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Abstract:
The origin of red beds is a longstanding, unresolved problem that has raised many contentious discussions. Multiple hypotheses describe how red beds form yet there is still much unknown about the ubiquity, timing, and source of the hematite minerals that color the strata. These uncertainties are complicated by an absence of such mass accumulation of hematite on today’s continents and the lack of a depositional model that explains why the blue, red, and purple colors rapidly alternate through stratigraphic successions. We therefore need an explanation that can account for hematite production at a regional scale and the seriation of color at the bed scale. Solving this puzzle has implications for many pursuits (e.g., paleomagnetism, redox geochemistry, organic carbon burial) and can shed light on other intervals of the geologic past (e.g., Precambrian BIFs) and perhaps Martian hematite. In this study, I examine scientific drill cores of Late Triassic red beds from the Chinle Formation in the Petrified Forest National Park, Arizona. These units have been sampled for color through high-resolution core scans conducted at the CSD facility, Minnesota, USA. I compare the color data to hematite concentrations collected through lower-resolution stratigraphic sampling with a benchtop spectrophotometer. Stratigraphic variations in color and hematite are argued to be indications of an orbital climate control on red bed formation. Comparing the core data to stratigraphically equivalent outcrop intervals provides a set of predictions to test for the timing and amount of diagenetic hematite formed in sandstones and other units of the Colorado Plateau.
