Sediment Dispersal Patterns Research Articles

Local controls on sediment accumulation and distribution in a fjord in the West Antarctic Peninsula: implications for palaeoenvironmental interpretations

We analyse surface sediment and its distribution in Flandres Bay, West Antarctic Peninsula, in order to understand modern day sediment dispersal patterns in a fjord with retreating, tidewater glaciers. The surface sediment descriptions of 41 cores are included in this study. The sediment facies described include muddy diatomaceous ooze, diatomaceous mud, pebbly mud, sandy mud and mud, with scattered pebbles present in most samples. In contrast to a traditional conceptual model of glacial sediment distribution in fjords, grain size in Flandres Bay generally coarsens from the inner to outer bay. The smallest grain size sediments were found in the bay head and are interpreted as fine-grained deposits resulting from meltwater plumes and sediment gravity flows occurring close to the glacier front. The middle of the bay is characterized by a high silt percentage, which correlates to diatom-rich sediments. Sediments in the outer bay have a high component of coarse material, which is interpreted as being the result of winnowing from currents moving from the Bellingshausen Sea into the Gerlache Strait. Palaeoenvironmental reconstructions of glacial environments often use grain size as an indicator of proximity to the ice margin. After a detailed analysis of a large number of cores collected in the study area, our findings highlight the variability in sedimentation patterns within a fjord and provide a valuable evidence of the complexity that may occur in the sedimentary record. Keywords: Flandres Bay; Antarctic Peninsula; sediment distribution; grain size. (Published: 12 August 2016) To access the supplementary material for this article, please see the supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 25284, http://dx.doi.org/10.3402/polar.v35.25284

Provenance identification and sedimentary analysis of the beach and bar systems in the Palaeogene of the Enping Sag, Pearl River Mouth Basin, South China Sea

During deposition in the Palaeogene, the Pearl River Mouth Basin (Enping Sag) was filled by sediments derived from northern and southern source regions. The northern sources are the fold belt Caledonian and Hercynian metamorphic rocks that are widely exposed along the South China block and stacked with Mesozoic igneous rocks, and the southern sources are Mesozoic igneous rocks from the southern Panyu lower uplift. We analysed the characteristics of the provenance and sediment-dispersal patterns of the beach and bar systems in the Palaeogene third-order sequence framework on the basis of detritus, thin section, zircon and the geophysical response test data. The source and deposition areas were distinguished based on their palaeogeomorphology. The sedimentary material composition of the deposition area was determined based on the characteristics of the detrital assemblage and cathode luminescence, and the characteristics of the age distribution were determined in detail using detrital zircon U–Pb dating. This study suggests that the provenance system in the Palaeogene mainly consisted of Palaeozoic metamorphic rocks and Mesozoic igneous rocks, with a supplement of Proterozoic metamorphic rocks. The transport capacity of three large fault troughs that delivered the northern provenances gradually increased from the Wenchang Formation (E2w) to the Enping Formation (E3e), whereas the southern provenances were transported by four or five incised valleys in E2w and then submerged in E3e. In the 3D seismic area, the features of the beach and bar sedimentary systems were described and interpreted based an analysis of the well-based sedimentary facies, seismic reflection characteristics and multiple attribute clustering. The results show that the beach and bar systems by the short-axis braided deltas mainly developed in the upper member of E2w and that the beach and bar systems on the subaqueous high in E3e developed during the Palaeogene. In addition, the bedrock-beach bar sedimentary system in the lower member (E3eL) was transferred to the braided delta–beach bar sedimentary system in the upper member (E3eU).

Sequence stratigraphy and seismic geomorphology application of facies architecture and sediment-dispersal patterns analysis in the third member of Eocene Shahejie Formation, slope system of Zhanhua Sag, Bohai Bay Basin, China

