ABSTRACT
This dissertation treats various aspects of the pre-Silurian
history of the northern Appalachians. The primary focus is western
New England, and the stratigraphy, structure, and emplacement
history of the Taconic Allochthon. Detailed mapping in the Lake
Bomoseen area (Plates 1-3) and previously completed mapping are
used to discuss the stratigraphy (Chapter 3) and structure
(Chapter 4) of the Allochthon. The lithostratigraphy of the
Giddings Brook slice is revised. The Cambrian? Bull Formation
(revised) of the Nassau Group (new) consists of the Mettawee Slate
facies (revised), Bomoseen, and Truthville Slate Members. The
Lower Cambrian to Middle Ordovician Browns Pond, Middle Granville
Slate (new), Hatch Hill (revised), Poultney (revised), and Indian
River Slate Formations constitute the Mount Hamilton Group
(revised). The West Castleton and White Creek are now considered
Members of the Hatch Hill Formation. The Mount Merino and Pawlet
Formations comprise the Willard Mountain Group (new).
Chapter 3 also emphasizes along- and across-strike variability in
the stratigraphy of the Giddings Brook slice. First-order
facies-controlled variations are used to divide the Giddings Brook
slice into a number of paleogeographically distinctive sequences
(Nappes of Chapter 7) derived from different positions on the
ancient continental rise. The most important structural
conclusions derived from the Lake Bomoseen area are that the
northern end of the Allochthon is bounded by a folded, D1 age
thrust (the Basal Thrust) associated locally with melange and
slivers of carbonate. Comparable DI thrusts with tectonic melanges
are recognized within the Allochthon. Large-scale D2 folds with an
associated axial surface slaty cleavage define the map pattern,
fold the Basal Thrust, but show variability in amplitude,
wavelength, and style within the Allochthon. An unfolded D3 thrust
fault (the Frontal Thrust) marks the western edge of the
Allochthon. Similar age thrusts are prominent within the
Allochthon. These D3 thrusts also imbricate the structurally
subjacent shelf, and may sole into the Champlain Thrust.
Biostratigraphic correlations of shelf and continental rise
sequences are used to examine the relationship between
transgressive-regressive history of the shelf with changes in type
of sediment and mode of sedimentation on the coeval continental
rise in Chapter 5. A close correlation is demonstrated.
Chapter 6 discusses the implications of (1) a completely
conformable stratigraphic relationship between the medial
Ordovician Pawlet flysch and underlying Taconic sequence in the
western Giddings Brook slice, and (2) Taconic-, metasedimentary-,
and volcanic-derived clasts within the Pawlet greywackes. These
observations suggest that the Allochthon was thrust-stacked from
east to west in an accretionary prism environment prior to being
emplaced onto the coeval shelf. Thrust stacking and obduction of
the Allochthon is correlated with a medial Ordovician
arc-continental margin collision.
Chapter 7 emphasizes the importance of recognizing the difference
between nappes and slices. Nappes are paleogeographically
distinctive stratigraphic assemblages, whereas slices are
structural assemblages of nappes juxtaposed along thrust faults
decorated with shelf-derived carbonate slivers. The stacking of
nappes pre-dates obduction onto the shelf whereas the stacking of
slices post-dates it. Models accommodating this distinction are
discussed.
The Champlain Thrust juxtaposes sequences of the early Paleozoic
shelf that differ markedly in facies, total thickness, thickness
per time interval, and age span represented by the sequences.
Chapter 8 outlines three trigonometric models for estimating
displacement on such thrusts based on the first-order,
pre-thrusting geometry of modern Atlantic-type shelf sequences.
Calculations of displacement for the Champlain Thrust using these
methods suggest that the parautochthonous shelf sequence, Green
Mountain anticlinorium, and Taconic sequence were transported
westward 80 km or more. This estimate is supported by recently
published seismic reflection data.
Chapter 9 analyzes the pre-Silurian stratigraphy of the northern
Appalachians and defines about a dozen 'suspect terranes' (Plate
9.1). Particular attention is paid to terranes that record medial
Ordovician tectonism. Plate tectonic scenarios are constructed to
attempt to explain the stratigraphic, structural, metamorphic, and
magmatic histories of these terranes.
Rowley, D.B., 1983. Operation of the Wilson Cycle in western New
England during the Early Paleozoic: with emphasis on the
stratigraphy, structure, and emplacement of the Taconic
Allochthon. Unpublished PhD dissertation, State University of New
York at Albany. 602pp. (2 volumes), +xxvi; 4 folded plates (maps)
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 1983 R78
Copies of this PhD dissertation can be ordered
from Proquest UMI
Front matter (title,
table of contents, abstract, acknowledgements) - 0.8MB pdf
file
Photo pages in dissertation
(colour
and greyscale photos with captions): - 11.1MB pdf file
(150dpi screen images); print
resolution pdf file 46.3MB
Plate 1 - Geological
Map of the Lake Bomoseen area, Vermont; Northern Taconic
Allochthon & Parautochthon
(uncoloured geological outcrop map; scale
1:12,000) 5.1MB pdf file
in scanned parts; greyscale pdf image files,
rows of three with overlap: 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Plate 2 - Cross
Sections
(of the Lake Bomoseen area) - 2.7MB pdf file
Plate 9.1 - Suspect
terrane map of the Appalachians - 1.7MB pdf file
Plate 9.2a - Early
Paleozoic stratigraphic columns of the Newfoundland
Appalachians, and Humber zone of Quebec and western New England
- 1.8MB pdf file
Plate 9.2b - Early
Paleozoic stratigraphic columns of the Quebec, New Bruswick and
New England Appalachians - 0.8MB pdf file
Appendix - Stratigraphic
names and sources for Suspect terrane map of the Appalachians
- 0.6MB pdf file
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