Discoveries in the Bighorn Basin

bighornHow many undergraduate students can claim that their research explains the Earth’s formation? Not many, but UNC supports one such budding scholar, Miles Wentland. Miles is an Earth Sciences student at UNC who has an emphasis in Geology studying and is advised by Dr. Emmett Evanoff.

During the summer of 2011, Miles conducted field research in the Bighorn Basin in north central Wyoming. Now an expansive bowl-shaped area known for its beautiful scenery, extensive collection of fossils, and rich subterranean oil, over one hundred million years ago the basin was filled with a huge reservoir of water, the Sundance Sea.

In his research, Miles focused on one area of the Basin, an exposed outcrop of hardened sand. He closely inspected the kinds and distributions of fossils, described the appearance and relative structures of strata (geologically distinct layers of rock), and prepared a detailed map of the area. As he conducted his field study, he was consumed with questions about the forces of nature that produced current formations.

In Miles’s words, “In the Sundance formation of the Bighorn Basin, the origins of lens-shaped oolitic sand bodies roughly two square kilometers in area have come under debate. Ooids are spheroidal grains typically composed of calcium carbonate. They are formed in shallow marine environments by the precipitation of calcium carbonate on small particles that are rolled by tidal action. Previously, scholars have interpreted these oolitic sand bodies as the outcome of submarine sand waves; however, more recently, investigators have interpreted them to be aeolian dunes. If these sand bodies are aeolian dunes, then the area in which they were deposited was exposed above sea, allowing the sediment to be reworked by the wind…For my research project, I am trying to determine whether these sand bodies are marine sandwaves or aeolian dunes.” Miles explained that in order to distinguish an aeolian dune and a submarine sand wave, you have to look at the primary structures.

So far, Miles has discovered that structures in the sand bodies primarily consist of inverse graded sand flow cross-stratification, grain fall cross-stratification, and low crested climbing ripple cross-stratification with rare small lenses of lenticular cross-stratification, all of which he interprets as being formed by small localized dunes. Near the base of the outcrop he found bonded surfaces in the form of adhesion warts, small mound-like masses formed by wind on water-saturated sediment. The outcrop itself consists of layers composed of strongly cemented sediment sandwiched between layers of weakly cemented sediment. What is particularly interesting to Miles is that the well-cemented layers are composed almost entirely of climbing ripple cross-stratification, which, for him reveal a period of stability, such that climbing ripples were able to develop on the dune surface. Fossil material was primarily composed of highly fragmented Gryphea shells and was concentrated near the base and top of the sand body.  Several features are indicative of aeolian dunes: inverse graded sand flow cross strata, grain fall cross strata, low crested climbing ripple cross strata, and adhesion warts.

Miles hopes his research will help resolve the debate over the origins of the Bighorn Basin sand bodies, improve knowledge of the environment and the distribution of the Sundance Sea during the Jurassic period, and increase understanding of ancient oolitic sand bodies.

Like many other student scholars at UNC, Miles credits his research mentors for motivating him to conduct research. Miles reports that his faculty encouraged him to ask big questions and seek the answers himself.  Clearly, he has acquired the background knowledge, technical skills, and conscientious disposition necessary to pursue significant scientific dilemmas. 

Miles is considering attending a graduate program in either sedimentology or sedimentary petrology.  When asked what he has learned about himself through the research process, Miles replies, “That I really, really like rocks.”