Characterstics and origin of patterned ground in the Barton Peninsula, King George Island, Antarctica

Abstract

Patterned ground with distinct geometric shapes is well developed in the southwestern part of the Barton Peninsula, King George Island, Antarctica. The patterned ground consists of stone borders composed of clast-supported pebbles and boulders and central parts of coarse sand- to silt-size materials. The patterned ground can be classified into circular, polygonal, stepped, and striped types according to the shapes of the stone borders. The stone borders of the circular patterned ground have circular or elliptical shapes whereas those of the polygonal patterned ground have the shape of irregular polygons because they are interconnected with one another. Stepped patterned ground occurs as a terraced slope and has arrowhead-like or cuspate stone borders. Striped patterned ground consists of slope-parallel bands of coarse-grained (pebbly to cobbly) and fine-grained (granule to medium sandy) parts. The types of the patterned ground change according to the slope gradient with the circular and polygonal types dominant on gentle (0-10？°) slopes and the stepped and striped types common on steep (10-30？°) slopes. The difference in the shape of the patterned ground is interpreted to have formed by different degrees of asymmetric material circulation and downslope soil movement in association with self-organization of the soil materials in the active layer caused by repeated freeze-thaw cycles. The stepped patterned ground is in particular interpreted to have formed by slow downslope mass movement or solifluction of the water-logged active layer. The absence or poor development of vegetation in the central parts of the patterned ground, compared with the common presence of moss and lichen on the surface of the stone borders, and the good preservation of internal patterned ground and mudcracks in the central parts indicate that the materials in the central parts of the patterned ground are still in active circulation. When interpreting the timing of formation of the patterned ground on the basis of 14C or OSL ages, it is important to know whether the materials in the patterned ground are still in active circulation. In case the patterned ground is still in active circulation, the 14C or OSL ages of the soil materials are interpreted to have values within the circulation period of the soil materials. Otherwise, the ages may have no relation with the timing of formation of the patterned ground.