Bryozoan‐Rich Carbonate Units of the Erfoud Area ( SE Morocco) Record Latest Katian to Early Hirnantian Interglacial Intervals

ABSTRACT Carbonate intervals form distinctive units distributed throughout the Upper Ordovician stratal record of the clastic‐dominated Mediterranean Province of the Gondwana platform. In southern Morocco (eastern Anti‐Atlas), bryozoan‐rich deposits comprise the mixed carbonate‐siliciclastic Khabt‐el‐Hajar Formation, initially assigned to two superimposed lower Katian and Hirnantian units, but later generally regarded as a single upper Katian archive. Geological mapping and facies analysis revealed that carbonates are dominated by cross‐stratified calcarenites and were deposited in tidally influenced depositional systems within km‐scale, 10's of metre deep, channel‐like shelf incisions. Incision infills superimpose an initial regressive delta succession and developed upwards into a multistorey transgressive sequence, culminating with low‐energy marls and interspersed bryozoan boundstones. Diversified Late Katian and Hirnantian chitinozoan assemblages were recovered respectively from below the first incision surface, and within the maximum flooding interval; and glacigenic deposits have been recognized laterally. New age constraints and repeated incisions interpreted as a series of striking lowstand events support the idea of a record comprised of glacio‐eustatically driven regressive‐transgressive cycles. The Khabt‐el‐Hajar Formation is considered primarily as an early Hirnantian stratigraphic unit and contemporary with the Lower Second Bani Formation of the central Anti‐Atlas, although Upper Katian basal calcarenites cannot be ruled out. At high southern palaeolatitudes, Katian to Hirnantian bryozoan‐pelmatozoan meadows did not necessarily develop synchronously in response to an elusive pre‐glaciation climatic optimum but, rather, reflect distinctive flooding events linked to specific palaeoenvironmental conditions in each region. Those floodings reflect the interglacial transgressions known to have occurred in the Anti‐Atlas prior to the Hirnantian glacial maximum.