San Diego Formation
| San Diego Formation Stratigraphic range: Pliocene epoch, Neogene period | |
|---|---|
| Type | Geologic formation |
| Location | |
| Region |
San Diego County, California Baja California |
| Country |
United States, Mexico |
| Type section | |
| Named for | San Diego, California |
The San Diego Formation is a geologic formation in southwestern San Diego County in southern California (U.S.), and northwestern Baja California state (México).
Geology
It is a coastal transitional marine and non-marine pebble and cobble conglomerate deposit and marine sandstone rock with marine fossils, from a former bay, deposited during the Middle Pliocene to Late Pliocene ages (2—3 million years ago), of the Pliocene period during the Cenozoic Era.
This formation is found from the south side of Mount Soledad in San Diego County to Rosarito Beach in northern Baja California, including Tijuana, Mexico, and the southwestern corner of San Diego County from San Ysidro to Pacific Beach.
San Diego Formation deposits were formed in a large, open, crescent-shaped bay similar in size to Monterey Bay that existed on the coast in Pliocene times.[1][2]
Aquifer
The formation contains the San Diego Formation Basin, a large aquifer under the City of San Diego. The use of groundwater contributes to a regional effort to reduce demands for imported water. [3]
Fossils
Besides those of clams and other mollusks, quite a few bird fossils (which are generally rare) have been found in this geological formation. Among them is a possible ancestor of Cassin's auklet (Ptychoramphus aleuticus) and the loons Gavia concinna and G. howardae. The former was quite likely a close relative or even ancestor of the large black-headed[4] loons; the latter was perhaps a small relative of the large grey-headed[5] loons.[6][7]
Fauna
Cetaceans
Mysticetes
| Mysticetes reported from the San Diego Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
|
B. davidsonii[8] |
An extinct rorqual belonging to Balaenoptera. |
|||
|
"Balaenoptera" |
"B." portisi |
Formerly assigned to Balaenoptera, represents a new, unnamed genus. |
||
|
H. morrowi |
A cetotheriid. |
|||
|
"Megaptera" |
"M." miocaena |
Previously considered to be a relative of humpback whale, represents a distinct genus. |
||
Odontocetes
| Odontocetes reported from the San Diego Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
|
P. sternbergi[9] |
A close relative of the baiji. | |||
|
S. ceruttii |
A porpoise with a lower jaw extended few inches beyond the upper jaw (similar to a halfbeak).[10] | |||
Pinnipeds
| Pinnipeds reported from the San Diego Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
|
C. gilmorei[11] |
A relative of the northern fur seal. |
|||
|
Dusignathus |
D. seftoni[12] |
A walrus. |
||
|
V. chulavistensis[12] |
A walrus. |
|||
Sirenians
| Sirenians reported from the San Diego Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
|
H. cuestae |
A close relative of the Steller's sea cow. |
|||
References
- ↑ California Geological Survey, Regional Geologic Map No. 3, 1:100,000 scale Compiled by: Michael P. Kennedy and Siang S. Tan, 2008.
- ↑ Scott Rugh, Clams of Champions: The San Diego Formation, from sdnhm.org, the San Diego Natural History Museum website accessed November 26, 2013.
- ↑ City of San Diego.gov: San Diego Formation Basin, with map.
- ↑ Common loon (G. immer) and yellow-billed loon (G. adamsii)
- ↑ Pacific loon (G. pacifica) and Arctic loon (G. arctica)
- ↑ Brodkorb, Pierce (1953). "A Review of the Pliocene Loons" (PDF). Condor 55 (4): 211–214. doi:10.2307/1364769.
- ↑ Brodkorb, Pierce (1963). "Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes)". Bulletin of the Florida State Museum, Biological Sciences 7 (4): 179–293 (224).
- ↑ T. Demere. 1986. The fossil whale, Balaenoptera davidsonii (Cope 1872), with a review of other Neogene species of Balaenoptera (Cetacea: Mysticeti). Marine Mammal Science 2(4):277-298
- ↑ W. K. Gregory and R. Kellogg. 1927. A fossil porpoise from California. American Museum Novitates 269:1-7
- ↑ Rachel A. Racicot, Thomas A. Deméré, Brian L. Beatty, Robert W. Boessenecker. Unique Feeding Morphology in a New Prognathous Extinct Porpoise from the Pliocene of California. Current Biology, 13 March 2014 DOI: 10.1016/j.cub.2014.02.031
- ↑ A. Berta and T. A. Demere. 1986. Callorhinus gilmorei n. sp., (Carnivora: Otariidae) from the San Diego Formation (Blancan) and its impliations for otariid phylogeny. Transactions of the San Diego Society of Natural History 21(7):111-126
- 1 2 T. A. Demere. 1994. Two new species of fossil walruses (Pinnipedia: Odobenidae) from the Upper Pliocene San Diego Formation, California. Proceedings of the San Diego Society of Natural History 29:77-98
See also
- Geology of San Diego County, California
External links
- "Clams of Champions" article from "San Diego Formation"
- San Diego County Water Authority – Water Management – Local Resources
| Neogene Period | |||
|---|---|---|---|
| Miocene | Pliocene | ||
| Aquitanian | Burdigalian Langhian | Serravallian Tortonian | Messinian |
Zanclean | Piacenzian | ||
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