Sedimentation Geochemistry and Environmental Changes during the Late Pleistocene of Paleolake Qarhan in the Qaidam Basin

On the basis of the analyses of TOC, CaCO3, δ13Corg, δ18O, and δ13C of the shell bar section in the Qaidam basin, and compared with grain size data, the environmental change history of the high water level of paleolake Qarhan was reconstructed and it could be divided into five stages. From 39.7 to 35.8 kaBP was the development period of high paleolake level. From 35.8 to 33.6 kaBP and 33.6 to 27.2 kaBP, TOC and CaCO3 contents and δ18O values were high, whereas, δ13Corg values and median size content were low, reflecting a warm-humid climate and high lake level. During 27.2-22.3 kaBP and 22.3-17.5 kaBP, both temperature and the lake level were lower than those in the previous stages, but the climate was still warmer and more humid than that of today. The lake level decreased between 32.4 and 32.2 kaBP, 30.4 and 29.8 kaBP, and 28.4 and 27.2 kaBP. Generally, the climate was warm and humid in Qaidam basin and the high lake level sustained between 39.7 and 17.5 kaBP. The lake retreated abruptly at 17.5 kaBP, with a very strong increase in evaporation, which resulted in salt formation and the extinction of Corbicula.     

Eustasy and sea water Sr composition: application to high-resolution Sr-isotope stratigraphy of Miocene shallow-water carbonates

Oceanic ⁸⁷Sr/⁸⁶Sr‐isotope ratios are strongly influenced by rates of silicate weathering and therefore linked not only to glaciation but also to sea‐level change. The present study combines analysis of sequence stratigraphy and basin architecture with Sr‐isotope stratigraphy in Miocene shallow‐water sediments in southern Portugal and Crete (Greece). The common method is to use smoothed global sea water Sr‐isotope reference curves but here a different approach is chosen. Instead, measured Sr‐isotope curves are correlated with unsmoothed reference curves by identification of similar fluctuations in the order of several 100 kyr. Transgressive intervals are characterized by increasing Sr‐isotope ratios interpreted as corresponding to intensified silicate weathering as a consequence of deglaciation, while lowstand deposits have low Sr‐isotope ratios. Comparison of Sr‐isotope curves and sedimentary sequences in the studied basins with independent global δ¹⁸O data and data on global sea‐level might suggest a general relationship, supporting a connection to global climate change. Because of these relationships, the method presented herein has a high potential for use in high‐resolution age dating and is also applicable in shallow‐water sediments.     

川东南地区洗象池组碳氧同位素特征、古海洋环境及其与储集层的关系

本文在野外剖面调查的基础上,结合薄片观察,对川东南地区三汇剖面寒武系洗象池组237块碳酸盐岩样品进行了系统的碳氧同位素组成研究,结果表明,δ~(18)O值主要分布在-8‰～-6‰,平均为-7.63‰;δ~(13)C值介于-5.53‰～3.44‰之间。利用碳氧同位素数值计算古盐度及古温度结果表明,绝大多数Z值高于120‰,且δ~(13)C值大于-2‰,古海水温度主要集中在19～25℃,说明整体为海水-咸化海水沉积环境与温暖或炎热的亚热带气候。认为洗象池组沉积期海平面变化有五个阶段:早期缓慢上升与下降,中期快速海侵,中后期缓慢海退,后期动荡,末期海退。三汇剖面洗象池组储集层岩性主要为颗粒云岩及晶粒云岩,储集空间以溶蚀孔洞、粒间孔与晶间孔为主。多期的海平面的下降,对应碳同位素多旋回负漂,从而发育向上变浅的多旋回韵律性地层,形成纵向上的多套储集层,洗象池组储集层的形成与演化受海平面变化控制,主要发育在古地貌较高处与滩体向上变浅旋回的上部。另外,依据δ~(13)C值显著的正漂移,明确了芙蓉统地层的底界,为四川盆地寒武系地层的划分提供了证据。     

Early Miocene Mosses from Weichang,North China,and their Environmental Significance

Twenty-seven moss specimens collected from the Guangfayong section （Early Miocene,22.1 Ma） of the Weichang District,North China were investigated in the present study.Based on the morphological and anatomical features of gametophytes,all specimens were found to belong to three species：Leptodictyum riparium,Drepanocladus subtrichophyllus sp.nov.,and Amblystegium varium,all of which belong to the family Amblystegiaceae.The microhabitats and living environments of fossil mosses were also investigated based on comparison with living mosses.The results suggest that these mosses grew primarily at the edges of rivers,streams,and lakes and favored being submerged in streams or lakes in the Weichang District in the Early Miocene.     

