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In studies of neotectonism, alluvial-fan and talus deposits commonly are used as deformation markers, but rarely are studied themselves and in relation to adjacent faults. Herein we report on the facies, diagenesis and deformation of a talus succession and fault cataclasites in the central Apennines of Italy. The study site is located near the western end of the Assergi normal fault zone that accommodates >2000 m of vertical throw, but was dormant since a longer interval of time. The preserved talus succession is confined to the fault hangingwall. Deposition and deformation of the talus overlapped with the terminal phase of fault activity. The talus accumulated mainly from grain flows, cohesive debris flows and ephemeral fluid flows; it comprises (i) two superposed units of scree breccias, partly cemented before deformation, and intercalated with (ii) an interval of unlithified scree and soils. The exposed succession accumulated between ≥33–30 cal ka BP to less than ~22 cal ka BP. Talus breccias record complex diagenetic successions including eluviation/dissolution of primary matrix, growth of interstitial cements interrupted by episodes of dissolution and/or fracturation, and late-stage dissolution porosity development. Downthrow by faulting produced two types of folds, (i) a syncline-anticline pair with inclined fold axes roughly normal to the fault plane, and (ii) a recumbent fold with an axis subparallel to depositional strike of the scree slope; the complicated stratigraphic architecture of the deformed succession is truncated along and hidden beneath the topsoil of the present, uniform slope surface. Further deformation structures include conjugate fractures locally coated by speleothem flowstones, deformation bands, sediment fabrics characterized by planar clast contacts, and lithoclasts crushed in situ while embedded in the sediment. Cementation overlapped with and post-dated in-situ crushing of clasts. The core of the normal fault is an ultracataclasite that (i) shows different degrees of diagenetic recrystallization into micro- to pseudospar, and (ii) that is riddled with solution pores fringed or filled with successive ‘generations’ of calcite cement. These cements are locally sharply capped along discrete levels, and overlain by ultracataclasite with floating chunks of calcite cement crystals ripped off during increments of faulting. Stable isotopes of oxygen and carbon indicate that the ultracataclasites lithified under influence of meteoric waters, but at variable degrees of rock buffering; the calcite cements within the talus breccias and the flowstones along fractures, in turn, precipitated from meteoric-derived waters with low to negligible rock buffering. The structural juxtaposition of ultracataclasites (probably formed in 1–2 km depth) with talus breccias indicates that the preserved fault/talus ensemble records only the terminal phase of total faulting. The interstitial cements in talus, the flowstones on fracture walls, and the cements in ultracataclasites should be datable with the 234U/230Th errorchron method. This promises to be a new approach to derive age constraints on talus cementation and fracturation, and on palaeoactivity and final dormance of normal faults.

Slump structures in Upper Jurassic pelagic limestones of the Northern Calcareous Alps were studied using methods of ductile structural geology. The early deformation observed cannot be explained by conventional models for slumping, commonly describing slump complexes with an extending upper and contracting lower part. Instead, the structures suggest distributed bedding-parallel surficial stretching, and folding localized by roll-over normal faulting. The initially isoclinal and recumbent folds are pervasively overprinted by stretching, causing reorientation of fold axes into the downslope direction. Transport of folds separates antiformal and synformal hinges, and the resulting isolated hinges resemble intrafolial folds in metamorphic terranes. Only folds formed late in the process of lithification allow insight in the early stages of fold evolution. We suggest that this type of early deformation represents sediment creep that may be characteristic for slump structures in pelagic carbonates.

Styles of soft-sediment deformation in a syngrowth coarse-grained sediment gravity flow system are described from outcrops of the Upper Gosau Subgroup of the Northern Calcareous Alps. The deepwater sediments were deposited along the flanks and top of growing folds. Beside load and fluid escape structures, which are commonly found in sediment gravity flow systems, soft-sediment deformation is mainly related to fluidization of coarse-grained beds and downslope gliding of meter-thick sediment packages. Common structures affecting single or several beds are: hydroplastic folding of fine-grained beds in a coarse-grained fluidized matrix, symmetric or asymmetric mullions at the base of coarse-grained beds, and folding of heterolithic units into coarse-grained beds. Folds have varying geometries and styles, and fold axes are scattered. Soft-sediment folds also affect thick sediment packages. These folds are uniformly verging asymmetric metric to dekametric folds, formed at different degrees of lithification. Rheology of sandstones in such folds ranges from ductile to semi-brittle and brittle. Fold axes tightly cluster about one direction. The first group of deformational structures is attributed to slump-related deformation, whereas the second group represents folds related to tectonic deformation. A dislocation model and a shear zone model are used to interpret orientation of folds related to slump deformation. This considers processes taking place on the scale of the whole slump sheet and within the shear zone at the base of gliding units. Both models predict rotation of fold axes toward the transport direction of the slump. Field data support that fold axes scatter either about the downslope transport direction or about the strike of the slope.