Development of joint-controlled rock basins in Bohus granite, SW Sweden

The granite area of Bohuslan along the Swedish west-coast is characterised by an abundance of rock basins of different sizes. Within 163 km(2) large p art of the area over 400 basins occur, ranging in size from less than 0.005 to almost 2 km(2). These basins were measured, described and classified fr om air photos according to their length, width, area, altitude, shape, boun daries, openness and relation to joint configuration. The depth of basins w as collected from digital elevation data. Their distributions and shapes ar e clearly associated with the visible jointing patterns, as shown by their location along joints or joint intersections, by joint-guided enlargement a nd similarity between directions of long axis of basins and principal tecto nic lineaments in the Bohus granite. The patterns and characteristics of th e basins suggest that deep selective weathering had been the primary proces s involved in the origin and evolution of the basins. Later, they have been reshaped and possibly stripped of saprolites by glacial processes in the P leistocene. Dating of deep weathering responsible for basin initiation and origin is difficult, although the complex story of Mesozoic weathering, Lat e Cretaceous burial and Late Tertiary exhumation is not without support. (C ) 2001 Published by Elsevier Science B.V.