BOTOMAN (LOWER CAMBRIAN) TURBID- AND CLEAR-WATER REEFS AND ASSOCIATED ENVIRONMENTS FROM THE HIGH ATLAS, MOROCCO

Abstract

Exposures of the Botoman (Lower Cambrian), Lemclad and Issafen formations on the Lemclad syncline, southern High Atlas. provide an excellent example of the interactions between tectonic events, magmatic activity and carbonate productivity. The major factors that controlled the nucleation of carbonate factories on the Botoman High Atlas platform were: (i) synsedimentary tectonism, as normal faulting resulted in tilting of fault blocks causing irregular topographies and subsequent sharp erosion; (ii) volcanism, because pyroclastic influx smothered carbonate factories except in distal areas of the platform or during quiescent episodes of volcanic activity; and (iii) the influence of successive shoaling parasequences. The Botoman reefs exhibit a wide range of external morphologies, including tabular (biostromes) and domal (bioherms and patches) boundstones, which do not exceed 3.5 m of thickness. Although archaeocyathan-microbial reefs only developed under clear-water conditions, microbial reefs grew also under turbid-water conditions. Domal and digitate stromatoids, Girranella crusts, Epiphyton bushes and thromboid-stromatoid inter-growths document the ability of some microbial communities to develop heterotrophic strategies when submitted to a moderate terrigenous input. Turbidity was a major ecological factor that constrained development of filter/suspension-feeder and phototrophic organisms, but not necessarily of benthic non-phototrophic microbial communities.