Marina Rabineau

Testing sequence stratigraphic models by drilling Miocene foresets on the New Jersey shallow shelf

We present seismic, core, log, and chronologic data on three early to middle Miocene sequences (m5.8, m5.4, and m5.2; ca. 20–14.6 Ma) sampled across a transect of seismic clinothems (prograding sigmoidal sequences) in topset, foreset, and bottomset locations beneath the New Jersey shallow continental shelf (Integrated Ocean Drilling Program Expedition 313, Sites M27–M29). We recognize stratal surfaces and systems tracts by integrating seismic stratigraphy, lithofacies successions, gamma logs, and foraminiferal paleodepth trends. Our interpretations of systems tracts, particularly in the foresets where the sequences are thickest, allow us to test sequence stratigraphic models. Landward of the clinoform rollover, topsets consist of nearshore deposits above merged transgressive surfaces (TS) and sequence boundaries overlain by deepening- and fining-upward transgressive systems tracts (TST) and coarsening- and shallowing-upward highstand systems tracts (HST). Drilling through the foresets yields thin (

Kinematic keys of the Santos–Namibe basins

Abstract Understanding the genesis of the very peculiar 600 km-wide Santos Basin–São Paulo Plateau system and its narrow conjugate Namibe Margin is a kinematic and structural problem. Several hypotheses have been proposed in order to explain the genesis of this system that imply the same amount of horizontal movement. We investigate the consequences of the horizontal movement in the Santos Basin, based in plate kinematic reconstructions. The kinematic history of this system that we present here, based on the interpretation of seismic profiles and kinematic constraints, has the following consequences: (1) there is no evidence of a ridge jump sensu stricto but, rather, a southwards propagation in the Central Segment of the South Atlantic that starts in the northern part, between the NE Brazilian and Gabonese margins; (2) the Namibe margin evolved as a transform passive margin; (3) the opening direction of the Santos Basin–São Paulo Plateau system is oblique to the general opening motions of the South American and African plates; and (4) this opening is younger (6 Ma) than those of the other basins of the Central Segment of the South Atlantic.

The provenance of sediments in the Gulf of Lions, western Mediterranean Sea

In this study, we undertook a reconnaissance study of sediments provenance in the Gulf of Lions focusing over the last 16 ka. We used geochemical and isotopic tracers to determine the source of sediments and give insight into the weathering conditions prevailing. Sediments samples were selected both onshore and offshore from the western, eastern, and central part of the Gulf of Lions. We analyzed bulk sediments, coarse and fine silt, and clay fractions. Elemental and Nd isotope compositions appeared to differ from one grain size fraction to another one. These are interpreted in terms of zircon addition in the coarse silt fraction for the elemental concentrations and variable sources influences for the Nd isotope compositions. Our results indicate that sediments in the Gulf of Lions mainly originated from the Rhone River watershed although a contribution of Saharan dust is seen in one sample. Influence of Pyrenean small rivers is minor in these samples. Some Sr isotope compositions shifts are interpreted as reflecting variable amounts of chemical weathering that are consistent with published paleoclimatic reconstructions.

Deep structure of the Santos basin-São Paulo plateau system, SE Brazil

The structure and nature of the crust underlying the Santos Basin-Sao Paulo Plateau System (SSPS), in the SE Brazilian margin, are discussed based on five wide-angle seismic profiles acquired during the Santos Basin (SanBa) experiment in 2011. Velocity models allow us to precisely divide the SSPS in six domains from unthinned continental crust (Domain CC) to normal oceanic crust (Domain OC). A seventh domain (Domain D), a triangular shape region in the SE of the SSPS, is discussed by Klingelhoefer et al. (2014). Beneath the continental shelf, a ~100 km wide necking zone (Domain N) is imaged where the continental crust thins abruptly from ~40 km to less than 15 km. Toward the ocean, most of the SSPS (Domains A and C) shows velocity ranges, velocity gradients, and a Moho interface characteristic of the thinned continental crust. The central domain (Domain B) has, however, a very heterogeneous structure. While its southwestern part still exhibits extremely thinned (7 km) continental crust, its northeastern part depicts a 2–4 km thick upper layer (6.0–6.5 km/s) overlying an anomalous velocity layer (7.0–7.8 km/s) and no evidence of a Moho interface. This structure is interpreted as atypical oceanic crust, exhumed lower crust, or upper continental crust intruded by mafic material, overlying either altered mantle in the first two cases or intruded lower continental crust in the last case. The deep structure and v-shaped segmentation of the SSPS confirm that an initial episode of rifting occurred there obliquely to the general opening direction of the South Atlantic Central Segment.

