Decoding the ELPE hyperthermal: a new biotic and paleoclimate record from South Atlantic IODP Sites U1556/U1557

Extreme climate warmth (hyperthermal) events occur throughout the geologic record. In particular, several transient events are well documented for the early Eocene with the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) standing as the major star. Yet, earlier short-lived (10⁴–10⁵ years) warming events, correlated with abrupt negative carbon isotope excursions (CIEs), also struck in the Paleocene producing noticeable environmental disturbances (e.g., DAN-C2 event in the Danian, ~65.2 Ma and the ELPE event in the early late Paleocene, ~59 Ma). The Early Late Paleocene Hyperthermal Event (ELPE), also known as the mid-Paleocene biotic event (MPBE), was first discovered during ODP Leg 178 Shatsky Rise in the northern Atlantic as a prominent clay-rich ooze close to the first occurrence (FO) of the nannofossil Heliolithus kleinpellii, a marker for the base of nannofossil Zone CNP8 (=NP6), and the base of chron C26n. It was interpreted as an abrupt warming that possibly caused a brief switch in the source of deep waters at Shatsky Rise.The base of C26n marks the Selandian/Thanetian stage boundary as defined in the Selandian GSSP in the hemipelagic relatively expanded section at Zumaia that provides an astronomical template including the first documented ELPE event from a land section.

Here, a conspicuous ~40 cm clay-rich layer occurring at Hole U1556A (located ~1250 km west of the Mid-Atlantic Ridge at a 5002 m water depth) in interval 390-U1556A-29X-5, 70-110 cm (270.7 to 271.1 m CSF-B) (also occurring in Holes U1556C and U1557B) is investigated at high resolution. Paleomagnetic directional data is presented from four U-channel samples from sections 390-U1556A-29X3 to 390-U1556A-29X6 that confirm the presence of chron C26n, also in agreement with the FO of H. kleinpellii. Rockmagnetic and bulk rock stable isotope (d¹³C and d¹⁸O) measurements (155 samples) along with calcareous nannofossil determinations (80 samples) and XRD bulk mineral analysis (51 samples) were achieved spanning cores 390-U1556A-29X and 390-U1556A-30X at variable resolution (average 9 cm but 1.5–3 cm along critical intervals, shipboard age model indicating 0.49 cm/ky).

Quantitative analyses on calcareous nannofossils are carried out following the random settling technique to obtain the relative (%) and absolute abundance (coccoliths*gr^-1) data. The relative nannofossil fragmentation was also determined. Calcareous nannofossil assemblages are well to moderate preserved and diversified, and allowed determination of key biostratigraphic datums, and the main calcareous nannofossil dissolution events. During the ELPE, the total clay content reached up to 70 wt.%. Additionally, increased quartz and feldspar contents during this period suggests wind-driven sediment transport. Orbital chronology and paleoclimatic/paleoceanographic proxy data encompassing the ELPE event will be examined.