The Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian

Abstract

In this paper, we present a detailed review of upper Pliensbachian-lower Toarcian kerogen assemblages from the southern areas of the West Tethys shelf (between Morocco and northern Spain) and demonstrate the use of the Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian.The kerogen assemblages in the studied sections from the southern areas of the West Tethys shelf are dominated by the Phytoclast Group and terrestrial palynomorphs, although punctual increases in amorphous organic matter (AOM), freshwater (Botryococcus) and marine microplankton (dinoflagellate cysts, acritarchs, and prasinophyte algae) were observed at specific stratigraphic intervals. The opaque/non-opaque phytoclasts (OP/NOP) ratio was used to trace changes in palaeoclimate and other palaeoenvironmental parameters and reflect climate gradients associated with water availability during early Toarcian. During the Pliensbachian-Toarcian and Jenkyns events, changes in kerogen assemblages in the southern areas of the West Tethys shelf correlated with changes in the northern Tethys and Panthalassa shelf.The acceleration of the hydrological cycle associated with the aforementioned events was less intense in the northern Gondwana, southern and western Iberian basins, a reflection of the palaeogeographic position of these basins within the semi-arid climate belt when compared with the northern Iberian region and other northern areas of the West Tethys and Panthalassa shelf, inserted in winter-wet and warm temperate climate belts. AOM enrichment associated with the Pliensbachian-Toarcian and Jenkyns events reflects an increase in primary productivity linked with increased continental weathering, fluvial runoff and riverine OM, and nutrient input into marine areas, inducing water column stratification and promoting the preservation of OM.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5421485

Dinosaur extinctions related to the Jenkyns Event (early Toarcian, Jurassic)

“…During the Jenkyns Event, global warming also affected continental ecosystems. A decrease of 13 C fractionation during photosynthesis in C3 plants, confirms a turn to arid climate for emerged areas of Western Tethys during the Jenkyns Event (Rodrigues et al, 2019(Rodrigues et al, , 2021Ruebsam et al, 2020a). Other changes in terrestrial ecosystems affected diversity and composition of land plant assemblages (Slater et al, 2019;Jin et al, 2020) and an increase of wildfires in some areas (Baker et al, 2017).…”

Land-sea ecological connectivity during a Jurassic warming event

“…Data from Morocco and northern Spain have been interpreted as indicating that the acceleration of the hydrological cycle during the eTe was less intense in northern Gondwana, and southern and western Iberian basins, than in northern Iberia and other northern of the West Tethys and Panthalassa shelf (Rodrigues et al, 2021). At the same time, enrichment in amorphous organic matter during both the Pl-To and early Toarcian events has been interpreted as reflecting an increase in primary productivity linked to increased continental weathering, fluvial run-off and riverine nutrient input into marine areas, which then led to water column stratification (Rodrigues et al, 2021). These data suggest that our model could be applicable to the Boreal Realm, and with caution, also to Sub-Boreal and Tethyan Realms.…”