The riddle of the tors at Lauhavuori, western Finland

Abstract

The tor landscape surrounding the Lauhavuori Cambrian sandstone hill in southern Ostrobothnia was studied from morphological, sedimentological and geological points of view. Seismic and drill‑core surveys showed that the quartz sandstone superposes an unconsolidated, mechanically produced Upper Proterozoic weathering crust. Excavations and sedimentological analyses revealed that the local tors developed in coarse, porphyritic micro­cline granite as a result of cryptogenous chemical weathering of two‑fold nature, in Cretaceous‑Paleogene, and in Pliocene. The tors were exhumed in preglacial times, when modified by subaerial processes. Quaternary glacial erosion has been weak in the area, which has promoted the pre­servance of the sandstone, the tors, preglacial weathering crusts and para­utochthonous sediments formed out of these. Holocene reworking of former sediments and the weathering crust partly embedded, partly ex­humed the tors from underneath their earlier saprolite cover.