Magnetic fabric and sedimentological constraints on the paleocurrent changes within the early devonian strata from the northwestern Tarim, China

Abstract

The magnetic fabric technique is widely used to measure the direction of paleocurrent and paleostress due to its speediness, precision, and cheapness. However, correlating unique magnetic fabric patterns in weakly deformed rocks with hydrodynamic or tectonic regimes remains challenging. The Early Devonian sedimentary rocks in the Keziertage Formation have well-preserved sedimentary structures and were deformed by the Cenozoic non-plunging fold. This sequence offers a prime opportunity to explore the relationship between magnetic fabric evolution, paleocurrents, and weakly deformation. Furthermore, the paleocurrent characteristics of the Keziertage Formation reflect the provenance changes during the opening of the South Tianshan Ocean. Here, we report 120 sedimentary structure-based paleocurrents and 382 magnetic fabric data from the Keziertage Formation in the Kalpin area, Xinjiang. We find that: (1) During the weakly deformation stage, the minimum axis of susceptibility's imbrication direction serves as a reliable indicator for detecting paleocurrents at the coarse sandstone layer with well-developed cross-bedding; (2) While the maximum axis of susceptibility is more consistent with the tectonic stress rather than paleocurrents. Consequently, the complexity of magnetic fabric needs to be clearly verified when it is applied in the weakly deformed strata. In the northwest margin of Tarim, both the minimum susceptibility axes of magnetic fabrics and sedimentary structures indicate a shift in the paleocurrent direction, transitioning from southwest to northeast in the mid-to-upper Keziertage Formation. This indicates significant channel changes, potentially linked to a regional change in provenance due to the Early Devonian opening of the South Tianshan Ocean.