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1.
The uplifted Pleistocene terraces along the coast of southern Sinai exhibit a well developed reef system formed during isotope stage 9, and a younger one formed during isotope stage 5. An intermediate reef corresponding to isotope stage 7 occurs only as an erosional relic in the study area. The sediments comprise reefal framestones, peri-reefal facies, coral rubble, and siliciclastic-dominated beach and aeolian facies. The compositional and textural complexity of the sediments leads to a highly variable spatial distribution of diagenetic features. However, the geometric relationships and elemental analyses allow a reconstruction of the general diagenetic evolution: during the major eustatic sea-level highstand of isotope stage 9, the Older Reef was constructed and cemented with aragonite and high-Mg calcite. Climate was probably semiarid with some rainy periods which permitted the installation of ephemeral freshwater lenses, especially during the minor sea-level lowstand within isotope stage 9. In these lenses, and during the subsequent major sea-level lowstand, some freshwater dissolution occurred. The highstand during isotope stage 7 led to the construction of the Intermediate Reef. In the Older Reef, some high-Mg calcite precipitated at that time. Dolomite cement formed either in marine interstitial waters modified by some freshwater input, or in a hypersaline context. Phreatic-meteoric low-Mg calcite cement covers, and partly replaces, previous marine cements and dolomite, but is still attributed to the major highstand of isotope stage 7 when freshwater lenses could develop during minor sea-level lowstands. The subsequent major sea-level lowstand was dominated by an arid climate, and only a little freshwater corrosion occurred. The Younger Reef formed during the major highstand of isotope stage 5. Aragonite and high-Mg calcite cements, as well as some dolomite, are common within the reef, whereas freshwater cements are limited to beach and aeolian facies. Due to tectonic uplift, only the lower part of the Older Reef was reflooded during isotope stage 5, and only some aragonite crystals precipitated on top of dolomite or low-Mg calcite. The interrelationships between tectonics, sea-level variations of different orders, and climatic changes thus had a profound impact on the diagenetic history of these reef systems. 相似文献
2.
黄思静 《沉积与特提斯地质》1990,10(4):9-15
引言众所周知,原始的海相碳酸盐矿物为文石、高镁方解石和低镁方解石,但它们对成岩蚀变极度敏感,在大气淡水成岩环境中,文石和高镁方解石都会转变为成岩低镁方解石,同时,原始的低镁方解石也会有不同程度的蚀变。在进行古代碳酸盐岩的沉积环境和古海洋学研究时,往往需要测定岩石中的微量元素及氧、碳、锶等同位素组成,用以判断古海水 相似文献
3.
Relatively few studies have so far addressed diagenetic processes in Heterozoan carbonates and the role that sediment composition and depositional facies exert over diagenetic pathways. This paper presents a study of Oligocene shallow-water, Heterozoan carbonates from the Maltese Islands. We investigate stratigraphic distribution, abundance and timing of diagenetic features and their relationship to sediment composition and depositional facies. The studied carbonate rocks comprise rud- to packstones of the Heterozoan association predominantly containing coralline red algae, bryozoans, echinoids and benthic foraminifers. XRD analyses show that all high-Mg calcite has been transformed to low-Mg calcite and that no aragonite is preserved. Diagenetic processes include dissolution of aragonitic biota, neomorphism of high-Mg calcitic biota to low-Mg calcite and cementation by fibrous, bladed, epitaxial and blocky cements. Stable isotopes on bulk rock integrated with petrographic data suggest that the study interval was not exposed to significant meteoric diagenesis. We interpret early cementation to have taken place in the marine and marine burial environment. The distribution and abundance of early diagenetic features, determining the diagenetic pathway, can be related to the primary sediment composition and depositional texture. Sorting and micrite content are important controls over the abundance of diagenetic features. 相似文献
4.
