Characterisation and origin of New Zealand nephrite jade using its strontium isotopic signature

Nephrite jade occurs in three terranes (Dun Mountain–Maitai, Caples and Torlesse) in New Zealand, where it is associated with ultramafic and ophiolitic rocks in narrow metasomatic reaction zones at the margins of serpentinite (having harzburgite/gabbro/dolerite precursors) with silicic metasediments and metavolcanics. True nephrite fabrics are developed only locally where marginal shearing is intense, and late in the metamorphic history. ⁸⁷Sr/⁸⁶Sr values of these nephrites do not display the primitive values of their gabbro/dolerite precursor component i.e. 0.7030–0.7035, as expected if formed during serpentinisation. Rather, the nephrites have more evolved ⁸⁷Sr/⁸⁶Sr values inherited from the metasediment component at a later stage, and which fall within particular terrane groups: Dun Mountain–Maitai 0.7045–0.7060, Caples 0.7058–0.7075 and Torlesse 0.7085–0.7110. Rb–Sr ages and initial ⁸⁷Sr/⁸⁶Sr ratios of the metasediment component from in situ nephrite localities, when compared with their counterparts throughout the host terrane, show that nephrite Sr isotopic compositions are characteristic of the host terrane.     

Experimental deformation of a synthetic dunite at high temperature and pressure. II. Transmission electron microscopy

We have performed detailed transmission electron microscope on most of the deformed synthetic dunite specimens prepared in the study by Zeuch and Green (1984). We have identified three basic types of sub-boundaries, simple tilt walls in (100) and (001). composed by b = [100] and b = [001] edge dislocations, respectively, and twist boundaries in (010) composed of b = [100] and b = [001] screws. We have also observed more complex, asymmetric lilt boundaries in (100) and (001). Like the (010) twist boundaries, these asymmetric tilt walls are common only at the highest temperatures and lowest strain rates. Subgrain development is extensive at the higher temperatures and lower strain rates, and subgrains are composed of the above-mentioned three types of sub-boundaries; edge components in (100) and (001) ire “knitted” to screw components in (010) as described by Kirby and Wegner (1978) for naturally deformed olivine. In many areas of the samples which we studied, subgrain development is not observed, but parallel arrays of tilt boundaries of one type or the other are present. At higher temperatures and lower strain rates. “(100) organization” (Durham et al., 1977) is common; this structure consists of parallel arrays of (100) tilt boundaries with b = [100] screws connecting the sub-boundaries. At lower temperatures we have observed an analogous arrangement of (001) sub-boundaries and b = [001] screws, which we refer to as “(001) organization”. Under all experimental conditions, dislocations with b = [100] and b = [001] are present in approximately equal numbers. However, the two types of dislocations also have distinctly different geometries under all test conditions. We suggest that the transition from slip parallel to [001] to slip parallel to [100] with increasing temperature, which has been reported in earlier studies may also depend upon water content. The substructures which we observe are virtually identical to those seen in many naturally deformed peridolites. and we conclude that the mechanisms involved in both natural and laboratory deformation of olivine polycrystals are similar. On the other hand, the substructures reported here are very different from those observed in experimentally deformed olivine single crystals. It seems likely that these substructural differences reflect fundamental differences in the behavior oh single crystals and polycrystals. which are in turn reflected in different measured creep strengths.     

大化墨玉的矿物学特征

一种新的墨玉最近在广西大化瑶族自治县被发现.对该玉石的宝石学、岩石学、矿物学特征的系统研究表明,其质地细腻,主要组成矿物有阳起石和铁阳起石(95%以上),呈显微毛毡状、柱状结构,含特征次要矿物黑硬绿泥石,并常含黄铁矿、磁黄铁矿.作为一种新型的墨玉成因矿床,大化墨玉产于辉绿岩与围岩碳酸盐岩的内接触带,是夕卡岩化后热液交代作用的产物.与其他产地墨玉相比,宝石学特征基本相同,但大化墨玉成分上更富铁,主要由铁含量高的矿物组成,密度略偏高.其黑色是由高铁含量的阳起石-铁阳起石所致.     

