SCALE OF LAMINATION IN SEDIMENTARY ROCKS AS A GUIDE TO DEPOSITIONAL PROCESS ON MARS

Multiple criteria have been used in the attempt to characterize sedimentary environments and processes on Mars. The presence of “pin stripe” lamination was used as evidence for the presence of aeolian stratification at the Opportunity landing site at Meridiani planum. Here we quantify the distribution of lamination thickness in examples of proposed aeolian strata, and compare these to diverse terrestrial sedimentary rocks. Lamination thicknesses were measured from images of terrestrial environments (aeolian, sub-aqueous, and base surge deposits) and compared with those from Martian sediments based on images returned by Opportunity. Histograms were compiled for each environment in order to compare the Martian and terrestrial sediments. Martian laminae from the Burns formation (Meridiani landing site) have a mean thickness 0.195 cm, and a standard deviation of 0.083 cm from a count of 75 laminae (n=75). These results most closely resemble the distributions observed for terrestrial aeolian deposits from the Jurassic Page Sandstone, Colorado plateau. Page Sandstone aeolian deposits have a mean lamination thickness of 0.142 cm, and a standard deviation of 0.045 cm with n=427. The sub-aqueous, fluvial, “upper plane bed” facies from the Mt. Shields Formation (Belt Supergroup, 1.4 Ga), Montana, on the other hand, produced a similar mean for lamina thickness of 0.136 cm with a standard deviation of 0.049 cm with n=190. Finally, we measured lamination thicknesses for Tertiary pyroclastic base-surge deposits preserved at Hunts Hole, New Mexico. These base surge laminae have a mean thickness of 1.89 cm, an order of magnitude greater than the Martian lamina, and a standard deviation of 1.74 cm. with n=168. Although these distributions reflect a range of factors, our results demonstrate that the Martian sediments most closely resemble those from terrestrial aeolian environments. They also compare favorably with fluvial upper flow regime (“plane bed”) strata, but are quite different from volcanic base surge deposits. Although some overlap in lamination thickness occurs between the different data sets, the means of our datasets are consistent with previous studies that have been interpreted in terms of an aeolian origin for the pin-stripe laminations found on the Martian surface.