Johannes H. Schroeder 《Sedimentary Geology》1973,10(3):179-204
Well-rounded pebbles and cobbles of reef rock, which in bio- and lithofacies closely resembles the Recent algal cup reefs, occur in the basal conglomerate of the Pleistocene Devonshire Formation cropping out along Grape Bay on the south shore of Bermuda. The framebuilders of this rock include coralline red algae, vermetid gastropods, and barnacles. Study by petrographic microscope, electron microprobe, and SEM revealed aragonite-needle and spherulitic cements, high-Mg calcite micrite and palisade cements including calcified algal filaments. Two or three generations of these may occur in a given pore. By analogy with the Recent cup-reef material, on the basis of their composition (high strontium content of aragonite, high magnesium content of calcite) and of circumstantial evidence, these are considered submarine cements.In addition, a vadose blocky low-Mg calcite cement occurs, which never precedes any, but frequently succeedes one, two, or three of the above cements. Its fabrics vary: it may exhibit an increase in crystal size toward the center or not, it may or may not be bounded by the meniscus outline characteristic of the vadose diagenetic environment. The limitation of cement precipitation by a meniscus gives rise to a large diversity of forms determined by respective combinations of solution supply, permeability of the micro-environment, and substrate morphology. To illustrate the diversity, the meniscus cement is shown in relation to sediment particles, aragonite-needle cement, and calcified filaments.From the blocky low-Mg cement, selective neomorphism extends into some aragonitic gastropod shells; it is controlled, in part, by original shell structure. The resulting low-Mg calcite mosaic is characterized by relic structures and plane crystalline boundaries. Aragonite needles between blocky calcite cement and neomorphic calcite were not affected by the process of mineralogic alteration.This study shows that cements recognized earlier in Recent Bermuda cup reefs can be traced into the past and that additions to the diagenetic sequence can be distinguished. Knowledge of these features and their sequences should help decipher the diagenetic history of other fossil reefs. 相似文献
5.
Subías I. Yuste A. Fanlo I. Fernández-Nieto C. González López J.M. 《Geologie en Mijnbouw》1999,78(1):87-102
Mineralogical, textural and geochemical investigations were made to determine the post-depositional evolution of Devonian and Early Carboniferous carbonates from Valle de Tena. The carbonate association is made up of low-Mg calcite, which occurs as micrite, spar cements, neomorphic patches and spar filling veinlets. Non-stoichiometric dolomite and ankerite occur as cements (dolomite also as replacements) in the Middle Devonian, post-dating calcite types. All these phases pre-date tectonic stylolites, indicating compaction after stabilization of the carbonate minerals. Strontium concentrations indicate that Early Devonian and Early Carboniferous micrites initially precipitated as aragonite; Middle and Late Devonian micrites precipitated as high-Mg calcites. Both precursors were diagenetically stabilized to low-Mg calcites through interaction with meteoric waters in phreatic environments. Trace elements in dolomite and ankerite indicate precipitation from Sr-enriched meteoric water. All studied carbonates, except Middle Devonian limestones, precipitated in reducing environments, which favoured incorporation of Fe and Mn. Late calcite generations precipitated from more saline waters than micrites. Light 18O values in micrites suggest alteration mainly in meteoric-phreatic environments. The dolomites and ankerites precipitated from more 18O-depleted fluids than the calcites, suggesting a greater contribution from meteoric waters. Variations in 13C of micrites represent primary secular trends, according to published 13C variations. The 13C oscillations within each succession probably relate to sea-level oscillations. Strontium isotopes also point to a meteoric origin of diagenetic fluids. Model calculations suggest that O and Sr isotopes equilibrated between calcites and fluid at relatively low water/rock ratios, whereas C isotopic signatures are inherited from limestones. 相似文献
6.
引言研究标本由我所碳酸岩组采自海南岛南部的一个地点。在那里,沿岸覆于原生礁之上有一套由生物骨屑(主要是珊瑚)砂、砾所组成的、已被碳酸盐胶结的岩层,其厚约3米左右(图1)。此岩层一般称为“次生礁”。它是由当时原生礁盘上的生物被海浪击碎并冲带到礁盘上沉积下来的,这里属连岛砂堤沉积,它现已完全暴露地表。次生礁在它抬升过程中,下部被海蚀形成海蚀龛。 相似文献
7.