青藏高原北部中新统五道梁群湖相沉积碳氧同位素变化及古气候旋回

通过对中新统五道梁群湖相沉积进行全岩心钻探和碳氧同位素测试,获得青藏高原北部中新世早期古环境变化和古气候旋回的重要地质记录.五道梁群约150 m湖相沉积以灰岩、白云质灰岩与泥灰岩为主.仅在深度50.0～51.0 m出现湖相沉积间断,上下均为连续湖相沉积.深度140～145 m湖相沉积碳氧同位素剧烈变化,碳同位素(δ13C/‰)出现2次最低峰值,氧同位素(δ18O/‰)出现2次最高峰值;深度140.7 m湖相沉积碳同位素(δ13C/‰)和氧同位素(δ18O/‰)同时出现极低值.对应于渐新世/中新世界线深海沉积记录的Mi-1全球古气候事件.深度140.7～14.2 m湖相沉积碳氧同位素记录了Mi-1期后7次1.2 Ma天文周期的古气候旋回,深度62.6～9.86 m湖相沉积碳氧同位素记录了9次周期约17.4 ka的古气候旋回.根据湖相沉积碳氧同位素记录的古气候旋回,推断青藏高原北部五道梁盆地中新世早期古大湖发育时期为(24.1±0.6)Ma～(14.5±0.5)Ma,年均气温变化范围为19～21℃,平均约20.0℃.     

鄂尔多斯奥陶系碳酸盐岩碳氧同位素特征及其意义*

鄂尔多斯古生代海相地层沉积厚度巨大。鄂尔多斯奥陶系碳酸盐岩的碳氧同位素组成受后期成岩作用影响较小,基本保留了原始海洋的同位素组成： δ¹³C值分布于-7.30‰～2.26‰之间,均值-0.30‰;δ¹⁸O值分布于-13.14‰～-1.94‰之间,均值-6.38‰,碳氧同位素组成与全球基本一致。区域上,鄂尔多斯西缘具有相对较高的δ¹³C值,南缘次之,而东缘最低。纵向上,碳同位素组成逐渐增重,并在中晚奥陶世发生明显的正向偏移,δ¹³C均值由马家沟组的-0.36‰增加到平凉组的0.15‰,至背锅山组增加至0.68‰。碳同位素的区域分布差异表明鄂尔多斯西缘水体相对较深,南缘次之,东缘相对较浅,由早奥陶世至晚奥陶世水体逐渐加深,碳同位素组成反映的海平面变化趋势与沉积相演化一致。鄂尔多斯西南缘中晚奥陶世碳同位素组成的正向偏移,标志着较高的生产力和有机碳埋藏率,具有重要的石油地质学意义,西南缘的平凉组/乌拉力克组和背锅山组是下古生界最重要和有效的烃源岩层。     

浙江江山灯影组碳、氧同位素特征

通过测试分析了浙江江山灯影组碳酸盐岩的碳、氧同位素特征。结果显示δ^13C值在-2．11‰～2．71‰之间，底、顶部表现为负异常，主体部分比较平稳，变化频率不大。呈微弱的降低趋势；δ^18O值在-3．52‰～-8．76‰之间变化，整体比较平稳，从底到顶呈略降低的变化趋势。浙江江山碳、氧同位素的特征与国内外同期地层非常相似，具有全球可对比性，反映浙江江山地区在灯影初期海平面短暂下降，随后海洋环境相对稳定，直到灯影末期，与全球古环境发生强烈变化一样，本区海洋环境也发生了强烈变化。     

罗布泊中更新世以来盐湖碳酸盐碳氧同位素组成及其古环境意义

罗布泊是欧亚大陆腹地塔里木盆地东端的典型内陆干盐湖,中更新世以来在其北部尤其罗北凹地发育了巨厚的蒸发岩沉积是对全球变冷和青藏高原隆升的积极响应。通过对罗北凹地第一口深钻LDK01孔蒸发岩系中203个样品的自生碳酸盐含量、碳氧同位素测试与分析,讨论了罗布泊中更新世以来的古环境演化特征。研究表明:(1)δ~(18) O和δ13 C协同正向演化,但在蒸发作用强烈的干旱封闭湖泊中,流域降蒸比(P/E)的变化对湖泊水体δ~(18) O影响最为显著;(2)δ~(18) O和δ13 C周期性波动震荡特征,反映干湿交替的环境以及周缘水体对罗北凹地的补给;(3)罗布泊湖盆干旱加剧演化可能并非只受全球变化单一因素驱动,而是全球气候变化和高原隆升共同作用的结果。     

