THE THERMAL EVOLUTION AND TIMING OF HYDROCARBON GENERATION IN THE MARITIMES BASIN OF EASTERN CANADA - EVIDENCE FROM APATITE FISSION-TRACK DATA

Sandstone drill core and/or cuttings from six wells in the Gulf of St. Lawrence and Cabot Strait have been analyzed using the apatite fissio n track (AFT) method. Measured AFT ages for the late Paleozoic sandsto nes range from 26 +/- 7 to 184 +/- 28 Ma (2-sigma errors). The AFT dat a indicate that most Maritimes Basin strata were heated to temperature s in excess of 100-150 degrees C very soon after their deposition. The strata also attained significant vitrinite reflectance (R(0)) levels (i.e., reaching the oil window) early in the burial history. These fin dings imply the generation of hydrocarbons and coalbed methane in the early basin history (pre-250 Ma). In the Maritimes Basin AFT and R(0) data provide complementary information about the integrated thermal hi story, including maximum burial temperatures (from R(0) data), and inf ormation on the subsequent cooling history from AFT analysis. The pres ent study also supports the proposal made previously by others that su bstantial erosion of the Eastern Canadian margin (up to 4 km) has occu rred since the Permian and extends the AFT evidence for this erosional event to include the southern Gulf of St. Lawrence area. Thermal mode ls of the AFT data demonstrate that they are consistent with a history of exhumation of basin strata since late Permian time. The model-pred icted AFT age and track length histograms closely correspond to the me asured AFT parameters. AFT analysis also indicates present-day geother mal gradients of less than 40 degrees C/km.