It is increasingly unraveled that the paleoecology of Tethyan carbonate factories has shifted many times through Mesozoic among three different end-members, namely chlorozoan/chloralgal, foramol and microbial, following relevant paleoceanographic and paleoclimatic changes. Analysis of the main biofacies across selected key-markers coinciding with major paleoecologic shifts may thus provide evaluable clues to detect the intrinsic nature of the overall environmental conditions acting during biocalcification crises, OAEs and drowning unconformities of shallow-water factories. Of special interest is also the observation that chlorozoan-chloralgal carbonate platforms undergoing sharp environmental deteriorations did not support k-mode organisms; by contrast, the proper conditions for r-mode organisms to thrive were provided. Despite their characterizing presence across several drowning unconformities and/or crisis events of Phanerozoic carbonate platforms, brachiopods have received little attention as valuable environmental markers. This is relevant since brachiopods were a main component of r-mode assemblages which developed in Early Toarcian, latest Valanginian, late Early Aptian, earliest Cenomanian, and latest Campanian. With the exception of the latest Campanian event, all of these time intervals correspond to severe global environmental disruptions of the oceans and climate coupled to biocalcification crises. In addition, all of them correlate to major oceanic anoxic events in the Tethyan realm and/or platform drownings (Early Toarcian, Late Valanginian, late Early Aptian, Early Cenomanian and latest Campanian) (Graziano, 1999; Graziano et al., 2006; Graziano & Ruggiero Taddei, 2008). Aiming at improving understanding of the paleoceanographic turnovers during these events, we compare our own published data on Early Jurassic and Cretaceous brachiopod-rich successions of the Apennine and Apulia carbonate platforms (central-southern Italy) looking for common/contrasting paleoenvironmental features. Detailed sedimentologic, paleoecologic, biostratigraphic and taphonomic investigations have been carried out in this light. Nontheless, we compare our stratigraphic and paleoecologic data to the most recent paleoceanographic proxies (δ18O, pCO2, Mg/Ca ratios, pH, δ13C, and P content, among others; see Jones & Jenkyns, 2001; Weissert & Erba, 2004, among many others) in order to fulfill an integrated approach and to provide paleonvironmentally constrained interpretations. The remarkable association of brachiopoda with cyanobacteria, though in complex stratigraphic relationships, especially in Early Toarcian, Late Valanginian, late Early Aptian, and Early Cenomanian times accounts for drastic environmental deterioration of the surface oceanic waters which were highly unfavourable for oligotrophic, k-mode organisms. As a whole, the establishment of oligotypic benthic communities dominated by heterotroph, r-mode opportunist filter-feeding organisms (brachiopods, pelecypods, crinoids), and accompanying cyanobacteria, which replace the underlying well-diversified chlorozoan-chloralgal communities, is a common paleoecologic signature of all the investigated key-markers. More particularly, very similar sedimentary and paleoecologic features are displayed by the investigated Soaresirhynchia beds in the Lower Toarcian of the Gran Sasso Range (Abruzzo), the Peregrinella and Orbirhynchia beds in the uppermost Valanginian and uppermost Lower Aptian, respectively, of the Gargano Promontory (Apulia). This may possibly call for common paleoceanographic scenarios during distinct time intervals of the evolving hydrosphere-biosphere interactions in the Tethyan ocean. It seems that such time-independent similar shifts of main biofacies imply the development of mesotrophic-to-eutrophic, alkaline “green” waters supporting high primary productivity of the surface sea-waters. 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., BUONO G. & RUGGIERO TADDEI E. (2006). Lower Toarcian (Jurassic) brachiopod-rich carbonate facies of the Gran Sasso range (central Apennines, Italy). Boll. Soc. Paleont. It., 45, 61-74. 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. JONES C.E. & JENKYNS H.C. (2001). Seawater Strontium isotopes, Oceanic Anoxic Events, and seafloor hydrothermal activity in the Jurassic and Cretaceous. Am. J Sci., 301, 112-149. 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.

BRACHIOPODS AS SENSITIVE BIOMARKERS OF GLOBAL PALEOCEANOGRAPHIC EVENTS: A CASE HISTORY FROM THE JURASSIC-CRETACEOUS OF CENTRAL-SOUTHERN ITALY / Graziano, Roberto; Ruggiero, Emma. - (2009). (Intervento presentato al convegno 27th Meeting of the International Association of Sedimentologists tenutosi a Alghero (SS) nel 20-23 September 2009).