An important hydrocarbon reservoir is hosted by the third member of the Shahejie Formation (Es3) in the Zhanhua Sag of the Bohai Bay Basin. Using lithology, wire-line logs and three-dimensional (3-D) seismic data in the southern slope of Zhanhua Sag, we demonstrated the utility of stratal slice images for analyzing facies architecture and sediment-dispersal characters of complex depositional systems in Es3. The Es3, a para-second-order sequence, can be subdivided into three third-order sequences (from base to top: SQ1, SQ2, and SQ3). The facies architecture was analyzed by using the seismic geomorphology approach based on 3-D seismic data. Sediments of the Es3 sequences were derived from the southern Chenjiazhuang Uplift via six major incised valleys, four of them associated with slope-break belt in the southern zone, and others in the southwestern zone. Seismic stratal slices reveal different characteristics of the channels and lobes between south and southwest from source to sink. On the basis of an integrated analysis of well log, core data, seismic facies based on multi-seismic attributes, three depositional environments (e.g., “fan-delta”, “shallow lacustrine” and “turbidite” facies) have been recognized. Stratal slices indicate that the depositional environments of these sequences evolved from gravel- or sand-rich fan delta and turbidite to lacustrine mud, and lastly to mixed sand-mud fan delta systems. The results of high resolution 3-D depositional systems analysis showed that the third-order sequence located in different systems tracts of the para-second-order sequence would contribute to their systems tracts with the different types and scales of depositional systems. Types of slope belts, subsidence rate, sediment provenance and their evolution jointly control the sediment-dispersal characters in deposition area. The proposed sediment dispersal patterns may aid in the prediction of potential reservoir distribution.

Regional insights into the sedimentary organisation of the Walloon Subgroup, Surat Basin, Queensland

Despite more than a decade of intensive coal seam gas exploration and development in the Surat Basin, fundamental aspects surrounding the sedimentary organisation of the Walloon Subgroup remain unresolved. While generally agreed to have been deposited on a waterlogged alluvial plain, contradictory paleogeographic models describe the Walloon Subgroup as an internally draining fluvio-lacustrine system or, alternatively, as a southeast-prograding distributive trunk drainage system. The former invokes a radially organised fluvial catchment feeding a basin depocentre, suggesting that rivers within the study area flowed from east to west. In contrast, a prograding trunk drainage system assumes an axial system flowing southeastward towards a distant paleocoastline. Without a unifying conceptual model describing the organisation of the Jurassic depositional system, predictions about the distribution of alluvial subenvironments within the Surat Basin are difficult. This study tests previous hypotheses surrounding the Walloon Subgroup's sedimentary organisation by reconstructing regional variations in alluvial architecture, fluvial styles and sediment dispersal patterns. The workflow integrates borehole image log interpretation, wireline log analysis, core description and numerical modelling to explore the character and occurrence of subenvironments throughout the basin. Synthesis of interpretations suggests a composite meandering to anastomosing fluvial system containing both a south-oriented trunk drainage component and tributary rivers feeding the axial system from the east.

Sediment dispersal and accumulation off the present Huanghe (Yellow River) delta as impacted by the Water-Sediment Regulation Scheme

Surface sediment samples from 15 stations around the present Huanghe (Yellow River) river mouth were collected before, during and after the Water-Sediment Regulation Scheme (WSRS) in 2010 for grain size analysis. Hydrographic surveys conducted simultaneously at stations along three transects off the river mouth during the WSRS in 2013 were used to investigate the dispersal and accumulation of the Huanghe sediment off the present Huanghe subaqueous delta. During the WSRS period, the diluted water from the river covered all over the study area within the surface layer, whereas high-concentrated sediment was found in the bottom layers and to be limited in nearshore area shallower than 12m, indicating that the buoyant river plume was the main sediment dispersal pattern during the WSRS. At the early stage of the WSRS when large amount of clear water was released from the Xiaolangdi Reservoir, sediment eroded from the downstream riverbed in the lower reaches increased the median grain size of surface sediment at the river mouth. During the second stage when water discharge was reduced but sediment discharge was dramatically increased, the fine-grained sediment derived from the Xiaolangdi Reservoir mixed with the previously deposited coarser surface sediment, leading to the decreasing median grain size of surface sediment that approached to be poorly sorted. After the physical sorting from winter storms, the surface sediment was redistributed and varied regularly with water depth. As the median grain size of suspended sediment discharge to the sea has been significantly increased due to the WSRS, the river-delivered sediment mostly accumulated in the nearshore area, which effectively extended the subaerial delta and steepened the subaqueous slope off the present river mouth.

