USING DENDROLITE MORPHOLOGY TO CORRELATE UPPER CAMBRIAN FORMATIONS IN THE DELAMAR AND SPRING MOUNTAINS, SOUTHERN NEVADA

The uppermost Bonanza King Formation and correlative Highland Peak Formation (Late Cambrian, Marjuman-Steptoean Boundary) of southern Nevada and eastern California contain abundant microbial structures called dendrolites. These dark microbialites have branching or semi-laminated columnar and/or clustered morphologies and are found in thrombolitic and stromatolitic boundstone throughout the study area. Beds vary from thinly laminated to massive and display flat lying bedding to hummocky cross stratification. Local oolitic beds are common throughout the section, and interbeds of silty dolomite and calcareous shale are also observed. Measured heights of individual dendrolite columns in the study area average 21.3 cm with widths averaging 10.2 cm. Major and minor axes average 12.8 cm and 8.5 cm, respectively. Clustered dendrolites may comprise biohermal reefs that are found to be approximately 5 meters in length and average 49 cm in height.

This study assesses the capability of using dendrolites to correlate Upper Cambrian middle ramp deposits in the Delamar Mountains, Nevada to Upper Cambrian craton-margin deposits in the Spring Mountains, Nevada. In the Delamar Mountains, the dendrolite acme zone is approximately 45 meters thick and is limited to the Highland Peak Formation. The dendrolite acme zone found in the Spring Mountains is approximately 20 meters thick and ranges from the Bonanza King Formation up into the Dunderberg Shale Member of the overlying Nopah Formation. Physical variability in dendrolites at the macro and micro-scale used in conjunction with analysis of sedimentary structures allows detailed correlation between the Delamar and Spring Mountains and demonstrates a diachronous progradation of facies within the acme zone.