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Outcrop Examples of Falling Stage Systems Tracts: Quantification and Exploration Significance

Abstract

Although falling stage systems tracts (FSST) during forced regression have been widely accepted as a key component of stratigraphic sequences, the characteristics and models of FSST are only based on limited examples, therefore incomprehensive. Few attempts have been made to quantify the sedimentation of FSST or to evaluate its exploration significance. Here we present the outcrop examples of FSST from the Cretaceous Gallup system and the Ferron Notom delta to characterize various types of FSST. Criteria including sharp-based shoreface, subaerial erosional top, and coarse-grained sediment and lag are not necessary to interpret FSST or forced regression. Deposition of FSST appears to be thin but laterally extensive as a result of the limited accommodation and high sediment supply. Very fine- to fine-grained sandstones dominate FSST due to either fine-grained source rocks or distal depositional localities. Intensive bioturbation suggests that the deposits of FSST fell below wave base as a result of rising sea level during transgression, allowing ichnofauna to occupy the depositional environments. We quantify volumes of the sandstones in FSST, including applying a fulcrum method using the linked upstream incising channels’ dimension to estimate sediment budgets. The extensive sandstones and the overlying shales of transgressive systems tracts make ideal reservoir-seal pairs. The volumetric analysis suggests that FSST can be a good exploration candidate for both stratigraphic plays and structural prospects.