Hematite reconstruction of Late Triassic hydroclimate over the Colorado Plateau

Abstract

Hematite is the most abundant surficial iron oxide on Earth resulting from near-surface processes that make it important for addressing numerous geologic problems. While red beds have proved to be excellent paleomagnetic recorders, the early diagenetic origin of hematite in these units is often questioned. Here, we validate pigmentary hematite (“pigmentite”) as a proxy indicator for the Late Triassic environment and its penecontemporaneous origin by analyzing spectrophotometric measurements of a 14.5-My–long red bed sequence in scientific drill core CPCP-PFNP13-1A of the Chinle Formation, Arizona. Pigmentite concentrations in the red beds track the evolving pattern of the Late Triassic monsoon and indicate a long-term rise in aridity beginning at ∼215 Ma followed by increased oscillatory climate change at ∼213 Ma. These monsoonal changes are attributed to the northward drift of the Colorado Plateau as part of Laurentia into the arid subtropics during a time of fluctuating CO2. Our results refine the record of the Late Triassic monsoon and indicate significant changes in rainfall proximal to the Adamanian–Revueltian biotic transition that thus may have contributed to apparent faunal and floral events at 216 to 213 Ma.

Hematite-goethite ratios at pH 2–13 and 25–170 °C: A time-resolved synchrotron X-ray diffraction study

“…The transformation of ferrihydrite to hematite and goethite in soils typically is mediated by water (Bowles, 1992;Cornell and Schwertmann, 2003;Schwertmann et al, 2004). The hematite-goethite ratio varies with water activity, and the ratio has been used to reconstruct paleorainfall records across wide climate regimes in aerobic or anaerobic conditions (Kämpf and Schwertmann, 1983;Camargo et al, 2013;Hyland et al, 2015;Lagroix et al, 2016;Long et al, 2016;Silva et al, 2020;Lepre and Olsen, 2021). As suggested by these studies, more humid environments favor goethite, so that the hematite-goethite ratios decrease with increasing moisture (rainfall minus evapotranspiration).…”

Re-Visiting the Quantification of Hematite by Diffuse Reflectance Spectroscopy

“…Compared with other iron oxides, the characteristic absorption of hematite is uniquely particular at 500-600 nm due to its double electron excitation of the magnetically spin-coupled Fe ions within the crystal lattice [8,21,75]. To obtain a quantitative proxy for hematite, the raw DRS data were processed three ways using the Varian instrument software (Savitzky-Golay method with a smoothing factor of 99): (1) the first derivative was calculated directly [57]; the raw data were transformed into the Kubelka-Munk (K-M) functions ((1-R) 2 /2R) [19,66] to calculate the (2) first and (3) second derivative curves of the K-M function [66,74,75,77].…”

“…As one of the most stable iron oxides, hematite serves as a common and important paleomagnetic remanence carrier in sediments and rocks [10][11][12][13][14]. In addition, characterized by the distinct red color of natural hematite pigment, it can be further used to investigate the paleoenvironment conditions not only on the Earth [3,[15][16][17][18][19][20][21][22][23][24][25][26][27], but also on the other planets, in particular on Mars [1,[28][29][30][31].…”

Quantifying Soil Goethite/Hematite Ratios: A New Method Based on Diffuse Reflectance Spectra

“…This means that pedogenic Gt/Hm ratios exclude the effect of the duration of pedogenesis (e.g., Balsam et al., 2004), which has been a major issue in the application of various pedogenic and chemical weathering proxies to infer past climate and environment changes (e.g., Kong et al., 2020). Because of these advantages, the Gt/Hm ratios have been widely used as a valuable proxy of environmental and climatic changes in terrestrial (Ao et al., 2020; Balsam et al., 2004; Hao et al., 2009; Ji et al., 2001; Jia et al., 2018; Lepre & Olsen, 2021) and marine archives (Abrajevitch et al., 2009; Clift et al., 2014; Zhang et al., 2009; Zhou et al., 2021). However, the precondition for using Gt/Hm ratios necessitates the accurate quantification of their ratios.…”