Sedimentary Features Research Articles

Bouldery debris mantle deposited by cold-based ice offshore of the Vestfold Hills, East Antarctica

Streamlined subglacial sediments are common in seafloor bathymetric images from many glaciated margins. Less common are seafloor features left by cold-based ice. The shallow waters around the now largely ice-free Vestfold Hills in East Antarctica (Fig. 1a, e) show few streamlined sedimentary features, even though the area has clearly been glaciated as implied by striated bedrock, moraine ridges and abundant erratic boulders on adjacent exposed land. A likely explanation for the absence of streamlined subglacial landforms is that the area was glaciated by ice frozen to its bed. Fig. 1. Multibeam swath bathymetry, outcrop photo and topographic profiles of boulder-rich debris mantle and sand ribbons from the Vestfold Hills coastal zone, East Antarctica. ( a ) Sun-illuminated bathymetric image of Airport Beach Embayment showing the debris mantle. Ice-keel ploughmarks are shown outside the embayment. Acquisition system Kongsberg EM3002. Frequency 300 kHz. Grid-cell size 2 m. ( b ) Close-up of debris mantle showing individual boulders. ( c ) Photograph of bouldery debris mantle above sea level. Large boulder is 4 m in diameter. ( d ) Multibeam image of sand ribbons and boulders. ( e ) Location of study area (red …

Terminal moraines in the fjord basins of sub-Antarctic South Georgia

Sub-Antarctic South Georgia (54° 17′ S, 36° 30′ W, 3755 km2) is a large heavily glacierized island that is 170 km long, 39 km wide and rises to elevations of 2934 m. The island has extensive evidence of past glacial expansion with moraines preserved on land (Bentley et al. 2007), in the fjords (Hodgson et al. 2014) and in glacial troughs that extend 60–100 km to the edge of the continental shelf where some terminate in trough-mouth fans (Graham et al. 2008). A paucity of chronological control means that, at present, it is not possible to identify which of these sets of features mark the limit of a more extensive ice cap from the Last Glacial Maximum (LGM). The glacial geomorphology of nine of the deep glacial fjords on South Georgia has been studied from ship-based geophysical surveys. Despite the different lengths, widths and orientations of the fjords, a relatively consistent pattern of large-scale (102–103 m) submarine geomorphological features is present (Hodgson et al. 2014). Most of the fjords have shallow (30–150 m) inner basins characterized by a range of seafloor sedimentary features including sediment gravity flows, debris fans and slope failures, all of which are associated with high glacigenic sediment supply. The inner …

Oceanographic processes and morphosedimentary products along the Iberian margins: A new multidisciplinary approach

Our understanding of bottom-currents and associated oceanographic processes (e.g., overflows, barotropic tidal currents) including intermittent processes (e.g., vertical eddies, deep sea storms, horizontal vortices, internal waves and tsunamis) is rapidly evolving. Many deep-water processes remain poorly understood due to limited direct observations, but can generate significant depositional and erosional features on both short and long term time scales. This paper represents a review work, which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the Iberian continental margins. This review explores the implications of the studied processes, given their secondary role relative to other factors such as mass-transport and turbiditic processes, and highlights three major results: a) contourite depositional and erosional features are ubiquitous along the margins, indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation; b) the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient, including the contourite terraces development; and c) contourites deposits exhibit greater variation than the established facies model suggests. Therefore, a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development. An integrated interpretation of these oceanographic processes requires an understanding of contourites, seafloor features, their spatial and temporal evolution, and the near-bottom flows that form them. This approach will synthesize oceanographic data, seafloor morphology, sediments and seismic images to improve our knowledge of permanent and intermittent processes around Iberia, and evaluate their conceptual and regional role in the margin's sedimentary evolution. Given their complexes, three-dimensional and temporally-variable nature, integration of these processes into sedimentary, oceanographic and climatological frameworks will require a multidisciplinary approach that includes Geology, Physical oceanography, Paleoceanography and Benthic Biology.

