Depositional Model of Early Cretaceous Coral-Algal-Rudist Reefs, Arizona

Abstract

Patch reefs composed mainly of corals and stromatolites are well developed in the Lower Cretaceous Mural Limestone of southeastern Arizona. This biota is similar to that forming buildups in the downdip Lower Cretaceous sections of the Gulf Coast at Fairway and Stuart City fields in Texas and the Golden Lane-Poza Rica field in Mexico. In contrast, updip Lower Cretaceous buildups in central Texas consist mainly of rudists, and corals are rare. The reefs of the Mural Limestone are up to 25 m thick and about 1.5 km long. They grew during the early Albian transgression from the Chihuahua trough into Arizona. The reef-core and flank facies are coral-stromatolite-rudist boundstone and coral-rudist fragment packstone. The reef-core facies is dominated by the colonial corals Actinastrea and Microsolena. The latter coral commonly is encrusted by stromatolites. Caprinids and thick-walled monopleurids are secondary in abundance. Associated perireef facies are peloid-ooid grainstone, mollusk-miliolid-orbitolinid wackestone, and ostracod-mollusk-skeletal algal wackestone and sandstone-shale. The perireef shallow shelf is characterized by Monopleura, Chondrodonta, Toucasia, and nerineids. The nearshore restricted lagoon and shoreface to tidal-flat environments were occupied by Exogyra and Crassostrea communities and the Arenicolites association. Where megafossils are absent, the shelf environment is characterized by assemblages of miliolids, Orbitolina, and agglutinated forams. The distribution of algal types is also closely related to environments. These facies and communities have predictable stratigraphic relations.