Atmospheric
Dust Archived in Pennsylvanian Carbonates of the
Sur, Sohini1, Gerilyn S. Soreghan2 (1)
Detrital fraction varies through
glacial-interglacial cycles in Upper Pennsylvanian carbonate mounds of the
Horseshoe Atoll, Midland basin. We are testing the hypothesis that these
variations reflect atmospheric dust flux and influenced shifts in productivity.
The studied core spans 2 carbonate glacio-eustatic
sequences that contain a small but measurable detrital
(inferred eolian) fraction. We conducted
high-resolution sampling (10 cm) to assess variation and grain size of the detrital fraction using low-field mass-specific magnetic
susceptibility (MS), detrital residue (via various
dissolution steps) volume and grain-size measurements. Our initial approach
using MS to assess variations of the detrital
fraction shows very high-frequency fluctuations within sequences and a general
increase (~1.5 times) close to the sequence boundaries. These data track
preliminary results of detrital residue volume and
grain size in that concentration and grain size of the detrital
fraction increase proximal to sequence boundaries, likely reflecting greater
aridity and/or lowered sea level combined with higher wind strength during
incipient glacials to incipient interglacials.
Currently we are exploring the promising relationship between MS and the detrital residue volume and grain size. If these co-vary,
then MS may be a proxy for detrital fraction/dust
flux and/or the relative wind intensity. We are also assessing the hypothesis
that high-frequency fluctuations in MS track high-frequency climate change and
variations in detrital fraction might cause shifts in
productivity via dust-induced nutrient seeding. The latter might also help
explain development of classic “cyclothemic” black shales, alternatively explained as a product of
upwelling-induced productivity, or anoxia resulting from salinity
stratification.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California