FROM ALLUVIAL FAN TO DISTAL TURBIDITIC SYSTEMS: PRELIMINARY RESULTS ON DEEP-WATER BYPASS PROCESSES BASED ON GILBERT-TYPE FAN DELTA OUTCROPS OF THE CORINTH RIFT (GREECE).
Résumé
Source-to-sink (S2S) can be seen as the integration with other earth science disciplines;
from geomorphology, sedimentary geology to basin geodynamic analysis. A major limitation
to go further is the access to the entire basin geometry (proximal to distal setting, “closed” box,
deep crustal and lithospheric geometries) as well as age constrains.
We present the preliminary results of a sedimentological and sequence stratigraphy
analysis of outcropping Gilbert-type deltas from the Corinth rift (Plio-Pleistocene). Drone acquisition
has also been carried out to propagate the correlations in 3D along steep cliffs. The
study case provides an unique opportunity to describe the sedimentary facies and correlated
them though space and time from the proximal to the most distal setting, in a very well
constrained basin geometry and timing. In this communication, we will mainly focus on deepwater
sediment bypass in terms of flow processes and associated stratigraphic expression, as it
is a key issue to address sedimentary budget analysis in a S2S perspective.
A new bottomset typology has been established including 4 end-members: (1) Gravely
bottomset, (2) Major erosion – by pass, (3) Fine-grained starved bottomset, and (4) Deep Water
Massive Sand (DWMS) bottomset. The relationship between the bottomset end-members and
their associated turbiditic system has also been characterized. (1) During Gravely bottomset
deposition, unconfined to low relief channel-levee complex occurs at the very end of the bottomset.
(2) The major erosion in bottomset occurs when the foresets present a maximal progradation
rate, the bottomset is eroded and bypassed. Coarse- to fine-grained sediments are
exported in the turbiditic system to form large channel-levee complex. (3) During Fine-grained
starved bottomset deposition, limited amount of sediment feed the turbiditic system from the
delta. Indeed, the major part of the sediments is stored in topset and foreset areas. (4) Deep
water massive sand bottomset forms coarse-grained slope apron geometry on the delta toe.
Coarse-grained material is massively stored in the bottomset, and only fine-grained sediments
are exported to the turbiditic system to form lobe complex. Superimposed onto this dynamic,
evidences of contouritic events have also been identified.