Outcrop Analog
for Hydrothermal Dolomite Reservoirs, Mohawk Valley, New York
Slater, Brian1, Richard Nyahay1,
Langhorne B. “Taury” Smith1 (1) New York State Museum, Albany, NY
Field mapping and structural, petrographic and geochemical analysis of a brecciated dolomite outcrop in the Lower Ordovician Tribes
Hill Formation of central New York suggest that it was
produced by faulting and hydrothermal fluid flow. Comparison with 3-D seismic
data and field maps suggest that the outcrop is a scaled analog for Trenton / Black River hydrothermal dolomite
reservoirs of eastern North America. The dolomite occurs as
a series of en echelon bodies in a host limestone. Dolomitization
occurs in fault-bounded synclines or “sags” with common anticlines flanking the
sags. Most porosity is related to vugs and open
fractures with some matrix porosity. Fluid inclusions, stable isotopes,
strontium isotopes and trace element data all support a high temperature origin
for the dolomites from fluids that passed through basement rocks or immature siliciclastics prior to dolomitization.
Cores drilled in and around the dolomite bodies show that the dolomite extends
vertically to the base of the formation with some degree of facies
control on dolomitization away from the faults.
Trenches cut across the outcrop help relate offset along faults to the overall
geometry of the dolomitized bodies. The faults appear
to be associated with right-lateral oblique strike slip motion with a component
of extension. Some faults change their sense of dip and motion as they cross
the dolomitized feature which is to be expected in a
wrench fault system. The exposure helps better understand highly complex
hydrothermal dolomite reservoirs.