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Abstract

In order to establish a standard chronologic biostratigraphic section for the Lower Tertiary of California certain requirements must be met. The sequence should, for the interval under consideration, be:

  1. under demonstrable superpositional control

  2. a continuous and uninterrupted lithologic sequence

  3. paleontologically controlled at both bottom and top (recognizable and definable paleontological criteria at base and top)

  4. continuously fossiliferous

The difficulties involved in fulfilling all of the above requirements are immediately apparent. Indeed, the ideal sequence probably does not exist. An attempt has been made in this report to approximate as closely as possible the ideal.

The first sequence of Lower Tertiary strata studied by the writer was that exposed in the vicinity of Media Agua Creek in the Temblor Range on the west side of the San Joaquin Valley in Kern County, California. Some 2,300 feet of marine Lower Tertiary strata exposed here are assigned to the Lodo and overlying Tejon formations (see Figs. 1, 2, 3). Most of this sequence is highly foraminiferal (see Table 1). An analysis of the microfossils in the light of related data from other sources indicates that ( 1 ) the Lodo formation of this section was laid down at depths varying between the littoral district and the edge of the continental shelf, in a sea with tropical or subtropical surface temperatures, and with open ocean connections prevalent during most of its deposition; (2) that the overlying Point of Rocks member of the Tejon formation was

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