Factors controlling the burial of organic carbon (OC) in Late Quaternary sediments on the NW Mexican continental margin are assessed using a suite of box and piston cores strategically located an the shelf-slope rise with respect to the intense oxygen minimum in this region. An OC concentration maximum occurs on the mid-slope, below the core of an intense water-column O-2 minimum, due to current winnowing on the outer shelf, the preferential accumulation of organic matter in fine-grained deposits, and the offshore decrease in the settling flux of organic detritus. The organic matter at all water depths is overwhelmingly marine. Hydrogen indices (HT) are higher on the slope (>300 mgHC/g TOC) than on the shelf (
Rates of accumulation of OC and opal are all higher in the interglacial intervals when compared with the glacial deposits over the last 140,000 yr. However, matrix-corrected HI values in the mid- and lower-slope cores are invariant and are similar to values in the laminated intervals from the oxygen-minimum site. Thus, cyclic changes in organic carbon accumulation on this margin have been controlled by production variations rather than differential preservation. HI values in Late Quaternary sediments from several continental margins, including NW Mexico, and euxinic basins correspond to type LI kerogen, irrespective of bottom water O-2 concentrations. Therefore, the preservation of oil-prone kerogen in productive margin settings does not appear to be restricted to sediments deposited under conditions of low bottom water O-2 concentrations as envisioned in models of petroleum source-rock deposition. Copyright (C) 1999 Elsevier Science Ltd.
|Number of pages||12|
|Journal||Geochimica et Cosmochimica Acta|
|Publication status||Published - Jun 1999|
- ROCK-EVAL PYROLYSIS
- ENHANCED PRESERVATION
- OXYGEN MINIMUM