KATZ, BARRY, and VAUGHN ROBISON, Texaco Inc., Houston, TX

ABSTRACT: Limitations of Organic Geochemical Paleoenvironmental Indicators

There have been numerous advances in analytical organic geochemistry. As a consequence, new data have become available. Much of these data, including both isotopic and biomarker data, are being utilized in the interpretation of the depositional environment of an oil's source rock setting. This paper will describe examples of two primary problems that exist with the interpretational schemes that have been developed to infer the nature of a source rock system from the geochemical character of an oil.

The first problem is related to the data base used to originally construct the interpretational schemes. The significance and environmental interpretation of various biomarker compounds has typically been based on data obtained from a single oil or a small suite of oils taken completely out of geologic context. As the data base expanded and additional data became available many "key" environmental indicators were found in oils derived from multiple and very often dissimilar depositional settings.

The second problem is related to the character of most source rock systems. There is substantial areal and stratigraphic variation in many of the geochemical attributes within individual source rocks. In fact, much of the variability in source systems is greater than differences observed among oils thought to be derived from different environmental settings within the same basin. Consequently, how these geochemical attributes will be commingled to yield a unique geochemical signature is unclear.

Clearly additional data, both geochemical and geological, are required prior to the acceptance of many of the organic geochemical environmental indicators. These data also indicate the importance of utilizing all of the available data rather than concentrating on the geochemical oddity.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.