干旱区生态环境知识资源中心

Ancient quarry surfaces in Petra, Jordan were studied in the hopes of assessing the effects of insolation on weathering. The Nabataeans prepared these vertical quarry surfaces by chiseling them to produce distinctive herringbone dressing patterns. These dressed faces were chosen because their surfaces were carved at the same time (100BCE to 100CE), are vertical surfaces with easy access, and have not been modified or obscured since their exposure. Using the original Nabataean-dressed surfaces as baselines, weathering features like tafoni, channels, and cavities were measured and mapped.

Northern-facing surfaces exhibited the least weathering with 70 +/- 1 0% of the original stone-dressing apparent with no recesses exceeding 2 cm in any dimension. The relatively minor weathering occurring on northern faces can be attributed to decreased weathering from lichens, since they are rarely found on other surfaces, and that less sunlight permits less frequent wetting and drying cycles. Southern faces displayed 40 +/- 10 % of the original dressing remaining with the scarce cavities rarely exceeding 15 cm in any dimension. The increased weathering on southern faces can be attributed to increased solar flux increasing daily heating and cooling cycles. Western faces and eastern faces, however, displayed the greatest surface recession with hardly any remaining original Nabataean stone-dressing (< 10 %) and numerous tafoni and cavities often exceeding 20 cm across. This was attributed to the ideal daily and yearly balance that occurs on these faces. It is speculated that the temperatures are hot enough to expand the rock, but also wet enough to cool it quickly - important cycles known to speed up rock weathering. These are important findings since prior research has shown the efficacy of wetting/drying and heating/cooling in and region sandstone weathering, but this study may explain the unique balance between moisture and insolation-induced weathering through the comparison of differing aspects on similar sandstones under similar microclimates - a previously obscure relationship important in understanding the slow deterioration of Petra’s important architectural heritage.