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The geologic and tectonic history of the Memnonia-Sirenum region of Mars has been reconstructed on the basis of geologic mapping and relative-age dating of rock units and structures using crater counts and superposition relations. Comparisons between the ages of rock unit formation and the orientations of the earliest structures associated with Tharsis demonstrate a strong interplay among tectonic, magmatic, and aqueous activity in the Memnonia-Sirenum region. Early Noachian geologic activity identified within this region includes the formation of large northeast-trending, extensional basins. Stratigraphic and tectonic evidence suggests that these basins formed concurrently with the early formation of Tharsis when the dynamo and associated magnetosphere were still in operation. In addition to the ancient basins, later Tharsis-influenced activity includes prominent tectonic fault systems associated with the formation of Tharsis and Arsia Mons. Detailed mapping of the faults indicates that structures associated with Memnonia and Sirenum Fossae resulted from the formation of Tharsis during the Middle to Late Noachian. Late-stage (Amazonian) activity also identified within this region includes valley networks and collapse depressions that are linked and/or occur among Tharsis-centered faults that cut features throughout this region, including Mangala Valles. • The Memnonia-Sirenum region contains some of the oldest stratigraphic units of the western hemisphere region of Mars. • The northeast trending basins and ranges identified appear to be the result of the initial Tharsis upwelling phase. • Continued upwelling resulted in the formation of the ridges and radial faults associated with the center of the uplift. • Basin development was influenced by changing hydrologic conditions linked to the formation of Tharsis. [ABSTRACT FROM AUTHOR]

This study demonstrates a novel approach to overcoming challenges associated with obtaining reliable radiocarbon dates for rock paintings. Using two independent methods, we obtained ages for Pecos River style paintings at Eagle Cave in Langtry, Texas. The first method employed plasma oxidation to isolate organic carbon directly from the paint layer for accelerator mass spectrometry C-14 measurement. The second method treated mineral accretion layers with phosphoric acid to isolate calcium oxalate for plasma oxidation cleaning, combustion, and C-14 measurement to obtain minimum and maximum ages for the paintings. Radiocarbon dates for the paintings are statistically indistinguishable, with a weighted average of 3280 ± 70 years BP calibrated to 1740-1420 cal BC (3690-3370 cal BP) at 2 sigma (95.4%) probability. Radiocarbon assays obtained for the overlying accretion layers are younger and underlying accretion layers are older. The chronological stratigraphy of the accretion and paint layers supports the validity of both dating methods. With accurate and reliable dating methods, rock paintings in the region can be studied alongside excavated cultural deposits to provide a more complete understanding of this hunter-gather society. These methods for dating rock paintings can be applied to many rock art provinces around the world. [ABSTRACT FROM AUTHOR]