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Crumeyrolle, Philippe1, Eduard Remacha2, Philippe Razin3, Ferran Bolano2, Gemma Gual2, Ferran Climent2
(1) Total, Pau, France
(2) Universitat Autonoma de Barcelona, Barcelona, Spain
(3) Bordeaux University, Bordeaux, France

ABSTRACT: Comparison of Fluvial, Deep and Shallow Delta-Front Channels-Fills Builts by Lateral Accretion in the Montanana Fluvio-estuarine, Morillo Turbidites and Sobrabe Delta Systems, (South-Central Pyrenees, Spain): Implications on Sediment Transfer Mechanism from Shelf to Deep Basin

The South Pyrenean Eocene basin comprises a wide range of fluvial, shallow marine and deep water clastic sediments. In this basin, channelized sandbodies showing lateral accretions were identified in various settings: the Morillo deep-water turbidite channels, the Sobrabe delta-front channels and the fluvio-estuarine channels of the Montanana sequence.
1. In the Morillo turbidite system, outcrops revealed channelized sinuous turbidite channels with lateral accretion surfaces associated with a range of facies showing analogies with sinuous migrating deep-water channels complexes recognized with 3D-HR in the Tertiary of West Africa.
2. In the shallow marine deltaic sediments of the Sobrabe Formation, sinuous “turbidite like” channels showing lateral accretion were also recognized and interpreted as a result of flood related hyperpycnal currents entering in the delta front (less than 50m).
3. In the Fluvio-estuarine sediments of the Montanana sequence, laterally accreted channels were also described.
Despite the significant difference in water depth and depositional processes, the described examples of laterally accreted channels show strinking facies and architecture similarities.
Lateral accretion surfaces occurring in the Morillo turbidite system, are the result of the deposition of successive turbidite currents forming individual isolated sandbodies or larger channel complexes, mostly made of F5 and F2 facies inbedded with thin-bedded overbank wedges.
In the Sobrabe delta-front, sandbodies with lateral accretion occur imbedded in slope to delta front nummulite-rich mudstones and siltstones disrupted by numerous truncations related to slump scar fill. These channels can be traced physically into flood dominated delta-front proximal and fluvial depositional systems.
The description of these turbidite or turbidite-like channels, ranging from deep to shallow water depth allow to understand the coeval complex interaction of shelf edge failures and hyperpycnal flood-related currents derived from fluvial channels as a mechanism for sediment transfer from shelf to deep basin and the generation of a continuum range of facies from flood-related fluvial to turbidite systems.

 

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.