USING FOSSIL PALYNOMORPHS TO CALIBRATE HEAT CONDUCTION INTO WET SEDIMENTS AROUND A BASALTIC SILL
At Clarkia, Idaho, a sill of the 14.5 Ma Priest Rapids Member of the Wanapum Basalt, Columbia River Basalt Group, was intruded into fossiliferous lakebed sediments. Fossils in the sediments include pollen from numerous tree and shrub species. It is well known that, upon various degrees of heating, initially transparent fossil palynomorphs darken progressively through golden, brown, and black shades before being destroyed. We are using changes in the optical properties of pollen to characterize heating of the sediments around this intrusive body.
Sediment samples were collected along a profile away from the sill contact. Previously unheated sediments were also collected from a site distant from the intrusion; these samples were heated under controlled laboratory conditions to construct a temperature calibration curve specific to the pollen species found in the Clarkia sediments. All samples were processed to remove carbonates and silicates and mounted in Euparal. Individual pollen grains were digitally imaged under constant lighting conditions, and their background-corrected color was analyzed using Adobe Photoshop.
Results show that sediments within 1 cm of the sill were heated to temperatures sufficient to completely blacken or destroy pollen (>325 °C), and sediments 1-2 cm from the sill were heated to temperatures near 300 °C. Further from the sill the temperature profile observed was relatively flat, dropping to ~250 °C at 95 cm from the sill contact. This profile suggests heat transport in the sediments was hydrothermally controlled. This information will be used to test numerical models of heat transfer in wet sediments on Earth and Mars.