Organic Geochemistry and Petroleum Potential for Cambrian-Silurian Source Rocks in the Baltic Basin Onshore Poland

The Upper Cambrian–Lower Silurian sediments of the Baltic Basin represent organic-rich clastic and carbonate rocks that are a key exploration target for hydrocarbons in northern Pomerania, Poland. The source rocks contain an average total organic carbon (TOC) content of 4.1 wt% (range: 0.7–9.6 wt%). The organic matter is primarily in the early to mid-oil window; however, both more mature and overmature organic matter also occur (average Tmax: 445 °C; range: 427–488 °C; average Ro: 1.3%; range: 1.0%–1.8%). These organic-rich rocks were mostly deposited under dysoxic rather than anoxic conditions. Fossils of oxygen-dependent benthic fauna are widely distributed, even in the darkest (black shale) lithologies. Nevertheless, short intervals lacking benthic fossils indicate episodes of anoxic bottom-water conditions. The Furongian–Lower Llandovery source rocks exhibit a low sedimentation rate, ranging from 1 to 19 m/Ma. Geochemically, the organic matter is dominated by type II kerogen. Petrographically, the kerogen consists mainly of graptolites and algae. Due to the predominance of planktonic-origin fauna and thermal maturity, the kerogen is relatively hydrogen depleted (average Hydrogen Index, HI: 169 mg HC/g TOC; range: 1–340 mg HC/g TOC). The present day petroleum potential of these source rocks varies from fair to good and very good. Bitumen analysis revealed a dominance of kerogen components, with only minor admixtures of light and heavy oils.