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We have used digital photography, image analysis and measurements in the field to determine the growth rates of Quaternary corals in the Wakatobi Marine National Park, Indonesia, and compared them to growth rates of similar corals in the same area. In the Quaternary deposits it was possible to measure the growth rates of two massive coral genera Porites and Favites. For each genus, the corals reworked from better‐illuminated upslope environments had higher growth rates than the in situ fossil corals. The calculated radial growth rates for the in situ Porites are slightly lower than, but of the same order of magnitude as, the modern Porites growing in 10 m water depth at Hoga (10.04 ± 3.34 mm yr?1 ± 1 s.d.; n = 3) and Kaledupa (15.26 ± 4.83 mm yr?1 ± 1 s.d.; n = 3). Sedimentation rates and underwater visibility are inferred to have been similar in the fossil site to that at the modern Kaledupa site. Decreasing light penetration due to increased water depth is inferred to have been a major influence on growth rates. The in situ massive corals with good growth banding are inferred to have grown in a comparable environment to modern Kaledupa and Hoga. The study highlights that it is possible to compare coral growth rates, and their influencing parameters, from modern and well‐preserved ancient examples. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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N. KATSUTA I. SHIMIZU H. HELMSTAEDT M. TAKANO S. KAWAKAMI M. KUMAZAWA 《Journal of Metamorphic Geology》2012,30(5):457-472
The Archean (2.8 Ga) Banded Iron Formation (BIF) of the Bell Lake region of Yellowknife greenstone belt, Canada is recrystallized to metamorphic assemblages of the amphibolite facies. This BIF is characterized by centimetre‐scale Fe‐rich and Si‐rich mesobands. In the Si‐rich mesobands, thin layers of magnetite microbands are developed in a quartz matrix. The Fe‐rich mesobands are composed mainly of Ca‐amphibole (hornblende), Fe–Mg amphibole (grunerite), and magnetite. The metamorphic foliation locally cuts across the mesoband boundaries, indicating the mesobanding was formed prior to peak metamorphism. Variations in mineral modal proportions between Fe‐rich mesobands and microbands are diagnostic of depositional compositional differences between beds. Micro‐X‐ray fluorescence imaging reveals metamorphic differentiation within Fe‐rich mesobands, with segregation of Fe–Mg amphibole, and the incompatible element Mn is concentrated at the margins of the Fe‐rich mesobands during the amphibole‐forming reactions. Ti was relatively immobile during metamorphic segregation and its distribution provides a record of the original structures in the Fe‐rich mesobands. 相似文献
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We address the question of the predictability of skarn textures and their role in understanding the evolution of a skarn system. Recent models of skarn formation show that skarns are ideal for application of self-organisation theory, with self-patterning the rule in fluid-rock interaction systems rather than the exception. Zonation in skarn deposits, a consequence of infiltration-driven metasomatism, can also be treated in terms of self-organisation. Other less commonly described features, such as scalloping, fingering and mineral banding, can be understood by application of reactive infiltration and hydrodynamics at the skarn front. Devolatilisation may trigger formation of back-flow fluxes that overprint previously formed skarn. The range of textures formed from such events can be used to discriminate between prograde and retrograde stages. Refractory minerals, such as garnet, magnetite and pyrite, readily retain overprinting events. Skarns are also composed largely of minerals from solid solution series (garnet, pyroxene, pyroxenoids, etc.) and therefore skarn mineralogy helps to establish trends of zonation and evolution. The same minerals can act as ‘chemical oscillators’ and record metasomatic trends.The Ocna de Fier-Dognecea deposit was formed in a 10 km deep skarn system. Zonation and evolution trends therefore represent only the result of interaction between magmatically derived fluids emerging at the source and limestone. From the same reason, the transition from prograde to retrograde regime is not influenced by interaction with external fluids. Thirdly, the mineralisation comprises Fe, Cu and Zn-Pb ores, thus facilitating comparison with skarn deposits that commonly are formed in shallower magmatic-hydrothermal environment. Copper-iron ores (magnetite+Cu-Fe sulphides), hosted by magnesian (forsterite+diopside) skarn, occur in the deepest and central part of the orefield, at Simon Iuda. Their petrological character allows interpretation as the core of the skarn system formed from a unique source of fluids emerging from the subjacent granodiorite. It formed first as a consequence of the local setting, where a limestone indented in the granodiorite permitted strong reaction at 650 °C and focussed the up-streaming, buoyant fluids. The first sharp front of reaction is seen at the boundary between the Cu-Fe core and Fe ores hosted by calcic skarn (Di70-90-And70-90), where Cu-Fe sulphides disappear, and forsterite gives way to garnet in the presence of diopside (Di90). Following formation of forsterite, devolatilisation and transient plume collapse is interpreted from a range of piercing clusters and trails. We presume lateral flow to have been initiated at the source, as the emerging fluids are in excess to the fluids driven into reaction by the plume. Formation of the other orebodies, up to 5 km laterally downstream in both directions, is interpreted as skarn fingering at the limestone side. The metasomatic front is perpendicular to the flow along the channel of schists placed between the limestone base and the granodiorite.A metal zonation centred onto the source is defined, based on metal distribution: Cu-Fe/Fe/Zn-Pb. The second front of reaction, at the