The Pennsylvanian phylloid algal mounds exposed in the Cervatina Limestone of the Cantabrian Zone (NW Spain) developed during the highstands of high-frequency shallowing-upward cycles and lack evidence of subaerial exposure at their tops. Mound core facies are composed of massive bafflestones with variable amounts of calcite cements and anchicodiacean phylloid algae with cyathiform thalli preserved in growth position. Through standard petrographic, isotopic (δ18O and δ13C), major and trace element (Ca, Mg, Fe, Mn, Sr) and cathodoluminescence analyses, five calcite cement phases (cement 1 (C1)–cement 5 (C5)) have been identified filling primary and secondary pores. Early marine diagenesis is represented by micritization and non-luminescent to mottled-dull luminescent high-Mg calcite fibrous marine cement (C1). A dissolution phase then occurred and created vuggy and moldic pores. Based on the absence of field or petrographical or geochemical evidence of exposure, it is inferred that dissolution occurred in near-surface undersaturated marine waters with respect to aragonite related to progressive organic matter oxidation. Secondary porosity was subsequently filled by dull-bright-dull bladed high-Mg calcite (C2), which precipitated in the early shallow burial from marine-derived pore waters. Remaining porosity was occluded by shallow-burial precipitates consisting of non-luminescent scalenohedral low-Mg calcite (C3) followed by non-ferroan dull luminescent calcite spar (C4). Latter phases of calcite spar exhibiting non- and dull luminescence (C5) are associated with burial calcite veins. Low δ18O values (around ?8‰), moderately depleted δ13C values (around 0.5‰) and the homogeneity of trace element contents of carbonate matrix, cements and vein-filling calcites suggest burial isotopic re-equilibration and recrystallization, probably in Early Permian times during post-thrusting orocline formation. 相似文献
8.
Quaternary pedogenic calcretes from the Kalahari (southern Africa): mineralogy, genesis and diagenesis 总被引：2，自引：0，他引：2
N. L. WATTS 《Sedimentology》1980,27(6):661-686
9.
我国海南岛及南海诸岛沿岸,广泛发育海滩岩。1980年我队赴海南岛考察现代沉积时,对海滩岩的分布、岩性特征及其与周围环境的关系进行了观察和采样。样品采自崖县鹿回头三亚湾水尾岭海蚀崖、西洲岛、小东海、东瑁岛、西瑁岛、天涯海角,乐东县莺歌海,文昌县渔业等地(图1)。有关的地质、地貌及岩性特征等,已有许多描述,对海滩岩的岩石学及成岩作用也有许多研究。本文侧重探讨海滩岩的胶结作用及与成岩环境的关系。 相似文献
10.
Pleistocene fluctuations of sea level have left marine and aeolian limestones intercalated with glacial red soils on the Bermuda Carbonate Platform (Atlantic, 64°50W, 32°20N). Successive eustatic highstands of similar amplitude drowned the tectonically stable platform and piled up similar sets of sediments. Up to three Pleistocene beaches are stacked in shorelines sections. Post-depositional diagenetic histories of these beaches can be linked to repeated changes in sea level and pore waters.This paper presents field evidence and petrographic results (microscope, X-ray, cathodoluminescence, SEMEDAX) for the diagenetic histories of two superimposed Pleistocene beaches in Whalebone Bay, Bermuda North Shore. The younger beach was deposited during isotopic stage 5e, about 120 ka ago. The age of the older beach may be isotopic stage 9 or older.Diagenesis drastically altered the older beach before the stage 5e transgression. Primary high-Mg calcite (HMC) and aragonite were no longer present. Marine skeletal grains were instead leached or recrystallized to low-Mg calcite (LMC). Primary and secondary pore space were largely reduced by LMC cement. Lines of needle relics reminiscent of marine aragonite cement occur as inclusions within syntaxial rim cements around echinoderm grains, indicating that a marine influence had at least once interrupted this period of freshwater alteration. Finally, before the rocks became buried by the sediments of the younger beach, a crust of marine, bladed HMC cement was precipitated throughout the pore space.The younger beach consists of skeletal grains that are, apart from the effects of non-selective dissolution, essentially unaltered. The sediments are only weakly lithified by cryptocrystalline LMC showing an alveolar texture, tangential fibres and other features characteristic of calichification. A younger post-depositional marine influence is not recorded.These results suggest that, under favourable conditions, diagenetic processes can document sea-level fluctuations. The recorded fluctuations, however, are difficult to assess because even major sea-level highstands may not produce a diagenetic imprint.
Correspondence to: R. Vollbrecht 相似文献
11.
