The role of climate and aeolian dust input in calcrete formation in volcanic islands (Lanzarote and Fuerteventura, Spain)

Abstract

Calcretes are widely described in non-marine settings with carbonates in their catchment, or vicinity areas, but in volcanic islands without carbonates in their substrate, calcretes are not very common. In Lanzarote and Fuerteventura Canary Islands, characterized by impressive volcanic landscapes, the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits. In these settings very well-developed calcretes cover large areas of the present landscape. The source of calcium required for the formation of these calcretes has not been discussed in much detail till now, although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes. The petrological and geochemical studies ( 87 Sr/ 86 Sr ratios, δ 13 C, δ 18 O, major, trace and REE) carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes. Canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits. Our study indicates that these interbeddings were the result of several stages in which, during dry periods, aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants, insects and bacteria played an important role in carbonate precipitation. The δ 18 O (−2.70 to +2.22‰ VPDB) and δ 13 C (−8.21 to +0.24‰ VPDB) values indicate that calcretes were formed by pedogenic processes. Comparison of calculated Δ 18 O values for the Canary calcretes with continental mid-latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island (oceanic) settings. Calcrete 87 Sr/ 86 Sr ratios (0.706357 to 0.709208) show strong affinity with those obtained in aeolian carbonate dust and marine deposits, and are relatively different from those obtained in basalts. REE, major and trace element concentrations show that Ca-bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the Sahara and Sahel or sand dunes.

Origin of calcium in pedogenic carbonate nodules from silicate watersheds in the Far North Region of Cameroon: Respective contribution of in situ weathering source and dust input

“…The present study demonstrated that the Ca contribution from in situ weathering is significant, which is different from many other studies emphasizing a dominance of atmospheric inputs (i.e. Quade et al, 1995;Capo and Chadwick, 1999;Chiquet et al, 1999;Hamidi et al, 2001;Van der Hoven and Quade, 2002;Rech et al, 2003;Lintern et al, 2006;Dart et al, 2007;Huerta et al, 2015). Only three studies reported a dominance of in situ weathering i.e.…”

“…For instance, in Morocco, Hamidi et al (2001) stated that dust is the main Ca source of secondary carbonates observed on a Ca-rich bedrock, 200 km inland. In the Canaries Island, Huerta et al (2015) studied secondary carbonates on Ca-rich bedrocks close to the coastline and they considered dust as the main Ca source instead of sea spray. In the Far North Region of Cameroon, 1000 km inland, the present study emphasized the importance of the in situ weathering, especially on Carich bedrock.…”

The antiquity of the Sahara Desert: New evidence from the mineralogy and geochemistry of Pliocene paleosols on the Canary Islands, Spain

“…1a). African dust is reported as a component of modern soils on the Canary Islands (Muhs et al, 2010) and is also found in paleosols of Pleistocene age (Huerta et al, 2015;Muhs et al, 2016;Menéndez et al, 2019;Roettig et al, 2019). These studies have demonstrated the presence of an African dust component by identification of minerals exotic to the Canary Islands.…”

Sedimentology and geochemistry of a human‐induced tufa deposit: Implications for palaeoclimatic research

“…However, the sample with the lowest δ 13 C was the one containing trace amounts of quartz (sample CAL‐5), not present in Gran Canaria rocks, but of aeolian origin. Consequently, quartz may be accompanied by variable amounts of carbonate grains derived from marine limestones (Menéndez et al ., ; Huerta et al ., ). If this sample is excluded, the δ 13 C range changes to +5·84 to +4·84‰ VPDB (mean = +5·47‰), whereas the range in δ 18 O remains invariable.…”