钙华沉积机制的研究现状及展望

通过分析大量相关文献并结合作者近年来的工作成果,总结了四种钙华沉积模式: 泉水、河流障、湖泊以及沼泽钙华沉积;综合讨论了气候环境、水文地质条件、水体的物理化学性质、生物作用等因素对钙华沉积的影响。针对目前研究中存在的问题,作者认为今后的工作要从碳酸钙沉积反应的热力学、动力学和晶体生长等微观过程进行研究,从而更加全面地认识钙华沉积的机制,以便为钙华景观的科学保护提供理论基础。      

钙华体次生有机体系的界面结晶作用研究

本文总结了钙华体次生有机体系中生物群落特征和界面结晶行为,根据生物在碳酸盐沉积中的角色,将钙华体中次生有机体系的界面结晶矿化类型分为生物控制矿化沉积和生物诱导矿化沉积。分述了碳酸钙沉积矿化相关的五种生物代谢活动,讨论了生物胞外聚合物（EPS）对碳酸钙矿物晶型和形貌的影响。针对目前钙华研究中存在的问题,今后应深入研究生物体主要构成元素、生物小分子和生物体内部组织在钙华形成或退化中的作用,进一步厘清钙华体与次生有机体系的多界面溶化方式,为钙华保护修复及钙华退化治理措施提供科学依据。      

温泉钙华沉积的影响因素

钙华是在泉水、河水、湖水、洞穴周围沉积的非海相碳酸钙沉积物。钙华是陆地水循环过程中物质迁移的一种表现形式,研究钙华的形成有助于了解局部水文循环中的物质迁移规律并间接了解古气候与古水文地质条件。部分温泉的泉口附近沉积有形态多样的钙华。本文综述温泉钙华的形成过程、钙华沉积的主要影响因素和它们之间的相互影响关系。水化学条件是钙华沉积的物质基础和必要条件,水动力条件是钙华沉积的充分条件,生物效应对钙华沉积起到加强的作用,沉积环境通过影响水化学条件或水动力条件间接控制钙华的沉积。     

钙华生物沉积作用研究进展与展望

弄清钙华生物沉积作用有助于更好地理解钙华微岩相结构和地球化学特征的气候环境指示意义。总结和综述了与钙华沉积相关的生物群落、生物成因钙华微岩相结构、钙华生物沉积作用过程及其对钙华地球化学特征影响的研究进展,并展望了未来的研究重点。细菌、藻类和苔藓等广泛参与到钙华沉积中,形成了许多不同类型的孔隙结构、晶体结构和纹层结构。生物沉积过程主要包括:①生物生长扰动水流使得CO2逸出;②代谢作用(如光合作用)过程诱导碳酸钙沉积;③"表面控制"过程影响晶体成核及生长。生物沉积作用驱动了元素的迁移转化,对沉积水体和钙华地球化学特征具有重要影响。钙华在地球生物学研究中具有重要潜力,未来需要加强现代钙华沉积中的物理化学和生物过程相互作用机制及其各自贡献的量化研究,以便准确地解译钙华沉积记录。     

雪宝顶区块流域钙华形成的生物作用研究

钙华不仅具有重要的景观旅游价值,而且对确定区内碳酸盐沉积特征、环境演化规律及同期环境生物的作用与贡献有重要的研究意义.本文在对比国内外典型钙华特征的基础上,以黄龙和九寨沟为例,对雪宝顶区块流域内钙华的沉积特征、环境化学与生物作用进行阐述,指出了雪宝顶区块流域冷水型钙华的形成与演化是化学沉积-溶解作用、生物沉积与溶蚀作用...     

钙华非经典沉积的纳米生长过程与调控机制初探——以九寨沟—黄龙钙华形成为例

钙华是自然界重要的岩溶碳酸盐沉淀之一,其形成过程往往受到生命活动的影响,弄清钙华生物沉积作用有助于更好地理解钙华微岩相结构和地球化学特征的气候环境指示意义。本文以黄龙-九寨沟钙华形成为例,阐述黄龙-九寨沟现代钙华纳米结晶特征、纳米钙华的生长和集合体形态,分析模拟实验中生物有机质对钙华生长和形貌的调控原因,揭示了生物活动和代谢产物对纳米钙华成核、生长及钙华晶体形貌的调控两途径四阶段机制;为探究钙华成因、碳酸钙生长调控机制、钙华退化的因素及其保护和可持续利用钙华景观具有重要的科学价值。      