鲕粒原生矿物识别及对海水化学成分变化的指示意义 总被引：1，自引：0，他引：1
鲕粒是碳酸盐沉积过程中一类非常特殊的颗粒类型, 为研究当时的沉积背景、水动力条件、气候环境, 甚至储层特征提供了重要线索。然而, 鲕粒的矿物组成及控制因素问题, 长期受到忽视。组成鲕粒的原生矿物类型在地质历史时期呈周期性变化, 在显生宙表现为三个以文石和高镁方解石占主导的时期以及两个以低镁方解石占主导的时期, 这也被称作“文石海”和“方解石海”时期。原生矿物的组成, 制约着鲕粒的纹层结构、保存程度以及成岩特征, 还蕴含着海水化学成分变化的线索。鲕粒原生矿物识别主要依据:①原生纹层结构;②保存程度;③微量元素浓度, 尤其是Sr-Mg的浓度。文石质鲕粒受文石不稳定性的影响, 原生结构保存程度较差;一般保存有典型的文石残余纹层结构(例如砖砌结构、溶解变形结构以及偏心结构等);在封闭成岩环境下原生矿物为文石质的鲕粒Sr浓度往往大于2 000 ppm;纹层结构主要为切线状(占主导)和放射状。方解石质鲕粒包括低镁方解石和高镁方解石两种类型:低镁方解石为稳定矿物, 原生结构一般保存良好。尽管高镁方解石也为亚稳定矿物, 但成岩转换后的保存程度好于文石。两者Sr含量一般均低于1 000 ppm, Mg含量一般在0~20 mol % MgCO3(两者以4 mol % MgCO3为界)。高镁方解石受成岩作用影响, 在纹层中往往保留有微粒白云石包裹体;海相地层中保存的方解石质鲕粒为放射状或同心-放射状结构。另外还存在一类由两种矿物共同构成的双矿物鲕粒, 可以通过分析两类纹层在结构和保存特征上的差异进行区分。鲕粒原生矿物成分随时间的波动变化受到海水化学条件, 尤其是Mg/Ca比值, 大气二氧化碳分压以及碳酸盐饱和度的控制。Mg/Ca比值的波动决定着鲕粒原生矿物类型的长期变化规律。一些突发性事件可能会扰动(区域)短时间尺度下鲕粒原生矿物的组成, 造成鲕粒原生矿物的转换。通过研究碳酸盐鲕粒原生矿物特征以及控制因素进而了解海水的化学特征, 是独立于古生物学和地球化学分析之外的一种较为可靠的沉积学方法。 相似文献
12.
Holocene carbonate sedimentation in Lake Manitoba, Canada 总被引：1，自引：0，他引：1
W. M. LAST 《Sedimentology》1982,29(5):691-704
The carbonate mineral suite of the modern offshore bottom sediment of the South Basin of Lake Manitoba consists mainly of high magnesian calcite and dolomite with minor amounts of low-Mg calcite and aragonite. The high-Mg calcite is derived from inorganic precipitation within the water column in response to supersaturation brought about by high levels of organic productivity in the basin. Both dolomite and pure calcite are detrital in origin, derived from erosion of the surrounding carbonate-rich glacial deposits. Aragonite, present only in trace amounts in the offshore sediments, is bioclastic in origin. The upward increase in the amount of magnesian calcite in the post-glacial sediment record is attributed to increasing photosynthetic utilization of CO2 in the lake. Stratigraphic variation in the amount of magnesium incorporated into the calcite lattice is interpreted as reflecting a variable magnesium input to the lake from ground water and surface runoff, and possibly variable calcium removal in the precipitating lake water. The effects of long-term chemical weathering at the source and size segregation explain the changes in dolomite content throughout the section. 相似文献
13.
Shells of the aragonite bivalve Neomiodon (Great Estuarine Group, Jurassic, Scotland) replaced by coarse neomorphic calcite contain oriented relics of the original aragonite ultrastructure. The presence of these relics in such old altered shells, as well as the high Sr content of the replacement calcite, indicate that the process of calcite replacement of aragonite is not a cumulative slow process involving repeated alteration events, but rather a rapid, one-step process. Aragonite relics, once encased in neomorphic spar, will survive as unequivocal evidence of original aragonite mineralogy, barring total remobilization of the enclosing stable calcite, a generally unlikely event. The retention of this residual aragonite and high-Sr calcite supports recent isotopic studies which suggest that the multiple phases of alteration (‘recrystallization’) invoked in earlier literature are unlikely events in the diagenesis of most undolomitized limestones. Retention of aragonite relics appears to be independent of whether alteration occurs in shallow meteoric or, as in the case of our Neomiodon material, deeper burial environments. Pseudopleochroism of the replaced Neomiodon shells appears to be due to organic, largely graphitic, relics, not to the aragonite relics. 相似文献
14.
