High-Frequency Carbonate/Siliciclastic Reciprocal Sedimentation Within the Upper San Andres Depositional Sequence (Permian, Guadalupian), Last Chance Canyon, Guadalupe Mountains, New Mexico: ABSTRACT

Abstract

The upper San Andres Formation and Cherry Canyon Sandstone Tongue in Last Chance Canyon form a third-order depositional sequence comprising at least 12 smaller scale, time-bounded depositional units. The intertidal through toe-of-slope facies associations, volumetric proportions of carbonate/siliciclastic sedimentation, and depositional topography change progressively throughout the sequence. These variations reflect the controls that produce the landward-stepping, vertically stacked, and seaward-stepping arrangements of units constituting the sequence. In Last Chance Canyon many of the small-scale depositional units have stratal geometries and carbonate/siliciclastic relationships that are analogous to third-order sequences. The oldest depositional unit is a point-sourced turbidite lobe that onlaps the underlying sequence boundary. Carbonate-rich slope sandstones form the next two units, which also onlap the sequence boundary. These three landward-stepping to vertically stacked units compose the transgressive systems tract (TST). Units within the TST record a progressive decrease in sedimentation rate, depositional energy, and siliciclastic content that reflects the sequence-scale transition from toe-of-slope siliciclastic turbidites to an increasingly carbonate-dominated ramp. Within each of the two youngest units, a basal sandstone hemicycle is overlain by a mounded fusulinid-rich carbonate hemicycle. The maximum flooding surface caps the TST and is overlain by the most carbonate-rich interval of the sequence. From basal tomore » upper slope, the facies in this unit are laminated mudstones and wackestones, crinoid-bryozoan bafflestone bioherms, brachiopod-sponge reefs, and fusulinid mounds. Seaward-stepping units compose the middle highstand systems tract (HST).« less