不同颜色青海软玉微观形貌和矿物组成特征

青海软玉颜色丰富,近年来对青海软玉矿物学的研究不少,但针对不同颜色青海软玉矿物学特征的研究还存在欠缺。本文利用偏光显微镜、扫描电子显微镜、电子探针及粉晶X射线衍射仪器,从透闪石微形貌特征、微观结构、矿物组成及结晶度四个方面,研究了青海软玉颜色与矿物学特征的对应关系。结果表明:白玉、烟青玉、糖玉中透闪石主要为纤维状,显微纤维变晶结构,结晶度为96. 12%～96. 88%;青白玉和翠青玉中透闪石主要为叶片状,显微叶片变晶结构,结晶度为97. 35%,97. 32%;青玉和碧玉中透闪石主要为叶片状,显微叶片-隐晶质变晶结构,结晶度为95. 48%,95. 29%;黄玉中透闪石主要为柱状,显微柱状变晶结构,结晶度为97. 84%。青海软玉主要组成矿物均为透闪石,含量在95%以上,部分次要矿物如翠青玉中的榍石、黄玉中的钙长石、青玉中的菱镁矿、碧玉中的铬铁矿、糖玉中的斜黝帘石只出现在特定颜色的青海软玉样品中。研究认为不同颜色青海软玉矿物学特征确实存在差异,这些特征为研究不同颜色青海软玉成矿环境及成矿条件提供了科学依据。     

和田软玉的化学成分和显微结构研究

采用场发射扫描电子显微镜（FE-SEM）系统对产自新疆和田的软玉样品的主要矿物组成、化学成分、显微结构等进行了较详细的研究,并与产自中国青海、辽宁、河南及韩国的软玉样品进行了比较。结果表明,各产地软玉样品的矿物组成、化学成分和显微结构有一定的差异。和田软玉样品中含有镁质绿泥石,而辽宁软玉样品中含有较多的闪锌矿,青海软玉样品中有含Zr元素矿物的颗粒,河南软玉样品中有含La与Ce元素较高矿物的颗粒;对纯度较高的软玉样品,仅依靠主成分很难区分其产地,但依靠其微量元素成分却能起到较好的鉴别作用;和田软玉样品中透闪石的显微结构较致密,纤维尺寸要小于其它产地软玉样品的。以上信息对确定软玉的产地具有较好的参考意义。     

东昆仑小灶火软玉中热液锆石U-Pb年龄及Hf同位素特征:对成矿时代的制约

小灶火软玉矿床位于东昆仑造山带西段,同新疆和田玉处于昆仑山脉同一条成矿带上。该矿床软玉种类主要为青玉,其中透闪石含量达99%以上,为特殊的镁矽卡岩矿床。对该矿区青玉及其相关的黑云二长花岗岩进行了系统的LA-MC-ICP-MS锆石微量元素、U-Pb及Lu-Hf同位素研究。结果显示,黑云二长花岗岩中均为具典型韵律振荡环带的岩浆成因锆石,锆石U-Pb定年得到其成岩年龄为415.8±1.7 Ma;锆石ε_(Hf)(t)值为1.5~6.6,亏损地幔Hf模式年龄(tDM)为779~965 Ma,指示黑云二长花岗岩为东昆仑原特提斯造山带后碰撞阶段新生的新元古代地壳物质熔融的产物。青玉中的锆石可分为两类,其中主要锆石群——I类锆石呈补丁状环带、面状环带或无环带,且具有与黑云二长花岗岩中的岩浆锆石明显不同的稀土元素及Hf同位素特征,显示典型的热液锆石特点,其U-Pb年龄416.4±1.5 Ma代表了青玉的形成时间;II类锆石(416 Ma、471 Ma、818 Ma)呈韵律振荡环带,为热液流体从围岩中捕获的继承锆石。小灶火地区成岩-成矿作用的同时性(~416 Ma)表明岩浆岩侵入是软玉矿床形成的岩浆岩条件,软玉成矿作用方式为热液交代和充填作用。值得注意的是,用热液锆石的Hf同位素来示踪软玉成矿流体性质时应十分谨慎,因为成矿热液中的Hf元素在同时结晶的两种不同矿物(热液锆石和透闪石)间发生了重新分配。     

Geochemistry and petrogenesis of placer nephrite from Hetian, Xinjiang, Northwest China

The Yurungkash and Karakash rivers, also known respectively as the White Jade and Black Jade rivers, located in Hetian, Xinjiang Province, Northwest China, are the two main sources in China of white, green, and black placer nephrite, with a long history (~ 5000 years) of exploration and mining. The twenty-nine placer nephrite samples collected from both rivers and analyzed in the present study possess fine-grained and compact microstructures. The mineral assemblages in the samples provide clues to the metamorphic/metasomatic processes that formed the nephrite, which was the result of one of the following reactions: dolomitic marble → tremolite, or dolomitic marble → diopside → tremolite. White nephrite from the Yurungkash River and green nephrite from the Karakash River are predominantly tremolite. Based on electron probe microanalytical data, backscattered electron images, and Raman spectra, two kinds of black nephrite from the Karakash River are identified: one dominated by actinolite aggregates, and another consisting of tremolite aggregates with graphite crystals up to 2 mm in length. Compared with black nephrite, white and green nephrites contain fewer mineral inclusions and have lower FeO and MnO contents. All the amphiboles in the nephrites have very low contents of Cr₂O₃ (0.00–0.07 wt.%) and NiO (0.00–0.05 wt.%) relative to serpentinite-related nephrite (0.07–0.43 wt.% Cr₂O₃, 0.08–0.36 wt.% NiO). Most of the nephrite samples have low total rare earth element (ΣREE) contents, ranging from 12.22 to 49.40 ppm. In two nephrite samples, relatively high ΣREE concentrations (161 and 190 ppm) are related to the presence of REE-bearing minerals. Whole-rock REE chondrite-normalized patterns of all samples are characterized by strong negative Eu anomalies (0.16–0.48), moderate light-REE enrichment (La/Nd_N = 1.8–5.0), and nearly flat heavy-REE distributions (Gd/Yb_N = 0.3–1.7). Nephrite samples from both river locations have δ¹⁸O and δD isotope compositions ranging from 1.1‰ to 5.6‰ and − 55.7‰ to − 72.4‰, respectively. These values are closer to those recorded in dolomite-related nephrites than those in serpentinite-related deposits. Importantly, δ¹⁸O and δD values correspond to fluid isotope compositions of δ¹⁸O = 1.6‰ to 6.1‰ (330 °C), 1.8‰ to 6.3‰ (350 °C), and 2.5‰ to 7.0‰ (430 °C), and δD = − 34.9‰ to − 52.5‰ (350 °C to 650 °C). These values are close to or within the field of magmatic water. Geochemical and petrographic characteristics point to a dolomite-related metamorphic/metasomatic origin for nephrite at both locations. The placer nephrite is likely to have been derived from primary nephrite deposits in the Kunlun Mountains around Hetian, based on the geological occurrence of the deposits.     

