LATE DEVONIAN CONODONTS FROM THE SHALLOW SHELF STRATA OF THE BROKEN RIB AND COFFEE POT MEMBERS, DYER FORMATION, CHAFFEE GROUP, COLORADO

The Dyer Formation in central Colorado is composed of carbonate strata deposited on a tropical carbonate platform during the Late Devonian. The Broken Rib Member, comprised primarily of biopackstones, biowackestones, and mudstones contains a diverse conodont fauna characterized by Bispathodus, Polygnathus, Pandorinellina, Icriodus, and Apatognathus. The taxa are relatively long ranging, indicative of the granulosus (Upper trachytera) Zone to expansa (Lower expansa) Zone based on the overlapping ranges of Polygnathus obliquicostatus and Icriodus costatus costatus. The Coffee Pot Member, comprised of dolomitized mudstones and intrarudstones characterized by rare stromatolites, karsted intervals, sandstones, and bioclastic beds has yielded conodonts from three horizons, in addition to a bed described by Sandberg and Poole (1977). Conodonts in the lower Coffee Pot include Pandorenellina cf. P. insita, Icriodus costatus darbyensis, and Polygnathus perplexus? indicative of the expansa Zone to ultimus Zone. In the upper Coffee Pot Member, above strata that exhibit unusually high (5-7 per mil) δ¹³C values characteristic of the highest Devonian Hangenberg Excursion, fused clusters of fragmented conodonts of ?Siphonodella, Pseudopolygnathus, and sand grains are suggestive of the Lower Carboniferous.