Lateral variability in clinoform trajectory,process regime,and sediment dispersal patterns beyond the shelf‐edge rollover in exhumed basin margin‐scale clinothems

Sediment supply rate and accommodation regime represent primary controls on the depositional architecture of basin margin successions, but their interaction is commonly inferred from 2D dip profiles and/or with limited constraints on sedimentary facies. In this study, three parallel (>40 km long) 2D depositional oblique‐dip profiles from outcrops of the lower Waterford Formation (Karoo Basin, South Africa) have been correlated. This data set provides a rare opportunity to assess the lateral variability in the sedimentary process record of the shelf‐to‐slope transition for eight successive clinothems over a 900 km² area. The three profiles show similar shelf‐edge rollover trajectories, but this belies significant along‐margin variability in sedimentary processes and down‐dip sediment supply. The depositional architecture of three successive clinothems (WfC 3, 4 and 5) also show along‐shelf physiographic differences. The reconstructed shelf‐edge rollover position is not straight, and a westward curve to the north coincides with an area of greater sand supply to the slope beyond a shelf dominated by wave and storm processes. All the clinothems thicken northwards, indicating an along‐margin long‐term increase in accommodation that was maintained through multiple shoreline transits across the shelf. The origin of the differential subsidence cannot be discriminated confidently between tectonic or compaction processes. The interplay of basin margin physiography, differential subsidence rate and process regime resulted in significant across‐strike variability in the style and timing of sediment dispersal patterns beyond the shelf‐edge rollover. This study highlights the challenge for accurate prediction of the sediment partitioning across the shelf‐edge rollover in subsurface studies.     

Modelling the drainage evolution of a river–shelf system forced by Quaternary glacio-eustasy

The Quaternary glaciations had a profound impact on the geomorphology and stratigraphy of passive continental margins. The challenge is to resolve the contributions of the main forcing controls relative sea‐level change and sediment flux. The key to answer this question is to understand the interaction between the marine and terrestrial environments, where river dynamics play an essential role. A comprehensible three‐dimensional numerical model is presented in order to investigate quantitatively the behaviour of river–shelf sedimentary systems under glacio‐eustatic conditions. Distinctive features observed in the model results include river avulsion, delta‐lobe switching, incision and knickpoint migration. An important event in the development of the modelled river–shelf system is the establishment of a direct and inextricable link between the drainage basin and the depocentre on the shelf edge, thereby bypassing the exposed shelf. This is termed as ‘drainage connection’. In the model, the timing of drainage connection occurs over a broad interval when the model run is repeated many times with small differences in the initial topography, reflecting the sensitivity of the system to its initial state. It demonstrates the inherent variability in the evolution of a sedimentary system as a consequence of non‐linear behaviour. A statistical approach to modelling is suggested in order to deal with this problem.     

Hinterland basin development and infilling through tectonic and eustatic processes: latest Messinian‐Gelasian Valdelsa Basin,Northern Apennines,Italy

This article reports a stratigraphic and structural analysis of the Neogene‐Quaternary Valdelsa Basin (Central Italy), filled with up to 1000 m of uppermost Miocene to lower Pleistocene strata. The succession is subdivided into seven unconformity‐bounded stratigraphic units (synthems, or large‐scale depositional sequences) that include fluvio‐deltaic and shallow‐marine deposits. Structures related to basin shoulders and internal boundaries controlled the Neogene location and geometry of different depocentres. During the Tortonian‐Messinian, a buried NE‐trending high related to regional, basin‐transverse lineaments separated two adjacent sub‐basins. During the lower Pliocene, compressional displacement along NW‐trending, thrust‐related highs controlled the distribution of depocentres and dispersal of sediment. Extensional tectonics, although previously considered the dominant deformation style affecting the rear of the Northern Apennines since the late Miocene, is no longer considered a dominant control on tectono‐sedimentary development of the Valdelsa basin. Instead, the Valdelsa Basin shares features with continental hinterland basins of orogenic belts where compression, extension, and transcurrent stress fields determine a complex spatial and temporal record of accommodation and sediment supply. In the Valdelsa Basin tectonics and eustatic sea‐level fluctuations were dominant in forcing the deposition of sedimentary cycles at several scales. Zanclean and Gelasian large‐scale depositional sequences were mainly controlled by crustal shortening, whereas a eustatic signal was preferentially recorded during the Piacenzian. Smaller scale depositional sequences, common to most synthems, were controlled by orbitally forced glacio‐eustatic cycles.     

Sediment flux from the Zhoushan Archipelago,eastern China

Knowledge of the sediment flux derived from different sources is critical for interpreting the sedimentary records associated with large river sedimentary systems. For the Changjiang River system, previous studies hardly focused on the sediment load from the adjacent Zhoushan Archipelago (ZA). Based on four prediction models, aiming to improve the understanding of the sediment load from the ZA during the Holocene, we show that the predicted sediment flux of the ZA ranges from ~0.7 to 26.5 Mt·yr^-1, with an average value of 10.7 Mt·yr^-1, and the islands with a relatively large area or high relief contribute greatly to the total flux. This sediment load is an order of magnitude lower than that of the Changjiang River, but it is similar to those of the local small rivers. Located in the core area of the southward dispersal path of the Changjiang River plume, the ZA also influences the sediment transport into Hangzhou Bay and over the Zhejiang-Fujian coastal seas. On the Holocene temporal scale, e.g., for the period from 6 ka BP to 2 ka BP, the sediments discharged from the ZA had a considerable effect on the shelf sedimentary system. This study provides evidence for an important role an archipelago can play in terms of sediment supply and transport in coastal and inner continental shelf regions.     

Morphology and sedimentary systems in the Central Bransfield Basin, Antarctic Peninsula: sedimentary dynamics from shelf to basin

A detailed regional characterization of the physiography, morphology and sedimentary systems of the Central Bransfield Basin (CBB) was carried out using swath bathymetry and high‐ and very high‐resolution seismic profiles. The basin margins show continental shelves with numerous glacial troughs, and continental slopes where relatively wide and flat slope platforms represent the middle domain in an atypical physiographic scenario in glaciated margins. Although the CBB is tectonically active, most of the morphologic features are sedimentary in origin, and can be classified into four sedimentary systems: (1) glacial‐glaciomarine, composed of erosional surfaces, glacial troughs, furrows and draping sheets; (2) slope‐basin, formed by trough mouth fans, slope aprons, the Gebra‐Magia instability complex and turbidity systems; (3) seabed fluid outflow system composed of pockmark fields; and (4) contourite, composed of drifts and moats. The sedimentary systems show a clear zonation from shelf to basin and their dynamics reflects the complex interplay among glacial, glaciomarine, marine and oceanographic processes involved in the entire shelf‐to‐basin sediment distribution. The CBB morphology is primarily controlled by glacial/interglacial cyclicity and physiography and to a lesser extent by tectonics and oceanography. These factors have affected the South Shetland Islands (SSI) and Antarctic Peninsula (AP) margins differently, creating a relatively starved SSI margin and a more constructional AP margin. They have also created two entire sediment‐dispersal domains: the shelf‐to‐slope, which records the glaciation history of the CBB; and the lower slope‐to‐basin, which records the imprint of local factors. This study provides a ‘source‐to‐sink’ sedimentary scheme for glaciated margins, which may be applied to the basin research in other margins, based on the characterization of sedimentary systems, their boundaries and the linkages among them. This approach proves to be adequate for the identification of global and local factors governing the CBB and may therefore be applied to other study areas.     