Ichnological and sedimentological features of the Hongguleleng Formation (Devonian–Carboniferous transition) from the western Junggar, NW China

Two sections of the Late Devonian to Early Carboniferous Hongguleleng Formation in the Sha'erbuerti and Xiemisitai mountains of western Junggar, NW China were logged in detail and studied with particular reference to their trace fossil content and sedimentary features. The Hongguleleng Formation is composed essentially of shallow marine deposits formed in a volcanic arc-related setting. It contains trace fossils including indeterminate ellipsoid structures, indeterminate shallow-pit structures, Chondrites intricatus, Chondrites targionii, Chondrites isp., Dolopichnus gulosus,?Multina isp., Nereites missouriensis, Nereites isp., Palaeophycus tubularis, ?Phycosiphon isp., ?Phymatoderma isp., Rhizocorallium commune, Rosselia cf. socialis, Teichichnus rectus, Teichichnus ispp., Thalassinoides isp., and Zoophycos ispp. These ichnofossils and related bioturbation structures constitute five distinct groups of ichnofabrics: Chondrites–?Phymatoderma, Rhizocorallium commune, anemone dwelling/burrowing, Teichichnus, and Zoophycos ichnofabrics, conforming to an upward trend from the Cruziana to Zoophycos ichnofacies. The volcanic arc setting provides a natural laboratory to investigate the colonisation styles of benthic faunas during the Devonian, especially for environments with widespread and relatively frequent depositional events disturbing background deposition. The distal event beds are especially suitable for the distinction of the relationship between background and post-event ichnofaunas. Simple and composite ichnofabrics have been distinguished. The simple ichnofabrics are typified by the indeterminate ellipsoid “ichnofabric” made by sea anemones, representing short colonisation event and in situ death and burial resulted from relatively high sedimentation rates even during the periods between volcanic explosions. The composite ichnofabrics are characterised by the Chondrites–?Phymatoderma, ?Multina–Zoophycos and multi-tier Zoophycos ichnofabrics, representing vertical migration of benthic faunas in pace with either distal event deposition or steadily accreted sea floor. The colonisation window in the arc-related setting is closely related to sedimentation rates and frequency of depositional events, determining the completeness of burrow system structure and maturity of benthic communities.

Late‐summer peak in sediment accumulation in two lakes with contrasting watersheds, alaska

The timing of clastic sedimentation in two glacial‐fed lakes with contrasting watersheds was monitored using sequencing sediment traps for two consecutive years at Allison Lake (Chugach Range, Alaska) and four months at Shainin Lake (Brooks Range, Alaska). Shainin Lake is a weakly stratified lake fed by distant glaciers, whereas Allison Lake is more strongly stratified and fed predominantly by proximal glaciers. At Shainin Lake, sediment accumulation started in late June and reached its maximum in mid‐August, just before lake mixing and during a period of low river discharge. The grain size of the sediment reaching the sediment trap in Shainin Lake was homogenous throughout the summer. At Allison Lake, pulsed sedimentation of coarse particles during late summer and early fall storms were superimposed on the fine‐grained sedimentation pattern similar to that observed at Shainin Lake. These storms triggered underflows that were observed in the thermal structure of the lake and deposited abundant sediment. The sequencing sediment traps reveal a lag between fluvial discharge and sediment deposition at both lakes, implying limitations to interpreting intra‐annual sedimentary features in terms of inflow discharge.

Hydrological and sedimentary controls over fluvial thermal erosion, the Lena River, central Yakutia

Water regime and sedimentary features of the middle Lena River reach near Yakutsk, central Yakutia, were studied to assess their control over fluvial thermal erosion. The Lena River floodplain in the studied reach has complex structure and embodies multiple levels varying in height and origin. Two key sites, corresponding to high and medium floodplain levels, were surveyed in 2008 to describe major sedimentary units and properties of bank material. Three units are present in both profiles, corresponding to topsoil, overbank (cohesive), and channel fill (noncohesive) deposits. Thermoerosional activity is mostly confined to a basal layer of frozen channel fill deposits and in general occurs within a certain water level interval. Magnitude-frequency analysis of water level data from Tabaga gauging station shows that a single interval can be deemed responsible for the initiation of thermal action and development of thermoerosional notches. This interval corresponds to the discharges between 21,000 and 31,000m3s−1, observed normally during spring meltwater peak and summer floods. Competence of fluvial thermal erosion depends on the height of floodplain level being eroded, as it acts preferentially in high floodplain banks. In medium floodplain banks, thermal erosion during spring flood is constrained by insufficient bank height, and erosion is essentially mechanical during summer flood season. Bank retreat rate is argued to be positively linked with bank height under periglacial conditions.