Palinspastic restoration of an exhumed deepwater system: A workflow to improve paleogeographic reconstructions

The Permian Laingsburg depocenter, Karoo Basin, South Africa, is the focus of sedimentological and stratigraphic research as an exhumed analog for offshore hydrocarbon reservoirs in deepwater basins. Thin-skinned thrust tectonics during the Permo-Triassic Cape Orogeny result in postdepositional deformation of the Permian basin fill. Regional-scale cross sections reveal two structural domains: a southern domain in the Laingsburg depocenter comprising 8–11-km wavelength north-verging fault-propagation folding, driven by buried low-angle ([Formula: see text]) reverse faults that coalesce at depth as part of a megadetachment below the Lower Paleozoic Cape Supergroup; and a northern domain to the north of the Laingsburg depocenter of short-wavelength, low-amplitude, asymmetrical folding facilitated by a detachment within the Permian Ecca Group. Five detailed structural cross sections permit the palinspastic restoration, and a calculation of the amount of shortening, across a [Formula: see text] area in the Laingsburg depocenter. Average shortening across the study area is −16.9% (5.8 km), and it decreases south to north. Shortening estimates from the Upper Ecca Group increase from 4.3 km near Matjiesfontein in the west to 10.4 km near Prince Albert in the east. Three-dimensional restorations of stratigraphic surfaces are consistent with these figures (−17%), and they allow paleogeographic and isopach thickness maps to be resorted to their configuration at the time of deposition. Structural restoration can be routinely used in outcrop studies to improve the accuracy of dimensions (e.g., volumetrics) and reconstructions (e.g., sediment dispersal patterns) derived from ancient sedimentary systems. The workflow presented here will add value to exhumed basin analogs by presenting prekinematic configurations at the frontal margins of fold-thrust belts.

Differential control of syndepositional faults on sequence stratigraphy and depositional systems during main rift I stage in the southeastern fault zone of Qingxi Sag, Jiuquan Basin, Northwestern China

In active rift basins, syndepositional faults exert a major control on sequence stratigraphic patterns and depositional system features, which together determine reservoir distribution, geometry, and quality. In this study, we analyze syndepositional fault characteristics of the main rift I stage in the southeastern fault zone of the Qingxi Sag, Jiuquan Basin. The syndepositional faults are marked by boundary fault with high dip angle and strong activity in the western section, and both boundary fault and associated secondary fault with relatively low dip angles and weak activity in the eastern section. In response to these different fault patterns and activity intensities, the resulting sequence stratigraphic and depositional system features are different in the western and eastern fault zones. The southeastern basin margin is divided into steep slope fault belt in the west and fault terrace belt in the east, and two corresponding types of sequence stratigraphic patterns developed. Contrastive analysis of the depositional systems highlights that they differed in sediment dispersal patterns, distribution scales, development positions, and sediment physical properties. Reservoirs associated with the depositional systems were further differentiated into four types. Analyzing the characteristics of the four types of reservoirs and their corresponding traps provides a useful reference for the deployment of future hydrocarbon exploration in the study area.

Provenance of Holocene sediments in the outer part of the Paleo-Qiantang River estuary, China

Abstract Core SE2 from the landward part of the modern Qiantang River (QR) estuary contains a 50 + m-thick succession of late Pleistocene to Holocene deposits that records the transgressive–regressive environmental transition from fluvial sedimentation, through a paleo-estuary phase and shallow-marine deposition, to the modern estuarine setting. Sand and silt samples from the Paleo-QR estuary phase were analyzed for heavy-mineral and geochemical compositions, as well as the U–Pb ages of detrital zircons, in order to investigate the source of the sediment during the Holocene. The Paleo-QR estuary sediments in core SE2, which accumulated between approximately 10,100 and 9500 cal yr B.P., contain a characteristic heavy-mineral assemblage of hematite–limonite, epidote, zircon, leucoxene and magnetite, consistent with derivation from the QR drainage basin. These data, as well as geochemical proxies including the fractionation patterns of trace and rare earth elements, and elemental ratios La/Sc and Th/Co, suggest that the Paleo-QR estuary sediments cannot be derived from the modern Changjiang River to the north, which is contributing to the infill of the present-day QR estuary. Two major zircon-grain age peaks (99–250 Ma and 740–1000 Ma) coincide with the main tectonic and magmatic events in the QR catchment, whereas the characteristic age peaks for the modern Changjiang River sediments (e.g. 200–400 Ma and 1800–2100 Ma) are absent. Because the portion of the Paleo-QR estuary sampled is interpreted to lie seaward of the contemporaneous bedload convergence, in the area experiencing flood-dominant, landward transport of sediment, the sand and silt are unlikely to have come directly from the QR. Instead, we infer that the sediments were derived from the offshore part of the QR incised valley by flood-tidal reworking and landward transport. During the Paleo-QR estuary period, the incised valleys of the QR and Changjiang River were separate from each other for a considerable distance offshore. Sediment supplied by the Changjiang River was trapped in its estuary such that there was no sediment exchange between the two systems as there is now. This case study indicates that the combination of sediment geochemistry, heavy-mineral composition, and zircon chronology can supply important constraints on sediment dispersal patterns, even in dynamic estuarine and coastal areas with complex sediment transport pathways.

