Magnetostratigraphy of the Pliocene Masol Formation, Siwalik Frontal Range, India: Implications for the age of intentional cut-marked fossil bones

Abstract

The sedimentary Masol Formation, at least 165 m thick, is located in the Indian Siwalik Frontal Range and outcrops in the Chandigarh Anticline. It includes a fossiliferous zone called the Quranwala Zone (QZ) in its lower part. These fossils are characteristic of the Late Pliocene (Tatrot). Previous magnetostratigraphy showed that the QZ was deposited during the Gauss chron, with a short magnetic excursion at the base of the QZ, but the Gauss-Matuyama reversal was imprecisely identified in the stratigraphy of the Masol Formation. Following cut marks on fossil bones discovered in the QZ, we conducted a new magnetostratigraphy study to clarify their age. Our results indicate that detrital hematite is the main magnetic carrier and confirm that the entire Masol Formation was deposited during the Gauss Chron, whereas the Gauss-Matuyama reversal is outside the study area. Comparison between the magnetic excursion previously found at the base of the QZ and others identified elsewhere in a different sedimentary context and dated between 2.62 and 2.95 Ma, gave a range of sedimentation rates between 0.41 and 3.75 m.kyr-1 for the minimum thickness of the Gauss chron recorded in the Masol Formation. However, only rates less than 1 m.kyr-1 are consistent with the Late Pliocene deposits observed in the Siwalik. Magnetostratigraphy and obtained sedimentation rates conclude that the cut and percussion marks on the fossil bones have a minimum age of 2.68 Ma and a maximum age of 2.95 Ma. This evidence of intentional hominin activity is thus the oldest known in Asia.