四川雅安绿色软玉的宝石矿物学特征

四川雅安地区新近发现一处颇具特色的绿色 浅绿色软玉矿产资源,该软玉在产出状态、外观特征、玉石结构、构造及成矿特点等方面明显有别于国内外同类型软玉矿床.采用X射线粉末衍射仪、扫描电子显微镜、傅里叶变换红外光谱仪及电子探针等测试方法,重点就该类软玉的物相、微组构、振动光谱、微区化学成分等特征进行了分析.观察与测试结果表明,雅安软玉具致密块状构造和典型的纤柱状交织结构,其主要矿物组成为透闪石（95％～98％）,还含少量钙铬榴石、铬铁矿及石英等次要矿物;红外吸收光谱显示其吸收谱带数目、峰位均与透闪石标准图谱相吻合;透闪石微区化学成分分析结果显示,雅安软玉相对贫Mg,富Fe,含Cr,其中w（FeOT）=1.810％～2.365％,w（Cr2O3）=0.019％～0.152％,Mg/（Mg＋Fe）在0.944～0.957区间内变化,其中Fe、Cr元素可能是导致雅安绿色软玉致色的主要因素.     

福建首次发现软玉

最近在福建南平地区发现软玉，其质地细腻，白色－浅绿色，ＲＩ＝１．６１￣１．６２，密度２．９７９￣２．９８９ｇ／ｃｍ＾３，硬度６．０￣６．１，矿物成分较为简单，为透闪石，局部含少量透辉石包裹体。化学成分接近于透闪石的理论成分，ＦｅＯ的含量很低，是一种品质较好的玉雕材料。     

中国三地软玉的矿物组成和成矿地质背景研究

为了查明新疆玛纳斯、青海格尔木、江苏溧阳产软玉的矿物组成和了解其品质与矿物组成的内在联系,为软玉的鉴别与质量评价等提供基础资料,采用偏光显微镜、电子探针、X射线粉末衍射等测试方法对3个产地的软玉样品进行了测试分析,从矿物成因特征、结构构造、矿物组成、化学成分等方面进行了对比分析。结果表明,新疆玛纳斯、青海格尔木、江苏溧阳的软玉虽然均由透闪石组成,但其晶体中Mg与Fe的离子数量明显不同,玛纳斯碧玉中的透闪石含有更多的Fe,其化学成分十分接近阳起石的;玛纳斯碧玉的成矿地质背景与格尔木和溧阳的有所差别,形成于蛇纹石化超镁铁岩中,富含FeOT和MgO,而溧阳和格尔木软玉则产于中酸性火成岩与白云质大理岩的接触带中,其FeOT的质量分数较低。软玉的颜色、韧性和透明度主要取决于其形成的地质背景条件。     

Effects of temperature on strength and compressibility of sand-bentonite buffer

Dense sand-bentonite buffer (γ_d = 1.67Mg/m³) has been proposed in Canada as one of several barriers for isolating nuclear fuel waste. The buffer will be required to function under conditions of high total pressures and elevated temperatures approaching 100°C. Summary results are presented from two test programs: (1) isothermal consolidated undrained triaxial (CIU¯) tests; and (2) isothermal drained constant-p′ (CID) triaxial tests. Specimens were consolidated at effective stresses up to 9.0 MPa and temperatures up to 100°C.

The results indicate parallel hardening lines at systematically lower values of specific volume at elevated temperatures. In shear, increased temperatures produced lower values of maximum deviator stressq_f, and higher pore water pressure changesΔu_f. The net result is curved peak strength envelops in plots ofq_f versusp_f′ that are higher at elevated temperatures, even though the strengths,q_f of individual specimens are lower. The critical state strength envelope is curved inq, p′-planes.

The effect of drained heating on buffer to 100°C is not marked. Compressibilities, stiffnesses, strengths, and pore water pressure generation are all affected, but none of the changes are great.     

The residual geological information in Liangzhu jades: Implications for their provenance

Liangzhu Culture in the lower reaches of the Yangtze River is world-famous for a large number of exquisite jade artifacts, but the provenance of nephrite materials has been a considerable controversy over the past several decades. Our research briefly summarizes evolutionary stages of unearthed nephrite artifacts, discusses a number of jades' secondary changes in the burial stage and then attempts to compare typical characteristics of Liangzhu jades with those of some nephrites within East Asia. The results show that although the weathering has obliterated some original information of Liangzhu jades, their residual information is still highly consistent with many aspects of Xiaomeiling nephrite, such as the mineral compositions, crystal morphology, textures of rocks and chemical compositions. These coincidences not only support that Xiaomeiling nephrite is one significant provenance of nephrites used by Liangzhu ancestors, but also reveal the hierarchical assignment system of Liangzhu Culture where Yuhang settlements dominate the allocation of jade resources. The distinct difference between different jade workshops in processing materials demonstrates convincingly that Liangzhu ancestors have been able to effectively identify some jade materials and a division of labor in the processing of jade artifacts has arisen, all of which support that Liangzhu Culture is a highly developed native civilization.     