塔里木盆地塔北与塔中地区东河砂岩段沉积特征对比

塔里木盆地东河砂岩是中国首例海相深层含油气沉积储层.笔者通过对塔里木盆地地质和地球物理资料综合研究发现,塔中和塔北东河砂岩均具有较高的成分和结构成熟度、典型的海相粒度参数和微量元素组合、明显的滨浅海沉积构造等特征,但在沉积特征细节和沉积环境等方面还存在着差异.塔北地区东河砂岩段沉积于滨岸及障壁岛-泻湖环境,塔中地区东河砂岩段沉积于河口湾-滨岸环境.进而阐明了塔中和塔北东河砂岩段沉积特征的垂向序列和沉积相平面分布特征.     

美国西尔斯盐湖钙华研究综述

钙华具有重要的科研价值.美国加利福尼亚州西尔斯湖内北部、中部和西南部广泛发育钙华丘,丘状体的高度从几厘米至45 m不等,通常高度为5～12 m.钙华丘内存在4种沉积相,分别为多孔海绵状钙华沉积相、结壳状钙华沉积相、柱状钙华沉积相和薄层结壳状钙华沉积相.从时空分布来讲,钙华呈两种沉积层序,分别为多孔海绵状钙华沉积相-结壳...     

塔中-塔北志留系沉积层序的不对称结构及其构造意义

志留系沉积期塔里木为一地势相对平坦、水体较浅的陆表海盆地,总体充填一套碎屑海岸和三角洲体系,从下至上可划分出5个三级层序。塔中和塔北志留系沉积层序表现出明显的不对称结构,塔北地区柯坪塔格组三级层序SQ-Skp1、SQ-Skp2和SQ-Skp3沉积较完整,发育潮坪、浅海陆棚、滨岸-三角洲体系;而塔中地区缺失SQ-Skp1和SQ-Skp2层序,SQ-Skp3以潮坪体系为主,局部发育小型三角洲。与此相对,塔中地区塔塔埃尔塔格组层序SQ-Stt沉积完整,而塔北地区缺失SQ-Stt水进体系域红泥岩段。塔中和塔北志留系沉积层序的不对称结构反映了塔中和塔北构造隆升的差异和演化,奥陶末构造运动对塔中影响较大,造成塔中隆起的隆升并一直处于水上隆起,直到柯坪塔格组上段SQ-Skp3层序沉积期才淹没充填,随后持续沉降,形成了完整的塔塔埃尔塔格组层序SQ-Stt;奥陶末构造运动对塔北影响较小,西部英买力地区局部隆升,而东部持续沉降,直到柯坪塔格组沉积之后塔北东部出现较大规模隆升,形成明显的上超不整合,并造成塔塔埃尔塔格组层序SQ-Stt水进体系域红泥岩段缺失。塔中和塔北构造演化控制了盆地的沉积层序和储盖组合发育,塔中缺失下储盖组合,而塔北缺失上储盖组合,对志留系圈闭形成和油气保存具有重要的影响。     

四川黄龙钙华藻类及其生物岩溶作用

从探索黄龙钙华的生物成因角度出发,对黄龙钙华藻类进行了采集、鉴定和分析,并对钙华藻类的生物岩溶作用做了初步探讨。研究得出黄龙钙华藻类分属于4门19属86种,优势种属为Tolypothrix属、Gloeocapsa属和Cymbella属。黄龙景区不同环境区域的优势藻类有所不同,藻类参与的碳酸盐沉积在不同岩溶景观中所起作用也有所差异。其中蓝藻参与的碳酸盐沉积主要表现于黄龙钙华坝景观的形成过程中,由硅藻参与碳酸盐沉积主要表现于斜坡滩华景观的形成过程中。藻类既能在钙华形成过程中发挥作用,藻类的生长也能侵蚀破坏钙华景观,在长期缺乏岩溶水补给的条件下,藻类对钙华景观的破坏性尤为突出。      

Biological Processes Responsible for Travertine Deposition: A Review and Future Prospect

