Tethyan carbonates have recorded a complex long-term stratigraphic evolution during Cretaceous reflecting relevant paleoecologic shifts due to major paleoceanographic disruptions. Many of these shifts parallel analogous, basically synchronous biotic turning points in the pelagic realm thus providing relevant clues for biosphere-geosphere interactions, especially during OAEs and/or drowning events of neritic factories. Despite recent, very detailed outcomes on their chronostratigraphy provided by a modern geochemical approach, most of these events lack univocal paleoecologic-paleoceanographic interpretations. This is particularly true regarding the individuation of the paleoenvironmental processes responsible for the observed biofacies shifts in a cause-and-effect scenario. Improving the knowledge of this issue relies, among others, on studies of well exposed platform to basin transitions which may serve to detect and compare the most diverse biosedimentary records from shallow- to deep-water environments. Based on an integrated approach including sedimentology, paleocology and event stratigraphy, we present the results of an original study on the late Valanginian and late Early Aptian facies shifts recorded across the slightly deformed transition between the Apulia Carbonate Platform (ACP) and Ionian Basin (IB) exposed in the Gargano Promontory (Apulia foreland, southern Italy). We also provide two biofacies models across this transition to compare the paleoecologic signatures recorded by the ACP-IB during two of the most relevant OAEs of the whole Mesozoic. Previous paleoenvironmental analyses on the Early Cretaceous ACP-IB transition cropping out in south-eastern Gargano have enabled the local drowning unconformities and the related shifts of biofacies to be recognized and interpreted in a regional/global frame displaying evident traces of sharp paleoceanographic disruptions during the Weissert and Selli OAEs (Graziano, 1999; Graziano & Ruggiero, 2008). Corresponding, coeval facies shifts have been revealed in the shallow-water successions of the western Gargano (Spalluto, 2004; Spalluto et al., 2005). Both the late Valanginian and late Early Aptian drowning events typically affects the platform margin and slope whereas persisting inner platform successions display the temporary disappearance of ciclically organized dm-thick peritidal deposits replaced by thicker (few metres) mollusc- and microbial-dominated subtidal deposits. This facies shift coincides with a rapid turn-over in biota characterized by mass exctinctions of k-strategist biota (e.g. green algae) and concomitant blooming of opportunistic biota (mostly cyanobacteria). In addition, the late Early Aptian event also displays a remarkable Ostreid-rich, thick-bedded interval with Palorbitolina lenticularis, and Salpingoporella dinarica. Platform margin successions, limited to the late Early Aptian event, display a major facies shifts from urgonian-like, low-energy and well diversified biofacies to oligotypic associations dominated by dysaster taxa as cyanobacteria (Bacinella irregularis), foraminifera (P. lenticularis) and brachiopods (Orbirhynchia nadiae). The platform flank is characterized by distinct incursions of pelagic tongues wedging out toward the platform margins which indicate sharp though episodic starvations during both the drowning events. In addition, the late Valanginian episode is characterized also by the bloom of further dysaster taxa as the brachiopod Peregrinella. Basinal successions document a major facies change, coupled to deposition of black shales, only in the case of the late Early Aptian event. As a whole, both the investigated intervals indicate a precise correlation with well-known biocalcification crises, evolving paloeclimatic conditions (namely cooling or warming-cooling trends) and marked spikes of δ13C curves (cfr. Weissert & Erba, 2004, among many others). References GRAZIANO R. (1999). The Early Cretaceous drowning unconformities of the Apulia carbonate platform (Gargano Promontory, southern Italy): local fingerprints of global palaeoceanographic events. Terra Nova, 11, 245-250. GRAZIANO R. & RUGGIERO TADDEI E. (2008). Cretaceous brachiopod-rich facies of the carbonate platform-to-basin transitions in southern Italy: stratigraphic and paleoenvironmental significance. Boll. Soc. Geol. It., 127, 407-422. SPALLUTO L. (2004). La piattaforma apula nel Gargano centro-occidentale: organizzazione stratigrafica ed assetto della locale successione di piattaforma interna. PhD Thesis, University of Bari, 173 pp. SPALLUTO L., PIERI P. & RICCHETTI G. (2005). Le facies carbonatiche di piattaforma interna del Promontorio del Gargano: implicazioni paleoambientali e correlazioni con la coeva successione delle Murge (Italia meridionale, Puglia). Boll. Soc. Geol. It., 124, 675-690. WEISSERT H. & ERBA E. (2004). Volcanism, CO2 and paleoclimate: a Late Jurassic-Early Cretaceous carbon and oxygen isotope record. Jour. Geol. Soc. London, 161, 695-702.

DECIPHERING SHALLOW-TO-DEEP WATER PALEOECOLOGIC SHIFTS ACROSS CARBONATE TRANSITIONS DURING OAEs: THE VALANGINIAN AND APTIAN OF THE APULIA PLATFORM AND IONIAN BASIN (SOUTHERN ITALY).

