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Early Cretaceous neritic carbonate community and facies response to palaeonvironmental and sea-level changes: New evidences from Apenninic carbonate platform of southern Italy
Mariarosaria Martino, Filippo Barattolo, Sabrina Amodio, Mariano Parente

Building: Muséum d'Histoire Naturelle de Genève
Room: Lobby /Hall/
Date: 2018-12-05 10:59 AM – 11:02 AM
Last modified: 2019-02-18

Abstract


The early Cretaceous marine sedimentary record is punctuated by several crises of carbonate production and perturbations of the global carbon cycle (Weissert & Erba, 2004; Föllmi & Godet, 2013). The earliest of these crises occurred during the Valanginian period. In the northern Tethysian domain, this crisis entailed the demise of carbonate platforms and major changes in carbonate producer communities. High trophic conditions are mirrored by the shift to a heterozoan neritic community that started close to the Berriasian/Valanginian boundary and persisted up to the early Barremian. Fossil assemblages, combined with lithofacies characteristics, are here used to reconstruct the Valanginian-Barremian paleoenvironmental history of the San Lorenzello section, which belongs to the Apennine Carbonate Platform (APC) of southern Italy. Unlike coeval northern Tethysian carbonate platforms, this platform did not record any drowning event during the Valanginian-Barremian. However, it responded to paleoenvironmental perturbations by biofacies changes that are here investigated.

The San Lorenzello section (233 m thick) is well exposed on the southern slope of the Monte Monaco di Gioia ridge (Matese Mountains), about 70 km North of Naples. The first 86 m were previously investigated by sedimentology, cyclostratigraphy, sequence stratigraphy and isotope stratigraphy (D’Argenio et al. 1997; Ferreri et al. 2004; Amodio, 2006; Amodio et al., 2008; Amodio et al., 2018). We have revisited this older interval using high-resolution biostratigraphy and present a work in progress on biota and facies evolution throughout the whole Valanginian-Barremian interval.

Based on lithofacies changes and related early diagenetic features, we propose a sedimentary model for the carbonates of the San Lorenzello section. According to our model this section was part of a wide and shallow carbonate platform that was influenced by waves and/or storms. A narrow, high-energy zone of migrating sandy shoals separated a more open from a more restricted lagoon. The sporadic occurrence of laminated and charophyte-bearing limestones suggests ephemeral tidal-supratidal settings with brackish ponds. The sea-level oscillations induced frequent and cyclic emersions of the platform, witnessed by karstification and pedogenesis of marine carbonates. Previous works also showed an eustatic control on the depositional sequences (superbundles in D’Argenio et al., 1997; Ferreri et al., 2004).

Taking into account the Chiocchini et al. (2008) and De Castro (1991) biozonal schemes, based on calcareous algae and benthic foraminifera, and supplementing these schemes with the data on biostratigraphic distribution of Salpingoporella species (Carras et al., 2006), the first results of our study leads to a considerable refinement of the biostratigraphy of the studied section. Our new investigations confirm that the lower part of this section is late Valanginian in age, as already indicated by Amodio et al. (2008). The first Vercorsella and Cuneolina species occur at 10-15 m from the base of the section. The next interval (between 20 and 60 m from the base of the section) is characterized by Actinoporella podolica, Salpingoporella annulata and Selliporella johnsoni, associated with Vercorsella camposauri, V. scarsellai, Cuneolina laurentii and Praechrysalidina infracretacea. This association points to a late Valanginian-early Hauterivian age. Within this interval, the occurrence of typical specimens of C. laurentii (between 40 and 50 m from the base of the section), the LO of S. johnsoni (at about 55 m) and the FO of P. danilovae (at about 58 m) allow identification of the Valanginian-Hauterivian boundary as occurring in the C. laurentii biozone sensu De Castro, 1991. The FO of Salpingoporella piriniae, preceded by the FO of S. melitae and S. muehlbergii, allows identification of the Hauterivian-Barremian boundary between 100 and 110 m from the base of the section, based on the review of the distribution of Salpingoporella species by Carras et al. (2006). The LO of Campanellula capuensis and Clypeina solkani, between 150 and 160 m from the base of the section, indicates the lower/upper Barremian boundary (Chiocchini et al., 2008; De Castro, 1991). The LO of S. annulata, found at about 145 m from the base, points to the late Barremian (Carras et al., 2006).

These new biostratigraphic data indicate that the Valanginian-Hauterivian boundary is about ten meters below the position indicated by Ferreri et al. (2004). The mismatch between the biostratigraphic position of the Valanginian-Hauterivian boundary of Ferreri et al. (2004) and the chemostratigraphic position of the same boundary, based on correlation with reference deep water sections by carbon isotope stratigraphy, was already underlined by Amodio et al. (2008). Our new biostratigraphy of the San Lorenzello section eliminates this mismatch and produces a close agreement between the biostratigraphic and C-isotope position of the Valanginian-Hauterivian boundary.

The C-isotope correlation between neritic and pelagic sections by Amodio et al. (2008) suggested that only the upper part of the Weissert event is recorded in the San Lorenzello section, followed by a time of a global decrease of C-isotope values. The upper Valanginian deposits, 40-50 m thick, are mainly composed of peritidal facies and punctuated by sedimentary gaps. This is consistent with the third order global sea-level fall (Haq, 2014) and cooling event hypothesized by some authors (e.g. Weissert & Erba, 2004). Starting from about 33m from the base of the section, sandy shoal facies become more frequent. These deposits record higher energy conditions at the Valanginian-Hauterivian transition and a deepening upward trend culminating in the Hauterivian interval (50-65 m overall thick), where more abundant open lagoonal facies occur. Some bivalve- rich horizons (at about 59, 63, 68, 71, 80, 93 and 96 m) characterize this portion of the section, where tidal facies are rare. This vertical facies evolution is consistent with the third order global sea-level rise starting in the Hauterivian and culminating at the base of the Barremian (Haq, 2014). The restoration of more restricted environmental conditions characterizes the lower part of the Barremian interval (from about 115 to 155 m), with alternating restricted lagoonal and inner shoal facies. Starting from 160 m, the uppermost part of the San Lorenzello section consists of alternating lagoonal limestones and massive dolomites. However, the occurrence of intervals partially covered by modern day vegetation and soil, hinders a detailed sequence stratigraphy interpretation.