Print this pagePaleoclimatic changes influence the development of organism, and cause sea-level rise and fall. Sea-level changes control the places of various sediments, redox conditions and the distributions of molecular markers in sediments. Hence some molecular markers can serve as indicators of paleoclimate and a link of paleoclimate and source rocks.
Four types of the molecular markers, combustion-derived PAHs, high-plant-derived PAHs, steranes and isoprenoids, are identified by GC-MS from 48 cuttings of the Middle Jurassic-Lower Cretaceous strata in Well 35/11-2 of the North Sea. Combustion-derived PAHs mainly with benzo[e]pyrene have been proposed to be the products of ancient vegetation fires. Abundant these PAHs reflect the paleoclimate of seasonal variations, which causes the alternations of the growth of land plants and occurrence of forest fires. High plants are considered to be major precursor sources for retene, cadalene and simonellite.
The results have shown four stages of the paleoclimate varying and the corresponding source rocks. Frequently fluctuated concentrations of these molecular markers, and wavily various TOC and SOM was associated with cool, semi-arid seasonal climate during Bathonian. Abundant combustion markers, high-plant-derived PAHs, C-29 sterane and low Ph/Pr corresponded to warm, seasonal climate and low sea level with the source rocks of low TOC and SOM, and poor kerogen from Callovian to middle Oxfordian. Low abundances of combustionderived PAHs, retene, cadalene, C-29 sterane, and high Ph/Pr coincided with warm, humid, not seasonal climate and high sea-level with the source rocks of high TOC and SOM, and good kerogen during early-middle Volgian. Relatively high abundances of combustion products, cadalene, C-29 sterane, and low Ph/Pr, TOC and SOM consisted with warm, semi-arid seasonal climate from late Volgian to Ryazanian.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid