The Berrazales carbonate spring deposit is a small outcrop constituted mainly by cascade-like geometries. Four main facies have been identified: Fibrous dense macrocrystalline formed by rapid degassing under high-flow conditions; Framestones of coated plant molds formed in moderate energy flow favoured by the presence of biogenic support; Micrite/Microsparite are primary precipitates in which crystalline aggregates nucleated on organic filaments and/or EPS; Banded micrite-coarse crystalline were the result of alternating physical-chemically and biologically induced precipitation in areas of varying flow-velocities. Most facies underwent different degrees of micritization processes. Micrite is distributed as thin lines penetrating the crystals, as irregular patches or as micrite layers. In the first case organic filaments penetrate crystals, suggesting that micritization is mainly biogenically driven. In the latter cases micritization is caused mostly by partial dissolution. Microbe participation in *Manuscript Click here to download Manuscript: Camuera Berrazales Manuscript Revised.doc Click here to view linked References micrite formation increased micrite MgCO 3 content in comparison with coarse crystalline facies. Isotopic analyses show positive δ 13 C values (+2.63 and +4.29‰ VPDB) and negative δ O (-5.65 and-4.48‰ VPDB) values. Positive δ 13 C values clearly indicate fluids of thermal volcanogenic origin. The Berrazales spring deposit studied here very probably is a small part of a larger carbonate building that was largely eroded by fluvial incision. Calculations of spring water temperature give a range from 20ºC to 35ºC, characteristic of a cold to warm spring favouring precipitation of calcite and important biogenic activity (framestones). Although the study deposit has textural characteristics of tufas, provide that the CO 2 sourced from deep fluids, it should be consider as thermogene travertine, being one more example of the difficulty of using those terms for ancient sedimentary deposits. Carbonate springs deposits, very rare in the Canary Islands, are good archives of recent volcanic activity, fluvial processes and vegetation regimes prevailing in the islands in recent times.
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.
Geochemical variations across laminated tufas and travertines may reflect the growth style of the carbonate build-up and not just climate-related changes. This work presents the study of a carbonate deposit, formed on a ravine wall in Gran Canaria Island (Spain), from a broken pipe system used for irrigation of banana plantations. The deposit is a few tens of metres long and has a stepped morphology formed by successive cascade-barriers and pools. The main facies are framestones of coated stems, laminated bindstones, phytoclastic wackestones and silty mudstones, all of which display micritic or coarse crystalline textures. Lamination from a framestone with coarse crystalline texture was studied from a petrological-sedimentological and geochemical perspective, and water palaeotemperatures were calculated. Lamination displaying five orders of magnitude, from daily to annual or higher, was controlled by the discontinuous supply of water. Lamination consists of crystalline laminae-discontinuity couplets at all observed scales. Estimated mean precipitation rates are 0Á7 mm year À1 , but discontinuity of sedimentation at all lamination orders may have involved greater precipitation rates. Whereas elemental geochemistry suggests variable conditions not far from chemical equilibrium, stable isotopes suggest that calcite precipitated under disequilibrium conditions. However, the small dimensions of the deposit and the relatively high flow velocities allowed lack of d 13 C and d 18 O isotope fractionation in CO 2 -HCO À 3 nor in HCO À 3 -calcite, leading to independent temperature calculations, both with mean values of 25°C. Isotopic trends found throughout lamination cannot be explained by strong changes in water temperature nor in d 13 C DIC or d 18 O w . The correction made to eliminate these isotopic trends yielded narrower temperature ranges. This paper discusses the accuracy of temperature estimations despite the difficulties coming from disequilibrium and how isotopic trends through time could be explained by the growth of the deposit and not by climate-related changes.
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