产于东西伯利亚的玉是发展当地独特石雕艺技的基石

本文研究了东西伯利亚玉矿的开发史。从新石器时代起,东西伯利亚的玉就已成为需求量很大的一种矿物资源。赋存于贝加尔湖区丰富的玉石促进了当地石雕艺技的蓬勃发展。西伯利亚的玉因形成机理迥异而绚丽多彩,该区玉石成因原则上可分为“去超基性岩化型”和“去碳酸岩化型”两种不同类型。东西伯利亚的玉成为重塑当地数千年来文明发展史的标志。文章概述了东西伯利亚的玉在亚洲北部古代社会中和当代科学研究中的重要价值和意义,讨论了该种玉的天然属性对艺术品和工业品制备过程中可能出现的各种问题,展示了东西伯利亚的玉的独特魅力及其与系列化设计工艺品间的差异。     

韩国软玉的宝石学特征及结构分析

通过宝石学常规测试、显微硬度计、偏光显微镜观察、扫描电镜测试等方法,对韩国软玉的宝石学参数、结构特征进行了研究。研究表明,韩国产软玉相对密度为2.88～2.95,摩氏硬度为5.45～6.17。偏光显微镜下观察,韩国软玉的主要结构为显微-隐晶质变晶结构,常见交代假像结构、交代残蚀结构、碎裂结构,表明其重结晶作用不强烈。扫描电镜分析表明,韩国软玉的矿物颗粒大小不均,以纤维状为主,同时粗纤维状、柱状斑晶含量较高,纤维状透闪石定向性排列较明显。     

新疆、青海、俄罗斯糖白玉的宝石学特征对比分析

为了查明新疆、青海、俄罗斯三地所产糖白玉的结构、成分和成因差异,在观察原料外观特征的基础上,采用常规宝石学方法、偏光显微镜、X射线粉末衍射仪和电子探针研究新疆、青海、俄罗斯糖白玉样品,从结构类型、矿物组成、化学成分和成因特征等方面进行对比分析。结果表明,以上三地糖白玉的主要矿物组成均为透闪石,次要矿物组成则各有不同。新疆、俄罗斯糖白玉以毛毡状变晶结构为主,青海糖白玉以纤维状变晶结构和纤维-隐晶质变晶结构为主;初步认定以上三地糖白玉的糖色为次生色,主要由褐铁矿导致。结合相关地质背景和风化作用特征,推测以上三地糖白玉不同的外观特征主要受玉体成矿后期和成矿期结束后周围环境变化的影响。     

Mantle heterogeneity and crustal recycling in Archean granite-greenstone belts: Evidence from Nd isotopes and trace elements in the Rainy Lake area, Superior Province, Ontario, Canada

The 2685–2752 Ma old granite-greenstone crust in the Rainy Lake area, Ontario, consists of metaigneous and metasedimentary rocks that range in composition from tholeiite to monzogranite and include anorthosite, trachyandesite, monzodiorite and high-silica rhyodacite. Major element, rare earth and other trace element data are the basis for modelling the formation of the crust by melting of large-ionlithophile element enriched and unenriched mantle, by melting of basalt at mantle to crustal levels and by melting of monzodiorite and tonalite at crustal levels.

