The Pt. Reyes Conglomerate

Galloway's Pt. Reyes Conglomerate (Tpr) Description

"Conglomerate of subangular to subrounded granitic cobbles and boulders and well rounded pebbles and cobbles of resistant volcanic porphyries in a coarse sandstone matrix, with interbeds of fine-grained, laminated sandstone and mudstone."

These rocks can be seen in exposures on the peninsula's headlands (color orange on map). Particularly good exposures can be seen in the exposures around the visitor's center at the lighthouse.

They are quite convincingly correlated with the Paleocene turbidites found well exposed in the Pt. Lobos Marine Reserve south of Carmel, California (Carmelo Fornation) and may well have been directly adjacent to the Monterey peninsula during their formation some 50-60 million years ago.

On the north side of the headland (at the end of Pt. Reyes South Beach) the tilted layers contain indications of biological activity.

The observations that are presented next are shown in the photo below which looks back down the beach. 

Observation site #2

On the bedding surfaces of these rocks one can see a curved track that passes just below the quarter in the picture below.

A different type of track (again the quarter is for size comparison)

These are likely traces of animals that were formed in a deep portion of the ocean, but we are not sure of what kind of organism made them.  Since they do not show much evidence of burrowing into the sediments they were probably simply grazing over the surface of the sediment. Some paleontologists study the traces that organisms create in the sediments, a study called Ichnology.  Information on this topic can be found at this Emory University webpage.

As an aside to our geology discussions:

Observation Site #1

Other animals create similar features, what do you think might have created the pattern observed in the photo below?

At the end of the trail above:
Any ideas what might have made this?
See what might have made this.
See what likely created it.
Some pictures of these organisms
Pt. Reyes info on elephant seals
Info on Año Nuevo State Reserve's colony of northern elephant seals

Up section to another missing period of time