Reconciling the roles of climate and tectonics in Late Quaternary fan development on the Spartan piedmont, Greece

Abstract

Abstract The evolution of five alluvial fan systems is discussed in relation to chronology and possible tectonic and climatic triggering mechanisms. Two types of fan have evolved on the Spartan piedmont, Greece. First relatively large, low-angle fans, comprising four segments (Qf1–Qf4) composed of debris-flow and hyperconcentrated-flow deposits, with fluvial sediments restricted to the upper deposits of the distal segments. Second small, steep telescopically segmented fans, which consist of three segments (Qf1–Qf3), formed predominantly by debris-flow and hyperconcentrated-flow deposits. Morphological analysis of surface soils coupled with mineral magnetic and extractable iron (Fe d ) analyses of B-horizons suggest that individual segments can be correlated across the piedmont and have equivalent age. Luminescence dating of fine-grained deposits suggests that Qf1 segments formed during marine isotope stage (MIS) 6, Qf2 segments during MIS 5, Qf3 segments during MIS 4–2, and Qf4 segments during MIS 2 and 1. Tectonics has exerted a limited influence on fan systems. Regional uplift provides the gross relief conducive for fan development. The locations of fans were determined by transfer faults of Tertiary age, while Quaternary faulting initiated short phases of fan incision. Climate change as manifested by cycles of aridity and low vegetation cover during stadials, and humidity and deciduous woodland during interglacials and interstadials, played a key role in fan evolution during the later Middle and Upper Pleistocene. Aggradation occurred during stadials, with minor deposition and intermittent erosion during most interstadials, and entrenchment during the interglacials and longer interstadials. Deposition during the Holocene is limited in extent.