--> Bridging the Gap Between Giant Gilbert-Type Bottomset and Associated Mixed Turbiditic-Contouritic Systems in a High Sediment Supply Setting

AAPG ACE 2018

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Bridging the Gap Between Giant Gilbert-Type Bottomset and Associated Mixed Turbiditic-Contouritic Systems in a High Sediment Supply Setting

Abstract

To bridge the gap between the marginal coarse-grained delta and the basin axis depocenter in high-sediment supply setting, we propose to study outcrops from the Ilias Gilbert-type delta to pro-delta along the southern margin of the Gulf of Corinth in Greece. An entire sedimentological profile is documented from source to sink based on standard field observations enhanced by 3D photogrammetric models (UAV acquisition). We primarily focus on the facies distributions, facies associations, internal architectures and the sandbody morphologies.

The Gilbert-type delta bottomset is classically described as produced by decantation (Gilbert, 1885) and limited mass transport deposit in the toe of the delta (Postma and Roep, 1985). However, this field based study reveals four bottomset-dynamics under specific processes integrated within a stratigraphic frame. Each bottomset dynamic has specific facies, facies association and architecture. One sandy-rich bottomset has been identified with a slope apron geometry produced by high-density turbidity during the transgressive stage. During the normal regression, the bottomset records a complete erosional by-pass stage, i.e. the sediments are totally exported throughout the pro-delta.

Downstream of the Gilbert-type delta bottomsets (i.e. > 500 m water depth), the sedimentary system is dominated by conglomeratic to sandy rich channels with an axis of 60° from the delta axis and located along slope. The channels are limited by both external and internal margin with specific facies and architectures only on the basinward-side. Channels are commonly characterized by low sinuosity geometries with a mean slope of 2°. The external margin could locally include sediment waves as well as Mass Transport Deposits. The facies, architecture of the margin and direction of the channel argue for a bottom-currents driven system feeding by the gravity driven sedimentary flows from the delta. The conglomeratic channel outcrops along more than 3 km, constituting a new coarse-grained end-member in the deep water depositional system.

This study provides the key elements to recognize the facies and architectures of the different bottomset typologies in relation with the associated pro-deltaic and mixed turbiditic-contouritic system. These sedimentary and stratigraphic models improve the prediction for the sand and conglomerate distribution and their connectivity within the various parts of the delta toe induces by a high-sediment discharge.