Abstract

Stratal geometries and platform trajectories in shelf-top carbonates contain a record of past eustatic, tectonic, and oceanographic changes throughout earth history. However, intrinsic structural processes such as faulting, fracturing, and differential compaction complicate the interpretation of stratal architecture in these settings. Large-scale stratal geometries cannot be used to constrain key depositional variables (e.g., water depth and facies relationships) until the relative contribution of specific structural and depositional processes can be quantified. These problems can be overcome using integrated structural and stratigraphic frameworks that employ stepwise reconstruction of shelf-top geometries using facies analysis and high-resolution spatial data.

This study examines the origins of seaward-dipping (up to 18°) shelf-top strata of the Permian Seven Rivers Formation in McKittrick Canyon, New Mexico. Traditional field mapping and a digital outcrop model compiled from airborne lidar allow quantitative assessments of the relationships among facies, structures, and stratal geometries. Results indicate that there are at least two origins for variations in stratal architecture in the Seven Rivers, including (1) primary dips associated with steepening of the bathymetric profile towards the shelf edge and (2) both landward and seaward rotation of fault blocks during deposition of successively younger strata. Removing compaction-driven deformation localized in front of the underlying Goat Seep margin allows more accurate estimates of reef depth and platform trajectory. Comparison of these results with previous studies suggests that neglecting either the depositional or the structural component of shelf-top architecture introduces significant errors into the reconstructed bathymetric profile. The Seven Rivers Formation serves as a useful analog for addressing challenges related to the interpretation of depositional profiles and platform histories in other steep-walled carbonate shelves.

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