Controls on sediment export from the Waipaoa River basin, New Zealand

A stability model of drainage basin mass balance is used to interpret historic and prehistoric patterns of sediment production, storage and output from the Waipaoa River basin, New Zealand and assess the sensitivity of basin sediment yield to land use change in the historic period. Climate and vegetation cover changed during the late Holocene, but the drainage basin mass balance system was stable before the basin was deforested by European colonists in the late 19th and early 20th centuries. In this meso‐scale dispersal system sediment sources and sinks are closely linked, and before that time there was also little variability in the rate of terrigenous mass accumulation on the adjacent continental shelf. However, despite strong first‐order geologic controls on erosion and extensive alluvial storage, sediment delivery to the continental shelf is sensitive and highly responsive to historic hillslope destabilization driven by land use change. Alluvial buffering can mask the effects of variations in sediment production within a basin on sediment yield at the outlet, but this is most likely to occur in basins where alluvial storage is large relative to yield and where the residence time of alluvial sediment is long relative to the time scale of environmental change. At present, neither situation applies to the Waipaoa River basin. Thus, the strength of the contemporary depositional signal may not only be due to the intensity of the erosion processes involved, but also to the fact that land use change in the historic period destabilized the drainage basin mass balance system.     

The sedimentary and tectonic evolution of the Amur River and North Sakhalin Basin: new evidence from seismic stratigraphy and Neogene–Recent sediment budgets

The North Sakhalin Basin in the western Sea of Okhotsk has been the main site of sedimentation from the Amur River since the Early Miocene. In this article, we present regional seismic reflection data and a Neogene–Recent sediment budget to constrain the evolution of the basin and its sedimentary fill, and consider the implications for sediment flux from the Amur River, in particular testing models of continental‐scale Neogene drainage capture. The Amur‐derived basin‐fill history can be divided into five distinct stages: the first Amur‐derived sediments (>21–16.5 Ma) were deposited during a period of transtension along the Sakhalin‐Hokkaido Shear Zone, with moderately high sediment flux to the basin (71 Mt year^?1). The second stage sequence (16.5–10.4 Ma) was deposited following the cessation of transtension, and was characterised by a significant reduction in sediment flux (24 Mt year^?1) and widespread retrogradation of deltaic sediments. The third (10.4–5.3 Ma) and fourth (5.3–2.5 Ma) stages were characterised by progradation of deltaic sediments and an associated increase in sediment flux (48–60 Mt year^?1) to the basin. Significant uplift associated with regional transpression started during this time in southeastern Sakhalin, but the north‐eastward propagating strain did not reach the NE shelf of Sakhalin until the Pleistocene (<2.5 Ma). This uplift event, still ongoing today, resulted in recycling of older deltaic sediments from the island of Sakhalin, and contributed to a substantially increased total sediment flux to the adjacent basinal areas (165 Mt year^?1). Adjusted rates to discount these local erosional products (117 Mt year^?1) imply an Amur catchment‐wide increase in denudation rates during the Late Pliocene–Pleistocene; however, this was likely a result of global climatic and eustatic effects, combined with tectonic processes within the Amur catchment and possibly a smaller drainage capture event by the Sungari tributary, rather than continental‐scale drainage capture involving the entire upper Amur catchment.     

What feeds shelf-edge clinoforms over margins deprived of adjacent land sources? An example from southeastern Brazil

In southeastern Brazil, the Serra do Mar coastal mountain range blocks the sediment influx from arriving at a ca. 1,500 km long continental margin comprising Santos and Pelotas basins. Despite this deprivation, the margin accumulated a ca. 1 km thick sedimentary succession since the Mid-Miocene. Examination of seismic reflection and oceanographic data indicates that shelf-margin clinoform formation exhibits a regional variability, with major sigmoidal clinoforms developed in the transitional area between both basins. Laterally, poorly developed oblique clinoforms constitute isolated depocenters along the shelf margin. The continuous clinoform development in the transitional area is attributed to the major influence on sediment transport patterns of several ocean bottom currents flowing along the margin, such as the Brazil Coastal Current, the Brazil Current and the Intermediate Water Brazil Current. These currents erode, transport and distribute sediments across the shelf break and upper slope from distant sediment sources located either north or south of the study area. The progressive southward strengthening of the Brazil Current could be responsible for a major southward sediment redistribution from the northern Campos Basin, and/or for sediment entrainment from northward-induced transport by the Brazil Coastal Current, originally derived from the De la Plata Estuary. In the transition between Santos and Pelotas basins, the Intermediate Water Brazil Current splits forming the Santos Bifurcation, allowing for a continuous depositional process and clinoform generation. We suggest that ocean bottom currents may shape other shelf-edge ‘contouritic clinoforms’ in continental margins mainly constructed by along-strike sediment transport largely driven by long-term geostrophic currents.     

