Early diagenesis of the Upper Devonian Escuminac Formation in the Gaspe ´ Peninsula, Que ´bec: sedimentological and geochemical evidence Abderrazzak El Albani a, * , Richard Cloutier b,c , Anne-Marie Candilier b a Laboratoire de Geobiologie et de Paleontologie, Universite ´ de Poitiers, UFR SFA, Bat. Sciences Naturelles, UMR 6046 40, avenue du recteur Pineau, F-86022 Poitiers Cedex, France b UPRESA 8014 du CNRS, Universite ´ des Sciences et Technologies de Lille, Sciences de la Terre, F-59655 Villeneuve d’Ascq Cedex, France c Parc de Miguasha, C.P. 183, Nouvelle G0C 2E0 Que ´bec, Canada Received 4 September 2000; accepted 27 April 2001 Abstract Clay mineral investigations, pyrolysis of organic matter, and microscopic observation of palynomorphs are used to interpret the diagenetic conditions of the Upper Devonian Escuminac Formation, Quebec, Canada. Pyrolysis of kerogen, vitrinite reflectance, and the presence of smectite show that the sediments of this formation have been subjected only to a shallow burial diagenesis; hence, the geochemical signatures are informative on the palaeoenvironment. Concretions are observed in the Escuminac Formation. Sedimentological and geochemical evidence suggest that these concretions were formed during early diagenesis from biodegradation of organic matter. The well-known fish-fauna of the Escuminac Formation show good preservation, due in part to extensive early diagenetic carbonate cementation. The occurrence of calcite cements and fibrous calcite is attributed to the early diagenetic transformation of pre-existing organic matter. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Escuminac; Fish; Preservation; Devonian; Diagenesis; Palaeoenvironment 1. Introduction The Escuminac Formation in south-eastern Que ´bec is known for its diverse and abundant Frasnian fossil fish assemblage (Schultze and Cloutier, 1996). For the past 30 years, the palaeoenvironmental interpre- tation of the Escuminac Formation has been a debated topic (Ve ´zina, 1991). The formation has been inter- preted as lacustrine (Dineley and Williams, 1968 a,b; Brideaux and Radforth, 1970; Hesse and Sawh, 1982; Gray, 1988; Rust et al., 1989), marine (Schultze, 1972; Schmitz et al., 1991; Cloutier et al., 1996), coastal marine (Schultze and Arsenault, 1985; Ve ´zina, 1991; Schultze, 1996), transitional (Chidiac, 1989, 1996), marine to brackish (Schultze and Cloutier, 1996), and estuarine (Hesse and Sawh, 1992; Cloutier et al., 1996). A series of geochemical parameters have been used to interpret the palaeoenvironmental con- ditions of the Escuminac Formation. The results of C, O, and B isotopes and B concentration (Chidiac, 1996), the 87 Sr/ 86 Sr, Na, F, Sr, and La analyses 0037-0738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0037-0738(01)00119-1 * Corresponding author. Tel.: +33-5-49453926; fax: +33-5- 49454017. E-mail address: abder.albani@univ-poitiers.fr (A. El Albani). www.elsevier.com/locate/sedgeo Sedimentary Geology 146 (2002) 209 – 223