Burial and thermal history of the Polish part of the Baltic region

Abstract

The burial history and thermal evolution of the western part of the Baltic region was reconstructed by means of 1-D modelling for eight boreholes penetrating the lower Paleozoic succession. The Neoproterozoic rifting presumably caused elevation of heat flow, while Cambrian to Mid Ordovician post-rift thermal sag of the Baltica passive margin led to systematic decrease of heat flow with time. Development of the Late Ordovician to Silurian flexural foredeep of the Caledonide collision zone was associated with intensive subsidence, a high rate of sediment deposition and rapid burial of the Upper Cambrian and/or Tremadocian, Upper Ordovician and lower Silurian source rocks, presumably sufficient for the early stage of oil generation. After post-Caledonian Early Devonian uplift, the western Baltic region was subject to Early Devonian to early Carboniferous subsidence and deposition, leading to further burial of the source rocks. Together with elevated heat flow, characteristic of the Variscan broad foreland, this caused further source rocks maturation and hydrocarbon generation. Late- to post-Variscan uplift and erosion (late Carboniferous to late Permian) resulted in complete removal of the Middle Devonian to lower Carboniferous strata and development of the major regional unconformity. During late Permian to Cretaceous time the western part of the Baltic region constituted an eastern flank of the Polish Trough, with the main phases of subsidence and burial during late Permian-Early Triassic time, related to rifting in the Polish Trough, and during Late Cretaceous time, related to the compressional regime. Maturity profiles in boreholes from the vicinity of the studied boreholes indicate the presence of a late Mesozoic (Late Cretaceous?) positive thermal event, causing further maturation of the source rock.