UCMP 7004, Simi Valley (Eocene of the United States)

Where: Ventura County, California (34.3° N, 118.7° W)

• Paleocoordinates: 39.6° N, 96.9° W (Wright 2013)

• coordinate estimated from map

• outcrop-level geographic resolution

When: Llajas Formation, Lutetian (48.1 - 41.0 Ma)

• From the "Domengine" horizon of the Eocene of Simi Valley.

• group of beds-level stratigraphic resolution

Environment/lithology: transition zone or lower shoreface; lithified, fine-grained, brown, yellow sandstone

• The "Stewart bed" is located in a section of transition from shallow-marine to outer slope and shelf facies. A nearshore environment is interpreted for that portion of the shallow-marine (transgressive) facies which consists of laminated beds alternating with bioturbated beds. In such cases, the finely laminated sand represents storm-influenced stratification, and the biogenic reworking is the inter-storm activity. Shell fragments commonly are concentrated as channel lags in surge channels. Fossils were apparently subjected to wave action because the apices of elongate shells such as Turritella are bimodally oriented in opposite directions. The deeper the water, the less amount of laminated sandstone and the more amount of bioturbated sandstone. Such areas, which were farther below effective wave base, existed 1) where the shallow-marine (transgressive) facies grades into the outer shelf to slope facies and 2) in the shallow-marine (regressive) facies. One of the deepest-water shallow-marine beds was the "Stewart bed."

Size class: macrofossils

Collected by R. B. Stewart; reposited in the UCMP

Primary reference: B. L. Clark. 1934. A New Genus and Two New Species of Lamellibranchiata from the Middle Eocene of California. Journal of Paleontology 8(3):270-272 [J. Marcot/J. Marcot]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 166460: authorized by Matthew Clapham, entered by Kristina Okamoto on 14.02.2015, edited by Jonathan Marcot and Patricia Holroyd

Creative Commons license: CC0 (CC0)

Taxonomic list

Bivalvia
 Carditida - Crassatellidae
"Crassatellites indentata" = Crassatella
"Crassatellites indentata" = Crassatella clam
 Carditida - Carditidae
Venericardia (Pacificor) calafia n. sp.5 Stewart 1930 clam
 Ostreida - Ostreidae
"Ostrea idriaensis" = Acutostrea idriaensis
"Ostrea idriaensis" = Acutostrea idriaensis Gabb 1869 oyster
 Ostreida - Malleidae
"Exputens llajasensis n. sp." = Nayadina (Exputens) llajasensis3
"Exputens llajasensis n. sp." = Nayadina (Exputens) llajasensis3 Clark 1934 oyster
Gastropoda
 Architaenioglossa - Ampullinidae
"Amaurellina clarki" = Pachycrommium clarki, "Globularia hannibali" = Eocernina hannibali
"Amaurellina clarki" = Pachycrommium clarki Stewart 1927 snail
"Globularia hannibali" = Eocernina hannibali Dickerson 1914 snail
 Cerithioidea - Turritellidae
Turritella uvasana etheringtoni1 Merriam 1941 turret shell
Turritella andersoni lawsoni1 Dickerson 1916 turret shell
 Sorbeoconcha - Cassidae
"Galeodea (Caliagaleodea) californica n. sp." = Galeodea californica4
"Galeodea (Caliagaleodea) californica n. sp." = Galeodea californica4 Clark 1942 snail
 Neogastropoda - Volutidae
"Volutocorbis lajollaensis" = Lyrischapa lajollaensis
"Volutocorbis lajollaensis" = Lyrischapa lajollaensis Hanna 1927 volute
 Neogastropoda - Turridae
Surculites mathewsonii Gabb 1864 turrid
Cephalopoda
 Nautilida - Aturiidae
Aturia myrlae2 Hanna 1927