Miocene coral assemblages in Anguilla, B.W.I., and their implications for the interpretation of vertical succession on fossil reefs
Miocene coral assemblages in Anguilla, B.W.I., and their implications for the interpretation of vertical succession on fossil reefs
复制标题
英属维尔京群岛安圭拉的中新世珊瑚组合及其对化石礁垂直演替解释的影响
作者：
A. Budd;K. Johnson;J. Edwards
三种常见的珊瑚组合已被定量确定在中中新世安圭拉（小安的列斯群岛）安圭拉形成的三维坐标的聚类分析来自非度量多维尺度的数据包括在25个点的178个1平方米的样方内确定的珊瑚物种的计数随机放置在5个地方的珊瑚丰富的镜头垂直曝光。共记录到18种。由此产生的集群intergrade，其特征在于适度高的差异，这是没有显着不同。它们包括：1）以Porites portoricensis为主的粗枝组合; 2）以Porites waylandi、Siderastrea conferta、Goniopora hill和G.（3）由Porites macdonaldi和Porites baracoaensis组成的一个扁平细枝组合。卡方检验结果表明，这些组合在空间上和层序上都是随机分布的。斑块状，intergradational分布的组合，他们同样可变的，但高diabetes，和他们的协会与钙质砂透镜体表明，他们可能都发展为小补丁礁或灌木丛的组成不同的浅，轻轻倾斜backreef平台。这三个组合在相似的环境条件下，在一个主要的礁区的平台上进行频繁的非生物干扰流沙。因此，仅仅存在具有不同形状的造礁珊瑚的独特组合，其本身并不一定意味着生态演替或大规模的物理环境梯度，就像在许多类似的珊瑚礁化石序列中通常解释的那样。
Three common coral assemblages have been quantitatively identified in the middle Miocene Anguilla Formation of Anguilla (Lesser Antilles) using cluster analysis on three-dimensional coordinates derived from nonmetric multidimensional scaling The data consisted of tallies of coral species identified at 25 points within 178 1 -meter-square quadrats placed haphazardly across vertical exposures of coral-rich lenses at five localities. Eighteen species were recorded. The resulting clusters intergrade and are characterized by moderately high diversities which are not significantly different. They include: 1) a thick-branched assemblage dominated by Porites portoricensis, 2) a mound-shaped assemblage including Porites waylandi, Siderastrea conferta, Goniopora hill, and G. imperatoris, and 3) a platylthin-branched assemblage composed of Porites macdonaldi and Porites baracoaensis. The results of chi-square tests show that the assemblages are randomly distributed, both in space and in stratigraphic sequence. The patchy, intergradational distribution of the assemblages, their equally variable but high diversities, and their association with calcareous sand lenses suggest that they probably all developed as small patch reefs or thickets of varying composition on a shallow, gently sloping backreef platform. The three assemblages developed under similar environmental conditions in one major reef zone on a platform subjected to frequent abiotic disturbance by shifting sand. The mere existence of distinctive assemblages of reef-building corals having different shapes, therefore, needs not in itself imply ecological succession or large-scale physical environmental gradients, as is commonly interpreted in many similar fossil reef sequences.