An earthquake, recorded…
The layers in this rock are called varves, and form when rhythmic conditions control sedimentation. An example would be the bottom of a mountain lake that gets covered in ice during the winter. The coarser grained layers might be brought by streams flowing into the lake during spring thaw and through the summer, carrying the winter’s worth of erosion load after its cycles of freeze thaw and grinding ice. The finer grained darker sediments would then slowly settle out of suspension when the turbulence of the streams or wind caused waves are quashed by father frost and the lake settles into quiescence.
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