Authigenic zeolites and their relation to silica diagenesis in ODP site 661 sediments (Leg 108, eastern Equatorial Atlantic

At ODP Site 661 from the continental margin of Northwest Africa, authigenic clinoptilolites were investigated in detail. Based on chemical data, crystal size and shape and their intergrowth with associated mineral phases, two types of clinoptilolite (type A and B) occur representing different diagenetic conditions under which the formation of zeolites took place. Clinoptilolite type A was found in a sediment section comprises numerous hiatuses and stratigraphically condensed sediments and could have been formed during early diagenesis. In contrast, clinoptilolite type B was precipitated in Campanian sediments during later diagenesis, after the transformation from opal-A to opal-CT had taken place. At Site 661, the silica source for the authigenesis of both clinoptilolite types is biogenic opal. Volcanic ash material occurs, but in low amounts and thus is not a prerequisite for the formation of clinoptilolite at Site 661

La sedimentation quaternaire recente dans le detroit de Makassar (Indonesie)

Corings have been obtained during the Misedor Cruise in the Strait of Makassar (Indonesia). Previous works showed that Recent Quaternary sediments originated from Kalimantan and Sulawesi. These deposits are associated either with settling processes or with paleogeographic events related to eustatic variations. At low sea level, gravity flow from Kalimantan supply deep-sea zones where deposits are arranged locally in stratodecreasing successions. During the rise of the sea level, inputs change both qualitatively and quantitatively. In addition to river-borne inputs (Mahakam), one can observe reworked sediments originating from the continental shelf in the course of its immersion. At high sea level (Holocene) inputs issued from Kalimantan contribute to the building of the Mahakam delta. Most of the deposits occurring in the ocean deeps and on the continental rise derive from the Sulawesi margin

Reply to discussion by Shanmugam on Mulder et al. (2001, Geo-Marine Letters 21 : 86-93) Inversely graded turbidite sequences in the deep Mediterranean. A record of deposits from flood-generated turbid

Geo-Marine Letters, v. 22, n. 2, p. 112-120, 2002. http://dx.doi.org/10.1007/s00367-002-0096-8International audienc

Variation des sources de sediments dans le detroit de Makassar (Indonesie) au quaternaire recent: Role des facteurs morphostructuraux et eustatiques

Mineralogical analyses of sediments from the Makassar Strait, collected during the Corindon and Misedor cruises (dredges, piston and box cores) show the existing differences between sediments supplied from Kalimantan in the West and sediments supplied from Sulawesi in the East. The Kalimantan source is characterized by quartzitic sand, with rare feldspars, heavy minerals consisting mainly of pyroxene (hypersthene) and amphibole and predominant illite-kaolinite in the clay mineral assemblage. In contrast, the Sulawesi source differs by a great abundance of feldspars, lithoclasts and micas with predominant amphibole and pyroxene (augite) and major illite-chlorite clay minerals

Bottom currents, contourites and deep-sea sediment drifts: current state-of-the-art

This paper provides both an introduction to and summary for the Atlas of Contourite Systems that has been compiled as part of the International Geological Correlation Project - IGCP 432. Following the seminal works of George Wust on the physical oceanography of bottom currents, and Charley Hollister on contourite sediments, a series of significant advances have been made over the past few decades. While accepting that ideas and terms must remain flexible as our knowledge base continues to increase, we present a consensus view on terminology and definitions of bottom currents, contourites and drifts. Both thermohaline and wind-driven circulation, influenced by Coriolis Force and molded by topography, contribute to the oceanic system of bottom currents. These semi-permanent currents show significant variability in time and space, marked by periodic benthic storm events in areas of high surface kinetic energy. Six different drift types are recognized in the ocean basins and margins at depths greater than about 300 m: (i) contourite sheet drifts; (ii) elongate mounded drifts; (iii) channel related drifts; (iv) confined drifts; (v) infill drifts; and (vi) modified drift-turbidite systems. In addition to this overall geometry, their chief seismic characteristics include: a uniform reflector pattern that reflects long-term stability, drift-wide erosional discontinuities caused by periodic changes in bottom current regime, and stacked broadly lenticular seismic depositional units showing oblique to downcurrent migration. At a smaller scale, a variety of seismic facies can be recognized that are here related to bottom current intensity. A model for seismic facies cyclicity (alternating transparent/reflector zones) is further elaborated, and linked to bottom current/climate change. Both erosional features and depositional bedforms are diagnostic of bottom current systems and velocities. Many different contourite facies are now known to exist, encompassing all compositional types. We propose here a Cl-5 notation for the standard contourite facies sequence, which can be interpreted in terms of fluctuation in bottom current velocity and/or sediment supply. Several proxies can be utilized to decode contourite successions in terms of current fluctuation. Gravel lag and shale chip contourites, as well as erosional discontinuities are indicative of still greater velocities. There are a small but growing number of land-based examples of fossil contourites, based on careful analysis using the recommended three-stage approach to interpretation. Debate still surrounds the recognition and interpretation of bottom current reworked turbidites

Sediment flux distribution in the Southern Brazil Basin during the late Quaternary: the role of deep-sea currents

International audienc

Impact de la trangression holocene sur la sedimentation dans le detroit de Makassar (Indonesie)

Biomarker data associated with isotopic curve partial differential super(18)O served to establish a stratigraphic scale and thereby a chronology of fluctuations in the circulation and sedimentation of the Kalimantan continental rise throughout the last climatic cycle. During the glacial maximum, period of low sea-level sediments were deposited by turbidity currents originating from Kalimantan. During deglaciation, during rise of the sea-level and more particularly in the Holocene, material issued from Kalimantan either contributed to the building of the Mahakam delta or was dispersed over the shelf. Sulawesi inputs, less abundant and mineralogically different from Kalimantan material, were observed onto the Kalimantan rise. During this same period, circulation in the Makassar strait slowed down progressively while stratification became more marked and practically permanent in the Holocene