EXPLORATION OF POTENTIAL SEISMITES: ARCHEAN NAUGA FORMATION, TRANSVAAL SUPERGROUP, SOUTH AFRICA

Late Archean carbonate strata of the Nauga Formation, Transvaal Supergroup, South Africa, were examined near the town of Prieska. Here, the Nauga Formation consists largely of <5 cm-thick, grey-weathered carbonate beds capped by a 1-2 cm-thick interval of brown-weathering carbonate, and interspersed volcanic tuffs. Although tuffs are generally <10 cm-thick, in the basal <20 m of exposed section, volcanic tuffs are substantially thicker and make up nearly 80% of the exposed strata. Basal strata are also associated with deformation of carbonate (e.g. brecciation and contorted bedding) that may reflect seismic- or seismically-derived wave-activity. Unusual inverted coniform deformation structures also appear throughout the Nauga Formation, and appear related to the occurrence of ash fall tuffs. Here we explore the detailed structure of these inverted coniform structures and place constraints on their potential mode of origin.

In the field, these structures consist a recessive, grey-weathering carbonate phase and a resistant, brown-weathering phase, which form isolated to linked, often stacked, inverted cones. Here we combine an analysis of field photographs, standard cathodoluminescence and petrographic analysis, and SEM analysis, to interpret the formation of these unusual features. Within photographs, we analyzed the layering of grey and brown-weathering phases within the outcrop and relationship between these two phases. Deformation features are generally rare in grey-weathering phases, while brown-weathering phases show downward sagging and rare upward injecting flames. Petrographic analysis shows that these two phases consist of non-planar spar and Fe-rich planar dolomite, respectively. These analyses, combined with SEM, will ultimately help us better understand the material conditions of rock units during deformation, which may help constrain their specific mode of origin.