Relationships between shelf‐edge trajectories and sediment dispersal along depositional dip and strike: a different approach to sequence stratigraphy

Analysis of shelf‐edge trajectories in prograding successions from offshore Norway, Brazil, Venezuela and West Africa reveals systematic changes in facies associations along the depositional dip. These changes occur in conjunction with the relative sea‐level change, sediment supply, inclination of the substratum and the relief of the margin. Flat and ascending trajectories generally result in an accumulation of fluvial and shallow marine sediments in the topset segment. Descending trajectories will generally result in erosion and bypass of the topset segment and deposition of basin floor fans. An investigation of incised valley fills reveals multiple stages of filling that can be linked to distinct phases of deepwater fan deposition and to the overall evolution of the margin. In the case of high sediment supply, like the Neogene Niger and Orinoco deltas, basin floor fans may develop systematically even under ascending trajectory styles. In traditional sequence stratigraphic thinking, this would imply the deposition of basin floor fans during a period of relative sea‐level highstand. Facies associations and sequence development also vary along the depositional strike. The width and gradient of the shelf and slope show considerable variations from south to north along the Brazilian continental margin during the Cenozoic. During the same time interval, the continental shelf may display high or low accommodation conditions, and the resulting stacking patterns and facies associations may be utilized to reconstruct palaeogeography and for prediction of lithology. Application of the trajectory concept thus reveals nuances in the rock record that would be lost by the application of traditional sequence stratigraphic work procedures. At the same time, the methodology simplifies the interpretation in that less importance is placed on interpretation and labelling of surface boundaries and systems tracts.     

Seismic evidence for the Pleistocene depositional changes in Lake Hovsgol, Mongolia, and implications for the age model and the sediment grain size record of KDP-01 drill core

This paper seeks to arrive at a consistent interpretation of (1) the age model, (2) the grain size record, and (3) seismic reflection data from Lake Hovsgol (a.k.a Khubsugul or Hövsgöl), Mongolia, reported by Fedotov et al. (2007, earlier by Fedotov et al. 2002, 2004). In their most recent contribution, the grain size record of the KDP-01 drill core is interpreted as a climatic signal while little consideration is given to lake-level changes and hence to basin-wide changes in depositional setting evident from seismic profiles; also, a nearly linear age model is at odds with the seismic evidence for a major angular unconformity in the sediment strata. The lack of regional seismic stratigraphic analysis has thus led to an improbable interpretation of the Lake Hovsgol sediment grain size record and ultimately to an improbable scenario of Mongolian glaciation history. Using the available seismic profiles, here we show that the drill core penetrated several transgressive/regressive sedimentary sequences and a major angular unconformity. Therefore, the drilled sediment section cannot represent continuous sediment accumulation and the Brunhes age model across the unconformity cannot be nearly linear; the time interval representing a hiatus remains to be determined. The assumed nearly linear age/depth relationship in the upper 23 m above the angular unconformity is also an unlikely relationship, given the evidence of repeated changes in lake level, and hence in the depositional setting and sedimentation rates. We further propose a qualitative reference model for changes in the Lake Hovsgol depositional setting (presented as a step-by-step animation – see supplementary material) based on manually ‘backstripping and rebuilding’ the seismic pattern. We argue that this model provides a useful template of the likely sediment facies changes in the deep axial part of the Hovsgol basin: our crude model in fact captures the major depositional trends in the KDP-01 drill core section located some 10 km NW along the seismic line. We contend that changes in the depositional setting provide the first-order control on sediment grain size in the Hovsgol record. Our study provides important new constraints on the nature of sedimentary proxy records in Lake Hovsgol and on their interpretation as a record of Mongolian glaciation history.     

