© Terra Antartica Publication Terra Antartica 2003, 10(1), 17-26 Spectral Analysis of Physical Property Periodicities in Fine- Grained Sediments from the CRP-3 Drillhole, Ross Sea, Antarctica F. FLORINDO 1,2 , M. CLAPS 3 , F. NIESSEN 4 & J. DINARÈS-TURELL 1 1 Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, I-00143 Rome - Italy 2 School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH - UK 3 AGIP KCO, Coenstraat 7, 2595 WP, Den Haag - The Netherlands 4 Alfred Wegener Institute for Polar and Marine Research, P.O. Box 20161, D-27515 Bremerhaven - Germany Received 8 January 2001; accepted in revised form 8 May 2003 Abstract - An unexpectedly thick sequence of late Eocene-early Oligocene glaciomarine sediments was recovered in the upper 823 m of the CRP-3 drill-hole. Below this depth, sandstones of the Devonian Beacon Supergroup were recovered down to 939.42 meters below sea floor. We applied spectral analysis techniques to short arrays of physical property data (low-field magnetic susceptibility and wet bulk density) from the CRP-3 core to search for periodicities in selected fine-grained intervals. In the investigated intervals, physical property data clearly revealed the existence of a regular and strong cyclic signal that allow us to discard a stochastic mechanism as controlling these fluctuations. Maximum Entropy, Blackman-Tukey and the Continuous Wavelet Transform (CWT) technique were used to process the two data series. The results show the presence of stable and notable frequencies that suggest the existence of a deterministic external forcing in controlling the deposition of these lithological units. The ratio of these periodicities correspond to those associated with Milankovitch orbital perturbations and, consequently, provide evidence for an external forcing mechanism driving the dynamics of the Early Oligocene East Antarctic Ice Sheet, during early stages of its development. *Corresponding author (florindo@ingv.it) INTRODUCTION The third and final season of drilling associated with the Cape Roberts Drilling Project (henceforth CRP) was successfully completed in the Victoria Land Basin (VLB) of the Ross Sea, Antarctica, during the Austral Spring of 1999. The CRP was designed to continuously core through approximately 1500 m of a sedimentary succession beneath the western side of McMurdo Sound, Antarctica (Fig. 1). The project’s purpose was to establish the chronology of events associated with the onset and subsequent history of Antarctic glaciation and to date the onset of the West Antarctic rift system and uplift of the Transantarctic Mountains which represent the associated rift shoulder. The CRP-3 site is located 12 km east of Cape Roberts (77.01ºS, 163.64ºE) at a water depth of 299.7 m. The CRP-3 drill-hole (77.006°S, 163.719°E) was cored from a depth of 2.8 to 939.42 metres below sea floor (mbsf) with 97% recovery. A 790-m-thick Cenozoic glaciomarine sequence of sandstones (about 80% of the CRP-3 sequence) with minor diamictites, conglomerates and mudstones, was recovered in the upper part of the CRP-3 drill-core. Below this, a c. 30-m-thick interval (790-823.11 mbsf) of breccia with dolerite clasts was encountered. Below this depth, sandstones of the Devonian Beacon Supergroup (possibly the Arena Sandstone) were recovered (Cape Roberts Science Team, 2000). Our previous investigations on physical properties data from the CRP-1 and CRP-2/2A drill cores clearly Fig. 1 – Schematic cross-section through Cenozoic strata beneath the western flank of Roberts Ridge with relative ages and the location of CRP-1, -2 and -3 drill sites.