Clay mineral distribution and significance in Quaternary sediments of the Amazon Fan

Abstract

The clay mineral assemblages of samples from the Amazon Fan were investigated in middle Pleistocene to Holocene sediments from 16 Ocean Drilling Program Leg 155 sites and were placed in lithologic successions to study continental evolution and transport conditions. The sediments sampled along a transect parallel to the main channel reflect moderate differential settling processes, whereas those studied along a transect roughly parallel to the coast clearly suggest winnowing effects related to the North Brazil Current. High-resolution analyses of Holocene deposits reflect the dominant influence of downstream soil erosion relative to supply from the Andean range and the progressive increase of soil-derived relative to rock-derived outputs. The middle Pleistocene to uppermost Pleistocene and Holocene successions are marked by a constantly warm climatic background and by noticeable modifications in the rock-derived (illite, chlorite) and soil-derived (smectite, kaolinite) products. These products successively reflect sea-level changes, tectonic rejuvenation in the Andean range, regressive erosion, and rainfall increase.

The Missing Silica Sink: Revisiting the Marine Sedimentary Si Cycle Using Cosmogenic 32Si

“…Based on 32 Si sediment activities and transport-reaction modeling, the along shelf, migrating mudbank component of the Amazon-Guianas dispersal system sequesters~0.4-0.5 Tmol/yr (Rahman et al, 2016). The smectite content of clays in the Amazon River Mouth is 27-32%, increasing to 33-47% in the Amazon Fan and 51% in the Orinoco Delta (in the Orinoco River mouth it is 7-13%) (Bout-Roumazeilles et al, 2013;Debrabant et al, 1997;Parra et al, 1997), consistent with our estimate of substantial authigenic clay formation along this dispersal system. Diagenetic models based on K + and F À fluxes into Amazon Delta sediments and operational leaches predict authigenic clay formation in the proximal delta as~0.5 Tmol Si/yr (~50% of riverine inputs) (Rude & Aller, 1994;Michalopoulos & Aller, 1995), which leads to a bSi total burial in the Amazon-Guianas dispersal system of~1 Tmol/yr.…”

Clay mineralogy of surface sediments as a tool for deciphering river contributions to the Cariaco Basin (Venezuela)

“…The presence of smectite in the Unare area ( Figure 6) reflects the geological settings of the Unare River watershed that is mainly composed of Mesozoic sedimentary formations ( Figure A-2) where smectite is commonly associated with dominant kaolinite [Bay, 1981;Longa and Bonilla, 1987]. The contribution of the Amazon/Orinoco plume to the Cariaco sedimentation has been extensively investigated in the past few decades [Müller-Karger and Varela, 1990; [1997] and Pujos et al [1997]; Orinoco plume from Gibbs [1977]; Unare River from this study; Dragon's mouth from Pujos et al [1997]; Amazon River mouth from Gibbs [1967]; and Amazon fan from Debrabant et al [1997] and Rühlemann et al [2001]. -Karger and Aparicio, 1994;Clayton et al, 1999;Peterson et al, 2000;Lorenzoni, 2005;Peterson and Haug, 2006;Martinez et al, 2010].…”

“…[]; Amazon River mouth from Gibbs []; and Amazon fan from Debrabant et al . [] and Rühlemann et al . [].…”

Mechanisms of fossilization of the soft-bodied and lightly armored faunas of the Burgess Shale and of some other classical localities

“…To find whether this was the case, we can turn to the relation between tectonics and sedimentation. Detrital illite ultimately comes from erosion of shales, argillites, and slates exposed in young mountain belts (Chamley, 1989, p. 163-192;Pujos, Latouche, and Maillet, 1996;Debrabant, Lopez, and Chamley, 1997). At the time of the Burgess Shale deposition, the relevant margin of the Laurentian craton had not been subjected to mountain building for about 1.3 Ga (Hoffman and Bowring, 1984;Hoffman, 1989;Fritz and others, 1991;Dalziel, dalla Salda, and Gahagan, 1994;Cecile, Morrow, and Williams, 1997).…”

“…Released by weathering under an atmosphere comparable to today's and transported only a short distance from the continent, this iron would have been transported primarily as iron(III) hydroxide adsorbed on smectite particles brought into the sea by rivers (Froehlich and others, 1979;Aller, Mackin, and Cox, 1986;Lovley andPhillips, 1986, 1987;Lovley, 1991;Hedges and Keil, 1995;Debrabant, Lopez, and Chamley, 1997). The estimated mean iron(II) content in the argillite of the Phyllopod bed is 4.0 wt percent (sec 2); to produce this amount of iron(II) by the reduction of iron(III) hydroxide according to eq (1), an amount of organic carbon equal to 0.21 wt percent of the present argillite had to be oxidized into carbonate.…”