Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island:Transitions from a non-glacial, through glacially-influenced to a fully glacial state

A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise and establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the early Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop during the latest Miocene but did not become fully established until sometime during the interval between the end of the Pliocene and middle Pleistocene. Between these two time intervals, the northeast lateral migration of the Marguerite Trough also played a critical role in margin evolution, as it controlled ice sheet drainage pathways across the shelf, which in turn influenced development of slope and rise morphologies. Areas offshore from Adelaide Island differ from other areas of the PMAP due to changes in sedimentary processes that resulted from migration of the trough. This study confirms that the PMAP represents an exceptional locality for decoding, reconstructing and linking past tectonic and climatic changes. The study area specifically records not only the most relevant changes in depositional style, but also the relative importance of persistent along- and down-slope sedimentary processes. Our study approach can be extended to other areas and integrated with additional techniques to understand the evolution and the global linkages of the entire Antarctic continental margin and the ice sheets

Contourites and associated sediments controlled by deep-water circulation processes:State-of-the-art and future considerations

The contourite paradigm was conceived a few decades ago, yet there remains a need to establish a sound connection between contourite deposits, basin evolution and oceanographic processes. Significant recent advances have been enabled by various factors, including the establishment of two IGCP projects and the realisation of several IODP expeditions. Contourites were first described in the Northern and Southern Atlantic Ocean, and since then, have been discovered in every major ocean basin and even in lakes. The 120 major contourite areas presently known are associated to myriad oceanographic processes in surface, intermediate and deep-water masses. The increasing recognition of these deposits is influencing palaeoclimatology & palaeoceanography, slope-stability/geological hazard assessment, and hydrocarbon exploration. Nevertheless, there is a pressing need for a better understanding of the sedimentological and oceanographic processes governing contourites, which involve dense bottom currents, tides, eddies, deep-sea storms, internal waves and tsunamis. Furthermore, in light of the latest knowledge on oceanographic processes and other governing factors (e.g. sediment supply and sea-level), existing facies models must now be revised. Persistent oceanographic processes significantly affect the seafloor, resulting in large-scale depositional and erosional features. Various classifications have been proposed to subdivide a continuous spectrum of partly overlapping features. Although much progress has been made in the large-scale, geophysically based recognition of these deposits, there remains a lack of unambiguous and commonly accepted diagnostic criteria for deciphering the small-scaled contourite facies and for distinguishing them from turbidite ones. Similarly, the study of sandy deposits generated or affected by bottom currents, which is still in its infancy, offers great research potential: these deposits might prove invaluable as future reservoir targets. Expectations for the forthcoming analysis of data from the IODP Expedition 339 are high, as this work promises to tackle much of the aforementioned lack of knowledge. In the near future, geologists, oceanographers and benthic biologists will have to work in concert to achieve synergy in contourite research to demonstrate the importance of bottom currents in continental margin sedimentation and evolution.This is an open access article under the CC BY-NC-SA license(http://creativecommons.org/licenses/by-nc-sa/3.0/)

Sedimentary evolution of the Le Danois contourite drift systems (southern Bay of Biscay, NE Atlantic):A reconstruction of the Atlantic Mediterranean Water circulation since the Pliocene

The evolution of the Le Danois contourite depositional systems (CDS) during the Pliocene and Quaternary was investigated based on high-resolution seismic reflection data. From old to young, six seismic units (U1-U6) bounded by major discontinuities (H1-H6) were identified. Regarding variations of the bottom-current circulation, four evolution stages of the Le Danois CDS were identified, including onset (similar to 5.3 to 3.5-3.0 Ma), initial (3.5-3.0 to 2.5-2.1 Ma), intermediate (2.5-2.1 to 0.9-0.7 Ma) and drift-growth (0.9-0.7 Ma to present day) stages. The CDS associated with the Atlantic Mediterranean Water (AMW) along the middle continental slope initiated at similar to 3.5-3 Ma and was widely built after the Mid-Pleistocene Transition (MPT; 0.9-07 Ma). At a shallower water depth, a second CDS associated with the Eastern North Atlantic Central Water (ENACW) started to develop from the late Quaternary (similar to 0.47 Ma) onwards. In the AMW-related drift system, the Le Danois Drift was generated both under glacial and interglacial climatic oscilations. Repeated internal structures in unit 5 that consist of acoustically transparent lower parts, moderate amplitude upper parts and high amplitude erosional surfaces at the top, are compared with interglacial/glacial cycles since the middle Pleistocene to the present day. These cyclic features suggest coarsening-upward sequences of the Le Danois Drift and processes related to enhanced AMW during glacial stages. The estimated sedimentation rate of the Le Danois CDS reached a maximum during the MPT (at least similar to 27 cm/ky) and then decreased until present-day (similar to 5 cm/ky). Variations of sedimentary stacking patterns and processes of the Le Danois CDS imply full domination of the intermediate water mass along the central Atlantic and southwest European continental slopes from the late Pliocene (similar to 3.5-3.0 Ma) onwards

Contourite depositional systems along the Mozambique channel:The interplay between bottom currents and sedimentary processes

We present a combined study of the geomorphology, sedimentology, and physical oceanography of the Mozambique Channel to evaluate the role of bottom currents in shaping the Mozambican continental margin and adjacent Durban basin. Analysis of 2D multichannel seismic reflection profiles and bathymetric features revealed major contourite deposits with erosive (abraded surfaces, contourite channels, moats, furrows and scours), depositional (plastered and elongated-mounded drifts, sedimentary waves), and mixed (terraces) features, which were then used to construct a morpho-sedimentary map of the study area. Hydrographic data and hydrodynamic modelling provide new insights into the distribution of water masses, bottom current circulation and associated processes (e.g., eddies, internal waves, etc.) occurring along the Mozambican slope, base-of-slope and basin floor. Results from this work represent a novel deep-sea sedimentation model for the Mozambican continental margin and adjacent Durban basin. This model shows 1) how bottom circulation of water masses and associated sedimentary processes shape the continental margin, 2) how interface positions of water-masses with contrasting densities (i.e., internal waves) sculpt terraces along the slope at a regional scale, and 3) how morphologic obstacles (seamounts, Mozambique Ridge, etc.) play an essential role in local water mass behaviours and dynamics. Further analysis of similar areas can expand understanding of the global role of bottom currents in deep-sea sedimentation

An instance of Neanderthal mobility dynamics: a lithological approach to the flint assemblage from stratigraphic unit VIII of El Salt rockshelter (Alcoi, eastern Iberia)

The relationship between hunter-gatherer group mobility and lithic raw material procurement strategies is central to the study of Neanderthal productive behaviours. In this framework, determination of flint procurement sources through lithological analysis is key to infer Neanderthal group mobility patterns. El Salt rockshelter (Alcoi, Alacant, eastern Iberia) features different nearby flint sources, including primary outcrops and secondary deposits containing flint. In this study, we sourced the stratigraphic unit viii archaeological flint assemblage based on identification of geogenic and postgenetic lithological traits. Our results indicate that flint procurement at El Salt during the stratigraphic unit viii Neanderthal occupations was mainly linked to Pleistocene secondary deposits along the upper and middle courses of Serpis river. The artefacts were made predominantly on alluvially reworked nodules of different flint types. Connecting these procurement areas with their corresponding knapping products reveals a direct relationship between flint-source distance and degree of technical intervention, and defines a hypothetically unidirectional series of rivershore itineraries of procurement.This work has been accomplished during the valid period of the research project titled Clima e interacciones humanas en el Mediterráneo central ibérico durante el MIS 4 (IBEMIS4), granted by the Spanish central government (PID2019-107113RB-I00). The first author (AM) is funded by Universitat d’Alacant through a university faculty formation grant (UAFPU2018-049). The second (SSR) and the fourth (LP) are funded by the Valencian autonomous government through a predoctoral research-staff contracting grant (ACIF/2021/407) and a postdoctoral research-staff contracting grant (APOSTD/2020/202), respectively

Seasonal variability of intermediate water masses in the Gulf of Cádiz: implications of the Antarctic and subarctic seesaw

Global circulation of intermediate water masses has been extensively studied; however, its regional and local circulation along continental margins and variability and implications on sea floor morphologies are still not well known. In this study the intermediate water mass variability in the Gulf of Cádiz (GoC) and adjacent areas has been analysed and its implications discussed. Remarkable seasonal variations of the Antarctic Intermediate Water (AAIW) and the Subarctic Intermediate Water (SAIW) are determined. During autumn a greater presence of the AAIW seems to be related to a reduction in the presence of SAIW and Eastern North Atlantic Central Water (ENACW). This interaction also affects the Mediterranean Water (MW), which is pushed by the AAIW toward the upper continental slope. In the rest of the seasons, the SAIW is the predominant water mass reducing the presence of the AAIW. This seasonal variability for the predominance of these intermediate water masses is explained in terms of the concatenation of several wind-driven processes acting during the different seasons. Our finding is important for a better understanding of regional intermediate water mass variability with implications in the Atlantic Meridional Overturning Circulation (AMOC), but further research is needed in order to decode their changes during the geological past and their role, especially related to the AAIW, in controlling both the morphology and the sedimentation along the continental slopes

Secondary flow in contour currents controls the formation of moat-drift contourite systems

Ocean currents control seafloor morphology and the transport of sediments, organic carbon, nutrients, and pollutants in deep-water environments. A better connection between sedimentary deposits formed by bottom currents (contourites) and hydrodynamics is necessary to improve reconstructions of paleocurrent and sediment transport pathways. Here we use physical modeling in a three-dimensional flume tank to analyse the morphology and hydrodynamics of a self-emerging contourite system. The sedimentary features that developed on a flat surface parallel to a slope are an elongated depression (moat) and an associated sediment accumulation (drift). The moat-drift system can only form in the presence of a secondary flow near the seafloor that transports sediment from the slope toward the drift. The secondary flow increases with higher speeds and steeper slopes, leading to steeper adjacent drifts. This study shows how bottom currents shape the morphology of the moat-drift system and highlights their potential to estimate paleo-ocean current strength