Deep-seated relict permafrost in northeastern Poland

A research borehole drilled in northeastern Poland revealed a permafrost layer at least 93 m thick within the Cretaceous sedimentary succession below a depth of 357 m. Its entire thickness has not been determined, owing to the borehole depth limit (450 m). The relict of permafrost, unexpected in this part of Europe, is in the ice-water transition phase at a temperature close to 0 degrees C. We estimate that the permafrost has been preserved in an area of several square kilometres located above the central part of the Suwalki anorthosite intrusion, which is covered by similar to 800 m of sedimentary rocks. We show that the remnants of the Last Glaciation, which ended at c. 13.4 ka BP, can, even at present, affect the thermal regime of the outer zone of the Earth's crust. These findings are of significant importance for the reconstruction of past climate conditions.