Facies architecture and paleogeography evolution of regressive wave-dominated shorelines transitioning into tide-dominated estuaries: Early Devonian Subbat Member, Jauf Formation, Saudi Arabia

Abstract

The Paleozoic succession on the northern Arabian Plate was deposited during several regressive and transgressive events. The Early Devonian Subbat Member of the Jauf Formation comprises several smaller-scale intervals of the Paleozoic succession that were interpreted based on large-scale observations from outcrop and subsurface data. This study utilizes process-based sedimentology and investigates facies stacking, lateral continuity of sand bodies, and ichnofacies to interpret an open marine wave-dominated forced regressive system, that is followed by transgressive shorelines. This study integrates a total of 417 meters of the Devonian stratigraphy from four outcrops and two shallow cores. This dataset records a third-order sequence which developed through an extensive intra-plate siliciclastic influx in between two carbonate units during the deposition of the Subbat Member. This study illustrates the evolution of a falling-stage systems tract that is characterized by shoreface sand bodies and an erosional-based delta front in the lower Subbat Member. These sediments overlie a regressive surface of marine erosion (RSME), extending for hundreds of kilometers and transitioning to an overall transgression in the upper parts of the Subbat Member. This study interprets a total of seven facies associations (FAs): i) offshore, ii) wave-dominated delta, iii) shoreface to offshore transition, iv) fluvial channels, v) crevasse splays, vi) paleosol, and vii) estuarine facies associations. In the lower part of the Subbat Member, the wave-dominated delta and shoreface to offshore transitional FAs overlie the marine shelf strata of the offshore FA and develop a RSME. Fluvial channels and crevasse splays FAs are interpreted. Unique assemblages of trace fossils, in terms of intensity and diversity, ranging from the Nereites Ichnofacies to Skolithos Ichnofacies, play a major role in the understanding of the overall water depth and depositional setting. Distinctive terrestrial Prototaxites fossils are present in sheet-like bodies and are interpreted as part of extensive crevasse splays that formed during major river flooding events. This study provides a unique integrated approach using ichnology, sedimentology, and sequence stratigraphy to better understand the spatial and temporal facies distribution of a forced regressive sequence and refine the paleogeography of northern Arabia during Early Devonian time.