Late Quaternary turbidity current pathways to the Madeira Abyssal Plain and some constraints on turbidity current mechanisms

Turbidites deposited in the Madeira Abyssal Plain during the last 200 000 yr originated mainly from the flanks of the Canary Islands and from the Northwest African continental margin north of the Canaries. Derivation of these turbidites from sources to the east of the abyssal plain apparently contradicts flow direction indicators derived from the sediments on the plain, which indicate derivation from the north-east. However, two systems of shallow channels, mapped using side-scan sonar and 3.5-kHz data, link the easterly sediment sources to the north-eastern edge of the abyssal plain, reconciling the apparently contradictory flow direction data. A northern system originates in the area between Madeira and the Canary Islands and follows a westerly and then north-westerly path, in part cutting obliquely across regional bathymetric trends. It carries sediment from the African continental margin north of the Canary Islands, and from the eastern Canaries, to the north-eastern abyssal plain. The southern channel system carries material from the western Canary Islands more directly westward to the central part of the plain. The pathways of individual turbidites can be reconstructed in some detail, by combining channel mapping with published information on turbidite provenance and flow directions on the Madeira Abyssal Plain. Interaction between turbidity currents and channel morphology controls turbidite depositional patterns. Small turbidites are completely contained within channels 20 m deep and 2 km wide. It is proposed that these are relatively high-density flows which have evolved in crossing the almost flat floor of a basin south-east of Madeira before entering the channel system. Larger turbidites show evidence of flow stripping where they interact with channels, with the result that their coarse and fine fractions follow different paths to and across the abyssal plain.     

Late Quaternary aggradation rates and stratigraphic architecture of the southern Po Plain,Italy

The Po River Basin, where accumulation and preservation of thick sedimentary packages are enhanced by high rates of tectonic subsidence, represents an ideal site to assess the relations between vertical changes in stratigraphic architecture and sediment accumulation rates. Based on a large stratigraphic database, a markedly contrasting stratigraphy of Late Pleistocene and Holocene deposits is reconstructed from the subsurface of the modern alluvial and coastal plains. Laterally extensive fluvial channel bodies and related pedogenically modified muds of latest Pleistocene age are unconformably overlain by Holocene overbank fines, grading seaward into paralic and nearshore facies associations. In the interfluvial areas, a stiff paleosol, dating at about 12.5–10 cal ky BP, marks the Pleistocene–Holocene boundary. Across this paleosol, aggradation rates (ARs) from 16 radiocarbon‐dated cores invariably show a sharp increase, from 0.1–0.9 mm year^?1 to 0.9–2.9 mm year^?1. Comparatively lower Pleistocene values are inferred to reflect fluvial activity under a low‐accommodation (lowstand and early transgressive) regime, whereas higher ARs during the Holocene are related to increasing accommodation under late transgressive and highstand conditions. Holocene sediment accumulation patterns vary significantly from site to site, and do not exhibit common trends. Very high accumulation rates (20–60 mm year^?1) are indicated by fluvial channel or progradational delta facies, suggesting that extremely variable spatial distribution of Holocene ARs was primarily controlled by autogenic processes, such as fluvial channel avulsion or delta lobe switching. Contrasting AR between uppermost Pleistocene and Holocene deposits also are reported from the interfluves of several coeval, alluvial‐coastal plain systems worldwide, suggesting a key control by allogenic processes. Sediment accumulation curves from adjacent incised valley fills show, instead, variable shapes as a function of the complex mechanisms of valley formation and filling.     

