Alcatraz Island, recreation ground (Cretaceous of the United States)

Where: San Francisco County, California (37.8° N, 122.4° W: paleocoordinates 37.8° N, 82.6° W)

• coordinate estimated from map

• outcrop-level geographic resolution

When: Cenomanian (100.5 - 93.9 Ma)

• Valanginian age initially based on Buchia pacifica. According to Elder & Miller, 1993: Unfortunately, these specimens appear to have been lost, and recent investigation of their locality yielded no fossils (C. Wahrhaftig, oral commun., 1992). This locality is less than two hundred feet stratigraphically below the new inoceramid locality in an apparently continuous graywacke sequence (C. Wahrhaftig, oral commun., 1992). It seems unlikely that a Valanginian to Cenomanian age span would be condensed within such a stratigraphically short graywacke interval. This leads us to speculate that the crushed specimens illustrated by Armstrong and Gallagher (1977) might actually be the middle Cenomanian inoceramid, Inoceramus gradilis Pergament, which looks very similar to Buchia pacifica.

• bed-level stratigraphic resolution

Environment/lithology: submarine fan; lithified sandstone

Size class: macrofossils

Preservation: mold/impression

Collected in 1976

• Repository: not stated

Primary reference: C. F. Armstrong and K. Gallagher. 1977. Fossils from the Franciscan assemblage, Alcatraz Island. California Geology 30(6):134-135 [M. Clapham/M. Clapham]more details

Purpose of describing collection: general faunal/floral analysis

PaleoDB collection 185239: authorized by Matthew Clapham, entered by Matthew Clapham on 17.04.2017

Creative Commons license: CC BY (attribution)

Taxonomic list

Bivalvia
 Myalinida - Inoceramidae
 Pholadida - Pleuromyidae
Pleuromya sp. Agassiz 1845 clam