西太平洋富钴结壳形成年代的探讨

本文为我国首次采用生物地层法探讨西太平洋麦哲伦海山区富钴结壳的生长年代，生物地层法计年的样品，取自厚度为97mm结壳的自顶至底的20mm,35mm,58mm,62mm及75mm处，结果表明。在62mm处发现了具地层时代鉴定意义的始新世早期Discoaster multiradiatus,Discoaster elegans,Discoaster barbadiensis,Tribrachiatus orthostylus等钙质微体化石印痕，从而推断该区富钴结壳的生长年代可追朔至始新世或更老年代，此外，作者亦将此结果与中太平洋生物地层法的计年结果进行了对比并讨论了其地质意义。     

富钴铁锰结壳的控矿要素和成矿过程——以西太平洋为例

以西太平洋海山的麦哲伦海山群和马尔库斯-威克海山群为例,研究了富钴铁锰结壳（富钴结壳）形成过程中地质要素和海洋要素的作用,重点分析了海山漂移和沉降、水道开合、最小含氧带（OMZ）、大洋环流,以及气候变化等要素对富钴结壳形成的控制作用。基于对麦哲伦海山和马尔库斯-威克海山结壳样品剖面Mn／Fe值曲线的综合研究,结合控矿要素和成矿背景分析,将该区白垩纪以来富钴结壳的成矿过程划分为五个阶段：（1）自垩纪-始新世,（2）始新世末-晚渐新期,（3）晚渐新期-中中新期早期,（4）中中新期早期晚中新期早期,（5）晚中新期早期-现代,其中（2）、（3）阶段有利于发育富钴结壳。     

大洋磷酸盐化作用对富钴结壳元素富集的影响

中国首次对与大洋富钴结壳密切相关的磷酸盐化作用进行了研究。对取自西太平洋麦哲伦海山区一厚度为 10cm的富钴结壳样品 ,自顶至底以 5mm间距采取了 2 0个分层样品进行了成矿元素和稀土元素分析。结果表明 ,未被磷酸盐化的新结壳和磷酸盐化的老结壳间主要成矿元素的含量相差显著。老结壳中Fe、Mn、Si、Al、Zn、Mg、Co、Ni、Cu元素亏损 ,亏损次序为Co >Ni>Mg >Al>Mn >Si>Cu >Zn >Fe;而Ca、P、Sr、Ba、Pb元素含量增加 ,富集次序为P >Ca >Ba >Pb >Sr。研究认为 ,结壳中磷酸盐化作用的强弱制约着富钴结壳成矿元素含量的变化 ,磷酸盐化作用是造成老结壳中主要成矿元素Co、Ni等贫化流失的根本原因。研究还表明 ,磷酸盐化作用对富钴结壳的稀土元素丰度也产生一定影响 ,使老结壳的稀土总量和Ce含量高于新结壳 ,但未显著改变其稀土配分模式和分馏特征。研究证实 ,老结壳的Y正异常与磷酸盐化作用无关。磷酸盐化作用的研究为富钴结壳矿产资源的评价和综合利用提供了有用信息。     

麦哲伦海山区富钴结壳成矿条件分析

麦哲伦海山区是西北太平洋内受北西向转换断层控制的板内海底火山链，其形成时代为中株罗世－－白垩纪。独特的构造背景和地理环境，造就麦哲伦海山区成为世界上最重要的富钴结壳分布区之一。海山上覆盖着火山岩和沉积岩两类结壳基岩，基岩的形成时代、类型、分布位置等，对结壳性质有重要影响。富钴结壳于晚白垩世晚期开始形态，始新一－中新世发育最为有利。自株罗纪以来麦哲伦海山由南半球跨越赤道迁移到北关球，这一阶段南级冰盖的消融与生长和板块构造上起的海陆变迁，导致海山区最低含氧层深度和CCD面发生变化，结壳的生长出现间断，内部元素组分发生突变或渐变，麦哲伦海山上的结壳，一船呈现两个世代，新老壳层间在元素含量上有差异，老世代壳层中有6个元素成因组合，壳层中有4个元素成因组合。     

