Deep-sea paleoenvironmental evolution in the mid-Cretaceous of the Basque Pyrenees based on microfaunal analysis (Armintza section)

• DOI: 10.1016/j.csr.2023.105001
• Publication Date: 2023-05-02T05:38:48Z
• Authors: L.M. Agirrezabala; A. Malaxetxebarria; A. Pascual; J. Rodríguez-Lázaro
• Keywords: Cenomanian; Flysch

The mid-Cretaceous Black Flysch Group and Plentzia Formation constitute two key lithostratigraphic units in the evolution of Pyrenean rift system but many their paleoenvironmental characteristics are poorly known. In this work, a microfaunal analysis (planktonic benthic foraminifera ostracods) these at Armintza section has been carried out order to interpret conditions (paleodepth, oxygen level water masses) which they deposited, relate them contemporary tectono-sedimentary settings. Based on high proportion planktonic with respect total assemblages species, paleodepth ∼600 m is estimated for studied units. During syn-rift deposition organic-rich Gp. middle Albian-early Cenomanian times, relative abundance proportions different shell morphotypes suggest presence shallow mass stagnation deeper waters. Moreover, abundant hypoxia-tolerant species occurrence only rare platycopid ostracods indicate severe hypoxia (<1.5 ml/l) or even anoxia seafloor. A noticeable change recorded contact between Fm. (lower-middle transition). post-rift earliest developed assemblage shows an important increase intermediate waters, dominance keeled suggesting end inflow mass. addition, indicates development mild seafloor during interval.