Where: Contra Costa County, California (37.9° N, 122.0° W: paleocoordinates 40.4° N, 105.2° W)

• coordinate stated in text

When: Selandian to Selandian (61.6 - 41.3 Ma)

• Dickerson believed the bed as part of the Martinez formation (Paleocene), while Schenck believed it as part of the Chico formation (upper Cretaceous). This location is directly adjacent to a fault, with the western side mapped as lower Domengine Formation and the eastern side mapped as Great Valley Sequence by Graymer et al. (1994). Schenck argued for a Cretaceous age because he found a similar limestone with inoceramids within "a few hundred feet" and because the limestone was similar to one near Martinez. However, given the nearby fault, and the nearby presence of Cretaceous rocks (Dickerson (1914) also mentioned Inoceramus from this locality), a Cretaceous age may not be likely. Dickerson (1914) described an angular unconformity between the "Tejon" and the underlying limestone beds, but also distinguished the limestone (assigned to the "Martinez") from the Cretaceous and named several bivalves from UCMP 340 (said to be the same as UCMP 150). According to Zinsmeister (1983), "Weaver (unpublished manuscript, housed in the archives of the Department of Earth Sciences, University of California, Riverside) pointed out that Aturia dickersoni Schenck, which Miller thought came from the Martinez deposits in Pine Canyon west of Mount Diablo, was collected as float and was derived from the middle Eocene." No other Aturia are known from the Cretaceous, so this locality is probably early Cenozoic, even if no Cenozoic limestones are mapped by Graymer et al. (1994) (this may be the Ku? unit). Former "Martinez" Formation is often upper Paleocene (Thanetian) but could also be mid-Paleocene (Selandian), but if it is float from the Domengine Formation, it could be as young as middle Eocene.

• bed-level stratigraphic resolution

Environment/lithology: lithified, shelly/skeletal, gray limestone

Size class: macrofossils

Collected by Dickerson; reposited in the UCMP

Primary reference: H. G. Schenck. 1931. Cephalopods of the genus Aturia from western North America. University of California Publications, Bulletin of the Department of Geological Sciences 19:435-490 [M. Clapham/K. Okamoto/M. Clapham]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 166330: authorized by Matthew Clapham, entered by Kristina Okamoto on 09.02.2015

Creative Commons license: CC BY (attribution)