Sequence and sedimentary features of the Changxing Fm organic reefs and their control on reservoir development in the Yuanba Gas Field, Sichuan Basin

In the Yuanba area, Sichuan Basin, the gas reservoirs in the Upper Permian Changxing Fm are now at the development stage. With the smooth progress of development, it is urgent to characterize the reservoir architectures accurately and summarize the controlling factors for reservoir development. In this paper, research was mainly performed on the Changxing Fm organic reefs in terms of their sequence stratigraphy, sedimentary facies, and reservoir characteristics and architectures based on core observation and thin section analysis, combined with physical property data and logging curves analysis results. It is shown that the Changing Fm can be divided into two third-order sequences and six fourth-order sequences, their electric logs are characterized by abrupt change above and below the high-frequency sequence boundary and are consistent with the sedimentary cycles controlled by high-frequency sequences. Besides, the Changxing Fm organic reefs mainly represents zonal distribution outside SQ2 platform margin, and they are vertically composed of two obvious two reef sedimentary cycles and laterally developed in asymmetric patterns (early in the east and late in the west). Finally, in general, organic reef (bank.) reservoirs are mainly composed of low-porosity and moderate–low-permeability dissolved dolomite reservoirs, and they are mostly distributed at reef caps in the upper–middle parts of the two fourth-order sequences, with the characteristics of multiple beds, thin single beds, different types of reservoirs with different thickness interbedded with each other, strong heterogeneity and double-layer reservoir architectures. It is concluded that the distribution of organic reef microfacies in this area is controlled by high-frequency sequence, which is the key controlling factor for reservoir development and spatial distribution.

The consistency between Na content distribution at the subsurface and the lake body's movement in Lop Nur

ABSTRACTHistorically, Lop Nur was a large and famous salt lake that acted as an important geographic position along the ancient ‘Silk Road’, and was associated with the surrounding old civilizations, such as Loulan and Haitou. However, it dried up before 1972. It shows a clear ‘Ear’ feature on synthetic aperture radar (SAR) images. The objective of this paper is to interpret Lop Nur's environmental evolution during its drying-up process based on an analysis of its sodium sedimentary feature. The genetic algorithm-partial least squares approach is introduced as a modeling method to retrieve the subsurface sodium content from polarimetric parameters obtained by Cloude decomposition. As a result, the R2 and root-mean-square error can reach 0.7 and 9.1 g/kg. It is suggested that the subsurface salt content was the primary reason for the bright-grey strips textures on SAR images. Furthermore, our results show that the sodium content along the same strip changed, with its distribution exhibiting consistency with the lake body's movement driven by the strong wind. In future, high-precision topographical data will be considered, and should be helpful in the analysis of lake body movement. The method of this paper can also be applied in other similar dried salt lakes.

Climatic, tectonic and volcanic controls of sediment supply to an Oligocene Foredeep basin: The Val d'Aveto Formation (Northern Italian Apennines)

The Val d'Aveto Formation is a turbidite sequence deposited in the Northern Apennines during the Oligocene (32–29Ma). The occurrence of calcareous, siliciclastic, volcaniclastic and carbonatoclastic deposits makes the Val d'Aveto Formation a natural laboratory to study the interplay among climate, tectonics and volcanism in a subduction-related context. Eight logs have been studied in order to reconstruct the stratigraphic architecture of the succession. Ten different facies (one limestone senso lato facies, four siliciclastic facies, four volcaniclastic facies and one carbonatoclastic facies) have been recognized on the basis of their different sedimentary features, microtextures and matrix compositions (through thin section analysis and X-ray powder diffraction). For the first time, syn-volcanic facies (pyroclastic density current and epiclastic deposits) have been distinguished from post-volcanic facies in the volcaniclastic facies. Compositional trends of sandy to muddy detritus, together with image analyses on gravel dimensions, highlight spatial and temporal persistence of the syn-depositional volcanic activity across the source-to-sink system. Lithological and petrographic analyses on the gravel size fraction of the siliciclastic and volcaniclastic detritus point out a SE France provenance and reveal the strong influence that tectonics has on sediment production. The comparison between the geodynamic evolution of the source area and the stratigraphic evolution of the Val d'Aveto Formation can help unravel the importance of climate on the redistribution of tectonically produced sediments and shaping of the resulting submarine fan.