2012年马卡诺夫海盆与楚科奇深海平原浮游动物夏季的垂直分布及地理差异

利用2012年9月1—6日采自马卡诺夫海盆3个站位和楚科奇深海平原1个站位的分层浮游动物样品,研究了浮游动物在0—1 000 m水层的垂直分布以及地理差异。结果表明,浮游动物在上层分布密集而在深层比较稀少。4个站位在0—50 m、50—100 m和100—200 m水层的平均丰度分别为265.0、360.7和231.2 ind·m^-3,而在200—500 m和500—1 000 m的丰度只有64.4和36.9 ind·m^-3。在数量上占优势的种类中,植食性为主的拟长腹剑水蚤(Oithona similis)、北极哲水蚤(Calanus glacialis)和极北哲水蚤(Calanus hyperboreus)集中在200 m以浅的水层。虽然在200m以下杂食性种类矮小微哲水蚤(Microcalanus pygmaeus)、隆剑水蚤(Oncaea spp.)和细长长腹水蚤(Metridia longa)的丰度明显降低,但是占浮游动物总丰度的比例却明显更高。两个调查海区浮游动物种类组成相似,但是楚科奇深海平原大型桡足类极北哲水蚤的丰度较高,而小型桡足类丰度较低?垂直分布上差异主要在于500—1 000 m水层,马卡诺夫海盆站位丰度为22.7—92.6 ind·m^-3,而楚科奇深海平原只有1.6 ind·m^-3。深海区浮游动物丰度的地理差异说明生物泵的作用存在空间异质性。类似地理差异产生的原因在于楚科奇深海平原存在数量较多的极北哲水蚤,它们在春季融冰前就上升到表层摄食冰藻,显著降低了有机物的垂直通量。     

Early Eocene magnetostratigraphy and tectonic evolution of the Xining Basin,NE Tibet

The Cenozoic strata of the Xining Basin, NE Tibet, have provided crucial records for understanding the tectonic and palaeo-environmental evolution of the region. Yet, the age of the lower part of the sedimentary stratigraphy and, consequently, the early tectonic evolution of the basin remain debated. Here, we present the litho- and magnetostratigraphy of various early Eocene sections throughout the Xining Basin independently constrained by the U–Pb radiometric age of a carbonate bed. Our study extends the dated stratigraphy down to 53.0 Ma (C24n.1r) and reveals highly variable accumulation rates during the early Eocene ranging from 0.5 to 8 cm/ka. This is in stark contrast to the low but stable accumulation rates (2–3 cm/ka) observed throughout the overlying Palaeogene and Neogene strata. Such a pattern of basin infill is not characteristic of flexural subsidence as previously proposed, but rather supports an extensional origin of the Xining Basin with multiple depocentres, which subsequently coalesced into a more stable and slowly subsiding basin. Whether this extension was related to the far-field effects of the subducting Pacific Plate or the India–Asia collision remains to be confirmed by future studies.     

Flexural deformation controls on Late Quaternary sediment dispersal in the Garo-Rajmahal Gap,NW Bengal Basin

Subsurface deformation is a driver for river path selection when deformation rates become comparable to the autogenic mobility rate of rivers. Here we combine geomorphology, soil and sediment facies analyses, and geophysical data of the Late Quaternary sediments of the central Garo-Rajmahal Gap in Northwest Bengal to link subsurface deformation with surface processes. We show variable sedimentation characteristics, from slow rates (<0.8 mm/year) in the Tista megafan at the foot of the Himalaya to nondeposition at the exposed surface of the Barind Tract to the south, enabling the development of mature soils. Combined subsidence in the Tista fan and uplift of the Barind Tract are consistent with a N-S flexural response of the Indian plate to loading of the Himalaya Mountains given a low value of elastic thickness (15–25 km). Provenance analysis based on bulk strontium concentration suggests a dispersal of sediment consistent with this flexural deformation—in particular the abandonment of the Barind Tract by a Pleistocene Brahmaputra River and the current extents of the Tista megafan lobes. Overall, these results highlight the control by deeply rooted deformation patterns on the routing of sediment by large rivers in foreland settings.     

敦化盆地晚全新世泥炭沉积中化学元素记录的古气候分析

在对敦化吉祥泥炭剖面的Na、K、Mg、Ca、Fe、Cr、Mn、Sr、Ba和Pb等元素进行分析的基础上,采用Morlet一维连续小波分析其时频变化,将剖面晚全新世以来的古气候过程分为6个阶段:公元前730年前的温暖降温期;公元前730年～公元前205年的温和湿润期;公元前205年～公元255年早期温暖湿润,之后变凉干;公...     

