|
Adele Bertini, Florence University (Italy)
Maria Marino, Bari University (Italy)
Mariarita Palombo, Roma La Sapienza University (Italy)
Neri Ciaranfi, Bari University (Italy)
|
|
A primary objective for Earth scientists is the establishment of a standard, globally-applicable stratigraphical scale, which allows the worldwide chronostratigraphical correlation. The scientific community is also encouraged to establish "Regional" Stages geographically restricted in their function and purpose; however the definition of formal subdivision in marine and continental realm and their correlation are not easy even if at regional scale.
The approaches to establish an integrated time-scale in the Pliocene and Pleistocene interval are basically interdisciplinary; however correlations between biochronology, biostratigraphy, chronostratigraphy, climatostratigraphy, and composite regional stratigraphy are often very problematic. The criteria that could be employed in defining and correlating chronostratigrafic and biochronologic units in the Mediterranean, based on marine calcareous plankton and continental pollen and mammal fauna, are tentatively proposed for the Middle Pliocene to Pleistocene time span. Calcareous plankton biostratigraphy, mainly based on foraminifera and nannofossils, is well known for the Pliocene and Pleistocene marine successions and it provides high time resolution and accurate correlation at regional and global scale. Calcareous plankton bioevents are precisely correlated to marine oxygen isotope stages, magnetostratigraphic reversals as well as to Mediterranean sapropel stratigraphy thus making available a detailed astronomically tuned biochronology which may contribute in the recognition and definition of boundary and unit stratotypes for global stages. On the other hand, pollen assemblages are useful for the reconstruction of vegetation and climatic changes; because as contained in marine and non-marine sediments, pollen permits the correlation between onshore and offshore successions and then could contribute to establish global chronostratigraphic boundaries.
However the palynologic content must be used warily in describing both biozones and climatostratigraphic units, especially when they are not constrained to an established chronostratigraphic framework. Solely the integration of time-diagnostic evidence gives chronological value to ecobiostratigraphic events, thus enhancing stratigraphic resolution. As regard to terrestrial fauna, especially mammals, diachroneity in palaeobiological events together with discontinuity in the continental sedimentary record, the rarity of deposits in a virtually continuous sedimentation, the presence of ecological barriers, environmental conditions, and taphonomic and sampling biases prevent a reliable definition of boundaries and make any detailed biochronological framework subject to change in relation to new discoveries. The main purpose of the present study is to attempt a correlation between terrestrial and marine bioevents and global chronostratigraphic scale by means of stratigraphic events as magnetic reversals, stable isotopes stages and radiometric dating.
|
