Graduation Date

Fall 2017

Document Type

Thesis

Program

Master of Science degree with a major in Environmental Systems, option Geology

Committee Chair Name

WILLIAM MILLER

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

JEFFRY BORGELD

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

EILEEN HEMPHILL-HALEY

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Geology

Abstract

The Pullen and Saint George formations are coeval late Miocene-early Pliocene sedimentary formations in northwestern California. The type localities of both formations were studied from a micropaleontologic perspective that focused primarily on Foraminifera, but with additional observations of other fossil groups to reconstruct their past depositional environments. The results obtained in this study provided a photomicrographic inventory of the microfossils from both formations, aided in investigating changes in paleobathymetry of the formations during the late Miocene and early Pliocene based on Foraminifera, and allowed for interpretation of paleoecological signals from the foraminiferan associations. Foraminifera have not been previously described in the Saint George Formation and the Foraminifera of the section of the Pullen included this study had not been described in detail.

A monospecific association of Elphidium sp. was found in the Saint George Formation. This fact, coupled with the composition of the molluscan fauna, indicates that the strata of the Saint George Formation were deposited in a sheltered, likely brackish, shallow embayment. Sterrasters from the demosponge Geodia were also found, and also had not been previously described from the Saint George.

Foraminiferan associations in the Pullen Formation point to mid-to-lower bathyal depositional environments, supporting the interpretation of rapid subsidence near the Miocene-Pliocene boundary, followed by a slowly deepening environment following the initial subsidence. Foraminiferan evidence also suggests that periods of prolonged anoxia may have occurred during the deposition of the Pullen.

Citation Style

JOURNAL OF GEOLOGY

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