Publication Date

2016-05-09

Document Type

Honors Thesis

Department

Geosciences

Keywords

Paleoecology-California, Paleoecology-Cambrian, Fossils-California, Paleontology, Paleontology-Cambrian, Paleontology-California, Chemostratigraphy, Chemostratigraphy-Cambrian

Abstract

Archaeocyathans, the first calcifying metazoan reef-builders, thrived in tropical/subtropical oceans across the globe during the early Cambrian. To investigate the role of archaeocyathans in early Paleozoic carbonate production, we analyzed previously undescribed archaeocyathan patch reefs in the lower Cambrian (Series 2) Wood Canyon Formation in the western United States. Thirty-eight samples were taken from 4 laterally correlative patch reefs found in Titanothere Canyon, Death Valley National Park. From these samples, 32 thin sections were point counted to quantify the skeletal components of the reefs and the surrounding facies. Additionally, our group collected samples through stratigraphy to generate a carbon isotope curve from this carbonate-rich part of the Wood Canyon. On average, skeletal material is found to account for 12% of the points counted from samples taken from the reefs; of the 12%, archaeocyathans account for 52%, while echinoderm and trilobite fossils make up 29%. In the grainstone-wackestone beds flanking and immediately below the reefs, skeletal material accounts for an average of 17%, with archaeocyathans producing ~ 35% of the skeletal carbonate and echinoderm fossils producing 61%.Biostratigraphy and carbon isotopes provide constraints on the age of this part of the Wood Canyon Formation. The biostratigraphy places the upper Wood Canyon in the Fallotaspis/Nevadella zones, making this part of the section correlative with the Campito Formation of the White-Inyo successions. Carbon isotope values shift from -3‰ -0.6‰ in the basal ~15 m of this exposed section and then plateau at about -1.3‰ up to 55 m. Values show a small excursion to -3.8‰ at 75 m and then shift back to a plateau around - 2.3‰ for the remainder of the section. These values, in concert with the biostratigraphy, places the archaeocyathan reefs in Stage 3 (Atdabanian) of the Cambrian. The study provides both a link between Cambrian sections of the Death Valley region to the White-Inyo successions and otherwise supports previous findings that archaeocyathan reefs were ecologically complex systems, contributing to the skeletal production of marine carbonate by providing a habitat for a diverse community of calcifying animals.

Language

English

Comments

v, 41 pages : color illustrations, map. Honors project, Smith College, 2016. Includes bibliographical references (pages 35-37)

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