Bundled cross-strata from Martian rocks suggest an Earth-like cyclic self-organisation of bedforms

Abstract

Cross-strata on Mars are expressions of ancient bedforms formed due to sediment transport by either wind or water. Some of these cross-strata show peculiar features, including intercalated mudstone drapes, discontinuity surfaces and cyclic patterns in stratum thickness (i.e. bundled cross-strata). In this study, we evaluated the sedimentary features of five of these bundled cross-strata using images from the Curiosity rover in Gale Crater. These cross-sets are generally 0.08–0.20 m thick and up to 1.6 m wide. They accumulated in fluvial, deltaic-lacustrine and aeolian depositional environments approximately 3.6–3.1 Ga. These cross-strata were analysed with statistical methods with a focus on three parameters of the internal strata: thickness, angle and shape. Our results show variations in all these parameters, some of which are confirmed having a moderate to strong cyclic imprint at different scales. These cyclic patterns were attributed to a self-organisation related to the migration of superimposed bedforms over the host bedform under mostly unidirectional riverine- and wind-driven flows, similarly to what is observed in bedforms on Earth depositional systems and reproduced in flume experiments. Both high- and low-angle discontinuity surfaces were identified and were attributed to the migration of different-scale superimposed bedforms. This study shows how Martian sediment transport in the past had similar dynamics as on Earth also at the bed scale. At the same time, it helps to better understand the full range of depositional mechanisms on both Earth and other planets that are able to produce cyclicities not necessarily under varying flow strength and/or direction.