DOCUMENTING THE EFFECT OF POST-SAMPLING CALCAREOUS MICROFOSSIL DISSOLUTION IN ORGANIC AND/OR PYRITE-RICH SEDIMENTS USING THREE SAMPLING TECHNIQUES

Use of calcareous microfossils is central to many research applications, from biostratigraphy to geochemistry. However, the effects of post-sampling and/or post-coring dissolution in organic or pyrite-rich sediments are not well understood and are rarely taken into account, even though they can have a significant impact on the data. Sediment type plays a significant role in determining how much dissolution occurs and how quickly it proceeds, and it was assumed that dissolution would occur at a faster rate in sediments that contained greater amounts of pyrite, lignite, and glauconite.

In an attempt to understand the mechanics of dissolution and how it effects calcareous microfossil abundance and geochemistry, three different methods of short-term storage preservation were tested for efficacy: vacuum packing, argon gas replacement, and buffered water. These methods were intended to halt or slow down the dissolution process by either a) limiting the availability of oxygen to the system, thereby slowing the oxidation-reduction reaction or b) increasing the rate of acid consumption by increasing the alkalinity of the system. Abundance counts of calcareous nannofossil assemblages over a six-month period tracked dissolution trends in both siliclastic and carbonate-rich sediments. In most cases, slides made in the field had more abundant calcareous nannofossils than slides made from sediments stored via vacuum packing, argon gas replacement, or buffered water. Thin section and XRD analyses showed that less than 1% pyrite was enough to drive the oxidation-reduction reaction that resulted in dissolution, even in carbonate-rich sediments.