Late Quaternary clay mineral record in Central Lake Baikal (Academician Ridge, Siberia)

in Palaeogeography, Palaeoclimatology, Palaeoecology (2003), 193(1), 159-179

We investigated the mineralogical composition of two cores recovered on the Academician Ridge (Central Lake Baikal, Siberia). Sedimentological features show that the cores are unaffected by turbidity ... [more ▼]

We investigated the mineralogical composition of two cores recovered on the Academician Ridge (Central Lake Baikal, Siberia). Sedimentological features show that the cores are unaffected by turbidity currents. However, hemipelagic deposition is not continuous, but intermittently disturbed by syn- or post-sediment reworking (e.g., bioturbation, slumps, faulting). Such modes of deposition are consistent with the complex uplift history of the ridge. Bulk mineralogy suggests that terrigenous sediment supplies are constant through glacial/interglacial stages, and diluted by diatom-rich intervals related to warmer interglacial stages. The core stratigraphy is based on the correlation of the diatom zonation and opal abundance with the marine oxygen isotope reference curve SPECMAP. The similar to 8-m cores partly recover the last four interglacial/glacial cycles, i.e., since oxygen isotope stage 8. We test the use of clay minerals as a proxy for paleoclimatic reconstruction. The clays are more weathered during the diatom-rich intervals in agreement with warmer climate conditions. However, the mean clay composition does not change significantly through glacial/interglacial stages. This observation implies that, in the Academician Ridge sediments, a simple smectite/illite ratio (S/I) does not alone provide a reliable indicator of climatic variation. It reflects the complex clay assemblages, especially the smectite group, delivered to Central Lake Baikal. Smectites include primarily illite-smectite mixed layers, made of a mixture of montmorillonite and beidellite. According to their behavior after cation saturation, the illite-smectite mixed layers are primarily transformed smectites, with some neoformed smectites intermittently observed. In addition, Al-smectites occur in minor proportions. We conclude that the S/I ratio has a climatic significance only if it evolves in parallel with the weathering stage of the clays and is confirmed by a change in the composition of the smectites. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

Phosphate mineral occurrences in Lake Baïkal sediments : Paleo-environment or diagenesis record ?

Poster (2003)

Ba distribution in surface Southern Ocean sediments and export production estimates

in Paleoceanography (2002), 17(2, MAR-JUN),

[1] We present excess Ba (Baxs) data (i.e., total Ba corrected for lithogenic Ba) for surface sediments from a north-south transect between the Polar Front Zone and the northern Weddell Gyre in the ... [more ▼]

[1] We present excess Ba (Baxs) data (i.e., total Ba corrected for lithogenic Ba) for surface sediments from a north-south transect between the Polar Front Zone and the northern Weddell Gyre in the Atlantic sector and between the Polar Front Zone and the Antarctic continent in the Indian sector. Focus is on two different processes that affect excess Ba accumulation in the sediments: sediment redistribution and excess Ba dissolution. The effect of these processes needs to be corrected for in order to convert accumulation rate into vertical rain rate, the flux component that can be linked to export production. In the Southern Ocean a major process affecting Ba accumulation rate is sediment focusing, which is corrected for using excess Th-230. This correction, however, may not always be straightforward because of boundary scavenging effects. A further major process affecting excess Ba accumulation is barite dissolution during exposure at the sediment-water column interface. Export production estimates derived from excess Th-230 and barite dissolution corrected Baxs accumulation rates (i.e., excess Ba vertical rain rates) are of the same magnitude but generally larger than export production estimates based on water column proxies (Th-234-deficit in the upper water column; particulate excess Ba enrichment in the mesopelagic water column). We believe export production values based on excess Ba vertical rain rate might be overestimated due to inaccurate assessment of the Baxs preservation rate. Barite dissolution has, in general, been taken into account by relating it to exposure time before burial depending on the rate of sediment accumulation. However, the observed decrease of excess Ba content with increasing water column depth (or increasing hydrostatic pressure) illustrates the dependence of barite preservation on degree of saturation in the deep water column in accordance with available thermodynamic data. Therefore correction for barite dissolution would not be appropriate by considering only exposure time of the barite to some uniformly undersaturated deep water but requires also that regional differences in degree of undersatuation be taken into account. [less ▲]

Export production in the Bay of Biscay as estimated from barium - barite in settling material: a comparison with new production

in Deep-Sea Research Part I, Oceanographic Research Papers (2000), 47(4), 583-601

We present barium data for sediment traps deployed in a northeast Atlantic margin environment (Bay of Biscay). Fluxes of excess barium were measured with the objective of calculating carbon export ... [more ▼]

