High-Resolution Sequence Stratigraphy and Shoreline Trajectory of the Cretaceous Gallup System, New Mexico, U.S.A.

Abstract

Sequence stratigraphy is problematic when it is applied to actual data. It is still debatable that how sequences and systems tracts, as well as their associated surfaces, are defined. Laterally continuous outcrops of the Gallup Sandstone allow us to document a high-frequency sequence stratigraphy and its potential controlling mechanisms of a Late Cretaceous deltaic system in the Western Interior Seaway. We measured 69 sedimentological sections and walked out key surfaces along 60 km of laterally continuous cliffs and covered slopes that are oblique to paleo-depositional dip around Northwest New Mexico. Using bentonites as regional datums, we reconstructed the deposition of stratigraphic sequences with minimum distortion. The sequence stratigraphic scheme in this study consists of four systems tracts, including falling-stage systems tract, low-stand systems tract, transgressive systems tract, and high-stand systems tract. Shoreline trajectories and gradational accommodation successions are applied to understand the allogenic-controlled stacking patterns of parasequences and linked to define systems tracts and sequences. Wheeler diagram is also used to help to restore the evolution of sequences. Sharp-based shorefaces, associated with abundant gutter casts, may indicate a forced regression in a storm-dominated environment and define a sequence boundary. Also, the detached lower shoreface deposits are likely attributed to the forced regression and the following transgression. Parasequence sets show aggradation, progradation, retrogradation, and degradation, reflecting high-frequency relative sea level changes. In addition, the number of parasequences developed in a 2 Ma depositional duration may suggest eustatic control by precession-dominated Milankovitch Cycles. Overall, the high-frequency stratigraphic sequence of Gallup System is very likely resulted from the high-frequency eustatic sea level changes in an epicontinental ramp setting.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018