Fluvial interpretations of stratigraphic surfaces across Upper Triassic to Lower-Middle Jurassic continental red beds northeastern Mexico

Abstract

This work broadens the understanding of previous interpretations from Late Triassic-Early-Middle Jurassic reds beds in northeastern Mexico from the Huizachal Group. Proposed bounding surfaces in El Alamar, La Boca, and La Joya formations are informal. The surfaces are here assigned allostratigraphic hierarchies for genetic interpretations. The formations are continental and provide no sea-level markers to tie the surfaces to the marine base level, but these fluvial-alluvial environments produce various scales of traceable scour surfaces.Upper Triassic-Middle Jurassic sandstones were analyzed at ten localities. Sedimentary profiles provide details for two facies associations and two main facies, which share 20 sedimentary lithofacies. The documentation of fluvial architecture considers sedimentary structures and paleocurrents in the sand bodies to features of five fluvial styles driving the depositional system, including mixed debris flow and braided river systems, gravelly or sandy meandering river, ephemeral sand-bed meandering river, and ephemeral sheet-flood distal sand-bed river.This model provides greater detail for more accurate stratigraphic correlation to sedimentary conditions under which these rocks were deposited, as it allows identifying four major bounding surfaces that can be tied to fluvial processes of amalgamation, aggradation, degradation, or flooding. The exercise estimates provisional regional tracts in continental deposits with no apparent impact by the marine base level. Amalgamation surfaces are underneath laterally extensive sheets of amalgamated channel-belt architectural elements, the contacts with underlying surfaces are disconformable, but locally are angular unconformities. The amalgamated beds also include sediment-gravity flows deposited such as channelized debris flows. Aggradation underlies and binds volcaniclastic rocks and facies with common mass wasting deposits from creep or debris flows, as well as overland flow and gullying over broad alluvial plains forming upward-coarsening sequences. It locally records the rapid burial of landscapes by mass wasting, distinguishing it from typical valleys that are cut by normal channel processes. Degradation binds incised valleys that confine channels and floodplains, and unconformably overly fining-upward sequences. Flooding marks sediment accumulation formed by overbank flows in low-energy environments.