The CatBa (Cát Bà) island is the largest area locating on the Southwestern margin of HaLong bay. It is not only a famous tourist centre but also represents the most typical heritage of Paleo-Tethysian carbonate formations in Vietnam. The CatBa archipelago is fully constituted by Paleozoic carbonate formations with tow typical groups comprising Devonian laminated carbonate with mixture of many non-carbonate materials and Carboniferous-Permian thick-layer/block biochemical carbonate with pure calcite. Total carbonate rocks distributing on whole CatBa archipelago constitute spectacular cliffs, wonderful caves, blue-clear beaches, and location for growth of the primeval forest.Everything is growing on base of upper-Paleozoic carbonate formations. The carbonate formations on the CatBa archipelago represent Devonian Peri-Tethys and Carboniferious-Permian Shallow-Tethys distributing in the region. In the Devonian laminated carbonate, there are many clastic materials such as fragments of quartz, feldspar, mica, chert, and other rocks etc. Both carbonate groups created wonderland with many natural multiform landscapes on the Cat Ba island. Therefore, the CatBa island is not only tourist location, but also geo-museum or geo-park for evrybody liking see paleo-Tethys ocean in the late-Paleozoic period. The CatBa island is not only a national park for tourist visitors, but also to investigate natural models or museum of Petroleum system and other mineral resourves.
