The Correspondence between Radiolarian Faunal Variation and Geochemical Variation in the Lamar Limestone, Delaware Basin, West Texas: Implication to Radiolarian Paleoecology and Basin Evolution

Yuxi Jin,

Department of Geological Sciences and Engineering,

University of Nevada, Reno, Reno, Nevada, USA,

[email protected]

Although Permian radiolarian studies have made great progress on systematics and biostratigraphy, the knowledge of paleoecology of Permian radiolarians is still very insufficient. The Lamar Limestone of the Bell Canyon Formation, West Texas, is a marine carbonate unit representing the fine-grained basin-margin facies of the Permian Basin during the Late Guadalupian epoch. An abrupt faunal change from Follicucullus-dominated to spumellarian-dominated radiolarian fauna was observed in a preliminary examination of a 1.6 meter interval of the Lamar Limestone, yet no follow-up work has been done to determine the cause of this variation, nor if additional faunal fluctuations throughout the entire exposure of Lamar. The goal of this project is to test whether fluctuations in radiolarian faunas of the Lamar Limestone correspond to geochemical fluctuations, and to reveal the control mechanism implicated by the correspondence.

In total, 154 samples have been collected from two roadcuts of Highway 62/180. The variation in abundance of radiolarians in the lowest 3 meters of strata has been determined and work on the remaining 7 meters is in progress. The subsequent investigation will: (1) document vertical variation of radiolarian faunas from the two roadcuts, (2) analyze geochemical proxies for changes in paleosalinity, paleoproductivity, and terrigenous influx (elemental geochemistry, δ¹³C, δ¹⁸O, and TOC) across all observed faunal shifts, and (3) test the correlation of fossil and geochemical data by statistic methods. This study is expected to improve the understanding of Permian radiolarian paleoecology and new information in Permian Basin evolution, particularly with respect to changes in paleosalinity.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid