GEOLOGIC MAPPING OF THE SOUTHERN MARBLE MOUNTAINS (CENTRAL MOJAVE DESERT) USING FIELDMOVE FOR DIGITAL DATA COLLECTION AND RECORDING

The southern Marble Mountains in the central Mojave Desert, southern CA, USA, is a classic field locality known for its excellent rock exposure and early Cambrian fossil preservation. This small (~8 km²) area on the western edge of the Cadiz Summit USGS 7.5’ quadrangle has long been utilized by local universities and colleges as a natural laboratory for teaching geologic field methods, stratigraphy, and paleobiology courses. Since Fall 2016, Cal Poly Pomona’s GSC 2550L Field Methods Laboratory has utilized the southern Marble Mountains to teach geologic mapping using traditional field techniques (i.e., paper topographic basemaps, pencils, Brunton transits). In conjunction with analog mapping, digital geologic mapping of the field site and the collection of structural data (bedding orientations) was conducted using FieldMove software (Petroleum Experts) on an Apple iPad Mini 4 tablet. The digital mapping effort presented here allowed for direct comparisons between using analog & digital field mapping methods, specifically the relative ease-of-use, collection and recording of structural data, and post-fieldwork data processing. Over 150 georeferenced structural measurements were collected using FieldMove; in general, the digital measurements are consistent to those collected using a Brunton, with strike bearings ±10° and dip values nearly identical (±2°).

The stratigraphy of the study area consists of several distinctive, easily mappable rock units comprised of the early Cambrian cratonal sedimentary sequence deposited nonconformably on Proterozoic granitic basement. These include (from old to young): A) the Wood Canyon Fm., a fluvial “zebra-striped” crossbedded moderately sorted arkose & quartz pebble conglomerate; B) the Zabriskie Quartzite, a massive cliff-forming, well-sorted beach system quartz arenite; C) the Latham Shale, a poorly-exposed green-red mudstone famous for Olenellus trilobite fossils; D) the Chambless Limestone, a resistant light gray biomicrite with large (~2-3 cm) oncoid “eyes”; E) the Cadiz Fm., a shallow marine/tidal system composed of multicolored micaceous shale interbedded with two laterally extensive tan crossbedded oolitic limestone marker layers; and F) the Bonanza King Fm., a dark gray banded limestone. These units are all deformed by several late Cenozoic strike-slip faults and related transpressional structures.