POZYCJA CHRONOSTRATYGRAFICZNA GRANICY NEOGEN/CZWARTORZĘD

Abstract

CHRONOSTRATIGRAPHIC SETTING OF THE NEOGENE/QUATERNARY BOUNDARYAbstract. Many years’ consequent postulates of Quaternary scientists resulted in a decision of the Executive Committee of the International Union of Geological Sciences (IUGS) to ratify a proposal of the International Commission on Stratigraphy to lower the base of the Quaternary to the lower boundary of the Gelasian stage. Simultaneously, the lower boundary of the Pleistocene has been moved to the same position. The previous lower chronostratigraphic boundary of the Quaternary, represented by the Vrica stratotype in southern Italy, has been hardly recognizable outside the Mediterranean Region and neither biostratigraphic indices nor traces of extreme geological events could be found in this very place. On the other hand, an establishment of the Vrica site as the stratotype for the Neogene/Quaternary boundary (equivalent to the Pliocene/Pleistocene boundary) was a driving force to create the Gelasian as a new and uppermost stage of the Pliocene. The Gelasian filled a hiatus between the upper boundary of the Piacenzian stage at Castell Arquato and the boundary of the so-called Plio-Pleistocene at Vrica. The lower boundary of the Gelasian was defined at 2.588 Ma, close to a boundary of the palaeomagnetic epochs Gauss and Matuyama. The new lower boundary of the Quaternary reflects a principal transformation of the climate on the earth. A criticalchange occurred at about 2.7 Ma, when a severe reconstruction of the thermohaline circulation took place, caused by a final closure of the Panama Straits and inflow of freshwater to the Arctic Ocean. The latter favoured development of constant ice covers in the Arctic, a higher albedo of which resulted in initiation of the ice ages in the northern hemisphere.