Article: Chitinozoa from the Ordovician Sylvan Shale of the Arbuckle Mountains, Oklahoma
W. A. M. Jenkins
Chitinozoa referable to nine genera and twelve species (five new) are recorded from the Sylvan Shale of the Arbuckle Mountains in southern Oklahoma. They provide for the first time a means of dating, bio-stratigraphically subdividing, and correlating the entire formation. Its chitinozoan fauna indicates that the Sylvan Shale is of Upper Ordovician age throughout and confirms with additional fossil evidence the age of the lower beds. No abrupt changes break the general continuity of the chitinozoan succession but on the basis of gradual changes in the composition of its chitinozoan fauna the Sylvan Shale may be divided into three biostrati-graphical units. The fauna occurs throughout the Arbuckle Mountains and is recognizable in the subsurface of western Texas and in the Maquoketa Formation of eastern Iowa. It differs strikingly from the fauna in the underlying Viola and Fernvale Limestones, and from the faunas in the overlying formations of the Silurian-Devonian Hunton Group. The occurrence of reworked Sylvan chitinozoans in upper Sylvan strata indicates that during late Sylvan time uplift (hitherto unsuspected) took place, at least locally, in the southern mid-continent. The fauna is described systematically. Clathrochitina Eisenack 1959 is used in its original sense; Plectochitina Cramer 1964 is a junior synonym. Sagenachitina gen. nov. is proposed for species, hitherto referred to Clathrochitina, whose basal margins support finely divided networks. Acanthochitina rashidi, Ancyrochitina merga, Clathrochitina sylvanica, Cyathochitina agrestis, and Sphaerochitina lepta are new species.