SUBSURFACE DATA IN THE LOWER COLORADO RIVER CORRIDOR AND ITS IMPLICATIONS FOR TECTONIC MODELS OF BASIN EVOLUTION WITHIN THE PALO VERDE AND PARKER VALLEYS

Subsurface lithologic logs within the lower Colorado River corridor (LOCO) contain critical stratigraphic information that can be used to test tectonic models for the region. We have compiled 353 well logs and measured stratigraphic sections within LOCO in order to understand the subsurface extent of the Bouse Formation and post-Bouse sediments. The Bouse Formation, a Miocene-Pliocene sedimentary unit of carbonate and overlying siliciclastic sediments, records the integration of the Colorado River towards the Gulf of California. Post-Bouse units include Pliocene to Holocene sediments derived from the Colorado River and local tributaries. The subsurface data are used to create structure contours representing the three-dimensional top and base of the Bouse Formation. The accuracy of these maps relies on the variable quality of the original drillers’ description in the well logs. To address this issue we produce various versions of each well log while taking into account a range of possible stratigraphic unit interpretations and utilizing geologic mapping, 3D visualization of the data, and cross-sections to compare neighboring wells.

The structure contour maps of the Blythe basin reveal that large parts of the Bouse Formation lies below sea level. Similar maps and profiles also indicate that post-Bouse sediments below sea level are mostly in the Palo Verde Valley. A compilation of mapped Cenozoic faults show several northwest-striking right-lateral faults within northern Palo Verde Valley and several north-striking normal faults within the central Palo Verde Valley suggesting a potential tectonic control on at least the deep post-Bouse sediments. The similar lithology and thickness of the underlying Bouse Formation in both valleys suggests that differential compaction as an explanation is unlikely. The interpretations of key wells between the Palo Verde and Parker Valleys indicate either a north-south graben or a right-lateral pull-apart basin. The ambiguity in the stratigraphic interpretation of the well logs adds uncertainty, which we are attempting to address with additional surface and subsurface constraints and by utilizing geophysical logs and fence diagrams in the Palo Verde Valley and other valleys within LOCO where similar links between stratigraphic interpretations and structures may exist.