59th Annual Report on Research 2014

During the last year two students, Diar Ibrahim, a Ph.D. student from the University of Iowa and Mario Lira a M.S. student at Texas A&M continued work on their theses on detrital zircon geochronology of Middle-Late Ordovician quartz arenites in the western U.S. and U.S. Midcontinent with funds from this grant. The LA-ICP-MS at Texas A&M was finally repaired by the Spring of 2014 and Diar and Mario were both trained by Brent Miller to analyze zircons for provenance analysis on this machine. Both students completed their detrital zircon analyses in the summer of 2014. During the fall and spring of 2014 Diar Ibrahim described and correlated numerous cores of the St. Peter and Starved Rock sandstones in Iowa and Illinois. Additionally, 12 shale samples that occur within the Middle to Late Ordovician quartz arenites were analyzed at the Washington State University GeoAnalytical Laboratory for trace and major elements in the summer of 2014. These results will be used by Diar Ibrahim to determine their Chemical Index of Alteration (CIA) that should provide insights into the paleoclimate and weathering during their deposition. Diar's research (Fig. 1, 2, and 3) shows that the St. Peter Sandstone in Iowa records significant changes in provenance during deposition of this unit. Bill McClelland (Univ. of Iowa), Brian Witzke (retired Iowa Geological Survey) and I are working closely with Diar to interpret the results of his analyses. We expect that Diar will be complete his Ph.D. by the spring semester of 2015 and that three papers will be submitted to peer-reviewed journals from his research. Mario Lira's M.S. thesis is testing whether the Tooele Arch in Nevada and Utah affected Middle Ordovician sedimentation. Mario measured a series of stratigraphic sections surrounding the Tooele Arch (Fig. 4) to determining if their detrital zircons are different than detrital zircons on either side (N or S) of the Tooele Arch. Mario's preliminary data indicate that source terranes in the base of his sections were quite different than those at the top of his sections (Fig. 5) Mario is analyzing all of his zircon data and currently writing up his M.S. thesis with the intent to finish at Texas A&M by December 2014.

Diar Ibrahim presented preliminary results of his research at the AAPG/SEG Meeting at University of Oklahoma, Norman and the AAPG Sectional Meeting in Wyoming. Mario Lira presented preliminary results of his research at the National AAPG Meeting in Houston.

The main results of the research supported by this grant are:

1) detrital zircons for Middle-Late Ordovician quartz arenites of the western U.S. are remarkably similar indicating a uniform provenance from the Transcontinental Arch, mostly from the Trans-Hudson Orogen (1.8-1.9 Ga) and Archean terranes (2.5-2.9 Ga) such as the Wyoming Province. Almost all samples also include populations of 2.1 Ga zircons, and 0.8 – 1.2 Ga grains. The source for the 2.1 Ga grains is thought to be arc material associated with the Trans-Hudson Orogen, and the young zircons are derived from recycling Neoproterozoic-Cambrian quartz arenites.

2) detrital zircons for the Middle-Late Ordovician quartz arenites of the U.S. Midcontinent are quite dissimilar from the samples on the western side of the Transcontinental Arch containing major populations of 0.9-1.2 Ga, 1.4-1.5 Ga, 1.6-1.7 Ga, 1.8-1.9 Ga, and 2.4-2.8 Ga detrital zircon grains. The amount of Grenville age zircons, and zircons from 1.6-1.7 Ga (Yavapai-Matzatzal) source terranes are much larger than in the western US samples.

3) Changes in detrital zircon populations between the base and top of a unit (see TOC) indicates long-term sea level fluctuations controlled the source(s) of sediment for these units by burying or exposing the basement rocks along the Transcontinental Arch available for erosion and subsequent deposition.

4) There appears to be little recycling of pre-existing siliciclastic units during deposition of the Middle-Late Ordovician quartz arenites.

This grant has allowed me to follow an entirely new line of research, detrital zircon geochronology, and it has led to numerous collaborations at Texas A&M between Dr. Brent Miller, Dr. Tom Yancey, and me. The grant has allowed for a collaborative effort between Bill McClelland, Brian Witzke, and me. This grant has provided Research Assistantships for Mike Pickell and Mario Lira and provided the bulk of the funding for the analyses for Mike Pickell, Mario Lira, and Diar Ibrahim's theses. This research has taught these students quantitative techniques and how to integrate these into fundamental stratigraphic correlation to solve problems. These skills should provide all three of them with a good background for successful careers in the petroleum industry.