Calcaires du Bou Dahar

Lead, Zinc, and Baryte mining in the Bou Dahar district relies solely on artisanal methods managed by the public "CADETAF" cooperative. The cooperative’s claim area, spanning 60,000 km2 across the central and eastern High Atlas, along with exploration licenses held by ManagemGroup, together constitute North Africa’s largest calamine region. Data from CADETAF and ManagemGroup reveal over 1 million tons of zinc ore with more than 30% ZnO content extracted to date, including 559,403 tons of 16% Zn ore produced by ManagemGroup from 2012 to 2019. == Sequence evolution ==

The Bou Dahar platform is a well-preserved example of carbonate platform development within a tectonically active rift-basin environment. This region formed as part of the Jurassic High Atlas seaway, where tectonic activity shaped the basin, with influences from rifting, faulting, and transtensional forces. Early studies mapped the area’s Jurassic marine environments, with carbonate platform margins situated alongside deeper basin limestones. This platform records two primary periods of shallow-water carbonate growth: one during the Lower to Middle Liassic (Sinemurian to Domerian) and a subsequent phase spanning the Upper Liassic to Lower Dogger (Aalenian to Bajocian). However, only the earlier phase is preserved in Djebel Bou Dahar. This phase was abruptly interrupted at the Domerian-Toarcian transition, marked by the onlap of Toarcian shales and Aalenian lime mudstones over the platform, signaling a shift to deeper marine conditions. Early dolomitization preserved the fine microstructures within these sequences, aligning with the Hettangian-Lower Sinemurian Idikel Formation. Sequence III developed as a low-relief carbonate platform and varies in slope angle between northern and southern margins, with thickness peaking in northeastern synclines at around 100 meters. Thinning toward the center, it comprises laterally continuous skeletal and packstone deposits interspersed with sponge mounds, mirroring the Foum Zidet Formation. Sequence IV with a wedge-shaped geometry, reveals steep slopes and retrogradational stacking, indicating subaerial exposure at its base with ammonite-rich wackestone beds. This sequence thickens at the southern margin, where coral and sponge boundstones, extending to 140 meters, transition into grainstone and packstone accumulations along the slope. The eastern platform edge hosts cross-bedded grainstone layers, lacking intertidal deposits, characteristic of open-marine conditions. Sequence V, along Sequences IV to VI correlate with the Aganane Formation and Ouchbis Formations, being a progradational wedge, is thickest along the platform's southern and eastern edges, forming a concave-up clinoform structure, reaching 50-70 meters in height and indicating alternating subtidal and intertidal lithofacies and evidence of exposure events. Moving basinward, finer basinal sediments with green marls and peloidal wackestones emerge, suggesting periodic sediment starvation during the Early Pliensbachian. The final sequence, Sequence VI, fills the last stage of platform development with angular unconformity over older layers and CAMP basalts. This sequence encompasses varied facies belts surrounding a central paleo-high with subtidal and intertidal deposits, coated-grain bars, and coastal-plain sediments like red shales and calcretes. Clinoforms along the lower slope show a concave-up profile that flattens basinward, with deposits consolidating into a fan along the southern margin, evidence of sediment redistribution likely from mass wasting. == Paleoenvironment ==

The paleoenvironment of Bou Dahar is characterized by a dynamic evolution through distinct stages: pre-drowning, drowning, and post-drowning, each marked by specific sedimentological and ecological changes that reflect shifts in energy conditions and depositional environments. During the pre-drowning phase, the carbonate platform was dominated by tranquil lagoonal settings, indicative of low-energy environments. These conditions fostered the accumulation of microsparite carbonates, which are essential in maintaining the stable conditions found in lagoons. Microscopic examination of the sediments reveals a rich diversity of biogenic and non-biogenic components, categorized into nine distinct microfacies types. Local carbonate factories present a unique contrast with other coeval units in the Tethys, with siliceous sponge microbial boundstone mounds, which were more prevalent in Middle and Upper Jurassic systems. Despite their earlier emergence, these mounds show similarities to younger Jurassic formations in texture and biological components. They thrived in deep-water environments, particularly in areas that experienced low detrital input. Siliceous sponge mounds record distinct rare earth element and yttrium patterns among carbonate components, indicating that Early Jurassic seawater resembled modern distributions. Microbialites contained higher rare earth element concentrations, likely influenced by organic matter and diagenetic processes. These mounds thrived in well-oxygenated environments, emphasizing the need to examine individual carbonate types to understand their unique geochemical signatures. The coral calcareous sponge microbial boundstone aligns with the coral-microbolite-debris reef classification, indicating a high-energy, shallow-water habitat. == Fossil content ==

Foraminifera Sponges Hydrozoa Anthozoa Brachiopoda Gastropoda Polyplacophora Bivalvia ammonites Annelida Echinodermata Microproblematic/algae == See also ==