The origin of rhythmic bedding in the Pliocene Trubi Formation of Sicily, southern Italy

Abstract

Foraminiferal, palynological, stable isotope, geochemical, clay mineralogical and granulometric data have been gathered for the successive layers of four rhythmic alterations of relatively carbonate-poor and carbonate-rich beds in the Early Pliocene Trubi Formation of Sicily (southern Italy). The marly rhythmites consist of a grey layer and a white more indurated layer in which an additional beige less indurated layer is intercalated; they are therefore more complex than the well-known marl-limestone couples elsewhere. These rhythmites probably originate from the alternate predominance of increased dilution of river-supplied terrigenous material (grey) and decreased carbonate production in the surface waters (beige). The grey layers are considered to correspond to periods of increased local run-off and higher surface water temperatures and productivity. The beige layers signal more arid and cooler climatic conditions, lower surface water productivity and stronger or more frequent dust-loaded, southern winds. The white layers apparently reflect intermediate climatic and environmental conditions. These periodical changes, probably brought about by astronomical precession, appear to have occurred not only during the Pliocene, but also during the late Miocene.