LATE STAGE DISCHARGE ESTIMATES ALONG PORTIONS OF SAMARA VALLES, WEST OF JONES CRATER, MARGARITIFER TERRA, MARS

Although most valley networks in the Margaritifer Terra region formed in the Late Noachian into the Early Hesperian there is evidence for later drainage along medial and distal Samara Valles. Valleys originating within and incising the ejecta of the Late-Hesperian Jones crater are relatively more pristine and continuous, except where interrupted by a larger upper and smaller lower basin defined by the -1275 m MOLA contour. Estimating discharge along these relatively pristine segments helps us understand the duration and water source for late fluvial activity. Due to considerable uncertainties in our estimations, such as channel depth, width, valley infilling, and bed properties, we consider our discharge estimates to be an order of magnitude approximations.

We estimate discharge using a modified version of the Darcy-Weisbach equation,

Q = A(8g_mRs/f)^0.5 [1]

because drainage was unlikely characterized by bank full, equilibrium flow. Discharge was estimated at nine locations: two upstream of the upper basin and seven between the upper and lower basins. Channel dimensions and slopes were estimated using individual shot points along MOLA tracks crossing interior terraces, valley floor width measured perpendicular to terraces, and changing downstream elevation through the cross sections. Dimensions were then considered with a range of friction factors for various bed types to estimate discharge.

Resultant discharge estimates upstream of the upper basin are 7.4 x 10² to 1.7 x 10⁴ m³s^-1 but increase to 1.0-1.9 x 10⁵ m³s^-1 near the upper basin outlet breach to 1.5-8.9 x 10⁴ m³s^-1 between the upper and lower basins. A mean discharge of 9 x 10³ m³s^-1 above the upper basin suggests the basin could be filled in 60 days, while a mean discharge of 8 x 10⁴ m³s^-1 below the upper basin indicates impounded water could have drained in as little as 7 days. Even if actual discharge was an order of magnitude higher or lower than what we predict, our findings suggest that late fluvial activity across and beyond the Jones ejecta persisted for no more than months to years. Hence, this late-stage valley incision potentially created transient habitable environments late in Mars’ history.

[1] Mangold N. et al. (2021) Perseverance rover reveals ancient delta-lake system and flood deposits at Jezero crater, Mars, Sci., 374, 711-717. 10.1126/SCIENCE.ABL4051