## 6 Fault Trench Analyses at the Base of the Scarp
The fluvial deposits are certainly of the Late Quaternary age (presumably Holocene) and related to the Torrent de Solleric (see Figure 3), which runs parallel to the Sencelles fault around the excavated zone [19; 20]. The age of the clayey marks of units A and B is unclear. The occurrence of rizhoconcretions, carbonate nodules, and gley mottling suggests a subaerial or intertidal origin. The lack of datable material along the entire excavated trench impeded any chronological assignation for these units. However, it could correspond to the _Bonatova Fm._, the _Santantanty Fm._ (marls and calcisiltites), or some other member of the so-called Fini-Messinian Terminal Complex (see cross-section of Figure 2). These formations display mangrove to lagomare tidal facies in this sector of the Inca basin, and according to the borehole and geophysical data [17; 18; 38], they are close to the surface. In fact, detailed Very Low-Frequency electromagnetic profiles (VLF) carried out before the excavation of the trench detected a subsurface diapiric-like body in the hanging wall of the fault [20; 35]. This suspect clayey diaper is rooted at 60 m depth and its upper figure match-well with the deformation shown in the clayey antifirm of Unit A (see Figure 8 [PERSON] et al., 2001 [20]; p. 257). Three different colluvial units sourced by the fault scarp occurred only adjacent to the bedrock fault scarp in the fault trough (2.6 m width) generated by the flanking anticline. These colluvial units overlapped (Units C, D, H), burying the last 0.95 m of the excavated fault plane between meters 15 and 16 of the log (Figure 12). Finally, the upper 2.05-2.45 m remained exposed as the free face of the bedrock fault scarp. The colluvial Unit C is constituted by sandy marks (C1) grading laterally to yellow calcarenites (Unit C2), which include broken fragments, clasts, and large boulders (60 \(\times\) 40 cm) of the fault bedrock. Its matrix is a strongly cemented (recrystallized) coarse-medium-grained calcarenite, that includes numerous broken fragments of _Ostrea_ sp., coming from the bedrock. The sandy marks (Unit C1) presented a massive assemblage and are affected by an intense re-carbonation with many nodules of carbonate. The whole unit displayed a yellowish color (2.5Y7/6-8) and did not incorporate weathered material (i.e., terra rossa) from the calcarenitic substratum. Unit C can be interpreted as a littoral colluvial wedge (C2) grading laterally to a narrow littoral sag-pond (C1) that is accommodated within the trough generated along the fault zone above Unit B1. The anomalous dip of the base of C1 towards the fault plane, near its contact with the antifirm of unit A (meter 12 to 14 in the log) suggests that these littoral deposits have been slightly tilted due to the growth of the clayey bulge of unit A. Unit C constitutes the last evidence of littoral sedimentation along the fault zone, probably during the Lower Pleistocene, but the first evidence of probable surface faulting during the Quaternary within the excavated trench. The absence of weathered material in unit C suggests that it was formed soon after the sedimentation of littoral calcarenites (beach and dune sediments) in this zone. On the other hand, the intense secondary recarbonation affecting Unit C indicates a relatively long period of neither sedimentation nor fault activity until the deposition of the overlying Unit D.  
The colluvial Unit D contains angular and weathered clasts and boulders of the Pliocene bedrock (Unit PQ), pasted by a reddish sandy-clay matrix (2.5 YR 5/6) also including reworked and broken fragments of _Ostra_ sp. Unlike unit C, unit D is weakly cemented and easily removed by pick. Adjacent to the fault (meters 12 to 16; Figure 12) there are some clast-supported subangular boulders and gravels, these last with sizes ranging from 2 to 5 cm in diameter. These alluvial deposits are clearly sourced by the upthrown block of the fault and can be considered as a colluvial wedge related to Pleistocene to Holocene fault activity.