Palaeogene igneous rocks reveal new insights into the geodynamic evolution and petroleum potential of the Rockall Trough, NE Atlantic Margin

Data acquired from petroleum exploration well 164/7‐1 drilled in the UK sector of the Rockall Trough have yielded fresh insights into the igneous and thermal history of this frontier region. The well targeted a large four‐way dip closed structure of presumed Mesozoic age named ‘The Dome Prospect’. The structure is now known to have a magmatic, rather than a purely structural origin, which was the preferred pre‐well interpretation. The well encountered 1.2 km of Palaeocene age basaltic lavas, overlying Late Cretaceous mudstones which were intruded by over 70 dolerite sills ranging from <1.5‐ to 152‐m thick. ⁴⁰Ar/³⁹Ar dating of the dolerite intrusions indicates an Early Palaeocene age (63–64±0.5 Ma), which are among the oldest ⁴⁰Ar/³⁹Ar dates recognised in the North Atlantic Igneous Province. Radiometric dating of the overlying basaltic lavas proved unsuccessful, because of excessive alteration. Biostratigraphic dating of underlying and overlying sedimentary strata was utilised to constrain the age of the lavas to Late Paleocene to Early Eocene age (～55 Ma). Despite being related to two distinct events separated by ～8 Ma, the intrusives and extrusives are compositionally similar. The basaltic rocks from well 164/7‐1 possess Sr–Nd isotopic, major and trace‐element geochemical compositions similar to other volcanic and intrusive rocks of the British Tertiary Igneous Province and represent partial melts of both lithospheric and asthenospheric mantle associated with the proto‐Icelandic mantle plume head. Joint consideration of thermal maturity, potential fields and 3D seismic data indicate a deeper igneous body in addition to the sills encountered in well 164/7‐1. Jack‐up and arching mechanisms associated with both scales of intrusive body are believed to have developed the dome structure. The preferred interpretation is of a mafic laccolith, 17 km in diameter, ～7 km thick, intruded at 64.5 Ma, situated ～2.5 km below the bottom of the well. 3D thermal modelling suggests that all of Tranche 52 was thermally affected by the intrusion of the magmatic body. The thermal aureole, between 27 and 51 km in diameter, is not thought to play an important role in the hydrocarbon prospectivity of the surrounding Tranches in the NE Rockall Basin. Results show that hydrocarbon exploration prospects that are circular in map view should be interpreted with caution on volcanic continental margins. In sedimentary basins, where salt domes and shale diapirs are absent and igneous rocks prevalent, periclinal structures such as ‘The Dome Prospect’ should undergo a thorough multi‐disciplinary risk assessment.     

Late Quaternary palaeohydrology of the Konya Basin, Turkey, based on isotope studies of modern hydrology and lacustrine carbonates

The Konya plain in south central Anatolia, Turkey, which is now largely dry, was occupied around the time of the Last Glacial Maximum by a fresh-oligosaline lake covering more than 4000 km². Sediment cores from three residual water bodies (Pinarbai, Akgöl and Süleymanhaci) within the larger Pleistocene lake basin, have been analysed using a multidisciplinary approach. The sediment sequences are dated as spanning the last 50 Ka years, although breaks in sedimentation mean that there is only partial chronological overlap between them. Carbon and oxygen isotope analyses on lacustrine carbonate from the three cores give contrasting isotope profiles which reflect the different ages and independent hydrological behaviour of different sub-basins through the late Quaternary. Distinguishing changes that are regional from local effects is aided by modern isotope hydrology studies and by comparing the carbonate ¹³C and ¹⁸O values to diatom and other analyses undertaken on the same cores.     

