Architecture, Evolution and Stacking Patterns of the Paine Channel Complex, Upper Cretaceous Cerro Toro Formation, Silla Syncline, Magallanes Basin, Chile

William H. Crane¹ and Donald R. Lowe^2
1 ChevronTexaco, San Ramon, CA
² Stanford University, Stanford, CA

The Upper Cretaceous Cerro Toro Formation in the Silla Syncline, Magallanes Basin, Chile, includes approximately 1100 m of strata composed mainly of thin-bedded mudstone-dominated turbidites but including three thick divisions of coarse conglomerate and sandstone. Facies distributions, stacking patterns, and lateral relationships indicate that the coarse-grained sandstone and conglomerate units represent the fill of a complex of major deep-water channels trending down the axis of the Silla Syncline. The middle unit, informally named the Paine member, preserves a minimum of three discrete channel fill units, the uppermost of which, termed the Paine C, provides a superb cross-section of a deep-water channel about 3.5 km wide and shows explicit details about the process of channel evolution. Along its northern margin, the Paine C channel consists of laterally offset secondary channel margins each eroded into fine-grained mudstone and thin-bedded sandy turbidites. To the south, this channel is bounded by a single, deeply-incised margin. The evolution of the Paine C channel occurred through multiple cycles each involving: (A) erosion of underlying fine-grained, channel-fill sediments; (B) deposition of channel-fill coarse-grained sandstone and pebble to cobble conglomerate; and (C) cessation of coarse sediment deposition and deposition of fine-grained, thin-bedded turbidites within the channel. The thin-bedded turbidites deposited within and adjacent to the channel on the north do not appear to represent levee deposits but rather a separate fine-grained turbidite system that impinged on the Paine C channel from the north. Although the Cerro Toro channel systems were influenced by regional tectonics in the Magallanes Foreland Basin, observed architectures and stacking patterns are broadly similar to those observed in passive margin channel systems.

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