Wednesday, May 13, 2015

Quimper Sandstone Notes: Petrified Wood and Fossils at Oak Bay

No rest after being away so right back into the "field". One of my ventures took me to the west shore of Oak Bay. Oak Bay is south of Marrowstone and Indian Islands and was so named because of a stand of oak trees along the south shore of Indian Island where the Vancouver Expedition entered the bay. The oaks are still there in a county park along the south shore of Indian Island (Indian-island-Jefferson-County)

A fair bit of the west shore of Oak Bay is bedrock of the Quimper Sandstone and forms a bedrock platform beach with a covering of cobbles. 

Platform beach of bedrock

I came across a few fossils within the sandstone. The sandstone has been dated as Eocene based on forams studied by Arementrout and Berta (1977) which puts this unit in roughly the same time period as the Crescent Basalt.

Within the same outcrop that contained the snails and clams I noted a bit of wood sticking out of the rock. I have seen bits of carbonized wood and sticks in the Quimper before and in similar sandstones of similar age nearby on Marrowstone Island. But this stick was a bit of petrified wood.

Further along the shore I came across a small hole in the rock. A vertical vein of some sort of deeply weathered material has preferentially eroded creating a small hole in the rock. I suspect this might be a old clastic dike of silt that has weathered to clay but the weathering made it difficult to figure out the original rock type.

Armemtrout, J.M. and Berta, Annalisa, 19977, Eocene-Oligocene foraminfera sequence from northeast Olympic Peninsula, Washington: Journal of Foraminiferal Research, v. 7, no. 3, p 216-233.


Geoffrey Middaugh said...

Does carbonized wood mean it was burned before it was buried, or became carbonized after by pressure in the sediment?

Dan McShane said...

The wood carbonizes after burial. There are lots of coal (carbonized) wood in Eocene rocks of Western Washington, so the petrified wood that had mineral replacement of the wood was a bit of a surprise for me.