RESOLVING PATTERNS OF CRETAN FAN SEDIMENTATION: PRELIMINARY INSIGHTS FROM MINERAL MAGNETIC AND CHRONOMETRIC DATA

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Analysis of fan sediments and post-incisive soils was combined with optically stimulated luminescence (OSL) and U-series dating to reassess Nemec and Postma’s (1993) model of fan evolution on the Sfakian piedmont, southern Crete. Field mapping supports the assertion that sedimentation occurred in three developmental stages. Stage 1 sediments consist of angular debris flows that form small cone-like deposits. Stage 2 fluvial gravels form large, relatively steep stream flow-dominated telescopic fans, while stage 3 sediments consist of coarse sieve-type alluvium and localised mudflows. Irrespective of gradient, fan surfaces are capped by post-incisive soils that form a chronosequence comprising remnant chromic luvisols. Soils formed on stage 1 surfaces are characterised by highly eroded Bt horizons, but contain high concentrations of magnetic minerals. The stage 2 and 3 soils display less well developed profiles and record significantly lower magnetic values, indicating that the stage 1 soils and fan surfaces formed first, followed by stage 2 and 3 soils and fan surfaces.

Nannofossil data strongly suggest that stage 1 sedimentation commenced towards the end of the early Pleistocene. For stage 2 sedimentation OSL and U-series techniques produce remarkably similar age estimates (with differences being statistically insignificant [p>0.1]). Multiple phases of sedimentation between 79 ka and 68 ka culminated in the emplacement of lower fan units. Following a period of minor depositional and concomitant erosion, the formation of the middle fan units resulted from further sedimentation between 54ka and 33 ka. By comparison, the chronology for the formation of the upper fan units is currently less well constrained, although later sedimentation phases are dated to between 15.5 ka and 11.4 ka. The new chronometric data have two significant implications for the evolution of Sfakian fan systems. First, the timing of sedimentation phases and the formation of stage 2 fans apparently occurred over a much shorter timescale compared to a previous chronology proposed by Nemec and Postma (1983, 1985). Second, the estimated ages strongly suggest a close link between sedimentation and climate whereby major depositional phases were coincident with infrequent intense rainfall events during phases of rapid regional cooling and increased aridity during marine isotope stage (MIS) 4, 3 and 2.