Research suggests significant basin re-heating event in past
Research suggests significant basin re-heating event in past
Numerous studies of the shallow subsurface strata layers suggest that the basin has undergon a significant hydrothermal event in the recent past. Our proposed cosmic impact at the Saginaw Bay and across the central Michigan Peninsula may have provided the necesary energy by way of compressive shock waves traveing through the structure. We have highlighted a few passages from the excerpts below in bold for emphasis.
Atmospheric noble gas signatures in deep Michigan Basin brines as indicators of a past thermal event
Lin Ma (a) , Maria Clara Castroa, and Chris M. Halla,
a) Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building, Ann Arbor, Michigan, USA
Earth and Planetary Science Letters 277 (2009) 137–147
Received 27 May 2008; revised 9 October 2008; accepted 10 October 2008. Editor: R.D. van der Hilst. Available online 28 November 2008.
Abstract
Atmospheric noble gases (e.g., 22Ne, 36Ar, 84Kr, 130Xe) in crustal fluids are only sensitive to subsurface physical processes. In particular, depletion of atmospheric noble gases in groundwater due to boiling and steam separation is indicative of the occurrence of a thermal event and can thus be used to trace the thermal history of stable tectonic regions. We present noble gas concentrations of 38 deep brines (~0.5–3.6 km) from the Michigan Basin. The atmospheric noble gas component shows a strong depletion pattern with respect to air saturated water. Depletion of lighter gases (22Ne and 36Ar) is stronger compared to the heavier ones (84Kr and 130Xe). To understand the mechanisms responsible for this overall atmospheric noble gas depletion, phase interaction models were tested. We show that this atmospheric noble gas depletion pattern is best explained by a model involving subsurface boiling and steam separation, and thus, consistent with the occurrence of a past thermal event of mantle origin as previously indicated by both high 4He/heat flux ratios and the presence of primordial mantle He and Ne signatures in the basin. Such a conceptual model is also consistent with the presence of past elevated temperatures in the Michigan Basin (e.g., ~80–260 °C) at shallow depths as suggested by previous thermal studies in the basin.We suggest that recent reactivation of the ancient midcontinent rift system underneath the Michigan Basin is likely responsible for the release of both heat and mantle noble gases into the basin via deep-seated faults and fracture zones. Relative enrichment of atmospheric Kr and Xe with respect to Ar is also observed, and is interpreted as reflecting the addition of sedimentary Kr and Xe from associated hydrocarbons, following the hydrothermal event. This study pioneers the use of atmospheric noble gases in subsurface fluids to trace the thermal history of stable tectonic regions. © 2008 Elsevier B.V. All rights reserved.
Conclusions
We present noble gas concentrations in 38 deep brines (~0.5– 3.6 km) from the Michigan Basin. The atmospheric noble gas components (22Ne, 36Ar, 84Kr, and 130Xe) show a strong depletion pattern with respect to ASW with depletion of lighter gases (22Ne and 36Ar) being stronger compared to heavier ones (84Kr and 130Xe). To understand the mechanisms responsible for this overall atmospheric noble gas depletion, phase interaction models were tested. While oil– water and gas–water interaction models could not, under reasonable assumptions, explain both the extent and the observed atmospheric noble gas depletion pattern, the opposite is truewith amodel involving subsurface boiling and steam separation. Indeed, the latter not only explains the overall observed atmospheric noble gas depletion pattern, it also points strongly to the presence of a past hydrothermal event. This finding is consistent with the presence of primordial solar-like He and Ne signatures in the basin previously identified in these same brines (Castro et al., submitted for publication), and suggests a mantle origin for the occurrence of this thermal event. Such a boiling and steam separation model is also consistent with the presence of past elevated temperatures in theMichigan Basin (e.g., ~80–260 °C) at shallow depths as suggested by numerous previous studies in the basin.We suggest that recent reactivation of the ancient mid-continent rift (MCR) system underneath the Michigan Basin is likely responsible for the release of both heat and mantle noble gases into the basin via deep-seated faults and fracture zones. While heat has already escaped the system, such a thermal event can still be traced by the presence of the observed atmospheric noble gas depletion in addition to the previously identified high 4He/heat flux ratio at shallow depths in the basin (Castro et al., 2005, 2007). Enrichment of atmospheric Kr and Xe relative to Ar is also observed in these brines, an enrichment that cannot easily be solely accounted for by the boiling and steam separation model. This relative enrichment is interpreted as reflecting the addition of sedimentary Kr and Xe from associated hydrocarbons, probably during hydrocarbon generation and/or hydrocarbon migration and accumulation. Such enrichment would have occurred following the hydrothermal event that led to the boiling and steam separation of atmospheric noble gases and consequently, their depletion with respect to ASW. This study pioneers the use of atmospheric noble gases in subsurface fluids to trace the thermal history of stable tectonic regions.
Fractured hydrothermal dolomite reservoirs in the Devonian Dundee Formation of the central Michigan Basin
AAPG Bulletin; November 2006; v. 90; no. 11; p. 1787-1801; DOI: 10.1306/06270605082
© 2006 American Association of Petroleum Geologists (AAPG)
John A. Luczaj 1, William B. Harrison, III 2 and Natalie Smith Williams 3
1 Department of Natural and Applied Sciences, University of Wisconsin–Green Bay, Green Bay, Wisconsin 54311; luczajj@uwgb.edu
2 Michigan Basin Core Research Laboratory, Western Michigan University, Kalamazoo, Michigan 49008; harrison@wmich.edu
3 Department of Geosciences, Western Michigan University, Kalamazoo, Michigan 49008
Abstract
The Middle Devonian Dundee Formation is the most prolific oil-producing unit in the Michigan Basin, with more than 375 million bbl of oil produced to date. Reservoir types in the Dundee Formation can be fracture controlled or facies controlled, and each type may have been diagenetically modified. Although fracture-controlled reservoirs produce more oil than facies-controlled reservoirs, little is known about the process by which they were formed and diagenetically modified.
In parts of the Dundee, preexisting sedimentary fabrics have been strongly overprinted by medium- to coarse-grained dolomite. Dolomitized intervals contain planar and saddle dolomite, with minor calcite, anhydrite, pyrite, and uncommon fluorite. Fluid-inclusion analyses of two-phase aqueous inclusions in dolomite and calcite suggest that some water-rock interaction in these rocks occurred at temperatures as high as 120–150°C in the presence of dense Na-Ca-Mg-Cl brines. These data, in conjunction with published organic maturity data and burial reconstructions, are not easily explained by a long-term burial model and have important implications for the thermal history of the Michigan Basin. The data are best explained by a model involving short-duration transport of fluids and heat from deeper parts of the basin along major fault and fracture zones connected to structures in the Precambrian basement. These data give new insight into the hydrothermal processes responsible for the formation of these reservoirs.
