Because of the variety of microfossil groups involved, palynology can provide biostratigraphic zonations and correlations in both marine and non-marine sediments, as well as palaeoclimate and palaeoenvironmental interpretations. Playnofacies analysis, which involves the qualitative and quantitative assessment of terrestrial and marine organic matter in sediments, in conjunction with lithological and well wire-line log data, provides an effective method of interpretation of clastic depositional facies. A palynologist's services may also include visual analysis of a sediment's potential to generate hydrocarbon. This involves the visual estimation of kerogen colour, which is altered through geological time in response to the progressive effects of heat and pressure, which results in oil/gas generation. Visual colour analysis is expressed numerically on a scale from 1 to 5, referred to as "thermal alteration index" (TAI), which is applied in conjunction kerogen type to evaluate source rock potential. Source rock potential may be estimated from a specialized, complementary technique known as vitrine reflectance, another thermal alteration scale (%R?) which is based on the reflectivity of polished surfaces of vitrinitic (coalified) organic matter which increases with progressive thermal alteration.