Conjugate margin pattern of the Southwest Sub‐basin, South China Sea: insights from deformation structures in the continent‐ocean transition zone

AbstractEight cross‐sections from the continent‐ocean transition zone of the Southwest Sub‐basin, South China Sea, have been used to compare conjugate rifted margins that are typical of magma‐poor rift systems. The geological timing of the break‐up unconformity in the continental margins shows that the Reed Bank and the Dangerous Grounds in the south continental margin connect with the Zhongsha Islands and the western Phu Khanh Basin, which experienced northwest‐southeast oriented movement after the opening of the Southwest Sub‐basin. Detailed interpretations identify a range of deformational and sedimentary features in the continent‐ocean transition zones with and without rigid blocks. Remarkable structural similarities appear in the transition zone lying within the convex‐shaped area shaped by rigid blocks of the conjugate margin (e.g. the Zhongsha Islands and the Reed Bank) or within concave‐shaped areas sandwiched by rigid blocks. Rigid tectonic blocks such as the Zhongsha Islands and the Reed Bank played important roles in both the shaping of the continent‐ocean boundary and the initial continental break‐up. Copyright © 2015 John Wiley & Sons, Ltd.

Sedimentary features and exploration targets of Middle Permian reservoirs in the SW Sichuan Basin

The exploration direction and targets for the large-scale Middle Permian gas reservoirs in the Sichuan Basin are hot spots and challenges in current exploration researches. The exploration successes of large gas field of Cambrian Longwangmiao Formation in Gaoshiti-Moxi region, Central Sichuan Basin, indicated that prospective sedimentary facies belt was the basis for the formation of large gas fields. In this paper, based on seismic data, outcrop data and drilling data, the tectonic framework and sedimentary features of the Middle Permian in the SW Sichuan Basin were comprehensively studied. The following conclusions were reached from the perspective of sedimentary facies control: (1) during the Middle Permian, this region was in shallow water gentle slope belts with high energy, where thick reef flat facies were deposited; (2) the basement was uplifted during Middle Permian, resulting in the unconformity weathering crust at the top of Maokou Formation due to erosion; the SW Sichuan Basin was located in the karst slope belt, where epigenic karstification was intense; and (3) reef flat deposits superimposed by karst weathering crust was favorable for the formation of large-scale reef flat karst reservoirs. Based on the combination of the resources conditions and hydrocarbon accumulation conditions in this region, it was pointed out that the Middle Permian has great potential of large-scale reef flat karst gas reservoir due to its advantageous geological conditions; the Middle Permian traps with good hydrocarbon accumulation conditions were developed in the Longmen Mountain front closed structural belt in the SW Sichuan Basin and Western Sichuan Basin depression slope belt, which are favorable targets for large-scale reef flat karst reservoirs.

Sedimentary Facies and Depositional Environment of the Middle Devonian Geneseo Formation of New York, U.S.A.

