Joseph M. Kruger¹, Paul K. Link¹, Tracy J. Crane¹, Michael E. Perkins²

(1) Idaho State University, Pocatello, ID
(2) University of Utah, Salt Lake City, UT

ABSTRACT: Relationship Between Basin Geometry, Extensional History, and Sedimentation in Selected Neogene Basins: Northern Basin and Range Province

Gravity, seismic, borehole, and geologic data from two Neogene basins in southeast Idaho show that fault geometry and timing dramatically affects the stratigraphic evolution of these basins.

In the Lava Hot Springs area, movement above an inferred detachment formed a supradetachment subbasin filled with late Miocene conglomerates, tuffs, basalts, and lacustrine deposits of the upper member of the Salt Lake Formation. This half-graben is broken into several smaller half-graben by faults that probably sole into the underlying detachment. Movement along the detachment and upper plate faults appear to have controlled the timing and extent of alluvial fan, fluvial, and lacustrine deposition within this subbasin.

The presence of the upper member of the Salt Lake Formation in boreholes and in scattered locations surrounding Marsh Valley suggest it initially formed as a late Miocene supradetachment basin. These earlier deposits are largely buried by younger Plio-Pleistocene deposits associated with moderate-to high-angle block faulting. The timing and extent of alluvial fan, fluvial, marsh, and lacustrine deposits associated with this later phase also appear to be controlled by the location and timing of block faults within and along the margins of the basin, with fine grained deposition becoming widespread during peak episodes of block faulting.

Evolution of these basins suggest that potential source rocks would more likely be deposited during relatively rapid extension along block faults, or during breakup of a supradetachment basin into smaller subbasins. Potential reservoirs would more likely form between the source rocks in both faulting environments during episodes of slower extension.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado