Paper No. 225-5
Presentation Time: 9:00 AM-6:30 PM
NEW ARCHAEOCYATHAN REEFS AND CHEMOSTRATIGRAPHY OF THE LOWER CAMBRIAN WOOD CANYON FORMATION, DEATH VALLEY, USA
Archaeocyathans are the first calcifying metazoan reef-builders. They 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 of Death Valley, CA. The presence of archaeocyathan reefs in the Wood Canyon here also provides an opportunity to better link this part of the section with correlative strata of the White-Inyo Mountains in northwest California. Thirty-eight samples were taken from 4 laterally correlative patch reefs found in Titanothere Canyon, Death Valley National Park. From these samples, 33 thin sections were point counted to quantify the skeletal components of the reefs and surrounding facies. Additionally, samples were collected to generate a carbon isotope curve from this carbonate-rich part of the Wood Canyon. On average, skeletal material only accounts for 10% of samples taken from the reefs with the remainder consisting mostly of micrite and cement. Of the 10%, archaeocyathans account for 51%, 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 14%, (archaeocyathans are ~ 21%, echinoderm fossils are 73%).
Coupled biostratigraphy and chemostratigraphy constrain this interval of the Wood Canyon Formation to the Fallotaspis/Nevadella zones, which correlates to the Campito Formation of the White-Inyo successions. δ13C values shift from -3‰ to -0.6‰ in the basal ~15 m of this exposed section and then plateau at about -1.3‰ up to 55 m. Values show an excursion with a nadir of -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, place the archaeocythan reefs in Cambrian Stage 3 (Atdabanian of Siberia). The study helps to correlate Cambrian sections in Death Valley to the White-Inyo successions, and the point count results confirm that archaeocyathan reefs directly contributed to the skeletal production of marine carbonate and provided a habitat for a diverse community of calcifying animals.