--> Abstract: Widespread Hydrothermal Dolomitization of Ordovician Trenton and Black River Groups, Eastern North America, by Langhorne B. Smith and Graham R. Davies; #90078 (2008)

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Widespread Hydrothermal Dolomitization of Ordovician Trenton and Black River Groups, Eastern North America

Langhorne B. Smith1 and Graham R. Davies2
1New York State Museum, Albany, NY
2Graham Davies Geological Consultants (GDGC) LTD., Calgary, AB, Canada

Trenton-Black River hydrothermal dolomite reservoirs of eastern North America formed when hydrothermal fluids (80-170 degrees C) flowed up active margin-bounding and transtensional faults and dolomitized the formations within the first 500 meters of burial. An unequivocal hydrothermal origin can be demonstrated where primary fluid inclusion homogenization temperatures from the dolomites exceed maximum ambient burial temperatures by at least 10 degrees C. Using these criteria, virtually all of the dolomite found in the Trenton and upper parts of the Black River in Kentucky, Ohio, Michigan, Wisconsin and Ontario is of a hydrothermal origin. This is a very large volume of dolomite (hundreds to possibly thousands of cubic kilometers), that includes some areas of widespread, pervasive dolomitization.

An immense amount of fluid would be required to make that volume of dolomite, and new fluid flow models are required to solve the mass balance. These might include fault-driven forced episodic convection, recharge of basal aquifers that feed the faults by slowly descending saline brines sourced from seawater and/or mixing of hydrothermal fluids with in situ seawater at the site of dolomitization. Free convection in the absence of faults is not likely to play a significant role as permeability barriers would prevent hydrothermal conditions from developing. Additionally, there must be an element of fluid flow from the basement to explain fluid inclusion homogenization temperatures that commonly exceed the maximum ambient burial temperature for any part of the underlying sedimentary section.

This example, along with others such as the dolomitized Jurassic and Cretaceous of northern Saudi Arabia, suggests that hydrothermal dolomitization can be widespread and pervasive and should be considered along with other models when interpreting the origin of dolomitized reservoirs.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas