SEM TEXTURES OF QUARTZ FROM THE UPPER PALEOZOIC FOUNTAIN FORMATION (MANITOU SPRINGS, COLORADO) SUGGEST A POSSIBLE GLACIAL INFLUENCE ON DEPOSITION

Recent studies from modern glacial and proglacial environments demonstrate that glacial processes impart distinct microtextures on sand-sized quartz. We use SEM microtextural analysis of quartz from the upper Paleozoic Fountain Formation to test the hypothesis that these strata may reflect a glacial influence, rather than entirely non-glacial fan-delta deposition.

Analysis reveals reproducible variations of microtextures within various facies of the Fountain Formation. Microtextures of marine shoreface and foreshore facies exhibit common edge rounding, v-shaped cracks, and abrasion with minor deep troughs, grooves and steps. Grains from fluvial facies display prevalent conchoidal fractures, steps and sharp angular features (>50% of grains) with subordinate crescentic gouges, grooves, mechanically-upturned plates, v-shaped cracks and edge rounding. Furthermore, angular features, conchoidal fractures, grooves, steps and troughs increase in abundance up section.

Microtextures documented from fluvial systems consist chiefly of edge rounding and v-shaped cracks as a result of grain-to-grain collisions during traction flow. In contrast, microtextures from fluvial strata of the Fountain Formation bear a stronger similarity to those of glacio-fluvial sediments owing to the numerous steps, linear fractures, crescentic gouges and conchoidal fractures. Stratigraphically up section, marine facies also of the Fountain Formation appear to exhibit a glacial influence, evinced by the presence of deep troughs, gouges, steps and linear fractures, which are hard to reconcile with fluvial and shoreface processes alone.

Our preliminary data thus suggest that sediments in the proximal Fountain Formation fan-delta exhibit a glacial influence in this low-latitude setting. Additionally, the up-section trend in glacially influenced textures suggests a stronger glacial influence with time. If continued work provides further confirmation, then the paleogeographic context of the Fountain Formation requires significant revision. These data suggest that quartz microtextural analysis extends to ancient strata, and can help assess presence of ancient glaciation in the absence of ice-contact deposition.