Large-Scale Sedimentary Intrusions Sourced from Deep-Water Channel Deposits, Cerro Toro Formation, Chilean Patagonia: An Outcrop Analog to North Sea Reservoirs

Stephen M. Hubbard, Brian W. Romans, and Stephan A. Graham
Stanford University, Stanford, CA

Vertical to sub-vertical clastic intrusions up to 67 m wide and >100 m long crop out in the Magallanes foreland basin, associated with deep-water deposits of the Cretaceous Cerro Toro Formation. The three-dimensionally exposed features emanate from the margins of conglomeratic bodies that were deposited in channels that flowed axially along the basin foredeep. The remobilized sediment consists of poorly-sorted conglomerate, sandstone, and mudstone. The event responsible for the remobilization of the coarse-material involved significant overpressure, possibly related to gas charging of the unconsolidated depositional sediment body. A polygonal arrangement of the mapped intrusions suggests that their distribution is at least partially controlled by structure.

Improved 3-D seismic data acquired over the last decade has revealed that large-scale intrusions are commonly associated with deep-water deposits in the North Sea Basin, and that they can either act as conduits for fluid flow, or themselves contain significant accumulations of oil and gas. The outcropping intrusions in the Cerro Toro Formation represent excellent geometric analogs for numerous reservoirs associated with similar features in Paleogene strata of the North Sea Basin.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005