Paleozoic fluid history of the Michigan Basin; evidence from dolomite geochemistry in the Middle Ordovician St. Peter Sandstone

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doi: 10.1306/D42680A9-2B26-11D7-8648000102C1865D
Authors:Winter, Bryce L.; Johnson, Clark M.; Simo, J. A.; Valley, John W.
Author Affiliations:Primary:
University of Wisconsin-Madison, Department of Geology and Geophysics, Madison, WI, United States
Volume Title:Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes
Source:Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes, 65(2), p.306-320. Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States. ISSN: 1073-130X
Publication Date:1995
Note:In English. 50 refs.; illus., incl. 3 tables, geol. sketch maps
Summary:The isotope (Sr and O) and elemental (Mg, Ca, Mn, Fe, and Sr) compositions of the various dolomites in the Middle Ordovician St. Peter Sandstone in the Michigan Basin are determined and the variations are modeled in terms of fluid-rock interaction or as mixing relations. These geochemical models, combined with the paragenetic sequence of the dolomites and late anhydrite cement, suggest the existence of at least four distinct diagenetic fluids in the St. Peter Sandstone during the Paleozoic. Fluid 1 (Sr = 30 ± 10 ppm, Sr/Ca = 0.019, 87Sr/86Sr = 0.7093 ± 1) has a composition consistent with a modified older (pre-Middle Ordovician) seawater origin, which indicates that the flow path for this fluid had a major upward component. This fluid resulted in the first and volumetrically most important burial dolomitization event, producing dolomite in both carbonate and quartz sandstone lithofacies in the St. Peter Sandstone. Fluid 2 (Sr = 30 ± 10 ppm, Sr/Ca = 0.019, 87Sr/86Sr = 0.7084 ± 1, low Fe) has a composition consistent with a modified Middle to early Late Ordovician seawater origin, suggesting a major downward component for fluid flow. Fluid 2 produced dolomite cement in the carbonate lithofacies that postdates Fluid 1 dolomite. The composition of Fluid 3 (Sr > 50 ppm, Sr/Ca = 0.044-0.110, 87Sr/86Sr = 0.710-0.711, high Fe) is best interpreted to reflect a heated, deep basinal brine that had previously interacted with the K-feldspar-rich rocks near the Cambrian-Precambrian unconformity in the Michigan Basin, indicating a major upward component for fluid flow. Fluid 3 produced dolomite cement in quartz sandstone lithofacies that postdates Fluid 1 dolomite. Fluid 4 (87Sr/86Sr = 0.7085 ± 1) resulted in precipitation of late anhydrite in fractures. The 87Sr/86Sr ratio of the anhydrite is consistent with Fluid 4 originating as a dilute fluid that interacted extensively with Silurian gypsum in the Michigan Basin; this indicates that the flow path of Fluid 4 had a major downward component. The St. Peter Sandstone was an important migration pathway for many different types of fluids in the Michigan Basin, and the proposed fluid origins indicate that both upward and downward cross-formational fluid flow occurred during the Paleozoic. Older and younger modified seawater produced most of the burial dolomite in the St. Peter Sandstone.
Subjects:Alkaline earth metals; Carbonates; Diagenesis; Dolomite; Isotope ratios; Isotopes; Metals; Middle Ordovician; O-18/O-16; Ordovician; Oxygen; Paleozoic; Saint Peter Sandstone; Sr-87/Sr-86; Stable isotopes; Strontium; Water-rock interaction; Bay County Michigan; Clare County Michigan; Crawford County Michigan; Gladwin County Michigan; Michigan; Michigan Basin; Michigan Lower Peninsula; North America; United States
Coordinates:N443000 N445200 W0842200 W0845200
N434800 N441000 W0843700 W0850800
N434500 N441000 W0841000 W0843700
N433000 N440000 W0834500 W0841000
Abstract Numbers:95M/4510
Record ID:1995039860
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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