Norian vegetation history and related environmental changes: New data from the Chinle Formation, Petrified Forest National Park (Arizona, SW USA)

Abstract

Fossil plant assemblages including spores and pollen grains provide useful information on past ecosystems and the response of terrestrial biotas to various environmental perturbations. New quantitative palynological data from the Chinle Formation of the American Southwest suggest that a floral turnover occurred in the middle Norian (between 217 and 213 Ma). Analysis of plant communities reveals that this turnover was followed by a complete reorganization of the riparian vegetation, driven by changes in fluvial styles and the tectonic regime of the basin, as well as a gradual transition toward a more arid climate. Marked increases in Klausipollenites gouldii, Patina sporites spp., and Froelichsporites traversei are probable indicators of environmental stress, such as increased aridity, perturbations of atmospheric pCO 2 , acid rain, and atmospheric aerosol accumulation due to volcanism in connection with the Pangean rifting and uplift of the Cordilleran arc. Comparison of the vegetation turnover with younger assemblages from the Chinle Formation in New Mexico revealed similar floral turnover patterns, suggesting two distinct drier periods as a result of multiple climatic oscillations. The climate-induced floral turnover may have contributed to the vertebrate faunal turnover as the loss of wetland habitat space and an increase in xerophytic plants may have dwindled the supply of palatable vegetation for herbivores. The onset of the floral turnover in Arizona roughly corresponds to the Manicouagan impact event, but a direct causal link is still speculative.

New trilophosaurid species demonstrates a decline in allokotosaur diversity across the Adamanian-Revueltian boundary in the Late Triassic of western North America

“…Here we describe a new taxon of trilophosaurid from the Sonsela Member of the Chinle Formation that expands the range of trilophosaurid dental morphology and is the first definitive evidence of an allokotosaur in the Revueltian estimated holochronozone. This adds to a growing body of evidence supporting a multi-clade disruption in biodiversity across the Adamanian-Revueltian boundary in western North America (parker & Martz 2011;Baranyi et al 2018;parker et al 2018).…”

“…This pattern of change is similar to those of several large-bodied vertebrate clades across the Adamanian-Revueltian boundary in western North America, adding further evidence for a regional faunal turnover at this boundary. This evidence for biodiversity disruption at around 215 Ma in terrestrial vertebrate and plant assemblages from the Chinle Formation, in addition to that in paleo-Pacific marine invertebrates, points to a global pattern of biodiversity loss at this time (parker & Martz 2011;olsen et al 2011;onoue et al 2016;Baranyi et al 2018).…”

“…Allokotosaurs now add to several vertebrate clades with observed patterns of extinction and origination at the Adamanian-Revueltian boundary. Aetosaurs, a clade of largebodied, armored, herbivorous pseudosuchian archosaurs, undergo a genus-level change at this boundary (parker & Martz 2011;parker 2016;parker et al 2018 Trends of biotic change across this boundary have also been observed in fossil floral assemblages sampled at stratigraphic intervals throughout the Chinle Formation, characterized by a shift to xerophytic plant assemblages after the Adamanian-Revueltian boundary (reichgelt et al 2013;Baranyi et al 2018). Trilophosaurids and aetosaurs, the most common herbivores known from Triassic rocks in southwestern North America, would have depended on local plant communities as a food source, and changes in the floral community may have been a causative factor in their extinction and turnover at this boundary.…”

Magnetochronology of the Entire Chinle Formation (Norian Age) in a Scientific Drill Core From Petrified Forest National Park (Arizona, USA) and Implications for Regional and Global Correlations in the Late Triassic

“…The Adamanian-Revueltian transition has traditionally been placed within the Sonsela Member, near the base of the so-called Sonsela sandstone bed (=Jasper Forest bed; Lucas, 1998) or several meters above this bed in the lower part of the Jim Camp Wash beds (Martz & Parker, 2010). A marked palynozonal transition (Zone II to Zone III) occurs at about the same stratigraphic level within the Sonsela Member (Baranyi et al, 2018;Reichgelt et al, 2013). According to Ramezani et al (2011), a conservative constraint for the Adamanian-Revueltian boundary would be between their samples SBJ (approximately 219 Ma) and GPU (approximately 213 Ma; Figure 3).…”

Dryland continental mudstones: Deciphering environmental changes in problematic mudstones from the Upper Triassic (Carnian to Norian) Mercia Mudstone Group, south‐west Britain

“…alluvial sheet sandstones, evaporite pseudomorphs, tepees and sulphates) recognized in sheet sandstone facies. This culminated in deposition of the widespread, and relatively thicker, fluvial sands of the Arden Sandstone Formation and its wider correlatives that form a key line of evidence for the Carnian Pluvial Episode, a period of globally enhanced precipitation (Simms & Ruffell, ; Ruffell et al ., ; Baranyi et al ., , ).…”