The announcement went out today, so I guess it’s official! A thesis defense is an event open to the public, so if my research sounds interesting to you and you’d like to come by, you’re welcome to do so! I sure do have a powerpoint presentation and everything, all ready to go.
Date: Thursday, March 7
Time: 3:00 p.m.
Location: University of Colorado at Boulder, Benson Earth Sciences Room 380
Advisor: Mary Kraus
Sedimentary and Climatic Response to the Second Eocene Thermal Maximum in the McCullough Peaks Area, Bighorn Basin, Wyoming, U.S.A.
The Paleocene-Eocene Thermal Maximum (PETM) was followed by a lesser hyperthermal event, called ETM2, at ~53.7 Ma (Zachos et al., 2010). The carbon isotope excursion and global temperature increases for ETM2 were approximately half those of the PETM (Stap et al., 2010). The paleohydrologic response to this event is less well understood than the response to PETM warming. Although ETM2 is better known from marine than continental strata, the hyperthermal has been identified from outcrops of the alluvial Willwood Formation from the Deer Creek and Gilmore Hill sections of the McCullough Peaks area in the Bighorn Basin, Wyoming (Abels et al., 2012). The presence of ETM2 in Willwood Formation strata provides a rare opportunity to examine local continental climatic and sedimentary response to the hyperthermal.
Core drilled at Gilmore Hill was described and analyzed geochemically. The core consists of paleosols formed on mudrocks that are interbedded with siltstones and sandstones. Carbon isotope analysis of carbonate nodules from paleosols in the core shows that the top of the core, below a prominent yellow sandstone, most likely records the very beginning of the carbon isotope excursion that marks ETM2 (Maibauer and Bowen, unpublished data). The rest of the hyperthermal was likely removed by the sandstone deposition.
Analysis of bulk oxides in the paleosols provides quantitative estimates of precipitation through the core section (Sheldon et al., 2002; Nordt and Driese, 2010b). The estimates reveal a distinct drying trend leading up to ETM2 at Gilmore Hill. Red and brown paleosols, attributed to generally dry conditions, dominate the section directly below the onset of ETM2 and confirm drier conditions. In contrast, thick purple paleosols are associated with ETM2 at the Deer Creek site and suggest wetter conditions during most of the ETM2 interval. The prominent yellow sandstone at the top of the Gilmore Hill core was probably deposited during those wetter climate conditions. The core displays distinct changes in stratigraphic architecture: the bottom ~100m is mudrock dominated, and the top ~100m is sandstone dominated. Several PETM studies have suggested that large sandstones have developed in response to precipitation changes associated with global warming. Analysis of the stratigraphic architecture, in conjunction with carbon isotope and precipitation data, shows that the prominent sandstone that replaces ETM2 in the core was not caused by climate change. The sandstone is the uppermost part of the sandstone-rich interval whose base underlies ETM2 by more than 50m. Most of this sandstone-rich interval is accompanied by a range of climatic conditions. This study shows that the shift from mudrock to sandstone dominated stratigraphy at Gilmore Hill and possibly throughout the McCullough Peaks area was not caused by climatic change associated with ETM2.