豫西宜阳地区三叠纪早期孙家沟组上段湖相碳酸盐岩碳氧同位素和古环境分析

孙家沟组是华北板块二叠纪和三叠纪转折时期的沉积记录,选择记载气候变化的材料,揭示气候的连续性变化,对于分析华北板块在这一转折时期古环境的重大变革具有重要意义。本项研究选择地层出露良好的华北板块南部豫西宜阳地区,以孙家沟组上段呈韵律型发育的薄层碳酸盐岩为研究对象,分析这些碳酸盐岩层中碳酸盐矿物的碳氧同位素组成及其变化,结合宏观沉积环境的分析,揭示这些碳酸盐岩层的成因,以及它们所蕴含的古环境信息。研究表明,孙家沟组上段碳酸盐岩的碳酸盐矿物主要为自生碳酸盐,且没有发生显著的后期变化,碳氧同位素组成及其变化可以用于古环境的重建。根据孙家沟组上段碳酸盐岩碳氧同位素的组成和受控因素,结合宏观沉积环境分析,认为孙家沟组上段的盐酸盐岩形成于湖盆环境。δ~(18)O-7.97‰时,δ~(13)C和δ~(18)O呈明显的正相关关系,湖泊处于封闭环境,碳酸盐矿物富含白云石,且结晶程度较差;δ~(18)O-7.97‰时,δ~(13)C和δ~(18)O呈明显的负相关关系,湖泊处于开放环境,碳酸盐矿物富含镁方解石,且结晶程度较好。根据孙家沟组上段由下部到上部碳酸盐岩碳氧同位素的变化,揭示出当时的湖泊环境经历了由相对开放到相对封闭,再到相对开放的演化,并显示出温度变低,湿度变小,植被变差的演化趋势。孙家沟组上段湖泊环境的形成可能与南部北秦岭造山带的隆升有关,薄层碳酸盐岩层与上覆紫色泥岩层组成的韵律层主要与气候变化引起的降雨量有关。孙家沟组上段所记录的古环境及其变化与全球二叠纪末期生物大灭绝以后陆地环境的变化规律相吻合。     

Bamboo Leaf and Pollen Fossils from the Late Miocene of Eastern Zhejiang,China and their Phytogeological Significance

Fossil bamboo leaves and pollen from Upper Miocene deposits of the Shengxian Formation in Tiantai and Ninghai counties,eastern Zhejiang,China represent a rare record in Asia.The distinctive pseudopetiole and parallel venation of the leaf blades and the clearly thickened annulus of the pollen aperture place them in the subfamily Bambusoideae.Morphological analysis supports the determination of these fossil leaves as belonging to the genus Bambusium and two new species are described.Bambusium latipseudopetiolus Q.J.Wang et B.N.Sun sp.nov.has a distinctly wide pseudopetiole of 0.23 cm in width and 0.40 cm in length,several vascular bundles on parallel veins,and 5–8 lateral veins on both sides of the midrib.Bambusium longipseudopetiolus Q.J.Wang et B.N.Sun sp.nov.has a distinctly long pseudopetiole of 0.60 cm in length and 0.10 cm in width,several vascular bundles on the pseudopetiole,and 6 lateral veins on both sides of the midrib.Pollen grains from the same layer provide additional evidence of bamboos.They are characterized by 32.0–51.0 μm in diameter,a round pore 3.0–4.0 μm in diameter with a broad thickened annulus 2.5–3.5 μm around,and several conspicuous secondary folds on the exine surface.The morphological analysis leads to their assignment to Graminidites bambusoides Stuchlik.These fossils are important for the study of bamboo phytogeography in China.They demonstrate that there were bamboos growing in southeastern China during the Late Miocene and that bamboos in Zhejiang begin to diversify no later than the Late Miocene.In combination with bamboo fossils from other places,it seems that bamboos had a wide distribution across southern China during the Miocene,ranging from southwestern Yun'nan to southeastern Zhejiang.     