GRAZIANO, ROBERTO;
2009

Abstract

Tethyan carbonates have recorded a complex long-term stratigraphic evolution during Cretaceous reflecting relevant paleoecologic shifts due to major paleoceanographic disruptions. Many of these shifts parallel analogous, basically synchronous biotic turning points in the pelagic realm thus providing relevant clues for biosphere-geosphere interactions, especially during OAEs and/or drowning events of neritic factories. Despite recent, very detailed outcomes on their chronostratigraphy provided by a modern geochemical approach, most of these events lack univocal paleoecologic-paleoceanographic interpretations. This is particularly true regarding the individuation of the paleoenvironmental processes responsible for the observed biofacies shifts in a cause-and-effect scenario. Improving the knowledge of this issue relies, among others, on studies of well exposed platform to basin transitions which may serve to detect and compare the most diverse biosedimentary records from shallow- to deep-water environments. Based on an integrated approach including sedimentology, paleocology and event stratigraphy, we present the results of an original study on the late Valanginian and late Early Aptian facies shifts recorded across the slightly deformed transition between the Apulia Carbonate Platform (ACP) and Ionian Basin (IB) exposed in the Gargano Promontory (Apulia foreland, southern Italy). We also provide two biofacies models across this transition to compare the paleoecologic signatures recorded by the ACP-IB during two of the most relevant OAEs of the whole Mesozoic. Previous paleoenvironmental analyses on the Early Cretaceous ACP-IB transition cropping out in south-eastern Gargano have enabled the local drowning unconformities and the related shifts of biofacies to be recognized and interpreted in a regional/global frame displaying evident traces of sharp paleoceanographic disruptions during the Weissert and Selli OAEs (Graziano, 1999; Graziano & Ruggiero, 2008). Corresponding, coeval facies shifts have been revealed in the shallow-water successions of the western Gargano (Spalluto, 2004; Spalluto et al., 2005). Both the late Valanginian and late Early Aptian drowning events typically affects the platform margin and slope whereas persisting inner platform successions display the temporary disappearance of ciclically organized dm-thick peritidal deposits replaced by thicker (few metres) mollusc- and microbial-dominated subtidal deposits. This facies shift coincides with a rapid turn-over in biota characterized by mass exctinctions of k-strategist biota (e.g. green algae) and concomitant blooming of opportunistic biota (mostly cyanobacteria). In addition, the late Early Aptian event also displays a remarkable Ostreid-rich, thick-bedded interval with Palorbitolina lenticularis, and Salpingoporella dinarica. Platform margin successions, limited to the late Early Aptian event, display a major facies shifts from urgonian-like, low-energy and well diversified biofacies to oligotypic associations dominated by dysaster taxa as cyanobacteria (Bacinella irregularis), foraminifera (P. lenticularis) and brachiopods (Orbirhynchia nadiae). The platform flank is characterized by distinct incursions of pelagic tongues wedging out toward the platform margins which indicate sharp though episodic starvations during both the drowning events. In addition, the late Valanginian episode is characterized also by the bloom of further dysaster taxa as the brachiopod Peregrinella. Basinal successions document a major facies change, coupled to deposition of black shales, only in the case of the late Early Aptian event. As a whole, both the investigated intervals indicate a precise correlation with well-known biocalcification crises, evolving paloeclimatic conditions (namely cooling or warming-cooling trends) and marked spikes of δ13C curves (cfr. Weissert & Erba, 2004, among many others). References GRAZIANO R. (1999). The Early Cretaceous drowning unconformities of the Apulia carbonate platform (Gargano Promontory, southern Italy): local fingerprints of global palaeoceanographic events. Terra Nova, 11, 245-250. GRAZIANO R. & RUGGIERO TADDEI E. (2008). Cretaceous brachiopod-rich facies of the carbonate platform-to-basin transitions in southern Italy: stratigraphic and paleoenvironmental significance. Boll. Soc. Geol. It., 127, 407-422. SPALLUTO L. (2004). La piattaforma apula nel Gargano centro-occidentale: organizzazione stratigrafica ed assetto della locale successione di piattaforma interna. PhD Thesis, University of Bari, 173 pp. SPALLUTO L., PIERI P. & RICCHETTI G. (2005). Le facies carbonatiche di piattaforma interna del Promontorio del Gargano: implicazioni paleoambientali e correlazioni con la coeva successione delle Murge (Italia meridionale, Puglia). Boll. Soc. Geol. It., 124, 675-690. WEISSERT H. & ERBA E. (2004). Volcanism, CO2 and paleoclimate: a Late Jurassic-Early Cretaceous carbon and oxygen isotope record. Jour. Geol. Soc. London, 161, 695-702.
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