Detailed geologic maps are one of the most important tools
available to geologists for determining tectonic history. This
report is essentially a critique of selected maps (fig. 1), most
of which have been published since 1958 when currently accepted
concepts of the tectonic history of the region were first formulated
by R.J. Roberts and others. The purpose of this report is to
highlight the most significant stratigraphic and structural relations
displayed on these geologic maps, stressing the significance
of the maps individually and collectively for the tectonic history
of the region.
The age ranges of several stratigraphic units shown on many
of the maps are no longer valid, and the maps are unlikely to
be revised in the near future. Accumulating paleontological data
has led to improved stratigraphic concepts and therefore made
possible an improved understanding of the tectonic history. A
principal aim of this report is to make the revised ages of stratigraphic
units more widely known.
Existing maps represent tremendous physical and mental effort
by geologists over the last four or five decades, but unfortunately,
the tectonic interpretations in many cases seem to have been
driven more by ideology than by the observed structural relations.
As a result, interpretations are commonly at variance with the
map evidence as noted in the following pages.
This report necessarily demands much from the reader. For
maximum benefit from the discussions that follow, the reader
should examine the principal geologic maps to which reference
is made. Brief summaries of pertinent aspects of stratigraphy
and structure are presented, but to duplicate herein parts of
the many geologic maps to which reference is made, or to describe
in detail the stratigraphy and structure of each map area, would
be impractical. Simplified sketches of the maps would be useless;
the message is in the details.
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