At least 30 transgressive-regressive cycles of deposition are recognized from the upper Desmoinesian East Mountain Shale to the mid-Virgilian Wayland Shale in north-central Texas. Maximum regressive deposits are typically paleosol mudstones and fluvial sand- stones; maximum transgressive deposits are typically widespread, ammonoid-bearing, conodont-rich, dark phosphatic shales in more major cycles, and persistent fossiliferous shales or limestones overlying terrestrial deposits in more minor cycles. Delta complexes dominate the regressive sequences of many cycles.
Using biostratigraphic criteria of first, last, sole, or acme occurrence of ammonoid, conodont, and fusulinid taxa, we correlate 17 cycles in the Texas sequence directly with 17 glacial-eustatic cycles of similar magnitude in the northern midcontinent. This correlation suggests that glacial eustacy was the basic control over the cyclic sequence in Texas, that tectonic masking of the eustatic signal by nearby orogenic movement in Texas was negligible, and that delta shifting, though conspicuous, was only a secondary control over the cyclicity there. Minor cycles recognized between the correlated cycles also match well enough between Texas and the midcontinent to further discount potential tectonic or deltaic masking of glacial-eustatic cyclicity. This strengthens the likelihood of correlating glacial-eustatic events across larger parts of North America, and perhaps with other parts of the world.