Wrench Fault Architecture of Trenton Black River Hydrothermal Dolomite Reservoirs

Smith, Langhorne B. and Richard E. Nyahay

Reservoir Characterization Group, New York State Museum, Albany NY 12230

Trenton –Black River hydrothermal dolomite reservoirs commonly occur in en echelon grabens associated with transtensional faults. These en echelon grabens have historically been linked to Reidel Shear faults associated with an underlying strike-slip fault.  Reidel shear faults “step” in the opposite direction of their sense of motion (i.e. right-stepping Reidel shears indicate left-lateral strike-slip). 

Newly obtained 3-D seismic data suggests that the en echelon grabens at Rochester Field, Ontario, and York Field, Ohio, may not have formed between Reidel Shear faults.  The structural highs and lows associated with the faults in these data sets appear to occur in the opposite quadrants of the fault zones that should occur with Reidel Shears.  The grabens (and structural highs) in these data sets were most likely formed by right-stepping, right-lateral en echelon faults.  The sense of step is the same as the sense of movement on the fault – the opposite of Reidel Shears. A good modern analog for this style of faulting is the Dead Sea transform fault system, which has deep basins forming where en echelon strike-slip faults overlap.

The origin of the fault architecture in these Trenton-Black River Fields is not currently understood but we have several working hypotheses: 1) the fields formed in transfer zones between extensional faults; 2) fault style was inherited from an earlier episode of faulting; 3) The faults initially moved as left-lateral faults and formed Reidel Shears and were then reactivated in a right lateral sense; or 4) some other model not currently under consideration.