial erosion and channel incision take place. Filling of the fluvial channels occurs during rising sea level. Lowstand sediments (if present) are generally landslide deposits laid down on a basal alluvial plain. Uncorrected accelerator mass spectrometry (AMS) radiocarbon dates of mollusc shells show that the depositional environment was marine since 6.2 ka, becoming gradually more brackish as a result of progradation of the Pearl River delta. The computed average sedimentation rate for the period 6.2–4.1 ka is 4.4 m/1,000 year, and approximately 1 m/1,000 year since 4.1 ka.     

Sequence stratigraphy and cyclicity in the Middle Eocene of the Fayoum ranges,Western Desert,Egypt: Implications for regional sea level changes

The Middle Eocene deposits in the Fayoum Ranges are composed of complex alternative clastic (claystone and sandstone) and carbonate (limestone and dolostone) facies and dominated carbonate (limestone) facies. Facies are arranged mainly in regression and shallowing upward (emergence) cycles and sequences. Field stratigraphic and microfacies analysis of the study area permits recognition of four major sequences, reflecting 3rd-order cycles. Depositional sequences and cycles are bounded by subaerial erosive surfaces or caliche deposits, ferruginous crust, and by their correlative conformities. Sequence-1 consists of two shallowing-upward cycles (dominate carbonate facies), each of which starts with nummulitic wackestone, capped with nummulitic packstone including Globigerinatheka subconglobata subconglobata biozone. These cycles were deposited under tropical to subtropical conditions as evidenced by the carbonate nature of the rocks and the abundance of nummulites, which need warm conditions for their flourishing. Sequence-2 consists of four emergence cycles based with claystone and capped with wackestone including Morozovella lehneri biozone. The duration (Ma) of sequence-2 (Morozovella lehneri zone) is 3.05 Ma (44.25 Ma for the upper of TA3 3.3 to 41.2 Ma for the lower of TA3 3.5). Sequence-3 includes three rock units (includes Trucorotaloides rohri biozone). The lower unit involves lowstand systems tract, the middle unit contains transgressive systems tract and the upper rock unit includes highstand systems tract. The lowstand systems tract consists of emergence cycles of mixed clastic- carbonate facies, clays at the base and capped with wackestone and packstone facies. The transgressive systems tract consists of dominant carbonate facies, wackestone at the base and capped with packstone facies. Sequence 4 involves transgressive systems tract. The duration of both sequence-3 and sequence 4 has been estimated as 1.8 Ma.     

Sequence stratigraphy based on high-resolution seismic profiles in the late Pleistocene and Holocene deposits of the Venice area

The sequence-stratigraphic investigation by Very High-Resolution (VHR) seismic profiles allowed recognition of the detailed architecture of the late Pleistocene and Holocene succession of the Venice area. In this way deposits previously known by the analyses of scattered cores, mainly taken along the lagoon margin and the littoral strips, have been correlated at regional scale including the near offshore sector and the result has pointed out the lateral variability of the stratal architecture. Late Pleistocene deposits consist of an aggrading floodplain and fluvial channel fills accumulated during decreasing eustatic sea level, and they are coeval with offlapping forced regressive marine wedges in the Central Adriatic basin. The Holocene sequence is composed of three main seismic units separated by major stratal surfaces. Unit 1 (up to 9 m thick) is formed by channelized deposits separated by areas showing sub-horizontal and hummocky reflectors, and is bounded at the base by a surface that records prolonged conditions of subaerial exposure and at the top by a flatter surface resulting from erosion by marine processes. Deposits of Unit 1 are interpreted as estuarine and distributary channel fills, and back-barrier strata. Unit 2 is well distinguishable from Unit 1 only in the offshore area and at the barrier island bounding the Venice Lagoon, and is composed of a prograding marine wedge (up to 10 m thick) that interacts laterally with ebb tidal deltas. Unit 3 consists of a tidal channel complex and inlet deposits, which testify the evolution of the lagoon area. Tidal channels are entrenched in the lagoon mud flat (coeval with Units 1–2) and cut the Pleistocene–Holocene boundary in several places.Following current sequence-stratigraphic concepts, the Holocene sequence is composed of a paralic transgressive systems tract (TST) (Unit 1) overlying a sequence boundary (the Pleistocene–Holocene boundary) and overlain by a marine highstand systems tract (HST) (Unit 2) in seaward locations and by highstand lagoonal deposits landwards. TST and HST are separated by a downlap surface that is amalgamated with a wave ravinement surface in several places. Unit 3 is coeval with the upper part of Unit 2, and its development has been favoured by human interventions, which led to a transgression limited to the lagoon area.Local factors during the deposition, i.e. subsidence, sediment supply, physiography, and current/wave regimes, led to a significant lateral variability in the architecture of the Holocene sequence, as evidenced by the extreme thickness variation of the TST along both depositional strike and dip. The HST, instead, shows less pronounced strike variations in the stratal architecture. Also, present data clearly evidence that the human impact has a great relevance in influencing the late Holocene sedimentation.     

