My current research interests include:
- Determining the timing and origin of fluid flow and burial diagenetic events;
- Understanding the origin of remagnetization in sedimentary rocks with a particular focus on investigating the origin of synfolding remagnetizations; and
- Dating the timing and determining the origin of bolide impact breccias and dating the impact events.
Understanding the origin of remagnetization in sedimentary rocks and testing/developing a paleomagnetic/geochemical approach for dating diagenetic events
Diagenetic investigations are frequently limited by the difficulty in constraining the time frames in which most past events have occurred. Paleomagnetic analysis is one method that can provide information on such events. Remagnetization or acquisition of a secondary magnetization is usually tangible evidence of a secondary chemical (i.e., diagenetic) event and these events can be dated by isolation of the chemical remanent magnetization (CRM) carried by the diagenetic magnetic minerals and comparison of the pole position for the CRM to an independently established time scale, the Apparent Polar Wander Path. Field tests and geochemical/ petrographic studies are used to determine the origin of the fluid/diagenetic event and to relate the event to the authigenic magnetic phases.
|Graph illustrating that secondary magnetizations,
mostly CRMs, are very common. The # of magnetizations
on the y axis is based on published reports.
Current research in this area is focused in several areas areas:
We are also staring a project on determining the timing and
origin of burial diagenetic events in the Woodford Shale
Determining the origin of bolide impact breccias and dating impact events
We used paleomagnetism to constrain the timing of two features in Missouri (USA), the poorly-dated Decaturville impact, and the Weaubleau-Osceola structure, a supposed impact (see Elmore and Dulin, 2007). We use the information to evaluate the possibility of a serial impact which has been proposed for these as well as other features along the 38th parallel in North America. Previous studies at Decaturville suggested a Pennsylvanian-Cretaceous age range for impact. A mid Permian pole position for impact-related breccias at Decaturville, as well as cross cutting relationships, constrains the timing of the impact to the Pennsylvanian-mid Permian. Tilt test results from deformed strata at the Weaubleau-Osceola structure reveal a post deformational late Mississippian pole, which along with stratigraphic constraints, indicates that the deformation event can be no younger than late Mississippian. These results suggest that the Weaubleau-Osceola and Decaturville structures are different ages and can not have been caused by a serial impact. Additional studies are needed to date other impacts along the 38th parallel (e.g. (e.g. Crooked Creek impact).
Paleomagnetic constraints on the timing of the Decaturville impact and the Weaubleau-Osceola structure along the 38th parallel in Missouri: Testing the Serial Impact Hypothesis
PALEOMAGNETISM OF THE SIERRA MADERA IMPACT CRATER, TEXAS
Devin Dennie, Shannon Dulin,and I are collaborating with John Warme on a paleomagnetic study of the Upper Devonian Alamo Breccia (Guilmette Formation, Nevada) which is interpreted as a deposit that formed from a wet impact on the continental slope. The lower part of the deposit at some locations is interpreted as ejecta that was hot at deposition whereas as the upper part was reworked by tsunamis. The pictures below show clasts in the Alamo Breccia.
Devin Dennie is working on monomict and polymict carbonate and siliciclastic breccia clasts, as well as deformed country rock, at Sierra Madera (Trans-Pecos Texas), an exhumed complex impact structure. Stepwise demagnetization reveals a characteristic remanent magnetization (ChRM) that is removed between 580-680°C. The ChRM has southerly declinations and steep up inclinations or northerly declinations with steep positive inclinations. The normal and reverse directions pass a reversal test. Results from multiple clasts fail a conglomerate test, indicating a postdepositional remagnetization. The unblocking temperatures and rock magnetic studies indicate the ChRM resides in hematite. A second component is removed below 580°C and contains streaked directions between the ChRM and a southwesterly or northeasterly direction. Based on rock magnetic analysis this intermediate temperature component resides in both high and low coercivity phases. The origin of this component is under investigation. The pole for the ChRM falls near the 50-70 Ma part of the apparent polar wander path. Compared to the stratigraphic age range for the impact (40-100 Ma), the pole and the reversals suggest the impact is no younger than 50 Ma and no older than ~83 Ma. Petrographic observations show that flow banded glass is present in the breccia clasts and matrix, suggesting that the breccia was hot at deposition. The ChRM is tentatively interpreted as a thermal remanent magnetization (TRM) acquired during cooling of the breccia although a chemical remanent magnetization can not be ruled out without further analysis. If the ChRM is a TRM, it dates the impact to 50-70 Ma.
Testing the origin of Alamo Breccia using paleomagnetic analysis
A modified paleomagnetic conglomerate test was conducted to investigate the origin of the breccia. Reworking of clasts by tsunami would presumably produce deposition of cold clasts with random directions as opposed to hot clasts with grouped directions as expected in hot ejecta or melt breccias. Unfortunately, all the clasts are remagnetized. In most areas the breccia contains a Pennsylvanian characteristic remanent magnetization. At two locations there is an apparent Cretaceous or Tertiary component. Devin Dennie is currently investigating the origin of these magnetizations and preliminary results suggest they were caused by fluid alteration.