Drowning of a nearshore peat-forming environment, atane Formation (Cretaceous) at Asuk, West Greenland: sedimentology, organic petrography and geochemistry

摘要

The Cretaceous Atane Formation, Nuussuaq basin, West Greenland, is dominated by non-marine sandstones, shales, coals, and delta-front deposits. Marine incursions are frequent, however, and near Asuk, a coal seam is encased in shallow marine deposits. Notable changes in both petrography and geochemistry occur through the seam. At the base and top of the seam, the proportions of inertinite and liptinite incresase at the expense of the huminite maceral group, and within all maceral groups proportions of detrital macerals increase. Geochemical changes include systematic variations in TOC, TS, n-alkane, acyclic isoprenoid, aromatic hydrocarbon, and di- and triterpenoid biomarkers, which include a number of rearranged hopanes and hopenes, and six isomers of 28, 30-bisnorhopane. The variations reflect diagenetic changes related to the availability of clay, as well as changes in depositional environment going form shallow marine conditions, through fresh water mire back to open water conditions and to he eventual return of shallow marine conditions, shown by the occurrence of delta-front deposits containing Ophiomorpha nodosa trace fossils c. 50 cm above the top of the coal seam.c