1. Heavy Mineral Sorting Processes and Their Geochemical Detection in the Brushy Canyon Formation
Michael Tice, Department of Geology & Geophysics, Texas A&M University
College Station, TX 77843
Zircon (ZrSiO4) and rutile (TiO2) grains have buoyant densities in water about twice that of more common sand grains such as quartz and feldspar. They are also typically only minor components of sediments, and their concentrations can be effectively ignored in modeling. These properties make them ideal “test particles” for characterizing ancient flows from their resultant sandstones and siltstones.
We have shown that zircons and rutiles can be imaged in situ by x-ray fluorescence microscopy. We are now using this technique to determine depositional mechanisms and flow characteristics in rocks of the Brushy Canyon Formation. Results to date indicate that finely laminated siltstones comprising up to 90% of the formation are enriched in zircon grains relative to sandstones deposited by submarine flows (turbidity currents). This observation is consistent with transport to the basin by wind rather than by dilute turbidity currents as suggested by recent models. Thus, our work suggests that geochemical criteria can aid in the identification of ancient submarine windblown dust deposits. Continuing work is examining the use of dust geochemistry as a correlation tool. We are also comparing zircon, rutile, and feldspar grain size distributions in sandstones to estimate the densities of the depositing flows.
Windblown siltstone
1 mm
Turbidite
In situ detection of zircon grains in windblown siltstone and turbidite.