The following photographs show examples of both assemblages.
In the middle of this photograph, there is a life assemblage of boring clams of late Pleistocene age (slightly older than 47,000 years ago) in southern California. The man's finger is pointing to a clam consisting of both valves and in its original life position. The clams lived in a rocky shoreline environment and bored into a deep-marine siltstone of Miocene age (about 6 to 7 million years old). The layer of shells directly above the boring clams represents a storm deposit that buried the boring clams. It is a death assemblage consisting of shells transported and deposited at this site about 47,000 years ago. Its clam shells are all single valves that were deposited after death in a horizontal position.
This photograph shows a life assemblage consisting mainly of the large oyster Crassostrea titan. They consist of both valves that are closed together in their original living position; in this case, vertical. The oysters formed a bed, one-oyster thick that lived in very shallow-marine waters in central California during the late Miocene.
The turritellid shells shown in above photograph were transported and deposited at this site by wave action; note that they show preferred orientation. The species is the middle Eocene Turritella andersoni lawsoni, which was discussed in one of my earlier posts.
The above photograph shows a death assemblage of late Pliocene mollusk shells that were transported and deposited after death as a result of a storm deposit with local channeling into the layer beneath it. The larger shells are Turritella cooperi, which was discussed in one of my earlier posts.
The above photograph shows a death assemblage of late Pliocene mollusk shells that were transported and deposited after death as a result of a storm deposit. Turritella cooperi, which was discussed in one of my earlier posts, is readily identifiable, whereas most of the other shells are too broken up and constitute "fossil hash."
|Gari texta, an Eocene burrowing clam, 35 mm long.|