Post contributed by Axel Noblet, Laboratoire de Planétologie et Géodynamique de Nantes, CNRS/Université de Nantes, France
Jezero Crater on Mars will soon be explored by NASA’s Perseverance rover. This crater has been interpreted as a paleolake. It contains two fan-shaped deposits in the northern and western portions of the crater. These deposits have been interpreted as ancient deltas. The delta located in the western portion of Jezero (Image 1) displays some of Mars’ best-preserved fluvio-deltaic features, and exhibits a variety of structures such as inverted channels and point-bar strata (Image 2). This delta contains a precious record of various depositional environments, and in situ exploration can give us insight of Mars’ fluvio-lacustrine history. The association of well-preserved lacustrine features with orbital detections of carbonates along the inner margin of Jezero points toward high biosignature preservation potential for these deposits. Hence Jezero’s western delta contains a record of the evolution of Mars’ ancient climate and possible habitability. The presence of a long-lived lake system on Mars is astrobiologically significant, and the deposits within the Perseverance landing site could have preserved biosignatures that could be investigated and cached for a future sample return mission.
Image 1: 3D view of Jezero western delta, looking north from the center of the crater. The data visualized here is a CTX camera orthorectified mosaic draped over a CTX digital terrain model (horizontal resolution: 20m/px). The triangular ‘birdfoot’ shape of the delta is clearly visible, and inverted channels can be seen radiating from the apex of the delta. The inlet valley goes diagonally from the upper left of the image through the delta deposits. The crater floor appears as the smooth terrains on the lower part of the image.
Jezero delta is referred to as a ‘birdfoot delta’ because of its triangular shape and the protrusions that extend towards the center of the crater (Image 1). The erosional front of the delta displays sub-horizontal layers that represent exposures of the bedded structure in the delta. These layers have been interpreted as bottomset beds corresponding to fine material deposited in a distal, low energy environment. Atop this sub-horizontal bedding, curvilinear light and dark strata can be observed on the surface of the delta (Image 2). These strata correspond to scroll bars formed via lateral accretion of sediment in a meandering fluvial system.
Image 2: HiRISE images (25cm/px) of morphologies visible on the delta: (A) Cross-cutting inverted channels. The channel in the center of the image is approximately 2 km long and 0.2 km wide. (B) Indurated bottomset bedding exposed by erosion at the front of the delta. Curvilinear scroll bars are present on the delta, above the center of the image and at the upper left.
The stratigraphically highest depositional features on the delta are crosscutting linear ridges (Image 2). These have been interpreted as inverted channels deposits. This type of deposit forms when erosion removes a channel’s banks and preserves indurated material deposited on the channel’s floor. These features are indicative of channels laterally migrating across the surface of the delta in a coastal environment. The crosscutting relationship between these features indicates that they correspond to time-ordered avulsion events. The last event recorded on the delta is the incision of a valley connected to Jezero’s western inlet channel. The valley cuts mainly through the inverted channels unit and remains of inverted channel material outcrop on the floor of the valley. This incision episode marks either a low lake level period or a decrease in the sediment to water ratio in the fluvial system. These different morphological features record the evolution of Jezero’s lacustrine history, and may provide insights into Mars’ global climate history.
Further Reading
Fassett, C. I. and Head, J. W. (2005), Fluvial sedimentary deposits on Mars: Ancient deltas in a crater lake in the Nili Fossae region, Geophysical Research Letters, 32, https://doi.org/10.1029/2005GL023456
Goudge, T. A., et al. (2015), Assessing the mineralogy of the watershed and fan deposits of the Jezero crater paleolake system, Mars, Journal of Geophysical Research: Planets, 120, 775–808, https://doi.org/10.1002/2014JE004782.
Goudge, T. A., et al. (2018), Stratigraphy and paleohydrology of delta channel deposits, Jezero crater, Mars, Icarus, 301, 58-75, https://doi.org/10.1016/j.icarus.2017.09.034.
Horgan, B. H. N., et al. (2020), The mineral diversity of Jezero crater: Evidence for possible lacustrine carbonates on Mars, Icarus, 339, https://doi.org/10.1016/j.icarus.2019.113526
M. G. Kleinhans, 2005, Flow discharge and sediment transport models for estimating a minimum timescale of hydrological activity and channel and delta formation on Mars. Journal of Geophysical Research: Planets, 110, E12003, https://doi.org/10.1029/2005JE002521
Mangold, N., G. Dromart, V. Ansan, M. Massé, F. Salese, M. Kleinhans, C. Quantin-Nataf, K. Stack, 2020, Fluvial Regimes, Age and Duration of Jezero Crater Paleolake and its Significance for the 2020 Rover Mission Landing Site, Astrobiology, 20 (8) 994-1013, doi.org/10.1089/ast.2019.2132.
Salese, F., M. Kleinhans, N. Mangold, T. De Haas, V. Ansan, G. Dromart, 2020, Estimated minimum lifetime of the Jezero crater Delta, Mars, Astrobiology, 20 (8), 977-993, https://doi.org/10.1089/ast.2020.2228.
Schon, S. C., et al. (2012), An overfilled lacustrine system and progradational delta in Jezero crater, Mars: Implications for Noachian climate, Planetary and Space Science, 67, 28-45, https://doi.org/10.1016/j.pss.2012.02.003
Planetary Geomorphology Image of the Month 