Pyrite sulfur isotopes reveal glacial−interglacial environmental changes

Significance Changes in sulfur isotope ratios (34S/32S) of marine sulfur phases are often attributed to global biogeochemical perturbations. Sediments collected on the shelf of the Gulf of Lion revealed remarkable sulfur isotopic fluctuations in sedimentary pyrite over the last 500,000 years, ranging between −44.0‰ and 32.3‰. We suggest this pattern is related to changes in the local environmental deposition, specifically, sedimentation modulating connectivity with the overlying water column and resulting microbial activity. Besides providing new understanding of an important and poorly constrained aspect of past glacial−interglacial transitions, our results are critically important because they question the degree to which changes in sulfur isotopes in pyrite reflect global biogeochemical processes versus local depositional conditions. The sulfur biogeochemical cycle plays a key role in regulating Earth’s surface redox through diverse abiotic and biological reactions that have distinctive stable isotopic fractionations. As such, variations in the sulfur isotopic composition (δ34S) of sedimentary sulfate and sulfide phases over Earth history can be used to infer substantive changes to the Earth’s surface environment, including the rise of atmospheric oxygen. Such inferences assume that individual δ34S records reflect temporal changes in the global sulfur cycle; this assumption may be well grounded for sulfate-bearing minerals but is less well established for pyrite-based records. Here, we investigate alternative controls on the sedimentary sulfur isotopic composition of marine pyrite by examining a 300-m drill core of Mediterranean sediments deposited over the past 500,000 y and spanning the last five glacial−interglacial periods. Because this interval is far shorter than the residence time of marine sulfate, any change in the sulfur isotopic record preserved in pyrite (δ34Spyr) necessarily corresponds to local environmental changes. The stratigraphic variations (>76‰) in the isotopic data reported here are among the largest ever observed in pyrite, and are in phase with glacial−interglacial sea level and temperature changes. In this case, the dominant control appears to be glacial−interglacial variations in sedimentation rates. These results suggest that there exist important but previously overlooked depositional controls on sedimentary sulfur isotope records, especially associated with intervals of substantial sea level change. This work provides an important perspective on the origin of variability in such records and suggests meaningful paleoenvironmental information can be derived from pyrite δ34S records.

Controls on Holocene denudation rates in mountainous environments under Mediterranean climate

ABSTRACT: The Mediterranean domain is characterized by a specific climate resulting from the close interplay between atmospheric and marine processes and strongly differentiated regional topographies. Corsica Island, a mountainous area located in the western part of the Mediterranean Sea is particularly suitable to quantify regional denudation rates in the framework of a source‐to‐sink approach. Indeed, fluvial sedimentation in East‐Corsica margin is almost exclusively limited to its alluvial plain and offshore domain and its basement is mainly constituted of quartz‐rich crystalline rocks allowing cosmogenic nuclide 10Be measurements. In this paper, Holocene denudation rates of catchments from the eastern part of the island of Corsica are quantified relying on in situ produced 10Be concentrations in stream sediments and interpreted in an approach including quantitative geomorphology, rock strength measurement (with a Schmidt Hammer) and vegetation cover distribution. Calculated denudation rates range from 15 to 95 mm ka‐1. When compared with rates from similar geomorphic domains experiencing a different climate setting, such as the foreland of the northern European Alps, they appear quite low and temporally stable. At the first order, they better correlate with rock strength and vegetation cover than with morphometric indexes. Spatial distribution of the vegetation is controlled by morpho‐climatic parameters including sun exposure and the direction of the main wet wind, so‐called ‘Libecciu’. This distribution, as well as the basement rock strength seems to play a significant role in the denudation distribution. We thus suggest that the landscape reached a geomorphic steady‐state due to the specific Mediterranean climate and that Holocene denudation rates are mainly sustained by weathering processes, through the amount of regolith formation, rather than being transport‐limited. Al/K measurements used as a proxy to infer present‐day catchment‐wide chemical weathering patterns might support this assumption. Copyright

Nested Seismic Stratigraphy Using Profiles of Increasing Resolution

Appropriate type of seismic must be chosen to image geological targets (according to their depth and size). Here, we want to emphasize, that the use of nested seismic data of increasing resolution simultaneously enables a better seismic stratigraphic interpretation. To illustrate our purpose we will present a series of seismic profiles of different resolution but at the same position that enable a comparaison of different vertical scale and variable resolution (from Kilometric conventional seismic, to high resolution, very high resolution and ultra high resolution seismic data) coming from the same area in the Gulf of Lion.

