Comparison of sediment composition by smear slides to quantitative shipboard data: a case study on the utility of smear slide percent estimates, IODP Expedition 353, northern Indian Ocean
Phillips, SC; Littler, K
Date: 25 February 2022
Journal
Scientific Drilling
Publisher
Copernicus Publications / German Research Centre for Geosciences / International Continental Scientific Drilling Program / International Ocean Discovery Program
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Abstract
Abstract. Smear slide petrography has been a standard technique during scientific ocean drilling expeditions to characterize sediment composition and classify sediment types, but presentation of these percent
estimates to track downcore trends in sediment composition has become less
frequent over the past 2 decades. We compare ...
Abstract. Smear slide petrography has been a standard technique during scientific ocean drilling expeditions to characterize sediment composition and classify sediment types, but presentation of these percent
estimates to track downcore trends in sediment composition has become less
frequent over the past 2 decades. We compare semi-quantitative smear slide composition estimates to physical property (natural gamma radiation, NGR)
and solid-phase geochemical (calcium carbonate, CaCO3 %)
measurements from a range of marine depositional environments in the
northern Indian Ocean (Bay of Bengal, Andaman Sea, Ninetyeast Ridge)
collected during International Ocean Discovery Program (IODP) Expedition 353. We show that presenting smear slide estimates as percentages, rather
than abundance categories, reveals similar downcore variation in composition
to the more quantitative core analyses. Overall downcore trends in total calcareous components from smear slides (foraminifers + nannofossils +
shell fragments + authigenic carbonate) follow similar downcore trends to samples measured by CaCO3 coulometry. Total lithogenic components
(clay + mica + quartz + feldspars + lithic grains + vitric grains
+ glauconite + heavy minerals + iron oxides) and clay from smear
slides track reasonably well with NGR measurements. Comparison of site
averages of absolute percentages of total calcium carbonate from coulometry
and total calcareous components from smear slide observations reveals an overestimation in carbonate percentages in smear slides (likely due in part
to underestimation of the clay fraction), especially in sediments rich in smectite clays. Differences in sediment color between sites and settling of
clay particles during slide preparation may contribute to this discrepancy.
Although smear slide estimates range in accuracy depending on the training
of the operator, we suggest that sedimentologists describing cores obtained
during scientific drilling can use the percent estimates of sedimentary
components in smear slides to identify trends and cyclicity in marine
sediment records.
Camborne School of Mines
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