STRATIGRAPHIC, SEDIMENTOLOGIC, AND MINERALOGIC CHARACTERIZATION OF THE GOODENOUGH FORMATION (MIOCENE?), GRAND MESA, CO
The sedimentologic and stratigraphic characteristics of the Goodenough formation are poorly understood because it has been disrupted by glaciation and large-scale mass wasting. It ranges in thickness from 15 to 274 m and thins from southeast to northwest. In central and eastern Grand Mesa, it can be subdivided into two intervals. The lower interval, which is dominated by variegated, mottled, bentonitic siltstone and claystone and cherty limestone (wackestone-packstone), was deposited in lacustrine and flood-plain settings. The upper interval consists of fine to very coarse grained, poorly sorted, lithic to arkosic sandstone, granule-pebble-cobble, polylithic conglomerate, and variegated mudrock, and was deposited by fluvial processes. Conglomerate clasts are mainly diorite and andesite, but also include granite, meta-granite, gneiss, schist, quartzite, and marble. Sandstone framework grains are dominated by diorite, andesite, quartz, plagioclase, and K-feldspar. These observations suggest that the source areas for the fluvial facies were mid-Tertiary intrusives in the West Elk and Elk Mountains, plus arkosic strata of the Pennsylvanian-Permian Minturn and Maroon Formations from the western flanks of the Sawatch and Gore Ranges.