Mark Wilson November 13th, 2009
BROWNWOOD, TEXAS–It was nearly a five hour drive from College Station, Texas, through the Hill Country to our first Permian exposure in West Texas. (We passed, by the way, through Killeen and Fort Hood.) It was worth the trip for all the strange features we found on this outcrop of the Valera Formation.
We spent several hours measuring, describing and sampling this outcrop in ideal weather. We found plenty of examples of what we came here for: fossil microconchids, otherwise known as “worm tubes”.
We were surprised to also find abundant sea urchin (echinoid) spines in one of the limestone units here. These usually indicate normal marine salinity, but they are unaccompanied by other indicators such as brachiopods and bryozoans. A thick gypsum below our exposed rocks shows that we are likely dealing with elevated seawater salinity during the Permian in this area. A mystery. (And we love mysteries in this business.)
Tomorrow we visit a similar outcrop with microconchids. Now we have some hypotheses to test. Fieldwork is such a joy!