Stratigraphy, sedimentology and engineering aspects of Holocene organo-calcareous silts, Suva Harbour, Fiji

A deposit of post-glacial organo-calcareous silt 25–40 m thick blankets the floor of Suva Harbour and its marginal inlets, including Draunibota Bay, on the southeast coast of Viti Levu, Fiji. This deposit is notable for its involvement in a large number of foundation failures in the area. The organo-calcareous silt is the latest sedimentary infill over a late Pleistocene erosional surface which is dissected characteristically down to around 50 m below current mean sea level at the harbour margins, and to at least 90 m at the seaward end of the study area. The gross distribution of Pleistocene and Holocene sedimentary units is strongly influenced by Pliocene graben formation in the Mio-Pliocene bedrock. The silt deposit forms part of a transgressive and highstand systems tract related to the latest glacio-eustatic sea-level rise, and includes a series of lobate delta deposits currently prograding at the mouths of streams entering the harbour. The silt was deposited in a lagoonal/estuarine environment of restricted circulation in a marginal/back-barrier reef situation and received a variety of marine carbonate and terrigenous sediment contributions, as well as organic substances from both autochthonous and allochthonous sources. Undisturbed sampling indicates the silt to be homogeneous, non-layered and thoroughly bioturbated, but a distinct layering with a spacing in the order of 1–5 m, probably related to periodic influxes of terrigenous material, is obvious on continuous seismic profiles. Acoustic turbidity due to biogenic gas in thick accumulations over palaeo-channels may well represent zones of high pore fluid pressure, and indicate lower effective soil strength. There is also evidence that the passage of the overpressured gas front results in hydraulic fracturing and consequent degassing of the silt. The silt deposit displays a slight upward coarsening in response to shoaling conditions, accompanied by an upward increase in both organic carbon and calcium carbonate proportions, and a decreasing terrigenous contribution. The increase in organic carbon is closely mirrored by increased diagenetic development of bacterially-deposited agglomerates of iron sulfide crystals in the pore spaces. The resulting pore-space microstructure appears to exert a direct control on the in-situ void ratio, and hence directly affects the consolidation and strength characteristics of the sediment. Radiocarbon dates from the silt deposit indicate a consistent rate of deposition in the Draunibota palaeo-channel of 4.3 m/1000 yr since the marine transgressive front passed the site some 9600 yr B.P. The dates extend the reliable local sea-level data for southeast Viti Levu back some further 4000 years, and support an earlier contention that sea level reached its current position here at around 4000–4500 yr B.P., about 2000 years later than on the coast of southeast Australia. Water depth at the Cement Works Bridge site reached a maximum of 20 m some 5000 yr B.P. and, subsequently, has gradually shoaled to its present position just below mean sea level.     

台湾海峡晚更新世以来的高分辨率地震地层学研究

基于4 530 km高分辨率单道地震数据和钻孔资料,采用高分辨率地震地层学的方法,对台湾海峡晚更新世以来的地层进行了划分,自上而下共识别出R₀、R₁、R₂、R₃、R₄等5个主要反射界面,分别对应海底、3 ka BP前后高海平面、最大海泛面、海侵面和 Ⅰ 型层序界面,并以此划分出4个地层单元:晚全新世浅海-滨海沉积A,中全新世浅海沉积B,早全新世海侵沉积C,晚更新世陆相河流沉积D。在海平面变化的作用下,海峡地区先后发育低水位沉积D（低位体系域）,海侵沉积C （海侵体系域）、高水位沉积B和A（高位体系域）。研究了台湾海峡的典型地震相,提出了关于台中浅滩（云彰隆起）处的楔状沉积体的新观点,认为该楔状体为全新世中期以来形成的三角洲沉积受波浪和潮流作用改造而形成的潮流沙脊,其物质主要来源于台湾。识别出了晚更新世和早全新世古河道沉积,海平面变化和地势高低是其形成时间差异的主要因素。     