boundary between the Fe and Zn-Pb zone, has a sulphidation/oxidation character, with diopside giving way to a Fe-Mn-rich pyroxene, (HedJoh)>60+pyroxmangite±bustamite; garnet is minor. Johannsenite-rich pyroxene (Di20-40Hed20-40Joh40) is found in proximal skarn at the upper part of Simon Iuda, stable with Zn0.95Fe0.05S, at an inferred 570 °C. In distal skarn from Dognecea and Paulus, Mn-hedenbergite (Di<10Hed70Joh20-30) formed at 400 °C is stable with Zn0.84Fe0.16S. Extensive compositional fields, eutectic decomposition and lamellar intergrowths characterise pyroxene in the Zn-Pb zone, formed at the magnetite-hematite buffer in the presence of pyrite. Distal skarn has a reducing character, in comparison with the proximal. A drop in both fS2 and O2, with the zoned system moving closer to the pyrite-pyrrhotite buffer, is induced from the temperature gradient. Based on pyroxene mineralogy and calculated fS2, the metal zonation is confirmed as being formed upwards and outwards from the source.The Fe and Zn-Pb zones both have a patterned side coexisting with the unpatterned one. Patterning is seen at scales from macroscopic (rhythmic banding, nodular, spotted, orbicular, mossy, mottled textures) to microscopic scales (oscillatory zonation in garnet and silica-bearing magnetite). Following plume updraft, the path of decarbonation reaction controlled the motion of the skarn front until, towards the end of the prograde stage, a multiple steady state regime developed and produced rhythmic patterns on all scales. The activation of powerful patterning operators, represented by Liesegang banding alone, or coupled with competitive particle growth, show that the skarn front had the characteristics of an unstable coarsening front of reaction.A second retrograde event, carbofracturing, triggered by erratic decarbonation after cessation of infiltration, can be interpreted from overprinting textures in the Fe and Zn-Pb zone. A major drop in fO2 is inferred from extensive, pseudomorphous replacement of hematite by magnetite. Textures show progressive destruction of prograde assemblages, i.e., piercing clusters, shock-induced, fluid-pressure assisted brecciation and deformation, followed by healing of the disrupted assemblages. Release of trace elements accompanies both retrograde events, with a Bi-Te-Au-Ag association common to both. The importance of shock-induced textures is emphasised in the context of Au enrichment, especially when the retrograde fluids cross the main buffers in fO2-fS2 space.The presence of Bi-sulphosalt polysomes in the Fe zone indicates that patterning extends down to the nanoscale. The key role played by polysomatism in stabilising compositional trends that cannot otherwise be formed at equilibrium is a fertile ground yet to be adequately explored. 相似文献
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ZHANG Lingling BAO Zhenmin WANG Jue WANG Shi HUANG Xiaoting HU Xiaoli HU Jingjie 《海洋学报(英文版)》2007,26(5):153-158
Cytogenetic analysis was performed for the bay scallop(Argopecten irradians Lamarck 1819) and the Japanese scallop(Patinopecten yessoensis Jay 1857) by primed in situ labeling(PRINS) and propidium iodide(PI) banding techniques.The PRINS analysis revealed that major rRNA genes were clustered in two loci on the telomeric regions of the short arms on two acrocentric chromosome pairs in A.irradians and on two submetacentric pairs in P.yessoensis.The histone H3 gene sites differed in number and location between these two species.The C-band-like patterns revealed by PI staining varied considerably between these two species.A.irradians displayed terminal bands at long arms on all chromosomes,centromeric bands on some pairs and interstitial bands on five pairs.P.yessoensis exhibited only centromeric bands on all chromosomes.These results would contribute to the better understanding of karyotype evolution in A.irradians and P.yessoensis. 相似文献
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从生物学测定、孵化质量、染色体倍性、繁殖方式等方面对产于新疆阿其克库勒湖和青海尕海两品系孤雌生殖卤虫(Artemia spp．)进行了对比研究。结果表明，阿其克库勒湖卤虫的生物学测定值明显高于青海尕海卤虫；两地卤虫加工卵的孵化率和孵化速率没有明显差异；尕海卤虫孵化效率高于阿其克库勒湖卤虫；两地卤虫的染色体倍性均以二倍体为主，其中阿其克库勒湖卤虫有三倍体存在，尕海卤虫有四倍体。两地卤虫的胚后发育速度相近。研究过程中未观察到阿其克库勒湖卤虫进行卵胎生。 相似文献
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PHA体内注射后,按肾细胞直接法和银染法研究花尾胡椒鲷(Plectorhinchus cinctus)、胡椒鲷(Plectorhinchus pictus)染色体核型及Ag-NORs带.两种鱼核型公式均为2n=48,48t,NF=48.胡椒鲷具有1个大的NORs,呈圆球形,位于端部着丝粒染色体端部;花尾胡椒鲷也具有1个较小的NORs,呈2个棒状结构,位于端部着丝粒染色体的端部. 相似文献
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Poul V. Lade 《国际地质力学数值与分析法杂志》2006,30(4):307-333
Data from three‐dimensional experiments performed on sand in true triaxial equipment have been reviewed to sort out apparent disarray resulting from their interpretation. This has been done based on analyses made possible by recent developments and understanding of factors influencing sand behaviour: occurrence of shear banding, boundary conditions and/or specimen slenderness ratio, cross‐anisotropy, and stability of experimental technique. These factors are reviewed and test data from the literature are evaluated. Experimental data are divided into three groups in which: (a) homogeneous behaviour controls the sand strength; (b) shear banding affects the shape of the three‐dimensional failure surface in the midrange of values of b=(σ2?σ3)/(σ1?σ3), and (c) the data has been misinterpreted. Appropriate interpretation of three‐dimensional strength data for sand exhibiting isotropic, homogeneous behaviour is represented by a smoothly rounded triangular failure surface expressible in terms of the first and third stress invariants. Shear banding effects will cause the failure surface to be ‘indented’ in the midrange of b‐values in all sectors of the octahedral plane. Effects of cross‐anisotropy will result in lower strengths in sector III than in sector I of the octahedral plane, and the failure surface will appear as rotated around the stress origin in principal stress space. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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