Structure and Evolution of the Gulf of Lions : the Sardinia Seismic Experiment and the GOLD (Gulf of Lions Drilling) Project

Daniel Aslanian, Maryline Moulin, Philippe Schnurle, Frauke Klingelhoefer, Estelle Leroux, Marina Rabineau, Audrey Gailler, Francois Bache, Christian Gorini, Nobu Eguchi, Junichiro Kuroda, Andre Droxler, Karine Alain, Francois M. Roure, and Bil Haq

The study of the deep structure and evolution of passive continental margins is important for the understanding of rifting processes and the formation of associated sedimentary basins. Since the classical models of McKenzie (1978) and Wernicke (1985), understanding how passive continental margins form, that is to say mainly the way that continental lithosphere is thinned leading to subsidence, remains one of the main challenges in Earth Sciences. Many recent observations and discoveries have modified our basic views of margin formation. The conservational models paradigm, i.e. simple shear, pure shear or polyphase models, which exclude exchanges between lower continental crust and upper mantle and which are usually proposed to explain lithospheric stretching and consequent crustal thinning of passive continental margins, fail to completely explain all these observations. Furthermore, these models imply large amount of horizontal movement, whilst these movements are not observed in the field. In consequence, new concepts need to be built and tested.

One of the main obstacles to our understanding of margin formation is the unknown nature of the transitional domain between the unthinned continental crust and the true oceanic crust. Using paleogeographic constraints, wide-angle and reflection seismic profiles or modelling, some authors suggested that lower continental crust may have been removed from its original place and have flowed towards the middle part of the system or/and towards both extremities of the conjugate margins system (Aslanian et al., 2009; Huismans & Beaumont, 2011; Aslanian & Moulin, 2012). Another challenge is to understand how margins evolve starting in a structurally elevated position during its initial formation, with the presence of subaerial deposition of basalts, shallow water evaporites, subaerial erosion, and/or construction of a carbonate platform, towards a basin affected by strong subsidence during the plate divergence phase. Passive margins seem to be close to sea-level, even after the break-up as demonstrated by carbonates postdating the oceanic crust (e.g. on the central and the south Atlantic margins). We therefore need to be able to reconstruct paleobathymetries of the synrift and postrift deposits. The Gulf of Lions represents a unique natural laboratory to study both evolution and interaction of deep processes (geodynamics, tectonics, subsidence, isostasy) and more superficial processes (river behavior, sedimentary fluxes, sea-level changes, climate change, etc.).

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013