Quantifying the morphological degradation of terrestrial impact craters through a Denudation Index derived using drainage network signatures

Terrestrial impact craters,having dynamically modified the Earth's surface, depict characteristic radial, centripetal and concentric drainage patterns, by virtue of its morphology. These typical drainage patterns, developed in relatively pristine conditions, often during or immediately after its formation, are modified owing to progressive fluvial action. Crater denudation are influenced by climate, target lithology, morphology, and time.  Here, in the study, the crater denudation, designated as a function of fluvial activity by introducing a parameter titled ‘Denudation Index’ (DI), showcase how drainages modify the morphology of an impetus structure by quantifying the ratio of total first order radial/centripetal streams originating from the crater rim and central elevated area to the total first order streams. DI was calculated for 71 terrestrial craters, by keeping aside the buried, morphologically unexpressed, water filled, and data sparse craters. The DI, which is a measure of rim degradation caused by fluvial activity, is expressed on a scale of 0-1, as

               RI =  [(A_out/T_out)+(A_in/T_in)]/2                              (1)

               DI = 1–RI                                                               (2)

where, RI is Retention Index,  A_out is number of 1^st order streams flowing outward (i.e., radial) from rim, T_out is total number of 1^st order streams flowing radially from rim, A_in is number of 1^st order streams flowing inward (i.e., centripetally) from rim, and T_in is total number of 1^st order streams flowing centripetally from rim.

The DI of craters was correlated with relative morphology, age, lithology and paleoclimate. Paleoclimatic data was generated by reconstructing crater paleo-positions at 1 Ma interval through GPlates and deciphering the paleoclimate a crater experienced at a specific time utilizing Scotese Global Climate Model [1].

The study provides a series of relevant observations. The DI of craters impacting to crystalline target (such as DI_Decaturville= 0.55) is higher than ones on sedimentary target (DI_Rochechouart= 0.87). The observation can be attributed to the brittle nature of crystalline rocks aiding more advanced fracture formation and thereby, more extensive and sophisticated drainage network development. The DI of younger craters (DI_Hickman=0.67) (0.02–0.10 Ma) can be higher than older craters (DI_{Tabun-Khara-Obo}=0.64) (150±20Ma). The study also revealed that, in general, complex craters shows higher DI values, owing to older formation ages than simple craters.  The study also showed that craters in equatorial rainy climate are more denuded than craters in other climates. The above observations suggest that the cumulative effects of target lithology, climate and morphological traits strongly influence crater denudation. Thus, the study provides a new parameter (DI) and method for determining terrestrial impact crater denudation by depicting that drainage network of a crater, as we see today, is unique in itself, entailing significant influences of target lithology, crater age, crater morphology and paleoclimates.

Reference: Scotese, C.R., 2016. Global Climate Change Animation (540Ma to Modern), https://youtu.be/DGf5pZMkjA0.