Chronostratigraphic ranges of Early–Middle Miocene larger benthic foraminifera calibrated by planktonic foraminiferal assemblages (Sierra de Marmolance, Granada, SE Spain)

Abstract

An ∼ 300 m thick succession of bioclastic limestones and marls crops out in the Sierra de Marmolance (Subbetic Domain, External Zones, Betic Cordillera, SE Spain). Assemblages of planktonic foraminifera (PF) in the marls, underlying and laterally changing to limestones, indicate a late Burdigalian–early Serravallian age for the carbonates. Outcrop-scale geometry, stratigraphic patterns, facies distribution, and biogenic components reveal that Marmolance limestones formed on a prograding ramp with depth-related facies gradients. In the late Burdigalian–Langhian, from deeper to shallower, the facies are planktonic foraminiferal packstone and marls, Nummulites packstone, Neorotalia packstone, and lepidocyclinid packstone. In the early Serravallian, Nummulites packstone is missing and Risananeiza packstone and bioclastic rudstone with siliciclastics occur shorewards of lepidocyclinid packstone.

Altogether, 18 species of larger benthic foraminifera (LBF) were identified in the Marmolance succession. Among them, before the present study, Nummulites fichteli, N. vascus, N. kecskemetii, Eulepidina dilatata, Eulepidina formosoides, Nephrolepidina praemarginata, and Risananeiza crassaparies were considered exclusively Oligocene taxa, whereas Nephrolepidina morgani, N. tournoueri, Neorotalia viennoti, and Spiroclypeus sp. were supposed to disappear in the Early Miocene. In Marmolance, Nummulites vascus and N. cf. kecskemetii appear in Burdigalian and Langhian strata, whereas N. fichteli is only recorded in Langhian beds. Eulepidina dilatata, E. formosoides, Nephrolepidina morgani, N. praemarginata, N. tournoueri, N. viennoti, Risananeiza crassaparies, and Spiroclypeus sp. extend at least to the Serravallian. The presence of Nummulites in the Langhian of SE Spain partly fills the stratigraphic gap in the genus record from the end of the Oligocene to the living representatives in modern Indo-Pacific areas. These findings substantially modify the chronostratigraphic ranges and assumed diversity of Neogene LBF in the Mediterranean area.