Abstract

Detailed studies of the morphology, ontogeny, variation and stratigraphic distribution of the ostracodes of the Henryhouse and Haragan Formations indicate the presence of an unconformity at the Siluro-Devonian boundary in the Arbuckle Mountains. The ostracodes support other faunal evidence indicating a late Niagaran (early Ludlovian) age for the Henryhouse Formation and a Helderbergian age for the Haragan Formation.

The ostracode faunas of both stratigraphic units are large and diversified. The Henryhouse Formation contains 46 species representing 28 genera and 17 families. The Haragan ostracode fauna consists of 54 species, 28 genera and 17 families.

Biostratigraphic evidence for the unconformity between the two units is as follows: (1) at the specific level the two faunas are completely distinct, no species are common to both units; (2) the two faunas are fifty per cent distinct at the generic level, each fauna contains 28 genera and 14 genera in each fauna are restricted to one unit or the other; (3) the two faunas are nowhere known to occur together or interfinger with one another; and (4) the faunal change is abrupt. There is no evidence for an intermediate or gradational fauna between the two distinct faunas recognized.

The stratigraphic distribution of ostracodes in the Henryhouse and Haragan Formations indicates no distinct biostratigraphic zonation within either unit. Each species of significant abundance ranges throughout, or almost throughout, the formation in which it occurs.

The ostracode faunas obtained from all the outcrop areas of the Hunton Group are distinctive and readily identifiable and may be useful in distinguishing Henryhouse from Haragan strata in the subsurface as well as at the surface.