EARLY DEVONIAN SPRING PITS AND THEIR MODERN ANALOGUES, NW HIMALAYA

The limited fresh water resources of our planet are facing steadily increasing human and industrial consumption, as well as various threats by chemical, radioactive and biological pollution. With increasing difficulties in the exploration of new groundwater resources in future, the knowledge about groundwater processes and spring formation will increase in importance. In this investigation, cylindrical, vertical water channels and spring pits in Lower Devonian arenites are compared with active under water springs in a Himalayan lake; both, the active and the fossil example are explained by up-welling artesian ground water.

In the northwestern Himalayas, numerous, vertical, cylindrical structures are found in Lower Devonian arenites, which have been deposited in a barrier island environment; they are interpreted as channels for upward flow of ground water. Pipes initiated from a relative thin horizon; their upper termination formed spring pits. Rapid rise in relative sea-level possibly caused a rapid rise in ground water, resulting in the formation of springs. Due to the minor relief in this environment, the sea level rise affected a relatively large area and cylindrical structures can be found in widely separated sections.

Several circular depressions have been found on the bottom of a small lake in the Lingti Valley, NW Himalaya (India). Ongoing activity is indicated by boiling-like movement of a fluidized sediment/water mixture in central parts of the spring pits. Ground water flow towards the valley center in highly permeable alluvial fan material underneath lake mud causes a relatively raise in hydrostatic head that results in channelized up-ward flow of water and the formation of circular spring pits.

In both examples, artesian ground water formed spring pits at the sedimentary surface, well comparable in size and shape. Spring pits have commonly been found at the transition of marine/limnic/fluviatile and terrestrial environments, where high water saturation occurs and water table variations are frequent. Thus, spring pits may give indication for palaeo-environmental interpretation in the fossil record.