Calcareous nannofossil and dinoflagellate stratigraphy across the Cretaceous/Tertiary boundary at Hor Hahar, Israel

Abstract

In Israel, the Cretaceous/Tertiary (K/T) boundary at Hor Hahar occurs within the interval from the top of the Ghareb Formation (Maastrichtian) to just below the horizon of dark marl and clay within the overlying Taqiye Formation (Paleocene). The studied interval contains all the calcareous nannofossil zones: Micula prinsii (latest Maastrichtian), Markalius inversus — NP1 (earliest Paleocene), and Cruciplacolithus tenuis — NP2 (Early Paleocene). They correlate in sequence with the Abathomphalus mayaroensis, P0 P1a, P1b, and P1c planktic foraminiferal zones. The palynological assemblages consist mainly of dinocysts with only few pollen grains and spores. These assemblages are used to interpret five stratigraphic phases of environmental change across the K/T boundary in the Hor Hahar section. In the latest Maastrichtian, there is an overwhelming dominance of the nannofossil Micula decussata, which probably reflects environmental stress preceding the terminal Cretaceous mass extinction. A nearshore marine environment at the boundary is suggested by the increase in number of specimens of the dinocyst Cyclonephelium, and by the predominance of terrigenous organic matter sediment. There followed two episodes of transgression and regression. The calcareous cyst-producing dinoflagellate Thoracosphaera (Futterer, 1976) becomes dominant in two episodes at the boundary and approximately one meter above it. It alternates in abundance with the organic-walled dinoflagellates, which suggests that different environmental parameters were operating for each group. Maastrichtian dinocysts decline in abundance toward the K/T boundary. They reach greatest abundance and species diversity at the same strata where foraminiferids recover after their mass extinction at the boundary. Calcareous nannofossils recover only later in the early Paleocene. Changes in δ 13C and total organic carbon, as as well as dinocyst and nannofossil composition indicate an episode of strong ecological stress about one meter above the boundary.