西太平洋海山玄武岩的岩石学特征及与上覆富钴结壳的关系

通过对西太平洋海山玄武岩和玄武质火山角砾岩的岩石学特征及其气孔充填物成分变化的研究,讨论了海山玄武岩与上覆富钴结壳的关系。富钴结壳的基岩火山岩主要为碱性玄武岩和玄武质火山角砾岩。碱性玄武岩中气孔充填物为S型和C型,S型和C型气孔充填物不共存在同一个气孔中。S型气孔充填物的物质成分富Si、Fe、K、Mg、Al,Co含量一般为0.17%~0.46%,其成分与碱性玄武岩的组成类似,其物质来源可能与碱性玄武岩有关。C型气孔充填物为O、Ca、C及少量Si、Al、Mg、Fe、K等元素,C型气孔充填物可能与海水中物质的沉积有关。由Si、Al、Fe、Mg、K等元素变化曲线反映出的S型气孔充填物沉积过程与富钴结壳早期的沉积过程具有相似的趋势,说明富钴结壳早期沉积物的物质来源可能与碱性玄武岩有关,富钴结壳物质来源可能是碱性玄武岩和海水共同作用的结果。     

西太平洋富钴结壳生长与富集特征

通过对西太平洋麦哲伦海山区富钴结壳的大尺度细致研究 ,笔者较为深入地探讨了该区结壳的生长与富集特征。研究表明 ,该区结壳自古近纪开始生长 ,生长速率变化范围为 1.5～ 12 .3mm/Ma,速率相差近一个数量级 ,平均生长速率为 3.81m m/Ma;生长过程中成矿元素的地球化学行为呈现明显差异 ;环境发生“骤变”的 O/M界面 ,可能是结壳生长过程中其构造和色泽发生“突变”的一个重要年代 ;成矿元素成分的时序演化主要受控于海水化学和各种不同地质作用的综合影响 ,成矿与非成矿地质作用在生长过程中呈现为互为消长的特征。研究发现 ,该区结壳和太平洋深海粘土元素的分配系数间存在着显著的线性相关关系 ,相关系数为 0 .89,显示它们有相近的元素富集机理。此外 ,笔者还从元素的滞留时间、阳离子的电子键能及其在海水中的水解行为与结壳富集特征间的关系进行了探讨。     

麦哲伦海山群MK海山富钴结壳钙质超微化石生物地层学研究

富钴结壳是发育在深海海山之上的一种重要沉积矿产资源,建立准确可靠的年代学格架,无论对富钴结壳成矿作用研究还是对古海洋环境研究,都具有重要意义。但迄今为止,由于定年技术的限制,可靠的富钴结壳年代学框架资料并不多。文中以钙质超微化石生物地层学方法为主要手段,并结合Co经验公式法、样品的结构特征和磷酸盐化作用时代等资料,对麦哲伦海山群MK海山MKD13-3号富钴结壳样品的年代学框架进行了综合限定。研究结果如下。(1)该样品剖面从下到上可以分4层,分别为:磷块岩基岩,其中包括R层(残留层)结壳,时代为112.0~70.6Ma B.P.;I层,进一步划分为I-1和I-2层,其时代分别为55.0~48.0Ma B.P.和44.0~23.0Ma B.P.;Ⅱ层,时代为23.0~14.0Ma B.P.;Ⅲ层,时代为5.0~0Ma B.P.。(2)该富钴结壳样品在生长过程中发育了3个生长间断,分别为:基岩与I-1层之间的生长间断,时代为70.6~55.0Ma B.P.;I-1层与I-2层之间的生长间断,时代为48.0~44.0Ma B.P.;Ⅱ层与Ⅲ层之间的生长间断,时代为14.0~5.0Ma B.P.。     

西太平洋海底海山富钴结壳惰性气体同位素组成及其来源

采用高真空气体质谱系统测定了西太平洋麦哲伦海山富钴结壳不同层圈及其基岩的惰性气体丰度和同位素组成,结果显示:(1)西太平洋富钴结壳主要是水成成因,其中惰性气体来源不同,He 绝大多数来自宇宙尘(IDPs),少量来自陆源风成微粒;Ar 主要来自海水溶解的大气,少量来自陆源风成微粒或沉积岩建造水;Ne 和 Xe 主要来自海水中溶解大气, 少量来自宇宙尘;(2)在具三层结构的结壳中,亮煤层(致密层)的惰性气体同位素相对外层和疏松层有较大的不同,显示大洋磷酸岩化对早期沉积的结壳惰性气体组成有较大的影响,如导致~4He 的升高和~3He/~4He 的显著降低;(3)太平洋富钴结壳玄武岩基岩的~3He/~4He 非常低,为0.0095～0.074Ra,与本区磷块岩基岩(0.087Ra)相似,而远低于正常海底玄武岩的~3He/~4He 比值,显示这些基岩曾与富含放射性成因~4He 和 P 的上升洋流或沉积物中建造水发生过水/岩反应,这个过程将释放出较多的成矿元素,有利于富钴结壳的形成,海底海山玄武岩中较低的 He 同位素组成可作为富钴结壳的找矿标志之一。     

