Diagenetic Pore Fluid Evolution and Dolomitization of the Silurian and Devonian Carbonates, Huron Domain of Southwestern Ontario: Petrographic, Geochemical and Fluid Inclusion Evidence

Abstract

Core samples from two deep boreholes were analyzed for petrographic, stable and Sr isotopes, fluid inclusion microthermometry and major, minor, trace and rare-earth elements (REE) of different types of dolomite in the Silurian and Devonian carbonates of the eastern side of the Michigan Basin provided useful insights into the nature of dolomitization, and the evolution of diagenetic pore fluids in this part of the basin. Petrographic features show that both age groups are characterized by the presence of a pervasive replacive fine-crystalline (<50 µm) dolomite matrix (RD1) and pervasive and selective replacive medium crystalline (>50–100 µm) dolomite matrix (RD2 and RD3, respectively). In addition to these types, a coarse crystalline (>500 µm) saddle dolomite cement (SD) filling fractures and vugs is observed only in the Silurian rocks. Results from geochemical and fluid inclusion analyses indicate that the diagenesis of Silurian and Devonian formations show variations in terms of the evolution of the diagenetic fluid composition. These fluid systems are: (1) a diagenetic fluid system that affected Silurian carbonates and was altered by salt dissolution post-Silurian time. These carbonates show a negative shift in δ18O values (dolomite δ18O average: −6.72‰ VPDB), Sr isotopic composition slightly more radiogenic than coeval seawater (0.7078–0.7087), high temperatures (RD2 and SD dolomite Th average: 110 °C) and hypersaline signature (RD2 and SD dolomite average salinity: 26.8 wt.% NaCl eq.); and (2) a diagenetic fluid system that affected Devonian carbonates, possibly occurred during the Alleghenian orogeny in Carboniferous time and characterized by a less pronounced negative shift in δ18O values (dolomite δ18O average: −5.74‰ VPDB), Sr isotopic composition in range with the postulated values for coeval seawater (0.7078–0.7080), lower temperatures (RD2 dolomite Th average: 83 °C) and less saline signature (RD2 dolomite average salinity: 20.8 wt.% NaCl eq.).

Dolomitization of Paleozoic Successions, Huron Domain of Southern Ontario, Canada: Fluid Flow and Dolomite Evolution

“…The diagenetic history of the Cambrian, Ordovician, Silurian, and Devonian successions in the Huron Domain encompasses multiple episodes of calcite cementation, dolomitization, anhydrite cementation, mechanical and chemical compaction, dissolution, and silicification. It is understood (e.g., [2,3]) that these diagenetic processes occurred during deposition and continued upon burial. The paragenetic sequence shown in Figure 4 is based on petrographic relationships, spatial distribution, and geochemical evidence.…”

“…This program was then expanded to a regional scale, to determine if the conditions observed at the Bruce nuclear site were consistent across the Huron Domain of southern Ontario. Core samples from multiple deep boreholes within the Huron Domain of southern Ontario were analyzed for petrographic, stable, and Sr isotopic composition, fluid inclusion microthermometry, and major, trace, and REE to characterize diagenetic history, fluid composition, and sedimentary provenance (e.g., [2,3]).…”

“…Dong et al [14] showed that strata-bound dolostones form in a broad range of geologic and geochemical processes and generally result from large-scale fluid flow. Important aspects of dolomitization that need further thorough investigation are: (1) the source and supply of Mg [15,16]; (2) the plumbing mechanism necessary to transport Mg-bearing solutions to the site of dolomitization [17]; (3) the stoichiometry and recrystallization of dolomite [18][19][20][21][22][23], and (4) the effect of tectonics on the fluid flow [5,[24][25][26][27]]. An understanding of the genesis of ancient dolomites is only possible through detailed petrographic and geochemical studies of dolomitized sequences where the geologic history of the rocks is also reasonably well constrained.…”

“…Most recently, Al-Aasm [1], Al-Aasm and Crowe [2] and Tortola et al [3] assessed the nature and origin of strata bound dolomitization occurring in rock samples from Cambrian through Devonian carbonates and siliciclastics beneath the Bruce nuclear site and adjacent areas within southern Ontario. These latter studies better supported the notion of fluid compartmentalization between different stratigraphic successions.…”

Rift and salt-related multi-phase dolomitization: example from the northwestern Pyrenees

“…Examples of dolomitization are restricted to a single event either in an ancient carbonate platform with a well-known geodynamic evolution or in a modern carbonate platform, which provides the opportunity to identify the key control factors responsible for this diagenetic transformation and thus predict the distribution of dolomite in the carbonate platform (Adam and Rhodes, 1960;Barbier et al, 2011Barbier et al, , 2012Barbier et al, , 2015Butler et al, 1982;Choquette and Hiatt, 2008;Deffeyes et al, 1965;Illing, 1959Illing, , 1964Land, 1973;Sharp et al, 2010;Spencer-Cervato and Mullis, 1992;Stoakes, 1987;Wendte et al, 1998). In recent decades, many authors have described cases of pervasive dolomitization, which tends to be multi-phased, first relating to seawater in a near-surface to shallow burial environment and then caused by hydrothermal fluids channeled by structural pathways (Beckert et al, 2015;Biehl et al, 2016;Breesch et al, 2010;Cantrell et al, 2004;Di Cuia et al, 2011;Garaguly et al, 2018;Guo et al, 2016;Haeri-Ardakani et al, 2013a;Lukoczki et al, 2018;Tortola et al, 2020;Ye et al, 2019). In these numerous studies, temperature is one of the most critical parameters in the dolomitization reaction.…”