Late Pleistocene sediments and fossils near the mouth of Mad River, Humboldt County, California : facies analysis, sequence development, and possible age correlation

Graduation Date

1994

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Geology, 1994

Committee Chair Name

William C. III Miller

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Mad River, Stratigraphic, Paleontology, Sediments (Geology), Humboldt State University -- Theses -- Geology, Pleistocene, California, Geology

Abstract

Study of late Pleistocene sediments near the mouth of the Mad River revealed a sequence of nearshore marine and shallow bay deposits. This sequence, bounded by unconformities, is informally named the Mouth of Mad unit. The Mouth of Mad unit can be divided into four distinct depositional facies at the study site. The lowest facies are the Nearshore Sand and Estuarine Mud, which lie unconformably on a paleosol. The sand facies grades upward into a high-energy, interbedded Nearshore Sand and Gravel facies containing storm and rip-channel deposits. Above the sand and gravel is a Strand-Plain Sand facies. This sand is overlain by a laterally variable sequence of shell-rich Bay facies. The bay deposits can be further divided into five subfacies: 1) a Bioturbated Sand; 2) a Lower Tidal Flat Mud; 3) a Mixed Sand and Mud; 4) an oyster-rich Bay Mud; and 5) an Upper Tidal Flat Mud. The bay sequence is overlain unconformably by younger late Pleistocene marine terrace deposits. The depositional environments represented by these facies progress from a shoreline estuary to nearshore deposits, above storm wave base, and slowly back to shoreline, and finally to shallow bay conditions. The Mouth of Mad unit represents a transgressive-regressive sequence, involving the development of a protective spit. The uppermost mud within the Mouth of Mad unit has been dated, using thermoluminesence age estimation, at 176 ± 33 ka, placing it in the late Pleistocene. Amino acid racemization dating, fossil evidence, and the thermoluminesence date can be used to establish a tentative correlation between the Mouth of Mad unit and other nearby Pleistocene fossil-bearing deposits. The Mouth of Mad unit appears to be younger than the fossiliferous deposits at Elk Head, Crannell Junction, Trinidad Head, Moonstone Beach, and the Falor Formation near Maple Creek, and possibly time equivalent with gravel deposits exposed at the western end of School Road in McKinleyville.

https://scholarworks.calstate.edu/concern/theses/ht24wm73n

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