Sunday, September 9, 2012

Quimper and Pysht Fossils

I encountered a few fossils this week while in the field. The first were some marine fossils in the Pysht Formation on the north side of the Olympic Peninsula. Nothing dramatic perhaps, but careful study of small fossils allows for correlation or non correlation between geologic units that otherwise look very much the same and are a valuable tool in figuring out the age of a formation. Lots of detailed work goes into discerning the differences between small fossils that are difficult to the untrained or out practice.

23 to 30 million year old clam

The Pysht Formation is a marine unit on the north side of the Olympic Peninsula. The exact age is not well refined. Nesbitt, E.A.Martin, R.A.Carroll, N.P., and Grieff, J. (2010) have been working these fossils and others on the north Olympic Peninsula coast as well as magnetic signature and have placed the Pysht Formation on the order of 22 to 33 million year. As some key whale fossils have been found in the Pysht, the age of the formation is a big deal for whale evolution. 

Besides fossils, the Pysht Formation presents routine problems for the Washington State Department of Transportation. Large landslides and earth movement have broken across bedding plains within the siltstone and mudstone of the formation. These slides pose ongoing problems on State Highway 112 between Clallam Bay and Neah Bay. This formation is partly responsible for the slow twisty road when heading to the extreme northwest corner of the state. There are a number of landslides that will humble geologist that assess landslides. The fresh slide scarps cutting through the formation provide a chance to examine the ancient marine life that existed off the coast of North America prior to this chunk of sea floor being accreted to the continental margin.

The next day I came across a few more fossils in the similar aged Quimper Sandstone on the west shore of the Quimper Peninsula on the east side of Discovery Bay. The Quimper Peninsula is the peninsula on which Port Townsend is located. Most of the peninsula is glacial and other non bedrock units, but towards the south portion a variety of rocks are exposed not only along the shore but on the highland areas as well suggesting a structure of some sort. The Quimper Sandstone is much harder than the Pysht Formation, and is not so prone to large landslides. In this case good news for slope stability compared to the Pysht Formation.

Mollusk in Quimper Sandstone

The Quimper Sandstone also contains ample large concretions much like the concretions on the east shore of Marrowstone Island marrowstone-island-geology-trip.

Concretion in Quimper Sandstone

No comments: