Characteristics, evolution and distribution of Quaternary channel calcretes, southern Jordan

Abstract

Cemented and calcretized conglomerates of Quaternary age are found within ancient river channels exposed at various heights (between +1 and +125 m) above the current bed of the Wadi Dana in southern Jordan. In cross-section, the calcrete deposits are typically lensoid in shape and are found infilling palaeochannels cut into the bedrock. The fossilized channel sediments preserve evidence of past river conditions, sediment loads, source areas, phases of river down-cutting and sediment accretion, as well as post-depositional alteration processes.Samples have been analysed in thin section and under the scanning electron microscope in order to determine the calcrete micromorphology, cement types and crystal sizes. The results show that the river deposits have undergone significant displacement and replacement of the detrital grains by CaCO 3 , and this has resulted in the cementation in places of over 4 m of river material. The cements display an alpha-type fabric with no evidence of biogenic activity. The nature of the cement fabric within and between deposits differs as a function of two key variables: (i) the specific location within the channel and (ii) height above the modern wadi floor. Firstly, in many of the deposits cement crystal size varies, with sparite dominating at depth within impermeable palaeowadi channels, whereas on the flanks of the channels and near the top of the channels micrite is the main type of cement. These variations are thought to be a result of differences in the length of residence time of calcium carbonate-rich fluids in different parts of the channel and the spatially varying influence of evaporation. Secondly, distinct changes in cement fabric can be seen in channels of different ages with a reduction in the amount of micrite and an increase in the amount of secondary recrystallized pore-filling spar over time.

Calcrete profile development in Quaternary alluvial sequences, southeast Spain: implications for using calcretes as a basis for landform chronologies

“…On the channel flanks, particularly where these are steep, only small amounts of water are retained and so the amount of cementation occurring is significantly less. Thirdly, the coarse sparitic nature of these horizons is similar in character to channel calcretes described from Quaternary fluvial gravels within both the Tabernas basin of southeast Spain (Nash et al, 2001) and Jordan (MacLaren et al, 2001).…”

Rivers turned to rock: Late Quaternary alluvial induration influencing the behaviour and morphology of an anabranching river in the Australian monsoon tropics

“…Such deposits have been termed valley or channel calcretes, with recent studies and reviews of this extensive literature undertaken by Nash and Smith (2003) and McLaren (2004). However, these dryland studies have focused on the properties, distribution and the development of the actual calcrete deposits in small catchments or large palaeochannels.…”

Environmental impacts of ancient copper mining and metallurgy: Multi-proxy investigation of human-landscape dynamics in the Faynan valley, southern Jordan

“…Sedimentary deposits in the Faynan valley were formed through alluvial, colluvial, and aeolian processes, mostly originating from within the Faynan escarpment McLaren, 2004). Many of the archaeological sites, as well as the agricultural fields, were constructed on geological deposits formed between the late Pleistocene and late Holocene McLaren et al, 2004), and whose composition and depositional history varies with relationship to local and regional paleoclimate regimes (BarMatthews and Ayalon, 2004;Cordova, 2008;Frumkin et al, 1999;Hazan et al, 2005;Rosen, 2007).…”