Paleoenvironmental and tectonic evolution of the Liassic carbonate platform succession of Mt. Maranfusa (central western Sicily)

The upper part of the Liassic carbonate platform succession (Inici Fm., Hettangian-Sinemurian), outcropping at Mt. Maranfusa (central western Sicily) consists of a sequence of peritidal limestones, overlain by Jurassic to Cenozoic pelagic limestones and their siliciclastic Tertiary covers. The good exposure of this succession, pertaining to the trapanese domain, in the area between Palermo and Sciacca mountains, allowed to study in detail the facies sequences and structural features of the carbonate platform and of the sedimentary dikes, in order to improve knowledge on its paleoenvironmental and tectonic evolution. The Inici Fm. is constituted by subtidal cyclic sequences of wackestone\packstones with gastropods, megalodonts, oncoids, grain aggregates, dasycladacean algae and benthic foraminifers, followed by dismicrites with pisolitic levels of intertidal environment, and at the top, when they are present, bioclastics calcarenites with birdseyes of supratidal environment. At the top of the cycles we recognized often a peculiar type of layers constituted by: 1) dark gray, compact and well cemented limestones with blackish clasts. The microfacies analysis shows packstones consisting of carbonate grains and bioclasts coated with thin regular to highly irregular, laminae of brownish or yellowish micrite, creating small subspherical nodules, or irregular masses, named glaebule, often associated with pisoid. 2) millimetric reddish calcite laminae, locally deformed by elongated cavities, filled with greenish vadose silt, and bordered by radial fibrous cement. The crystals grow toward the inside of the cavity and crystallize at the expense of the silt fills. We classified for the first time the levels 1 as calcrete, while levels 2 were indicated as paleokarst. The facies sequences of the Inici Fm. are shallowing upward; the environment is attributed to a tidal flat and to the neighbour lagoon, pertaining to an inner carbonate ramp. The recognized calcretes are of pedogenic origin and were classified as alpha and beta calcrete (Wright, 1994). The paleokarsts for their characteristics were classified as paleospeleothems, which are important stratigraphic markers because they indicate periods of non-deposition and/or erosion during sea-level changes. Both the layers indicate phases of emersion during the deposition of carbonate platform succession. The study succession is crossed by three fault systems: NNW-SSE trending dextral transtensional fault system, NNE-SSW trending sinistral transtensional fault system, both late Lias–middle-late Miocene in age, often reactivating previous normal faults, and E-W trending transpressional fault system (Miocene). The first two fault systems are cut by neptunian dikes (Fischer, 1964), filled by several generations of Toarcian-early Miocene pelagic sediments layers. Another system of dikes, parallel to the stratification, is created by planar slip in the carbonate rocks; they are filled by pelagic sediments (late Lias-Dogger in age). The neptunian dikes are of tectonic origin with evidence of reactivation of faults, while parallel dikes (injection dike, Castellarin, 1982) are interpreted as to be due to flexure of the platform during the Jurassic tectonic events. So, in this paper we assert, for the first time, that the horizontal layers, previously described by many authors only as horizontal dikes, can be actually interpreted as: a) layers that are effectively horizontal dikes; b) pedogenic calcretes; c) paleospeleothems. As a consequence we identified some episodes of emersion in the evolution of the Trapanese carbonate platform during the Liassic.