HEAT CONDUCTION INTO WET SEDIMENTS AROUND A BASALTIC SILL: CALIBRATION USING FOSSIL PALYNOMORPHS
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 (Taxodiaceae -Taxaceae, Pinus, Picea, Psuga, Abies, Ulmus, Betula, Carya, Fagus, Quercus).
It is well known that initially transparent fossil palynomorphs darken progressively upon heating through golden, brown, and black shades, and are eventually destroyed, typically by temperatures above 250°C. This color change and corresponding changes in transmissivity and reflectance are related to thermally-induced changes in functional group composition of organic matter. These changes are also detectable by analytical methods such as infrared spectroscopy and nuclear magnetic resonance spectroscopy. Palynomorph analysis is widely used to determine the thermal maturity of sediments.
We are using changes in the color and associated characteristics of pollen in sediments around the Clarkia basalt sill to characterize heating of the sediments around this intrusive body. Unheated pollen samples collected from sediments distant from the sill will be heated under controlled laboratory conditions to calibrate the changes observed with temperature in individual species. Analysis of the sill thickness, and the chemical composition and crystallinity of the intruded basalt, will be used to estimate the total heat released into the surrounding sediments. This information, and the calibrated temperature profile away from the sill, will be used to test numerical models of heat transfer in wet sediments on Earth and Mars.