Magnetic polarity stratigraphy of Pliocene-Pleistocene marine sediments from Rhodos, eastern Mediterranean

Abstract

Abstract A magnetic polarity stratigraphy extending from the end of the Gilbert Chron (∼ 3.5 Ma) into the Brunhes Chron (0.73 Ma), has been constructed from three partly overlapping sections of an ∼25-m-thick sequence of marine Pliocene-Pleistocene sediments of the Sgourou Formation, Rhodos. The natural remanent magnetization is carried by detrital maghemite-magnetite phases. Normal polarity magnetic overprints, most likely of viscous origin, were successfully removed from normal polarity zones only. The secondary overprints of the reversed polarity magnetizations cannot be removed by alternating field (a.f.) demagnetization. Polarity zones have nevertheless been unambiguously determined by detailed analysis of the behaviour of the samples during step-wise a.f. demagnetization. The FAD of Hyalina baltica (base of Emilian), occurs below the Jaramillo subchron and is the only available biostratigraphic datum. Cytheropteron testudo (Pliocene-Pleistocene boundary) is not found in undoubted specimens within this sequence. On the assumption of a continuous accumulation rate, a one-to-one correlation with the established geomagnetic polarity time-scale (GPTS) has been performed. Within this time-frame a thin, but pronounced, volcanic ash layer is dated to ∼ 2.95 Ma, coinciding with the age of igneous activity on nearby islands (KAr dated to 3.0–3.15 Ma). Age-depth relationships suggest that deposition of the sediment occurred in three distinct phases with different deposition rates, and these are probably related to local tectonic events.