Frasnian conodont abundance and environmental control in northwestern Algerian Sahara

Abstract

The conodont abundance and diversity of the Frasnian (Upper Devonian) is analyzed in two well-exposed geological sections, so-called Ben Zireg and South Marhouma of the northwestern Algerian Sahara. The results presented herein show a significant conodont abundance in the Ben Zireg section with 117 elements/kg, which is higher than that observed in the South Marhouma section with only 14 elements/kg. The magnetic susceptibility measurements presented herein may suggest the impact of the terrigenous input on conodont abundance. Indeed, the strata belonging to the middle Frasnian substage in both sections expose higher MS values matching with lower conodont diversity. However, the decrease of the MS signal is correlated with a constant increase in conodont abundance This new quantitative MS-conodont, revealed by an inverse correlation between MS and conodont abundance, suggesting that MS could potentially serve as a proxy for paleoecological interpretations.

The comparison between Ben Zireg and southern Marhouma illustrates the key role of paleogeography in shaping conodont abundance along the stable Gondwana margin. Proximal areas such as Marhouma, located closer to the paleocontinents, were more exposed to elevated detrital input, which likely suppressed conodont proliferation and led to reduced abundance. In contrast, more distal settings like Ben Zireg were exposed to lower terrigenous influx, resulting more optimal ecological conditions that supported higher conodont abundance and diversity.