Uppermost Devonian (Famennian) to Lower Mississippian events of the western U.S.: Stratigraphy, sedimentology, chemostratigraphy, and detrital zircon geochronology

Upper Devonian to Lower Mississippian strata in Utah and Montana record global events through this important interval in Earth history. Late Famennian strata of the Beirdneau, Leatham, and Pilot Shale formations in Utah, and Three Forks and Sappington formations in Montana, record widespread deposition of generally fine-grained siliciclastic and carbonate strata. Integration of sedimentology, physical stratigraphy, chemostratigraphy, and published biostratigraphy allows for the recognition of important disconformities and regional stratigraphic patterns. These enable the reconstruction of uppermost Devonian to lowermost Mississippian depositional, tectonic, and eustatic history of the region. Carbon isotopic data allows for stratigraphic evaluation of the presence and absence of global bioevents of the Late Devonian, including the Annulata, Dasberg, and Hangenberg events, some of which are clearly recorded in hinterland deposits to the east in Colorado. While the Devonian–Mississippian boundary is also missing in our sections, a significant positive shift in δ13Ccarb in Lower Mississippian strata in Utah and Montana represents one of the largest positive δ13Ccarb isotope excursions of the Phanerozoic, linked to drawdown of atmospheric CO2 and glaciation in the Kinderhookian. Detrital zircon spectra from latest Devonian to Early Mississippian strata of Utah and Colorado include populations representing derivation from the Mazatzal and Yavapai provinces, Middle Proterozoic anorogenic granite bodies, and a small influx of Grenville and presumed Appalachian–Caledonian grains. Minor Paleoproterozoic and Late Archean peaks in Utah are likely multiple generation grains originally derived from the Peace River Arch of northwestern Canada and recycled in Ordovician rocks of Nevada. These patterns in detrital zircon geochronological data reflect, in part, changes in sediment dispersal patterns due to tectonic and eustastic variability within the Antler foreland basin during the Devonian–Mississippian boundary interval. This variability also led to irregular spatial patterns of unconformity development, as well as complicated physical stratigraphic and chemostratigraphic architecture.

A comparative study of the flux and fate of the Mississippi and Yangtze river sediments

Abstract. Large rivers play a key role in delivering water and sediment into the global oceans. Large-river deltas and associated coastlines are important interfaces for material fluxes that have a global impact on marine processes. In this study, we compare water and sediment discharge from Mississippi and Yangtze rivers by assessing: (1) temporal variation under varying climatic and anthropogenic impacts, (2) delta response of the declining sediment discharge, and (3) deltaic lobe switching and Holocene sediment dispersal patterns on the adjacent continental shelves. Dam constructions have decreased both rivers’ sediment discharge significantly, leading to shoreline retreat along the coast. The sediment dispersal of the river-dominated Mississippi Delta is localized but for the tide-dominated Yangtze Delta is more diffuse and influenced by longshore currents. Sediment declines and relative sea level rises have led to coastal erosion, endangering the coasts of both rivers.