Late Pleistocene-Holocene sediments on the Spanish continental shelves: Model for very high resolution sequence stratigraphy

Sequence stratigraphy analysis of high resolution seismic profiles (Geopulse, Uniboom and 3.5 kHz) of late Pleistocene-Holocene sediments has been carried out on five sectors of the Spanish continental margin. Four types of depositional settings are distinguished in these sectors: (1) low subsident ramps (Alborán Margin-Cádiz Gulf); (2) high subsident (2m/kyr) ramps (Alicante-Valencia); (3) “Ria”-type morphology on the Atlantic passive margin (Ria de Muros); and (4) fault-scarp morphology systems with subsidence (Balearic Margin). A Type 1 sequence is interpreted in all these sectors, being composed of lowstand systems tract, transgressive systems tract and highstand systems tract. This conforms to the basic concepts of sequence stratigraphy and each systems tract correlates with a particular part of the last eustatic hemicycle. Characteristic shelf features such as terraces, terraces with beach deposits and progradational sediment wedges evidence a complex stacking of lesser sub-sequences in all the systems tracts, which must be related to very-short period sea-level stillstands and fall. We propose a very high resolution sequence stratigraphy model in which the last sea-level hemicycle is punctuated by: “P” cycles (4500 years), which give rise to the neo-glacial events; “h” cycles (2200-950 years), and “c” cycles (500-50 years). These cycles interact with each other, thus establishing the placing of the high and low sea levels.

This attention to detail: (1) explains sedimentary evolution on both the shelf and upper slope during late Pleistocene-Holocene time; (2) illustrates some departures from the classical sequence stratigraphy model; and (3) also demonstrates that the late Pleistocene-Holocene eustatic curve is not one simple transgression but is modulated by three differing-period cycle groups below the Milankovitch band. Our model is delimited by fluctuating sea level during Pleistocene-Holocene times. Such features should be identifiable on any continental margin. However, localized features occur due to subsidence and continental shelf morphology which determ ine the location and depth of sedimentary bodies generated in each eustatic cycle.     

Lower Cretaceous lacustrine successions,North Yellow Sea Basin,eastern China: Rift basin sequence stratigraphy and stacking patterns in response to magmatic activity

A series of Mesozoic rift basins formed in eastern China were associated with magmatic activity and subduction along the Eurasia, Izanagi and Pacific plate margins. The impact of magmatic activity on lacustrine sequence development was documented with well-log and 3-D seismic data from the Jupiter Depression in the North Yellow Sea Basin. We identified key surfaces, retrogradational and progradational parasequence sets, and defined the characteristics of systems tracts and the internal sequence components for the Lower Cretaceous (K₁SQ1). A 2-D SEDPAK numerical stratigraphic forward modeling was used to further constrain sequence development in the Jupiter Depression by considering different modeling parameters and the spatial-temporal characteristics of magmatic activity. Modeling results were compared and matched with the sequence architecture observed from seismic and well interpretations. Magmatic activity impacts on the development of the K₁SQ1 sequence in the North Yellow Sea Basin include topographic variation, lake level fluctuation, and sediment supply ratios. Results suggest that magmatic upwelling uplifted the northwestern area of the Jupiter Depression and formed its slope break during the late Jurassic or early Cretaceous. Along with uplifting, relative lake level dropped sharply and lake accommodation was reduced, but with increased sediment supply. Therefore, sediment accumulated along the slope break as a lowstand systems tract. Later on, as lake level continuously rose, transgressive and highstand systems tracts were developed. The proposed stacking pattern provides an analog, and a useful model, for lacustrine sequence development in response to magmatic activities in eastern China and other rift basins of similar tectonic setting.     

