AUTHORS: Scifoni A., Corda L., Mariotti G., Brilli M.
YEAR: 2007
Bathurst Conference Norwick (UK)
Three sections from the central Apennine region (central Italy), spanning from the lowermost Albian to Cenomanian-Turonian, have been studied. Two of these are characterized for the presence of a regional gap, documented by bauxitic deposits, while the remaining presents no visible stratigraphic discontinuities. The sections pertain to the Latium-Abruzzi carbonate platform and are described from a sedimentological, biostratigraphical and isotopic perspective. These successions consist of carbonates deposited on open-to-restricted lagoonal and peritidal-supratidal settings, most probably under a cyclic control. The aim of this work is to provide new insights for integrated regional correlations between our sections and other coeval sections, also from pelagic settings, and for interpreting the occurrence of particular biofacies.
By combining facies analysis and isotope stratigraphy we try to.
– interpret the carbon- and oxygen-isotope records in terms of environmental changes (trophic resources, oceanic circulation, climate);
– eventually correlate these excursions with the globally recognized events;
– evaluate if there is a possible link between some observed biofacies events and the isotopic signature.
Our data suggest a good correlation between three major positive carbon excursions recorded in our shallow-water carbonates and the existing isotope curves from deep-sea environments during the Albian-Cenomanian time interval. In particular the isotope record of one of the studied sections (Serra del Pruno) clearly shows a good correlation with some well known anoxic events (OAE1d, OAE2, MCE). Furthermore the negative trend evidenced by the oxygen-isotope curve may account for a climate warming trend through the Albian-Cenomanian time interval culminating in the following Cenomanian-Turonian climax. Basing on these data we can suggest that the central Apennine platform limestones represent a good archive of middle Cretaceous palaeoceanography and in particular of the major changes in carbon reservoirs. This is particularly important by considering the nature of this cyclic successions, and especially the fact that these are characterized by the presence of major gaps, spanning some My, evidenced by residual deposits.
We recognized the occurrence, in all the analyzed sections, of three clearly visible Alveolinids-rich cenomanian metric horizons: Sellialveolina viallii, Cisalveolina lehneri and Cisalveolina fraasi. It is likely to note a good correlation between such occurrences and the contemporaneous positive shifts in the 13C values suggesting a link between the isotopic pattern and the rapid spreading of these larger foraminifera. It is known that biotic assemblages are strongly influenced by environmental factors, including temperature, seawater chemistry, weathering rates, carbonate saturation state and nutrient availability.
Nevertheless it is difficult to discriminate among these factors, the concomitant spreadings of Alveolinids and the time-equivalent carbon-isotope excursions let us to suggest an environmental control as major driving factor. In particular we may assume that rapid increases in nutrient availability, as recorded by positive 13C values, reasonably may favour and/or enhance the Alveolinids bloom. Furthermore, this work suggests that similar considerations could be considered as a work hypothesis also for other family of organisms (e.g., green algae), hence evidencing a new perspective in carbonate study.