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Paleoecology of the upper Miocene Castaic formation, Los Angeles County, California

Citation

Stanton, Robert James (1960) Paleoecology of the upper Miocene Castaic formation, Los Angeles County, California. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-02232007-112028

Abstract

The Castaic formation comprises the upper Miocene marine sediments deposited in the Soledad Basin, northwestern Los Angeles County, California. The Soledad Basin is topographically the eastern extension of the Ventura Basin. Geologically, the two basins of deposition are separated by the San Gabriel fault along which an uncertain amount of lateral movement has taken place. Therefore, detailed correlation of the sediments of the Castaic formation with contemporary sediments of the Ventura Basin is not possible. The age of the Castaic formation is Mohnian and Delmontian. The sediments were deposited in part along an open coast and in part within a broad, open embayment.

Late Miocene movement on the San Gabriel fault, relatively up on the southwest, defined the western margin of the basin of deposition. A land mass on the west side of the fault northwest of Castaic, created the embayment of the northwest part of the basin. It is likely that a submerged extension of this land southeast of Castaic formed a sill along the western margin of the rest of the basin and restricted the circulation of bottom water.

The formation is about 7000 feet thick. It consists mainly of interbedded sandstone and mudstone. The two rock types occur in units 25 to 250 feet thick. Coarse-grained basal sediments were deposited at the margin of the basin of deposition. Megafossils are largely confined to the basal sediments. The nature of the basal sediments deposited at the margin of the transgressing late Miocene sea is related to the provenance and the relief along shore. Conglomeratic basal sediments were deposited along the northeast margin of the basin along a steep shore composed of the well-indurated Martinez formation. These sediments were derived locally from the conglomerate and sandstone beds of the Martinez formation.

Sandy and thin conglomeratic basal sediments were deposited along the southeast margin of the basin. Near-shore relief was low. The sediments were derived largely from the finer-grained, less consolidated sediments of the Mint Canyon formation. The very coarse-grained, poorly-sorted Violin breccia was derived from a nearby source of considerable relief that was northwest of the embayment.

The fauna of the Castaic formation is largely molluscan. Other phyla are represented by one species of brachiopod, two species of echinoderm, a balanid, a bryozoan, foraminifers and fish remains--both bones and scales. Approximately 100 species are present. Probably new species of Nerita, Colus (Anomalosipho), Marginella, and Arene occur in the formation. Other forms in the Castaic formation previously unreported or rarely reported from upper Miocene sediments of California are Anadara (Anadara) trilineata trilineata, Glycymeris cf. G. branneri, Chlamys hodgei, Sondylus sp., Eucrassatella cf. E. subgibbosa, Pseudochama sp., Corbula luteola, Periploma cf. P. discus, Tegula gallina, Calyptraea (Trochita) sp., Polinices (P.) uber, Oliva spicata. The fauna is comparable to that found at present at the northern limit of the recent Panamic molluscan province.

All the near-shore assemblages in the formation are essentially contemporaneous. Faunal variations are indicative of environmental variations which existed along the margin of the basin. In particular, the geographic distribution of the fauna can be related to differences in water depth and substrate, and to environmental differences associated with bay versus open coast habitat.

Analysis of the fauna suggests that: oxygen content of the water was probably less than normal at the bottom of the basin; the water was of normal marine salinity; most of the megafauna and associated sediments were deposited in water less than 25 fathoms deep; the maximum depth of the sill which probably existed along the western margin of the basin was about 100 fathoms; the marine climate was apparently uniform geographically within the basin of deposition and was much like that found at present off the southwest coast of Baja California. The average maximum annual surface temperature was about 22°C. The average minimum annual surface temperature was about 19°C. The Castaic formation was deposited at the northern limit of the late Miocene Panamic molluscan province.

Bathymetric distribution as well as geographic distribution of a fauna must be considered in any paleozoogeographic study in order to determine paleoclimate.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geological and Planetary Sciences
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Lowenstam, Heinz A.
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1960
Record Number:CaltechETD:etd-02232007-112028
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-02232007-112028
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:720
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:15 Mar 2007
Last Modified:26 Dec 2012 02:31

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