Assessment of thermal evolution of Paleozoic successions of the Holy Cross Mountains (Poland)

Poland is considered the most prospective country for shale gas production in Europe. Hydrocarbon
generation/expulsion scenarios, drawn in the latest intensive exploration phases, tend to overestimate
maturation levels when compared with brand new data acquired after recent drillings. We tested an
integrated workflow to correlate published and original thermal maturity datasets for the Paleozoic to
Jurassic successions cropping out in the Holy Cross Mountains. These successions, when preserved in
subsurface, host the major source rocks in the area. The application of the workflow allowed us to
highlight the burial and thermal evolutionary scenarios of the two tectono-stratigraphic blocks of the
Holy Cross Mountains (Łysog ory and Kielce blocks) and to propose this approach as a tool for reducing
levels of uncertainty in thermal maturity assessment of Paleozoic successions worldwide. In particular,
published datasets including colour alteration indexes of Paleozoic microfossils (conodont, acritarchs)
and vitrinite and graptolite reflectance data, show differences in levels of thermal maturity for the
Łysog ory (mid mature to overmature) and Kielce (immature to late mature) blocks. Original data, derived
from optical analysis, pyrolysis, and Raman spectroscopy on kerogen, and X-Ray diffraction on finegrained
sediments, mostly confirm and integrate published data distribution. 1D thermal models, constrained
by these data, show burial and exhumation events of different magnitude, during the Late
Cretaceous, for the Łysog ory (maximum burial depths of 9 km) and Kielce (burial depths of 6 km) blocks
that have been related to the Holy Cross Fault polyphase activity. In the end, Palynomorph Darkness
Index and Raman spectroscopy on kerogen, for Llandoverian and Cambrian rocks, turned out to be
promising tools for assessing thermal maturity of Paleozoic organic facies devoid of vitrinite macerals.