SPONGE-MICROBIAL STROMATOLITES AND CORAL-SPONGE REEF RECOVERY IN THE TRIASSIC OF THE WESTERN TETHYS DOMAIN

manic Basin) comprise very particular sponge-microbial stromatolites that formed within the extremely shallow, perilitoral zone (Szulc, 1997). The stromatolites are capping emergent oolitic bars or form the lining of deep (up to 1.5m) karstic fissures. The stromatolites are composed of interfingered, microbial laminites and small (< 0.5 cm), lenticular sponge bodies. They display a variety of morphology, ranging between mm-thin flat laminites to 50 cm-thick columnar fabrics. Internal structures are relatively poorly preserved, nonetheless the dictyid Hexactinellidea seem to be the main sponge component of the Triassic stromatolites. The aphanitic and peloidal automicrite carbonate fabrics typical of the spongean-microbial association are also recognizable. The Lower Triassic sponge-microbial stromatolites could be recognized as a “disaster form ” enabling survival and recovery of the sponge buildups after the Permian-Triassic extinction. Regarding the paleoecological context of this interval of the Phanerozoic, the stromatolites represent a “Lazarus form. ” These Lilliputian metazoan-bacterial buildups most likely enabled a survival and recovery of the reef-forming organisms after the P/T mass extinction. In Middle Triassic times (Pelsonian), the hexactinellid sponges accompanied first by scleractinian corals gave rise to the oldest in situ reefs found in the Western Tethys province. The best developed Pelsonian sponge-coral buildups occur in Upper Silesia (Poland) where they form bioherms of some 2-80 meters across and several meters high (Szulc, 2000)