更新世以来,剧烈的构造运动已将巴布亚新几内亚合恩半岛东北海岸的晚第四纪珊瑚礁阶地抬升上千米.阶地中造礁珊瑚的成岩变化和成岩产物的组构特征反映了该礁的成岩历史,充分体现该区快速构造上升的影响.海水潜流带和淡水渗流带为上升礁的主要成岩环境.生物钻孔、生物碎屑填隙、珊瑚文石针粗化、珊瑚骨骼的溶解和新生变形转化,以及其不同矿物成分和组构的种种胶结物的胶结作用是造礁珊瑚经历的主要成岩作用.地球化学资料表明其成岩变化发生于开放的化学体系之中. 相似文献
15.
Calcitic, aragonitic and mixed calcitic-aragonitic ooids from the mid-Proterozoic Belt Supergroup, Montana 总被引：2，自引：0，他引：2
MAURICE E. TUCKER 《Sedimentology》1984,31(5):627-644
A great variety of ooid types occurs within the Siyeh and Snowslip Formations of the mid-Proterozoic Belt Supergroup, Montana. Cortical layers are inferred to have been composed either of calcite in a radial-concentric or radial-with-dark-rays fabric or, aragonite in a radial or concentric fabric. The calcitic cortical layers record their original fabrics but the originally aragonitic cortical layers have been replaced by calcite in a range of textures and by quartz and dolomite. Some formerly aragonitic cortical layers are replaced by calcite spar which contains relics of the original cortical structure. Others consist of calcite spar without inclusions, or columnar calcite which grew radially from the nucleus, commonly a calcitic ooid. Some ooids were wholly composed of calcite, others were of aragonite, but two phase ooids were common, mostly consisting of an inner calcitic part and an outer aragonitic part. Probable microdolomite inclusions suggest a high Mg content of the calcitic cortical layers. The depositional environment of these oolites was probably analogous to Baffin Bay, Texas, where a similar range of ooid types is forming today. 相似文献
16.
A marked increase in manganese content from shallow to deep marine lithofacies can be observed within the carbonate fraction of the Middle Ordovician sequence in eastern Tennessee. The distribution of manganese is controlled by: (1) the original aragonite and calcite mineralogy of shallow and deep marine environments, respectively; (2) preferential substitution of manganese for calcium in the rhombohedral structure of calcite; (3) anoxic depositional and diagenetic environments; and (4) possibly, volcanism. 相似文献
17.
Brick-like texture and radial rays in Triassic pisolites of Lombardy,Italy: A clue to distinguish ancient aragonitic pisolites 总被引：1，自引：0，他引：1
Triassic pisolites from the Calcare Rosso, Lombardy, Italy, were formed in a hypersaline vadose environment and now show alternating dolomite and calcite laminae. The calcite consists either of microsparite laminae with a brick-like fabric, or of a mass of mosaic crystals with the external form of square-ended rays.These features suggest that the original laminae and rays were aragonitic, like those of the Holocene supratidal pisolites of the Persian Gulf, which consist of alternating laminae of unoriented nannomicrite with Mg-rich mucilaginous material, and aragonitic fibers with radial orientation separated by mucilaginous films. It is suggested that the transformation to brick-like and ray textures passed through the following diagenetic path: (1) original formation of fibrous aragonite laminae; (2) local aggrading recrystallization of aragonite fibers to large square-ended rays during hypersaline phases; (3) dolomitization of Mg-rich mucilaginous nannomicrite laminae during hyposaline phases; (4) inversion of the aragonite fibers and rays to calcite on a piece-by piece basis that preserved the original textural details, when the pH or Mg/Ca ratio dropped.The brick-like and ray fabrics have not been found in laminae of continental freshwater pisolites because these were deposited as equant and stable crystals of low-Mg calcite. These textures consequently make it possible to establish the chemistry of the depositional and early diagenetic milieu for some ancient pisolitic rocks. 相似文献
18.
