BILLO, SALEH M., King Saud Univ., Saudi Arabia

ABSTRACT: Geochemistry and Petroleum Potential of Red Beds

Despite the belief that the source of red coloration in red beds is of diagenetic origin, a controversy regarding the genesis of red beds ensues mainly from the geologic occurrences of red continental rocks that have drab gray or green marine equivalents with no apparent difference in their heavy mineral content. A depositional environment that is usually oxidizing may change to reducing to adapt to their new interstitial environment. Hematite coating, of which as slight as 0. 1 % is plenty to give a sediment a pure red color, is known to be stable under negative Eh, or reducing, environments at fairly high pHs. Low-oxygen or reducing milieus are also vital for preserving hydrocarbons. Red beds throughout the world are associated with evaporites. Their facies associations reflect deposition in fluvial and fluvial marine paralic environments in which oil pools could, and did, occur. The red beds that are forming today in a desert climate in Baja California appear to be modern counterparts of the Late Paleozoic red beds of Colorado. The continental redbed facies of the Sespe formation in the Ventura region of California give a good example of highly productive Tertiary sediments that grade into marine deposits westward. These sediments are widely distributed in the region and have dark organic shales at the top of the Miocene. Both the Ventura and Los Angeles graben basins supervene on land while other basins occur offshore to the west. Many traps have formed in these Tertiary basins by anticines, domes, and faults. Oil with high gravity (30 to 57° API) has filled the heap.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico