# DIPPING LAYERED DEPOSITS ON MARS: IMPLICATIONS FOR CLIMATE-DRIVEN MID-LATITUDE PROCESSES

Evan Blanc, Susan J. Conway, Frances E G Butcher, Anna Grau Galofre, Nicolas Mangold, Axel Noblet

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Evan Blanc, Susan J. Conway, Frances E G Butcher, Anna Grau Galofre, Nicolas Mangold, et al. "DIPPING LAYERED DEPOSITS ON MARS: IMPLICATIONS FOR CLIMATE-DRIVEN MID-LATITUDE PROCESSES." 56th Lunar and Planetary Science Conference (LPSC), USRA, Mar 2025, The Woodlands, United States. hal-05375951

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**DIPPING LAYERED DEPOSITS ON MARS: IMPLICATIONS FOR CLIMATE-DRIVEN MID-LATITUDE PROCESSES.** E. Blanc¹, S. J. Conway¹, F. E. G. Butcher², A. Grau Galofre¹, N. Mangold¹, A. Noblet³
¹Laboratoire de Planétologie et Géosciences, CNRS, Nantes, France (evan.blanc@etu.univ-nantes.fr),
²School of Geography and Planning, University of Sheffield, UK, ³University of Western Ontario, London, Canada.

**Introduction:** Viscous Flows Features (VFFs), putative debris-covered glaciers [1,2], are abundant from 30° to 60° in both hemispheres of Mars. We have identified distinctive dipping layered deposits (DLD) associated with VFF, which typically occupy alcoves on shallow hillslopes (Fig. 1). Previous research identified these deposits in regional studies and interpreted them as ice-dust mantling units or remnants of extensive ice sheets [3-6]. The objective of this study is to determine the origin of these DLD through systematic mapping across Mars' mid-latitudes combined with detailed morphological/surface analyses.

<figure><img src="image_2.png" /><figcaption>Fig. 1 HiRISE images of Dipping Layered Deposits: (A) ESP_050793_1365 and (B) ESP_073595_1380 showing our azimuth and length measurement.</figcaption></figure>

**Methods:** We used the Context Camera (CTX) MurrayLab mosaic (6 m/pixel) [7] to map individual packages of DLD with 2 or more layers (Fig. 1B). Our initial mapping region was between 40 and 44° in both hemispheres, was incrementally extended when DLD were found near the mapping boundaries. For each DLD we drew a line orthogonal to the layers, extending across the whole layer package in the downslope direction (Fig. 1B), to provide azimuth and package width measurements. We recorded the number of layers present in each package and the underlying slope value from the MOLA gridded elevation data at ~450 m/pix. We used High-Resolution Imaging Science Experiment images (HiRISE, 25 cm/pixel, [8]) and elevation data (1 m/pix) to derive DLD layer orientations, thickness and dip angle. We used images from HiRISE and the Colour and Stereo Surface Imaging System (CaSSIS, 4-5 m/pixel, [9]) to make detailed surface texture observations.

**Observations:** A total of 7,774 DLDs were mapped across latitudes 28–52°N and 28–48°S. Clusters of DLD were identified in areas with dense concentrations of VFF, including Promethei Terra, Deuteronilus-Nilosyrtis Mensae, Reull Vallis, and Phlegra

Montes. We find that 50% of DLDs are situated within 20 km of a VFF. The average package-width of DLDs is 500 m in the northern hemisphere and close to 2 km in the southern hemisphere. DLDs typically have 2-4 layers yet can have several tens of layers (Fig. 1), and are generally found on slopes <10° at MOLA-scale.

DLD conform to the underlying hillslope and the layer-thickness does not appear to change significantly down-slope. DLD azimuths generally align with the orientation of the regional slope (Fig. 2). Yet they are typically found on locally reversed slopes (Fig. 2A), i.e. hillslopes that face upslope relative to the broader regional topography. This suggests a preference for deposition and/or preservation in areas where the local slope direction contrasts with the overall regional gradient. Detailed observations of DLD surface textures highlight the presence of orthogonal fractures which are often accompanied by pitted textures.

