Abstract
Detailed analysis of Lower to Middle Devonian K-bentonites in the
Appalachian Basin reveals physical and geochemical characteristics
within supposed single eruptive event deposits that indicate a
more
complex depositional history is recorded in many of these volcanic
beds. Variations in bedding showing multiple coarse and
fine-grained
layers within a K-bentonite layer can be seen in some Devonian
K-bentonite beds. Microscopic irregularities show variations in
the
orientation of volcanic grains, and subtle phenocryst layers
within a
K-bentonite suggest changes in depositional environment where
changing
water and wave regimes rework and redeposit material on the sea
floor.
The presence of fossil layers within the same K-bentonite across
the
basin suggests that the bed records colonization by marine fauna
during
its deposition. In addition, geochemical, inconsistencies within
the
same layer show evidence that these layers may record more than
one
eruptive event in a single layer. Based on the analytical methods
used
in this study many K-bentonite beds are shown to record a more
complex
preservational and eruptive history than previously thought. By
examining physical, petrologic, and elemental geochemical
characteristics of these beds, it is seen that many Devonian
K-bentonite beds do not in all cases represent the altered remains
of
single eruptive events.
K-bentonites either (1) contain volcanic material from a single
eruptive event, (2) are the result multiple eruptive events,
expressed
as a subtle, multiple-layered K-bentonite, or (3) a mixing of
volcanic
material from a few to many ashfall events where no
distinguishable
boundary can be seen. The presence of distinctive physical
features
within layer samples and/or inconsistent trace elemental
abundances
within phenocrysts from subdivisions of the same bed support the
interpretation that more than one eruptive event may have taken
place.
Data collected in this study strongly supports modern ideas that
many
Devonian K-bentonites contain more significant volcanic
information
than previously thought.
Benedict, L., 2004. Complexity of Devonian K-bentonites in the
Appalachian foreland basin: geochemical and physical evidence
supporting multi-layered K-bentonite horizons.
Unpublished MSc. thesis, State University of New York at Albany.
244
pp., +xiii
University at Albany Science Library call number: SCIENCE
Oversize
(*) QE 40 Z899 2004 B46
MS thesis text scanned
image pdf (8.2MB)
Appendix 1 - Sample
Localities (greyscale scanned image pdf 7.2MB)
Appendix 2 - Geochemical
Data (greyscale scanned image pdf 14.7MB)
Return to MS Theses completed in the
Geological
Sciences Program, University at Albany