Le facies carbonatiche di piattaforma interna del Promontorio del Gargano: implicazioni paleoambientali e correlazioni con la coeva successione delle Murge (Italia meridionale, Puglia)

New research based on detailed facies analysis and lithostratigraphic study of the inner shelf carbonate succession outcropping in the middle-west Gargano area is reported. The outcropping succession of the inner shelf facies of the Apulian carbonate Platform corresponds, in the Apulia region, to the western part of the Gargano Promontory, to the greater part of the Murge Plateau and to the Serre Salentine area (fig. 1a). The whole succession is late Jurassic-Cretaceous in age and shows a wide hiatus (late Cenomanian-Turonian p.p.) marked by an erosive surface with bauxite deposits. The field analysis has allowed us to reconstruct a stratigraphic interval of inner shelf carbonates about 900 metres thick (fig. 2). On the basis of facies analysis we propose to divide the succession into three different stratigraphic intervals which are, from bottom to top, the following: - Monte Calvo member: 300-350 metres thick interval made up of light grey micritic limestones and dark grey-black dolomites. The lower and the middle part of this stratigraphic interval shows the sedimentological features of lagoonal environments (from open to restricted) and consists of biopeloidal wackestone/packstone with abundant green algae (fig. 3a and fig. 3b) and benthic foraminifers, peloidal wackestones/packstone with abundant spongiostromata oncoids. The upper part shows more developed peritidal conditions consisting of peloidal wackstone/packstone with fecal pellets (fig. 3d) and radial ooids (fig. 3e) and microbialites (flg. 3f) with desiccation features passing upward to dolomitic limestones and dolomites locally laminated (fig. 3c) and with fenestral fabrics. Groups of beds with Clypeina jurassica (fig. 3a) and Campbelliella striata (fig. 3b) are recognized as stratigraphic markers respectively in the middle and in the upper part of this stratigraphic interval. Age: Callovian p.p.Valanginian p.p; - Borgo Celano member: 500 metres thick interval of white and light grey bioclastic wackestone/packstone with abundant green algae, mollusc floatstones with requienids and gastropods shells (fig. 4a and fig. 4b), biopeloidal packstones/grainstones with Cayeuxia sp. (fig. 4c), intercalated with laminated and graded oolitic grainstones (fig. 4d) showing keystone vugs and vadose cements. The lower part shows the sedimentological features of open lagoonal environments with low or moderate energy locally passing to high-energy peritidal lithofacies. The middle and the upper part of the succession show gradually more developed peritidal lithofacies (fig. 4e). Green clays are often intercalated with previous lithofacies and indicate intertidal/supratidal exposure (fig. 4f). Dinosaur footprints have been recently described on clay layers (GIANOLLA et alii, 2000). Age: Valanginian p.p.- early Aptian p.p; - ostree and requienie member: 80 metre thick interval of light grey bioclastic and biogenic limestones with abundant ostreids and requienids (fig. 5a and fig. 5b), echinoderrns, oncoids (fig. 5d) and micritic intraclasts passing upward to wackestone/packstone with orbitolinids (fig. 5e) and to microbialites (fig. 5f) with desiccation features, ostreid floatstones/rudstones developed in the lower part of the succession and orbitolinid wackestones developed in the upper part are recognized as stratigraphic markers. The latter is well-known also in the Murge area (upper part of the Palorbitolina lenticularis layer, LUPERTO SINNI, 1979) Age: Aptian p.p. The detailed facies analysis and the paleoecologic study of the benthic communities has allowed us to highlight the sedimentary evolution of the studied succession during Callovian p.p.-Aptian p.p. times. Two types of lithofacies associations have been recognized. The first type is made up of benthic communities with small requienids and gastropods associated with a micropopulation very rich in green algae (chloralgal lithofacies) and non skeletal grains. This type of community characterizes the most part of the lower and middle interval of the studied succession (Monte Calvo member and Borgo Celano member) and implies healthy platform conditions. The second lithofacies association consists of a benthic community with ostreids, requienids and gastropods associated with a micropopulation with abundant benthic foraminifers. This type of community characterizes the upper part of the studied section (ostree and requienie member) and implies conditions of an unhealthy platform. The whole studied succession lias not shown strong lithologic contrasts or well-developed unconformities. Therefore, we propose to include the entire studied Succession in a single lithostratigraphic unit with the rank of formation. In spite of this, we have recognized three units with different lithofacies characteristics which allow us to classify them as members. This stratigraphic framework proposed for the middle/upper Jurassic-lower Cretaceous inner platform succession can be considered as an alternative to that of the Geologic map of Italy (fig. 1b) and to that of the previous litho and biostratigraphic works (tab. 1). Moreover, the integration between new data collected on the middle-west Gargano with the critical analysis of published data in the equivalent succession (facies and age) of the Murge allow us to propose a correlation between the two compound sections reconstructed for the Gargano (fig. 2 of this study) and for the Murge (RICCHETTI, 1975) areas (fig. 6). This correlation allows us to extend the stratigraphic nomenclature of the Calcare di Bari, prior to this work used only in the Murge area, to apply also to the inner platform succession outcropping in the Gargano Promontory