Navajo Sandstone concretions record extended magnetic chronology

This study investigates iron oxide concretions from the Jurassic Navajo Sandstone in Utah as potential recorders of long-term magnetic field variations. Using a combination of alternating field and thermal demagnetization, physical abrasion, chemical analysis, and magnetic modeling, we reveal multiple magnetic components with contrasting directions within individual concretions. Finite Element Magnetic Modelling demonstrates the sensitivity of magnetic signatures to small changes in layer thickness. X-Ray Fluorescence spectrometry confirms high iron concentrations in concretion crusts. Our results support a two-stage formation model involving initial iron hydroxide precipitation followed by progressive transformation to hematite. This extended formation process suggests these concretions may record paleomagnetic field changes, though their reliability as magnetic recorders need to be verified in more details. The identification of both goethite and hematite phases, coupled with their distinct magnetic behaviors, has implications for understanding similar concretionary structures observed on Mars. However, environmental differences between terrestrial and Martian settings require careful consideration when making such comparisons.