The rocky shelf of the Méloine is one of the many platforms with pitfalls that line the front coast of Brittany (Battistini and Martin, 1956). It is located between 4 and 11km off the Primel cliffs. It is composed of 4 rocky islets, some of which emerge at low tide. We can thus distinguish from south to north: the rocks of Tripods, Melamine, Garo-Karreg Bridge in Hir and a last unnamed massif bordering the northern boundary of the batholith. The whole is stretched N50, i.e. parallel to the direction of older cadmium fractures. These reefs are separated by corridors or slight depressions oriented E-W, several hundred meters wide. The rocks of the Melamine belong to the large family of late Hercynian "red" granites (300 Ma, Rollet in Augris and Simplet, 2011; Ballèvre et al., 2013) of which the most famous is that of Ploumanac'h. They form a link in the monilithic belt of the Variscan granites of Northern Armorica, parallel to the directional faults of the English Channel (Chauris, 2002; Barrière et al., 1986). The place of this granite is discussed in the hypothesis of a subduction under the domnonian domain (northern part of the Armorican Massif, Lefort, 1975). It is affected by powerful mylonitic bands, straightened and oriented W.NW - E.SE (Barrière et al., 1986). The mapping of this archipelago shows that it is cut to the north, at a depth of 50 m, by an N140 fault attached to the family of Hercynian dropouts. This fault could also have guided the main channelization of the old rivers offshore as a direct extension of the second drainage system in Lannion Bay during the ice ages (Simplet et al., in Augris & Simplet, 2011). This archipelago had to remain until about 10,000 years BP a peninsula extending the Primel-Plougasnou coast to the NE, effectively enclosing Morlaix Bay. This date marks the moment from which the 43 m bathymetric threshold was flooded during the rapid rise (10 mm/year) from sea level to the Holocene. Soon, the archipelago broke away from the coast and before 9000 years BP, its 3 passes located topographically below 30 m deep, saw the establishment of a powerful E-W tidal circulation, connecting the bay of Morlaix to that of Lannion, at the origin of the initial construction of the sandy bodies attached to the reefs. The surface area occupied by outcropping rock is 32% (9.8 km2), that of subcrop rock composed of basement flakes emerging from the seabed and sometimes covered with boulders is 22% (6.75 km2). The northern passes are relatively filled with sediment. The southern pass, between the Tripods and the Meloine, has a very flattened geometry, levelled and maintained by powerful tidal currents, as can be observed in other archipelagos (Bajjouk et al., 2013). Almost 50% of the area is covered with sediment. In detail (Ehrhold et al., 2015c), granulometric analyses show that they are broken down into 5 main facies: 

1 - A paving of pebbles (CL1a) and gravelly pebbles (CL1b) in the passes and at the foot of the reefs (16.3%).
2 - Gravel (GL1b) and stony gravel with little shell (GL1a), constituting thin corridors elongated in the direction of the currents (6.1%).

3 - Locally areas of very shelly gravel (GB2b), particularly at the base of the Trépieds Bank (0.6%).

4 - Sandy gravels (GB1c to GB2c) moderately to very shelly around the archipelago (4.75%).
5 - Homogeneous coarse to gravelly shellfish sands (SB1c to SB2b) covered with megarids (12.7%), and constituting the surface part of the sedimentary bodies trapped in the archipelago.
6 - Medium very shell-like sands (SB2d) components the nature of peripheral sedimentary bodies (4.92%) described in the study by Morlaix (Ehrhold et al., 2011b) and Lannion (Augris and Simplet, 2011).

The distribution of surface sedimentary formations underscores the complexity of sedimentation processes in these environments where structural heritage plays a major role in the nature of sedimentary deposits. Underwater morphology reinforces the tidal circulation that causes the reworking and deposition of sediments. While specifying the work of Boillot (1964) and Beslier (1981), our results show that the Méloine rocky plateau is the site of intense circulation of sedimentary material, as shown by the numerous current figures detected by imagery and bathymetry. This plateau is permeable to sedimentary exchanges, particularly gravelly-shell material, between the two large bays of this region. Its western edge is under the dominant influence of the flow, and conversely for the eastern edge.

Residual bedload transport map