The investigation of biological processes responsible for travertine deposition allows us to better understand the travertine petrographic and geochemical signatures as proxies of climatic and environmental change. This paper reviewed the organisms associated with travertines, the biotic micro-fabrics formed within travertines, the biological processes associated with travertine precipitation and their controls on travertine geochemical properties. Prospects of the future research on biological processes responsible for travertine precipitation were provided. Bacteria, algae and mosses are the most important organisms that involve in the precipitation of travertines. The growth of these organisms leads to the formation of a range of various porosity, crystal fabrics and lamination within travertines. Three main biological processes responsible for travertine deposition can be classified, including \mathrm{①} a process of aquatic plant growth generating a turbulent condition and consequent CO₂ evasion, \mathrm{②} a metabolic (mainly photosynthetic) process mediating carbonate precipitation and \mathrm{③} a ‘surface-control’ process influencing nucleation and crystal growth. These processes play an important role in the migration and transformation of elements in travertine-depositing system and thus determine the properties of water chemistry and geochemistry of carbonate deposits. Travertine deposits have great potential to be valuable records for the geobiological study. Further investigation is required to simultaneously track biotic and abiotic interactions in modern travertine-depositing environments and quantify the contribution of these two processes and apply the results to accurately interpret travertine records.     

Determination of horizontal extension from fissure-ridge travertines: a case study from the Denizli Basin,southwestern Turkey

Travertine deposits reflect some aspects of the regional tectonics because of the close association between travertine deposits and active fractures, that later of which provide conduits along which travertine-depositing waters may rise. Fissure-ridge travertines form above extensional fissures which are located in the hanging walls of normal faults, in step-over zones between fault segments, or in active or recently active) volcanic provinces. Numerous active and inactive fissure-ridge travertines are located in the hanging walls of normal faults in the Denizli Basin. A typical fissure-ridge comprises a central fissure along its long axis and flanking bedded travertines dipping away from the fissure. Central fissures of travertine ridges have been dilating since the initiation of the fissures. Samples from both the margins and centres of banded travertine deposits were dated by Th/U methods in order to determine dilation rates. Individual fissures have been dilating at average rates of between 0.008 and 0.1 mm yr^–1 during travertine deposition, and ~ 0.001 and 0.007 mm yr^–1 after cessation of travertine deposition. There is a noticable decrease in dilation rate from west to east in the Denizli Basin, and this decrease in dilation rate may be related to decrease in overall extension in southwest Turkey, which decreases eastward.     

U/Th dating of fissure ridge travertines from the Kirsehir region (Central Anatolia Turkey): structural relations and implications for the Neotectonic development of the Anatolian block

Travertines exposed in several locations in Central Anatolia are the important lithological product for the interpretation of local neotectonics. The fissure-type travertines provide significant information about stress orientation during deposition. Two travertine masses cropping out in the Kirsehir region have been studied and dated by the U-series method to obtain new chronological constraints, determine dilation rates and contribute to studies on the recent tectonic evolution of the area. The Kusdili and Kayabasi travertine masses are located on the hanging wall of the Kirsehir Fault, similar to numerous fissure ridge banded travertine deposits which are inactive today in the region. While individual fissures of the Kusdili travertine mass (Late Pleistocene-Holocene) have been dilated at rates of between 0.303 and 0.386 mm yr–1 during deposition, the Kayabasi travertine mass (Late Pleistocene) produced measured dilation rates of between 0.136 and 0.187 mm yr–1. The central fissures, filled by banded travertine, roughly follow the ridge crests. While the ridge crest has a NNE-SSW trend in the Kayabasi travertine mass, the ridge crest of the Kusdili travertine mass shows a NE-SW trend. This difference may be related to the clockwise rotation of the stress tensors from Late Pleistocene to Late Pleistocene-Holocene in the region.     

Determination and significance of the Mn(II) Zero-Field Splitting (ZFS) interaction in the geochemistry of travertines

An analytical approach, based on the electron paramagnetic resonance (EPR) spectroscopy of Mn(II) in travertines, has been developed in order to obtain relevant information about the local inhomogeneity of calcite and about the thermodynamic conditions which control the formation of travertine deposits. This information is crucial to constrain the precipitation of travertine under different geochemical contexts. An empirical correlation between the spectral features and the zero-field splitting (ZFS) interaction has been established through numerical simulations of EPR spectra. The variability of the investigated parameters and the applicability of the method have been tested on several travertines from Central Italy.     

