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首页> 外文期刊>Facies >Varying growth rates in bamboo corals: sclerochronology and radiocarbon dating of a mid-Holocene deep-water gorgonian skeleton (Keratoisis sp.: Octocorallia) from Chatham Rise (New Zealand)
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Varying growth rates in bamboo corals: sclerochronology and radiocarbon dating of a mid-Holocene deep-water gorgonian skeleton (Keratoisis sp.: Octocorallia) from Chatham Rise (New Zealand)

机译：竹珊瑚的生长速率各不相同：来自Chatham Rise（新西兰）的全新世中层深水古尔冈骨架（Keratoisis sp.：Octocorallia）的硬化年代学和放射性碳测年

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摘要

A branched mid-Holocene bamboo coral skeleton of the isidid gorgonian genus Keratoisis (Octocorallia) recovered at southwestern Chatham Rise (New Zealand) from an average water depth of 680 m is described with respect to sclerochronology and age determination. Growth rates of the Mg-calcitic internodal increments were investigated by the counting of colour bands and radiocarbon dating. Growth banding is produced by varying orientations of crystal fan bundles towards the image plane. The skeleton shows three growth interruptions, which are documented in all branches. AMS C-14 ages decrease from base to top of the trunk and from the central axes to the margins of the branches, documenting a simultaneous vertical and lateral growth. The data provide a maximum age of 3,975 +/- 35 years BP, and a record spanning 240 +/- 35 years. While calculated longitudinal growth rates amount to an average of 5 mm year(-1) during a 55-year record, average lateral linear extension rates of 0.4 mm year(-1) are an order of magnitude lower, still allowing for a seasonal to annual resolution of colour bands on a macroscopic scale and for a daily to monthly resolution on microscales of individual crystal generations to fascicle bundles. Hence, the isidid skeleton provides a high-resolution archive of paleoceanographic dynamics in deeper water masses. Concentric incremental accretion around the central axis in the early growth stages changed into a unilaterally asymmetric growth during late-stage evolution, probably triggered by the establishment of a stable system of unidirectional currents and nutrient flux. While colour band counts, related to the AMS C-14 ages, support a seasonal to annual accretion of macroscopic growth bands in the inner concentric and complete outer parts of the skeleton, incremental growth rates at the condensed side are highly variable, as documented by hiatuses and unconformities. Thus the specimen proves that growth rates of bamboo corals may vary within individual skeletons and strongly deviate from the annual mode, hence showing implications on paleoceanographic proxy analyses.
机译：从硬化年代学和年龄确定的角度，描述了在西南查塔姆河谷（新西兰）从平均水深680 m处发现的，等腰古生的角鲨属Keratoisis（Octocorallia）的全新中支竹珊瑚骨架。通过计算色带和放射性碳测年研究了Mg钙结节间增量的增长率。生长带是通过改变晶体扇束朝向像平面的方向而产生的。骨架显示三个增长中断，记录在所有分支中。 AMS C-14的年龄从树干的底部到顶部，从中心轴到分支的边缘逐渐减少，证明了垂直和横向的同步增长。数据提供的最高年龄为BP 3975 +/- 35岁，记录范围为240 +/- 35岁。在55年的记录中，虽然计算得出的纵向增长率平均为5毫米年（-1），但平均横向线性延伸率仅为0.4毫米年（-1），低了一个数量级，但仍允许季节性宏观范围内色带的年分辨率，单个晶体世代到束状束的微观尺度上的每日至每月分辨率。因此，扇贝体骨架提供了更深水域中古海洋动力学的高分辨率档案。在生长的早期阶段，围绕中心轴的同心增量会转变成在后期的演化过程中的单边不对称生长，这可能是由建立稳定的单向流和养分流系统触发的。虽然与AMS C-14年龄有关的色带数量支持骨架内同心和完整外部的宏观生长带从季节到年度的增加，但凝结侧的增量增长率变化很大，裂痕和不合格之处。因此，该标本证明竹珊瑚的生长速率可能在单个骨骼中变化，并且与年度模式有很大偏差，因此对古海洋学代用分析显示出了影响。

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