Formation of lacustrine dolomite in the late Miocene marginal lakes of the East Mediterranean (Northern Israel)

The study focuses on the formation of lacustrine dolomite in late Miocene lakes, located at the East Mediterranean margins (Northern Israel). These lakes deposited the sediments of the Bira (Tortonian) and Gesher (Messinian) formations that comprise sequences of dolostone and limestone. Dolostones are bedded, consist of small‐sized (<7 μm), Ca‐rich (52 to 56 mol %) crystals with relatively low ordering degrees, and present evidence for replacement of CaCO₃ components. Limestones are comprised of a wackestone to mudstone matrix, freshwater macrofossils and intraclasts (mainly in the Bira Formation). Sodium concentrations and isotope compositions differ between limestones and dolostones: Na = ~100 to 150 ppm; ~1000 to 2000 ppm; δ¹⁸O = ?3·8 to ?1·6‰; ?2·0 to +4·3‰; δ¹³C = ?9·0 to ?3·4‰; ?7·8 to 0‰ (VPDB), respectively. These results indicate a climate‐related sedimentation during the Tortonian and early Messinian. Wet conditions and positive freshwater inflow into the carbonate lake led to calcite precipitation due to intense phytoplankton blooms (limestone formation). Dry conditions and enhanced evaporation led to precipitation of evaporitic CaCO₃ in a terminal lake, which caused an increased Mg/Ca ratio in the residual waters and penecontemporaneous dolomitization (dolostone formation). The alternating lithofacies pattern reveals eleven short‐term wet–dry climate‐cycles during the Tortonian and early Messinian. A shift in the environmental conditions under which dolomite formed is indicated by a temporal decrease in δ¹⁸O of dolostones and Na content of dolomite crystals. These variations point to decreasing evaporation degrees and/or an increased mixing with meteoric waters towards the late Messinian. A temporal decrease in δ¹³C of dolostones and limestones and appearance of microbial structures in close association with dolomite suggest that microbial activity had an important role in allowing dolomite formation during the Messinian. Microbial mediation was apparently the main process that enabled local growth of dolomite under wet conditions during the latest Messinian.     

广西环江凹陷深部岩溶缝洞充填物碳氧同位素特征及古环境意义

深部岩溶是碳酸盐岩地区深部油气资源勘探中不可避免的问题。深部岩溶发育期次的确定是岩溶储层地质的技术难题。广西环江凹陷在页岩气钻井中发现大量深部溶洞且充填物丰富多样,成为深部岩溶发育期次研究的良好素材。文章对HD1-4钻井揭露的深部岩溶缝洞充填物及地表岩溶缝洞充填物进行碳氧同位素分析,揭示出环江地区的4种不同岩溶环境：同生期或准同生期岩溶环境、表生期大气淡水岩溶环境、中浅埋藏岩溶环境、深埋藏或热液岩溶环境,环江地区深部岩溶发育为4期不同岩溶环境叠加的效果,主要受到热液岩溶环境和大气淡水岩溶环境的影响。     

The uppermost Middle and Upper Albian succession at the Col de Palluel, Hautes-Alpes, France: An integrated study (ammonites, inoceramid bivalves, planktonic foraminifera, nannofossils, geochemistry, stable oxygen and carbon isotopes, cyclostratigraphy)

An integrated study of the ammonites, inoceramid bivalves, planktonic foraminifera, calcareous nannofossils, geochemistry, stable carbon isotopes, and cyclostratigraphy is provided for the upper Middle to upper Upper Albian sucession exposed in the Col de Palluel section east of Rosans in Hautes-Alpes, France. The Albian-Cenomanian boundary interval described by Gale et al. at Mont Risou is re-examined, a total thickness of 370 m of the Marnes Bleues Formation. Zonal schemes based on ammonites, inoceramid bivalves, planktonic foraminifera, and calcareous nannofossils are integrated with the stable carbon isotope curve and key lithostratigraphic markers to provide a sequence of more than 70 events in the uppermost Middle Albian to basal Cenomanian interval. Time series analysis of the Al₂O₃ content of the 500 m Albian sequence present in the Col de Palluel and Risou sections reveals the presence of the 20 kyr precession, 40 kyr tilt, 100 kyr short eccentricity, and 406 kyr long eccentricity cycles. Correlation using planktonic foraminiferan and nannofossil data provide a link between the Col de Palluel and Risou sections and the Italian sequence at Gubbio, and in the Piobbico core. This provides a basis for the extension of the orbital time scale of Grippo et al. to the sequence. It reveals a major break in the Col de Palluel succession at the top of the distinctive marker bed known as the Petite Vérole that may represent as much as 2 Ma. It also provides a basis for the estimation of the length of the Albian Stage at 4.12 Ma, 0.8 Ma for the early Albian, 2.84 Ma for the Middle Albian, and 3.68 Ma for the late Albian substages.     

Occurrence of Middle Miocene Fossil Cyprinid Fish in the Northern Qaidam Basin and its Paleoenvironmental Implications

With a thick sequence of early Eocene to Pleistocene terrestrial records, the Qaidam Basin on the northern Tibetan Plateau provides an important sedimentary archive for understanding the paleoenvironmental evolution of the northeast Tibetan Plateau. In this study, specimens of fossil fish remains are collected from the late Middle Miocene (Serravallian, ~12Ma) of the middle member of the Shang Youshashan Formation, Dahonggou (DHG) section, in the northern Qaidam Basin. Based on a systematic study of these materials, the remains have assigned to Cyprinidae, with typical pharyngeal teeth and dorsal fin spines with serrations on the posterior edge. Our discovery improves understanding of the cyprinid fish distribution characteristics in the Qaidam Basin during the Cenozoic. Co-occurrences of terrestrial brackish ostracod species Cyprideis and long chain alkenonesin the layer indicate that the studied cyprinid fish lived in a generally large brackish to saline water body during the late middle Miocene (Serravallian), when the climate of Qaidam Basin was still not sufficiently dry to form an extreme saline water lake.     

Fluid generation, vein formation and the degree of fluid–rock interaction during decompression of high-pressure terranes: the Schistes Lustrés, Alpine Corsica, France

Centimetre‐ to decimetre‐wide quartz+calcite veins in schistes lustrés from Alpine Corsica were formed during exhumation at 30–40 Ma following blueschist facies metamorphism. The δ¹⁸O and δ¹³C values of the veins overlap those of the host schistes lustrés, and the δ¹⁸O values of the veins are much higher than those of other rocks on Corsica. These data suggest that the vein‐forming fluids were derived from the schistes lustrés. Fluids were probably generated by reactions that broke down carpholite, lawsonite, chlorite and white mica at 300–350 °C during decompression between c. 1400 and 800 MPa. However, the δ¹⁸O values of the veins are locally several per mil higher than expected given those of their host rocks. The magnitude of oxygen isotope disequilibrium between the veins and the host rock is inversely proportional to the δ¹⁸O value of the host rock. Additionally, calcite in some schists is in isotopic equilibrium with calcite in adjacent veins, but not with the silicate fraction of the schists. Locally, the schists are calcite bearing only within 1–20 cm of the veins. The vein‐forming fluids may have been preferentially derived from calcite‐bearing, high‐δ¹⁸O rocks that are common within the schistes lustrés and that locally contain abundant (>15%) veins. If the fluids were unable to completely isotopically equilibrate with the rocks, due to relatively rapid flow at moderate temperatures or being confined to fractures, they could form veins with higher δ¹⁸O values than those of the surrounding rocks. Alteration of the host rocks was probably inhibited by isolation of the fluid in ‘quartz‐armoured’ veins. Overall, the veins represent a metre‐ to hectometre‐scale fluid‐flow system confined to within the schistes lustrés unit, with little input from external sources. This fluid‐flow system is one of several that operated in the western Alps during exhumation following high‐pressure metamorphism.     

藏北安多晚侏罗世古环境、古气候与地球化学元素关系研究

藏北安多地区毗邻羌塘盆地南界,属于藏北地层分区。研究区沙木罗组地层为一套稳定的浅海相碎屑岩和碳酸盐岩建造,依次发育风化壳沉积,潮坪相沉积以及混合台地相沉积,有大量生物礁产出。本文通过对沙木罗组地层中采集到的18件样品进行常量、微量元素及碳氧同位素测试,结合沉积相分析,旨在探索本区晚侏罗世古海平面升降、氧化还原条件以及古气候的演化规律。研究发现,Ni、Sr、Cu、V、Cr、Ni/Co及δ~(13)C等变化能反映氧化还原环境的变化,而Mn、Na、Sr/Cu、P、Ti及δ~(18)O和Z值的波动能指示古气候的变化。研究结果表明:研究区的古环境演化共经历了3个阶段:(1)风化壳阶段的强氧化环境;(2)潮坪阶段的半氧化半还原环境;(3)台地区与三期生物礁建造相对应的3次氧化与还原环境转换。古气候演化也经历了3个阶段:(1)风化壳区的干旱气候;(2)潮坪区的半干旱半湿润气候;(3)台地区3次干湿气候的频繁转换,分别与本区的3个造礁期相对应。     

