Eogenetic diagenesis of Chinle sandstones, Petrified Forest National Park (Arizona, USA): A record of Late Triassic climate change

Abstract

Fluvially derived tuffaceous Chinle sandstones from Petrified Forest National Park provide a well‐preserved Late Triassic archive of climate information. Petrographic analysis of 38 Chinle sandstones provides new insight into the depositional history and evolution of palaeoclimate during Chinle deposition. This study focuses on the relationship between climate and meteoric diagenesis as a guide for constraining climate change in western equatorial Pangea during the Late Triassic. Petrographic analysis of Chinle sandstones reveals their wide range of textural attributes, as well as pedogenic and shallow burial diagenetic features that occurred during the Late Triassic. These diverse petrological characteristics are indicative of the evolving Late Triassic climate, when placed into a well‐constrained stratigraphic and geochronological framework. The stratigraphic succession is characterized by variations in the abundance of framework grains, detrital matrix, weathering intensity of feldspar and volcanic rock fragments, and the mineralogy of clay cements. Climate records from Chinle palaeosol geochemistry indicate a progression from wet to dry conditions. This trend is also reflected in the meteoric diagenetic features of Chinle sandstones. During deposition of the lower Chinle, elevated rainfall promoted the weathering of labile volcanic detritus to kaolinite, whereas feldspars (especially plagioclase) were partially or completely dissolved. In the upper Chinle, a trend towards drier conditions favoured the formation of smectite and less feldspar dissolution resulting in a higher abundance of well‐preserved plagioclase grains. Shallow burial meteoric weathering reactions in Chinle sandstones reflect the evolving climate during the Late Triassic.

Nurse logs: A common seedling strategy in the Permian Cathaysian flora

“…Those identified in Antarctica were adapted to an ever-wet, peat-forming environment ( Decombeix et al., 2021 ). The Mesozoic (Late Triassic) nurse log of southwestern United States was documented from a conifer forest inhabiting a moist overbank environment under a temperate to subtropical paleoclimate ( Daugherty, 1963 ; Jin et al., 2018 ). The Cretaceous (Aptian) nurse logs from Patagonia derive from a conifer-dominated forest growing in middle latitude temperate climatic settings with strong seasonality and subject to regular volcanic ash falls ( Vera and Loinaze, 2022 ).…”

A model for the early diagenesis of humid climate, fluvial strata influenced by adjacent salt deposits: Grande Anse Formation, Cumberland Basin, Canada

“…Although lower member examples show a wider scatter, there is complete overlap of data from the lower and upper members suggesting that, rather than a major change in climatic conditions during deposition of the studied succession, as interpreted in different stratigraphic units (cf. Buck et al ., 2010; Weibel et al ., 2017; Jin et al ., 2018), the redder lower member was simply subject to good drainage (Besly & Turner, 1983), and the gradation to more grey beds upsection simply reflects lower topographic gradients, poorer drainage, and thus a higher average water table.…”

Description of the metoposauridAnaschisma brownifrom the New Oxford Formation of Pennsylvania

“…In both North America and Morocco (the western part of metoposaurids’ range), there is no evidence for other large-bodied stereospondyl taxa co-existing with or succeeding metoposaurids. The general paleoclimate of the southwestern United States has been well studied from a variety of perspectives, especially in the Chinle Formation (e.g., Dubiel et al, 1991, 2011; Atchley et al, 2013; Baranyi et al, 2018; Jin et al, 2018; Rasmussen et al, 2020) and indicates a humid climate during deposition of the lower units, with a progressively arid and seasonally pronounced shift throughout the Norian. Similar seasonality has been inferred from histological data of the Moroccan metoposaurids (Steyer et al, 2004), while the Polish and Indian taxa seem to have been subjected to a comparatively mild climate that did not lead to growth cessations (Konietzko-Meier and Klein, 2013; Teschner et al, 2020).…”