ABSTRACT

The Stonehenge Limestone (Lower Ordovician) and Conococheague Limestone (Upper Cambrian) crop out in Maryland's Great Valley west of Hagerstown. These peritidal carbonates contain numerous intraclastic beds. Twenty-eight samples from seven localities were analyzed in this study. Azimuth measurements of 1699 intraclast long axes show a preferred orientation with the vector mean for all measurements being 24 degrees (N24° E).

Based on previous studies of modern gravels and ancient conglomerates I interpret the orientation of the intraclast long axes as having been aligned transverse to flow. Deposition of the intraclasts were probably influenced by wave action and/or tidal currents which moved normal to the shoreline. The intraclast orientation pattern suggests that the strandline trended north-northeast (i.e., parallel to the grand vector mean).

Rocks exposed at the easternmost localities of the Stonehenge Limestone reflect currents which had little directional variation and were strong enough to produce uniform clast orientation. To the west, flow direction was not uniform and currents were weak. This may reflect deposition in environments farther from the open waters which lay to the east. Intraclast orientation patterns measured in the Conococheague Limestone from the easternmost localities also indicate nonuniform flow and/or weak currents.