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

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