Nannofossil stratigraphy and paleoenvironments of the Israel Judea Group

The calcareous nannoplankton from the sediments of the Judea Group (Albian–Cenomanian) of the Carmel area (NW Israel) and the Southern Coastal Plain has been studied. The identified rich assemblages in the Carmel area consist of 113 taxa (borehole CT8) and 95 taxa (borehole CT2). On the Coastal Plain (borehole Negba 1), the impoverished assemblage of 24 taxa is recorded.

The detailed calcareous nannofossil biostratigraphy of the Carmel area has been established and compared with planktic foraminiferal zones. In the Coastal Plain, different stratigraphical intervals are recorded and correlated with planktic foraminiferal zones.

The novel nannofossil data indicate that the Isfiye Formation and the Tavasim Volcanics (V2) calculated as 98.2 Ma in the Carmel area are Late Albian, and the Arqan Fm. is Late Albian–Middle Cenomanian.

The Albian–Cenomanian boundary in the Carmel area is drawn at the level of the first occurrence of Thalmanninella globotruncanoides (planktic foraminifera) in the lower part of the Arqan Fm. at ~52 m above the top Tavasim Volcanics in CT8 and at ~35.65 m above the Tavasim Volcanics in CT2. This is supported by the appearance of Th. brotzeni (planktic foraminifera) at 26 m (CT8) and 6.55 m (CT2) below, and C. kennedyi (nannofossils) above this level. Our novel stratigraphical data prompt a revision of the revision of the litho-stratigraphic table and updating the Arqan Fm. age.

On the Coastal Plain, only wide stratigraphic intervals can be recognized due to rarity of nannofossils: the upper part of the Yagur Fm is Late Albian–Early Cenomanian, the Lower and Upper Members of the Negba Fm is Albian–Late Cenomanian, and the upper part of the Upper Member of the Negba Fm is Late Cenomanian.

The quantitative analysis of the calcareous nannoplankton suggests that the general dominance of Watznaueria spp. throughout the whole successions in the Carmel Area reflects the original signal and points to quite warm, open marine or coastal, generally oligotrophic conditions. Due to poor nutrient supply, the productivity of the calcareous nannoplankton was quite low except for two phases of higher fertility within Subzone NC10a and Zone NC11*. Low values of the Shannon index, Evenness and Species richness can be interpreted as reflecting unstable environment. The Isfiye Formation (Late Albian) accumulated in temperate, oligotrophic conditions. The lower part of the Arqan Formation was deposited under temperate climate but mesotrophic conditions. The higher part of the Arqan Formation (Early Cenomanian) was deposited in oligotrophic waters and relatively warm climate. The uppermost part of the Arqan Formation (Middle–Late Cenomanian) was accumulated during a progressively cooling period, although characterised by alternating warming and cooling phases and oligotrophic conditions.

The calcareous nannoplankton quantitative data correlate very well with those obtained from planktic foraminifera (Lipson-Benitah et al., 1997) from the nearby area, and with cycles and sequences established by Haq et al. (1988), and suggest nutrification during phases of a risen sea level in the Late Albian and Early Cenomanian.

The biostratigraphy in the Carmel Area shows no hiatuses in the studied section, but carbon isotope data reflect different pictures. In the borehole CT2 (Isfiye Fm., depths 169.90–152.60 m), the Oceanic Anoxic Event (OAE) 1d and Middle Cenomanian Event (MCE) I (Arqan Fm., depths 74.10–65.0 m) are detected; these reflect well the globally recorded carbon isotopic anomalies. Considering that the isotopic signal is not diagenetically altered and the δ¹⁸O signal is not affected in the CT2, the oxygen isotopes suggest temperate conditions during the Late Albian–Early Cenomanian (~26°C) followed by a warming period in the late Early Cenomanian, with temperatures gradually increasing toward the Middle Cenomanian to ~32°C.

In the borehole CT8, carbon isotope data seem to be affected by diagenetic alteration showing no evidence of the positive isotopic anomalies, which identify OAE 1d and MCE I worldwide. Temperature and nutrient variations in CT8 correspond to the western Tethys record, thus suggesting that the detected paleoclimatic variations occurred at a supra-regional scale.