We present barium data for sediment traps deployed in a northeast Atlantic margin environment (Bay of Biscay). Fluxes of excess barium were measured with the objective of calculating carbon export production rates from the surface mixed layer and thus contribute to the understanding of organic carbon transport in a margin environment. Therefore, it was necessary to properly understand the different processes that affected the barium fluxes in this margin environment. Seasonal variability of POC/Ba flux ratios and decrease of barium solubilisation in the trap cups with increasing depth in the water column probably indicate that the efficiency of barite formation in the organic micro-environment varies with season and that the process is relatively slow and not yet completed in the upper 600 m of water column. Thus barite presence in biogenic aggregates will significantly depend on water column transit time of these aggregates. Furthermore, it was observed that significant lateral input of excess-Ba can occur, probably associated with residual currents leaving the margin. This advected excess-Ba affected especially the recorded fluxes in the deeper traps (>1000 m) of the outer slope region. We have attempted to correct for this advected excess-Ba component, using Th (reported by others for the same samples) as an indicator of enhanced lateral flux and assigning a characteristic Ba/Th ratio to advected material, Using transfer functions relating excess-Ba flux with export production characteristic of margin areas, observed Ba fluxes indicate an export production between 7 and 18 g C m(-2) yr(-1). Such values are 3-7 times lower than estimates based on N-nutrient uptake and nutrient mass balances, but larger and more realistic than is obtained when a transfer function characteristic of open ocean systems is applied. The discrepancy between export production estimates based on excess-Ba fluxes and nutrient uptake could be resolved if part of the carbon is exported as dissolved organic matter. Results suggest that margin systems function differently from open ocean systems, and therefore Ba-proxy rationales developed for open ocean sites might not be applicable in margin areas. (C) 2000 Elsevier Science Ltd. All rights reserved. [less ▲]

Significance of random illite-vermiculite mixed layers in Pleistocene sediments of the northwestern Atlantic Ocean

in Clay Minerals (2000), 35(4), 679-691

The clay mineralogy of Pleistocene sediments of eleven sediment cores at three ODP sites from 30 degrees N to 60 degrees N northwestern Atlantic Ocean has been investigated. The sediments are ... [more ▼]

The clay mineralogy of Pleistocene sediments of eleven sediment cores at three ODP sites from 30 degrees N to 60 degrees N northwestern Atlantic Ocean has been investigated. The sediments are characterized by the presence of random illite-vermiculite mixed layers (I-V) (up to 32% of the clay mineral assemblage). The I-V clays are much more abundant during interglacial periods than during glacial ones. They are attributed to detrital supply through erosion of high-latitude continental areas from which they are derived mainly from chemical weathering of micaceous phyllosilicates. Their spatial distribution and the specific conditions for their formation through weathering suggest that I-V mixed layers are mainly derived from the Canadian Shield. They were transported From their source to marine deposition areas by rivers, deep water masses or nepheloid layers. Due to the specific conditions required For the Formation of I-V, its occurrence and abundance are used as a palaeoclimate and palaeocirculation proxy for northwestern Atlantic Pleistocene sediment. [less ▲]

Advective excess Ba transport as shown from sediment and trap geochemical signatures

in Geochimica et Cosmochimica Acta (1999), 63(16), 2353-2367

We report the results of a geochemical study of sediment and trap material. Major and trace elements (Zr, Ba, rare earth elements, and Th) were analyzed on bulk sedimentary material collected along the NE ... [more ▼]

We report the results of a geochemical study of sediment and trap material. Major and trace elements (Zr, Ba, rare earth elements, and Th) were analyzed on bulk sedimentary material collected along the NE Atlantic margin. Our aim is to test the widespread use of Ba-barite as a proxy for paleoproductivity in a continental margin area. This environment is of great interest because atmospheric-oceanic exchanges are important. In sediments, the geochemical signatures remain close to an upper crust reference, with flat shale-normalized rare earth elements patterns and constant elementary ratios. The calculated biogenic fraction of Ba or excess Pa (20-45%) remains lower than the excess Ba record in trap material (80-99%). The evolution of the geochemical signature along the margin reflects variable dilution of a detrital Post Archean Australian Shale-like component by a biogenic carbonaceous seawater-derived component. The trap material displays a wide range of variation in its trace element content (e.g., Ba similar to 150-3000 ppm, Zr similar to 2-100 ppm), except for the abyssal site, which is characterized by constant signature. In the two other sites, all of the trace element contents increase with water depth and present pronounced seasonal changes at each sampled water depth. The amount of excess Ba also increases in the deepest traps, and its evolution throughout the year mimics the change of the other analyzed trace elements. In contrast, its relationships with particulate organic carbon are not obvious. In term of fluxes, two periods of enhanced excess Ba fluxes are observed: (1) excess Pa flux increases with the detrital-like elements like Th especially during winter, and (2) excess Pa flux is enhanced without any change for the other trace elements during spring. To explain the first case, a supply through lateral advection is proposed. Such transient input of significant excess Ba flux will have a great impact on the yearly averaged estimation of the export production. Indeed, only the second case reflects a bloom in the biological productivity of the water column and must be taken into account in a mean calculation of the export production. Finally, a normalization of the excess Ba by detrital-like element like Th will help to discriminate between a real increase of the excess Ba due to local productivity change (high excess Ba and high excess Ba/Th ratio greater than or equal to 10,000) and any input due to advection process (high excess Ba but low excess Ba/Th ratio < 2000). Copyright (C) 1999 Elsevier Science Ltd. [less ▲]

