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Overview

My ACS-PRF project is focused on the Upper Ordovician Red River Formation, Williston Basin, North Dakota, which is an overall shallowing (and “brining”) upward supersequence composed of three third order depositional sequences. The supersequence is an example of very broad and shallow, tropical, arid carbonate shelf that developed along the western passive margin of North America.

The research on this project started in May 2009 with the first four-week fieldwork at the North Dakota Geological Survey Wilson M. Laird Core Library in Grand Forks, North Dakota; the second four-week fieldwork took place in May-June 2010. During the two field seasons, my students and I did a detailed bed-by-bed analysis of 34 cores spanning the upper Red River, and described in detail facies and their stacking patterns. We documented evaporite horizons (as 3^rd-order sequence boundaries), argillaceous horizons, and upward-shallowing parasequences and parasequence sets. We are now drafting columns in Illustrator®, and utilizing detailed stacking patterns of facies to define temporal changes in relative sea level. We sampled carbonate mud matrix of muddy carbonates for carbon and oxygen isotopes; three stable isotope profiles have been obtained based on 220 samples. We also sampled dolomites for trace elements; ICP mass spectrometry of 25 samples has been done by the ACME labs in Vancouver, BC.

Five students have worked on this project, and all continued to be involved. The participation of four of the students was supported through the grant, and one was funded by a St. Lawrence University fellowship. Each student has been able to focus on a particular aspect of the research, as follows: 1) Kyle Marvinney's research project centers on the stoichiometry of C-interval dolomites; 2) Katie Hoskinson's thesis will describe in detail facies and the facies stacking pattern of the B-interval; 3) Ben Rendall's research project examines on green algae as potential major carbonate producer during the Late Ordovician Katian; 4) Jake Colony's thesis is focused on the relationship between facies and porosity/permeability; and 5) Krystina Kornecki will construct detailed structural and isopach maps of different horizons and facies using the Surfer® software.

Preliminary Results

I was able to track three third-order sequences across the Williston Basin in North Dakota. The transgressive systems tracts of all sequences consist of subtidal, lagoonal facies of predominantly skeletal mudstone-wackepackstone with abundant burrow structures giving mottled appearance to the rock. The lower two sequences (Sequences 1 and 2) have highstand systems tracts composed of porous, peritidal laminated dolomites, whereas late HSTs consist of supratidal anhydrites. The late HST of Sequence 3 consists of peritidal laminites; anhydrite is present only in the basin depocenter and pinches out laterally. Lowstand systems tracts are not preserved in Williston Basin because of its updip position on a broad shallow shelf.

The mean d18O value for limestone is -6.1‰ PDB. The mean value for oxygen isotopes of dolomite whole rock is -4.87‰ PDB, i.e., on average, dolomites are 1.26‰ heavier than limestones. Such a small positive shift in oxygen isotope values between dolomite and limestone suggests that the dolomites picked up lighter signature due to burial at great depth (9,000 to 14,000 feet). The low strontium content (33-308 ppm) resembles Plio-Pleistocene Bahamian dolomites of inferred marine origin. The Red River dolomite isotope values overlap the strontium compositions of the Tertiary dolomites, but the oxygen isotopes are much lighter (5.5 to 10‰), suggesting recrystallization of the dolomite in the presence of isotopically more negative fluids. The high Mn2+ (mean value 151 ppm) and high Fe2+ (mean value 1082 ppm) in dolomite indicate that the pore waters were reducing and that a significant source of iron and magnesium was present; these values suggest that some of the early dolomites have been overprinted with burial.

The positive excursions in carbon isotopes and their possible relation to North American carbon chemostratgraphy (Bergstrom et al., 2008, 2010) are currently being tested.

Changes to the Research Plan

The original research plan was to log both the upper and the lower Red River. However, the cores through the lower Red River could not be found at the Core Library in Grand Forks. It is likely that these cores have never been recovered because the lower Red River is not a reservoir. Therefore, we focused on the upper part of the formation, and have logged the cores from all counties in North Dakota where Red River was recovered.

The new research equipment (XRD and SEM-CL) acquired through a private funding agency and the NSF (co-PI Antun Husinec) will enable us to study the diagenesis of dolomites.

Dissemination of Results

During the spring of 2010, these research results were presented at the 2010 Northeastern/Southeastern GSA Meeting (Baltimore, MD) and the 2010 American Association of Petroleum Geologists Annual Convention (New Orleans). More presentations are planned for the upcoming 2010 International Association of Sedimentologists Meeting (Mendoza, Argentina), the 2010 GSA Meeting (Denver, CO), and the 2011 AAPG (Houston, TX).

In addition, I am currently working on a manuscript that focuses on carbon-chemostratigraphy of the upper Red River.

Awards

Katie Hoskinson, who worked on the project last spring, won one of 15 Outstanding Undergraduate Student Poster Awards for her Red River poster presentation at the 2010 Joint Northeastern-Southeastern Sections Meeting of the Geological Society of America in Baltimore, Maryland. Some 253 undergraduate students presented posters at the meeting. Katie was also among four students acknowledged for their outstanding presentations by the Eastern Section of the Society for Sedimentary Geology (SEPM).

Future Plans

We will finish drafting all the columns and their respective wireline logs in Illustrator®, utilize facies stacking patterns, and analyze stable isotope and trace element data versus facies types. The work on the project continues with emphasis on X-Ray diffraction and cathodoluminescence analysis of dolomites.