Ripple marks are typically generated by currents moving in one direction or by the to-and-fro motion of waves in shallow water to depths of a few tens of feet at the most.
Ripple marks and mud cracks are preserved in the Precambrian Bass, Hakatai, Dox, and Nankoweap Formations.
In Estonia fossil ripple marks have been identified in Cambrian and Devonian siliciclastics as well as in Ordovician and Silurian carbonate rocks.
1), west of the Keila-Riisipere railway, has provided an opportunity for detailed study of ripple marks in the Upper Ordovician section.
Ripple marks are oriented roughly in the north--south direction (NE 10[degrees], SW 190[degrees]).
However, ripple marks that could be measured were only observed on two levels--on the upper surface of the Paaskula Member, described in detail below, and in a restricted area in the lower part of the Saue Member of the Kahula Formation.
In the quarry the uppermost bed of the member with ripple marks consists of yellowish-grey seminodular micritic limestones with bioclasts of bryozoans, brachiopods, echinoderm columnals, algae (Fig.
The surface with ripple marks has pyritic impregnation and has been partly eroded before the formation of younger deposits.
Ripple marks in the Vasalemma quarry have flat-topped, sometimes rounded, straight or sinuous crests.
The clearly asymmetric ripple marks occurring in siltstones of the Lower Cambrian Lukati and Tiskre formations have the wavelength of 10-20 cm and RI 3-32 and 5-16, respectively (Pin-us 1971, 1978).
Short wavelengths of ripples and possible occurrence of cross ripple marks have been reported from the Saku Member (L = 10 cm) of the uppermost Vasalemma Formation and from the topmost Ordovician Porkuni Stage (L = 2-4 cm) (Polma 1982).