The role of mass-transport complexes in controlling channel avulsion and the subsequent sediment dispersal patterns on an active margin: The Magdalena Fan, offshore Colombia

Submarine channel avulsion is a fundamental process in the evolution of submarine fans that records abrupt changes in the sediment dispersal patterns, and the development of sand-rich splay deposits. On passive margins, changing flow conditions have been invoked to explain the location and timing of channel avulsion. On tectonically active basin margins, processes such as seismic activity, seabed faulting and folding and emplacement of mass-transport complexes (MTCs) are additional triggers. This study is based on the detailed mapping and interpretation of the first 1000 m below seabed of a 1900 km2 3D seismic volume in the southern Magdalena Fan, offshore Colombia, a tectonically-active margin. The emplacement of a large MTC deposit (>400 km2 in area and 200 m in thickness) is interpreted to have controlled the avulsion node of a major channel-levee complex-set and influenced the evolution of the subsequent avulsion lobe complex-set. The basal surface of the MTC is highly erosional resulting in net degradation of the seascape. Substrate entrainment by the MTC left behind a narrow erosional remnant ridge that formed a bathymetric anomaly upon which a channel-levee complex-set developed. The irregular levee geometries above the remnant ridge led to instability and levee collapse prior to channel avulsion. Map view geometries and seismic amplitude extractions suggest that the initial avulsion lobes were mud-prone and relatively erratically distributed, and evolved to form well-defined sand-prone lobes. The distribution, morphology and evolution of the avulsion lobe complexes were strongly influenced by the bathymetric anomalies on the MTC top surface which, are generally coincident with protruding megaclasts.The role of MTC emplacement in triggering submarine channel avulsion and the development of sand-prone deposits in proximal locations has important implications for hydrocarbon exploration and production. This study serves as a high-resolution, shallow-subsurface analogue for less well-imaged avulsion cycles on tectonically-active basin margins that are prone to MTCs.

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.

Evolution of the Gelasian (Pleistocene) slope turbidite systems of southern Marche (Peri-Adriatic basin, central Italy)

Examples of slope channels and canyons being diverted by structurally related sea-floor topography are commonly found both on the modern seabed and in the subsurface, in deep-water fold and thrust belts but their depositional histories have rarely been documented using examples from outcrop. The synthesis of outcrop (original geological field mapping at 1:10,000 scale) and subsurface data sets from the early Pleistocene stratigraphic succession of the Peri-Adriatic basin provides a window into the overall evolutionary pattern of large intraslope turbidite systems that, during the Gelasian (2.58–1.80 Ma), shed Apennine-derived clastic sediments into the adjacent deep-water basin. Trends from mapping and paleocurrent indicators converge to indicate that the sea-floor bathymetric expression of a thrust-related anticline, the north-trending Jesi-Nereto-Zaccheo structure, likely influenced the downslope transport direction of gravity flows and sediment dispersal pattern. During early and middle Gelasian time, coarse-grained turbidite deposition occurred on the western flank of the intraslope anticline by westerly sourced, northward-flowing turbidity currents, indicating that the opposing sea-floor topography was sufficient to cause the diversion of turbidite systems, forcing them to travel near parallel to the east-facing regional paleoslope for significant distances. By very late Gelasian time, the intraslope accommodation space on the western flank of the anticline had filled and turbidites were dispersed through dip-oriented conduits incising across the crest of the underlying structure.

Application of Numerical Model in Suspended Sediment Transport Studies along the Central Kerala, West-coast of India

The objective of the present study is to understand the sediment transport along the central Kerala coast. The data used in the study include winds, tides, bathymetry and the satellite derived suspended sediment concentrations (SSCs). A sediment transport model - MIKE 21 Mud Transport (MT) - for combinedcurrents, and SSCs is used to quantify and to find out the movement of fine sediments along the coast. MIKE MT is interrelated with the other modules of MIKE 21 Hydrodynamics (HD) module. The HD module simulate the water level variations and flows in response to a variety of forcing functions in coastal areas. Suspended sediment transport in the coastal waters of central Kerala is simulated utilizing the SSC data derived from Oceansat-2 Ocean Colour Monitor (OCM) satellite imagery, using the MIKE-21 MT model for the period 18thto 24thJanuary 2011. The SSCs of 18thJanuary 2011 are considered as the initial condition in MIKE 21 MT model and the model is simulated for the period from 18th to 24th January 2011. The simulated SSCs are compared with satellite derived SSCs. The results exhibit good coefficient of determination among these variables. Sediment dispersion patterns are explained in relation to simulated tidal currents, dominated by the southward flowing coastal currents, which are more consistent in its direction and magnitude along the coast. It is observed that tides, winds and currents arethe important physical factors that control the dispersal patterns. The results suggest that sediment transport is from north to south during the study period i.e., in January 2011.

