47 Salvage Geology I

Friday, 26 March 2004
1:00 PM - 5:00 PM

THE ANNVILLE REEF: AN EXAMPLE OF PRIVATE-PUBLIC COOPERATION FOR SCIENCE AND EDUCATION

Paper number: 47-9
Program: THEME SESSIONS
Time: 3:40 PM – 4:00 PM

Authors

Abstract

An expansion of the Pennsy Supply Company's dolostone and limestone quarry at Hummelstown, Pennsylvania, exposed a tract of the Ordovician Annville Formation developed in a hitherto unknown microbial reef facies. This reef facies has not been recognized elsewhere in the Annville. In fact, except for one mention of a possible bryozoan, and a published date based on recovered conodonts, no fossils have been documented previously from this formation, which has a strike length of more than 100 km and ranges to approximately 75 m in thickness. The reef facies in the Annville contains abundant shells and opercula of the gastropod Maclurites (strongly suggestive of a Middle Ordovician age), as well as pelmatozoan fragments and bryozoa. The low-relief reef structures consist primarily of microbial (thrombolitic?) boundstone. Conodonts occur in both the boundstones and the inter-reef wackestones/packstones; they also indicate a Middle Ordovician age (late Whiterockian; Chazyan; Phragmodus flexuosus Zone). The limestones of this reef tract are exposed in high-relief (1-3 m) karst pinnacles with pitted and rilled surfaces due to dissolution by groundwater in the thin covering soil.

Because this is the only known record of macrofossils, and of this facies, in the Annville, and because the entire exposure is scheduled to be quarried away, the operating company agreed to preserve some of the reef pinnacles for scientific posterity. Quarry operators blasted several selected large pieces loose, ranging from about 1/2 to 4 tons each, and donated and transported them to the campus of the U.S. Geological Survey in Reston, VA. They are now on permanent exhibit as part of the outdoor "rock walk" display there, where thousands of students and other visitors annually will be able to see, touch, and study them. Rather than becoming solely the subject of a scientific paper or two, part of the Annville reef, demonstrating its lithologies and fossils, is now permanently available for [non-destructive] examination, and should remain so even long after the in situ exposure is gone.