only a few fragmentary fossils. Higher organic content and finer laminations return a short while later, forming the lower part of the fossil-rich Meride Limestone. The Meride Limestone probably represents a period of increased instability on the growing carbonate platforms, sending surges of carbonate grains into the basin. Skeletons tend to be even better preserved than in the Grenzbitumenzone, suggesting that the basin deepened further or acquired extensive microbial mats. A section of dolomite, the "Dolomitband", forms the top of the Lower Meride Limestone. It also marks the start of the Upper Meride Limestone, which is similar to the lower part of the formation but has only a few fossiliferous sections. The Upper Meride Limestone eventually becomes dominated by very finely-laminated marls and shales with increased clay content. This clay-rich interval, indicative of increased terrestrial runoff within the shrinking basin, is known as the "Kalkschieferzone". Late Triassic By the beginning of the Late Triassic, a major marine regression (sea level fall) threatened the fossil-rich basin and carbonate system of the Middle Triassic. During the Carnian (around 237 to 227 Ma), the first stage of the Late Triassic, carbonate platforms were replaced by shallow-water and coastal sediments. This formation, the Pizzella Marls, is diagnosed by a higher amount of siliciclastics (sediments eroded down from terrestrial rocks) and evaporites (mineral deposits from dried water), such as gypsum. In the succeeding Norian stage (around 227 to ~208 Ma), carbonate platforms and rising sea levels were renewed with vigor, depositing a massive expanse of carbonate known as the Dolomia Principale or Hauptdolomit. The Dolomia Principale is a brittle, crystalline rock mass which was fractured by normal faults not long after it was first formed. This is an early pulse of an overall extensional tectonic regime, a period of rifting which would eventually break up Pangea. By the time of the Rhaetian stage (~208 to 201 Ma), the Dolomia Principale was buried by a shorter but more stable sequence of shallow-water marl and carbonate, the Tremona Series. Early Jurassic Rifting continued into the Early Jurassic, alongside marine sedimentation. From the Hettangian to Pliensbachian stages (201 to 183 Ma), the area reacquired a deeper basinal environment. These basin sediments are preserved as the Moltrasio Limestone, a thick sheet of micrite (fine-grained limestone) with abundant cherty and marly beds created by turbidites (mudslides). Jurassic sediments are preserved to the east, south, and west of Monte San Giorgio;