Chemical and stable isotope composition of recent hot-water travertines and associated thermal waters, from Egerszalok, Hungary: Depositional facies and non-equilibrium fractionation
Chemical and stable isotope composition of recent hot-water travertines and associated thermal waters, from Egerszalok, Hungary: Depositional facies and non-equilibrium fractionation
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DOI：
10.1016/j.sedgeo.2008.08.004
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发表时间：
2008-11-15
影响因子：
2.8
通讯作者：
Kovacs, Magdolna B.
中科院分区：
文献类型：
--
作者：
Kele, Sandor;Demeny, Attila;Kovacs, Magdolna B.
结合岩相学，矿物学，地球化学和稳定同位素分析进行了积极形成Egerszalok钙华丘，以确定碳酸盐沉淀的因素，从而影响使用钙华古气候重建。氧、碳和氢的稳定同位素分析表明，生物和非生物因素控制着钙的沉积。与形态有关的释气过程对同位素组成有重要影响。持续的CO2脱气和温泉口和系统远端之间热水的温度变化，导致沉淀的碳酸盐岩的稳定碳和氧同位素组成增加（相对于V-PDB从+2.7到+4.3份千分之一，相对于V-SMOW从+10.5到+14.7份千分之一）。在弹簧孔（T类似于67摄氏度）的方解石几乎由纯方解石组成，其δ C-13值为+2.7千分之一（相对于V-PDB），使分类成为温成岩和热成岩之间的中间层。在较低温度的水中，远离泉孔，不同数量的具有较高Sr浓度的文石（5-35%）从溶液中沉淀出来。这一现象在热泉碳酸盐沉积中是例外的，并且可以用由于与形态相关的释气而导致的快速碳酸盐沉淀来解释。热水的氧和氢同位素测量证实蒸发导致有限的动力学同位素分馏。然而，δ O-18值的钙钛矿没有显示同位素偏移远离平衡分馏曲线。这很可能与方解石的快速沉淀和沿着流路的输送有关。这是从实验曲线略有位移，并确定一个经验的“曲线”。我们的研究表明，这种转变可能会导致约8摄氏度的差异，在古温度计算取决于分馏曲线使用。(C)2008 Elsevier B. V.保留所有权利。
Combined petrographical, mineralogical, geochemical and stable isotope analyses were conducted on an actively forming Egerszalok Travertine mound to determine the factors that govern carbonate precipitation and thus influence the use of travertines in paleoclimate reconstruction. Stable isotope analyses of oxygen, carbon and hydrogen demonstrate both biological and abiological factors to control travertine deposition. Processes of morphology-related outgassing had major effects upon isotopic composition. Continuous CO2 degassing and temperature change of the thermal water between the spring orifice and distal parts of the system, caused stable carbon and oxygen isotope compositions of the precipitating travertines to increase (from +2.7 to +4.3 parts per thousand relative to V-PDB and from +10.5 to +14.7 parts per thousand relative to V-SMOW, respectively). The travertines at the spring orifice (T similar to 67 degrees C) are composed of almost pure calcite with a delta C-13 value of +2.7 parts per thousand (relative to V-PDB) enabling classification as intermediate between thermometeogene and thermogene. In lower temperature water, away from the spring orifice, various amounts of aragonite (5-35%) with higher Sr concentrations precipitate from solution. This phenomenon is exceptional in hot spring carbonate deposits and could be explained by fast carbonate precipitation due to the morphology-related outgassing. Oxygen and hydrogen isotope measurements of the thermal water confirmed evaporation to be causing limited kinetic isotope fractionation. However, delta O-18 values of the travertine do show isotope shifts away from the equilibrium fractionation curve. which is most probably related to the rapid calcite precipitation and transportation along the flow path. Our data closely follow the tempera ture-Delta O-18(calcite-water) relationship observed for other travertine localities. This is slightly displaced from the experimental curve and determines an empirical 'travertine curve'. Our study shows that this shift may result in an approximately 8 degrees C difference in paleotemperature calculations depending upon which fractionation curve is used. (C) 2008 Elsevier B.V. All rights reserved.