Retrieval of coastal ocean currents using MCC technique on satellite imagery for supplementing altimeter derived currents

Abstract. Maximum Cross Correlation (MCC) technique have been used to derive coastal currents from sequential OCM derived suspended sediment concentration (SSC) maps and the MCC currents are integrated with the Ocean surface current analysis-Real time (OSCAR) ocean currents along the coastal regions of the Southern India. OSCAR currents are mainly depended on the oceanographic measurements from the satellite altimeter which have limitations in the coastal region and in representing the mesoscale properties dominating the coastal ocean. Sequential pair of atmospherically corrected and georeferenced OCM image is used to derive SSC, along the southern coast of India. Maximum Cross-Correlation (MCC) method is applied on the sequential time lapsed images of OCM for matching the suspended sediment dispersion patterns. The MCC technique involves computing of cross-correlation coefficients and identifying correlation peaks. The spatial change of the sediment pattern occurs due to the advection by the currents and the extent of the change corresponds to the speed and direction of the current. From the first image, template window is selected, which is searched in the second image within large region defined as the search window. The movement of the SSC pattern is calculated based on the maximum cross correlation in successive images. Error statistics are calculated between the spatially coherent MCC vectors and OSCAR currents. Based on statistical analysis, an error threshold of 30 degree for current direction and 0.06m/sec for current speed was given to MCC currents and MCC currents beyond the error limit are rejected, while the MCC current within the error limit is merged with the OSCAR ocean currents. The merging of MCC currents has spatially enhanced the OSCAR currents. MCC method is significant in calculating the coastal currents and its mesoscale properties, which dominate the coastal surface flow field and can be used in supplementing the OSCAR ocean currents. Merging of both the currents, have effectively resulted in preparing contiguous maps of coastal ocean currents.

Seasonal controls on sediment transport and deposition in Lake Ohau, South Island, New Zealand: Implications for a high‐resolution Holocene palaeoclimate reconstruction

AbstractLaminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high‐resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid‐latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin‐wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high‐resolution palaeoclimate record from this temperate lake.

Lithofacies of transgressive–regressive sequence on a carbonate ramp in Vindhyan basin (Proterozoic): a case of tidal-flat origin from central India

Palaeoenvironment of late Proterozoic carbonate deposits of Vindhyan basin of central India has been studied using lithofacies analysis, petrographical character and sediment dispersal patterns. Based on field parameters, 12 lithofacies were identified from five sections. For environmental interpretation, these lithofacies have been grouped into two major lithofacies associations namely a lower association A comprising reefal lithofacies, algal lithofacies, oolitic-intraclastic lithofacies, stromatolitic limestone lithofacies and an upper lithofacies association B, which includes nodular limestone lithofacies, large-scale planar cross-bedded lithofacies, parallel and ripple cross-laminated lithofacies, lenticular and flaser bedded lithofacies, shaly limestone lithofacies, synaeresis cracked lithofacies, deformed limestone lithofacies and finally, channelized and sandy limestone lithofacies. Reefal lithofacies and oolitic-intraclastic lithofacies were deposited under subtidal conditions. Synaeresis cracked lithofacies, lenticular and flaser bedded lithofacies, channelized and sandy limestone lithofacies were deposited under intertidal conditions whereas stromatolitic limestone lithofacies deposition ranged between subtidal to intertidal domains. Lithofacies character of the rock succession as well as the microfacies associations recognized petrographically indicate that the depositional environment belongs to platform interior with restricted circulation to marginal sand shoals in a carbonate ramp setting. Due to calcium-carbonate-saturated water, the diagenesis took place in stagnant marine phreatic environment where little compaction occurred, with abundant micrite as primary groundmass, and rapid cementation by calcite took place. With palaeocurrent current direction towards south and azimuthal dispersion of 270°, a pattern akin to a marine system is corroborated.

