Unveiling coastal aeolian facies in the Upper Jurassic record of eastern Iberia: new insights from the dinosaur fossil–bearing Villar del Arzobispo Fm (Teruel, E Spain)

Abstract

The Upper Jurassic Villar del Arzobispo Fm is a mixed siliciclastic-carbonate succession that crops out in the Riodeva area (Teruel, eastern Spain) and preserves abundant dinosaur fossils. In this area, the succession has been interpreted as representing the preserved accumulation of an inner carbonate platform that evolved upwards into a predominantly siliciclastic fluvial system with minor marine carbonate incursions. However, preliminary studies performed in this area have revealed the presence of aeolian deposits intercalated with tidal, scarce alluvial and marine deposits, suggesting deposition in a coastal plain setting, rather than a fluvial system. In this work, we analyse the aeolian deposits of the Villar del Arzobispo Fm to reconstruct the depositional environments of the unit. For the first time, we describe the occurrence of dome-shaped aeolian dunes in the Mesozoic record of Iberia. The studied deposits are arranged in metre-thick sandstone beds (up to 10 m). Beds exhibit flat bases and tops, and a lateral continuity up to 300 m and occur interbedded with edaphized, reddish siliciclastic mudstone. Two facies associations are distinguished. The Aeolian dune facies association consists on fine-to medium-grained, well-to very well-sorted sandstone, which displays different types of large-scale cross-bedding. (1) Tangential cross-bedding is arranged in up to 2 m-thick sets, displaying tangential foresets (angles of 20-35°) and reactivation surfaces; internally, it is formed by mm-to cm-thick laminae that pinch out upwards and downwards. (2) Low-angle cross-bedding is arranged in sets up to 2.7 m-thick, displaying low-angle foresets (< 15°), laterally extensive bottomsets and reactivation surfaces; internally, it consists of mm-to cm-thick laterally continuous laminae. (3) Dome-shaped cross-bedding is arranged in up to 4 m-thick sets, consisting of convex-up, steeply dipping foresets (up to 35°) with preserved topsets. These features are typical of migrating aeolian dunes. Specifically, the tangential cross-bedding may result from the accumulation of grainflow packages on the lee side of dunes exceeding the angle of repose, whereas the low-angle cross-bedding may result from the accumulation of wind ripples in the dune plinths. Deposits displaying steeply dipping, convex-up foresets with preserved topsets are interpreted as dome-shaped dunes. The Interdune facies association comprises two facies. (1) Near-horizontally laminated sandstone with mm-to cm-thick layers of carbonaceous detritus occurring as drapes; these drapes commonly pass updip into the bottomsets and rarely the lower part of the foresets of aforementioned aeolian dune deposits. (2) Decimetrethick, fine-grained, climbing-rippled sandstone beds, interbedded with tangential cross-bedded sandstone. These facies suggest deposition in wet aeolian interdunes that were subjected to episodic aqueous floods. The fact that the studied deposits are interbedded with tidal and marine deposits, suggests that interdune flood events might have been caused by storms or spring tides in this coastal palaeoenvironment. Ephemeral flash flood events likely also occurred. Collectively, these facies relationships indicate that, during the Late Jurassic, coastal aeolian dunes developed in a coastal plain setting in eastern Iberia; this plain was also influenced by tides and affected by episodic alluvial deposition