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

Marco Tortola,Richard Crowe,Ihsan S. Al-Aasm

doi:10.3390/min10020140

Marco Tortola, Richard Crowe + Show 1 more

Open Access

https://doi.org/10.3390/min10020140

Copy DOI

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.).

Highlights

The Michigan Basin has been the subject of several diagenetic studies in the last three decades (e.g., [1,2,3,4,5,6,7,8])
Four types of dolomite occur in the Silurian formations (Figure 4) and are classified following the criteria proposed by Sibley and Gregg [47]
Examination of cores, petrographic studies, microthermometric and geochemical analyses of Silurian and Devonian carbonates of the eastern side of the Michigan Basin (Huron Domain) led to the following conclusions regarding dolomitization and other related diagenetic processes observed in these successions:

Summary

Introduction

The Michigan Basin has been the subject of several diagenetic studies in the last three decades (e.g., [1,2,3,4,5,6,7,8]). Guelph limestones to the center of the Michigan basin (e.g., [6,7,8]). Numerous diagenetic processes such as dolomitization and Mississippi Valley Type (MVT) mineralization, salt dissolution, precipitation of late-stage cement and oil, and gas generation and migration have influenced the Paleozoic succession in the Michigan Basin [9]. The presence of fractures and faults in the Michigan intracratonic Basin represented an important control on the modification of host limestones and mobilization of dolomitizing fluids within the basin [4,10,11,12]

Objectives

Methods

Results

Conclusion