Provenance study of Paleocene and Cretaceous clastic sedimentary rocks from the Davis Strait and the Labrador Sea, based on U-Pb dating of detrital zircons

Abstract Cretaceous–Paleocene strata of the Labrador Shelf and the Davis Strait are composed of clastic sedimentary and volcanic rocks, and some of these strata are considered possible petroleum reservoirs. The U-Pb provenance distributions of detrital zircons from nine different wells located in Davis Strait and on the Labrador Shelf, and which penetrate these rocks, were studied by LA-ICP-MS in order to assess sediment dispersal patterns and distribution of potential reservoirs. Samples from the mid-Cretaceous Bjarni Formation, the Upper Cretaceous Markland Formation, and the Paleocene Cartwright Formation were analysed. Based on U-Pb provenance data, the Bjarni Formation can be divided into northern and southern depositional areas. The northern area is dominated by 3000 Ma and 3200 Ma zircons, interpreted as derived primarily from the Hopedale block; in contrast, the southern area is dominated by 1800-1700 Ma ages, interpreted to be derived from the Makkovik Province and the Grenville Province. Markland Formation strata also show a variation in ages from north to south. Strata in the northern area are dominated by Archean zircons, with the main population at 3600–3500 Ma and significant numbers of 3800-3700 Ma and 2800-2700 Ma ages; in the southern area, no Eoarchean zircons were noted and strata are instead dominated by 3200-3100 Ma, 2900-2800 Ma, and 1800 Ma zircon populations. The Saglek block is interpreted as the dominant source for the northern area, mixed with sediment from the Hopedale block; the source for the southern area is inferred to be a combination of the Hopedale block and the Makkovik Province. Finally, the Cartwright Formation also shows distinct variations in source depending on the area. The northernmost samples yield a range of ages, and hence represent a large source area, with dominant zircon ages of 2800-2700 Ma. The middle area is dominated by a broad peak in ages from 3200-2550 Ma, whereas the southern area is dominated by Paleoproterozoic ages, with a large population at 1800 Ma. The general pattern for the Cartwright Formation is similar to that of the Bjarni and Markland formations in that the sediment transport direction was northerly and the main sources are interpreted to have been the Saglek block, Hopedale block, and the Makkovik Province. In addition, signatures from the Grenville Province, the Nain Plutonic Suite, and the Appalachian Orogen are also present. The detrital zircon patterns of the wells are consistent with Labrador as the main source region and the overall pattern indicates that the main sediment transport direction was generally northerly from Early Cretaceous until Paleocene time.

Reciprocal Changes In Foreset To Bottomset Facies In A Gilbert-Type Delta: Response To Short-Term Changes In Base Level

Abstract Results of a detailed sedimentological study of the mid-Pleistocene Gilbert-type Ilias delta at the southern coast of the Corinth Rift, Greece, are reported. The study indicates that the development of a turbidite-dominated facies assemblage (TFA) of delta foreset deposits is associated with an oblique delta-brink geometry, which signifies a deficit of delta-front accommodation due to the falling or stable base level. A debrite-dominated assemblage (DFA) of foreset deposits forms when the base level is rising and the delta-brink geometry becomes sigmoidal, signifying an increase in delta-front accommodation. The comparison of coeval foreset and toeset to bottomset deposits in the delta indicates a reverse pattern of reciprocal changes in facies assemblages, with the foreset TFA deposits corresponding to delta-foot DFA deposits, and with the foreset DFA deposits corresponding to delta-foot TFA deposits. This reciprocal alternation of TFA and DFA facies assemblages is attributed to changes in the delta-front accommodation driven by short-term base-level changes, with a degree of “noise” in the facies record due to the system autogenic variability and regional climatic fluctuations. The study sheds a new light on the changing pattern of subaqueous sediment dispersal in Gilbert-type deltaic systems in response to base-level changes. It also indicates a new possibility for the recognition of a hidden record of such changes in other similar ancient deltas on the basis of their detailed facies analysis.

SEDIMENT TRANSPORT AND DISPERSAL IN THE NEARSHORE OF “FLASH-FLOOD” RIVERS.

River sediment dispersal on the near-shore of "flash-flood† rivers is investigated using a coupled wave-current-sediment transport model. Besòs and Llobregat rivers (short and mountainous rivers in NW Mediterranean Sea, near to Barcelona City) are used as examples to study the sediment transport under "flash-flood† regime. The modeling system COWAST which includes the coupling between the water circulation model ROMS and the wave model SWAN, is applied to assess the sediment dispersal mechanisms and deposition in the coastal area off the two river mouths. Preferential depositional areas such as mud-belts were identified from the simulations. The sediment dispersal pattern obtained by the model agrees with observational measurments. Complementary numerical simulations revealed sorting of sediment grain size in the cross-shelf direction.