Turnover of larger foraminifera during the Paleocene-Eocene Thermal Maximum and paleoclimatic control on the evolution of platform ecosystems

Abstract

Figure 1. Location map with studied sections projected on line perpendicular to direction of platform progradation. Contours indicate elevations of Galala Mountains. ABSTRACTThe larger-foraminifera turnover (LFT) during the Paleocene-Eocene transition constitutes an important step in Paleogene larger-foraminifera evolution, involving a rapid increase in species diversity, shell size, and adult dimorphism. A platform-to-basin transect in Egypt provides new data on timing and causal mechanisms through correlation with planktic biozonations and through integration with regional paleoenvironmental data. The LFT coincides with the boundary between shallow benthic biozones SBZ4 and SBZ5 and closely correlates with the Paleocene-Eocene Thermal Maximum (PETM). Enhanced oligotrophy from the late Paleocene onward favored the diversification of K-strategist larger foraminifera. We suggest that a short-term eutrophication during the PETM led to a temporary decline of extreme K-strategist larger-foraminifera species, providing opportunities for new taxa with different ecological strategies to develop. During post-PETM oligotrophic conditions, these new taxa were able to evolve rapidly and soon dominated early Eocene larger-foraminifera assemblages, whereas many Paleocene taxa gradually disappeared. The success of larger foraminifera during the early Paleogene appears climatically controlled. Because of the vulnerability of corals to high surface-water temperatures, the late Paleocene to early Eocene global warming may have favored larger foraminifera at the expense of corals as the main carbonate-producing component on carbonate platforms at lower latitudes.

Late Paleocene–early Eocene Tethyan carbonate platform evolution — A response to long- and short-term paleoclimatic change

“…In this paper we use the nomenclature for the platform stages developed by Scheibner et al (2005) in the Galala Mountains (Egypt; Fig. 2).…”

Circum-Tethyan carbonate platform evolution during the Palaeogene: the Prebetic platform as a test for climatically controlled facies shifts

“…The massive transient temperature peak during the Palaeocene-Eocene thermal maximum caused a Tethyan-wide decline of coral communities. Palaeocene ranikothalids and miscellanids were replaced by Eocene nummulitids and alveolinids (Scheibner et al 2005). This evolutionary trend, known as larger foraminifera turnover, is directly linked to the negative carbon isotope excursion of the Palaeocene-Eocene thermal maximum (OrueEtxebarria et al 2001;Scheibner et al 2005).…”

“…Palaeocene ranikothalids and miscellanids were replaced by Eocene nummulitids and alveolinids (Scheibner et al 2005). This evolutionary trend, known as larger foraminifera turnover, is directly linked to the negative carbon isotope excursion of the Palaeocene-Eocene thermal maximum (OrueEtxebarria et al 2001;Scheibner et al 2005). Carbonate shelves were now dominated by photo-autotrophic larger benthic foraminifera assemblages throughout the Tethys (third phase of the global communifty maturation cycle; Hottinger 2001; Tethyan platform stage III; Scheibner & Speijer 2008a, 2008b.…”

Evolution and Geological Significance of Larger Benthic Foraminifera

“…The Paleocene exhibited a cooler climate than the Late Cretaceous. In the Early Paleocene, the absence of other reef-building, high-temperature tolerating organisms in the low latitudes, enabled larger foraminifera to occupy this vacant niche and rapidly evolve (Scheibner et al 2005). The Danian and Selandian mark the start of the recovery period for the larger foraminifera.…”

“…The breakdown of the stable oligotrophic environment of the larger benthic foraminifera resulted in the disappearance of most of the extreme K-strategists (Hottinger, 1983). The replacement of SBZ4 by SBZ5 faunas (see Chart 6.2), as indicated by the gradual disappearance of Paleocene taxa such Ranikothalia and Miscellanea and the rise of Nummulites and Alveolina, suggests that such an interruption may have taken place in platform environments at low-latitude continental margins (Scheibner et al, 2006;BouDagher-Fadel et al, 2015;Li et al 2016). The Early Eocene witnessed the appearance of many new larger foraminifera genera (85% of which were cosmopolitan).…”