Abstract

NUNEZ-RICARDO, S; MARCHANT, M; HAYWARD, B  and  HEBBELN, D. Mid-Pleistocene"Stilostomella extinction event" off northern Chile (25°S). Cienc. mar [online]. 2007, vol.33, n.3, pp.301-309. ISSN 0185-3880.

Based on sediment samples from core site GeoB 3388-1 from the Iquique Ridge off northern Chile (25°S), we report the last appearance datum (LAD) of seven species that belong to the Stilostomella extinction group. The Stilostomella extinction was the last major turnover in deep-sea benthic foraminifera. It is documented in previous works for the southeastern Pacific (SEP) and is extended here by our results, giving further qualitative indication of this important extinction event. The Stilostomella extinction involves the disappearance of elongate species presenting cribrate (Chrysalogonium), slit lunate, hooded with two teeth (Pleurostomellidae), or secondarily toothed and necked (Stilostomellidae) apertures. The LAD of Myllostomella sp. Hayward 2002 (518 cm, 0.79 Ma) in core GeoB 3388-1 is remarkably consistent with a previous record for the SEP, but is prior to other previous worldwide reports (0.65-0.57 myr); thus, we conclude that the timing of the SEP extinction was different from that in the Atlantic Ocean and southwestern Pacific. Additionally, the LAD of Myllostomella sp. corresponds to an increase in both benthic δ¹³C and CaCO₃ content, suggesting that a profound change in nutrient availability and circulation occurred in the SEP during the Mid-Pleistocene Transition. The precise mechanistic cause of the Stilostomella extinction (cooling, increased oxygenation of bottom waters, changes in food supply) is yet to be resolved.

Keywords : Stilostomella group; Pleistocene; deep-sea benthic foraminifera; southeastern Pacific; Chile.

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