太平洋海山成矿系统与成矿作用过程

文中初步探讨了太平洋海山富钴结壳成矿系统的结构与成矿作用过程。海山成矿系统的控矿要素主要包括地质要素和海洋要素,地质要素主要包括海山的形成、迁移、沉降和水道的开合等,海洋要素主要包括大洋温盐环流、最低含氧带(OMZ)、文石溶跃面、碳酸盐补偿深度和海山周围海水的动力情况等。重点分析了海山漂移和沉降、水道开合、最低含氧带变化、大洋环流以及气候变化等要素对富钴结壳成矿的控制作用。海山为富钴结壳成矿提供了一个容矿空间,稳定的基岩,即长期稳定的容矿空间,是富钴结壳成矿的基本条件;海山的形成年龄、海山的迁移和水道的开合决定并改变了富钴结壳的成矿背景条件,促使海山成矿系统发生演化。最低含氧带作为富钴结壳成矿的地球化学障,是直接的矿源层;而海山周边的地形旋涡沟通了最低含氧带与富氧、富铁的深层和底层水,使得最低含氧带中的成矿金属离子得到氧化,进而发生胶体凝聚沉淀,形成富钴结壳。以西太平洋海山成矿系统为例,将该区白垩纪以来富钴结壳成矿作用过程划分为5个阶段:(1)白垩纪—始新世,(2)始新世末—晚渐新世,(3)晚渐新世—中中新世早期,(4)中中新世早期—晚中新世早期,(5)晚中新世早期—现代,其中(2)、(3)阶段有利于发育富钴结壳。     

麦哲伦戈沃罗夫盖特平顶海山钴结壳资源评价

为能科学、快速量化地圈定出大洋海山钴结壳优质矿区,笔者基于国际海底管理局提出的矿区选取模型,利用我国西太平洋海山钴结壳资源调查的公开的拖网采样资料,综合钴结壳的分布规律和证据权法所得海山钴结壳资源预测后验概率图,将西太平洋麦哲伦海山区戈沃罗夫盖特平顶海山圈定为钴结壳资源前景较好的远景区,并采用人机交互式的矿区圈定方法圈定出符合国际海底管理局规章要求的7个群组共100个钴结壳矿块。据此估算出戈沃罗夫盖特平顶海山湿结壳资源量为69 487.6×10⁴ t;圈定的100个矿块主要分布在2 000~3 000 m斜坡上,湿结壳资源量为14 092×10⁴ t,干结壳资源量为9 789.35×10⁴ t;锰金属量为1 961.3×10⁴ t,铜金属量为10.17×10⁴ t,钴金属量为54.06×10⁴ t,镍金属量为34.87×10⁴ t。这些数据表明,戈沃罗夫盖特平顶海山规模较大,钴结壳资源前景潜力大,可作为钴结壳深入调查和矿区申请备选海山。     

海南岛东部海域滨珊瑚Sr/Ca比值温度计 及其影响因素初探*

文章采用全谱直读等离子体原子发射光谱(ICP-AES)的方法测定了1986~1996年海南岛东部海域滨珊瑚的Sr/Ca比值,建立了该海域月分辨率的Sr/Ca海水表面温度计方程:SST(℃)=170-16 (mmol/mol),n = 133,r=0.80,p=0.01, 此与韦刚健等在西沙海域建立的温度计方程:SST(℃)=169-16.7 (mmol/mol)一致,这表明南海中、北部海域也出现有相似的微量元素温度计。此外,文章还分析了在某些年月份SST的实测值和计算值出现的显著差别,探讨了可能造成的海洋气象环境因素。     

High precision measurements of Mg/Ca and Sr/Ca ratios in carbonates by cold plasma inductively coupled plasma quadrupole mass spectrometry

