The soils, Geomorphology and erosion history of the leipsokouki catchment, Nomos of Grevena, Greece

Abstract

The soils, geomorphology and Holocene alluvial and colluvial record have been established for a small catchment in central northern Greece. The seventeen soil series have been defined and mapped and exhibit high spatial diversity. The soils form from Tertiary mudstones, sandstones, Plio-Pleistocene conglomerates, and Holocene alluvium. The soil orders vertisol, mollisol, alfisol, inceptisol and entisol have been identified. Mature soils derived from calcareous mudstone are dark brown shrink-swell vertisols and vertic mollisols. Mature soils from sandstones and conglomerates are reddish brown to yellowish brown reflecting chemical weathering and clay translocation, they are classified as alfisols and inceptisols. Many recent silty and sandy soils occur on hillslopes, eroding areas and on very late Holocene alluvium in the valley bottom. Three distinct phases of valley alluviation are recognised based on terrace height, stratigraphy and degree of soil development. They are:-1) The Syndendron alluvium which is early Holocene in age (>9 ka BP) and its formation is related to the last deglaciation. 2) The Sirini alluvium which began to aggrade 2,200 years BP and was interrupted at least three periods during which soil formation occurred, aggradation probably ceased 1,500 years ago. The Sirini fill reaches heights of 10 m in the mid catchment and has been reincised to the level of bedrock. This alluvial aggradation is interpreted as a response to human induced soil erosion. 3) The Leipsokouki alluvium is composed of two low terraces one at 1-2 m and a second at 3 - 4 m and is a valley aggradation in response to a modern phase of erosion. It is poorly dated, but is less than 500 years old based on archaeological evidence. Soil erosion is common on hillslopes, and gullies are eating into terraced farmland. Five phases of colluvial filling on slopes are recognised. They are; a) >12 ka BP reddish brown colluvial fills, b) 4.0 - 3.5 ka BP Middle Bronze colluvial fills, c) 3.0 - 2.5 ka BP Iron Age colluvial fills, d) 2.2 - 1.4 ka BP Hellenistic - Roman colluvial fills, e) <500 year BP Ottoman - modern colluvial fills. The mid Holocene colluvia represent redistribution of soil materials into paleochannels and depressions. This redistribution of soil was not of sufficient magnitude to result in sediment deposition in the valley and so no corresponding alluvial fill is present. The Hellenistic - Roman colluvial fills are higher energy deposits and were preceded by a period of incision and gullying, they are correlated with the Hellenistic - Roman valley aggradation and are interpreted as human induced. The youngest colluvial fills result from erosion in the last 500 years and are correlated with the Leipsokouki aggradation terraces in the valley bottom. Early Holocene events are interpreted as relating to deglaciation and thus have a climatic control, while late Holocene events (<2.5 ka BP) are interpreted as having an anthropogenic cause.