NORMAL-PARAFFINS IN SHALES AS AN INDICATOR OF DEPOSITIONAL ENVIRONMENT

Normal paraffin compositions were determined for marine sediments from coastal and pelagic environments and for shales in the Jurassic-Creta ceous bedded chert sequence from the Franciscan terrane, western North America. The pelagic sediments and shales from a lower horizon of the bedded chert sequence are characterized by short-chained n-paraffins. The coastal sediments and shales from the upper horizon show high abu ndance of n-paraffins, especially for long-chained ones and a strong o dd-carbon predominence. The comparison of n-paraffin compositions of s hales with those of marine sediments suggests that the bedded chert se quence had deposited in continuous environments from pelagic to coasta l. This inference is in harmony with that based on the major, minor, a nd rare earth element compositions. The result suggests that shales in the Franciscan bedded chert sequence preserve well the normal paraffi n signals acquired at the deposition and demonstrates that the normal paraffin composition can be a useful indicator of sedimentary environm ent. Copyright (C) 1997 Elsevier Science Ltd.