苏北平原龙冈LG孔晚第四纪地层与环境演化记录

通过研究已经获得的苏北平原龙冈LG孔岩芯野外描述、照片、粒度、¹⁴C测年、有孔虫、孢粉、重矿物等原始测试分析数据,并参考邻区发表成果和该区新近补充的资料数据,再分析和讨论了LG孔的地层层序、年代框架和环境演化记录等内容。结果表明：① LG孔34.8 m岩芯保存了MIS 4以来沉积环境演化记录,先后经历了河漫滩、河湖相洪泛平原（第二硬黏土层）、较开放潮滩的潮间带和潮下带、较开放潮滩的潮下带、较开放潮滩的潮间带和潮上带下部、河湖相洪泛平原（第一硬黏土层）、潮上带滨海沼泽和海岸沙堤等一系列环境演化过程,其中潮滩环境的MIS 3海侵层发育;② 西冈贝壳沙堤龙冈段的全新统厚度很薄,一般在10 m以内,由于LG孔可见两个硬黏土层,应位于古河间地而非下切古河谷区,且以其第一硬黏土层顶面作为全新统底界更为合理,故原报道该孔全新统厚达25 m难以成立;③ 老于末次冰盛期的常规和加速器¹⁴C测年数据皆存在着不同程度的误差和不确定性,加之淤泥和钙质结核等测年材料易受污染等,故LG孔第二硬黏土层中的2个¹⁴C测年数据明显偏年轻,皆不宜用于解释地层年代。     

Late Quaternary paleolimnology of Walker Lake,Nevada

Diatoms, crustaceans, and pollen from sediment cores, in conjunction with dated shoreline tufas provide evidence for lake level and environmental fluctuations of Walker Lake in the late Quaternary. Large and rapid changes of lake chemistry and level apparently resulted from variations in the course and discharge of the Walker River. Paleolimnological evidence suggests that the basin contained a relatively deep and slightly saline to freshwater lake before ca. 30 000 years B.P. During the subsequent drawdown, the Walker River apparently shifted its course and flowed northward into the Carson Sink. As a result, Walker Lake shallowed and became saline. During the full glacial, cooler climates with more effective moisture supported a shallow brine lake in the basin even without the Walker River. As glacial climates waned after 15 000 years ago, Walker Lake became a playa. The Walker River returned to its basin 4700 years ago, filling it with fresh water in a few decades. Thereafter, salinity and depth increased as evaporation concentrated inflowing water, until by 3000 years ago Walker Lake was nearly 90 m deep, according to dated shoreline tufas. Lake levels fluctuated throughout this interval in response to variations in Sierra Nevada precipitation and local evaporation. A drought in the Sierras between 2400 and 2000 years ago reduced Walker Lake to a shallow, brine lake. Climate-controlled refilling of the lake beginning 2000 years ago required about one millennium to bring Walker lake near its historic level.Through time, lake basins in the complex Lake Lahontan system, fill and desiccate in response to climatic, tectonic and geomorphic events. Detailed, multidisciplinary paleolimnologic records from related subbasins are required to separate these processes before lake level history can be reliably used to interpret paleoclimatology.This is the fifth of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series.     

Erosion surfaces and Neogene landscape evolution in the NE Duero Basin (north-central Spain)

We present a chronological model of erosion surface development in the Iberian and Cantabrian Ranges of north-central Spain. We map four erosion surfaces and interpret these to be related to Duero basin continental sediments and tectonic activity from Upper Oligocene to Plio-Pleistocene. The oldest erosion surface, SE1, formed across Upper Oligocene–Lower Miocene synorogenic deposits; while surface SE2 was contemporaneous with the Middle Miocene alluvial systems, ending with an uplift stage in the Astaracian. The two most recent erosion surfaces, SE3 and SE4, developed during extensional tectonic episodes and are associated with the deposition of Upper Páramo sedimentary units at the end of the Miocene (Upper Turolian) and alluvial fan deposits, known as rañas (Plio-Pleistocene). With the exception of SE1, which seems to be associated with a relatively wet climate, the surfaces formed during periods of marked aridity and generally warm temperatures. Through geostatistical reconstruction of the best preserved surface (SE2), applying ordinary kriging method to the topography (DEM) of the erosion surface and its correlating sedimentary plains, we identify the deformation processes which occurred on this surface after its formation.     

Regional three-dimensional gravity modelling of the NE Atlantic margin

A series of three‐dimensional models has been constructed for the structure of the crust and upper mantle over a large region spanning the NE Atlantic passive margin. These incorporate isostatic and flexural principles, together with gravity modelling and integration with seismic interpretations. An initial isostatic model was based on known bathymetric/topographic variations, an estimate of the thickness and density of the sedimentary cover, and upper mantle densities based on thermal modelling. The thickness of the crystalline crust in this model was adjusted to equalise the load at a compensation depth lying below the zone of lateral mantle density variations. Flexural backstripping was used to derive alternative models which tested the effect of varying the strength of the lithosphere during sediment loading. The models were analysed by comparing calculated and observed gravity fields and by calibrating the predicted geometries against independent (primarily seismic) evidence. Further models were generated in which the thickness of the sedimentary layer and the crystalline crust were modified in order to improve the fit to observed gravity anomalies. The potential effects of igneous underplating and variable upper mantle depletion were explored by a series of sensitivity trials. The results provide a new regional lithospheric framework for the margin and a means of setting more detailed, local investigations in their regional context. The flexural modelling suggests lateral variations in the strength of the lithosphere, with much of the margin being relatively weak but areas such as the Porcupine Basin and parts of the Rockall Basin having greater strength. Observed differences between the model Moho and seismic Moho along the continental margin can be interpreted in terms of underplating. A Moho discrepancy to the northwest of Scotland is ascribed to uplift caused by a region of upper mantle with anomalously low density, which may be associated with depletion or with a temperature anomaly.     

Late Quaternary Palaeoenvironment of Spring Lake,Alberta, Canada

Palaeoenvironmental investigations based upon sediment cores taken from Spring Lake in the Peace River District of Alberta, Canada (latitude 55° 31 N; longitude 119° 35 W) show that the sedimentary record spans the Holocene period. Chemical and diatom changes coincide with regional climatic change since deglaciation (about 11 000 yr. B.P.). Calcite laminations in the basal 3 metres of the cores are evident, and were probably formed through elevated water temperature although photosynthetic removal of CO₂ undoubtedly contributed. The disappearance of the laminations, and concurrent decrease in calcite X-ray diffraction peaks ca. 5000 yr. B.P. may have been caused by a change from a partially meromictic to a dimictic lake as the climate changed. Benthic and alkaline diatoms dominate before 5000 yr. B.P., while the planktonic Stephanodiscus hantzschii dominated between 5100 and 4200 yr. B.P. probably owing to increased nutrient levels. From ca. 4200 yr. B.P. until the present, benthic Fragilaria spp. and more circumneutral diatoms were dominant. Palaeoproduction, as measured by chlorophyll derivates, was highest in the early developmental stages of the lake, decreased coinciding with a major disturbance of the sediments and lowered water levels, and then gradually increased again until present. Only during the earlier period of peak production does biogenic calcite formation appear more important than calcite deposition caused by high water temperatures.     

Faulting, seismic-stratigraphic architecture and Late Quaternary evolution of the Gulf of Alkyonides Basin–East Gulf of Corinth, Central Greece

