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Zellers, S.D., 1995

Sequence biostratigraphy, seismic stratigraphy, and subsidence/uplift history of the offshore Yakataga Formation, northeastern Gulf of Alaska

Bibliographic Reference

Zellers, S.D., 1995, Sequence biostratigraphy, seismic stratigraphy, and subsidence/uplift history of the offshore Yakataga Formation, northeastern Gulf of Alaska: University of Texas, Austin, Ph.D. dissertation, 299 p., illust., maps.


Interbedded marine and glacial-marine deposits of the Yakataga Formation (late Miocene to Recent), which underlie the northern Gulf of Alaska continental shelf, are the focus of an integrated study to understand the depositional and climatic history of the late Cenozoic Gulf of Alaska. Yakataga strata accumulated on a tectonically active, glaciated continental margin; they record initial late Cenozoic glaciation in the Gulf of Alaska (latest Miocene to earliest Pliocene) and the onset of major northern hemisphere glaciation during the late Pliocene. Foraminiferal sequence biostratigraphy, seismic stratigraphy, and tectonic subsidence/uplift analyses define and characterize eight seismic stratigraphic sequences on the Yakataga continental shelf. Foraminiferal biostratigraphy establishes age, paleoenvironmental, and paleoclimate relationships. These studies and seismic stratigraphy show that the base of the Yakataga Formation is an unconformity offshore that developed as a result of a change in Pacific Plate motion during the early Pliocene. Analyses of benthic foraminifera demonstrate that paleobathymetry fluctuated from inner neritic through middle bathyal. Pleistocene paleoenvironments were deeper on average than those in the Pliocene. Cluster and polytopic vector analyses show that the complex faunal patterns are due to heterogeneities in environments and mixing of faunas due to a variety of marine and glacial-marine processes. Many paleobathymetric fluctuations are non-synchronous between well sections and exceed 200 m; these fluctuations are mainly due to differential uplift and subsidence on discrete tectonic blocks. Isopach and structure contour maps illustrate the geometry of sequences, and demonstrate that depocenters shifted across the margin through time. Tectonic subsidence/uplift analyses quantify the controls on accomodation; these results show that tectonics and sediment-loading subsidence are the primary controls on the magnitude of accomodation on the margin. The youngest (upper Pleistocene) sequence boundaries may have formed during eustatic lowstands as glacial ice advanced and eroded parts of the margin that had been tectonically uplifted. The base of each of the oldest (Pliocene and lower Pleistocene) Yakataga sequences is bounded by a tectonically formed or tectonically enhanced sequence boundary; neither the relationship to eustasy nor the mode of formation of the oldest boundaries can be determined with the available data.

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