Ichnologic signature of disturbance and recovery from an oceanic flood deposit on the Eel Shelf, northern California

Graduation Date

2011

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Environmental Systems: Geology Option, 2011

Committee Chair Name

William C. III Miller

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Trace fossil, Ichnology, Ichnofacies, Disturbance, Oceanic flood deposit, Lapispira, Eel River, Humboldt State University -- Theses -- Geology, Eel Shelf

Abstract

The Eel Shelf of northern California is a dynamic depositional setting of episodic fine-grained flood sediments derived from the Eel River. X-radiographs of box cores were used to assign biogenic sedimentary structures to ichnogenera. The identified ichnogenera were then associated into fairweather, disturbance and recovery ichnofacies. Eel River flood events create large sedimentary discharges, which annually deposit mud layers averaging 2-3 cm thick. However, rare, 15 yr return periods flood events can rapidly deposit sediments up to 10 cm over portions of the Eel Shelf. This study concentrates on the oceanic flood deposit that occurred in 1995. The high-volume, rapid depositional event influenced a change in organism bioturbation patterns that can be recorded using X-radiographs obtained from box cores. On the middle Eel Shelf the normal fairweather biogenic sedimentary structures are consistent with the Cruziana Ichnofacies. During and immediately after the event, fugichnia (animal escape structures), and Skolithos dominate the event sediments. The event trace association is characteristic of the higher-energy Skolithos Ichnofacies. With return to the normal sedimentation regime, the event deposits begin to be overprinted by the reoccurrence's of the fairweather traces typical to the Cruziana Ichnofacies. The recovery deposit association is mixed, consisting of ichnogenera of the fairweather Cruziana and event Skolithos Ichnofacies. This mixed recovery ichnofacies is identified herein as a Skolithos-Cruziana Ichnofacies. Based on the rapid return of the original Cruziana Ichnofacies-type structures, the temporary shift in trace fossil associations is likely driven not by the transportation of allochthonous trace makers, but by changes in autochthonous trace-maker behavior.

https://scholarworks.calstate.edu/concern/theses/k930c058t

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