Provenance of the Numidian Formation deposits (Oligo-Miocene) in northern Algeria: Insights from sandstone petrography, palaeocurrent data, geochemistry, and zircon geochronology

Abstract

The provenance of the Numidian Formation deposits remains a matter of debate as to whether the source rock of the detrital material that fed the Maghrebian Flysch Basin is of European or African origin. The Numidian Formation is built mostly of Oligocene to Miocene deep-sea turbiditic sandstones and mudstones, which are widely exposed across the Mediterranean (Italy, Tunisia, Algeria, and Morocco). This study applies, for the first time, an integrated provenance analysis of the Numidian Formation in Algeria, combining detrital zircon UPb geochronology, sandstone petrography, geochemistry, and palaeocurrent orientation to constrain their source rock. Palaeoflow analysis, based on flute and groove casts indicates a predominant flow direction from the southeast to the northwest. Petrographic data show that most samples consist of quartz-arenitic sandstones, derived from igneous and metamorphic rocks. These sandstones exhibit evidence of prolonged transport and sedimentary recycling sediments, characterized by a predominance of rounded to well-rounded grains associated with a minor proportion of subangular grains. Trace elements and REE patterns suggest a felsic-intermediate source, while certain samples indicate intermediate mafic rocks and varying degrees of weathering.

Tectonic analysis suggests a passive continental margin setting, though some samples show evidence of a continental island arc influence. UPb geochronology conducted on 205 zircon grains yielded three main age groups: (1) Neoproterozoic (980–549 Ma, 24 %); (2) Mesoproterozoic (1527–1000 Ma, 17 %); and (3) Paleoproterozoic (2469–1636 Ma, 24 %). Additionally, a small number of younger grains (1 %) from one sample correspond to the Silurian age (436–428 Ma). Th/U ratio and cathodoluminescence (CL) images highlight the dominance of zircons with igneous origin over those of metamorphic origin. The age and morphological characteristics of zircons, along with petrographic, geochemical, and palaeoflow data, strongly support an African origin for the studied deposits. Their polycyclic nature suggests they were reworked from older sources, including the Continental Intercalaire, Nubian Sandstones, and Cambro-Ordovician sandstones found in southern Libya and Algeria.