Angular unconformity: Telheiro Beach in Portugal
The angular unconformity at Telheiro Beach in Portugal is a textbook example of how immense spans of geological time are preserved in the rock record. Here, two sharply contrasting formations meet: the deformed schists and metagreywackes of the Upper Carboniferous Brejeira Formation and the flat-lying red sandstones of the Triassic Grés de Silves Formation.
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| Angular unconformity at Telheiro Beach: Tilted Carboniferous Brejeira Formation schists overlain by horizontal Triassic Grés de Silves sandstone. Credit: Francisco Sousa. |
The Brejeira Formation originated as deep-marine sediments that were compressed, folded, and metamorphosed during the Variscan orogeny. Subsequent uplift and prolonged erosion stripped away overlying strata, leaving tilted and truncated layers exposed at the surface. This landscape was later buried by the horizontally bedded “new red sandstones” of the Grés de Silves Formation, deposited in arid continental environments dominated by rivers and floodplains.
The sharp angular contrast between these formations marks a major gap in the geological record. This unconformity represents tens of millions of years during which tectonic deformation, uplift, and erosion erased entire chapters of Earth’s history before Triassic deposition resumed.
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| Angular unconformity at Telheiro Beach: steeply tilted Carboniferous schist overlain by flat-lying Triassic Grés de Silves sandstone. |
Telheiro Beach captures this sequence with unusual clarity. In a single outcrop, one can touch rocks shaped by late Paleozoic mountain building and, directly above, Triassic strata recording desert floodplains. The unconformity is a powerful reminder of the Earth’s dynamic cycles of deposition, orogeny, erosion, and renewed sedimentation operating across deep time.
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