Characterizing Tectonic and Hydrologic Processes Shaping Earth and Mars

WashU affiliated authors: Paul K. Byrne (Dept. of Earth and Planetary Sciences)

Abstract: Planetary surfaces provide a window into the geologic past of planets and can offer clues into their history of deformation. For example, endogenic forces such as tectonic activity resulting from secular planetary cooling can produce fault-driven topography that can be investigated to understand processes occurring at depth. Conversely, exogenic forces such as impact cratering can provide markers for surface dating and can aid in constraining the timing of unobservable subsurface processes like faulting. Further, humans can act as drivers of surface and environmental changes through modifications of the landscape. The impacts of these changes can be long-lasting and have consequences for interconnected ecosystems in fluvial environments. This dissertation explores how tectonic, impact, and fluvial processes have altered surfaces on Earth and Mars. Lobate scarps can be found across the Martian surface and, based on similar features on Earth, are interpreted as antiformal fault-propagation folds that form from the distortion of the hanging wall. For Chapter 2, I employed a semi-automated method for extracting surface displacement along fault-strike to produce displacement profiles. Then, spectral analyses, both Fourier and S-Transform, were used to characterize segmentation and infer fault growth histories through fault linkage. Finally, the spectral data were used to compare maximum displacement– length ratios and were further analyzed for fault segmentation. Statistically significant differences were found in Dmax/L ratios using an assumed homoclinal fault dip angle of 30° between faults in the northern lowlands (n = 24; Dmax/L = 2.9×10–3  0.9×10–3 ) and southern highlands (n = 25; Dmax/L = 9.2×10–3  1.9×10–3 ), with faults in the north exhibiting less displacement for a given length than faults in the south. As demonstrated through calculations of differing fault dip angles on calculated Dmax/L scaling, these results may be explained by variations in fault geometry. Contrasting mechanical stratigraphy between successive units can promote fault-bend over homoclinal fault-propagation folding, accommodating horizontal fault displacement without a concomitant vertical surface topographic response. To explore the age of these structures and thus the timing of global contraction resulting from secular cooling of Mars’ interior, buffered crater counting (BCC) was used to constrain the timing of landform formation in Chapter 3. Absolute model ages for individual scarps ranged from 4.4 to 3.5 Ga using a range of 2-13 craters per scarp, falling within the Early Noachian to Early Hesperian periods of Mars’ geologic history. An aggregate of 148 craters was used to provide a model age for the area encompassing all 28 scarps. Ages based on the aggregate counts are 3.8−0.02 +0.01 Ga (per the Hartmann PF and CF) and 3.9−0.01 +0.01 Ga (for the Neukum/Ivanov models), respectively. As a whole, then, the most recent activity on these faults appears to terminate at the Noachian-Hesperian boundary. Finally, Chapter 4 investigated landscape responses to c. pre-1930’s land forest clearing and farming on the North Carolina Piedmont in a now reforested watershed in William B. Umstead State Park. The predicted unchannelized-to-channelized transition (i.e., channel heads) were located using local slope and contributing drainage area relationships. For the 40 channels used for this analysis, slope-area predicted locations were compared to observed channel heads to determine that 23 channel heads are located downslope of their predicted equilibrium location on the landscape. Using a mean migration distance of 174.4 m [S.D. = 109.6 m] per stream, an average per-channel contribution of 282.6 m3 [S.D. = 177.6 m3 ] of future erosion is predicted as the channel heads migrate up-valley from their observed (current) to predicted (future) locations. Using an estimate of total erosion (90,419 ± 56,838 m3 ) for the 23 km2 area that encompasses the state park and an average soil bulk density of 1.3 g/cm3 , the mass of soil from future erosion of channel heads is predicted to be 1.1 x 108 ± 6.7 x 107 kg (68% conf.) (i.e., 106 ± 67 t). This amount of soil and sediment contains approximately 9.5 x 105 ± 2.8 x 105 kg (68% conf.) (951 ± 277 t) of carbon, 4.4 x 104 ± 1.2 x 104 kg (44 ± 12 t) of total nitrogen, and 1.3 x 104 ± 3.9 x 103 kg (13 ± 4 t) of phosphorus. This work shows that historical land use may play a larger role than typically appreciated, in part and specifically through the re-establishment of equilibrium channel head locations. The impacts of this geomorphic process are likely to continue for hundreds to thousands of years to come.

Citation or DOI: Atkins, Rachel Marie. “Characterizing Tectonic and Hydrologic Processes Shaping Earth and Mars.” (2021).