CLIMATIC IMPLICATIONS OF SILTSTONE IN THE PERMIAN RED BEDS OF KAY COUNTY, OKLAHOMA

Extensive deposits of Permian red siltstone extend through Kansas, Oklahoma, and North Texas, although their provenance, transport mechanism, and climatic implications remain largely unknown. The Leonardian-aged Wellington Formation of Kay County, Oklahoma consists of cyclic silt-dominated red beds intercalated with evaporites marking an abrupt change in depositional style from the underlying limestone-shale cyclothems that compose most of the Wolfcampian Chase Group. This study attempts to determine the nature of the cyclic deposition of the Wellington Formation and specifically test whether much of the clastic sediment is eolian in origin with subsequent overprinting, in part, by marine and pedogenic processes.

This study focuses on two cores located in Kay County, Oklahoma: a 300-feet core from the Wellington Formation and a core from the underlying Chase Group. The Wellington core consists almost entirely of laminated to massive mud to silt-sized sediment, suggesting deposition by suspension settling in a low-energy environment. The Wellington core exhibits a series of upwardly shallowing facies successions, consisting of (1) a basal dark gray dolomitic mudstone intercalated with laminated fine-grained dolomite, (2) a variegated mudstone with mudcracks, (3) a pale red siltstone with root traces exhibiting mottled or convolute bedding, and (4) a massive dark red siltstone with ped-like structures, slickensides, and anhydrite laminations. This facies assemblage contrasts markedly with the underlying Chase Group, which consists of limestone-shale cyclothems. The limestone facies mark periods of highstand and consist of upwardly shallowing successions and the clastic facies mark periods of lowstand, consisting of reddish-brown and greenish-gray mudstone with local paleosols and thin lenticular sandstone deposits.

In addition to reflecting glacioeustasy, the upwardly shallowing cycles of the Wellington Formation also reveal evidence of a longer-term change in aridity, which we suspect is consistent with an eolian transport mechanism for these Leonardian red beds. Additional methods in progress to test for an eolian signal include whole rock geochemistry and textural and grain size characterization.