Variations in sediment transport at the central Argentine continental margin during the Cenozoic

Abstract

[1] The construction of the sedimentary cover at most passive continental margins includes gravitational downslope transport and along-slope contourite deposition, which are controlled by tectonics, climate and oceanography. At the eastern continental margin of Argentina the history of deposition and erosion is intimately linked to the evolution of the South Atlantic and its water masses. Here we present a detailed seismic investigation of the mixed depositional system located between 41 S and 45 S. The study provides a northward complement to prior investigations from the southern Argentine margin and together with these may be used as background information for future ocean drilling in the region. Prominent features in our seismic cross sections are submarine canyons, mass wasting deposits, contourite channels, and sediment drifts. Four major seismic units above regional reflector PLe (65 Ma) are separated by distinct unconformities of regional extent. Using a dense grid of reflection seismic profiles, we mapped the depocenter geometries of the seismic units and derived a chronology of the depositional processes during the Cenozoic. While the Paleocene/Eocene (65-34 Ma) is characterized by hemipelagic sedimentation under relatively sluggish bottom water conditions, strong Antarctic bottom water (AABW) circulation led to widespread erosion on the slope and growth of a detached sediment drift during the Oligocene and early Miocene (34-17 Ma). After deposition of an aggradational seismic unit interpreted to represent the Mid-Miocene climatic optimum (17-14 Ma), gravitational downslope sediment transport increased during the middle to late Miocene (14-6 Ma) possibly related to tectonic uplift in South America. The Pliocene to Holocene unit (<6 Ma) is very heterogeneous and formed by interactions of downslope and along-slope sediment transport processes as indicated by the evolution of canyons, slope plastered drifts and channels.

IODP workshop: developing scientific drilling proposals for the Argentina Passive Volcanic Continental Margin (APVCM) – basin evolution, deep biosphere, hydrates, sediment dynamics and ocean evolution

“…However, a number of papers published since 2009 reported new high-resolution and/or multichannel seismic surveys (Fig. 4), often combined with multi-beam bathymetric data, which show the common occurrence of layered sediments and prominent sediment drifts on the Argentine and adjacent Uruguayan margins (e.g., Hernández-Molina et al, 2009Violante et al, 2010, Krastel et al, 2011Lastras et al, 2011;Muñoz et al, 2012;Grützner et al, 2011Grützner et al, , 2012Grützner et al, , 2016Preu et al, 2012Preu et al, , 2013Voigt et al, 2013;Uenzelmann-Neben et al, 2016; see also Hinz et al, 1999). There has also been significant progress studying the climatic records in surficial and near-surface sediments recovered in sediment cores from the Argentine margin (e.g., Chiessi et al, 2007;Bozzano et al, 2011;Govin et al, 2012;Bender et al, 2013;Razik et al, 2013;Razik, 2014;García Chapori et al, 2014, demonstrating that this margin also contains important modern sedimentary deposits.…”

“…Cretaceous shelf sediments here are expected to be black shales, sandstones and coarser-grained deposits (Loegering et al, 2013) while Cre- Interpreted seismic line across the Argentine margin featuring distinct drift deposits, channels, and thickness of deposits. Ocean current distribution within the water column: AABW is Antarctic Bottom Water; LCDW is Lower Circumpolar Deep Water; UCDW is Upper Circumpolar Deep Water; NADW is North Atlantic Deep Water (see Grützner et al, 2012). Predicted age and character of the sediment deposits need to be determined through sampling to understand in detail the evolution of the margin in response to climate changes.…”

“…Hernández-Molina et al (2010) and Grützner et al (2012) suggested that sediments from about the Cretaceous-Tertiary boundary to the Eocene-Oligocene boundary are thick along the margin and are characterized by being parallel to subparallel reflections of low to moderate amplitude. This is generally a time of low to moderate bottom current activity and a warm climate.…”

“…4; the "giant drift" of Hernández-Molina et al, 2010 andGrützner et al, 2012). This drift is buried to the west by the flanks of younger and shallower deposits (termed "mounded drifts") of mid-to late Miocene age, which developed sequentially within the south-central portion of the Argentine margin.…”

“…Drifts are also present farther north along the margin (e.g., Hernández-Molina et al, 2015) with drifts apparently associated with flows of Antarctic Intermediate Water (AAIW), Upper Circumpolar Deep Water (UCDW), North Atlantic Deep Water (NADW), Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW). Violante et al (2010) and Grützner et al (2011Grützner et al ( , 2012Grützner et al ( , 2016 suggested that increased sediment flux to the margin during the Miocene may in part be related to an uplift in the Andes that in turn is due to increased Miocene Pacific Ocean crustal spreading and subduction rates, which peaked at about 10 to 20 Ma (Pardo-Casas and Molnar, 1987;Martinod et al, 2010). However, the routes or processes by which…”