We present a new high precision analytical method for the determination of Mg/Ca and Sr/Ca ratios in carbonates using an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS) with a 650-W cold plasma technique and a desolvation introduction system. Signal intensities are detected in pulse-counting mode and Mg/Ca and Sr/Ca ratios are calculated directly from intensity ratios of ²⁴Mg/⁴³Ca and ⁸⁶Sr/⁴³Ca using external matrix-matched standards for every 4–5 samples to correct for instrumental mass discrimination and low-frequency ratio drift. Significant matrix effect of Ca content on Mg/Ca determination (− 0.018 Mg/Ca (mmol/mol)/[Ca] (ppm)), can be overcome by diluting [Ca] to 6–8 ppm in the sample solution or using an empirical correction. The Sr/Ca ratio affects the Mg/Ca determination, with a factor of − 0.32% Mg/Ca per mmol/mol. This is mainly caused by the influence of doubly charged ⁸⁶Sr, which biases the intensity measurement of the ⁴³Ca⁺ ion beam. This effect results in a trivial offset of less than 0.1% on Mg/Ca measurements for Quaternary foraminiferal and coral samples. The internal precision of our method ranges from 0.1 to 0.2%. Replicate measurements made on standards and samples show long-term external uncertainties (2σ) of Mg/Ca = 0.84% and Sr/Ca = 0.49%. The minimum sample size requirement is only 3.5 μg of carbonate. The application of this newly developed technique on the planktonic foraminifera Globigerinoides ruber from a core recovered in the southern South China Sea yields a glacial–interglacial difference in sea surface temperature (SST) of 3 °C. Three-year coral Sr/Ca data suggest that the seasonal SST ranged from 22.6–23.8 °C in winter to 26.9–27.9 °C in summer in Nanwan, south Taiwan, during 2000–2002. The coral-Sr/Ca inferred SSTs in 2002 match well with instrumental records, which demonstrates the validity of this ICP-QMS method.     

南海北部珊瑚Sr/Ca和Mg/Ca温度计及高分辨率SST记录重建尝试

利用全谱直读等离子体光谱(ICPAES)的分析方法精确分析了南海珊瑚的SrCa和MgCa比值,结合实测表层海水温度(SST),标定了海南岛南部三亚海域和西沙海域两个滨珊瑚的SrCa和MgCa温度计。在此基础上,尝试对两个南海北部全新世时期的珊瑚进行SST记录重建。结果显示约540aB.P.(小冰期)西沙海域夏季月均SST较现代低约1℃,而约6500aB.P.(大暖期)海南岛三亚海域夏季月均SST则高出现代1.0～1.5℃。     

The impact of salinity on the Mg/Ca and Sr/Ca ratio in the benthic foraminifera Ammonia tepida: Results from culture experiments

Over the last decade, sea surface temperature (SST) reconstructed from the Mg/Ca ratio of foraminiferal calcite has increasingly been used, in combination with the δ¹⁸O signal measured on the same material, to calculate the δ¹⁸O_w, a proxy for sea surface salinity (SSS). A number of studies, however, have shown that the Mg/Ca ratio is also sensitive to other parameters, such as pH or , and salinity. To increase the reliability of foraminiferal Mg/Ca ratios as temperature proxies, these effects should be quantified in isolation. Individuals of the benthic foraminifera Ammonia tepida were cultured at three different salinities (20, 33 and 40 psu) and two temperatures (10-15 °C). The Mg/Ca and Sr/Ca ratios of newly formed calcite were analyzed by Laser Ablation ICP-MS and demonstrate that the Mg concentration in A. tepida is overall relatively low (mean value per experimental condition between 0.5 and 1.3 mmol/mol) when compared to other foraminiferal species, Sr being similar to other foraminiferal species. The Mg and Sr incorporation are both enhanced with increasing temperatures. However, the temperature dependency for Sr disappears when the distribution factor D_Sr is plotted as a function of calcite saturation state (Ω). This suggests that a kinetic process related to Ω is responsible for the observed dependency of Sr incorporation on sea water temperature. The inferred relative increase in D_Mg per unit salinity is 2.8% at 10 °C and 3.3% at 15 °C, for the salinity interval 20-40 psu. This implies that a salinity increase of 2 psu results in enhanced Mg incorporation equivalent to 1 °C temperature increase. The D_Sr increase per unit salinity is 0.8% at 10 °C and 1.3% at 15 °C, for the salinity interval 20-40 psu.     