Trajectory analysis and inferences on geometric relationships of an Early Triassic prograding clinoform succession on the northern Barents Shelf

A sedimentary succession studied along three parallel seismic lines details a platform-edge progradation of 21–36 km in a northwesterly direction across the northwestern Barents Shelf. The intra-shelf clinoform succession is bounded at bottom and top by Base Olenekian and Early Ladinian seismic reflectors. The ca 800 m thick succession can be resolved into seven distinct clinothems. The system is characterized by an early sub-horizontal platform-edge trajectory with extensive progradation, limited relative sea level rise and restricted accommodation. Thereafter the system outlines a largely ascending trajectory, marking a major rise in relative sea level and creation of significant accommodation. The platform-edge appears to back-step along one line suggesting that relative sea level rise out-paced sediment influx and preserved a clinothem with a trajectory characterized by accretionary transgression. Thereafter the trajectory is overall ascending regressive, with some variation of the trajectory angle, culminating in a flat and finally descending trajectory with oblique clinoforms outlining extensive progradation and another period of limited accommodation. The clinoforms downlap onto a succession of basin-floor deposits which appear to comprise at least two separate periods of deposition, forming two separate units. The first five clinothems downlap onto the first basin-floor unit. The shift to downlap onto the second unit occurs around the second period of extensive platform-edge advance, suggesting limited accommodation promoted bypass of significant amounts of sediment to the basin floor.The Gardarbanken High has been considered an obstacle to Early Triassic sediment progradation in this part of the basin. This inference can be corroborated based on the seismic attributes, which show sediment infill and onlap near the High. The influence is also noticeable in the reduced slope relief near the High, indicating that the basin floor was topographically higher. However, other geometric attributes cannot provide any definitive measures of structural influence.The thickness of preserved topsets and the distance from the platform-edge to the toe pinch-out point of each clinothem is found to be inversely proportional. This relationship is most marked in the fully developed sigmoidal clinoforms, whereas the link appears weaker in the oblique clinoforms. A near-perfect correlation between clinothem average vertical thickness (the average sedimentary rock accumulation within the clinothem) and advance of the toe is found, with only a relatively close relationship between clinothem average vertical thickness and advance of the platform-edge. In the studied system it therefore appears the advance of the toe is governed solely by sediment influx while the advance of the platform-edge is also influenced by relative sea level.     

Stratigraphic signatures of punctuated rise in relative sea-level in an estuary-dominated heterolithic succession: Incised valley fills of the Toarcian Ostreaelv Formation,Neill Klinter Group (Jameson Land,East Greenland)

The Ostreaelv Formation (latest Pliensbachian–Toarcian) of the Neill Klinter Group is exposed along a >105 km wide, ENE-trending section in Jameson Land, East Greenland. Deposition took place in a large embayment (Jameson Land Basin) that was connected to the proto-Norwegian-Greenland Sea. Lithofacies in the Ostreaelv Formation range from clean sandstone to muddy heterolithic facies typified by strong grain-size contrasts.The Ostreaelv Formation is divided into four distinct and overall retrograding allostratigraphic units each composed of a characteristic set of tide-influenced, tide-dominated and wave-influenced facies associations. The allostratigraphic units are bounded by subaerial unconformities, interpreted as sequence boundaries, and are up to 75 m thick and 16 to >20 km in width. The allostratigraphic units include a sandy heterolithic estuary bay-head delta succession overlain by two sandy tide-dominated estuary fill successions, interbedded with a muddy heterolithic offshore marine succession. Each of the three estuarine allostratigraphic units was accumulated in an incised valley formed during fall in relative sea level and filled during successive transgressions with sediment supplied from marine and reworked fluvial deposits.In the three incised valleys fluvial sediments were deposited on top of an initial subaerial unconformity surface (SU) and were later reworked by succeeding transgressive ravinement along a transgressive surface (TS), thus creating combined SU/TS sequence boundaries. The data from the Ostreaelv Formation also provides knowledge and conceptual understanding of valley infill processes (tidal current, wave and fluvial energy), and both lateral and vertical variations in lithofacies architecture within incised valleys.Moreover, the study provides quantitative input data, such as incised valley dimensions, sand-containing capacity, and geometry to subsurface reservoir characterisation and modelling efforts of estuary fill successions.     

