Abstract The Northern Calcareous Alps (Eastern Alps, Austria) represent a well‐preserved example of the early stages of inversion of a salt‐bearing passive margin, which occurred in a fully submarine setting. Late Jurassic shortening led to widespread thrusting and folding that nucleated preferentially, although not exclusively, along salt structures developed during the Triassic passive‐margin stage. The presence of a highly effective basal décollement permitted the propagation of deformation without generalized uplift in the area, which was limited to thrusts, folds and squeezed salt structures. The development of individual structures was controlled by the orientation of pre‐existing salt structures, the thickness of supra‐salt stratigraphy, the lateral propagation of deformation, and, possibly, the redistribution of salt within salt structures prior to contraction and the influence of sub‐salt basement faults. Syn‐tectonic sediments make it possible to reliably reconstruct the timing of structural inversion. These same sediments were in turn controlled by structural evolution, with depocenters developing roughly parallel to the inverting structures. The structures documented here are evidence for Late Jurassic shortening across the central Eastern Alps, totaling a few to few tens of kilometers. This is the first systematic description of structures of Late Jurassic age in the Eastern Alps and provides a framework within which to understand the abundance of syn‐tectonic deposits of this age in the area. Particular attention is paid to the Totengebirge–Trattberg contractional system, an outstandingly long set of structures, whose continuity and significance has gone previously unrecognized.
The Trogkofel massif in the Carnic Alps, Austria/Italy, consists of a succession up to 400 m thick of limestones deposited along a platform margin (Trogkofel Limestone; Artinskian). The top of the Trogkofel Limestone is erosively overlain by the Tarvis Breccia. Up-section, the Trogkofel Limestone consists of well-bedded shallow-water bioclastic limestones with intercalated mud mounds, overlain by thick-bedded to unbedded limestones (bioclastic grainstones, packstones, rudstones) and cementstone mounds rich in phylloid algae, Tubiphytes, bryozoans and Archaeolithoporella. In the cementstone mounds, bioclasts are coated by thick fringes and botryoids of fibrous calcite, and of calcite spar that probably represents calcitized aragonite. Primary and intrinsic pores are filled by microbialite, and/or by mudstone to bioclastic wackestone. Shallow-water bioclastic grainstones are cemented by isopachous fringes of fibrous calcite, or by sparry calcite. Throughout the succession, evidence for meteoric-vadose dissolution is present. The Trogkofel Limestone is riddled by palaeokarstic dykes and caverns filled by (a) isopachous cement fringes up to a few decimetres thick, and/or (b) by red, geopetally-laminated lime mudstone to biolithoclastic wackestone; geopetal laminasets locally display convolute bedding. Small dissolution cavities are filled by grey internal sediment, or by crystal silt. Brecciated internal sediments overlain by unbrecciated, geopetallylaminated infillings record deformation during or after deposition of the Trogkofel Limestone. Polyphase fractures cemented by calcite may cross-cut both internal sediments and host rock.
Mos t of fourteen tufa locations mainly in the western part of the Eastern Alps contain a significant to prevalent portion of microbially-induced calcium carbonate. The investigated tufas are situated on substrata of limestone, dolostone, marlstone, conglomerate, gneiss, phyllite and slate. Most larger tufa occurrences comprise significant areas wherein tufa formation is low or had halted. Two major groups of “microbial tufas” are distinguished, (1) crystalline microbial calcium carbonate, and (2) micropeloidal to micritic calcium carbonate. Crystalline microbial calcium carbonate is present in two major fabrics. (1A) Calcified “microbushes” of outward-radiating clusters of slightly tangled tubuli each encased by a single crystal of calcite of subrounded to subcircular cross-section. Larger volumes of tufa may be composed of stacked laminae built by laterally arrayed microbushes. (1B) Knobs to crusts that, internally, consist of fan-like arrays of tubuli encased within large single crystals of calcite. Both the microbushes and the microfans are interpreted as calcified cyanobacterial aggregates of Rivularia type. The crystalline microbial calcites may readily recrystallize and provide a substrate for further, “inorganic” calcite growth, resulting in cementstone texture that shows little evidence of its microbially-induced origin. (2) Micropeloidal to micritic calcium carbonate includes micropeloidal grainstone, “filamentous-micropeloidal” grainstone, (fenestral) lime mudstone with stromatolithic or cauliflower lamination, and thrombolithic lime mudstone. The micropeloids and the filamentous-micropeloidal arrays may have been produced by coccoid and filamentous cyanobacteria, at or near the tufa surface. A major portion of calcium carbonate of this category, however, is present within the pore space of tufas, where it formed in association with light-indepedent microbes and/or with dead microbes, small phytoclasts and organic compounds. Deduced rates of present tufa formation are within the range of known rates, but show distinct variations both within and among locations.
Although the Central Apennines of Italy are frequently struck by earthquakes related to normal faulting, so far, no detailed regional study into long-term development and mode of normal faulting exists. The studied Assergi and Campo Imperatore fault zones (AFZ, CIFZ) – two adjacent S-dipping faults ~20 km in length with km-scale offset – juxtapose Quaternary hanging wall deposits to Meso-Cainozoic footwall ranges up to 1000 m in relief. Along each fault zone, lateral growth of faults by segment linkage (isolated fault model) coexisted with constant-length faulting. The AFZ and the eastern and central part of the CIFZ are dormant at least since the LGM. The faults display different morphologies depending on the time of faulting relative to the Last Glacial Maximum (LGM). Our study shows that even adjacent major normal fault zones may differ markedly with respect to, each, age of inception, the ratio of geologic/topographic offset, and the style of fault growth (segment linkage versus constant-length mode). Study of the different sectors of the CIFZ allowed to deduce a concept for long-term development of range-front fault morphology and associated slopes. (1) Surface offset by active faulting is followed, or accompanied, by incision of numerous small alluvial-fan catchments with narrow outlet spacing into the fault footwall. (2) Upon headward and lateral erosion, provided the fault is dormant or very slow, the small fan catchments merge into fewer larger catchments with larger outlet spacing. In this stage, the master fault itself may become exposed by differential erosion, forming a wide steep slope. (3) Finally, upon continued fault dormance, the steep master-fault slope degrades to a lower-dipping slope typically veneered by scree. On these slopes, scarps excavated by differential erosion expose Riedel shears of the master faults , and represent a late stage of fault-scarp degradation. The history of faulting of the CIFZ may indicate that normal fault segments first acquire offset at constant length until reaching a threshold, then link with neighbouring fault segments into longer fault zones. Because the Assergi basin along the AFZ was drained and open, sediment was cleared out, and footwall topography directly reflects fault offset, i.e., the geologic/topographic fault offset ratio is ~1. It is thus improbable that footwall relief along the AFZ had reached a steady state. For the CIFZ, in turn, a geologic/topographic offset ratio >>1 implies that this fault zone originated well-before present topography emerged. To derive footwall range relief, long-term throw rates of 0.6–1.2 mm/a are required. The CIFZ initiated in its central sector (phase 1), then lengthened eastwards (phase 2) before the western sector activated (phase 3 and 4). This is recorded by morphological features including: (a) maximum height of the front range in the central to east-central sector, (b) maximum size and depth of alluvial-fan catchments incised into the footwall of the central sector, (c) maximum width and height of triangular slope facets in the central fault sector combined with maximum spacing of intercalated alluvial-fan outlets. In the westernmost part of the CIFZ, surface offset along the master fault indicates young fault activity, most probably after the LGM.
