CENOZOIC BASIN DEVELOPMENT AND STRIKE-SLIP DISPLACEMENT ALONG THE DENALI FAULT SYSTEM, EASTERN ALASKA RANGE, ALASKA: A PROVENANCE APPROACH

Analysis of Eocene-Pliocene sedimentary and volcanic strata exposed along and within the McCallum-Slate Creek fault system provides new insight into basin development and strike-slip displacement along the Denali fault system (DFS). These strata are exposed in distinct thrust sheets that are part of an active regional south-verging transpressional thrust belt located on the south side of the DFS. Our dataset consists of measured stratigraphic sections, paleocurrent data, clast compositional data, and U-Pb zircon and ⁴⁰Ar/³⁹Ar geochronology on bedrock and detrital samples.

Eocene or younger strata consist of deformed conglomerate with a minimum thickness of 366 m and are exposed in a thrust sheet proximal to the DFS. Detrital zircon (n= 916) results indicate that the maximum depositional age (MDA) of these strata is 49 Ma and that sediment sources for these strata had dominant ages of 58, 102, and 158 Ma. Oligocene and early Miocene strata characterize a medial thrust sheet and consist of conglomerate with a minimum thickness of 549 m. The MDA for these strata is ~21 Ma and is consistent with a ⁴⁰Ar/³⁹Ar tephra age of ~20 Ma. Detrital zircon (n=2151) results indicate sediment sources for these strata had dominant ages of 26, 124, 204, 297, and 312 Ma. Late Miocene-Pliocene strata characterize the more distal thrust sheet and consist of lacustrine and alluvial fan strata with a minimum thickness of 564 m. ⁴⁰Ar/³⁹Ar tephra ages from these strata range from ~6 to ~4 Ma. Detrital zircon (n=2667) results indicate sediment sources for these strata had dominant ages of 5, 26, 89, 92, 98, 101, 123, 156, 166, and 294 Ma.

Our working hypothesis is that the Eocene-Pliocene strata record distinct stages of basin formation, sediment provenance, and deformation along the DFS and related structures. In addition, low-temperature thermochronology on basement rock along the DFS indicate that stages of basin formation are correlative with periods of rapid cooling. We present reconstructions of each stage of basin development and use provenance data to interpret the locations of the strata prior to displacement on these major strike-slip faults. Our findings suggest large-scale, strike-slip displacement since the Eocene with potential unique sediment sources identified at ~250 km and ~400 km to the east of the present location of the exposed strata.