南极普里兹湾表层沉积物的元素组合特征及物源分析

利用中国南极科学考察第18—27航次在普里兹湾获得的20个表层沉积物样品,测定了其中C、N、Ca和Ti等多种常、微量元素的含量,分析了元素组合对指示物源的意义,探讨了普里兹湾的沉积环境和物质来源。结果表明:研究海域表层沉积物中元素含量的变异系数均较大,元素的平面分布、相关性和聚类特征出现两种模式;一类以OC、TN和S元素为主的元素组合指示了海洋生物来源,而另一类元素组合K、Ti和Rb等指示了陆源碎屑来源;湾内中心及东南部区域的沉积作用主要受控于上层水体的生物生产,而西侧的弗拉姆浅滩和艾默里冰架前缘陆架区的沉积物则包含大量冰筏碎屑的输入。     

普里兹湾陆架表层沉积物粒度特征及其环境指示意义

基于对普里兹湾陆架表层沉积物粒度分析,结合海区动力环境特点,初步探讨了考察区类型、组成及冰海沉积作用特点。研究区表层沉积物大体可分为:砾(G)、泥质砂质砾(ms G)、砾质泥(g M)、砾质泥质砂(gm S)、含砾泥((g)M)、含砾泥质砂((g)m S)、砂(S)、砂质粉砂(s Z)和粉砂(Z)九种类型。依据沉积物粒度特征与地形变化,可将研究区划分为东部含砾泥质区和西部含砾砂质区。在东部含砾泥质区,包括四夫人浅滩、Svenner水道区、普里兹水道区和埃默里海盆区,沉积作用主要受海流影响,冰筏碎屑的影响有限,沉积物总体较细,粘土和细粉砂含量较高,粗粉砂和砂含量较低。在西部含砾砂质区,包括弗拉姆浅滩和埃默里冰架前缘,沉积作用受冰山、埃默里冰架和海流的共同影响,沉积物中粘土含量较低,砂和砾石含量较高,但也有个别站位可能受冰间湖的影响,沉积物粒度偏细。     

Stratigraphic response to spatiotemporally varying tectonic forcing in rifted continental basin: Insight from a coupled tectonic‐stratigraphic numerical model

The role of spatiotemporally varying tectonic forcing in the development of stratigraphic patterns along passive margins and continental rift basins has been recognized for decades, but the exact nature of the stratigraphic response is still debated. This study develops a coupled tectonic‐stratigraphic numerical model with a fixed absolute lake level and constant climate conditions to quantify the signatures of spatiotemporally varying tectonic forcing on the stratigraphic record. This model consists of a three‐dimensional rift basin with a range of geomorphic features and produces a number of well‐recognized stratigraphic patterns, which are commonly interpreted to be caused by lake‐/sea‐level or climate fluctuations. This study demonstrates that the shoreline and grain‐size front are decoupled through the adjustment of the depositional slope and sediment dispersal under spatiotemporally varying tectonic forcing, especially in underfilled basins. Under such a decoupled situation, the pathway of the migrating subsidence centre correlates with the pathway of the grain‐size front, a result of competition between spatiotemporally varying tectonic forcing and autogenic sediment transport. The model results also highlight the significance of three‐dimensional variability in the stratigraphic response to tectonic forcing, which may be overlooked or misinterpreted and suggests a high degree of uncertainty in re‐establishing the base‐level cycles from the stratigraphic record alone. Moreover, spectral analysis of the modelled stratigraphy and tectonic forcing suggests that low‐frequency tectonic signals are more likely to be recorded in the stratigraphy with a lag time, whereas high‐frequency tectonic signals are likely to be shredded, mixed with autogenic signals, or buffered through sediment‐routing systems. Finally, quantitative measurements of the stratigraphic architecture of the Nanpu sag in the Bohai Bay Basin, China are used to tune the numerical model of this study to illustrate how to evaluate the role of tectonic forcing on the development of characteristic stratigraphic sequences.     

