Hello again, colleagues! At the moment I'm researching the origin of Menzelinsky reef (or biogerm) located in the northeast of Tatarstan republic (Volga-Ural oil province). Many lances was broken over the problem of Volga-Ural "reefs", nobody knows their real place in a wide number of organogenous carbonate structures. They were considered to be mainly algal biogermic hills with mild slopes located on earlier basement's highs. But recent discovery of Menzelinskoe oilfield breaks such stereotypes. There aren't defined basement high under it, instead, the reef located in the most submerged depression zone of Kama-Kinel channel system. Next, the structure is very high, about 400 m (actual amplitude) with plane diameter of about 1500 m, so it doesn't seem to be a simple biogerm. Lithologically it seems to be strongly recrystallized mostly algal carbonate, but in almost all thin plates I 've found well rounded organic debri cemented with crystal calcite (or dolomite). There aren't single continuous "skeleton" of organic remains on their intravital positions. Almost all carbonates are detrital.