SEQUENCE STRATIGRAPHIC AND PALEOECOLOGIC ANALYSIS OF AN ALBIAN CORAL-RUDIST PATCH REEF, ARIZONA, USA

Fossilized reefs can preserve critical information about changes in marine environments over a relatively short period of time. The interpretation of these changes is often hindered by the complexity of reef growth with respect to architecture, biotic zonation, and time. High-resolution mapping and data collection incorporating both sequence stratigraphical and paleoccological principles are needed to document the architectural complexity of reef development. To demonstrate this, we present a case study in which both principles are integrated to build a new stratigraphic framework for an Albian-aged rudist-coral patch reef outcrop (Paul Spur, Bisbee, AZ, USA). The dataset reveals that the outcrop preserves five stages of development: (1) initial shoal deposition; (2) pioneer reef growth; (3) reef diversification; (4) reef hiatus; and (5) rudist shoal development. These stages represent periods of deposition and reef growth within high-frequency transgressive-regressive sequences. Interpretations of sedimentological and paleoecological data are then used to demonstrate the variable influence of different environmental controls on reef growth. Prevailing wind and current direction act as higher order controls on overall reef architecture by influencing windward-leeward asymmetry. Fluctuations in relative water depth as well as sedimentation rate, source, and type is an important influence on reef community and growth habit. Though corals and rudists cohabited during much of the reef's history, corals dominated when water depth was greater and external sediment influx lesser, whereas rudists dominated in shallow water depths and during periods of high external sediment influx. This work demonstrates that detailed evaluation of stratigraphy and palcoccology, as well as careful consideration of timelines and heterogeneity, is essential for building an accurate stratigraphic framework that allows a more thorough understanding of processes driving reef growth.