ABSTRACT Extensive glaciers covered the High Atlas mountains in Morocco during the late Pleistocene. On the northern escarpments of the Marrakech High Atlas, a series of cirques perched at ~3000–3500 m above sea level (asl) fed their valley glaciers that, in some cases, extended to as low as 2000 m asl. Cosmogenic exposure dating with 10 Be and 36 Cl has shown that at least three phases of glaciation are preserved in glacial deposits over the last glacial cycle at 50, 22, and 12 ka, which appear to correlate with marine isotope stage (MIS) 3, the global Last Glacial Maximum (LGM), and the Younger Dryas chronozone. This geochronological framework is sufficiently robust to allow for time-constrained glacier-climate reconstructions. The glaciers associated with these three phases of advance had equilibrium line altitudes (ELAs) of 2761 m asl (ca. 50 ka), 2919 m asl (ca. 22 ka), and 3213 m asl (ca. 12 ka). Glacier-climate modeling suggests that all of these phases were driven by both colder temperatures and wetter conditions than today. The dominant moisture supply to these glaciers in all phases would have been sourced from Atlantic depressions. The influence of an extended and enhanced West African monsoon on glacier development during African Humid Periods is unlikely to have been a significant influence on glacier dynamics. The climate conditions associated with the three glacier phases indicate sustained moisture supply to the highest mountain areas when records from other areas, such as the Middle Atlas lakes and marine sediment cores offshore, indicate marked aridity.

Abstract Lithology is acknowledged to be an important internal catchment control on flow processes to adjacent alluvial fans. However, the role of inherited structural configurations (e.g. bedrock attitude) in catchment connectivity and sediment transport is rarely considered. We examine four young (<100-year-old) active tributary junction alluvial fan systems from the Dadès Valley in the High Atlas of Morocco in terms of their catchment-scale connectivity, sediment transfer and resulting alluvial fan processes. The catchments occur on the same lithologies (limestones and interbedded mudstones), but experience different passive structural configurations (tilted and structurally thickened beds). The fan systems react differently to historical peak discharges (20–172 m 3 s −1 ). Catchments containing tectonically thickened limestone units develop slot canyons, which compartmentalize the catchment by acting as barriers to sediment transfer, encouraging lower sediment to water flows on the fans. Syn-dip catchments boost connectivity and sediment delivery from translational bedrock landslides as a result of steep channel gradients, encouraging higher sediment to water flows. By contrast, translational landslides in strike-oriented drainages disrupt longitudinal connectivity by constricting the valley width, while the gradients of the main channels are supressed by the attitude of the limestone beds, encouraging localized backfilling. This diminishes the sediment to water content of the resulting flows.

Abstract Carbonate platforms affected by salt tectonics form important hydrocarbon reservoirs. In an effort to gain new insights of the impact of diapirism on carbonate systems we have undertaken an integrated structural and sedimentological study of Jurassic carbonate platforms of the Moroccan High-Atlas basin. In this natural laboratory, the scale of outcrop exposure is similar in area to a large offshore seismic data set, and field observations provide high details on the geometries and facies distributions around diapiric structures. The Atlas intracontinental basin initiated during the Triassic, contemporaneously with Atlantic rifting. The Triassic synrift sequence includes thick shales and evaporite deposits accumulated in multiple tectonic sub-basins. A thick (>5000m) Jurassic sequence was deposited during an overall post-rift stage in a west-southwest/east-northeast shallow-marine basin open towards the NeoTethys. Since the Sinemurian, sedimentation was mainly carbonates. However, geodynamic events linked with the evolution of the Atlantic margin produced several phases of clastic influx leading to the development of mixed systems (Toarcian and Bathonian). During the Early Pliensbachian, an extensional tectonic event triggered synsedimentary diapiric movements which locally lasted until the Cretaceous. These movements were responsible for the development of narrow diapiric ridges of large extent (>100km), controlled by normal west-southwest/east-northeast relay faults. These ridges were separating several kilometers-wide elongated mini-basins, which subsidence was induced by salt/shale withdrawal. Regionally, diapiric movements have been discontinuous in time and space, leading to significant thickness variations within the different stratigraphic units. However, diapirism has not had any major influence on the nature and distribution of sedimentary systems at the basin scale. The impact of diapirs remains essentially localized in the immediate vicinity of these structures (km-scale), where they affected both stratigraphic geometries and facies distribution. This impact appears to be very different in oolitic and mixed ramp systems in which subtle differentiation of depositional profiles controlled progressive facies variations, or in bioconstructed carbonate systems in which diapiric movements had a major role on the location and morphology of platform margins and associated “micro-rim-basins.” In return, the geometry of the diapirs has been clearly influenced by the lithology of surrounding rocks.