STRATIGRAPHIC AND STRUCTURAL CLASSIFICATION OF PREHISTORIC QUARRIES WITHIN THE GREAT VALLEY PROVINCE OF THE APPALACHIAN FOLD-THRUST BELT, NEW YORK RECESS
The normal faulted section hosts quarries within the Neoproterozoic through Lower Cambrian succession; namely the Hardyston and Leithsville formations. The rocks are down faulted and preserved in graben-like depressions, with dip orientations ranging from 10⁰ to 30⁰ west. Such field relationships are ideally suited to the development of prehistoric quarries.
The thrust-ramp section supports quarries cropping out within the Limeport and Allentown formations of Middle Cambrian age. Attitude measurements are steeper in the thrust-ramp section, ranging from 30⁰ west to almost vertical at some locations. The differences in dip orientation between the normal faulted and thrust-ramp sections impacts the style of quarrying, the instruments required to extract chert, and the resulting chain of operation of production events.
Rocks are folded into tight, plunging antiforms and synforms in the duplex section. Additionally, the section is repeated by synthetic and antithetic faults. Dip orientations are steep and change from west to east through the vertical. Quarries developed within the highly deformed Upper Cambrian through Lower Ordovician Stonehenge, Rickenbach and Epler formations are smaller, and more complex, than those in the less strained Hardyston through Allentown formations. Exceptionally large quarries are found in the Lower to Middle Ordovician Ontelaunee Formation due to the unit’s greater stratigraphic thickness; thus providing more extensive exposures of chert.