Paleogeographical significance of benthic Foraminifera from the Mengkarang formation (early Permian, Sumatera)

摘要

Previous investigations of Mengkarang Formation (Sumatera, Indonesia) suggested some paleogeographical interpretation debates. Expedition in the period between 1900 and 1941 concluded that Mengkarang Formation was located in cold environment indicated by cold Gondwanan faunas found in the formation. Afterward, a study in 2013 delivered a warm tropical climate paleogeographical interpretation rather than cold water taxa from the Gondwanan-Perigondwanan region. This current study focused on biostratigraphy analyses supported by detail petrographic analyses to provide additional insight into detail paleogeographical interpretation of Mengkarang formation. A significant amount of smaller benthic foraminifera (Ammonia umbonata, Ammonia beccari, Cibicides tobatulus, and Elphidium sp.) suggested inner to the middle neritic depositional environment. While petrographical analyses suggested that this formation dominated by sub-angular grains of lithic fragment (pyroclastic rock-tuff), feldspar, quartz, and trace of chlorite. Matrix and cement consist of interstitial carbonate, clay, silica, and oxide. The current conclusion from these biostratigraphy and petrography analyses conclude more detail paleogeographical interpretation of Mengkarang Formation. This formation should be deposited in inner to middle neritic marine environment with the source of sediment came from Karing Volcanic Complex thanks to carbonate cementation during the deposition.