| The Shenglihe oil shale, an Early Cretaceous marine oil shale mine site found recently in the northern part of the central uplift zone of Qiangtang Basin, is characterized by high values ranging from 15.05% to 20.34% with an average value of 17.695%. Ash and tar content are 55.23% and 11.0% respectively in the shale. Kerogen determined is TypeⅡ1 or Ⅱ2. Samples of the oil shale were dated by Re-Os technique using Carius Tube digestion, Os distillation, Re extraction by acetone and ICP-MS measurement. An isochron giving an age of 101±24 Ma with aninitial 187Os/188Os ratio of 1.84±0.11(n=11, MSWD = 3.5) is obtained. The Re-Os age obtained is younger than the geological age derived from biostraigraphic data. Omitting samples XP-13-2-A, B and C, regression of the scat-tered Re and Os data for the remaining samples gives a Re-Os date of 89±10 Ma, with an initial 187Os/188Os ratio of 1.890±0.046 (n=8, MSWD = 0.78). When only the data points Omitted samples XP-13-3-A, B, C and D are regressed，the results are indistinguishable from the previous regression: the age being 113±29Ma and the initial 187Os/188Os ratio being 1.80±0.13 (n=7, MSWD = 3.1), which indicates the former (89±10 Ma) is younger than the true depositional age, and these initial 187Os/ 188Os ratios are more radiogenic than the initial 187Os/ 188Os ratio associated with regression of the full data set (11 samples). It may be associated with the time of hydrocarbon formation while the older age( 113±29 Ma) may be associated with the time of the true depositional age of the Shenglihe oil shale. |
