Antun Husinec, PhD , St. Lawrence University
My students and I have now spent a total of 2 field seasons (summers of 2009 and 2010) or 8 weeks in total in North Dakota logging detailed cores through the Upper Ordovician Katian Red River carbonates and evaporites of the Williston Basin. We sampled the sections for facies and carbon and oxygen isotopes. We are presently doing lab sampling of rock samples for additional stable isotopes as well as for sulfur isotopes. The sections are being compiled into columnar sections on the computer, and porosity/permeability data is being plotted against facies to track its relationship. The available North Dakota Geological Survey (NDGS) wireline logs of non-cored wells with both gamma-ray and combined porosity-density curves are being digitized. Dolomites have been analysed for Ca, Mg, Mn and Sr for whole rock, as well as for C-O isotopes. Dolomites have also been analyzed by cathodoluminescence petrography to study the cement stratigraphy, and for stoichiometry by XRD. The available NDGS core plug data and thin-sections were analyzed for permeability-porosity relationship to facies.
The Upper Ordovician Katian Red River Formation is a carbonate-evaporite supersequence that formed within the intracratonic Williston basin, in the interior of the shallow and very broad, tropical, arid carbonate shelf that developed along the western passive margin of North America. It is an overall shallowing (and “brining”) upward supersequence up to ~210 meters thick, composed of three long-term, 3rd-order depositional sequences. The details of sequence framework and parasequences stacking were described in the last year’s report.
Samples for δ13C analysis were collected from three cores in western North Dakota, including: Simpson #1 (Williams County), Federal #10-1 (Dunn County), and Urlacher State Unit #1 (Hettinger County). The carbon isotope signal was split into stages in order to facilitate discussion and enable correlation with the North American carbon isotope stratigraphy. Eight carbon-isotope stages were identified based on positive excursions, shifts from positive to negative values, and relatively uniform values. I was able to document three major δ13C positive excursions in the Upper Ordovician succession of the Williston Basin; these excursions are stratigraphically above the Guttenberg (GICE) and below the Hirnantian (HICE) carbon isotope excursions, and can be correlated across the basin. The first excursion (RR-II) with an amplitude of up to 2‰ occurs in the “C”-laminated horizon. The second excursion (RR-IV) reaches an amplitude of 2‰. It is dated as mid-Richmondian in age, based on the occurrence of calcareous alga Dimorphosiphon in “B” interval. The third excursion (RR-VI) with an amplitude of 2-4‰ occurs in the middle part of the “A” interval, above the “A” anhydrite or “A” laminite interval. My very preliminary interpretation would be that the RR-II positive excursion corresponds to the Whitewater, the RR-IV to the Waynesville excursion of the mid-continent. The youngest Red River excursion (RR-VI) would fall above the preserved Richmondian succession in the Cincinnati region and below the Vaureal succession on Anticosti Island in Quebec.
Based on standard petrography and cathodoluminescence study of non-covered thin-sections, we were able to identify at least four major generations of the Red River dolomite. Generation I dolomite is found within burrows and commonly in association with hardgrounds. We suggest that the dolomitizing brines flowed downward through the nonlithified or poorly-lithified permeable burrows within early lithified limestones. This seepage reflux was driven by an increase in salinity towards the upper HST. Although with increased salinity, the environment was still inhabited by normal marine biota. Generation II formed syndepositionally as tidal flats prograded accross the basin during the late highstand systems tract. The association of these dolomites and evaporites suggests that the waters became Mg-charged through precipitation of gypsum, and were subsequently filtered down through the sediment at or very shortly after the time of deposition. Generation III dolomite is associated with stylolites and wispy dissolution (kerogenous) seams that were formed during compaction with increasing burial depth. Stylolites and seams served as conduits for alteration by dolomitizing fluids. Generation IV dolomite formed from reducing brines during late burial.
Dissemination of Results
Since the last project report, the research results were presented at the 2010 International Association of Sedimentologists Meeting (Mendoza, Argentina), the 2010 GSA Meeting (Denver, CO), the 2011 AAPG (Houston, TX). Presentations are also planned for the 2011 GSA in Minneapolis, and the 2012 AAPG (Long Beach, CA).
In addition, I am still working on a manuscript that focuses on carbon-chemostratigraphy of the upper Red River. My student Ben Rendall and I will soon submit a paper that focuses on algal biostratigraphy of the Red River to the Palaios journal.
The past AAPG convention in Houston has been very fruitful. My Red River research group has been recognized with awards three times: (1) Society for Sedimentary Geology (SEPM) Certificate of Recognition for an excellent technical oral presentation to Antun Husinec; (2) SEPM Best Student Poster Award, 1st place and $1,000 to Jake Colony; (3) SEPM Best Student Poster Award, 3rd place and $500 to Ben Rendall.
Recently, I have been awarded an internal grant from the St. Lawrence University to travel to Wyoming and sample for stable isotopes a section through the Bighorn Dolomite beds with abundant calcareous algae (Dimorphosiphon). These beds are time equivalent to the B-Interval of the Red River. The results and preliminary data of this study should enable me to submit a stronger proposal to the ACS in the near future. This proposal would logically expand upon my current research in North Dakota to the Bighorn Mountains, and potentially would advance the understanding of cyclic carbonate depositional systems and paleoceanographic and paleoclimatic changes across the Western United States during the Late Ordovician transition from greenhouse to icehouse Earth.