Triassic (about 252-247 Ma). Slightly younger sediments from the late Anisian (the first stage of the Middle Triassic, 247-242 Ma) are called the Bellano Formation. The Servino and Bellano Formation can be difficult to differentiate, but together they reconstruct a period of transgression (rising sea levels) encroaching onto a sandy coastline dotted with deltas and floodplains. As the Anisian stage continued, the coastal sandstone of the Bellano Formation was replaced with calcareous marine deposits. These were the first of many massive carbonate platforms building up on a branch of the Tethys Sea which was expanding westwards. The shallow carbonate platform of Monte San Giorgio and surrounding areas is known as the Salvatore platform, which is now preserved as the San Salvatore Dolomite. It reconstructs a warm, tropical environment, with the most common fossils belonging to algae and shelled invertebrates. Only the lower portion of the San Salvatore Dolomite is preserved on Monte San Giorgio, corresponding to a particularly shallow and saline period in the history of the platform. Stromatolites and other algal laminations are generally the only fossils found in the Lower Salvatore Dolomite. Grenzbitumenzone / Besano Formation Near the end of the Anisian, the southern edge of the Salvatore platform deepens abruptly, giving way to a more sterile basin developed between carbonate platforms. The basin is now preserved as a relatively narrow band of dark dolomite and shale, running east to west along the edge of Monte San Giorgio. This formation has been called the Besano Formation (in Italy) or the Grenzbitumenzone (in Switzerland). It represents the first of several sections on the mountain enriched with well-preserved fossils. The Grenzbitumenzone, especially its shale layers, is enriched with organic material derived from cyanobacteria. This accumulation of organic material presumably made the bottom of the basin anoxic or dysoxic, with low oxygen levels in the seawater. The only fossils of seabed-living organisms belong to Daonella, a thin-shelled bivalve adapted to low oxygen. Fossils of free-swimming animals are more diverse, with marine reptiles, fish, and shelled cephalopods being the most prominent. Terrestrial and shallow-water organisms such as shrimps, conifer branches (Voltzia), and land reptiles (Ticinosuchus) were occasionally washed into the basin as well. Meride Limestone The basin responsible for the Grenzbitumenzone continued to persist through the Ladinian, though the Grenzbitumenzone itself transitioned into a less fossiliferous formation known as the San Giorgio Dolomite. This formation has lower organic content, no shale, and