One of the challenges in reconstructing the water history of Jezero crater, Mars, is understanding the relationship between the deposition of the western and the northern deltas. Although the western delta appears to be less eroded and younger than the northern delta, multiple scenarios for their deposition have recently been proposed, including simultaneous formation of the northern and western fans/deltas. In our study, we combined topographical and compositional data to determine the origin of the low-calcium pyroxene (LCP) and olivine/carbonate units which were found within the northern and western deltas. We investigated whether these units are representative of the structure of the northern delta, and after analyzing the combined topographic and compositional profiles, no prominent stratigraphic correlations showing parallel layering were found. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data shows that the closest possible source of LCP is the western delta and the watershed of the western inlet. Therefore, we interpret the uppermost LCP unit within the northern delta as material transported from the western inlet which draped the already existing topography of the northern delta. That means that the northern delta (except for several locations between the delta and buttes) was already eroded to the current topography before the deposition of the LCP unit. To test this interpretation, we modeled the distance at which sediments transported from the western inlet through the channel on the western delta would be deposited. The results are consistent with the location of the LCP unit on top of the northern delta. That leads to the conclusion that there was a period when an active western inlet provided sediments which covered parts of the already eroded northern delta. Therefore, the main body of the Jezero's northern delta is older than the western delta but was partly covered with a relatively thin younger layer of material from the western inlet.
