MESSINIAN STROMATOLITE-THROMBOLITE ASSOCIATIONS, SANTA-POLA, SE SPAIN- AN ANALOG FOR THE PALEOZOIC

Stromatolite-thrombolite associations are the dominant facies forming large portions of the Santa Pola carbonate platform (SE Spain) during deposition of the Terminal Carbonate Complex (TCC). The TCC, the last period of marine sedimentation in the Western Mediterranean associated with the Messinian Salinity Crisis, comprises a NE-SW trending thromb olite reef with occasionally interlayered stromatolite horizons and a predominantly stromatolite and oolite facies in the back-reef area. Th e stromatolites are mainly dome shaped, but fine-columnar or wavy-undu lose forms can occur. The stromatolites form huge bioherms, extending tens to hundreds of metres. They are finely laminated with alternating layers of dolomicrite and dolomicrospar. The dolomicrite layers appea r to be a primary dolomite precipitate, whereas the dolomite crystals in the dolomicrospar layers apparently formed around a meta-stable nuc lei which was subsequently dissolved or degraded. The low content of s and-sized particles in the stromatolitic layers indicates formation un der low-energy conditions, possibly on a tidal flat. As reported from other areas in the Western Mediterranean, deposition of the TCC at San ta Pola was apparently cyclic, whereby stromatolites generally termina te each depositional cycle. Subtidal Conophyton stromatolites, possibl y the only known occurrence younger than Palaeozoic, are, however, fou nd on the reef slope at the base of the first TCC depositional cycle, The dolomitic: nature of the unadulterated stromatolitic laminations a nd the association of stromatolites and thrombolites as platform build ers were a common feature in the Early Palaeozoic but are unusual in p ost-Ordovician carbonate facies. We propose that the conditions during TCC deposition were very restricted, possibly reflecting an environme nt similar to that of the Early Palaeozoic.