The Svalbard Eocene‐Oligocene (?) Central Basin succession: Sedimentation patterns and controls

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

Miocene shelf‐edge deltas and their impact on deepwater slope progradation and morphology,Northwest Shelf of Australia

Late‐middle Miocene to Pliocene siliciclastics in the Northern Carnarvon Basin, Northwest Shelf of Australia, are interpreted as having been deposited by deltas. Some delta lobes deposited sediments near and at the shelf break (shelf‐edge deltas), whereas other lobes did not reach the coeval shelf break before retreating landward or being abandoned. Shelf‐margin mapview morphology changes from linear to convex‐outward in the northern part of the study area where shelf‐edge deltas were focused. Location and character of shelf‐edge deltas also had significant impact on along‐strike variability of margin progradation and shelf‐edge trajectory. Total late‐middle and late Miocene margin progradation is ca. 13 km in the south, where there were no shelf‐edge deltas, vs. ca. 34 km in the north where shelf‐edge deltas were concentrated. In the central area, the deltas were arrested and accumulated a few kilometres landward of the shelf break, resulting in an aggradational shelf‐edge trajectory, in contrast to the more progradational trajectory farther north. This illustrates a potential limitation of shelf‐edge trajectory analysis: only where shelf‐edge deltas occur, there is sufficient sediment available for the shelf‐edge trajectory to record relative sea‐level fluctuations reliably. Small‐scale (ca. 400 m wide) incisions were already conspicuous on the coeval slope even before deltas reached the shelf break. However, slope gullies immediately downdip from active shelf‐edge deltas display greater erosion of underlying strata and are wider and deeper (>1 km wide, ca. 100 m deep) than coeval incisions that are laterally offset from the deltaic depocenter (ca. 0.7 km wide, ca. 25 m deep). We interpret this change in slope‐gully dimensions as the result of greater erosion by sediment gravity flows sourced from the immediately adjacent shelf‐edge deltas. Similarly, gullies also incised further (up to 6 km) into the outer shelf in the region of active shelf‐edge deltas.     

Axial and transverse deep-water sediment supply to syn-rift fault terraces: Insights from the West Xylokastro Fault Block,Gulf of Corinth,Greece

Deep-water syn-rift systems develop in partially- or transiently-linked depocentres to form complicated depositional architectures, which are characterised by short transport distances, coarse grain sizes and a wide range of sedimentary processes. Exhumed systems that can help to constrain the tectono-stratigraphic evolution of such systems are rare or complicated by inversion tectonics. Here, we document a mid-Pleistocene deep-water syn-rift system fed by Gilbert-type fan deltas in the hangingwall of a rift margin fault bounding the West Xylokastro Horst block, on the southern margin of the Gulf of Corinth, Greece. Structural and stratigraphic mapping combined with digital outcrop models permit observations along this syn-rift depositional system from hinterland source to deep-water sink. The West Xylokastro Fault hangingwall is filled by two distinct sediment systems; an axial system fed by coarse-grained sediment gravity flows derived from fault-tip Gilbert-type fan deltas and a lateral system dominated by mass transport deposits fed from an evolving fault-scarp apron. Abrupt changes in stratigraphic architecture across the axial system are interpreted to record changes in relative base level, sediment supply and tectonics. Locally, depositional topography and intra-basinal structures controlled sediment dispersal patterns, from bed-scale infilling of local rugose topography above mass transport complexes, to basin-scale confinement from the fault scarp apron. These acted to generate a temporally and spatially variable, heterogeneous stratigraphic architecture throughout the basin-fill. The transition of the locus of sedimentation from a rift margin to a fault terrace through the syn-sedimentary growth of a basinward fault produced regressive surfaces updip, which manifest themselves as channels in the deep-water realm and acted to prograde the system. We present a new conceptual model that recognises coeval axial and transverse systems based on the stratigraphic architecture around the West Xylokastro fault block that emphasizes the lateral and vertical heterogeneity of rift basin-fills with multiple entry points.     

