Paper Abstracts

K-feldspar in ancient cross-bedded sandstones

J.H. Whitmore, R. Strom

Discipline: Geology

Abstract: We studied the petrology of a number small ergs in the western United States, beach and dune sands along the California and Oregon coastlines and cross-bedded sandstones from the western United States and Great Britain. In our studies of these sandstones, many of which are purported in the conventional literature to be eolian, we frequently encountered angular K-feldspar sand grains. In our literature review and in our own observations along the California and Oregon coastlines, we found that fluvial and shoreline processes are not sufficient to cause rounding of sand grains of any type, even after energetic longshore transport or frequent tidal activity. Conversely, when sand grains are picked up by eolian processes and transported to coastal dunes they are quickly rounded, even over short distances. K-feldspar is rounded faster than quartz because it is softer and cleaves easier. We frequently encountered rounded K-feldspar grains in the small ergs we examined despite many of them being close in proximity to sources of angular K-feldspar sand grains. In larger ergs, all types of sand grains become quickly rounded (angular grains can occur if there are local fluvial or coastal sources for them). The frequency of angular K-feldspar grains that we found in cross-bedded sandstones purported to be eolian causes us to question whether these deposits are truly eolian. Angular K-feldspar may be a reliable petrographic criterion for identifying ancient fluvial and marine deposits. Coupled with other criteria, angular K-feldspar sand grains are a crucial piece of data creationists can use to argue that these sandstones are aqueous rather than eolian.