Recognizing key sedimentary facies and their distribution in mixed turbidite–contourite depositional systems: The case of the Pacific margin of the Antarctic Peninsula

Abstract

Interplay of deep‐water sedimentary processes is responsible for building a myriad of features and deposits across mixed turbidite–contourite systems, from <5 cm beds to >200 km long sedimentary drifts. Investigations of the spatial and temporal variability of their sedimentary facies and facies associations is crucial to reveal the dynamics between along‐slope bottom currents and down‐slope turbidity currents, as well as their impact on drift construction and channel erosion. This study focuses on extensive modern mixed (turbidite–contourite) systems, developed across the continental rise of the Pacific margin of the Antarctic Peninsula. Nine sediment cores were sampled and analysed, through grain size and geochemical methods, to study the sedimentary facies at high‐resolution (ca 1 to 20 cm). Three main facies associations have been identified across distinct morphological features (i.e. mounded drifts and trunk channels), comprising intercalations of hemipelagites, bottom current reworked sands (which include fine to coarse‐grained contourites) and gravitational facies (turbidites and mass‐transport deposits). These facies associations reflect fluctuations of the background sedimentation, oscillations of the bottom‐current velocity and of the frequency of gravity‐driven currents. The sedimentary record features cyclic alternations during the Late Quaternary (>99 kyr), suggesting that variations between along‐slope bottom currents and down‐slope turbidity currents are strongly linked to glacial–interglacial cycles during Marine Isotope Stages 1 to 6. Sedimentary records affected by bottom currents on polar margins, such as those of the Antarctic Peninsula, are essential to decipher the facies and facies sequences of bottom‐current deposits, as the low degree of bioturbation throughout most of the sediments allows us to observe the original sedimentary structures, which are poorly preserved in similar deposits from other continental margins.

Eocene to middle Miocene contourite deposits in Cyprus: A record of Indian Gateway evolution

“…Early diagenesis may have led to rapid lithification that preserved original sedimentary structures for units having high percentages (>90%) of carbonate bioclasts. Polar margins are another setting where primary sedimentary structures are well preserved, but in this case because environmental conditions do not favour benthic activity (Rodrigues et al, 2022a).…”

“…Detailed sedimentologic analysis has provided some criteria for discriminating facies-scale bottom current deposits from turbidites or other deepwater pelagic deposits. Specific contourite sedimentary facies have been described by a number of studies (e.g., Stow and Lovell, 1979;Stow, 1982;Stow and Holbrook, 1984;Stow and Piper, 1984;Pickering et al, 1989;Faugères and Stow, 1993;Gao et al, 1998;Faugères et al, 1999;Stow et al, 2002aStow et al, , 2013aStow et al, , 2013bRebesco, 2005;Llave et al, 2006;Øvrebø et al, 2006;Shanmugam, 2006Shanmugam, , 2012Shanmugam, 2014;Stow and Faugères, 2008;Stow et al, 2013aStow et al, , 2013bRebesco et al, 2014;de Castro et al, 2020de Castro et al, , 2021ade Castro et al, , 2021bStow and Smillie, 2020;Hüneke et al, 2021;Rodrigues et al, 2022a). Recent research proposes new diagnostic criteria for contouritic sedimentary facies (Alonso et al, 2016;Brackenridge et al, 2018;Rodríguez-Tovar and Hernández-Molina, 2018;de Castro et al, 2020de Castro et al, , 2021ade Castro et al, , 2021bStow and Smillie, 2020;Yu et al, 2020;Hüneke et al, 2021;Rodríguez-Tovar, 2022) based on statistical analyses (as Principal Component Analysis, PCA) of texture, micro...…”

“…The main diagnostic criteria for discriminating ancient contourite deposits applied in this work can be summarized in terms of evidence of: sedimentary condensation (sensu Föllmi, 2016), reworking, reactivation surfaces, smaller grain-size variations, small-scale hiatuses, sedimentary condensation/omission, variations in sedimentary processes (bed load versus suspension load), current velocity, sedimentation rates, and paleo-environmental conditions. Such criteria have been proposed and evaluated by numerous reports (McCave, 2008;Rebesco et al, 2014;Rodríguez-Tovar et al, 2019ade Castro et al, 2020de Castro et al, , 2021ade Castro et al, , 2021bHüneke et al, 2021;Rodrigues et al, 2022a). More specific diagnostic criteria include: a) particles representing bioclasts from skeletons of planktonic biota recycled from deep-marine pelagic muds, b) bands of coarser grainstone with higher concentration and/or reworking of foraminifera (and other bioclast types) within calcarenite beds, c) muddy contourites varying from mud-supported (wackestones) to grain-supported (packstones) and back again, d) intensely, pervasively bioturbated contourite beds with indistinct boundaries, e) mud-rich (packstone) and heterogeneous middle parts of particle-supported contourite beds relative to particlesupported lower parts of turbidite beds (globigerinid grainstones), and f) wavy layering in sandy contourites with local faint lamination or parallel-and cross-lamination (traction sedimentary structures) characterised by layer-specific proportions of bioclasts.…”

“…Partial reworking of a turbidite division (usually the top) with only minor sediment transport would qualify as BCRS. They may or may not include a component of lateral displacement, and usually appear in a contourite drift environment, for example in the channel-drift transition (de Castro et al, 2020(de Castro et al, , 2021a, or in mixed levee-drift systems (Shanmugam et al, 1993a(Shanmugam et al, , 1993bFonnesu et al, 2020;Fuhrmann et al, 2020;Rodrigues et al, 2022aRodrigues et al, , 2022b. Mutti et al (2014) defined a facies association similar to BCRS in which genetically distinct processes (turbidity currents and bottom currents) produce vertically and laterally associated facies.…”

Carbonate contourite drifts in the southwest South China Sea: Sedimentary, paleoceanographic and economic implications

“…Bottom currents are vital oceanographic processes of redistributing sediments (Hanebuth et al, 2015;de Castro et al, 2021;Rodrigues et al, 2022), shaping seafloor morphology (Howe et al, 2006;Hernández-Molina et al, 2017;Yin et al, 2022), influencing marine ecosystems (Loeb et al, 2010;Cimino et al, 2020), and transporting pollutants (Martin et al, 2017;Kane and Clare, 2019). The persistent bottom currents that are commonly driven by winds, thermohaline circulation, eddies, and tides can create alongslope sedimentary features on the continental margin through geological timescales (Hernández-Molina et al, 2008;Rebesco et al, 2014).…”