The lack of landmasses at both poles, the position of Gondwana over the equator, abundant evaporites as well as the lack of preserved glacial deposits during the Cambrian to Middle Ordovician, suggest relatively mild temperatures at this time. Well-preserved fossil-rich carbonate rocks and shales, such as the Chengjiang succession, indicate shallow warm seas and environments in which marine animals and other organisms flourished. From time to time the climate became arid and shallow lagoons dried up, leaving behind evaporate deposits such as salt and gypsum, still preserved today in Hunan Province in China. |