The planktic foraminiferPlanorotalitesin the Tethyan middle Eocene

Abstract

Morphologically uniform, low-trochospiral foraminifera are a common, though not very well-preserved component\ud of foraminiferal assemblages across the interval including the Middle Eocene Climatic Optimum (MECO) at the Alano\ud (northeastern Italy) and Monte Cagnero (central Italy) Tethyan sections. The morphology of these specimens, combined with their state of preservation, made it difficult to assign them to a benthic or planktic group. We measured their stable isotope (oxygen and carbon) composition and compared them with those of trochospiral, epifaunal benthic (Nuttallides truempyi (Nuttall, 1930)) and planktic foraminifera (Acarinina and Subbotina) in the same samples. Despite the preservation, the isotopic analysis showed that the low-trochospiral forms were undoubtedly planktic foraminifera calcifying in the mixed layer.\ud We assign them to the species Planorotalites capdevilensis (Cushman & Bermudez, 1949). Their abundance, distribution and stable isotope values suggest that P. capdevilensis may have been mixed-layer dwellers without photosymbionts, adapted to slightly more mesotrophic conditions than symbiont-bearing, larger acarininids and morozovelloidids. The oxygen isotope data for benthic and planktic species in the two sections are similar, but the carbon isotopic values of all foraminifera are 1.0–1.5 lower at the Alano section than at Monte Cagnero, probably because the Alano sediments were deposited in the more restricted Belluno Basin, the Monte Cagnero sediments in the more open oceanic setting of the Umbria-Marche Basin

The Middle Eocene Climatic Optimum (Meco) Impact on the Benthic and Planktic Foraminiferal Resilience From a Shallow-Water Sedimentary Record

“…Benthic foraminifera represent one of the most widely applied groups in paleoceanographic and paleoenvironmental reconstructions in the geological record, as their assemblages can provide useful information on several environmental parameters at the sea floor, such as organic matter, oxygen availability, depth, salinity, and temperatu-re (e.g., Van der Zwaan et al 1999;Gooday 2003;Murray 2006;Jorissen et al 2007). Previous investigations were done on paleoenvironmental reconstruction and biostratigraphy across the MECO from Tethyan successions but in deep-water settings (e.g., Boscolo Galazzo et al 2013;Boscolo Galazzo et al 2016;D'Onofrio et al 2021). The investigation of the benthic foraminiferal assemblages at Sealza section, coupled with isotopic records and total organic carbon (TOC), provides, for the first time, evidence of the paleoenvironmental changes across the MECO in a shallow-water setting, and provides new insights on the resilience of both planktic and benthic communities in neritic environments.…”

Small but mighty: how overlooked small species maintain community structure through middle Eocene climate change

“…Yet our understanding of planktonic foraminifera ecosystem dynamics across the MECO remain relatively understudied compared with other periods of the Eocene such as the EOT (e.g., Pearson et al 2008; Wade and Pearson 2008; Pearson and Wade 2015). The MECO resulted in a global crisis for muricate taxa (Luciani et al 2010; Edgar et al 2013), varying symbiotic taxon responses (Luciani et al 2010; Edgar et al 2013; Gebhardt et al 2013; Arimoto et al 2020; Kearns et al 2021), and increased abundance of ecologically flexible (Galazzo et al 2015; Kearns et al 2021) and small opportunistic taxa (Luciani et al 2010). What we lack, however, is an integrated assemblage perspective on these idiosyncratic changes, pieced together from different sampling localities.…”