Low-Mg calcite marine cement in Cretaceous turbidites: origin, spatial distribution and relationship to seawater chemistry 总被引：2，自引：0，他引：2
Lower Cretaceous (Hauterivian) bioclastic sandstone turbidites in the Scapa Member (North Sea Basin) were extensively cemented by low-Mg calcite spars, initially as rim cements and subsequently as concretions. Five petrographically distinct cement stages form a consistent paragenetic sequence across the Scapa Field. The dominant and pervasive second cement stage accounts for the majority of concretions, and is the focus of this study. Stable-isotope characterization of the cement is hampered by the presence of calcitic bioclasts and of later cements in sponge spicule moulds throughout the concretions. Nevertheless, trends from whole-rock data, augmented by cement separates from synlithification fractures, indicate an early calcite δ18O value of+0·5 to -1·5‰ PDB. As such, the calcite probably precipitated from marine pore fluids shortly after turbidite deposition. Carbon isotopes (δ13C=0 to -2‰ PDB) and petrographic data indicate that calcite formed as a consequence of bioclastic aragonite dissolution. Textural integrity of calcitic nannoplankton in the sandstones demonstrates that pore fluids remained at or above calcite saturation, as expected for a mineral-controlled transformation. Electron probe microanalyses demonstrate that early calcite cement contains <2 mol% MgCO3, despite its marine parentage. Production of this cement is ascribed to a combination of an elevated aragonite saturation depth and a lowered marine Mg2+/Ca2+ ratio in early Cretaceous ‘calcite seas’, relative to modern oceans. Scapa cement compositions concur with published models in suggesting that Hauterivian ocean water had a Mg2+/Ca2+ ratio of ≤1. This is also supported by consideration of the spatial distribution of early calcite cement in terms of concretion growth kinetics. In contrast to the dominant early cement, late-stage ferroan, 18O-depleted calcites were sourced outwith the Scapa Member and precipitated after 1–2 km of burial. Our results emphasize that bioclast dissolution and low-Mg calcite cementation in sandstone reservoirs should not automatically be regarded as evidence for uplift and meteoric diagenesis. 相似文献
19.
湘南泥盆系碳酸盐岩中锶的分布特点及其环境意义 总被引：4，自引：0，他引：4
湘南泥盆系碳酸盐沉积环境,可分为台地和台盆两大类和六种相类型.250块岩样的分析结果表明,Sr和Sr/Ca×1000的含量比值变化与沉积环境密切相关,即由浅水台地相到深水台盆相,其比值从0.27增至2.37.其原因是由于不同沉积环境中碳酸盐矿物组份不同.影响了锶的分布.因此锶的含量可作为相分析的工具. 相似文献
20.
Coral proxy records of sea surface temperature (SST) and hydrological balance have become important tools in the field of tropical paleoclimatology. However, coral aragonite is subject to post-depositional diagenetic alteration in both the marine and vadose environments. To understand the impact of diagenesis on coral climate proxies, two mid-Holocene Porites corals from raised reefs on Muschu Island, Papua New Guinea, were analysed for Sr/Ca, δ18O, and δ13C along transects from 100% aragonite to 100% calcite. Thin-section analysis showed a characteristic vadose zone diagenetic sequence, beginning with leaching of primary aragonite and fine calcite overgrowths, transitional to calcite void filling and neomorphic, fabric selective replacement of the coral skeleton. Average calcite Sr/Ca and δ18O values were lower than those for coral aragonite, decreasing from 0.0088 to 0.0021 and −5.2 to −8.1‰, respectively. The relatively low Sr/Ca of the secondary calcite reflects the Sr/Ca of dissolving phases and the large difference between aragonite and calcite Sr/Ca partition coefficients. The decrease in δ18O of calcite relative to coral aragonite is a function of the δ18O of precipitation. Carbon-isotope ratios in secondary calcite are variable, though generally lower relative to aragonite, ranging from −2.5 to −10.4%. The variability of δ13C in secondary calcite reflects the amount of soil CO2 contributing 13C-depleted carbon to the precipitating fluids. Diagenesis has a greater impact on Sr/Ca than on δ18O; the calcite compositions reported here convert to SST anomalies of 115°C and 14°C, respectively. Based on calcite Sr/Ca compositions in this study and in the literature, the sensitivity of coral Sr/Ca-SST to vadose-zone calcite diagenesis is 1.1 to 1.5°C per percent calcite. In contrast, the rate of change in coral δ18O-SST is relatively small (−0.2 to 0.2°C per percent calcite). We show that large shifts in δ18O, reported for mid-Holocene and Last Interglacial corals with warmer than present Sr/Ca-SSTs, cannot be caused by calcite diagenesis. Low-level calcite diagenesis can be detected through X-ray diffraction techniques, thin section analysis, and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions. 相似文献