Sedimentologisk undersökning av de övre glacifluviala avlagringarna i Vombsänkan, södra Skåne

Sammanfattning: The Vomb Plain in central Skåne is a large sand and gravel field. lts youngest glacifluvial deposits have been investigated from a sedimentological point of view in order to define proximal to distal environments of the ancient braided river system. The following parameters have been used in studying the sandurfield: The average grain size composition and the maximum size of clasts at sites from different part of the field, paleocurrentanalysis, petrological composition of gravel clasts, the surface slope gradient between the proximal parts and the distal parts and identification of facies associations at six different sites. The investigation reveales a general trend in paleocurrent direction of the depositivy stream from east to west. The average surface slope gradient of the sandur field, in its entirety between Sjöbo and Gårdstånga is 1m/km while in the gravelly eastern part, between Sjöbo and Vomb it is 2,5m/km. The maximum diameter of clasts decrease from 300 mm at Lillås, in the eastern part, to 50 mm at Harlösa. Glacifluvial streams entered the sandur field from the northeast and the southeast, but yet the streams came from the same glacier. This is indicated by paleocurrent directions from the south or southeast at Blädde and Hemmestorp, in the southern part of the plain, and minor but significient differences in the litological composition of gravel clasts between the six sites. The lithofacies sequences have been compared with Miall's (1977, 1978) facies model for the braided rivers depositional environment. Lillås, furthest to the east concurres well with Miall's facies model for a Scott type sequence, which he finds typical for a proximal part of the braided river system. The sequences at the sites Sjöbo soptipp and Sjöbo cement resemble the Donjek type sequences and probably were deposited in a intermediate braided river depositional environment. At the Blädde and Hemmestorp sites the facies assemblages recognized are a combination of the Platte and Donjek types sequences, typical for the intermediate to distal reaches of the braided river depositional environment. The facies sequences at the Harlösa site is similar to the facies model for the Platte type sediments and is probably the most distal deposit in our investigation.