Swath bathymetry, single‐channel seismic profiling, gravity and box coring, ²¹⁰Pb down‐core radiochemical analyses and sequence stratigraphic analysis in the Gulf of Alkyonides yielded new data on the evolution of the easternmost part of the Gulf of Corinth. Three fault segments, the South Strava, West Alkyonides and East Alkyonides faults, dipping 45, 30 and 45°, respectively, northwards, form the southern tectonic boundary of the Alkyonides Basin. Two 45° southwards dipping segments, the Domvrena and Germeno Faults, form the northern tectonic margin. The Alkyonides Basin architecture is the result of a complex interaction between fault dynamics and the effects of changes in climate and sea/lake level. Chrono‐stratigraphic interpretation of the seismic stratigraphy through correlation of the successive seismic packages with lowstands and highstands of the Late Quaternary indicates that the evolution of the basin started 0.40–0.45 Ma BP and can be divided in two stages. Subsidence of the basin floor during the early stage was uniform across the basin and the mean sedimentation rate was 1.0 m kyear^?1. Vertical slip acceleration on the southern tectonic margin since 0.13 Ma BP resulted in the present asymmetric character of the basin. Subsidence concentrated close to the southern margin and sedimentation rate increased to 1.4 m kyear^?1 in the newly formed depocentre of the basin. Actual (last 100 year) sedimentation rates were calculated to >2 mm year^?1, but are significantly influenced by the presence of episodic gravity flow deposits. Total vertical displacement of 1.1 km is estimated between the subsiding Alkyonides Basin floor and the uplifting Megara Basin since the onset of basin subsidence at a mean rate of 2.4–2.75 m kyear^?1, recorded on the East Alkyonides Fault. Gravity coring in the Strava Graben and in the lower northern margin of Alkyonides Basin proved the presence of whitish to olive grey laminated mud below thin marine sediments. Aragonite crystals and absence of the marine coccolithophora Emiliania huxleyi indicate sedimentation in lacustrine environment during the last lowstand glacial interval.     

Late Cretaceous to Cenozoic geodynamic evolution of the Atlantic margin offshore Essaouira (Morocco)

After Mesozoic rifting, the Atlantic margin of Morocco has recorded the consequences of the continental collision between Africa and Europe and the relative northward motion of the African plate over the Canary Island hotspot during Cenozoic times. Interpretation of recently acquired 2D seismic reflection data (MIRROR 2011 experiment) presents new insights into the Late Cretaceous to recent geodynamic evolution of this margin. Crustal uplift presumably started during the Late Cretaceous and triggered regional tilting in the deep‐water margin west of Essaouira and the formation of the Base Tertiary Unconformity (BTU). An associated hiatus in sedimentation is interpreted to have started earlier in the north (presumably in the Cenomanian at well location DSDP 416) and propagated to the south (presumably in the Coniacian at well location DSDP 415). The difference in the total duration of this hiatus is postulated to have controlled the extrusion of Late Triassic to Early Jurassic salt during the Late Cretaceous to Early Palaeocene non‐depositional period, resulting in regional differences in the preservation of salt structures: the Agadir Basin in the south of the study area is dominated by salt diapirs, whereas massive canopies characterised the Ras Tafelnay Plateau farther north and salt‐poor canopies and weld structures the northernmost offshore Essaouira and Safi Basins. Accompanied by volcanic intrusions, a presumably Early Palaeogene reactivation of previously existing basement faults is interpreted to have formed a series of deep‐water anticlines with associated gravity deformation of shallow‐seated sediments. The orientation of the fold axes is roughly perpendicular to the present day coast and the extensional fault direction; therefore, not a coast‐line parallel pattern of extensional faults, related to the rifting and break‐up of the margin, but rather a coast‐line perpendicular oceanic fracture zone might have caused the basement faults associated with the deep‐water folds. Both the volcanic intrusions and the formation of the deep‐water anticlines show a comparable age trend which gets progressively younger towards the south. A potential tempo‐spatial relationship of the BTU and the reactivation of basement faults can be explained by the relative northward motion of the African plate over the Canary Island hotspot. Regional uplift producing the BTU could have been the precursor of the approaching hotspot during the Late Cretaceous, followed during the Early Palaeogene by a locally more pronounced uplift above the hotspot centre.     

民勤盆地东北部晚第四纪深湖亚相地层空间分布及其环境意义

民勤盆地位于石羊河下游,现今大面积地区已被风沙覆盖.前人的研究报道了在民勤盆地的东部曾经发育过一个面积巨大的"腾格里古大湖",然而尚不明确民勤盆地是否也曾被湖水覆盖.为此,本文收集整理了民勤盆地中8个水文地质钻孔的地层资料,利用GIS技术重现了研究区地表以下50 m深度内的湖相地层的空间分布特征.分析发现,在盆地的不同地区普遍发育了2~3层深湖亚相地层,部分地区甚至多达4层,各湖相层厚度介于0.5~32 m.区域地层对比结果显示,在某个时段研究区大范围地区普遍发育了深水湖泊,而其他时段则在不同地区零星发育了小湖泊.结合研究区已有的测年资料,本文认为在晚第四纪某个时段(倒数第二层深湖亚相发育阶段),整个研究区内曾经存在一个规模较大的连通湖泊;但民勤盆地晚第四纪不同阶段深湖亚相地层差异明显的空间分布特征,可能反映了湖盆沉积中心自东向西、再向北东的迁移过程.     

