Footprints of palaeocurrents in sedimentary sequences of the Cenozoic across the Maurice Ewing Bank

Abstract

<p>High-resolution 2D multichannel seismic data collected by the Alfred Wegener Institute in 2019 across the Maurice Ewing Bank, the high-altitude easternmost section of the Falkland Plateau in the SW South Atlantic, are integrated with information from DSDP Leg 36, Sites 327, 329, and 330 and Leg 71 Site 511. A seismostratigraphic model is defined, including five units ranging in age from the Middle Jurassic to Quaternary and are interpreted with respect to the evolutional history of the oceanic circulations in the South Atlantic sector of the Southern Ocean. Sedimentary sequences of late Cretaceous and early Paleogene include little and restricted evidence of current activity, attributable to shallow-intermediate depth connections between the developing South Atlantic and Southern Ocean. In contrast, sedimentary sequences of the late Eocene/Oligocene and Neogene reveal a strong history of current-related erosion and deposition. These features exhibit specific water-depth expressions attesting to the long-term activity of different water masses, in stable circulation patterns as those of the present day. We thus suggest that proto-Upper and -Lower Circumpolar Deep Waters have been shaping the bank since the Oligocene. This implies that this bathymetric high has been acting as a barrier for the deep and bottom water masses flowing within the Antarctic Circumpolar Current since its establishment about the Eocene-Oligocene boundary.</p>

Fossilized silica diagenetic fronts: Implications for palaeoceanographic evolution across the Falkland/Malvinas plateau

“…3, AWI-20190004, CDPs 2500-5500) and Parasound profiles (Uenzelmann-Neben, 2019), together suggest that oceanic circulation on the Falkland/Malvinas Plateau has been relatively stable since at least the Middle-Late Miocene. Palaeoceanographic investigations using contouritic features across the MEB also concluded a relatively uniform intensity and pathway for LCDW since at least the Middle Miocene (Najjarifarizhendi and Uenzelmann-Neben, 2021). In today's oceanic setting, the oceanographic data place the velocity core of the LCDW at depths of 2000-3000 m, overspilling the F/MB and entering the Argentine basin (Arhan et al, 1999(Arhan et al, , 2002Orsi et al, 1999).…”

“…Seismic reflection profiles correlated to drilling data show the study area to consist of Precambrian basement overlain by a sedimentary succession up to 3 km thick, that records deposition since the Middle-Late Jurassic (Figs. 3, 4) (Najjarifarizhendi and Uenzelmann-Neben, 2021). Previous work by Najjarifarizhendi and Uenzelmann-Neben (2021) on the MEB, has divided the succession into five main units, shown in Fig.…”

“…The F/MB lies between the more elevated F/MI and MEB, with average water depths of 2600 m, and forms a 500 km-wide basin containing a sedimentary column up to ca. 3000 m thick above basement (Lorenzo and Mutter, 1988;Najjarifarizhendi and Uenzelmann-Neben, 2021;Richards et al, 1996).…”

“…2 (Shipboard_Scientific_Party, 1974a, b, c;. No downhole geophysical logs were acquired at the four DSDP sites, but velocity measurements on cored sections yielded interval velocities which we used to convert from the depth to time domains (Najjarifarizhendi and Uenzelmann-Neben, 2021). The velocity data were used to correlate information from the drill sites with seismic profiles in order to construct an age-constrained stratigraphic model for the eastern part of the Falkland/Malvinas Plateau (see Appendix B).…”

“…7). Using an average thermal gradient of 45 • C/km and seafloor temperature of 1 • C for the F/MB, the estimated temperature at the TZ A/CT equals 22.3 • C. Taking 35 • C as the minimum required temperature for onset of Opal-A/CT conversion (Berndt et al, 2004;Hein et al, 1978;Kuramoto et al, 1992;Neagu et al, 2010), the calculated temperature at the present depth of TZ A/CT in the F/MB One possible explanation for the cessation of upward movement of the TZ A/CT in the F/MB is a rapid temperature drop at the seafloor in response to the onset of the ACC, when southern-sourced cold water masses reached the plateau at about the Eocene-Oligocene boundary (e. g. Barker, 1977;Najjarifarizhendi and Uenzelmann-Neben, 2021;Scher and Martin, 2006a;Scher and Martin, 2006b;Uenzelmann-Neben et al, 2017). Benthic foraminiferal proxy records at DSDP Site 511 suggest a temperature drop from 8 to 12.5 • C in the Eocene to ca.…”