Piero Pieri

Filling and cannibalization of a foredeep: the Bradanic Trough, Southern Italy

Abstract The Bradanic Trough (southern Italy) is the Pliocene-present-day south Apennines foredeep. It is a foreland basin as subsidence due to westward subduction of the Adria Plate involves the continental crust of the Apulian domain. The infill succession of the Bradanic Trough is characterised by the presence of a long thrust sheet system (the so called ‘allochthon’) that occupied part of the accommodation space created on the foreland by subduction. The upper part of the infilling succession crops out along numerous sections. About 600 m of the 3–4 km basin-fill succession is exposed as the Bradanic Trough has experienced uplift during Quaternary times. Outcropping successions are mainly characterized by shallow-marine deposits comprising carbonates of the Calcarenite di Gravina Formation, silty clay hemipelagites of the Argille subappennine Formation and coarse-grained bodies of the ‘Regressive coastal deposits’. The Calcarenite di Gravina Formation (Middle-Late Pliocene-Early Pleistocene in age) crops out in a backstepping configuration onto the flanks of the Apulian Foreland highs. It displays evidence of strong transgression onto a karstic region previously dissected in a complex horst and graben system. The Argille subappennine Formation (Late Pliocene-Middle Pleistocene in age) succeeds the carbonate sedimentation on the foreland side of the basin and represents the shallowing of the basin in the other sectors of the Bradanic Trough. Toward the Apennines chain, in the wedge-top area of the foredeep, the Argille subappennine Formation covers the allochthon, while in the depocentre (in the foredeep sensu stricto) the same formation overlays turbidite deposits. The latter characterize the deeper part of the successions, and are mainly buried below the allochthon. The Regressive coastal deposits (Early-Late Pleistocene in age) represent the upper part of the succession. They consist of coarse-grained wedges that lie on the hemipelagites of the Argille subappennine Formation in, alternatively, conformable or erosional contact. The wedges of the Regressive coastal deposits stack in a downward-shifting configuration, which indicates deposition during uplift. The Quaternary development of the Bradanic Trough differs from that of the central and northern Appennines foredeep. The latter is characterized by aggradation of shallow-marine and alluvial sediments in a subsiding remnant basin, whose filling records a basin-scale depositional regression. In contrast, the Bradanic Trough is characterized by a basin-scale erosional regression and the last evolutive phase of this sector of the Apennines foredeep is best defined as a cannibalization phase rather than a filling or overfilling phase.

Note illustrative della carta geologica dell'area urbana di Bari in scala 1:25.000

Notes to the geological map of the urban area of Bari (southern Italy) 1:25.000 scale.This paper shows the results coming from the detailed geological mapping performed on the urban area of the city of Bari (Puglia region, southern Italy). It is a large area (about 50 km2), with many inhabited places, and intensely urbanized. For this reason a geological map that could provide an up-to-date and useful tool for professional geologists daily working on the region, was realized.The area represented in the geologic map of the urban area of the city of Bari, at the scale 1:25.000, lies on the eastern Murge, which represents the central part of the Apulian foreland, the south-Apennines foreland. In the Murge area, the foreland is characterized by a thick Mesozoic sedimentary succession overlain by relatively thin and discontinuous Quaternary deposits. Locally, the exposed Mesozoic succession is about 150 m thick, and is represented by a part of the Calcare di Bari Fm, made up of biopeloidal and peloidal wackestones/packstones alternated with stromatolitic bindstones with frequent intercalations of dolomitic limestones and grey dolostones. Depositional environments are related to a low-energy inner-platform depositional system and biostratigraphic data allowed us to refer the age of the succession cropping out in the city of Bari to the Late Albian-Early 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. Basically 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 up to 20 m, and its depositional environments are related to alluvial or offshore systems. The age is early Pleistocene (Gelasian?-Calabrian). Regionally, the Calcarenite di Gravina Fm represents the record of the lower Pleistocene subsidence of the Apulia foreland.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 thickness of the three synthems forming the supersynthem is usually few metres thick and the age ranges from middle to late Pleistocene. These synthems record a phase of regional uplift which started at least from middle Pleistocene; this uplift, in combination with the Pleistocene glacioeustatic oscillations, produced several relative sea-level changes which caused the distribution of these synthems to different altitudes above sea level.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 little canyons, characterizing the area and locally named lame. These deposits consist of either well cemented or poorly cemented carbonate conglomerates with a reddish silty-sandy matrix. The thickness of these deposits ranges from few metres up to 10 m and the age is middle Pleistocene-late Pleistocene.The picture is completed by upper Pleistocene-Holocene actual and present-day alluvial deposits, made up of carbonate gravels with reddish fine-grained matrix.