Geochemical mechanisms of travertine formation from fresh waters in southern Siberia

The subject of study was the chemical composition of common fresh-water springs precipitating travertines in tectonically passive regions of the Kolyvan'-Tomsk folded area and northwestern Salair. Attention was paid to the specific character of manifestation, mineralogy, and petrography of the produced travertines. Results of the study of isotopic composition of carbon in hydrocarbonate ion of waters and carbonate travertines are reported. It is shown that the genetic type of CO₂ accompanying the formation of travertines is biogenic. Study of the equilibrium of the underground waters with aluminosilicate and carbonate minerals has shown that the travertines are the product of evolution of an equilibrium-nonequilibrium water-rock system. New mechanisms of travertine formation from cool fresh waters are proposed.     

Depositional system and palaeoclimatic interpretations of Middle to Late Pleistocene travertines: Kocabaş, Denizli,south‐west Turkey

Travertine deposits in western Turkey are very well‐exposed in the area of Kocaba?, in the eastern part of the Denizli Basin. The palaeoclimatic significance of these travertines is discussed using U/Th dates, stable isotope data and palynological evidence. The Kocaba? travertine occurrences are characterized by successions of depositional terraces associated with palaeosols and karstic features. The travertines have been classified into eight lithotypes and one erosional horizon, namely: laminated, coated bubble, reed, paper‐thin raft, intraclasts, micritic travertine with gastropods, extra‐formational pebbles and a palaeosol layer. The analysed travertines mostly formed between 181 ka and 80 ka (Middle to Late Pleistocene) during a series of climatic changes including glacial and interglacial intervals; their δ¹³C and δ¹⁸O values indicate that the depositional waters were mainly of basinal thermal origin, occasionally mixed with surficial meteoric water. Palynological results obtained from the palaeosols showed an abundance of non‐arboreal percentage and xerophytic plants (Oleaceae and Quercus evergreen type) indicating that a drought occurred. Marine Isotope Stage 6 is represented by grassland species but Marine Isotope Stage 5 is represented by Pinaceae–Pinus and Abies, Quercus and Oleaceae. Uranium/thorium analyses of the Kocaba? travertines show that deposition began in Marine Isotope Stage 6 (glacial) and continued to Marine Isotope Stage 4 (glacial), but mostly occurred in Marine Isotope Stage 5 (interglacial). The travertine deposition continued to ca 80 ka in the south‐west of the study area, in one particular depression depositional system. Palaeoenvironmental indicators suggest that the travertine depositional evolution was probably controlled by fault‐related movements that influenced groundwater flow. Good correlation of the stable isotope values and dates of deposition of the travertines and palynological data of palaeosols in the Kocaba? travertines serve as a starting point for further palaeoclimate studies in south‐west Turkey. Additionally, the study can be compared with other regional palaeoclimate archives.     

Rapid facies changes in Holocene fissure ridge hot spring travertines, Rapolano Terme, Italy

Holocene hot water travertine continues to form at Terme San Giovanni, near Rapolano Terme, central Italy, although artificial diversion of the water has reduced deposition. Mesothermal water (≈38–39 °C) emerging from fault-controlled vents located on a hilltop has created a linear fissure ridge 240 m long and up to 10 m high. Active parts of the ridge crest are covered by small cones; inactive parts are locally neotectonically fissured and have small pools. Ridge deposits include crystalline crust, paper-thin raft and shrub lithotypes. The ridge has both smooth and terraced marginal slopes, dominated by crystalline crusts with small shrubs in terrace pools. At the base of the ridge, there is a rapid transition to lateral flats and depressions, where water from the ridge collects and deposits shrub, irregular pisoid, reed, paper-thin raft and fine-grained and organic-rich travertines. Water channelled to nearby valley sides deposits thick crystalline crusts on valley slopes and waterfall overhangs, locally with small pools filled by smooth spherical pisoids. On the valley floor, mixing of waters forms varied stream-fill deposits that include micritic reed, paper-thin raft and coated bubble travertines. The diversity of travertine facies observed results from the location of the Terme San Giovanni hot springs on a hill crest, thus providing a wide array of downslope locations for further deposition. The abrupt facies transitions observed are characteristic of hot spring carbonates and result from a combination of rapid decrease in precipitation away from vents, variations in local surface topography and the feedback effect of travertine deposition itself, which dams and diverts water flow.