Structure, Dolomites Look Good

Some geologists refer to it as "HTD" or hydrothermal dolomite.

AAPG member Graham Davies uses the term "thermobaric" dolomite to acknowledge that high pressures are as important for dolomitization as the existence of hot, saline fluids.

(Davies also uses the term "implosion" dolomite to explain the processes that created rocks with breccia clasts "floating" in saddle dolomite crystals. He describes some hydrothermal dolomite fabrics as "ladder zebras" and "chevron zebras," adding a level of sophistication that includes a structural descriptor.)

"These are dramatic fabrics," explained Davies, president of Calgary-based Graham Davies Geological Consultants. "We're dealing with an extremely dynamic system that is not only temperature driven, but pressure driven."

Whatever the descriptor, this rock is characterized by coarsely crystalline, high temperature saddle dolomite, and forms the prolific reservoir trends of the Trenton-Black River that stretch across continental North America.

The Trenton-Black River fairway — containing the world class Albion-Scipio and Lima-Indiana oil fields — crosses into Canada where it is virtually unexplored to date.

An exploration renaissance, however, is under way in Canada's eastern provinces. Fueled by a new understanding of the mechanisms that create hydrothermal dolomites — and the critical role that wrench faults play as conduits for high pressure, high temperature dolomitizing fluids — Canadian oil and gas companies too are re-evaluating geological and geophysical data bases for Trenton-Black River potential.

Papers published by the mining industry indicate the very processes that generated Mississippi Valley Deposits have, in fact, created the HTD reservoirs that host commercial accumulations of oil and gas across North America.

Using a tool kit developed to explore for HTD plays in the Devonian and Mississippian strata of Western Canada the Northwest Territories, Canadian E&P firms are tackling Appalachia with new exploration analogs. Canadian firms familiar with the Rocky Mountain front have identified both thin-skinned and thick-skinned tectonics in Appalachia — analogous to leading edge or Triangle Zone geometries observed in the Rockies — that set up large thrust plays involving the Trenton-Black River formations.

Western Newfoundland

Western Newfoundland is a field geologist's paradise when it comes to teaching the theories of orogenesis and plate tectonics — very few places in the world can boast outcrops of oceanic basalts and pillow lavas juxtaposed against Cambro-Ordovician platform carbonates that have been thrusted during more than one orogeny.

Add hydrothermal dolomite reservoirs to the tectonic mix, and geologists get pretty … excited.

"This really was one of the proving grounds for plate tectonics, where Appalachia came together," said Steven Millan, chief executive officer and chairman of Newfoundland-based Canadian Imperial Venture Corporation (CIVC).