Parting lineation

It is meanwhile widely accepted that parting lineation forms in the turbulent, viscous boundary layer immediately above the sediment-water interface.

After all it is this lateral inrush of fluid, which “sweeps up” the grains in the grooves and redeposits them in long parallel ridges underneath the lifting turbulences.

Parting lineation is restricted to coarse silts as well as to fine- and medium-grained sands (i. e. to grain sizes of 16 to 500 μm).

Hydraulically it is characteristic for the lower part of the upper plane bed regime and results from fairly high current velocities of 0.6 to 1.3 meters per second.

[5] Geological formations like for instance the Old Red Sandstone or the Buntsandstein also give proof of the shallow marine character.

Parting-step lineation,[8] which is characterized by step-like parting surfaces, has been reported by Banerjee from varves deposited in glacial lakes.

[10][11] Remark: in the marine environment parting lineation doesn't have to be associated solely with the upper plane bed regime, it has been reported for instance from the erosive stoss side of ripple marks, megaripples and dunes.

Due to its varied and rather widespread occurrence parting lineation is not a unanimous indicator for depositional environments.

This can be equated to: where λ represents the measured spacing, Ut the shearing velocity and η the viscosity of the fluid.