Enhanced accumulation of organic matter: the Shunga event

A number of sedimentary formations deposited globally around 2.0 Ga ago are characterised by high abundances of organic carbon. These formations often contain occurrences of highly concentrated, matured organic material representing metamorphosed oil, now pyrobitumen. Apart from their common names pyrobitumen or anthraxolite, different terminology has been used for these rocks within the pertinent literature, including shungite, thucolite, or Precambrian “coal”. Given their long and frequently complex geologic history, these sedimentary formations exhibit a variable and sometimes substantial degree of metamorphic (thermal) overprint. Consequently, many of them show undisputable signs of thermal mobilisation, migration and likely loss of hydrocarbons/bitumen. This includes the so-called shungite rocks on the Fennoscandian Shield.