Reconstruction of Late-Quaternary sea- and lake-level changes in a tectonically active marginal basin using seismic stratigraphy: The Gulf of Cariaco,NE Venezuela

The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic–stratigraphic units were identified in the upper ~ 200 m of the sedimentary infill. Detailed seismic–stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130 kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lake-level fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5 kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting.     

3D seismic analysis of karstified interbedded carbonates and evaporites,Lower Permian Gipsdalen Group,Loppa High,southwestern Barents Sea

This paper presents a detailed seismic analysis of a hitherto undescribed Permian succession interpreted to consist of interbedded anhydrite and carbonate from the northern flank of the Loppa High, western Barents Sea. The Fafner succession forms a locally restricted transgressive unit down-dip on the rotated Loppa High. It is subdivided into four seismic sequences each interpreted to be composed of a basal transgressive anhydrite overlain by highstand carbonates. Fafner seismic sequences 2 and 3 include well-developed buildup complexes which in map view form polygonal patterns.Analysis of attribute maps indicates that the Fafner succession is overprinted by two dissolution systems related to two prominent events of subaerial exposure, creating numerous paleo-sinkholes, breccia-pipes, and collapsed composite cavern systems.The stratigraphical position of the Fafner succession, below the Mid Sakmarian – Artinskian Bjarmeland Group and above the Top Ørn unconformity, resembles that of the Lower Permian Gipshuken Formation on Spitsbergen, and the Fafner succession is thus regarded as its offshore equivalent.     

Forced regression systems tracts on the Bengal Shelf

A vertical succession of five composite sequences has been identified within the upper 100 m of the outer Bengal Shelf by means of high-resolution multi-channel seismic data. Each sequence consists predominantly of up to 100 km long and some 10 m thick forced regression systems tracts. The internal reflection pattern of the regressive units show mainly prograding oblique clinoforms. Intervening transgressive systems tracts are represented by seismically transparent or chaotic layers. On the outer shelf three of the sequences cause shelf aggradation and retrogradation, and two of them cause mainly shelf progradation. Based on the hierarchy of systems tracts, their calibration by comparison with eustatic sea-level curves and reconstructed paleoshoreline positions the composite sequences are interpreted as eccentricity driven eustatic 4th order (Milankovitch) cycles with a periodicity of about 100 ky. Internal unconformities mark cycles of 5th or higher order. An average subsidence of the outer shelf is estimated to be less than 0.4 mm/year during the last 345 ky. The correlation between the shelf growth pattern and sea-level fluctuations is consistent with the enhanced deposition on the eastern Bengal submarine fan from 465 to 125 ky B.P., as was observed by other authors.     

渤海海峡及周边海域浅地层结构及地层声速的拾取

通过系统分析渤海海峡及周边海域的高分辨率浅地层剖面与3口钻孔的资料,将研究区地层自上而下划分为T0、T1、T2、T3、T4、T5、T6、T7、T8共9个反射界面及SU11、SU12、SU13、SU2、SU3、SU41、SU42、SU43、SU5共9个声学地层单元,SU1地层单元对应全新世海相沉积,其底界为一海进侵蚀面,削蚀对应晚更新世晚玉木冰期陆相沉积的SU2地层单元。SU3地层单元对应晚更新世晚玉木间冰期的海相沉积,通过侵蚀间断面与上覆SU2呈不整合接触。SU41地层单元对应晚更新世早玉木冰期晚期的陆相沉积,SU42地层单元对应晚更新世早玉木亚间冰期的海相沉积,与上覆SU41呈侵蚀不整合接触,SU43地层单元对应晚更新世早玉木冰期早期的陆相沉积,其顶界面为海进侵蚀面,与下伏地层呈不整合接触,SU5对应晚更新世玉木—里斯间冰期的海相沉积。对比分析浅地层剖面地层单元与钻孔沉积地层,确定了研究区海底面之下不同地层单元对应的平均声学速度,为后续的地层层序的研究奠定了基础。研究区"海侵-海退-海侵-海退-高水位"的沉积过程,决定了地层平均声速随深度自下而上呈现由高-低-高-低的变化模式。