I searched about stromatolite formation and I realized how microbial activity plays a role in formation of algal mats which function as sediment trap which
in turn after cementation forms layers of lamina, in growth pattern of dark and light bands, but it is not yet obvious to me why the layers are dark and light? Is it due to presence and absence of organic matter? Or it is as a result of tidal currents, which in turn control the sediment size and leads to light and dark colors?
Or other processes are effective?