--> Exhumation of a Proximal Foredeep and Associated Thust Belt Evidenced by Porosity Versus Depth Trends: the Upper Cretaceous Vivian Sandstones in Western Marañón Basin (Perú)

AAPG/SEG International Conference & Exhibition

Datapages, Inc.Print this page

Exhumation of a Proximal Foredeep and Associated Thust Belt Evidenced by Porosity Versus Depth Trends: the Upper Cretaceous Vivian Sandstones in Western Marañón Basin (Perú)

Abstract

Abstract

The quartz-rich sandstones of the Upper Cretaceous Vivian Formation constitute the most important reservoirs of the prolific Marañón foreland basin of northern Perú,. The Vivian sandstones are largely fluvial in the northeastern part of the basin with marine (shoreface to open shelf) influence toward the foredeep located to the west and northwest. The Vivian Formation is made up of two sandy units (Lower Vivian or Vivian A and Upper Vivian or Vivian B) with an intervening thin, mud-prone interval.

Porosity versus depth analysis from several wells in the western (deepest) part of the basin shows a simple trend of decreasing porosity with increasing depth for the Vivian sandstones. This trend indicates that overburden stress (compaction due to burial) is the controlling factor that determines porosity reduction. Further west closer to the mountain front the Vivian sandstones exhibit anomalously low porosities showing a distinct and systematic diversion from the regional porosity versus depth trend. The depth difference between these anomalous low porosities at shallow depths and similar porosities of the regional trend can be used as a proxy to estimate the exhumation of the basin during the Andean deformation in the latest Miocene. The value (circa 1,800 meters) is consistent with exhumation estimates derived from other methods and suggests that parts of the foredeep have been partially cannibalized and uplifted. This porosity deterioration is particularly severe for piggy back basins (i.e. Santiago basin) and foredeep portions adjacent to the thrust belt.