Carboniferous – Triassic Unconformity in Telheiro

The outcrop of the Tehlheiro Unconformity located on the southwest coast of Portugal testifies the late phase of Pangea as a supercontinent and its initial break-up. The most striking geological characteristics of this cliff are:

a. A flattened surface at the top of the cliff with preserved gravel beds corresponding to a Quaternary raised beach;

b. The Silves Sandstone Formation (Upper Triassic) is composed of reddish sandstone and siltstone beds, with thin intercalations of conglomerate. The beds exposed in the cliff correspond to the lower part of the formation. Its reddish color and the sedimentary structures like cross bedding suggest deposition in the middle part of continental alluvial fans under an arid climate. These strata represent the first stage of Pangea breakup (Gama et al., 2021).

c. Angular unconformity between the Silves Formation on the top and the Upper Paleozoic flysch turbidites metasedimentary rocks of the Brejeira Formation at the bottom, encompassing ~72 Ma. During this period a basement uplift and erosion of a significant part of the Variscan Chain took place.

d. Brejeira Formation [Bashkirian (320 Ma) – Moscovian (307 Ma)] is composed of a thick (>1000m) turbidite sequence formed by shale and graywacke alternations that exhibit clear sedimentary structures (Oliveira, 1990; Jorge et al., 2013). This formation was affected by the Variscan orogeny, that produced subvertical fols and shistose cleavage (Ribeiro et al., 2007).

e. At the bottom of the cliff the current marine abrasion platform is visible.