Abstract

The Betic Cordillera of southern Spain represents an uplifted foreland fold-thrust belt. Source rock types of the Betic Cordillera include metamorphic (mainly phyllite, schist, quartzite, and gneiss), sedimentary (siliciclastic and carbonate), volcanic (felsic to intermediate pyroclasts), and mantle-derived (peridotite, gabbro, serpentinite, and serpentine schist) rocks. The fluvial systems range that transect the Betic Cordillera are the major detrital source of sediment along the southern Spanish coast, supplying sand to beaches and offshore depositional systems in the Alboran Sea basin.

Three key sand petrofacies derived from the Betic mountain belt reflect the main clastic contribution of known source rocks. All the sands are quartzolithic, ranging from quartz-rich to lithic-rich.

Fluvial systems draining the Sierra de Los Filabres, the Sierra Nevada, the Sierra de Gador, and the Málaga Mountains, and their related beaches constitute a metamorphic-sedimenticlastic quartzolithic sand petrofacies (Qm34±10 F4±3 Lt62±9; Lm72±14 Lv2±4 Ls26±13), derived dominantly from the Nevado-Filábride, Alpujárride, and Maláguide complexes. This quartzolithic petrofacies extends from northeast of Almeria to Torremolinos (southwest of Málaga), and northeast of Algeciras. Only one beach sand sample, east of Cabo de Gata, is volcanolithic. Volcanic detritus (mainly having felsitic textures) is derived from Miocene (15-7 Ma) pyroclastic sequences cropping out in the southeast of the chain.

This metamorphic-sedimenticlastic quartzolithic petrofacies changes in the coastal stretch from Torremolinos to Marbella, where drainage systems cut across the Serrania de Ronda. Here source rock types include peridotite, gabbro, and serpentinite of the Ronda Peridotite Massif, and metamorphic rocks of the Málaguide and Alpujárride units. The fluvial and beach sands of this area are quartzolithic (Qm32±12 F10±3 Lt58±11), and include abundant peridotite and serpentinite grains. The latter quartzolithic petrofacies changes abruptly from Algeciras to Cádiz, where the sand becomes quartz-rich (Qm77±5 F4±2 Lt19±4). This sand petrofacies is derived predominantly from recycling of sedimentary sequences, mainly the quartzarenite turbidite units of the Gibraltar Arc (the Algeciras Flysch). This petrofacies is characterized by higher proportion of quartz grains and abundant sedimentary lithic fragments (Lm1±3 Lv1±1 Ls98±3).

The three onshore petrofacies plot in the recycled-orogen provenance compositional field and the lithic to transitional to quartzose recycled subfields of Dickinson (1985). They vary from lithic, to transitional and quartzose depending on their source lithologies in the Betic foreland fold-thrust belt. These actualistic petrofacies best describe the nature and distribution of sand petrofacies derived from a collisional fold-thrust belt where primary and recycled source rocks are interfingered.

Deep-marine turbidites of the Alboran Basin have basinwide quartzolithic sands having close compositional relations with Betic Cordillera onshore sand petrofacies. Comparison of detrital modes from mainland to deep-marine environments provides a suitable basis for interpreting the Miocene to Pleistocene sand dispersal history in the Alboran Basin. These modern quartzolithic petrofacies are used to interpret analogous ancient collisional sandstone petrofacies of the Alpine orogenic belt of the western-central Mediterranean region and of other collisional orogenic systems, as a broader point of view.

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