Sediment and trap geochemical signatures along the NE Atlantic margin: Excess Ba advective transport and export production estimation

in Mineralogical Magazine (1998), 62A(Part 1), 432-433

Changes in the Western Boundary Undercurrent outflow since the Last Glacial Maximum, from smectite/illite ratios in deep Labrador Sea sediments

in Paleoceanography (1997), 12(1), 79-96

High-resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the Labrador Sea, located at the inlet (SW Greenland Rise) and outlet (Labrador ... [more ▼]

High-resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the Labrador Sea, located at the inlet (SW Greenland Rise) and outlet (Labrador Rise) of the Western Boundary Undercurrent (WBUC) gyre. At the two sites, smectites transported from the eastern Iceland and Irminger basins by the WBUC are observed. Clay mineral changes are used as proxies for the paleointensity reconstruction of the WBUC. On the Greenland Rise, a clay mineral index (smectite/illite (S/I) ratio) is defined. A S/I ratio of similar to 1 characterized the Last Glacial Maximum. It increased after similar to 17 ka, and reached a maximum value of 4 during the early Holocene, The mineralogical changes are gradual and do not show any reversal during the Younger Dryas, This pattern, which is confirmed by first-order estimations of smectite and illite fluxes, suggests gradually increasing sedimentary fluxes and WBUC intensity since the Last Glacial Maximum, A peak in the velocity of the WBUC at similar to 9 ka, as recorded by clay assemblages, is consistent with other regional studies based on pollen, foraminifera, or grain-size measurements, A massive dilution of smectites by illite and chlorite (S/I approximate to 3) occurs at similar to 8.5 ka. It corresponds to a period of rapid sediment accumulation and reflects an intensified illite-rich detrital supply by meltwaters from the southern Greenland Ice Margin. On the Labrador Rise, the smectite content varies between 20 and 60% with no obvious trend through time. The mineralogical composition is strongly influenced by ice-rafted deposition and by the abundance of fast deposit units (cf, Heinrich layers in the North Atlantic) which contain abundant detrital carbonates spilled-over from the North-West Atlantic Mid-Ocean Channel. In such layers, smectites are present but are diluted by the addition of illites, chlorites, and kaolinites. This provides evidence for a discrete and continuous WBUC supply of fine particles from the Irminger and Iceland Basins as far as the southeastern part of the Labrador Basin, Early deglacial smectite-rich layers (up to 60%) are also observed at this site, They indicate an increase in the outflow of the WBUC at similar to 13.5 ka, (Bolling-Allerod), as previously reported from grain size or foraminiferal assemblage studies. [less ▲]

Clay mineral signature of the NW Atlantic Boundary Undercurrent

in Marine Geology (1996), 130(1-2), 19-28

Surface sediments were sampled along 2 transects, across the Iceland and Irminger basins and in the Labrador Sea. Clay mineral assemblages (deduced from X-ray analyses of the carbonate-free <2 mu m ... [more ▼]

Surface sediments were sampled along 2 transects, across the Iceland and Irminger basins and in the Labrador Sea. Clay mineral assemblages (deduced from X-ray analyses of the carbonate-free <2 mu m fraction) are largely dominated by smectites (about 60%) in the Iceland and Irminger basins. In the Labrador Sea, smectites are present along the Greenland Slope, but absent or rare in sediments from the Labrador Slope. They may, however, represent up to 50% of the clay fraction at depths between 2800 and 3400 m along both margins of the Labrador Sea, i.e., along the axis of the Western Boundary Undercurrent (WBUC). A detrital supply from the adjacent continents is unlikely. The WBUC is thought to be responsible for erosion and transport of fine particles from the smectite-rich Irminger and Iceland Basins, then for their redeposition in the Labrador Sea. These results suggest that clay minerals can be used as paleocurrent indicators in the Northwest Atlantic. [less ▲]

Apports de la géochimie des argiles dans un sédiment océanique - Exemple des sédiments néogènes de l'Océan Indien Nord.

in Bulletin Société Française Minéralogie Cristallographie (1994), 6(2), 25