Eocene palaeoenvironments and palaeoceanography of areas adjacent to the Drake Passage: insights from dinoflagellate cyst analysis

Abstract

A proper understanding of the palaeoceanographic evolution of the Drake Passage during the Palaeogene is hampered by the lack of precise tools to date and correlate the sedimentary units of areas adjacent to the region. In this work, considering recently published radiometric U-Pb dates, we revised the age of a previous dinoflagellate zones for the middle to upper Eocene units of the Austral-Magallanes Basin. The quantitative analysis of middle to late Eocene dinoflagellate cyst assemblages from different localities close to the Drake Passage allowed us to reconstruct the palaeoenvironmental conditions and the possible surface ocean currents during this time in the area. Assemblages dated between 41.3 and 38.1 Ma represent relatively warm waters in inner shelf settings, while those ranged between 36 and 35 Ma reflect coastal areas with cool, nutrient-rich surface waters. The proposed surface ocean circulation pattern, based on dinoflagellate cysts distribution between 41.3 and 38.1 Ma, agrees with the results of a palaeoclimatic numerical model simulation performed with a Drake Passage shallow opening of 100 m depth. At c. 36 Ma, several Antarctic gonyaulacacean taxa tolerant to relatively warmer waters were replaced by some Antarctic peridinacean species better adapted to colder conditions. This change could be linked to a progressive deepening of the Drake Passage that is estimated to have reached 1000 m depth promoting a cooling in the South Atlantic. Such passage depth would have enabled stronger flows from the Pacific to the Atlantic Ocean, which is reflected by the increase of cosmopolitan species.

Correlation of Middle to Upper Eocene Units from High Latitude Southwestern Atlantic Sites

“…Olivero et al (2020, figure 2), based on the mentioned scheme together with new radiometric dates from Leticia Formation, synthesized the chronostratigraphic scheme for the basin as shown in Figure 2.1. This proposal was recently reinterpreted by Amenábar et al (2022) considering the available isotopic information provided by the previous authors and adding the isotopic data from Leña Dura and Loreto formations (Bijl et al, 2021), both from the Austral-Magallanes Basin, in southern Chile. The latest modified scheme also reinterpreted the isotopic ages published by Dutton et al (2002) and Ivany et al (2008) for La Meseta Formation, in the James Ross Basin (Fig.…”

“…37-27 Ma, late Eocene-Oligocene than the ages previously suggested based on biostratigraphic studies, i.e., 46 to 33.5 Ma, Lutetian to Priabonian for the Upper Member of the Río Turbio Formation (Guerstein et al, 2014;González Estebenet et al, 2017). Recently, this biostratigraphic scheme has been updated based on radiometric U/Pb data published by different authors that allowed to calibrate the dinoflagellate cyst bioevents (Amenábar et al, 2022;Fig. 2.2).…”

“…Circles: localities studied in this work, MA, Man Aike Formation; YCF, Upper Member of Río Turbio Formation (upper part of the core, from sample 130 to the top); YCF, Upper Member of Río Turbio Fm (lower part of the core, up to sample 280); RT, Leticia Formation (Río de la Turba section); Le, Leticia Formation (Cabo Campo del Medio section); AM, La Meseta Formation. Square: localities studied by other authors; LD T-1, Leña Dura Formation (Well T-1, Laguna Blanca region, Chile, Bijl et al, 2021); LD-SELK 65, Leña Dura Formation (Well SELK-65, Isla Riesco, Chile, Bijl et al, 2021); LP, Loreto Formation (Río Los Palos section, Isla Riesco, Chile, Bijl et al, 2021); site DSDP 511, Malvinas Plateau (Houben et al, 2019); site ODP 696, orcadas de Sur, Weddell Sea (Houben et al, 2019); 2, Map of southern South America with the extension of the Austral-Magallanes Basin which is outlined in dotted line (modified from Nullo et al, 1999); 3, Map of the northern Antarctic Peninsula displaying the limits of the James Ross Basin, drawn in dotted line (del Valle et al, 1992) at 34.10 Ma and the increase of the protoperidiniacean species allows to compare the top of this zone with the bottom of the zone SPDZ16, calibrated with the upper part of the magnetochron C13r (34.7-33.7 Ma) (Amenábar et al, 2022). These dating differences in both Austral-Magallanes and James Ross basins require an extensive thoughtful discussion to reach the most agreed age.…”

“…Due to the age discrepancy of the units and the need for accurate stratigraphy, Amenábar et al (2022; Fig. 2.2) reinterpreted the geochronological information on the basis of the recently available radiometric data from Santa Cruz (Fosdick et al , 2020; Leonard et al , 2020) and Tierra del Fuego (Olivero et al , 2020) provinces and southern Chile (Bijl et al , 2021), and they also recalculated ages of Antarctic Peninsula based on McArthur et al (2020).…”

“…In our analyzed samples the RTF4 zone has not been registered; however, considering the updated information recently published by Houben et al (2019, ), the LO of the Antarctic Vozzhennikovia spp. at 34.10 Ma and the increase of the protoperidiniacean species allows to compare the top of this zone with the bottom of the zone SPDZ16, calibrated with the upper part of the magnetochron C13r (34.7–33.7 Ma) (Amenábar et al , 2022).…”