Emsian (Lower Devonian) conodont stratigraphy and correlation of the Anti-Atlas (Southern Morocco)


Authors: Aboussalam ZS, Becker RT, Bultynck P

Published in: Bulletin of Geosciences, volume 90, issue 4; pages: 893 - 980; Received 3 September 2014; Accepted in revised form 7 July 2015; Online 27 November 2015

Keywords: Emsian, conodonts, ammonoids, lithostratigraphy, biostratigraphy, chronostratigraphy, global events, Morocco,

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Based on revised previous records and many new data from the Tafilalt, Maider, eastern and western Dra Valley, the Emsian litho- and conodont biostratigraphy of the Anti-Atlas is reviewed, with some data on the Pragian below and the basal Eifelian above. More than 14.000 platform and single cone elements are assigned to 62 species/subspecies of 16 genera, partly in open nomenclature. The region is characterized by rather episodic polygnathid occurrences despite a predominant outer shelf biofacies with abundant dacryoconarids and goniatites. The studied Tafilalt polygnathid succession is as follows: rare records of Eoctenopolygnathus pireneae (Pragian), Eolinguipolygnathus excavatus Morphotype 114 Zone (basal Emsian, with Eol. radula sp. nov.), Eol. catharinae Subzone (of Eol. gronbergi Zone), Linguipolygnathus inversus Zone (with dominant Eol. jacksoni), Eol. laticostatus Zone (at the top of the lower Emsian), a regional basal upper Emsian interregnum (locally with the last L. inversus), L. bultyncki Zone (with L. cooperi cooperi Subzone), Polygnathus patulus Zone, Po. partitus Zone (basal Eifelian). Abundant icriodids provide an alternative zonation, from base to top with Latericriodus steinachensis Zone (lower/middle Pragian), Caudicriodus celtibericus Zone (upper Pragian/basal Emsian), Lat. bilatericrescens gracilis Zone, Lat. bilatericrescens bilatericrescens Zone, Lat. latus Zone, Icriodus fusiformis Zone (basal upper Emsian, with Icriodus ovalis sp. nov. and I. praerectirostratus sp. nov.), and I. corniger corniger Zone. Criteriognathus miae and Crit. steinhornensis provide an alternative ozarkodinid zonation in the Pragian to lower Emsian. The conodont sequences are correlated with the regional ammonoid zonations and global event succession. It contributes to the current chronostratigraphic revision of the Emsian. The Zinzilban basal Emsian GSSP level may project into the lower “Pragian Limestone” of the Tafilalt. The proposed revised basal Emsian GSSP level at the first appearance of Eol. excavatus Morphotype 114 is correlated in the Tafilalt with the base of the Devonobactrites Shale. A significant change of conodont faunas and facies took place at the top of the Mimagoniatites Limestone (main Daleje Event). The significant icriodid radiation of the I. fusiformis Zone is relevant for the debate on Emsian substage subdivision. Lenzites gesinae Klug, 2001 is designated as the type species of the new goniatite genus Klugites.