BRACHIOPODS AS SENSITIVE BIOMARKERS OF GLOBAL PALEOCEANOGRAPHIC EVENTS: A CASE HISTORY FROM THE JURASSIC-CRETACEOUS OF CENTRAL-SOUTHERN ITALY

GRAZIANO, ROBERTO;RUGGIERO, EMMA
2009

Abstract

It is increasingly unraveled that the paleoecology of Tethyan carbonate factories has shifted many times through Mesozoic among three different end-members, namely chlorozoan/chloralgal, foramol and microbial, following relevant paleoceanographic and paleoclimatic changes. Analysis of the main biofacies across selected key-markers coinciding with major paleoecologic shifts may thus provide evaluable clues to detect the intrinsic nature of the overall environmental conditions acting during biocalcification crises, OAEs and drowning unconformities of shallow-water factories. Of special interest is also the observation that chlorozoan-chloralgal carbonate platforms undergoing sharp environmental deteriorations did not support k-mode organisms; by contrast, the proper conditions for r-mode organisms to thrive were provided. Despite their characterizing presence across several drowning unconformities and/or crisis events of Phanerozoic carbonate platforms, brachiopods have received little attention as valuable environmental markers. This is relevant since brachiopods were a main component of r-mode assemblages which developed in Early Toarcian, latest Valanginian, late Early Aptian, earliest Cenomanian, and latest Campanian. With the exception of the latest Campanian event, all of these time intervals correspond to severe global environmental disruptions of the oceans and climate coupled to biocalcification crises. In addition, all of them correlate to major oceanic anoxic events in the Tethyan realm and/or platform drownings (Early Toarcian, Late Valanginian, late Early Aptian, Early Cenomanian and latest Campanian) (Graziano, 1999; Graziano et al., 2006; Graziano & Ruggiero Taddei, 2008). Aiming at improving understanding of the paleoceanographic turnovers during these events, we compare our own published data on Early Jurassic and Cretaceous brachiopod-rich successions of the Apennine and Apulia carbonate platforms (central-southern Italy) looking for common/contrasting paleoenvironmental features. Detailed sedimentologic, paleoecologic, biostratigraphic and taphonomic investigations have been carried out in this light. Nontheless, we compare our stratigraphic and paleoecologic data to the most recent paleoceanographic proxies (δ18O, pCO2, Mg/Ca ratios, pH, δ13C, and P content, among others; see Jones & Jenkyns, 2001; Weissert & Erba, 2004, among many others) in order to fulfill an integrated approach and to provide paleonvironmentally constrained interpretations. The remarkable association of brachiopoda with cyanobacteria, though in complex stratigraphic relationships, especially in Early Toarcian, Late Valanginian, late Early Aptian, and Early Cenomanian times accounts for drastic environmental deterioration of the surface oceanic waters which were highly unfavourable for oligotrophic, k-mode organisms. As a whole, the establishment of oligotypic benthic communities dominated by heterotroph, r-mode opportunist filter-feeding organisms (brachiopods, pelecypods, crinoids), and accompanying cyanobacteria, which replace the underlying well-diversified chlorozoan-chloralgal communities, is a common paleoecologic signature of all the investigated key-markers. More particularly, very similar sedimentary and paleoecologic features are displayed by the investigated Soaresirhynchia beds in the Lower Toarcian of the Gran Sasso Range (Abruzzo), the Peregrinella and Orbirhynchia beds in the uppermost Valanginian and uppermost Lower Aptian, respectively, of the Gargano Promontory (Apulia). This may possibly call for common paleoceanographic scenarios during distinct time intervals of the evolving hydrosphere-biosphere interactions in the Tethyan ocean. It seems that such time-independent similar shifts of main biofacies imply the development of mesotrophic-to-eutrophic, alkaline “green” waters supporting high primary productivity of the surface sea-waters. 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., BUONO G. & RUGGIERO TADDEI E. (2006). Lower Toarcian (Jurassic) brachiopod-rich carbonate facies of the Gran Sasso range (central Apennines, Italy). Boll. Soc. Paleont. It., 45, 61-74. 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. JONES C.E. & JENKYNS H.C. (2001). Seawater Strontium isotopes, Oceanic Anoxic Events, and seafloor hydrothermal activity in the Jurassic and Cretaceous. Am. J Sci., 301, 112-149. 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.
2009
BRACHIOPODS AS SENSITIVE BIOMARKERS OF GLOBAL PALEOCEANOGRAPHIC EVENTS: A CASE HISTORY FROM THE JURASSIC-CRETACEOUS OF CENTRAL-SOUTHERN ITALY / Graziano, Roberto; Ruggiero, Emma. - (2009). (Intervento presentato al convegno 27th Meeting of the International Association of Sedimentologists tenutosi a Alghero (SS) nel 20-23 September 2009).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/358035
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