ABSTRACT
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
foreland basin.
3. Melt inclusion chemistry might be the more
effective tool for differentiating closely spaced K-bentonites
than that of apatite.