MICROTEXTURAL ANALYSIS OF THE FRENCH MASSIF CENTRAL QUARTZ SAND TO INFER COLD CLIMATE WEATHERING (PENNSYLVANIAN-PERMIAN, LODEVE BASIN, FRANCE)

The Lodeve Basin (southern France) contains a thick record of continental sedimentation spanning Late Carboniferous through Permian time in equatorial eastern Pangea. This region of the French Massif Central was part of the Hercynian-Variscan orogenic system in late Paleozoic time. Although the setting is paleo-tropical, some research has suggested the possible influence of upland (mountain) glaciation on sedimentation here. We are applying quartz microtextural analysis to test this hypothesis.

Quartz microtextural analysis employs documentation of fracture features and associated surface textures on sand-size quartz using the scanning electron microscope (SEM). For initial data analysis, the observed microtextures can be classified into three categories: 1) high-stress fractures, formed in a sustained high-stress environment, such as glacial transport, that cause grooves, deep troughs, and gouges on the grain surface; 2) percussion fractures, such as V-shaped cracks and edge rounding created through grain-to-grain contact during saltation in a fluvial environment; and 3) polygenetic fractures such as arc-shaped steps, linear steps, linear fractures, and conchoidal fractures, which can originate by various non-unique processes.

We processed samples from two Permo-Carboniferous units of the Lodeve Basin: the Croix de Mounis Formation, a diamictite of indeterminate (possible glacially influenced) origin, and a sandstone-conglomerate from a fluvial unit of the Rabejac Formation. To liberate the quartz grains, we soaked the samples in 2N HCl, then applied the citrate-bicarbonate-dithionite (CBD) process to remove iron oxides. Analysis is ongoing, but preliminary results indicate distinct occurrence of high-stress fractures on grains from the Croix de Mounis Formation. Future plans involve additional data collection followed by quantitative data analysis to assess whether or not observed differences in occurrences of high-stress versus other microtextures are statistically significant.