The imprint of orbital and millennial-scale sea level oscillations on the Gulf of Lion sedimentary record, Mediterranean Sea, of the last 500 ka
Abstract
The Quaternary building of the fluvial-influenced margin of the Gulf of Lion was controlled by glacio-eustatic oscillations that generated a stacking of deltaic regressive progradational units (RPUs) in the outer shelf and upper slope during successive sea level falls of the last glacial periods (100 kyr cycles). However, since no borehole data was available, recognition of those lowstand units was only possible by means of seismic profiles, which allowed identifying a stacking of five RPUs, whose should correspond to the last five cycles of sea level fall, last 500 ka. In addition, abrupt inundation and slow exposition of the shelf in response to a 100 kyr sea level cycle controlled the volume of water in the shelf exposed to atmospheric-induced mechanisms such as Dense Shelf Water Cascading (DSWC), which is at present highstand a key mechanism for the transfer of sediment and organic matter to the deep basin. Grain-size data together with oxygen isotopic-based chronostratigraphy from the 300 m length PRGL1-4 borehole drilled in the interfluve of the Aude/Hérault canyons within EC-PROMESS1 project clearly shows five major upwards fining sequences corresponding to the last five cycles (100 kyr) of sea level falls. Correlation of these analytical sequences with high-resolution seismic profile at this site allowed re-interpretataion of the upper slope seismostratigraphy as seven units are documented instead of the five previously identified from seismic reflection profiles only. In addition, grain-size results from PRGL1-4 allowed us to describe an outer shelf/upper slope depositional model based on the alternation of elevated fluxes of fine-deltaic deposits during lowstands and reduced fluxes of shelf-eroded coarse material during highstands mainly transported by erosive processes as DSWC. Consequently, grain-size records in the Gulf of Lion margin respond to sea level oscillations. On the millennial-time scale, the 70 km wide shelf resulted very sensitive to sea level oscillations of higher frequency, as those occurred during Marine Isotopic Stage (MIS) 3. Independently of the age model used, grain-size increases recorded in PRGL1-4 during MIS3 suggest that relative high sea levels occurred at the onset of all Dansgaard-Oeschger (DO) warm interstadials in Greenland, including the shortest ones. However, the non-linear response of grain-size with sea level prevent us to establish nor the magnitude of those sea level fluctuations neither the exact timing of the sea level rises, which could also initiate during previous cold stadial.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.U51A0009F
- Keywords:
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- 1616 GLOBAL CHANGE / Climate variability;
- 1641 GLOBAL CHANGE / Sea level change;
- 3002 MARINE GEOLOGY AND GEOPHYSICS / Continental shelf and slope processes;
- 4901 PALEOCEANOGRAPHY / Abrupt/rapid climate change