MACRO- AND MICROFACIES INTERPRETATIONS OF THE MICROBIALITE-SPONGE HINTZE'S REEF IN THE LOWER ORDOVICIAN FILLMORE FORMATION, HOUSE RANGE, WESTERN UTAH
Hintze’s Reef is more than three meters thick at Section C (Hintze, 1951) in the House Range and is made up of interconnected mounds: steep-sided structures up to 2.5 meters wide that were built upon a stabilized grainstone substrate. Each mound within the reef is composed of a stromatolitic core surrounded by non-laminated (possibly dendrolitic) microbialite that contains fragmentary metazoan fossils and carbonate mud. This non-laminated fabric likely stabilized the reef, making continued upward growth possible. Lithistid demosponges, many in life position, are preserved throughout the reef. Individual mounds within the reef are bounded by shelly grainstone-filled channels that vary in width, reflecting episodes of high current energy that deposited larger grains into the topographic lows between the rigid mounds. In outcrop, the grainstone-filled channels resemble lenses between the larger interconnected mounds; thus, the reef has an egg-carton-like morphology in three dimensions. Polished slabs and thin sections of the non-laminated microbialite reveal a variety of microbial structures, including Wetheredella and representatives of the Girvanella and Renalcis groups, as well as branching, clotted, peloidal, and fenestral fabrics.