First occurrence of a phacopid trilobite faunule from the Upper Devonian of Saoura Valley, Algeria and biodiversity fluctuations

Abstract

Phacopid trilobites are relatively widespread in Devonian deposits of north Gondwana and some have been collected from several sections of the Saoura Valley in SW Algeria. New occurrences of phacopids assigned to Trimerocephalus, Dianops and Phacops sensu lato are described from this area and comparisons are made with closely allied species from Morocco and Europe. The trilobite assemblages of the ‘Argiles de Marhouma’ Formation are considered to be Frasnian–Famennian in age. These new occurrences have been integrated into an analysis of Upper Devonian phacopid biodiversity. Diversity fluctuations reflect environmental changes, bioevents and stratigraphic turnovers throughout the Upper Devonian. Peak diversity was attained after the post-Kellwasser event.

New Late Devonian phacopid trilobites from Marhouma, SW Algerian Sahara

“…In the upper part of the "Argiles de Marhouma" Formation specimens of Dianops cf. algeriensis Crônier et al, 2013 occur in shaly marlstones at locality 4 (N 29°57´56.4˝, W 2°04´08.8˝) that did not provide any conodonts. After Crônier et al (2013) these levels (Member 3c of the "Argiles de Marhouma" Formation) belong to the Famennian IV according to clymeniids.…”

“…nov. (locality 2, N 29°57´37.6˝, W 2°06´10.9˝). Equivalent levels ("Argiles de Mahouma" Formation, member 2, Crônier et al 2013Crônier et al , p. 1004 revealed the presence of Houseops? cryphoides (Richter & Richter, 1926), T.?…”

“…Conodonts from this level (Palmatolepis gracilis gracilis, P. quadrantinodosa inflexoidea) indicate the Lower marginifera Zone. Crônier et al (2013) determined Phacops tamtertensis from an equivalent level in section Tamtert-Zereg further to the East. In the upper part of the "Argiles de Marhouma" Formation specimens of Dianops cf.…”

“…After Crônier et al (2013) these levels (Member 3c of the "Argiles de Marhouma" Formation) belong to the Famennian IV according to clymeniids. Dianops algeriensis Crônier et al, 2013, D. vicarius Chlupáč, 1961 typhlops (Gürich, 1896), Phacops zeregensis Crônier et al, 2013 of middle to late Famennian age were described by Crônier et al (2013) from the Zereg area.…”

“…The first comprehensive study on Late Devonian phacopids in SW Algeria was recently carried out by Crônier et al (2013). They concerned Famennian occurrences in several localities of the Saoura Valley.…”