Late Permian to Middle Triassic correlations and palaeogeographical reconstructions in south-western European basins: New sedimentological data from Minorca (Balearic Islands, Spain)

Sébastien Linol (1) , Antoine Bercovici (1) , Sylvie Bourquin (1) , J.B. Diez , Et Al.

1 GR - Géosciences Rennes

Description of sedimentary sections and interpretations of sequence stratigraphic evolution of Permian­Triassic red beds of Minorca, allow a new proposal of palaeoenvironment reconstructions. The Permian sediments mainly correspond to floodplain and pond deposits with sheetflood sand-bed rivers (environment DE 1), within a warm and semi-arid climate, and the preserved succession forms one complete stratigraphic cycle. The retrogradational phase of this cycle is represented by alluvial/colluvial deposits grading upwards to environment DE 1 and to extensive floodplain and pond deposits. The progradational phase is characterized by increasing fluvial influence (with palaeocurrent mainly oriented to the SW), palaeosol horizons, and preservation of a Late Permian palynoflora. The uppermost part of this succession is truncated by a major erosional surface. The sediments above this unconformity are characterized by braided river deposits (environment DE 2) with palaeocurrent oriented to the SSW within the more basal conglomeratic facies and to the WNW in overlying units. The absence of extensive floodplain deposits, a paucity of evidence for biogenic activity and palaeosols, together with the presence of ventifacts indicate an arid climatic setting for the succession. This environment evolved from braided rivers (palaeocurrents mainly oriented to the SE, environment DE 3) with in situ palaeosols and reworked breccias to fluvial­coastal and shallow marine deposits (environment DE 4) dated as upper Anisian to Ladinian. This succession characterizes a retrogradational trend. Although the transition between DE 2 and DE 3 was not observed, a switch in palaeocurrent directions may indicate a change in source area. A comparison at a regional scale with other Peri-Tethyan basins allows the succession to be placed within a broader palaeoenvironmental and stratigraphic context during Late Permian to Middle Triassic. During the Late Permian, sedimentation occurred in alluvial, playa-lake or ponded environments where fluvial systems generally flowed southward, except in south-eastern France (oriented to the NE). Within these SW European basins, such as Minorca, the Late Permian succession shows a major retrogradational (evolution from fluvial or alluvial fan deposits to extensive lake, playa or floodplain deposits) and a progradational trend (fluvial or alluvial fan deposits). The Permian­Triassic transition corresponds to an unconformity overlain by braided river deposits with arid climate indicators (aeolian deposits: ventifacts and aeolian dune sedimentation). At the scale of western Europe, this arid episode is dated as Smithian and the Induan age sedimentation deposits seem to be preserved only in the central part of the Germanic Basin. As with all other Peri-Tethyan basins, environment DE 2 of Minorca (above the major erosional surface) is attributed to the Smithian. In the upper part of the studied succession, braided river deposits indicative of less arid climatic conditions are preserved. This succession contains the earliest Mesozoic palaeosols, dated as Anisian by palynomorphs, and expresses a vertical evolution from fluvial to open marine depositional environments attributed to the Muschelkalk transgression.

Mots clés: Permian­Triassic transition; Arid event; Fluvial environment; Palaeoenvironmental reconstructions; South-western European basins

Domaines: Stratigraphie

Sébastien Linol, Antoine Bercovici, Sylvie Bourquin, J.B. Diez, Et Al.. Late Permian to Middle Triassic correlations and palaeogeographical reconstructions in south-western European basins: New sedimentological data from Minorca (Balearic Islands, Spain). Sedimentary Geology, 2009, 220 (1-2), pp.77-94. ⟨10.1016/j.sedgeo.2009.06.003⟩. ⟨insu-00425174⟩