Abstract Detailed facies characterization of the Middle Devonian Geneseo Formation in the Northern Appalachian Basin (NAB) shows a rich assembly of sedimentary features and textures that suggest shelfal mud deposition in a storm-dominated, shallow epeiric sea. At the time of deposition, Acadian uplift supplied fine-grained detritus from the east and stimulated delta growth. As sediment was shed from the hinterland, distribution of mudstone facies was controlled by a combination of autogenic processes and a general rise in sea level. The vertical and lateral distribution of nine mudstone facies observed in this succession indicates an overall shallowing-upwards trend (westward progradation of Catskill delta) with multiple modes of sediment transport and deposition. The water column became more oxygenated upsection as indicated by an increase in benthic fauna diversity (e.g., Leiorhynchus and Orbiculoidea), increasing bioturbation diversity (e.g., Chondrites, Palaeophycus, Planolites, Teichichnus, Thalassinoides, and Zoophycos), and a decline of organic-carbon content (via oxidation and consumption). Physical and biological attributes of this mudstone-dominated succession are used to reconstruct sedimentary processes and depositional conditions. Although a stratified-basin model has previously been proposed for the Geneseo Formation, observations made in this study do not support that interpretation. Collectively, our observations indicate shelfal mud deposition above storm-wave base, in a relatively energetic environment with persistent lateral transport and advection by oscillatory flow, wave-induced currents, river-flood, and storm-wave generated offshore-directed underflows, as well as storm setup-relaxation flows.

A geological assessment of airborne electromagnetics for mineral exploration through deeply weathered profiles in the southeast Yilgarn Cratonic margin, Western Australia

Mineral exploration in regolith-dominated environments is challenging, requiring the development of new technical tools and approaches. When airborne electromagnetics (AEM) is combined with information on stratigraphy, mineralogy, geochemistry, drilling and landscape observations in a geological context, it becomes a powerful approach to describe the architecture of the regolith cover. This has significant implications for mineral exploration in any regolith-dominated terrain (RDT). This research presents two case studies of AEM data, integrated in a geological context for mineral exploration in the Yilgarn craton margin/Albany–Fraser Orogen (AFO).In one of the study sites presented (study site 1: Neale tenement), the availability of AEM data allowed for lateral and vertical extrapolation of the information contained in datasets at specific locations, thereby creating a 2D architectural model for the regolith cover. In addition, it was determined: (1) the total thickness of the regolith cover and its variability (between 2m and ~65m); (2) that low conductivity transported overburden and silcrete units, with a total thickness between ~5 and 45m, is widely distributed, capping the upper saprolite; and (3) that the silcrete unit varies laterally from being completely cemented to permeable, and that these permeable areas (“windows”) coincide vertically with mineralogical/textural/moisture/salt content changes in the underlying saprolite, resulting in increased conductivity. This has been interpreted as resulting from more intense vertical weathering, and consequently a higher vertical geochemical dispersion of the basement signature towards surface. AEM has been used to assist in identifying and describing the lateral continuity of these “windows” in areas with no direct field observations. Surface geochemical sampling above these permeable areas may deliver more reliable geochemical basement signatures.In the second study site (Silver Lake tenement) the AEM data was strongly influenced by the high conductivity of the hypersaline groundwater. This had a significant effect on the AEM response, resulting in reduced depth penetration and reduced resolution of subtle conductivity contrasts between cover units. Despite this, the AEM data set, combined with geological observations in the area, was able to map the presence and extent of a buried palaeochannel network, the most significant architectural sedimentary feature in the cover. This interpretation allowed for a more efficient drilling campaign to be designed to sample the fresh basement rock suites in the area, by avoiding drilling into palaeochannels.Integrated and constrained by the geological context, the application of AEM conductivity models by geologists is envisioned as one of the most promising tools within the exploration geologist toolbox to understand the architecture of the cover.

Arsenic solid-phase speciation in an alluvial aquifer system adjacent to the Himalayan forehills, Nepal

