Structural evidence of enhanced active subsidence at the bottom of a maar: Rincón de Parangueo, México

Abstract

Rincón de Parangueo is a Quaternary maar that has been recently desiccated. The crater was partially occupied by a soda lake, and near the shoreline microbialites have formed. Evaporites (mainly trona and halite) precipitated as the water level dropped. Active subsidence of the lake floor (c. 24 m since 1980) produced countless structures close to the lakeshore, where deformation is extensional. Closer to the depocentre, in the western half of the basin, gliding/spreading produced folds and mud-injection domes. The most remarkable structure throughout the basin is a monocline that forms a ring-like, nearly continuous scarp, approximately 15 m high, which in the eastern half of the basin was produced as a fault-propagation fold developed above the buried diatreme–country rock boundary. A more diffuse (wider) monocline, locally associated with compressive structures, occurs in the western half of the basin. These structures are interpreted as having developed above a gently inclined, irregular lake sediment–country rock (andesite) interphase. The monocline was modified by high-angle extensional faults/fractures with large heaves/apertures. In the eastern half of the basin, there is a second (outer) scarp, approximately 13 m high, formed by a high-angle, listric, normal fault. Rollover antiforms occur in the hanging wall of this structure. Rincón is an example of centripetal gravitational gliding/spreading.

Subsurface Sediment Mobilization in the Southern Chryse Planitia on Mars

“…In the scenario of Komatsu et al, these domes should be formed by mud emplacement underneath an old sedimentary volcano or other surficial edifices without major mud eruption. However, no fracture patterns such as radial faults as expected above domical intrusions or mud injections (e.g., Aranda‐Gómez et al, ; Jackson & Pollard, ; Withjack & Scheiner, ; Yin & Groshong, ) are observed. The domes also have small central knobs on their summit plateaus (Figure c), which Komatsu et al () interpreted as vent structures made of accumulated sediment, similar to terrestrial gryphons.…”

Mobile mud layer underneath the desiccated maar lake of Rincón de Parangueo and insights into its microbial fingerprints

“…RP maar is part of a volcanic complex (Valle de Santiago Volcanic Field; VSVF) formed by a continental lava shield, four maar-type volcanoes, and a lava dome, located near the town of Valle de Santiago . RP represents the youngest eruption reported so far in the area, with a maximum eruption age of 137 ± 89 Ky (Aranda-Gómez et al, 2017).…”

“…The sediments, exposed exceptionally by the lake desiccation, display a simple concentric carbonate facies distribution in RP (Figure 1a) (Aranda-Gómez et al, 2017;Sánchez-Sánchez et al, 2019). The platform bench is a nearly flat or gently inclined plane with a sedimentary sequence characterized by the presence of abundant oncolites.…”

“…The morphology and sedimentation of the crater bottom have been profoundly affected since then by the rapid subsidence (ca. 1 m year -1 ) and the large set of semicircular faults and fractures with throws mainly toward the center of the crater, forming a 15 m high topographic scarp (Rocha-Treviño, 2015;Aranda-Gómez et al, 2017). Nowadays, most of the crater surface is characterized by a dry carbonate plain, and only small residual brine ponds are present in the depocenter of the crater.…”

“…These abrupt changes in the environmental conditions allowed the presence, near the surface, of saturated mud that lost its layering structure and showed widespread evidence of mobilization and fluid migration manifested on the surface sediments. Structures observed include mud injection domes, brine pools, and gas seeps such as CO 2 and CH 4 (e.g., Aranda-Gómez et al, 2017;Paz et al, 2020). Paz et al (2020) suggested that the CH 4 emanating from the maar bottom has a biogenic origin.…”