The impact of sediment-stabilizing biofilms on the architecture of sedimentary structures (Mellum Island, Southern North Sea)
Abstract: Sedimentary structures described in this paper evolve from the impact of physical forces on biostabilized sediments in modem siliciclastic tidal tlats: (i) erosional remnants are more or less sharp-edged planar rises mainly occurring in the intertidal-supratidal transitional zone where microbial mats develop. ( ii ) In deposits composed of a multitude of subrecent mars buried by quartz-sandy sediments, gas diffusion is recorded by hollow pores of 0.5-3 mm in diameter arranged like pearl strings in the sandy interlayers. ( iii ) In contrast to the grain-supported interlayers. microbial mat-supported sediments are more often of finer grain size. usually without contact to each other and predominantly arranged with their long-axis parallel to the sedimentary surface. The panicle orientation may be the result of reduction of mechanical friction by the soh matrix surrounding the quanz grains that aid the rotation of the grains to an cnergrtically suitable position. In grain-supported interlayers between mat horizons, there is no similar orientation of grains. (iv) Organic layers resulting from the overgrowth of ripples by biofilms and microbial mats show a specific intrasedimenrary sinoidal pattern. To recognize such a sedimentary record of tidal flat deposits both ecological and hydrodynamic knowledge of the environment is necessary.