Landscape evolution and geodynamic controls in the Gulf of Cadiz (Huelva coast, SW Spain) during the Late Quaternary

The coastal evolution of the El Abalario area (Huelva, southern Spain) during the Late Pleistocene and Holocene is reinterpreted after a refinement of the available geochronology by means of optically stimulated luminescence (OSL) dating. New data come from the analysis of soft sediment deformation, palaeosols, geomorphological mapping, and published seismic surveys on the onshore and offshore Gulf of Cadiz.The present structure of El Abalario dome resulted from the complex interaction of littoral-catchment processes and sea-level changes upon an emergent coastal plain, conditioned by the upwarping of the underlying Pliocene–Pleistocene prograding deltaic sequence. Upwarping is probably related to escape of over-pressurized fluids, accompanied by dewatering, prior to (?) and during OIS (Oxygen Isotopic Stage) 5. Continued upwarping produced the large NW–SE gravitational fault of Torre del Loro (TLF) in the southwestern flank of the dome, roughly parallel to the present coastline during OIS 5–OIS 4. The resulting escarpment favoured the accumulation of aeolian sand dunes (units U1, U2, and U3) from OIS 5 to early OIS 1. Unit U1 (OIS 5) ends upwards in a supersurface with a thick weathering profile that suggests moist and temperate climatic conditions. Unit U2 accumulated mainly during OIS 4 and OIS 3 with prevailing W/E winds. The supersurface between U2 and U3 records a part of OIS 2, with relative low sea level. Sedimentation of unit U3 took place during the Last Deglaciation (radiocarbon and OSL ages) with prevailing W/SW winds, under a temperate moist climate, that became more arid towards the top (Holocene). A major supersurface with an iron crust-like layer (SsFe) developed during the Holocene Climatic Optimum (OIS 1) under wetter and more temperate conditions than before, fossilizing the TLF. The supersurface is covered by younger aeolian dunes (U4, U5, U6, and U7) transported by W–SW winds since the Late Neolithic–Chalcolithic cultural period (5.0 ky cal BP).     

Giant sublacustrine landslide in the Cretaceous Songliao Basin,NE China

Mass failure deposits in lacustrine settings are some of the most understudied facies associations in the ancient or modern rock record. We integrated seismic data and well logs to investigate the external morphology, internal architecture and deformation and reservoir distribution of the sublacustrine landslides in the Cretaceous Nengjiang Formation of the Songliao Basin (SLB). A large‐scale sublacustrine landslide, named the Qi‐Jia sublacustrine landslide (QJSL), has been identified in the Nengjiang Formation of the SLB. The QJSL is currently the largest known sublacustrine landslide in the world. This landslide covers an area that exceeds 300 km², with an estimated volume of 30 km³. Seismic imaging and mapping reveal that the QJSL can be recognized by several distinguishing seismic characteristics: discontinuous and internal chaotic seismic facies, compressional structures in the downslope region, irregular top and basal surfaces and erosional grooves in basal shear surfaces. The QJSL is 20–200 m thick, and is composed of a succession of fine‐grained deposits. Sandy layers are present but sparse and thinner than 16 m, and form reservoirs of the petroleum discoveries in this area. Our analyses show that the mechanism that triggered the collapse of the QJSL is attributed to rapid deposition and deltaic progradation. This study demonstrates that sand‐rich sublacustrine landslides formed at delta front slope can serve as conventional reservoirs in the lake centre, and provide a new target for subaqueous hydrocarbon exploration and development.