The last British Ice Sheet: growth, maximum extent and deglaciation

The growth, maximum lateral extent and deglaciation of the last British Ice Sheet (BIS) has been reconstructed using sediment, faunal and stable isotope methods from a sedimentary record recovered from the Barra Fan, north-west Scotland. During a phase of ice sheet expansion postdating the early "warmth" of Marine Isotope Stage 3 (MIS 3), ice rafting events, operating with a cyclicity of approximately 1500 years, are interspersed between warm, carbonate-rich interstadials operating with a strong Dansgaard-Oeschger (D-O) cyclicity. The data suggest that the BIS expanded westwards to the outer continental shelf break shortly after 30 Ky BP (before present) and remained there until about 15 Ky BP. Within MIS 2, as the ice sheet grew to its maximum extent, the pronounced periodicities which characterize MIS 3 are lost from the record. The exact timing of the Last Glacial Maximum is difficult to define in this record; but maxima in Neogloboquadrina pachyderma (sinistral) ع⁸O are observed between 21-17 Ky BP. A massive discharge of ice-rafted detritus, coincident with Heinrich event 1, is observed at about 16 Ky BP. Deglaciation of the margin is complete by about 15 Ky BP and surface waters warm rapidly after this date.     

Sediment‐budget modelling of multi‐sourced basin fills: application to recent deposits of the western Adriatic mud wedge (Italy)

We analysed modern mass‐accumulation patterns on the western Adriatic mud wedge (Italy), an elongated belt of shelf mud formed by coalesced prodeltas of the Adige, Po, and Apennine rivers, as part of an integrated strategy aimed at producing a quantitative sediment budget model for muddy continental shelves sourced by multiple compositionally distinct fluvial systems. Sediment provenance and source‐specific accumulation rates of surface sediments were quantified by combining results of grain‐size analysis and geochemical analysis of specific size fractions with bulk mass accumulation rates. Statistical classification algorithms adapted to compositional data were used to partition the total (geochemical) variation of sediment properties into size‐related and provenance‐specific factors. We identified geochemically distinct fluvial end‐member sediment types in two different grain‐size fractions, which were grouped into sediments derived from the Apennine rivers, and sediments derived from the Po and Adige rivers. Compositional fingerprints (end‐member compositions) of each source area were estimated by taking into account relative rates of fluvial sediment supply from rivers as predicted by numerical modelling. The end members allow us to explain geochemical compositional variation of mud‐wedge surface sediments in terms of provenance and size‐selective dispersal, and map mass accumulation rates of sediments from individual source areas (grain size<63 μm), as well as bulk sand accumulation rates (grain size>63 μm) across the western Adriatic mud wedge. The source‐specific rates of fine‐grained sediment supply derived from geostatistical estimates of mass‐accumulation rates were used to calibrate the numerical model of sediment supply to present‐day conditions.     

Stratigraphic evolution of the upper slope and shelf edge in the Karoo Basin, South Africa

The Permian Ecca Group of the Karoo Basin, South Africa preserves an extensive well-exposed siliciclastic basin floor, slope and shelf-edge delta succession. The Kookfontein Formation includes multiple sedimentary cycles that display clinoform geometries and are interpreted to represent the deposits of a slope to shelf succession. The succession exhibits progradational followed by aggradational stacking of deltaic cycles that is related to a change in shelf-edge trajectory, and lies within two depositional sequences. Sediment was transferred to the slope via overextension of deltas onto and over the shelf edge, resulting in failure and re-adjustment of local slope gradients. The depositional facies and architecture of the Kookfontein Formation record the change from a bypass- to accretion-dominated margin, which is interpreted to reflect a decrease in sediment transport efficiency as the slope gradient decreased, slope length increased and shelf-edge trajectory rose. During this time the delivery system changed from point-sourced basin-floor fans fed by slope channels to starved basin-floor with sand-rich slope clinoforms. This is an example of a progradational margin in which the younger slope system is interpreted to be of a different style to the older slope system that fed the underlying sand-rich basin floor fans.