Precambrian rocks of Central Telemark, Norway: II. Ripple marks and mud cracks. Appendix: Norwegian literature on ripple marks and mud cracks.

Ripple marks are very common in the area investigated (2000 square km). In one outcrop, where there is a 32 m thick sequence of quartzite, 26 rippled surfaces have been studied, and drawn as sections by means of plasticine casts. Several types, same of them unusual, are described: ripple-drift cross-lamination, symmetrical ripple marks with cross-lamination, etc. It was found impossible to decide whether the asymmetrical ripple marks were formed by currents or distorted oscillation waves. The thickness of the quartzite sequence increases remarkably in the possible down-current direction. In a diagram is included wave-length, amplitude and ripple-index of 63 predominantly Norwegian ripple marks. Two exposures of mud cracks in quartz-rich beds show an extremely regular pattern with deep cracks, whereas the originally more clay-rich sediments found in two other localities brake up more irregularly, with shallow cracks of several generations.