The Anisian continental-marine transition in Sardinia (Italy): state of the art, new palynological data and regional chronostratigraphic correlation

L Stori,A Ronchi,J López-Gómez,J F Barrenechea,R De La Horra,J Martín-Chivelet,V Borruel-Abadía,J B Diez,M Juncal

doi:10.1007/s41513-021-00184-x

Abstract

The scarce evidence of paleontological records between the upper Permian and the Anisian (Middle Triassic) of Western Europe could reflect (1) large stratigraphic gaps in the continental successions and/or (2) the persistence of disturbed conditions after the Permian–Triassic Boundary extinction event and the succession of ecological crises that occurred during the Early Triassic. In this context, the study of palynological associations, integrated with the stratigraphical and sedimentological data, plays a key role in dating and correlating the successions of the Western European domain and improves our understanding of environmental and paleoclimatic conditions. In some cases, pre-Anisian paleontological evidence is lacking, as in Sardinia (Italy), where a long gap encompasses the middle Permian (pars) to late Lower Triassic successions. Although fragmented and disseminated, the continental Lower-Middle Triassic sedimentary successions (Buntsandstein) of Sardinia have proved crucial to our understanding of the evolution of the southern edge of the Paleo-Europe and the different timings of the Tethys transgression (Muschelkalk facies) in some of these areas. Various paleogeographic reconstructions were attempted in previous works, without providing any consensus on the precise position of Sardinia and its surrounding seaways in the Western Tethys domain during this time interval. At present, the configuration and distribution of the subsiding and emerging landmasses and the temporal development of the transgressions of the Western Tethys during the Middle Triassic remain unclear. This work focuses on the stratigraphical, sedimentological and palynological aspects of three Middle Triassic continental-marine sedimentary successions in Sardinia, with particular attention to the analysis of the palynological associations sampled there, and it also provides a detailed review of all previous palynological publications on the Sardinian Anisian. The studied successions are: Su Passu Malu section (Campumari, SW Sardinia), Arcu is Fronestas section and Escalaplano section (Escalaplano, Central Sardinia). These sections were also correlated to other significant sections in the SW (Scivu Is Arenas) and NW (Nurra) parts of the island.

Highlights

The late Palaeozoic era witnessed the formation of the Pangaea supercontinent, derived from the collision of Gondwana, Laurussia and several other microplates between the Carboniferous and the early Permian (e.g. Stampfli & Borel, 2002; Stampfli et al, 2013; Pastor Galán et al, 2015)
The dismantling of the Variscan orogenic system and the widespread evolution of the late Palaeozoic rifting phases produced several small basins filled with terrestrial sediments, and the deposition of these sequences occurred in seasonal to semi-arid conditions: the continentalization of the climate after Pangaea led to pronounced warming and aridification throughout the late Permian (Wignall, 2007), which persisted into the Early Triassic
Our study focuses on Sardinia, Italy, a key location for understanding the Lower-Middle Triassic sedimentary record of the Western Tethys domain

Summary

Introduction

The late Palaeozoic era witnessed the formation of the Pangaea supercontinent, derived from the collision of Gondwana, Laurussia and several other microplates between the Carboniferous and the early Permian (e.g. Stampfli & Borel, 2002; Stampfli et al, 2013; Pastor Galán et al, 2015). The dismantling of the Variscan orogenic system and the widespread evolution of the late Palaeozoic rifting phases produced several small basins filled with terrestrial sediments, and the deposition of these sequences occurred in seasonal to semi-arid conditions: the continentalization of the climate after Pangaea led to pronounced warming and aridification throughout the late Permian (Wignall, 2007), which persisted into the Early Triassic This latter period was characterized by severe hothouse conditions (e.g., Bourquin et al, 2011) and high temperatures (Payne et al, 2007; Sun et al, 2012), which underwent great fluctuations, influenced by strong and enduring volcanic activity in the Siberian Traps Large Igneous Province (Svensen et al, 2009), thereby contributing to a perturbation of the carbon cycle through the massive injection of CO2 into the atmosphere, causing ocean acidification and anoxia. The persistence of volatile environmental conditions and the significant instability of the ecosystem throughout the Early Triassic delayed the biotic recovery after the major P–T boundary extinction event (Wignall, 2007)

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Conclusion