LATEST MIDDLE CAMBRIAN METAZOAN REEF FROM NORTHERN IRAN

Middle and Late Cambrian reefs were built mainly by cyanobacterial com munities. A few reefs with a metazoan as well as an algal component, h owever, are known from this interval. A Middle Cambrian reef formed pr imarily by spicular demosponges is described here from the Mila Format ion in the Elburz Mountains, northern Iran. The reef is enclosed withi n calcareous grainstones which contain terminal Middle Cambrian (late Mayan) trilobites. The Mila Formation reef was constructed by sponges of the family Anthaspidellidae and bacterial (algal?) sheaths, and is the earliest metazoan reef to be documented from the interval after th e demise of archaeocyath sponges. The reefal community is typical of s ubsequent reefal communities of Early-Middle Ordovician age. The Ordov ician examples differ only by the incorporation of additional metazoan elements.