How Sedimentation Rate Impacts Lacustrine Stratigraphy: An ³⁹Ar/⁴⁰Ar Record from the Laguna del Hunco Formation, Argentina

Justin Gosses, University of Wisconsin, Madison / Geology and Geophysics Dept., Madison, Wisconsin, USA, [email protected]

When investigating the effect sedimentation rate has on lacustrine stratigraphy over several million years, finding enough dateable material is frequently the critical issue rather than the resolution of the geochronologic methodology. This study attempts to surmount that problem by investigating a lacustrine formation that contains a large amount of dateable material.

The Laguna del Hunco Formation of Chubut Province, Argentina is an Eocene age caldera lake formation. The lacustrine strata contain large amounts of volcaniclastics and are inter-bedded with large numbers of volcanic deposits. Locating dateable material is not a serious issue. The study will use ³⁹Ar/⁴⁰Ar dating methods and extensive field work to create a geochronologic history and a stratigraphic record in order to examine possible connections between sedimentation rate and stratigraphy. In particular, are there connections between sedimentation rate and expression of depositional environment? Also, what is the most important control on sedimentation rate in this formation?

Initial geochronologic results are still preliminary but imply extremely fast deposition followed by exponentially slower deposition. Field work and lab work this coming fall and winter will concentrate on establishing a detailed stratigraphy and making connections between the stratigraphy and sedimentation rate.

The geochronologic data also allows important conclusions in regional paleobotony, mammalian paleontology, and volcanology. Stratigraphic work will allow the first detailed stratigraphy of the Laguna del Hunco Formation. The combined stratigraphic and geochronologic results may suggest implications for how stratigraphic variations are connected to sedimentation rate in the lacustrine record.