ABSTRACT
Stratigraphies previously proposed for the Taconic sequence of
southern Washington County, eastern New York, have incorrectly
defined and positioned lower Cambrian black slate units. The
proper sequence of Cambrian (?) through Cambrian lithologies is
(terminology from Jacobi, 1977): Bomoseen green wacke, Truthville
green slate, Browns Pond black slate, Mettawee purple and green
slate, and West Castleton and Hatch Hill black slates. This and
the entire Taconic sequence is conformable within the western
Giddings Brook slice. The detailed lithostratigraphy reported by
Jacobi (1977) and Rowley (1980) in northern Washington County can
be followed at least some 45 kilometers to the south (Fort Miller,
Schuylerville, Cossayuna and Cambridge 7½' quadrangles) in the
westernmost portions of the allochthon. Within some units,
variations between "sub-domains" can be recognized. Lithologic
characteristics suggest that each sub-domain records deposition at
slightly different positions (distal/proximal) on the
Cambro-Ordovician North American continental rise. These
stratigraphic sub-domains correspond with areas of internally
coherent structure (fold and cleavage orientation, sense of
structural facing). Together these define an assemblage of
imbricate thrust sheets within the western Giddings Brook slice.
The basal Taconic thrust and thrusts internal to the allochthon
cut obliquely across fold axes, hinge lines and cleavage in the
allochthon and the underlying Hudson flysch. Allochthon
emplacement clearly post-dates the earliest regional slaty
cleavage development and two generations of large-scale tectonic
folding. Tectonic slivers and fault rocks (Bald Mountain Terrane)
present along the basal Taconic thrust initially formed as the
allochthon ramped over the Cambro-Ordovician North American
continental shelf. The fold-thrust mode of deformation continues
in the underlying flysch sequence of the Hudson River lowlands.
The progressive development of structures observed within these
units is analogous to the formation of structures within the
leading edge of a subduction-accretion assemblage.
Halite single crystals loaded dry and then placed in brine are
preferentially dissolved at surfaces adjacent to regions of high
plastic strain. Riecke's Principle satisfactorily accounts for the
observed distribution of dissolution rates in these and the
circular hole experiments performed by Sprunt and Nur (1977), but
plastic strain probably dominates over elastic strain in the free
energy calculations. Faster dissolution of crystalline material
with high defect concentrations is the mechanism suggested to be
responsible for this phenomenon.
Although pressure gradients may dominate over strain energy terms
in chemical potential calculations along grain-to-grain contacts,
the role of permanent strain should be considered in the total
physicochemical process of diffusive mass transfer (pressure
solution). Of particular importance is knowledge of the rate
limiting step in the transfer sequence, which may occur at grain
boundary-pore fluid junctions. There the kinetics of
dissolution/precipitation may play a significant role.
The thermodynamic and kinetic criteria for equilibrium between
states are not truly equivalent. This becomes an important
consideration when forward and reverse reactions of a given change
of state occur by different reaction pathways, as may be the case
for dissolution/precipitation at a strained solid-fluid interface.
The possibility then arises that solution transfer mechanisms
exist which are driven by kinetic rate differentials rather than
the energy change between solid and solution state. A complete
theoretical analysis of any model designed to represent
solid-fluid interactions during deformation will require a
knowledge of state energy levels, reaction mechanisms and their
associated activation energies, and the various parameters of
diffusion within each state and along phase interfaces. Not only
must the effects of deformation through fluid-assisted diffusive
mass transfer be considered, but also the role of fluid phases in
the plasticity of crystalline material. These two general
processes may be easily confused in both experimental analogues of
geologic systems and the naturally occurring rocks themselves.
Bosworth, W.B., 1980. Structural geology of the Fort Miller,
Schuylerville and portions of the Schaghticoke 7½' quadrangles,
eastern New York, and its implications in Taconic geology; and
experimental and theoretical studies of solution transfer in
deforming heterogeneous systems. Unpublished PhD dissertation,
State University of New York at Albany. 237pp., +xv; 4 folded
plates (maps)
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 1980 B68
Copies of this PhD dissertation can be ordered
from Proquest UMI
Front matter (title,
table of contents, abstract, acknowledgements) - 0.45MB pdf
file
Photo pages in dissertation
(greyscale
photos
with captions) - 5.3MB pdf file
Plate 1 - Geological
Map of Gavettes and Bald Mtns (Taconic Allochthon near
Middle Falls, NY)
(coloured geological outcrop
map; scale 1:12,000) - 5.4MB pdf file
Plate 2 - Geological
Map of Schuyler and Willard Mtns (Taconic Allochthon near
Middle Falls, NY)
(coloured geological outcrop
map; scale 1:12,000) - 8.5MB pdf file
Plate 3 - Geological
Map of Hudson River Lowlands (Fort Miller and Schuylerville
Quadrangles)
(coloured geological outcrop
map; scale 1:24,000) - 12MB pdf file
Plate 3 - (trimmed
to map only) Geological Map of Hudson River Lowlands (Fort
Miller and Schuylerville Quadrangles)
(coloured geological outcrop
map; scale 1:24,000) - 8MB pdf file
Plate 4 - Geological
Cross Sections (of the Taconic Allochthon in the Fort
Miller-Schuylerville map area)
(coloured geological
cross-sections; scales 1:12,000 and 1:24,000) - 3.5MB pdf file
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