Alluvial aquifers contaminated by geogenic arsenic often lack direct solid-phase speciation data, hindering efforts to understand landscape-scale spatial heterogeneity and controls on As mobility. Here, we examine solid-phase As and Fe speciation of alluvial aquifer, river and hyporheic-seep sediments along a topographic gradient at the Himalayan foothills/upper-Ganges floodplain margin. We employ a combination of X-ray absorption spectroscopy, selective extracts, electron microscopy and X-ray fluorescence. Source-river sediments were found to contain a mixture of solid-phase As(V) and As(III) species, while vertically heterogeneous bore-hole sediments also contained a solid-phase As-sulfide species. In general, the abundance of reduced As species [As(III)+As-sulfide] increased with depth below ground surface, as well as down the topographic gradient from the foothills to the floodplain. Although Fe(III) oxides diminished with depth, goethite-rich nodules were present above the seasonal water table minima and contained 10–100 fold more As than the corresponding bulk sediments [~50–800mgkg−1; mainly As(V)]. In contrast, organic-rich clay layers below the seasonal water table contained abundant As-sulfide species (~30–80% of solid-phase As), as well as authigenic pyrite enriched in As [up to ~8500mgkg−1]. Results indicate that aquifer sediments contain discrete facies that are strongly enriched in As due to post-depositional diagenetic coupling between As retention and redox-dependent Fe mineralization. In riverine hyporheic-seeps, ferrihydrite traps As(V)/As(III) species (~30–200mgkg−1) in a readily exchangeable form, creating a pool of solid-phase As vulnerable to downstream reworking and subsequent reductive mobilization. A paucity of Fe(III) oxides in aquifer sediments at tube well-screen depth suggests that the abundant As(III)(aq) in floodplain tube wells is more likely attributable to downward transport or desorption of As(III)-species, than to contemporary reductive dissolution of As-bearing Fe oxides in sediments at well-screen depth. In contrast with the lower Gangetic plain, where large-scale floodplain sedimentary features are a key control on solid-phase As and Fe speciation, in these alluvial sediments solid-phase As and Fe speciation appears to be controlled mainly by physiographic properties (elevation; depth; seasonal water table) that influence local redox conditions.

A contourite depositional system along the Uruguayan continental margin: Sedimentary, oceanographic and paleoceanographic implications

For the first time, a multidisciplinary approach to evaluate the influence of bottom currents in the Uruguayan continental margin is presented. Bathymetric data and multichannel 2D and 3D seismic reflection profiles were used to construct a morphosedimentary map to interpret and decode sedimentary and oceanographic processes along the Uruguayan continental margin. Based on these results, an extensive contourite depositional system on the margin is described, which contains an impressive array of large erosive, depositional (drifts) and mixed (terrace) features, which have been generated primarily by the near-bottom flows associated with water masses of Antarctic and subantarctic origin. From the Eocene–Oligocene boundary up to present time, the long-term influence of water masses from higher southern latitudes, in combination with down-slope sedimentary processes have strongly controlled the overall margin morphology. Most of the features described here, were formed during the middle/late Miocene epoch due to paleoceanographic shifts that include the arrival of Antarctic Intermediate Water along the margin, which in combination with deeper Antarctic Bottom Water are fundamental in the margin evolution. In combination with Quaternary climatic and eustatic changes in sea level, fluctuations of the Brazil–Malvinas Confluence influenced subsequently glacial and interglacial stages as recognized in sedimentary features defined here. These paleoceanographic changes controlled the sedimentary stacking pattern and the locations of high amplitude reflections along the contourite terraces, which could be associated with sandy deposits. A more detailed understanding of the margin will improve interpretations of variations in the South Atlantic subtropical gyre and further constrain general climatic and ocean circulation models.

Evolution of the gulf of Cadiz margin and southwest Portugal contourite depositional system: Tectonic, sedimentary and paleoceanographic implications from IODP expedition 339

