PALEOECOLOGICAL RECONSTRUCTION USING POINT COUNTS AND ANALYSIS OF SILICIFIED FAUNAS FROM LOWER TRIASSIC CARBONATES, MUDDY MOUNTAINS, SOUTHERN NEVADA

Lower Triassic carbonates have been the subject of many paleoecological studies, often to assess the pattern and timing of faunal recovery from the end-Permian mass extinction. Various paleoecological methods have been utilized, such as point counting of carbonates, bulk sample analysis, and quantification of silicified faunas; however, rarely have these methods been used in complementary analyses. Here, we report new data from Virgin Limestone carbonates exposed in the Muddy Mountains of southern Nevada. Point counts of thin sections were performed on 11 carbonate samples that also preserved silicified fossils. We dissolved these samples and collected their insoluble residues to quantify and determine the dominant silicified fossils in each sample. In seven samples, the dominant fossil components did not match the most abundant fossils in residue. In some cases, bivalves were dominant in thin section but essentially absent from residue; in others, fossils such as crinoids and gastropods were abundant in residue but rare or absent in thin section. Additional petrographic examination confirmed that crinoids and gastropods are occasionally preferentially silicified whereas bivalves are often partially silicified or not silicified at all. These data suggest that examining silicified faunas in the context of their carbonate host rocks reveals biases that may affect paleoecological reconstructions based solely on one method or the other.