43. PLEISTOCENE FANGLOMERATE DEPOSITION RELATED TO UPLIFT OF THE TROODOS OPHIOLITE, CYPRUS1Andrew Poole2 and Alastair Robertson3 |
ABSTRACTThe Pleistocene Fanglomerate Group of the southern part of Cyprus exemplifies coarse alluvial clastic deposition within a zone of focused tectonic uplift, related to collision of African and Eurasian plates, as documented by Ocean Drilling Program Leg 160. During the Pleistocene, the Troodos ophiolite was progressively unroofed, resulting in a near-radial pattern of coarse clastic sedimentation. The Pleistocene Fanglomerate Group depositionally overlies Pliocene marine sediments. Along the southern margin of the Troodos Massif the contact is erosional, whereas along its northern margin a regressive fan-delta (Kakkaristra Fm.) intervenes. The Pleistocene Fanglomerate Group is subdivided into four units (termed F1-F4), each of which were formed at progressively lower topographic levels. A wide variety of alluvial units are recognized within these, representing mainly high-energy coarse alluvial fans, channel fans, braidstream, and floodplain environments. A near-radial sediment dispersal pattern away from Mt. Olympos is indicated by paleocurrent studies, based on clast imbrication. Provenance studies indicate relatively early unroofing of the ophiolite, but with only minor localized erosion of ultramafic rocks from the Mt. Olympos area. Clasts of erosionally resistant lithologies, notably ophiolitic diabase and Miocene reef-related limestone, are volumetrically over-represented, relative to friable basalt and early Tertiary pelagic carbonate sediments. The younger Fanglomerate Group units (F3 and F4) can be correlated with littoral marine terraces previously dated radiometrically at about 185-219 ka and 116-134 ka, respectively. However, the earlier (F1 and F2) Fanglomerate Group units can, at present, be dated only as early to middle Pleistocene. The principle variables that affected deposition of the Pleistocene Fanglomerate Group as a whole are tectonic uplift isostatic effects, glacio-eustatic sea-level change, short- and long-term climatic change, and lithology. However, the dominant control was tectonic uplift that apparently peaked during early and middle Pleistocene time. Aggradation of fluvial sediments (F1 and F2) took place at times of relative sea-level high with associated terrace formation. This was followed by downcutting during periods of relative sea-level fall when surface uplift continued. The dominant control on the younger (F3 and F4) units was glacio-eustatic sea-level change, during a time when littoral marine sediments accumulated, and rates of surface uplift may have decreased. Finally, the Holocene alluvial deposition was also affected by anthropogenic effects, notably deforestation. |
|