The contourite depositional system (CDS) along the southwestern Iberian Margin (SIM), within the Gulf of Cadiz and offshore areas of western Portugal bear the unmistakable signal of Mediterranean Outflow Water (MOW) exiting the Strait of Gibraltar. This locality records key information concerning the effects of tectonic activity on margin sedimentation, the effects of MOW dynamics on Atlantic circulation, and how these factors may have influenced global climate. Over the last four decades, numerous studies have been conducted on the late Miocene, Pliocene and Quaternary sedimentary stacking pattern of Neogene basins along the SIM for both academic and resources exploration purposes. However, understanding of the region rests primarily on basic seismic stratigraphy calibrated with limited data from only a few exploration wells. The Integrated Ocean Drilling Program (IODP) Expedition 339 recently drilled five sites in the Gulf of Cadiz and two sites on the western Iberian margin. The integration of core and borehole data with other geophysical databases leads us to propose a new stratigraphic framework. Interpretation of IODP Exp. 339 data along with that from industry sources and onshore outcrop analysis helps refine our understanding of the SIM's sedimentary evolution.We identify significant changes in sedimentation style and dominant sedimentary processes, coupled with widespread depositional hiatuses along the SIM within the Cadiz, Sanlucar, Doñana, Algarve and Alentejo basins. Following the 4.5Ma cessation of a previous phase of tectonic activity related to the Miocene–Pliocene boundary, tectonics continued to influence margin development, downslope sediment transport and CDS evolution. Sedimentary features indicate tectonic pulses of about 0.8–0.9Ma duration with a pronounced overprint of ~2–2.5Ma cycles. These more protracted cycles relate to the westward rollback of subducted lithosphere at the convergent Africa-Eurasia plate boundary as its previous NW–SE compressional regime shifted to a WNW–ESE direction. Two major compressional events affecting to the Neogene basins at 3.2–3Ma and 2–2.3Ma help constrain the three main stages of CDS evolution. The stages include: 1) the initial-drift stage (5.33–3.2Ma) with a weak MOW, 2) a transitional-drift stage (3.2–2Ma) and 3) a growth-drift stage (2Ma-present time) with enhanced MOW circulation into the Atlantic and associated contourite development due to greater bottom-current velocity. Two minor Pleistocene discontinuities at 0.7–0.9Ma and 0.3–0.6Ma record the effects of renewed tectonic activity on basin evolution, appearing most prominently in the Doñana basin. Several discontinuities bounding major and minor units appear on seismic profiles. Quaternary records offer the clearest example of this, with major units of about 0.8–0.9Ma and sub-units of 0.4–0.5Ma. Sedimentation is controlled by a combination of tectonics, sediment supply, sea-level and climate. This research identifies time scales of tectonic controls on deep-marine sedimentation, specifically over periods of 2.5–>0.4Ma. Shorter-term climatic (orbital) mechanisms control sedimentation at time scales of ≤0.4Ma. The role of bottom water circulation and associated processes in shaping the seafloor and controlling the sedimentary stacking pattern on continental margins has to be seriously reconsidered in future multidisciplinary studies. This is not only because of the common occurrence of sandy contourite deposits in deep water setting and their economic interest for hydrocarbon exploration, but principally because they archive the heartbeat of the interior Earth and therefore have important sedimentary and paleoceanographic implications.

Classifications, sedimentary features and facies associations of tidal flats

Significant progress has been achieved in the research of tide-dominated environments in the past two decades. These studies highlight both the importance and diversity of tidal flats in modern coastal environments. Based on their developing settings, tidal flats are subdivided into nine types, which are in turn grouped into sheltered or exposed spectrums according to the magnitude of exposure to waves. The ternary coastal classification model is revised with an embedded triangle to highlight non-open coast tidal flats as major second-order morphological elements to the first-order coastal environments including deltas, estuaries and lagoons. A new continuous spectrum of open coast depositional settings is proposed from muddy tidal flats of tide dominance with wave influence, through sandy tidal flats of mixed energy (tide-dominated), and tidal beaches of mixed energy (wave-dominated), to beaches of wave-dominance with tide influence. It is worth noting that no open coast setting is absolutely exempt from wave or tide influence. Three diagnostic criteria for the intertidal-flat deposits are proposed. Upon an upward-fining succession, (1) regular changes vertically from flaser bedding, through wavy bedding and to lenticular bedding are diagnostic of most of intertidal flats; (2) cyclical tidal rhythmites point to sheltered intertidal flats typically at the inner part of macrotidal estuaries; (3) rhythmic alternations of storm and tidal deposition are diagnostic of exposed intertidal flats, especially the open coast types. Intertidal-flat deposits are generally topped by saltmarsh deposits, but underlain by different subtidal successions, like thick subtidal channel-fills, sand-bar complexes (sheltered coastal settings), and upwards coarsening successions of subtidal flats or thick subtidal sand ridge/bar complexes (exposed coastal environments).

