Resumen de Il Quaternario del Tirreno Abissale. Interpretazione stratigrafica e paleoclimatica del Pozzo DSDP 132
M.B. Cita, Giuliano Ciampo, E. Ferone, M. Moncharmont Zei, R. Scorziello, E. Taddei Ruggiero
A continuously cored well, with excellent core recovery, was drilled in the central Tyrrhenian Basin during Leg XIII of the Deep Sea Drilling Project in September 1970. Paleontological investigations on the Pleistocene section, some 70 m thick, were oriented to decipher the climatic record of this area, which is located close to the type-areas of all the Pliocene and Pleistocene marine stages. Semiquantitative investigations on 227 samples, based on the visual estimate of the relative abundance of planktonic foraminiferal species and on the number of taxa present in each assemblage, resulted in the construction of an inferred climate curve (total fauna curve). This curve has been correlated by means of four different and independent criteria (biostratigraphic, lithostratigraphic, paleoclimatic and paleomagnetic) with a similar curve constructed for the Eastern Mediterranean (Ionian Basin, DSDP Site 125) as well as with some long piston cores; it can therefore be considered as a generalized climatic curve for the Mediterranean.
Paleomagnetic investigations by Ryan on the same cores allowed to recognized the Brunhes/Matuyama boundary, the Jaramillo and Olduvai events of the Matuyama normal epoch; as a consequence, the generalized climatic curve for the Mediterranean is calibrated with the absolute time-scale by means of the paleomagnetic stratigraphy.
During the upper part of the Brunhes normal epoch, or in the last 400,000 years, the climate curve is characterized by important climatic fluctuations, which could be correlated with the Würm and Riss glaciations and with the Würm-Riss interglacial. A short cold episode near the Brunhes/Matuyama boundary is correlated with the Mindel glaciation and with the Flaminian erosional phase of the Tyrrhenian coast. A short cold interval near the Jaramillo event is tentatively correlated with the Günz glaciation and with the Cassia erosional phase.
The Pleistocene predating the Jaramillo event and older than 1 my, is characterized by climatic fluctuations of lesser magnitude than those recorded in the Brunhes epoch, without marked cold episodes. They are interpreted as «pre-glacial», or predating the Alpine glaciation, and are related to the North-Atlantic (Arctic) glaciation which began some 3 my ago.
Periods of stagnation, induced by glacio-eustatism and related to rising sea-level, are recognizable in the Pleistocene record of the Tyrrhenian, though less pronounced than in the Eastern Mediterranean.
Quantitative investigations on 44 samples from Core 1 of Site 132 resulted in the construction of a number of frequency curves relative to discrete taxa, with special emphasis to the climatically significant ones. The curve considered more significant to show the climatic changes is that plotting the relative abundance of the «warm» indicators, plus the reverse of the «cold» indicators (both being cumulative curves). This curve is very similar to the inferred curve based on semiquantitative evaluations, with only minor differences. This significant curve is compared with other climatic curves obtained for the Eastern Mediterranean and for the Caribbean by studying the paleontological content of piston cores; it is also compared with Emiliani's curve based on the isotopic composition of foraminiferal shells; the fit of all these curves in the considered interval is very good.
