PARTICLE SIZE DISTRIBUTIONS OF GLACIAL GRINDING EXPERIMENTS AND IMPLICATIONS FOR PAST MARTIAN CLIMATE

Dust in the Martian atmosphere might have influenced the ancient climate through radiative forcing, inducing precipitation, and nutrient dispersal for biotic processes. Dust in the sedimentary record can originate through different processes (glacial grinding, eolian saltation, fluvial comminution, bolide impacts, chemical weathering) that reflect the climate linked to those processes. Different processes might exhibit unique particles size distributions (PSD), that, in turn, impart different climate effects. Fine sediments are prone to chemical alteration and capable of deposition far from source locations by eolian suspension; thus, laboratory produced, unaltered samples are useful in characterizing true PSDs of various erosional processes.

We investigated the PSDs produced by simulated glacial grinding of basalt rocks as Martian analogs. Angular styluses of basalt rock were cut from whole rock, weighted to replicate a contact force of 200-300 N, and abraded across a basalt slab representing bedrock. Sediments from the grinding experiments were collected and measured using a Laser Particle Size Analyzer (LPSA). Preliminary results indicate the dust-sized (<63 µm) sediments produced exhibit modes of roughly 20 µm. The volume of coarse dust produced exceeding 5 µm in size is significantly greater than the volume of dust below 5 µm.

If, as others have suggested, Mars hosted past glaciers accompanied by subglacial grinding, and those rocks had similar compositions to our analogs, the products of glacial grinding would include more coarse (>5 µm) dust than fine (<5 µm). Given that coarse dust is thought to contribute an atmospheric warming effect, compared with a cooling influence from fine dust; our results suggest that dust from glacial grinding of basalt rocks might have contributed a warming effect on past Martian climates.