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
Recommended Citation
Ryan, Trenton J., "Paleoecology of foraminifera from the late Miocene - early Pliocene Pullen and Saint George formations, northwestern California" (2017). Cal Poly Humboldt theses and projects. 76.
https://digitalcommons.humboldt.edu/etd/76