A review on bivalve shell,a tool for reconstruction of paleo-climate and paleo-environment

Environmental information can be extracted from bivalve shell geochemistry. In this review, the latest research progress and the existing problems as well as the focus of future research on stable oxygen and carbon isotopic composition and trace elemental ratios of bivalve shell were investigated. Oxygen isotopic signatures of bivalve shell have been proved precipitate in equilibrium with their host water and used as a robust tool to reconstruct ancient water temperature. In order to reconstruct quantitative paleo-temperature information, the future research on bivalve shell oxygen isotope should combine with the study of ancient water oxygen isotope. Metabolic effect pre- vents the direct application of stable carbon isotopic composition of bivalve shell from extracting dissolved inorganic carbon information. The contribution of metabolic carbon to bivalve shell is species specific. Stable carbon isotopic composition of dissolved inorganic carbon could be reconstructed if the metabolic contribution could be accounted for. Explore ways to remove contribution of metabolic effects to bivalve shell is the future focus of the research. There is no consensus on the effect of temperature on bivalve trace element ratios, which may be also species spe- cific, each proxy should ideally be validated and calibrated for each species before being used to interpret past climate and environmental conditions. Future research needs to pay attention to the bivalve shell biomineralization process, which controlled bivalve shell trace element ratios. Cultivation experiment is an important way to obtain the relevant conclusions.     

Stable carbon isotope composition of terrestrial leaves: inter‐ and intraspecies variability,cellulose and whole‐leaf tissue difference,and potential for climate reconstruction

Stable carbon isotope analysis of terrestrial plant leaves preserved in Quaternary lake sediments has the potential to provide high‐resolution reconstructions of past climatic conditions. Preferably, δ¹³C measurements should be made on a single leaf component, e.g. cellulose, but this approach is often precluded by limited leaf availability. Previous work suggests that reliable palaeoclimatic information also may be derived from δ¹³C measurements on whole‐leaf tissue, given a similar degree of leaf decomposition between samples. Leaf δ¹³C data for 12 Scandinavian species of dwarf‐shrubs, shrubs and trees, and a comparison of δ¹³C data on recent and late Holocene Salix herbacea leaves, revealed that the δ¹³C signal registered by holocellulose is largely reflected by measurements on whole‐leaf tissue. Holocellulose was found to be consistently enriched in ¹³C, although this δ¹³C offset was smaller for subfossil leaves. This supports the use of δ¹³C measurements on whole‐leaf tissue for climate reconstruction, at least for leaves preserved in soft, late Holocene sediments with minimal diagenetic effects. Leaf carbon and nitrogen data on fresh leaves of the same 12 Scandinavian species, and corresponding data on late Holocene Salix herbacea leaves, suggest that the leaf C:N ratio is a suitable indicator of the degree of leaf decomposition. Copyright © 2003 John Wiley & Sons, Ltd.     

江西峨嵋洞石笋微层特征及其形成机制

生长快速、具有年纹层的洞穴石笋是研究过去季节-年际尺度气候变化的重要地质载体之一。本研究对江西峨嵋洞长度为60 mm的现代石笋EM1进行微层分析、高分辨率的氧、碳同位素测试分析,研究了石笋微层特征及其形成机制。研究表明峨嵋洞石笋微层具有典型的"南方型"微层特征：肉眼可见的暗褐色致密亚层,在透射光下为透光层,在紫外光下为不发光层;肉眼可见的乳白色疏松亚层,在透射光下为不透光层,在紫外光下为发荧光层。暗褐色致密亚层的方解石δ18O值由年内最小变为最大而δ13C值为年内偏正峰值,乳白色疏松亚层的方解石δ18O值由年内最大变为最小而δ13C值为年内偏负峰值。月-季节分辨率的δ18O和δ13C记录为反相关关系,δ18O滞后于δ13C变化约3~4个月。研究认为峨嵋洞石笋微层的形成可能主要与春季-早夏较多降水和有机质淋滤（形成乳白色疏松亚层）以及盛夏高温干旱（形成暗褐色致密亚层）的配置有关。部分乳白色疏松亚层内还发育有极细的荧光层,被证实为年内层（伪年层）,其成因很可能与春季至早夏多次强降水造成的数次有机质脉冲沉积有关。