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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 77 (1993)

Issue: 3. (March)

First Page: 386

Last Page: 401

Title: Recurring Patterns of Total Organic Carbon and Source Rock Quality within a Sequence Stratigraphic Framework

Author(s): Stephen Creaney (2), Quinn R. Passey (3)


Sequence stratigraphy has been combined with total organic carbon (TOC) analysis from well logs, core, and cuttings to develop a model of TOC accumulation in marine source rocks. Routine well profiling of TOC in marine source rocks has revealed that recurrent patterns in the vertical distribution of TOC occur that can be explained with sequence stratigraphic concepts. The model assumes that the principle controls on organic carbon accumulation are (1) the presence of low oxygen conditions at the sediment/water interface, and (2) sedimentation rate. Under these circumstances, TOC will vary inversely with terrigenous clastic influx. If accommodation is high, clastic influx is low in distal locations, and the resulting weight-percent TOC in basinal sediments is increased. Th maximum TOC in a vertical profile through a single marine sequence probably correlates to the maximum flooding surface. TOC decreases above this surface due to increasing sediment dilution during highstand progradation and decreases below it with the higher sedimentation rate of the older transgressive systems tract. Commensurate with TOC increase towards the maximum flooding surface, the organic matter type becomes more marine and therefore increasingly oil prone. Several marine source rock examples are presented as well as a lacustrine example, which also conforms to the marine model.

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