Sediment Transport due to Trawling in La Fonera Submarine Canyon - A Numerical Modelling Approach

The process of resuspension by bottom trawling leads to recurrent transfer of sediment from shallower to deeper areas, and occurs practically worldwide. Recent studies have shown the importance of trawling as a driver of sediment transfer in canyons. Our aim is to assess trawling impact on sediment dynamics in La Fonera submarine canyon (NW Mediterranean). Our methodology combines inverse modelling and the implementation of a numerical process-based model, and allows us to simulate trawling-induced flows in the canyon on the basis of trawling fleet activity (derived from Vessel Monitoring System data). The model simulates turbidity current hydrodynamics and deposition for events whose magnitude and initial volume concentration is defined from the inverse analysis. Mooring data in the axis of a tributary valley is used to validate the model hypothesis. Based on the good agreement found between modelled transport and measurements at the mooring site, we have quantified fishing activity over the fishing grounds and obtained the propagation patterns of the resuspended sediment towards the canyon axis and beyond. Trawling-induced sediment flows lead to the development of new trawl-driven depocentres.

Arcabouço estratigráfico e ciclicidade deposicional dos sistemas sedimentares do Pleistoceno Médio-Holoceno da plataforma sul da Bacia de Campos, Brasil

A analise sismica de ~ 3.000 km de dados sismicos sparker de reflexao monocanal permitiu a proposicao de um arcabouco estratigrafico englobando a secao rasa (~ 300 milissegundos) da plataforma continental sul da Bacia de Campos. Cinco sequencias sismicas foram reconhecidas (Sq1 – Sq5), limitadas por superficies erosivas de escala plataformal (superficies S1 – S5), interpretadas como sequencias deposicionais formadas por oscilacoes glacioeustaticas e limites de sequencias (discordâncias regionais) esculpidos durante longos periodos de exposicao subaerea total da plataforma, indicando condicoes de diminuicao de nivel de base e destruicao parcial de espaco de acomodacao sedimentar. As sequencias Sq1 – Sq4 sao dominantemente regressivas, compostas principalmente por prismas de regressao forcada de borda de plataforma/talude superior. A sequencia superficial Sq5 e constituida essencialmente de unidades retrogradantes restritas a plataforma continental, interpretadas como compondo uma sequencia eminentemente transgressiva. A correlacao entre dados sismicos e cronoestratigraficos de um poco exploratorio disponivel na area permitiu posicionar a deposicao desta sucessao estratigrafica entre o Pleistoceno Medio-Holoceno (ultimos ~ 500 ka). Alem disso, a correlacao entre a base de dados com curvas globais de variacoes eustaticas, baseadas nas razoes isotopicas de δ 18 O (estagios isotopicos marinhos), permitiu ainda sugerir que a sucessao estratigrafica Sq1 – Sq4 registra sequencias regressivas de quarta ordem, refletindo deposicao durante ciclos glacioeustaticos de ~ 100 – 120 ka de duracao e de alta amplitude de oscilacao eustatica (± 100 – 145 m), que caracterizam o sinal eustatico nos ultimos ~ 500 ka. A sequencia Sq5 seria uma sequencia ainda em formacao, constituida por depositos transgressivos e de mar alto formados durante o Pleistoceno Tardio-Holoceno.

ABSTRACT: A Comparison of Late Quaternary Deltaic/Estuarine Depositional Systems from Wave- and Tide-Dominated Shelves

In the stratigraphic record, shelf sand bodies encased in mudstones are concurrently interpreted as shelf ridges or (lowstand) shorefaces. A comparison of Quaternary continental margins with high sediment supply and high subsidence rate (in the order 200300m/million year) demonstrate that both types of sand bodies can be preserved. The Rhone (NW Mediterranean Sea) and the Yang Tze (East China Sea) both exhibit large sand bodies, up to 30 m thick, 3-10 km wide and 10 to more than 100 km long. Their seismic internal structure displays clinoforms dipping at about 58. Despite a very similar morphology and internal structure, these sand bodies are interpreted as resulting from very different processes. On the wave-dominated Rhone deltaic margin, they correspond to forced-regressive shoreface sands, encased in prodeltaic muds. They parallel the paleobathymetric contour lines and they are encased in prodeltaic mud. The corresponding deltaic facies are not preserved. On the tide- and storm-dominated Yang Tze margin, sand is concentrated into large tidal ridges formed during post-glacial sea-level rises. They also are encased in prodeltaic muds, but deltaic/estuarine facies have also been preserved and their orientation is almost perpendicular to the general paleoshoreline. In the stratigraphic record, only three-dimensional exploration could allow to determine to which category such sand bodies belong. The Danube wave-dominated deltaic margin is a third category where most of shelf sediment consist of prodeltaic muds and deltaic heterogeneous deposits. Sand dunes from the last deglacial sea-level rise are observed, but they have no preserved equivalent in the Pleistocene.