All metaigneous rocks lie on a ¹⁴³Nd/¹⁴⁴Nd vs. ¹⁴⁷Sm/¹⁴⁴Nd isochron with an age of 2737 ±42 Ma and an initial ¹⁴³Nd/¹⁴⁴Nd of 0.509178 ±33 (ε_Nd = +1.9). This age is consistent with U-Pb zircon ages, which suggests the Nd isotopic system has been unaffected since the crust-forming events. The positive initial ε_Nd's are further evidence for time-averaged depletion in Sm/Nd relative to CHUR for the Archean mantle. The similarity of the initial Nd isotopic composition for both mantle-derived and crustally-derived rocks suggests rapid recycling of crustal components, which were previously derived from depleted mantle sources.

Initial ¹⁴³Nd/¹⁴⁴Nd ratios on individual rocks range from ε_Nd = +3.3 to ε_Nd = −0.4. Younger granitoids have lower ε_Nd values (+1.5 to −0.1) relative to tholeiites and monzodiorites crystallized from mantle-derived melts (+3.3 to +1.0). Thus, incorporation of slightly older crust (ca. 100–200 Ma) in some of the granitoid source areas is possible. Mantle-derived rocks form an isochron of 2764 ±58 Ma that represents a minimum age for enrichment processes in the mantle sources for the Rainy Lake area. Consideration of data from the Abitibi belt suggests such enrichment processes in the mantle may have preceded crust-forming events in a wide area of the Superior Province, perhaps by as much as 50–70 Ma.     

The Tashisayi nephrite deposit from South Altyn Tagh,Xinjiang,northwest China

The Tashisayi nephrite deposit is located in South Altyn Tagh.in Qiemo County,Xinjiang Province,northwest China.It is a recent discovery in the vast,well-known Kunlun-Altyn nephrite belt distributed along the south of the Tarim Basin,producing more than half of the nephrite from the whole belt in 2017.Field investigations revealed that it is a dolomitic marble-related(D-type)nephrite deposit,but little is known about its age of formation and relationships between the granites and marble.Here we report field investigations,petrography of the neph rite,as well as petrography,geochemistry,geochronology of the zoisite-quartz altered intrusive rock and adjacent granites.An A-type granite is identified with a SHRIMP U-Pb zircon age of 926± 7 Ma,suggesting it was emplaced in an extensional tectonic environment at that time.The altered intrusive rock has a cluster of U-Pb zircon age of 433± 10 Ma.with similar trace element features to the A-type granite,suggesting it was formed in an extensional regime at this later time.Nephrite formed because of the metasomatism of dolomite marble by hydrothermal fluids.It is inferred that Ca~(2+) was released from the dolomitic marble by metasomatism forming Ca-rich fluids,which caused alteration of both the intrusive rocks(6.00-8.22 wt.% CaO)and granite(1.76-3.68 wt.% CaO)near the nephrite ore bodies.It is also inferred that Fe2+ from the granite migrated towards the dolomite marble.The fluids gave rise to the formation of Ca-minerals.such as zoisite,in the nephrite and altered intrusive rock,and epidote in the granite.Based on the contact relationships.similarity in hydrothermal processes,and consumption of Ca~(2+),the Tashisayi nephrite is considered to have formed at the same time as the alteration of the intrusive rocks,i.e.～433 Ma.The geochronological similarity(～926 Ma.433 Ma)of South Altyn and North Qaidam may suggest that tectonically they belong to one single complex in the past,which was offset by the Altyn Tagh fault(ATF).The similar formation ages of the nephrites from Altyn Tagh(433 Ma)and the previously studied areas of West Kunlun(378-441 Ma)and East Kunlun(416 Ma)indicate that these nephrites formed during the closure of Proto-Tethys and in the accompanving post-collisional.extensional environment.     

The influence of the Nurek Reservoir on local earthquake activity

The Nurek Reservoir is located in an area of high seismicity. An average of 5–6 earthquakes of (Russian energy class)K = 10 and 1–2 earthquakes ofK = 11 per year occurred in the vicinity of the reservoir. The largest local earthquake recorded fell in the energy classK = 14 (1956).

