Reports: ND852114-ND8: Characterizing Quartz Microtextures in a Proglacial and Nonglacial Fluvial System as a Means Toward Improved Paleoenvironmental Analysis: A Pilot Study

Gerilyn S. Soreghan, University of Oklahoma

Overview: This project is a preliminary test of the hypothesis that distinctive quartz microtextures are imparted by wet-based glacial activity, and such textures survive for a significant transport distance and can thus be used to infer the influence of glaciation, well after the ice has melted. This study forms a pilot for a systematic study of quartz microtextures in end-member fluvial environments (including  nonglacial and glacial), with the ultimate goal of quantifying the use of microtextural analysis as a means to refine interpretations of fluvial paleoenvironments in Earth’s “deep-time” record. During the 2012-13 grant year, PhD student Leslie Keiser applied this approach of studying quartz microtextures to the Permian Cutler Formation of western Colorado, a unit proposed (in previous studies) to be of both non-glacial “hot-fan” and proglacial “cold-outwash” origin. This unit formed in the tropical region of the Pangaean supercontinent, so the possibility that it may record cold paleoclimatic conditions is quite significant to global climatic  reconstructions for this time. Additionally, this unit forms frontier hydrocarbon prospects in the Paleozoic section of the San Juan Basin (currently untapped at this deep level), so understanding its depositional origin is of applied interest. Ms. Keiser collected a large amount of data on quartz microtextures from various subenvironments of this unit -- proximal lacustrine (possibly proglacial) to distal fluvial. She then applied a series of both semi-quantitative and rigorous quantitative tests to look for patterns in the data.  The latter entailed a series of statistical treatments, including multidimensional scaling (MDS), a non-parametric multivariate ordination technique. This approach represents a significant advance over published approaches that do not employ quantitative treatments. Results of this work to date indicate that microtextures from quartz grains of the proximal lacustrine (hypothesized proglacial) facies are indeed statistically distinct from quartz microtextures of the other (more distal) facies, and include high-stress textures typical of the intense physical erosion imparted by glacial grinding, such as (micro)grooves. To date, this research supports the inference of a proglacial origin for the (Permian) Cutler Formation, and demonstrates the utility of a quantitative approach in discerning this.  

Impact on Student: This grant provided partial support for my PhD student, Leslie Keiser. Indeed, it provided the critical support needed to sustain Leslie through to completion of her PhD (defended in May 2013); hence, this PRF support has had a substantial (positive) impact on Dr. Keiser’s nascent career as a geoscientist. PRF support enabled Leslie to conduct the fieldwork to collect the samples, and --critically-- the extensive lab work with the scanning electron microscope (SEM) to collect a large dataset on quartz grain microtextures that enabled her to craft two primary manuscripts and one secondary manuscript. All three manuscripts are currently either in revision or in review at peer-reviewed journals. The process of preparing her work for publication, through PRF support, has greatly improved Leslie’s analytical and writing skills.  As a specific example, she delved deeply into advanced statistical analyses. Leslie grew enormously in confidence in the latter stages of her PhD, and is now employed full time as a petroleum geologist at Conoco-Phillips.

Impact on PI: This grant has taken me (the PI) in new research directions in several ways. Firstly, this PRF research includes plans to immerse myself and students into the realm of the sedimentology of modern systems, with the promise of developing “proxies” for climate applicable to ancient strata. To date, I have focused on Earth’s “deep-time” record, so this is very new for me. Secondly, this research involves intensive work with scanning electron microscopy, physical weathering and fracture formation, quartz microtextural analysis, and advanced statistical analysis-- all new subdisciplines for me.

Impact on Field: If our approach is successful, it will enable clarification of paleoenvironmental interpretations for fluvial systems from various geologic ages, even given one-dimensional (e.g., core) access to a system. Such information is critical for prediction of reservoir character, owing to the influence of paleoenvironmental setting on channel belt geometry, proportion, and sand connectedness. It will also be of great benefit to paleoclimatic interpretations, because it is otherwise very difficult to assess whether a fluvial system emanated from proglacial or nonglacial drainage basin in the deep-time record, yet this determination has major implications for paleoclimatic reconstructions.