Continental-scale drainage and basin-scale petroleum systems – how do they interact?
Paula Robinson and David Macdonald
University of Aberdeen, School of Geosciences Aberdeen AB24 3UE, UK
The pod of active source rock at the heart of a petroleum system is limited to part of a single basin. In continental settings, the drainage network that supplies the reservoir sands can be on the scale of 35% of a continent (e.g. Amazon) and feed several basins; in such cases sand quality of the potential reservoir unit is largely independent of the basin. In strike-slip systems, a single river can feed several basins sequentially, so the local behaviour of the depositional system is influenced by the same tectonic processes that created the basin and controlled deposition and maturation of the source rock. However, composition and reservoir quality of the sand being delivered to each strike-slip basin depends on the geology and scale of the catchment.
This paper presents a study of sediments from the modern Colorado River, from the Pliocene palaeo-delta of the Colorado in the Fish Creek-Vallecito Basin (Anza Borrego, southern California), and from the Los Angeles Basin where palaeo-Colorado deposits have been postulated. We use heavy mineral analysis to deduce the origin of the various sediment families. There is a petrographic distinction between locally derived sands and incoming Colorado sands in the Fish Creek-Vallecito Basin, however the distinction is less clear in the Los Angeles Basin.
The exploration implications for southern California will be discussed, focusing on distribution of high-quality reservoir sands via the palaeo-Colorado. General conclusions are drawn for other small basins that interact with large fluvial systems on other strike-slip margins.
AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects