Date of Award


Document Type

Union College Only

Degree Name

Bachelor of Science



First Advisor

John Garver




basin, formation, grain, ma, age


The bedrock of southern Alaska consists of a number of accreted allochthonous terranes and basin sequences that rest above them. The boundary between the inboard Wrangellia superterrane and the outboard Chugach accretionary complex occurs along the Border Ranges fault system. Strata of the Cook Inlet-Matanuska basin lie on the Wrangellia terrane adjacent to the Chugach, and these sedimentary rocks provide insight into the exhumation and erosion histories of these adjacent terranes. The detrital zircon fission track (DZFT) grain-age distributions from five samples from the Paleocene-Eocene Chickaloon Formation and one sample from the overlying Eocene Wishbone Formation reveal that the sandstones have two distinctive grain-age patterns. All samples contain a DZFT grain-age population at ~55 Ma inferred to represent syndepositional volcanism in the adjacent Talkeetna arc, as well as an older Early Cretaceous (~126 Ma) population likely derived from plutonic rocks of the Talkeetna Arc. Three samples from the Mio-Pliocene Sterling Fm. on the margin of the Cook Inlet basin have a broad distribution of cooling ages between ~200 and ~20 Ma that contain a progressively higher proportion of grains in an ~20 Ma population in samples farther east across the Cook Inlet. This grain-age pattern indicates the importance of this young exhumed terrane in the NE part of the basin, while the thermotectonic source is unclear, but likely in the Central Alaska Range. Variation between the well-defined populations of the Matanuska basin and the broadly distributed grain ages from the Sterling Formation suggests that the Early Cretaceous population (c. 126 Ma) identified in the Paleocene-Eocene Chickaloon Formation and the Eocene Wishbone Formation, was likely derived from the Jurassic plutons of the Talkeetna arc, not the Chugach terrane to the south.