The Swift Run Formation was at least an extra mile hike from the Garth Run Formation and is noted in the map below. This outcrop was a sedimentary conglomerate with graded bedding and Catoctin inclusions. The Catoctin formation contains subareal, flood basalt's that are now greenschist. One of the begging questions on this stop was whether or not the beds are upright or have been overturned. This can be determined by taking the angles of the bedding and the cleavage or foliation. It was determined that the Swift Run outcrop was, in fact, upright, because the angle of the cleavage was steeper than that of the bedding.
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| Image of Swift Run Formation - green arrow - and the Garth Run Formation - Red pin. Image from Google Earth |
Swift Run sits on top of the Grenville basement province but below the Catoctin formation. The primary structures that were noted in this outcrop were graded, hummocky, and cross bedding as well as rip up casts of mud. Foliation was noted as a secondary structure. The predominant rock type was an arkosic sandstone and metamorphosed mudstone. Swift Run is not found in many locations, which suggests that it filled lower valleys at a time of higher relief that was later over-topped by the eruption of basalt's that became the Catoctin.
The breaking up of Rodinia, roughly 600 million years ago, was the driving force for the erupted basalt layers that are now known as the Catoctin. The rifting event caused an area of lower topography or a valley that can be observed in present day Africa. In a very interesting structure lecture not long ago we learned that because of the amount of time it takes for these valley's to fill with sediment they are a sink for fossils - even human remains.
The measurements taken at Swift Run included primary and secondary structures noted above.
Pictures here of primary and secondary structures