**Discussion:** The observation of orthogonal fracture networks and pitted textures on DLD surfaces suggest that they could host – or have previously hosted – a component of subsurface ice [10]. However, we find no evidence of downslope deformation. The presence of ice and lack of significant deformation seems to indicate DLD could be dust deposits with small volume of ice. In some locations, DLD appear to be fragmentary remnants of larger deposits. Hence, they could represent locations where deposition preferentially occurred, or where the preservation potential is higher.

DLD have regular layering, the thickness and distribution of which may reflect Martian climate cycles. The layers conform to underlying slopes, suggesting topographic control on deposition. Diverging azimuth patterns (Fig. 2) suggest that the deposits may be influenced by the interaction of a fluid with the martian surface, for example the circulation of the atmosphere (i.e. aeolian processes) or the flow of glacial ice. These characteristics lead us to consider three formation hypotheses, all followed by post-depositional erosion and/or sublimation:

(1) *Glacial Hypothesis:* DLD may be remnants of an ancient regional ice-sheet, with debris layers incorporated at their base through basal deformation, in analogy to a lodgment till deposit on Earth. Ice flow encountering the stoss-face of a topographic undulation in the bed could have preferentially deposited material here.

(2) *Ice-rich Mantling Hypothesis:* A mantling deposit rich in ice and dust, deposited under a different
climatic regime to the present day, may have undergone compaction and creep down the slope, preserving distinct layers and locally, distinct ice-dust proportions. This hypothesis links debris-rich deposits on slopes to less debris-rich areas nearby (VFFs).

(3) Aeolian Hypothesis: DLD may be martian loess deposits, composed of fine wind-transported dust settled against slopes, perhaps synchronously with ice particles, and with layering forming as a result of pulses of dust availability. Slopes would have favored the deposition of dust particles, offering greater resistance to erosion, and favoring preservation.

**Conclusion:** We present the first global-scale map of Dipping Layered Deposits. Together with our detailed structural and surface analysis, we suggest three possible formation processes for the DLD. The first explores the presence of a regional ice sheet, implying long period of intense glaciation in the mid-latitudes. The second considers the possibility of a mantling deposit which covered the mid-latitudes, suggesting episodic deposition events and a origin link between DLDs and VFFs. The third hypothesis points to layered icy loess deposits following pulses of dust availabil

ity, which points to a dustier and drier past climate. The ubiquitous distribution of these deposits signals an important and to date unknown global-scale deposition process which could contain important information on Mars' past climate.

**Acknowledgments:** We acknowledge the French Space Agency CNES for supporting HiRISE and CaS-SIS related work, and the ANR TRITON Graduate Program. FB acknowledges a Leverhulme Trust Early Career Fellowship.

**References:** [1] Butcher, F. E. G. (2022) *Oxford University Press*, ISBN 9780190647926. [2] Holt, J. W. et al. (2024), *Science*, 322, 1235-1238. [3] Carr, M. H. (1987) *Nature*, 326, 30-35 [4] Morgensten, A. et al. (2007), *JGR Planets*, 112, E6. [5] Soare, R. J. et al. (2013) *Icarus*, 225, 971-981. [6] Baker and Head (2015), *Icarus*, 260, 269-288. [7] Dickson, J. L. and al. (2024), *Earth & Space Sci.*, 11(7), e2024EA003555. [8] McEwen, A. S. et al. (2007), *JGR Planets*, 112, E5S02. [9] Thomas, N. et al. (2017), *Space Science Rev.*, 212, 1897-1944. [10] Mangold, N. (2005), *Icarus*, 174, 336-359.

<figure><img src="image_3.png" /><figcaption>Fig. 2 (A) Orientation trends of DLD where colors represent azimuths, and background is MOLA elevation. (B) Orientations in Deuterolinus Mensae where azimuths are shown by arrows. (C) A diagram illustrating DLD azimuths in relation to the regional slope direction.</figcaption></figure>