Ironstone deposits hosted in Eocene carbonates from Bahariya (Egypt)—New perspective on cherty ironstone occurrences

This paper gives new insight into the genesis of cherty ironstone deposits. The research was centered on well-exposed, unique cherty ironstone mineralization associated with Eocene carbonates from the northern part of the Bahariya Depression (Egypt). The economically important ironstones occur in the Naqb Formation (Early Eocene), which is mainly formed of shallow marine carbonate deposits. Periods of lowstand sea-level caused extensive early dissolution (karstification) of the depositional carbonates and dolomitization associated with mixing zones of fresh and marine pore-water. In faulted areas, the Eocene carbonate deposits were transformed into cherty ironstone with preservation of the precursor carbonate sedimentary features, i.e. skeletal and non-skeletal grain types, thickness, bedding, lateral and vertical sequential arrangement, and karst profiles. The ore deposits are composed of iron oxyhydroxides, mainly hematite and goethite, chert in the form of micro- to macro-quartz and chalcedony, various manganese minerals, barite, and a number of subordinate sulfate and clay minerals. Detailed petrographic analysis shows that quartz and iron oxides were coetaneous and selectively replaced carbonates, the coarse dolomite crystals having been preferentially transformed into quartz whereas the micro-crystalline carbonates were replaced by the iron oxyhydroxides.A number of petrographic, sedimentological and structural features including the presence of hydrothermal-mediated minerals (e.g., jacobsite), the geochemistry of the ore minerals as well as the structure-controlled location of the mineralization suggest a hydrothermal source for the ore-bearing fluids circulating through major faults and reflect their proximity to centers of magmatism. The proposed formation model can contribute to better understanding of the genetic mechanisms of formation of banded iron formations (BIFs) that were abundant during the Precambrian.

Submarine geomorphology and sea floor processes along the coast of Vestfold Hills, East Antarctica, from multibeam bathymetry and video data

AbstractA survey of nearshore areas in the Vestfold Hills, Antarctica, using high-resolution multibeam swath bathymetry provided both a detailed digital bathymetric model and information on sediment acoustic backscatter. Combined with underwater video transects and sediment sampling, these data were used to identify and map geomorphic units. Six geomorphic units identified in the survey region include: rocky outcrops, basins, pediments, valleys, scarps and embayments. In addition to geomorphic units, the data revealed sedimentary features that provide insights into post-glacial sediment transport and erosion in the area. Ice keel pits and scours are common, and sea floor channels, scour depressions and sand ribbons indicate transport and deposition by wind-driven currents and oceanographic circulation. Gullies and sediment lobes observed on steep slopes indicate mass movement of sediment. Some of these processes have not been directly observed to date, but their effectiveness in shaping the modern sea floor is clearly indicated by the sea floor mapping data. The embayments preserve a mantle of boulder sand probably deposited by cold-based glaciers which were flanked by faster-flowing ice in adjoining regions.

The depositional environments of Schöningen 13 II-4 and their archaeological implications

Geoarchaeological research at the Middle Pleistocene site of Schöningen 13 II-4, often referred to as the Speerhorizont, has focused on describing and evaluating the depositional contexts of the well-known wooden spears, butchered horses, and stone tools. These finds were recovered from the transitional contact between a lacustrine marl and an overlying organic mud, originally thought to be a peat that accumulated in place under variable moisture conditions. The original excavators proposed that hominin activity, including hunting and butchery, occurred on a dry lake shore and was followed by a rapid sedimentation of organic deposits that embedded and preserved the artifacts. Our geoarchaeological analysis challenges this model. Here, we present evidence that the sediments of Schöningen 13 II-4 were deposited in a constantly submerged area of a paleolake. Although we cannot exclude the possibility that the artifacts were deposited during a short, extreme drying event, there are no sedimentary features indicative of surface exposure in the sediments. Accordingly, this paper explores three main alternative models of site formation: anthropogenic disposal of materials into the lake, a geological relocation of the artifacts, and hunting or caching on lake-ice. These models have different behavioral ramifications concerning hominin knowledge and exploitation of the landscape and their subsistence strategies.