Hydrocarbon fluid inclusions in authigenic quartz from the Torinosu Limestone at Sakawa town, Kochi Prefecture, Japan

Abstract

Hydrocarbon fluid inclusions in authigenic quartz from the Jurassic Torinosu Limestone and associated sediment at Sakawa town, Japan, were studied by microthermometry, ultraviolet (UV) fluorescence, and Raman spectroscopy. The quartz contained abundant liquid hydrocarbon and subordinate vapor hydrocarbon fluid inclusions, and tiny solid inclusions of bitumen, calcite, and rarely pyrite. Aqueous fluid inclusions and aqueous components in hydrocarbon inclusions were absent. Under UV irradiation, most of the liquid inclusions from the limestone and associated sediment displayed intense whitish–blue and deep–blue luminescence, respectively. Further, these liquid inclusions were homogenized at around 24 °C and 53 °C, respectively. Small numbers of liquid inclusions from the associated sediments contained a liquefied gas–condensate. Raman measurements indicated the presence of aromatic compounds and the absence of H2O or CO2 molecules in the liquid and vapor inclusions.