Note illustrative della Carta Geologica d’Italia alla scala 1:50.000, F° 438 "Bari"

The area represented in the F° 438 “Bari”, at the scale 1:50.000, lies in the northern part of the Murge (Apulia region, southern Italy). The Murge is part of the Apulian Foreland, which represents the south-Apennines foreland made up of a uniform crustal structure with a Variscan crystalline basement and an approximately 6 km thick Mesozoic sedimentary cover overlain by relatively thin and discontinuous Tertiary and Quaternary deposits. The Mesozoic deposits extensively cropping out in the F° 438 “Bari” are represented by the Calcare di Bari Fm, showing in this area a thickness of 470 m. The lower and the upper boundaries of this formation do not crop out in the studied area. Mostly, the Calcare di Bari succession is made up of biopeloidal and peloidal wackestones/packstones alternated to stromatolitic bindstones with frequent intercalations of dolomitic limestones and grey dolostones. Mollusksrich layers (mostly rudist shells) with fl oatstone/rudstone texture occur in the lower and upper parts of the successions. These layers are easily recognizable in the fi eld and form up to some tens of meters thick strata sets. These strata sets were formerly used as reference layers (“livelli guida”) for lithostratigraphic correlations. They correspond to “livello Palese”, “livello Sannicandro” and “livello Toritto”, already recognized in the previous edition of Carta Geologica d’Italia. Furthermore, in the middle part of the succession, 20 thick dolomitic breccias alternate to massive dolostones laterally fading (towards east) in peritidal limestones. Due to these peculiar lithologic features, this lithofacies has been distinguished and mapped (lithofacies CBAa). The upper part of the succession is made up of fl oatstones/rudstones alternated to intrabioclastc rudstones and burrowed mudstones/wackestones. Most of the Calcare di Bari succession shows facies features related to peritidal environments; only the features of upper part suggest relatively more distal and deeper environments belonging to an external platform setting. The Calcare di Bari succession bears macro-(mollusks) and microfossils (benthic foraminifers), and the biostratigraphic data allowed us to refer the age of the whole succession of the Calcare di Bari Fm to the early Albian p.p.-late Cenomanian. The lower Pleistocene Calcarenite di Gravina Fm unconformably lies on the Calcare di Bari Fm. The lower boundary is transgressive and is locally marked by reddish residual deposits (terra rossa) and/or by brackish silty deposits passing upward to shallow-water calcarenites rich in bioclasts. Mainly this formation is made up of litho-bioclastic calcarenites and calcirudites with packstone/ grainstone texture, rich in mollusks, red algae, serpulids, echinoids and benthic foraminifers. The thickness of this unit ranges from few metres to 20 m, and its depositional environments are related to alluvial or offshore systems. The age is early Pleistocene (Gelasian ?-Calabrian). The argille subappenine fm conformably lies on the Calcarenite di Gravina Fm, and crops out only in a very restricted area in the southeastern corner of the sheet. The argille subappenine fm is made up of burrowed silty clays interbedded to dark grey marly clays, silts and fi ne-grained sand. The outcropping thickness is about 2 m, but by drilling data it appears at least 8 m. Frequently, mollusks, bryozoans and serpulids fragments are present; micropaleontological content is represented mainly by benthic foraminifers ad rarely by planctonic foraminifers and nannofossil. The facies features are related to offshore environments. The age is early Pleistocene (Calabrian). The Murge supersynthem groups all the marine terraced deposits unconformably lying on all older units and consists of a heterogeneous assemblage of mixed silicoclastic and carbonate sediments formed in shallow-marine and transitional environments. The formation of these deposits took place in the general regressive phase that, starting from the latest early Pleistocene, interested all the Apulian Foreland due to the regional uplift. This latter, in combination with the Pleistocene glacioeustatic oscillations produced several relative sea-level changes which caused the distribution of these sediments to different heights above the present-day sea-level position. The thickness of the fi ve synthems forming the supersynthem is usually few metres and the age ranges from middle to late Pleistocene. The lame delle Murge supersynthem groups all the terraced alluvial deposits cropping out in the studied area. These deposits unconformably lie on the previous units and are placed at different heights inside present-day little canyons, characterizing the area and locally named “lame”. These deposits consist of either well cemented or poorly cemented carbonate conglomerates with a reddish siltysandy matrix. The thickness of these deposits ranges from few metres up to 10 meters and the age is middle Pleistocene-late Pleistocene. The picture is completed by upper Pleistocene-Holocene actual and presentday alluvial deposits, made up of carbonate gravels with reddish fi ne-grained matrix. As regards the structural features of deposits cropping out in the F° 438 “Bari”, it is possible to observe a S-SW trending monoclinal dissected by several faults and folded by gentle anticlines and synclines, affecting only the Cretaceous succession of the Calcare di Bari Fm. Quaternary units are undeformed and show a tabular arrangement. Main structures are represented by high-angle NW-SE, WNW-ESE and EW oriented faults, dipping towards NE or SW, which show extensional and/or transtensional features and bounding morphostructural depressions fi lled by Quaternary deposits. In the southwestern part of the studied area two of these faults bound a narrow graben (“Murge basse” graben) fi lled by the Calcarenite di Gravina Fm. In the eastern and northeastern part of the sheet a system of conjugated faults bounds a broad morphostructural depression fi lled by Quaternary deposits. High-angle N-S and NE-SW oriented faults, dipping towards NW or SE, intersect faults of the previous system and locally offset them suggesting a younger tectonic activity. These faults controlled the development of the hydrographic network because most of the little canyons fl ow parallel to them. The tectonic structures mapped in the F° 438 “Bari” are referred to different tectonic phases. The oldest one probably began during Cretaceous times when, as many authors agree, the regional monocline formed. Also some of the faults mapped in the area probably formed during the Cretaceous, but they were reactivated during the Tertiary Appenninic orogenic phases. NW-SE, NNW-SSE and E-W oriented faults form the main system in the whole Murge area as they determined the main morphological features of this territory. Moreover, the distribution of the Calcarenite di Gravina Fm., fi lling morphostructural depressions bounded by faults, suggests that this system of faults was active before the sedimentation of this unit. The second system of faults offset the previous one and also deposits of the Calcarenite di Gravina Fm fi lling structural depressions, suggesting that faults of this system were active after the deposition of this unit. Their activity should be related with the change of the geodynamic context which, starting from late Early Pleistocene times, produced the regional uplift of the whole foreland area.