In Situ Radiometric and Exposure Age Dating of the Martian Surface

Abstract

We determined radiogenic and cosmogenic noble gases in a mudstone on the floor of Gale Crater. A K-Ar age of 4.21 ± 0.35 billion years represents a mixture of detrital and authigenic components and confirms the expected antiquity of rocks comprising the crater rim. Cosmic-ray-produced (3)He, (21)Ne, and (36)Ar yield concordant surface exposure ages of 78 ± 30 million years. Surface exposure occurred mainly in the present geomorphic setting rather than during primary erosion and transport. Our observations are consistent with mudstone deposition shortly after the Gale impact or possibly in a later event of rapid erosion and deposition. The mudstone remained buried until recent exposure by wind-driven scarp retreat. Sedimentary rocks exposed by this mechanism may thus offer the best potential for organic biomarker preservation against destruction by cosmic radiation.

Gale crater and impact processes – Curiosity’s first 364 Sols on Mars

“…The ages were determined by crater counts on the southern ejecta blanket by Thomson et al (2011), Bustard et al (2012) and Le Deit et al (2013) are $3.7 Gy (see Michael and Neukum (2010) and Michael (2013) for current methodology). This age is also consistent with the Ar-Ar dating (4.16 ± 0.4 Gy) of the crust formation age of materials now in Yellowknife Bay (Farley et al, 2013), regional stratigraphic relationships, including the Late Hesperian-Early Amazonian resurfacing of northern terrains and formation of fretted valleys.…”

“…Based on an age of 3.2-3.3 Ga for the sediments, and an estimated maximum burial depth of 20-40 m for the surface of Yellowknife Bay (including the missing 5 m), an average erosion rate on the order of $8-14 mm/Myr is required to get down to the current surface. This erosion rate from Gale is consistent with the range of rates (1-30 mm/Myr), estimated by Golombek et al (2006aGolombek et al ( ,b, 2014 Farley et al (2013), ascribes this to retreat of a scarp that is now about 60 m from the drill site. Converting this age to a vertical erosion rate, assuming a scarp retreat model, involves an assumption about the fraction of exposed bedrock older and younger than 78 Myr.…”

Conceptual Design of an In Situ K-Ar Isochron Dating Instrument for Future Mars Rover Missions

“…Geologic interpretation of this age measurement is rather difficult, because it is a model age based on whole-rock measurement. More specifically, sedimentation age estimated from this measurement ranges from 1.6 to 4.5 Ga. 7) Thus, the absolute age of the Noachian-Hesperian boundary is yet to be determined. In such complicated geological background, isochron dating is particularly preferred because it can obtain an accurate age for a rock.…”

“…[3][4][5][6] Recently, the NASA Curiosity rover performed the first in situ dating experiment on Martian rock and obtained an age of 4.21 ± 0.35 Ga for a mudstone on the floor of the Gale crater. 7) However, the age of the mudstone does not necessarily reflect the age of the geologic unit covering the Gale crater; it could be crystallization age of surrounding basaltic crustal rocks or could be sedimentation age of the mudstone. Geologic interpretation of this age measurement is rather difficult, because it is a model age based on whole-rock measurement.…”

Fluvial Landforms and the Post-Noachian Environment on Mars

“…While obliquity and other known variations in Mars climate make it unlikely that erosion rates on the Hale deposits were uniform over this period (e.g., Golombek et al, 2014), long term average rates for just a few meters of denudation on the distal Hale deposits are on order of 10 -2 to 10 -3 m/Myr. For comparison, other estimates of erosion since the Late Amazonian are generally similar (e.g., Golombek et al, , 2014Grant et al, 2006;Warner et al, 2010;Farley et al, 2014), but are often predicted for bedrock units rather than the less competent materials presumed to comprise the Hale-related deposits. An exception includes the initial degradation of small craters in Meridiani Planum where rates as high as 10 -1 to 10 0 m/Myr (Golombek et al, 2014), though this may relate to local disequilibrium of the geomorphic surface caused by the impact and crater formation rather than long term erosion rates .…”