Fluid compartmentalization and dolomitization in the Cambrian and Ordovician successions of the Huron Domain, Michigan Basin

Evidence indicates that the formations were subjected to high temperatures (average 115 °C) that cannot be explained by burial history alone. This suggests the occurrence and migration of hydrothermal fluids within the low permeability dolomite horizons, possibly during Paleozoic orogenesis. Dolomite and calcite fracture infill isotopic and fluid inclusion data point to two possibly individual diagenetic fluid systems; i) an earlier Cambrian system that is characterized by a pronounced negative shifts in oxygen and carbon isotopic composition (δ18O average −9.0‰ for dolomite and −13.9‰ for calcite, respectively; and δ13C −3.06‰ for dolomite and −4.82‰ for calcite, respectively), a more radiogenic (Sr87/Sr86 ratios range from 0.70977 to 0.71100), warm (Th values range from 84 to 156 °C for dolomite; average 113.6 °C and 87-141 °C for calcite; average 101.5 °C) and saline signature (salinity range from 23.2 to 27.2 wt% NaCl eq for dolomite; average 24.3 for dolomite and 23.6 wt% NaCl eq for calcite); and ii) a later Ordovician system that is characterized by less negative shifts in both oxygen and carbon isotopes (δ18O average −8.7 ‰for dolomite and −7.5‰ for calcite; and δ13C average + 0.37‰ for dolomite and −0.36‰ for calcite, respectively), hypersaline (salinity range from 22.4 to 30.1 wt% NaCl eq.; average 27.0 for dolomite and 27.5 to 29.7 for calcite; average 29.2), comparable homogenization temperature (Th ranges from 85 to 132 °C for dolomite; average 109.6 °C and 66-153 °C for calcite; average 107.2 °C) and a less radiogenic (Sr87/Sr86 ratios range from 0.70818 to 0.71 000) fluid system. The observation of highly discrete, strata-bound dolomites combined with only trace quantities of saddle dolomite and its associated geochemical signature suggest that diagenesis, as a result of hydrothermal fluids, was neither pervasive in volume or extent within the north western Huron Domain.