Sea surface temperature record off central Japan since the Last Glacial Maximum using planktonic foraminiferal Mg/Ca thermometry

We conducted paired measurements of the Mg/Ca ratio and δ¹⁸O of planktonic foraminifera, Globigerina bulloides, from a sediment core (MD01‐2420) off central Japan in the northwest Pacific, to reconstruct current movements since the Last Glacial Maximum (LGM). These methods make it possible to determine the magnitude and timing of the sea surface temperature (SST) changes and to reconstruct the variations of the past seawater δ¹⁸O (δ¹⁸Ow) off central Japan. The amplitude of Mg/Ca‐based SST changes between the Holocene and the LGM was about 10°C. The strong resemblance of the SSTs estimated from both methods, Mg/Ca‐based and δ¹⁸O‐based, suggests that the SST changes were caused primarily by latitudinal displacement of the Kuroshio–Oyashio currents and no distinct change in the carbonate dissolution of the core. The southward migration of the water mass was 5–6° in latitude at the LGM. The values for regional δ¹⁸Ow changes, which were obtained by subtracting the ice volume contribution from the calculated δ¹⁸Ow, describe the millennial‐scale water mass migration over the last 30 kyr. Copyright © 2005 John Wiley & Sons, Ltd.     

中更新世气候转型时期南海生态环境的南北差异

中更新世气候转型在南海浮游有孔虫、氧同位素和其它生物记录上主要反映在900 ka BP前后发生高频率变化，特别是指示表层水骤然降温。北部冬季表层水温从24~25℃降至17~28℃，而南部也从26~27℃降至23~24℃。总的降温趋势与开放西太平洋一致，直接反映了西太平洋暖池在900 ka BP之后MIS22期间有明显的减弱。表层水大幅度降温还发生在后继的MIS 20、18、16几大冰期，说明主要冰期旋回周期由41 ka转变为100 ka经历了长达400 ka的过渡时期，并且冬季风增强也在过渡时期的后半段最明显。南海南北生物组合和δ18O值的差异，突出了中更新世气候转型期边缘海区南北气候梯度反差和冬季风在冰期增强的讯号。结论是：生态环境系统反应总体表现与冰期旋回一致的同时，还包含了独特的地区性系统演变特征。但是，南海—西太平洋地区在0.9 Ma BP前后表层海水盐度因东亚冬季风和海平面下降的定量变化，以及这些变化对气候转型时期海—气耦合过程和生态环境系统的影响，尚缺乏足够的资料和证据。     

南海南部晚第四纪表层海水温度的变化及其与极地冰芯古气候记录的比较

本次研究选取南海南部"太阳号"95航次17961-2柱状样(8°30.4′N,112°19.9′E,水深1795m,柱长10.3m)的175块样品进行浮游(Globigerinoides ruber)和底栖有孔虫(Cibicidoides wuellerstorfi)的氧碳稳定同位素及浮游有孔虫G.ruber壳体的Mg/Ca比值测定,再造了距今约140ka以来时间分辨率约800年的表层海水温度(SST)变化,揭示末次冰期南海南部的SST曾降温达约5℃,且存在类似Dansgaard-Oeschger(D/O)事件的千年尺度波动。将南海南部的研究结果与极地冰芯古气候记录进行对比,发现在千年时间尺度上南海南部SST的变化特征与南极冰芯的古气候变化相一致,而与格陵兰冰芯^δ18O所展示的锯齿状形态D/O事件的变化不一样,且最近的两个末次冰消期南海南部SST与代表高纬冰盖体积大小的底栖有孔虫^δ18O几乎同步变化,反映南海南部热带海区古气候变化的特殊性,为进一步研究低纬热带海区在全球古气候变化中的作用提供了新证据。     

Sea‐surface temperature and salinity changes in the northwest Pacific since the Last Glacial Maximum

The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr. Under the present hydrographic condition, a clear relationship between the sea‐surface temperature (SST) and oxygen isotope differences from benthic to planktonic Foraminifera is observed in this region. Using this relationship, we find decreased SSTs of 12–13°C (maximum 15°C) in the southernmost core site at the Last Glacial Maximum (LGM), indicating the Oyashio Current shifted southward. The SSTs at the southern two core sites abruptly increased more than 10°C at 10–11 ka, suggesting the Kuroshio Current shifted northward over these sites at 10–11 ka. In contrast, the northern two core sites have remained under the influence of the cold Oyashio Current for the past 25 kyr. With the reasonable estimate of bottom‐water temperature decrease of 2.5°C at the LGM, the SSTs estimated by this new method give exactly the same SST values calculated from Mg/Ca ratio of planktonic Foraminifera, allowing palaeosea‐surface salinities to be reconstructed. The result suggests that the ice volume effect was 1.0 ± 0.1‰ at the LGM. Copyright © 2004 John Wiley & Sons, Ltd.     

