Pulses of Middle Eocene to Earliest Oligocene Climatic Deterioration in Southern California and the Gulf Coast

Palaios ◽  
1991 ◽  
Vol 6 (6) ◽  
pp. 564 ◽  
Author(s):  
Norman O. Frederiksen
Keyword(s):  
Southern California ◽  
Gulf Coast ◽  
Middle Eocene

Review of the bivalve genus Plicatula from Cretaceous and lower Cenozoic strata of California and Baja California

1997 ◽  
Vol 71 (2) ◽  
pp. 287-298 ◽  
Author(s):  
Richard L. Squires ◽  
Louella R. Saul
Keyword(s):  
New Species ◽  
Los Angeles ◽  
Lower Cretaceous ◽  
Southern California ◽  
Upper Cretaceous ◽  
Baja California ◽  
Middle Eocene ◽  
Baja California Sur ◽  
Northern California ◽  
Three New Species

The Cretaceous and early Cenozoic species of the shallow-marine, warm-water bivalve Plicatula from California (United States) and Baja California (Mexico) are reviewed, and three new species are named. All of these species are representatives of Plicatula and not of the closely related taxon Harpax, which is associated with high-latitude and cool-water regions. The earliestknown Cretaceous species of Plicatula from the study area is P. variata Gabb, 1864, from Lower Cretaceous (Hauterivian Stage) strata in northern California, and our studies show it to be conspecific with Plicatula onoensis Anderson, 1958.Plicatula allisoni new species is from Lower Cretaceous (Albian Stage) strata in Baja California, Mexico. Plicatula modjeskaensis new species is from Upper Cretaceous (Turonian Stage) strata in the Santa Ana Mountains, southern California. A possible new species from the same strata is also mentioned. A poorly preserved specimen of Plicatula? sp. is known from Upper Cretaceous (upper Campanian to lower Maastrichtian) strata in northern California.The only Paleocene species of Plicatula from the study area is P. ostreiformis Stanton, 1896, from lower Paleocene strata of Lake County, northern California, and our studies show it to be conspecific with Ostrea buwaldana Dickerson, 1914. The only previously described Eocene species of Plicatula from the study area is P. juncalensis Squires, 1987, from lower middle Eocene (“Capay Stage”) strata of Los Angeles County, southern California. Plicatula surensis new species is from middle lower Eocene (“Capay Stage”) strata in Baja California Sur, Mexico. In addition, there is a Plicatula? sp. from Eocene strata of Baja California Sur, Mexico.Although Plicatula is of uncommon occurrence north of Baja California, its thermophilic trait makes it useful in recognizing periods of warm climate.

scholarly journals Differing histories of Eocene angiosperm diversity in eastern North America and western Europe: dependence on paleogeography

1992 ◽  
Vol 6 ◽  
pp. 105-105
Author(s):  
Norman O. Frederiksen
Keyword(s):  
North America ◽  
Western Europe ◽  
Environmental Heterogeneity ◽  
Gulf Coast ◽  
Middle Eocene ◽  
Late Eocene ◽  
Middle Part ◽  
Eastern North America ◽  
Climatic Fluctuations ◽  
Angiosperm Pollen

Studies of Eocene angiosperm pollen floras in eastern North America (my work, especially in the eastern Gulf Coast) and western Europe (Boulter, Krutzsch) have shown significant differences in floral diversities between the two regions: in western Europe, maximum diversity was in the early Eocene and it decreased thereafter, in eastern North America, maximum diversity was in the middle part of the middle Eocene. The hypothesis presented here is that paleogeography was an important control on the diversity histories in the two regions: eastern North America was part of a large terrestrial landmass, whereas the terrestrial depositional basins of western Europe were on islands or peninsulas surrounded by the sea. Migrations between eastern and western North America were relatively easy, but migrations within what is now western Europe involved island-hopping, which explains distinct diachroneity of some angiosperm first appearances among different basins there. Western European basins were in contact with a large land mass during late Paleocene time but became isolated and smaller during the middle to late Eocene marine transgression. These changes resulted in decreased genetic exchange and increased probabilities of extinction due to (1) greater competition among species because of a reduced number of niches and (2) presence of small, isolated species populations, leading to local variations in extinctions, which probably explain the observed diachronism of taxon last appearances in different areas of Europe. Terrestrial climatic cooling in western Europe may be linked to decreasing contact between the NW European Tertiary Basin and the warm Tethys Seaway during the middle and late Eocene. In short, some combination of low environmental heterogeneity, geographic isolation, and long-term climatic deterioration probably caused the decrease in angiosperm diversity during the middle and late Eocene in western Europe.Several factors encouraged increasing or stable diversity in eastern North America but were far less effective in western Europe: (1) Eastern North America underwent greater climatic fluctuations during the Eocene (thus, immigration of taxa with different climatic preferences took place at different times), whereas the islands and peninsulas of western Europe had more uniform, maritime climates. (2) Evolution and immigration of r-selected taxa in eastern North America were favored by distinct dry seasons at certain times during the Eocene and by repeated marine transgressions and regressions that created opportunities for evolution and immigration of r-selected plants on and to freshly exposed coastal plain. In contrast, the predominantly maritime climates of western Europe in the early and middle Eocene favored K-selected plants, which had fewer possibilities for evolution and which had greater difficulty in migrating because island-hopping taxa are mainly r-selected. (3) “Arcto-Tertiary” taxa adapted to cooler climates lived and evolved in the uplands of the Appalachian Mountains, whereas western Europe was relatively flat in the Eocene –another example of its relative lack of environmental heterogeneity.

Occurrence of the rare genus Anapteris (Bivalvia: Corbulidae) in the Eocene of California

1994 ◽  
Vol 68 (1) ◽  
pp. 168-171
Author(s):  
Charles R. Givens
Keyword(s):  
Type Species ◽  
Southern California ◽  
Middle Eocene ◽  
Left Valve ◽  
Posterior Area

Anapteris van winkle (1919) is a distinctive corbulid genus characterized by the left valve having a peculiar wing-like flare anteriorly and both valves having the posterior area set off by a prominent umbonal keel (Vokes, 1945; Keen, 1969). Heretofore this genus has been known only from the type species, A. regalis Van Winkle (1919; 1921), which has been recorded only from the upper middle Eocene (Bartonian) Piney Point Formation in Virginia (Ward, 1985). The purpose of this note is to record the second known occurrence of Anapteris. The genus is present in the lower middle Eocene of southern California, where it is represented by Corbula wardii Hanna (1927).

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