RESPONSE OF MACROBENTHOS TO CHANGES IN PALAEOENVIRONMENTS IN THE LOWER-MIDDLE PLEISTOCENE (LUCANIA BASIN, SOUTHERN ITALY)

Abstract

The Lucania Basin is part of the Bradano Trough, whose internal sectors were subject to continuous subsidence during the Early
Pleistocene. This led to the deposition of a muddy sequence with a thickness in excess of 500 m in the Montalbano Jonico area
(Lucania). During the Middle Pleistocene, a general shallowing took place, starting from the more internal sectors of the Lucania Basin.
The regressive succession exposed in the badland area of Montalbano is candidate of the Early/Middle Pleistocene boundary stratotype. The restored sequence was obtained from selected partial sections correlated by means of nine volcaniclastic layers, each of themcharacterised by distinct macrofauna assemblages. A gap of unknown thickness (probably a few tens of metres) divides the succession
in two intervals: the lower one (A) consists of muddy deposits, the upper one (B) of muddy to sandy deposits, overlain by organogenic
calcarenites in the uppermost part. Integrated palaeoecologic, taphonomic and ichnologic analyses were performed in order to reconstruct bathymetric fluctuations and environmental changes, based on biotic responses. Palaeocommunities from the lower interval point
to background environments with moderate sedimentation rate, low hydrodynamic level and low oxygen content, punctuated by numero us events of mass deposition. Palaeodepths range from the upper bathyal to the shelf break. Through interval B, palaeodepths range from the shelf break to the inner shelf-nearshore. This interval includes genetically different shell beds. The inferred background environments are characterised by sedimentation rates and water-energy ranging from low to high, under fully aerobic conditions. Like in the lower interval, blanketing events are numerous. Within the general regressive trend, several fifth- and sixth-order cyclothems are recognised throughout the sequence. Vertical changes in the fossil communities within individual cycles indicate changes in water depth that parallel climatic fluctuations, as proved by climatic indicators in interval B. Further, the sea-level curve proposed in the present work matches well the local oxygen isotope curve, but the bathymetric range of some of the cycles suggests a tectonic control superimposed on the climatic influence.