--> Abstract: Organic Matter Variations in a Depositional Sequence: Implications for Use of Source Rock Data in Sequence Stratigraphy, by M. A. Pasley; #91004 (1991)
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Organic Matter Variations in a Previous HitDepositionalNext Hit Previous HitSequenceNext Hit: Implications for Use of Source Rock Data in Previous HitSequenceNext Hit Stratigraphy

PASLEY, MARK A., Louisiana State University, Baton Rouge, LA

Variations in the amount and type of organic matter preserved in shelf sediments are predictable within a Previous HitsequenceNext Hit stratigraphic framework. These variations can be documented using routine petroleum source rock evaluation techniques. The type and preservation of organic matter is related to the rate of allochthonous shelf sedimentation. Each Previous HitdepositionalNext Hit systems tract in a Previous HitsequenceNext Hit has a distinct Previous HitdepositionalNext Hit style (aggradational, retrogradational, or progradational) that affects changes in the amount of terrigenous influx. Therefore, integration of source rock data with sedimentologic and regional stratigraphic results provides greater resolution in locating the critical surfaces (Previous HitsequenceNext Hit boundaries, transgressive surfaces, and surfaces of maximum starvation) that bound Previous HitdepositionalNext Hit systems tracts within the Previous HitdepositionalNext Hit Previous HitsequenceNext Hit.

This integrated Previous HitsequenceNext Hit stratigraphic approach has been applied to conventional cores of Upper Cretaceous strata in the San Juan basin of New Mexico. Fine-grained marine sediments in transgressive systems tracts possess high total organic carbon and yield relatively high amounts of hydrocarbons during pyrolysis. Petrographically, this organic matter is composed primarily of amorphous macerals. Both the lower Juana Lopez and the Mancos Shale above the Tocito Sandstone provide examples of organic matter deposited in the transgressive systems tract. In contrast, marine Previous HitdepositionalNext Hit systems of both the lowstand and highstand systems tracts contain less total organic carbon and less pyrolyzable hydrocarbons. Petrographic analysis of organic matter in these rocks reveals abundant macerals f terrestrial origin. This methodology not only improves systems tract Previous HitidentificationNext Hit in fine-grained, basinward intervals but also reveals those portions of the Previous HitdepositionalNext Hit Previous HitsequenceTop that are most favorable for marine petroleum source rock formation.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)