Distribution of benthic foraminiferal populations in surface sediments of the Saguenay Fjord, before and after the 1996 £ood Julie Leduc a; Ã , Guy Bilodeau a , Anne de Vernal a , Alfonso Mucci b a Centre de recherche en ge ¤ochimie isotopique et en ge ¤ochronologie (GEOTOP), Universite ¤ du Que ¤bec a ' Montre ¤al, P.O. Box 8888, Succursale Centre-Ville, Montreal, QC, Canada H3C 3P8 b Earth and Planetary Sciences, McGill University, 3450 University street, Montreal, QC, Canada H3A 2A7 Received 6 March 2001; accepted 19 September 2001 Abstract In the summer of 1996, a ‘flash’ flood occurred in the Saguenay-Lac-St-Jean region (Quebec) leading to the deposition, in less than 2 days, of an estimated 6^15U10 6 m 3 of sediments at the head of the Saguenay Fjord. In order to evaluate the impact of such a sedimentary event on the benthic meiofauna, foraminiferal analyses were performed in surface sediment at eight stations in 1994, 1997, 1998 and 1999 along the main axis of the fjord. A 10-cm sedimentary sequence taken from a box core collected in 1997 from the deepest part of the fjord and spanning the last ca. 35 years provides a reference state for pre-flood foraminiferal assemblages. A significant change in foraminiferal assemblages is observed downcore, with the decrease of Spiroplectammina biformis relative to Adercotryma glomerata. 210 Pb measurements suggest that this change occurred during the late 1970s. Surface samples (0^1 cm) collected between 1997 and 1999 in the inner basin also reveal a decrease of S. biformis percentages. Given the relative stability of this environment, such a change in faunal assemblages could be related to reduced industrial waste inputs or to a differential preservation of taxa. The 1996 flood had a major negative impact on the concentration and species diversity of benthic populations near the head of the fjord (Baie des Ha! Ha!), where the flood material is up to 50 cm thick. However, two years after the flood, benthic foraminiferal populations recolonized the sediments in the Saguenay Fjord. ß 2002 Elsevier Science B.V. All rights reserved. Keywords: foraminifera; benthic; distribution; Saguenay Fjord; £ood 1. Introduction The Saguenay Fjord is a strati¢ed marine envi- ronment characterized by variable sedimentation rates, from 0.2 cm/yr to a few centimeters per year (e.g. Smith and Walton, 1980). It has been the site of many dramatic geological events over the past centuries (Smith, 1962). These include several strong earthquakes (Smith, 1962; Basham et al., 1985) and landslides, such as the Kenogami and St-Jean-Vianney landslides which occurred in 1924 and 1971, respectively (Schafer and Smith, 1988). Moreover, the Saguenay Fjord has been a¡ected by industrial activities upstream and 0031-0182/02/$ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0031-0182(01)00429-1 * Corresponding author. Fax: +1-514-987-3635. E-mail address: leduc.julie@uqam.ca (J. Leduc). PALAEO 2788 21-5-02 Palaeogeography, Palaeoclimatology, Palaeoecology 180 (2002) 207^223 www.elsevier.com/locate/palaeo