--> Abstract: Post-Rift Hydrocarbon Systems, Greater Amazon Mouth, Brazil: Transition from Shelf to Basin and Source Distribution Controls, by D. M. Advocate, S. W. Young, A. H. Ross, T. P. Buerkert, J. E. Nealand, and K. L. Mahon; #90933 (1998).

Datapages, Inc.Print this page

Abstract: Post-Rift Hydrocarbon Systems, Greater Amazon Mouth, Brazil: Transition from Shelf to Basin and Source Distribution Controls

Advocate, David M.; Steven W. Young; Arthur H. Ross; Thomas P. Buerkert - Exxon Exploration Co.; Jack E. Neal; Keith L. Mahon - Exxon Production Research Co.

Three post-rift marine hydrocarbon systems in the Amazon Mouth are characterized with maturation, migration and Neogene reservoir distribution controlled by rapid deposition related to Andean tectonics. Two of the potential hydrocarbon source intervals (Upper Cretaceous and Paleogene) are present on the shelf and upper rise, but their basinward extension is inferred (Fig. 1). Extrapolation of the potential sources from the shelf position into the basin requires an understanding of controls on distribution and preservation of organic matter. Amazon Mouth sources have three main controls: (1) paleogeography, (2) oceanic conditions and (3) terrestrial river input (Fig. 2).

The Upper Cretaceous (Limoeiro) clastic source is well documented on the shelf where it is fair to good quality (TOC 1-5 %, HI 150-500). This source should improve basinward where terrestrial input and siliciclastic dilution decrease. Source thickness may be a risk, but oil-prone, clastic-starved marine shales are predicted in the deep basin. The primary control on the distribution of Turonian source is mainly oceanic circulation and productivity.

The Paleogene (Amapa) source is also encountered on the shelf, but is less oil-prone (TOC 1-5%, HI 200-350) than the Upper Cretaceous in the area. Based on map distribution and biomarker data, we interpret this source to be limited to a back-reef lagoonal environment and not present seaward of the carbonate shelf edge. The key to better organic enrichment is interpreted to be paleogeography: carbonate highs cause restricted circulation and increase Potential for organic preservation.

Source potential is also postulated for the Miocene-Pleistocene (Pirarucu) interval. Tropical, Tertiary-age depocenters around the world have encountered hydrocarbons with distinctly terrestrial signatures. The Amazon Mouth region possesses many attributes that allow terrestrial sources capable of oil generation, but more data is required to test this concept.

Hydrocarbon maturation is driven by rapid Miocene to present burial that causes the Limoeiro to be locally overmature. Postulated Pirarucu sources may be mature for oil in some areas. Rapid sedimentation resulted in deep listric faults, shale diapirs and toe-thrust structures that provide abundant vertical migration pathways. The presence of interbedded Tertiary sources and sands would allow for simple migration scenarios.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil