Triassic Diapirs of the Saharan Atlas (Algeria): Geosites of International Scientific Importance

Abstract

The Saharan Atlas of Algeria preserves a unique distal record of the Central Atlantic Magmatic Province (CAMP), one of the largest igneous provinces on Earth, associated with the breakup of Pangea. This contribution proposes the formal recognition of the Triassic evaporitic diapirs of the western Saharan Atlas (Algeria) as geosites of international significance by evaluating their scientific, educational, and geoheritage value within a modern geoconservation framework.

The investigation of the Ain Ouarka diapir reveals two major evolutionary stages: a Late Triassic magmatic rifting stage and a post-magmatic Rhaetian–Hettangian stage. The magmatic record comprises a volcano-sedimentary succession containing three distinct basaltic units (B1, B2, and B3), with a cumulative thickness of 10–15 m. Previous geochemical studies classify these lavas as low-Ti continental tholeiites characterized by a pronounced negative Nb anomaly and enrichment in Light Rare Earth Elements (LREEs). Stratigraphic modeling indicates a progressive upward decrease in LREE enrichment, reflecting an increasing degree of partial melting of a spinel-bearing lherzolite source, from approximately 6–10% in the lower unit to 15–20% in the upper unit.

Beyond their petrological significance, these diapirs constitute a natural laboratory for studying syn-sedimentary tectonics. They preserve clear evidence of ductile deformation and brittle structures, including reverse faults and monogenic breccias, which record crustal instability and block tilting during the early development of the Atlasic basins. Importantly, these outcrops represent the easternmost documented occurrence of CAMP volcanism, marking the waning expression of this vast magmatic province near the 5°E longitude boundary.

To safeguard this rare and non-renewable geological heritage, a comprehensive geoconservation strategy is proposed. This strategy includes the legal designation of these sites as Local Natural Monuments, the installation of interpretive infrastructure based on the Abiotic–Biotic–Cultural (ABC) approach, and the active involvement of local communities as “geosite guardians.” These measures are essential for preserving the Saharan Atlas as a key observatory for future scientific research, geoeducation, and sustainable geotourism at both national and international levels.