Potential drilling locations at the Argentine continental margin to investigate the Cenozoic history of South Atlantic deep water circulation


Contact
Jens.Gruetzner [ at ] awi.de

Abstract

Persistent geostrophic currents interacting with sea-floor topography and available sediment sources are capable of eroding, transporting and depositing fine-grained particles into mounded and elongated sediment drifts. These drifts show enhanced accumulation rates when compared to pure pelagic sequences and are thus attractive targets for high resolution paleoceanographic studies. Several expeditions of the IODP/ODP (e.g. 162, 172, 303, 306, 339, 342) therefore have successfully targeted giant contourite drifts. An unexplored area in this context is a prominent contourite depositional system (CDS) located in the southernmost sector of the extensional Argentine margin. Here the thermohaline circulation is characterized by the interaction of northwardflowing Antarctic water masses (Antarctic Intermediate Water, AAIW; Circumpolar Deep Water, CDW; Antarctic Bottom Water, AABW) and southward-flowing North Atlantic Deep Water (NADW). The transfer of heat and energy via these water masses constitutes an important component in maintaining the global ocean conveyor belt. We investigate an extensive set of high quality seismic reflection profiles from the Argentine continental margin to detect, characterize and map sedimentary features related to bottom current activity and to reconstruct past changes in the abyssal circulation. Typical margin-parallel morphosedimentary features such as (1) a set of four terraces on the slope and rise, (2) channels separating the terraces, (3) a giant buried sediment drift, and (4) sheeted drifts on the abyssal plain indicate that along slope (contour current) transport dominates over downslope (turbiditic) processes at the southern Argentine margin. Along the central Argentine margin the relative importance of the permanent, steady bottom currents and the shorter-duration, unsteady mass wasting processes on sediment deposition was variable in time and space. Based on a detailed investigation of a continental slope terrace at the southern margin and the mapping of depocenter geometries of four major seismic units at the central margin a chronology of the depositional processes during the Cenozoic was derived: While the Paleocene/Eocene (~65 – 34 Ma) is characterized by hemipelagic sedimentation under relatively sluggish bottom water conditions, strong AABW circulation led to widespread erosion on the slope and growth of a large detached sediment drift during the Oligocene and early Miocene (~34 – 17 Ma). After deposition of an aggradational seismic unit interpreted to represent low bottom current activity during the Mid-Miocene climatic optimum (~17 – 14 Ma), a current reorganization through the emergence of Lower CDW took place at approx. 14–12 Ma when the Valentin Feilberg Terrace started growing. Current controlled sedimentation under moderate flow speed commenced at the southern Argentine margin during the middle to late Miocene (~12 – 6 Ma) but at the same time gravitational down-slope sediment transport increased at the central Argentine margin possibly related to tectonic uplift in South America. The Pliocene to Holocene unit at the southern Argentine margin indicates strengthening of bottom flow after 6 Ma possibly due to a general change in deep water mass organization following the closure of the Panamanian gateway. At the central Argentine margin this unit is very heterogeneous and formed by interactions of down-slope and along-slope sediment transport processes as indicated by the evolution of canyons, slope plastered drifts and channels. The available multichannel seismic profiles constitute a high-quality site survey and the results from our project may be used as background information for future ocean drilling in the region which would reveal important aspects of the deep water history and provide better age constraints. We here suggest a transect of drill sites on continental slope terraces in different water depths at the southern Argentine margin. Inferred sedimentations rate of >8 cm/1,000 years would make these drill sites suitable for high-resolution paleoclimatic studies of the Cenozoic.



Item Type
Conference (Poster)
Authors
Divisions
Programs
Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
Gemeinsames Kolloquium - DFG-Schwerpunktprogramme ICDP (International Continental Scientific Drilling Program) und IODP (Integrated Ocean Drilling Program), 25 Mar 2013 - 27 Mar 2013, Freiberg, Germany.
Eprint ID
32252
Cite as
Gruetzner, J. , Uenzelmann-Neben, G. and Franke, D. (2013): Potential drilling locations at the Argentine continental margin to investigate the Cenozoic history of South Atlantic deep water circulation , Gemeinsames Kolloquium - DFG-Schwerpunktprogramme ICDP (International Continental Scientific Drilling Program) und IODP (Integrated Ocean Drilling Program), Freiberg, Germany, 25 March 2013 - 27 March 2013 .


Share

Research Platforms
N/A

Campaigns


Actions
Edit Item Edit Item