Diagenetic sulphurs have been observed in subsurficial sediments from Odiel River Estuary. These sulfurs display three distinct morphologies: microcrystal aggregates, framboidal aggregates and euhedral pyrite macrocrystals. The genesis of these pyrite morphologies occurs in non-strictly-anoxic environments with a continuous sulphate and iron support where the bacterial activity induces a fast nucléation and growth of microcrystals. These optimal environmental conditions present in the Odiel estuary allow an accelerated evolution from framboidal morphologies to euhedral macrocristals during early diagenetic stages