Reassessment of the Early-Middle Eocene Planktic Foraminiferal Biomagnetochronology: New Evidence From the Tethyan Possagno Section (Ne Italy) and Western North Atlantic Ocean Odp Site 1051

Abstract

We examined a planktic foraminiferal biostratigraphic record from the Tethyan Possagno section (Venetian Prealps of northeastern Italy) spanning the lower–middle Eocene transition, from Chron C24r to the base of Chron C20r and from Zones E1 to lower E8. Our results provide an updated magnetochronological calibration from the Tethyan realm of the lowest and highest occurrences of the zonal markers. All the foraminiferal biostratigraphic events utilized in the most recent and widely used zonal schemes have been recognized. Most of them are in reasonable agreement with the known magnetochronological calibration, such as those at the Paleocene/Eocene boundary and lowermost Eocene. However, a number of events, specifically the bases of Morozovella aragonensis, Acarinina cuneicamerata, and Guembelitrioides nuttalli, occur at a significantly lower position at Possagno than in the most recent zonal schemes. A comparable magnetostratigraphic position has been recorded for the first two bioevents in the western North Atlantic Ocean ODP Site 1051 (Blake Nose, Atlantic Ocean). Furthermore, the base of A. cuneicamerata and the top of Morozovella subbotinae occur in reverse order with respect to previous schemes, thus negating the effectiveness of Zone E6 as now used. We propose an alternative definition of the Zone E6/E7a boundary by substituting the base of Astrorotalia palmerae for that of A. cuneicamerata. This proposal avoids combining E6 and E7a into a single zone. Additionally, we recorded a significantly different magnetostratigraphic position for the base of Turborotalia frontosa, a critical event for the Ypresian-Lutetian boundary placement. Our biostratigraphic dataset is unique in the integration of deep-benthic foraminiferal events with magnetostratigraphy and calcareous plankton data. Because biostratigraphic data of planktic foraminifera from the Possagno section derive from the same sample set analyzed for calcareous nannofossils, we were able to outline an integrated, updated, calcareous plankton stratigraphy of the lower–basal middle Eocene from a Tethyan location

Did Photosymbiont Bleaching Lead to the Demise of Planktic ForaminiferMorozovellaat the Early Eocene Climatic Optimum?

“…This is important for stratigraphic reasons because rare specimens might be missed. The position of the T c of M. marginodentata at Site 1051 is in perfect agreement with the T of this species in the Tethyan Possagno section (Luciani & Giusberti, ), whereas the true T of M. marginodentata is more consistent with stratigraphic concepts presented by Berggren and Pearson (). Due to our detailed counting in samples collected at fairly high temporal resolution, our record of lowest and highest occurrences of Morozovella species differs from that reported by the Shipboard Scientific Party ().…”

“…Washed residues were dried at <50 ° C. The taxonomic criteria adopted in this study follow Olsson et al () and Pearson et al (). Planktic foraminiferal biostratigraphy comes from Luciani et al (), who applied the zonal scheme of Wade et al () but included a modification (Luciani & Giusberti, ). Specifically, Zones E6 and E7a have to be combined at Site 1051 because the first appearance of Acarinina cuneicamerata is diachronous and the alternative marker species, Astrorotalia palmerae , is absent.…”

“…The succession predominantly consists of “siliceous nannofossil chalk,” with the siliceous component including radiolarians, diatoms, and sponge spicules (Shipboard Scientific Party, ). Calcareous plankton biostratigraphy (Luciani & Giusberti, ; Mita, ; Norris et al, ) and polarity chrons, once recalibrated (Cramer et al, ; Luciani et al, ), indicate a ~100 m depth interval spanning from ~53.5 to ~47.5 Ma according to the Global Polarity Time Scale 2012. This implies a modest sedimentation rate (>1.6 cm/kyr) for much of the early Eocene.…”

“…The black δ 13 C curve shows data generated by Cramer et al (2003); the red curve is from this study. Plankic foraminiferal zones were assigned by Luciani et al (2016) following the zonation scheme presented by Wade et al (2011), but as modified by Luciani and Giusberti (2014). Magnetostratigraphy comes from Ogg and Bardot (2001), but with an important modification to polarity chron labeling as discussed in subsequent literature (Cramer et al, 2003;Luciani et al, 2016).…”

Global Extent of Early Eocene Hyperthermal Events: A New Pacific Benthic Foraminiferal Isotope Record From Shatsky Rise (ODP Site 1209)

“…Planktic foraminiferal (Petrizzo, ) and calcareous nannofossil (Bralower, ) biohorizon zonations published for Site 1209 have to be updated to the revised schemes of Wade et al () and Agnini et al (). This updated biostratigraphic scheme would provide a further stratigraphic tool to correlate hyperthermals and, at the same time, evaluate the synchronicity of planktic foraminiferal and calcareous nannofossil events that show some diachrony in the early Eocene (Luciani et al, ; Luciani & Giusberti, ; Westerhold et al, ). Updating the biozonal scheme of Petrizzo () and Bralower () is beyond the objectives of this study, requiring investigations on well‐selected additional samples.…”