Differences and similarities in Plio-Pleistocene Planktonic Foraminifera through the western and eastern Mediterranean basins: Insights from ODP Site 967 (3.7–2.3 Ma)

The Plio-Pleistocene Transition (PPT, 2.7-2.4 Ma) marks a major climatic reorganization with the onset of Northern Hemisphere glaciation. While the western Mediterranean¹ has served as a standard for biostratigraphic and paleoceanographic reconstructions during this period, the eastern Mediterranean, remains less explored. This study (3.7–2.3 Ma) provides the first quantitative planktonic foraminiferal data from ODP Leg 160 Site 967 (Eratosthenes Seamount, 2554 mbsf, well-developed sapropel), aiming to elucidate regional similarities and differences in faunal dynamics and bioevents across the two basins.

The Mediterranean biostratigraphy¹ for studied time interval is mainly based on genus Globorotalia, but the eastern record shows low abundance respect to the western ones.

Despite astronomically tuned sapropel records, the biostratigraphic correlation is very difficult.

When compared the eastern Mediterranean Site 967 to western planktonic foraminiferal biozones, key bioevents, including the Last Occurrence (LO) of Globorotalia puncticulata dated at 3.57 Ma, and First Occurrences (FO) of Globorotalia bononiensis and Globorotalia crassaformis, show approximately synchronous timings but contrast in relative abundances. Notably, the LCO of G. bononiensis at 2.46 Ma in the western Mediterranean appears inconsistent in the eastern record, whereas G. crassaformis provides a more reliable marker, suggesting a need for revised regional biozonation schemes.

An outstanding feature is the temporal disappearance of Globorotalids (G. bononiensis and G. crassaformis) at ca. 2.4 Ma, an event not observed in western records where these taxa continued to persist beyond this interval. 

The Neogloboquadrina atlantica signature, although resemble the western Mediterranean cooling signal, is minimally expressed in the eastern Mediterranean, emphasizing limited Atlantic water influence and distinct oceanographic control. Also, the Sphaereodinellopsis signal seems to mimic very well the western record with a synchronous LO at ca. 3.2 Ma.

As expected from the palaeoceanography of the eastern Mediterranean, micropaleontological analyses reveals a warm-water and oligotrophic assemblages including Globigerinoides ruber white (morphotypes Type b-platys, c-elongate, d-kummerform), Globoturborotalita rubescens, Globigerinoides obliquus, the Trilobatus sacculifer gr., Orbulina universa, and Globigerinella spp. Conversely, nutrient-dependent and cooler-tolerant species, such as Turborotalita quinqueloba, Globigerinita glutinata, and Globigerina bulloides, peak in abundance near sapropels, marking episodic productivity increases.

High Globigerinoides abundances underscore sustained warm, salty, and stratified water conditions, punctuated by clear paleoenvironmental shifts from red-to-black sapropel phases (~3.2 Ma). This shift is characterized by an acme end of Neogloboquadrinids and incipient warming and increased humidity, shown in oxygen stable isotope G. ruber signal. Another outstanding change is the G. ruber white morphotype faunal turnover and reductions in Globigerinoides obliquus around 3.0 Ma.

As final remarks, the acme end of Trilobatus sacculifer gr., the LO of total Globorotalids and LRO of Globigerinoides obliquus seem to approximate the Gelasian boundary (~2.6 Ma), with important paleoenvironmental and ecological reorganization marked by the decline of warm taxa and an expansion of cooler and productive waters.

Correlation reveals similarities and differences in planktonic foraminiferal abundance highlighting complex basin-specific responses to global climate forcing. These findings advance understanding in paleoceanography and biostratigraphic correlation frameworks crucial for reconstructing PPT climate evolution.

¹Lirer, F. et al. (2019). Earth-Science Reviews, 196, 102869