Port Des Canonge Formation

The Port des Canonge Formation is a lower–middle Permian-age geologic formation in the Mediterranean island of Mallorca. It consists of red to brown-colored sedimentary rocks (red beds) such as sandstone and mudstone, and is located in what back then was the western peri-Tethys Ocean.

Geological Context

The Permian geological context of Mallorca is part of the larger framework of the Balearic Islands, an extension of the Betic fold and thrust belt formed during the Alpine orogeny. On the islands, only Mallorca and Menorca have exposed Permian beds, likely derived from sedimentary successions deposited in isolated basins along the eastern edge of the Iberian plate, sharing a structural connection with the Iberian Peninsula, emerged during the collapse of the Variscan orogeny in the late Carboniferous to early Permian. This collapse led to a transtensional and extensional tectonic regime, creating semi-graben structures that facilitated sediment accumulation.

Palaeogeographically, these basins were located in the western peri-Tethys and shifted from approximately 7°S to 4°N latitude throughout the Permian, experiencing a tropical, semi-arid, and seasonal climate.

On Mallorca, Permian rocks are primarily found along the coastal cliffs of the Serra de Tramuntana and partially inland, though often obscured by forest cover. The base of the Permian succession is faulted against underlying Carboniferous rocks, and the transition to the overlying Lower Triassic Punta Roja Formation is marked by an unconformity.

Paleoenvironment

The Port des Canonge Formation overlies the coarse deposits of the Bec de s’Àguila Formation (colluvium and alluvial fan deposits) and is overlain by the Pedra de s’Ase Formation (fluvial environment with rare floodplain deposits). The two main outcrop areas of the Port des Canonge Formation, the Racó de s’Algar-Pedra de s’Ase section and the Port des Canonge-Hort de sa Cova section, show a thickness of approximately and , respectively.

The Port des Canonge Formation represents an intra-continental fine-grained meandering river system with extensive floodplain deposits, flowing southeast along the basin's main axis. It is composed of red sandstones and red lutites organized in fining-upward sequences, dominated by lateral accretion surfaces from channel bars and overbank deposits. Breccia lithofacies occur as basal lags or isolated beds, reflecting reworked floodplain sediments. Sandstone lithofacies include ripple-marked, laminated, and massive sands, indicating waning flows and overbank deposits. Lutites are characterized by massive and laminated facies, disrupted by plant roots and invertebrate burrows, recording periods of low sedimentation or subaerial exposure. Decreased subsidence rates favored a longitudinal fluvial system, while significant accommodation space allowed for the deposition of mudstones and fine sandstones.

The system is marked by lateral accretion surfaces and stabilized riverbanks, likely due to abundant floodplain vegetation, which prevented channel widening. Evidence of this vegetation includes developed soils, occasional plant remains, and logs despite the oxidized conditions.

Palaeosols with carbonate nodules, calcrete hardpans, and gleyed patches developed under dry conditions, pointing to seasonal desiccation of ponds, which likely functioned as waterholes. Fossils, including tetrapod tracks and skeletons, rhizocretions, and plant remains, emphasize the ecological importance of these floodplain environments.

The formation's palaeocurrents suggest a southeast-directed flow, consistent with the meandering river interpretation. Overall, the facies suggest a semi-arid, dynamic fluvial system shaped by meandering rivers and seasonal dry periods.

Dating

No radiometric dating is available for the Port des Canonge formation due to the absence of volcanic layers in it. In 2022, based on tetrapod footprint associations, Matamales-Andreu ''et al.'' assigned it an Artinskian–Kungurian (upper lower Permian) age. In addition, the overlying Pedra de s'Ase Formation was dated to the middle Permian (Roadian–Wordian) by a particular palynological association and paleomagnetic data. A year later, however, Matamales-Andreu ''et al.'' proposed (with some doubts) that the age of the upper part of the Port des Canonge Formation could also reach the base of the middle Permian (lower Roadian).

Paleobiota

The Port des Canonge Formation contains numerous fossils. The terrestrial vertebrate fauna, represented by both footprints and skeletal remains, is remarkable in showing a mixture of tetrapods typical of the early Permian (pelycosaurs and moradisaurines) with others rather characteristic of middle and late Permian assemblages (non-mammalian therapsids).

Invertebrates

Tetrapods

Plants

Multiple large logs along carbonaceous debris have been found in Cova des Carbó.

Notes

References

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Permian System of Europe
Cisuralian
Guadalupian
Paleontology in Spain