First application of high-resolution X-ray computed tomography to quantify the fossil record of foraminifera: The Nicola bed, Monte San Nicola, Sicily; type area for the Quaternary System

Abstract

The distinctive microlaminated Nicola bed marks the base of the Quaternary System at the type locality of Monte San Nicola in southern Sicily. We have analysed a sediment block that traverses the Nicola bed at the Mandorlo section located ∼400 m WNW of the GSSP. Primary sedimentological and ichnofabric analysis of the polished surface combined with X-ray computed tomography (CT) reveals changes in dissolved bottom water oxygen levels before, during and after deposition of the Nicola bed, beginning with a progressive but rapid transition to anoxia at its onset. A more gradual recovery to oxygenated conditions followed Nicola bed deposition. Planktonic foraminifera are recognised by X-ray CT as either empty or infilled near-spherical voids, and the individual volume (≈size) is estimated for each test in addition to its position in the sediment block. Pronounced foraminiferal abundance peaks through the Nicola bed, with a frequency of hundreds of years, suggest (quasi-)cyclical changes in the mixed layer of the water column, thereby implicating either high-frequency oscillations within the climate system or the long-term modulation of solar cycles. This is the first study to explore the distribution of foraminiferal tests through a sediment block using X-ray CT, revealing its potential as an inexpensive non-destructive method for the quantitative study of microfossils at extremely high stratigraphic resolution.