Pacific West Coast Cretaceous molluscan faunas: time and aspect of changes
Cretaceous deposits of the West Coast of North America, from central Baja California to southern Alaska, yield molluscan faunas that commonly contain some forms of tropical aspect, some suggestive of cool water, and some which are typically or uniquely found in North Pacific deposits. The Aptian-Albian faunas of the Alisitos Formation of northern Baja California are entirely tropical in aspect, but may have been moved northward relative to the North American plate, as may have the older deposits of the Vizcaino Peninsula that contain buchias of boreal or North Pacific affinities. The faunas with the coolest aspect are those of the Early Cretaceous late Valanginian Stage, which contain buchias of the boreal Canadian lineage, and/or the Late Cretaceous Senonian to early Maestrichtian faunas that are dominated by North Pacific taxa. Nonetheless, both these Early and Late Cretaceous faunas include warm-water elements. In the northern occurrences of these faunas, the warm-water taxa are farther north than are comparable living taxa. Shifting faunas southward to compensate for their warmer water elements would displace the cooler water components (which during most stages comprised more than half of the faunas) too far into tropical areas. Cretaceous island arcs may have afforded protection from southerly flowing cooler currents and allowed various warm-water forms to live unexpectedly farther north. The strong North Pacific element in these faunas makes it unlikely that they originated elsewhere, or that the relatively cool or warm fluctuations they record are a result of successive exotic origins. The cooling at the end of the Valanginian was followed by a warming trend.
- Research Organization:
- Los Angeles County Museum of Natural History, CA
- OSTI ID:
- 6931219
- Report Number(s):
- CONF-8604187-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 70:4; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
Similar Records
Tectonic controls on sedimentation in Mesozoic convergent margin basin of Baja California (Mexico)
Paleogeography of Late Cretaceous clastic shelf deposits, northeastern Sacramento Valley, California
Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
ALASKA
ALLUVIAL DEPOSITS
ANIMALS
AQUATIC ORGANISMS
CALIFORNIA
CRETACEOUS PERIOD
FEDERAL REGION IX
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC DEPOSITS
INVERTEBRATES
MESOZOIC ERA
MOLLUSCS
NORTH AMERICA
OREGON
PALEONTOLOGY
USA
WASHINGTON