At the end of 1972, after the water level had risen to 100 m, earthquake activity increased sharply. Three events ofK = 12 were recorded during one month and the total number of earthquakes (K 7) exceeded three times the former mean level of seismicity.

Spatial and temporal properties in the epicentral distribution showed a migration from the southwest toward the reservoir.

Earthquake mechanisms of 215 events ofK 9 since 1960 were analysed. Fault plane solutions for some of the earthquakes which occurred after the impoundment were found to be different from the ordinary ones.     

中国软玉矿床类型及其矿物学特征

文章将中国11个产地的软玉（透闪石玉）矿床分为岩浆热液型和变质热液型两大类。其中岩浆热液型又根据侵入体的性质分为中酸性岩型、基性岩型、超基性岩型;变质热液型根据母岩特点分为碳酸盐岩型和蛇纹岩型,并从围岩和侵入岩体特征、矿体产状及大地构造背景等方面,对比分析了软玉矿床的相似性和差异性,总结了各产地软玉的品种、矿物成分、结构构造等矿物学特征;简单分析了软玉的找矿远景。     

Foraminiferal depth palaeoecology of Late Pliocene shelf sequences and systems tracts, Wanganui Basin, New Zealand

High-resolution foraminiferal census of benthic taxa was undertaken on 113 closely spaced samples drawn from the Late Pliocene (ca. 2.6−1.7 Ma) cyclothemic marine strata of the Rangitikei Group, eastern Wanganui Basin, New Zealand. These strata comprise a ca. 1 km thick progradational stack of twenty, sixth-order, depositional sequences that accumulated in shelf and shoreline palaeoenvironments. The sequences are correlated with δ¹⁸O Stages 100−58, and each 41 ka glaciallinterglacial stage couplet is represented by an individual sequence comprising transgressive (TST), highstand (HST), and regressive (RST) systems tracts.

Statistical analysis of the census data identifies thirteen foraminiferal associations within the cyclothemic strata, that are grouped into seven depth- and lithology-related biofacies spanning the entire range of marginal marine to outer shelf palaeoenvironments. Foraminiferal palaeobathymetric analysis of the Rangitikei Group sequences reveals cyclical changes in water-depth of ca. 100–200 m amplitude with frequencies corresponding to the 41 ka obliquity orbital rhythm. Water-depth changes of this magnitude are consistent with a glacio-eustatic origin for the cyclothems, which correspond to an interval of Earth's history when successive continental glaciations of the Northern Hemisphere are known to have occurred. Furthermore the derived water-depth changes are also consistent with lithofacies and sequence stratigraphic inferences regarding palaeodepth of the sequences.

Individual sequences display a clear deepening-upward trend from shoreline to mid-shelf water-depths within TSTs. The level of resolution provided by the microfaunal analysis was insufficient to resolve the precise position of the maximum flooding surface (MFS) and its relationship to the downlap surface (DLS). However, the turn around from rising to falling relative sea level (maximum water-depth) corresponds to a < 5 m interval of section spanning the top of TSTs and lower portions of HST's. A progressive shoaling trend to shoreline and marginal marine environments is indicated for the overlying RSTs.

The amplitudes of water-depth changes for asymmetrical sequences, Rangitikei_nt motif (nondepositional transgression) (100–200 m), are somewhat greater than glacio-eustatic sea-level changes derived from the deep-sea δ¹⁸O record (50–100 m). This implies a significant subsidence contribution to relative sea-level changes. Notwithstanding the effect of subsidence and sedimentation on relative sea level, fluctuations in glacio-eustatic sea level are regarded as the primary factor controlling relative sea-level changes recorded in the Late Pliocene Wanganui Basin succession. Foraminifer-derived palaeobathymetric cycles within sequences display the same frequency, relative magnitude and symmetry as their correlative cycles on the δ¹⁸O sea-level curve.