Geochemical fingerprinting of volcanic airfall deposits: A tool
in stratigraphic correlation
Soumava Adhya 2009
A Dissertation Submitted to the State University of New York at
Albany in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
College of Arts and Sciences, Department of Earth & Atmospheric
Advisor: J.W. Delano
Biotite phenocrysts, melt inclusions in quartz and plagioclase
phenocrysts, and glass shard chemistry of proximal and distal YTT
ash successfully discriminate it with other closely spaced ash
layers. This research reports for the first time, the presence of
melt inclusion bearing plagioclase from Pleistocene volcanic ash
from India and correlates it chemically to the YTT. The Pleistocene
ash from Sulu Sea ODP was not produced by YTT eruption.
Chemical fingerprints of volcanic airfall
deposits obtained from high-precision electron microprobe analysis
of glass and phenocrysts phases provide geochemical correlations
with temporal precision unattainable by other methods. In this
research electron microprobe analysis (EMA) techniques, to
fingerprint chemically and correlate fresh and altered volcanic
airfall deposits, have been utilized to test the value of this
tool for future research on stratigraphic correlation. The
following samples were chosen from within a variety of sedimentary
rocks widely separated spatially and temporally:
~450 Ma old upper Middle Ordovician
K-bentonites (altered volcanic airfall deposits) collected from
eastern United States.
Relatively fresh Pleistocene tuff from ~74 ka
old Youngest Toba Tuff (YTT) eruption in Sumatra (Indonesia).
Fresh Pleistocene volcanic ash from India, and
Sulu Sea ODP cores.
This research confirms 14 K-bentonite correlations, of which 10
are reported for the first time, based on chemical compositions of
apatite phenocrysts and melt inclusions in quartz phenocrysts.
Significant K-bentonite research findings include:
1. Chemical correlation of Hounsfield
K-bentonite and the Milibrig K-bentonite.
2. Several new chemical correlations of
K-bentonite beds from within the Ordovician rocks in Taconic
3. Melt inclusion chemistry might be the more
effective tool for differentiating closely spaced K-bentonites
than that of apatite.
The best discriminating elements observed are:
1. Toba biotites - Mn, Ti, Cl, Mg and Fe.
2. Ordovician apatites - Mn, Mg, Fe, Cl, and F
3. Melt inclusions and glass shards - Ca, Fe, Mg,
Mn, Cl, Ti, K and Na.
Using a dual approach, i.e., glass as well as phenocryst chemical
signatures, makes a better tool for differentiating or correlating
vertically closely spaced or geographically widely spaced volcanic
Adhya, S., 2009. Geochemical fingerprinting of volcanic airfall
deposits: A tool in stratigraphic correlation. Unpublished PhD
dissertation, State University of New York at Albany. 346 pp.,
+ xi, +186 pp. appendices.
University at Albany Science Library call number: SCIENCE MIC
Film QE 40 Z899 2009 A34
Copies of this PhD dissertation can be ordered
from Proquest UMI (a digital text pdf is available, with
colour photos and diagrams; 9MB)
Front matter (title,
table of contents, abstract, acknowledgements) - 0.16MB pdf
PhD dissertations completed in the Geological Sciences
Program, University at Albany