Temperature effects on the calcite skeletal composition of deep-water gorgonians (Isididae)

We test for and calibrate a proxy for ocean temperature based on the skeletal composition of the widely distributed, deep-sea gorgonians in the family Isididae (bamboo corals), through use of three complementary methods: a short-term comparison of element/Ca ratios to a four-year temperature record, a long-term comparison with oceanographic records spanning forty years, and a geographic comparison of Isidids collected at sites ranging from the tropics to Antarctica. The assays consistently support a temperature-dependency for Mg/Ca ratios and suggest S/Ca is indirectly affected by temperature, but indicate little or no effect of temperature on P/Ca and Sr/Ca. The consensus relationship between Mg/Ca and temperature for Isidid calcite from the comparisons with the temperature time-series is T = −0.505 + 0.048 Mg/Ca, where T is in °C, Mg/Ca is in mmol/mol, and the applicable range is 3-6 °C. The results of the geographic assay, though imprecise, suggest the applicable range extends to temperatures below freezing. The scatter of data points around the regression of temperature and Mg/Ca is wide in all assays. This could reflect the effect of factors other than temperature on Mg/Ca ratios, but is also likely to reflect limitations of the field data, the effects of assumed constant growth rates in the corals and instrumental analytical error. The combined effects of micro-scale variability in growth rates and wide confidence intervals for each data point suggests that environmental reconstruction from Isidid internode calcite from sparse data or at time scales less than decades be done with caution. Comparisons within and among colonies do not indicate strong vital effects on ontogenetic variability in the corals, other than possibly close to the central pore of the coral. However, similar Mg/Ca ratios for Isidids from Antarctic and more temperate regions suggest adaptation to local conditions and hence a role for physiology at higher taxonomic levels, at least. Taxonomically higher level vital effects are also suggested by large differences between gorgonian families in their regressions between Mg/Ca and temperature, by Mg/Ca ratios that overlap over a wide temperature and habitat range, and for a non-linear relationship between temperature and the slope of the Mg/Ca-temperature relationship across the order.     

Oxygen and carbon isotope and Sr/Ca signatures of high-latitude Permian to Jurassic calcite fossils from New Zealand and New Caledonia

Calcite fossils from New Zealand and New Caledonia provide insight into the Permian to Jurassic climatic history of Southern High Latitudes (southern HL) and Triassic Southern Intermediate Latitudes (southern IL). These results permit comparison with widely studied, coeval sections in Low Latitudes (LL) and IL. Oxygen isotope ratios of well-preserved shell materials indicate a partially pronounced Sea Surface Temperature (SST) gradient in the Permian, whereas for the Triassic no indication of cold climates in the southern HL is found. The Late Jurassic of New Zealand is characterized by a slight warming in the Oxfordian–Kimmeridgian and a subsequent cooling trend in the Tithonian. Systematic variations in the δ¹³C values of southern HL samples are in concert with those from LL sections and confirm the global nature of the carbon isotope signature and changes in the long-term carbon cycle reported earlier.Systematic changes of Sr/Ca ratios in Late Triassic brachiopods, falling from 1.19 mmol/mol in the Oretian (early Norian) to 0.67 mmol/mol in the Warepan (late Norian) and subsequently increasing to 1.10 mmol/mol in the Otapirian (~ Rhaetian), are observed. Also Sr/Ca ratios of Late Jurassic belemnite genera Belemnopsis and Hibolithes show synchronous changes in composition that may be attributed to secular variations in the seawater Sr/Ca ratio. For the two belemnite genera an increase from 1.17 mmol/mol in the Middle Heterian (~ Oxfordian) to 1.78 mmol/mol in the Mangaoran (~ late Middle Tithonian) and a subsequent decrease to 1.51 mmol/mol in the Waikatoan (~ Late Tithonian) is documented.