Modelling Ediacaran metazoan-microbial reef growth
Modelling Ediacaran metazoan-microbial reef growth
复制标题
模拟埃迪卡拉后生动物-微生物礁的生长
DOI：
10.1111/sed.12832
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发表时间：
2020
期刊：
影响因子：
3.5
通讯作者：
Curtis A
中科院分区：
文献类型：
--
作者：
Curtis A
在整个显生界，固着的后生动物与各种微生物碳酸盐密切相关地生长，形成珊瑚礁。大约5.5亿年前，第一批具有钙质坚硬部分的后生动物出现在埃迪卡拉纪末期，大约5.5亿年前，这些后生动物通常也与微生物席、血栓岩和叠层石共生，形成了已知的最古老的后生微生物礁。这些坚硬的部分还形成了第一批骨架(生物碎屑)碳酸盐沉积，在显生宙期间增加到主导浅海碳酸盐沉积生产。本文以纳米比亚纳马群(约547 Ma)的生物礁复合体为基础，描述了埃迪卡拉纪微生物-后生生物礁及其生物碎屑产物之间的生长动力学和沉积相互作用，并建立了第一个三维数值模型来对这些动力学进行参数化。观察到这些礁石形成了大圆丘和圆柱体，毗邻当地高速率的生物碎屑沉积堆积，并通常演变为覆盖着沉积物的平顶表面。这个模型是简约的，体现了一个单一的动态规则：后生动物附着在微型闪石土丘上，这些土丘径向生长成自由空间，与后生动物的产量成比例地脱落生物碎屑。由于空间竞争，模型将土丘演变为柱状，并在土丘扩张和抑制之间产生一种振荡的相互作用，导致微生物土丘和碎屑沉积物的相互作用。这一动态表现为生物碎屑沉积的比例是非线性的。生物碎屑沉积物的窒息也被证明既降低了随后的土丘生长速度(按体积计算)，也淹没了叠层石不断生长的垫面：在生物碎屑沉积物沉积速度达到阈值后，沉积物终止了所有叠层石的生长。这些模型表明，野外观测的一般特征可以用单一的动力学规则来解释，来自生物礁的生物碎屑可能对埃迪卡拉纪的寒武纪微生物-后生动物生物礁动力学做出了重要的局部贡献--这一贡献在整个显生宙仍然是重要的。
Throughout the Phanerozoic, sessile metazoans grew in close association with various microbial carbonates to form reefs. The first metazoans with calcareous hard‐parts appeared in the terminal Ediacaran,ca550 million years ago, and these also commonly grew associated with microbial mats, thrombolites and stromatolites, to form the oldest known metazoan–microbial reefs. These hard‐parts also formed the first skeletal (bioclastic) carbonate sediments, which increased to dominate shallow marine carbonate sedimentary production during the Phanerozoic. Here the growth dynamics and sedimentary interactions between Ediacaran microbial–metazoan reefs and their bioclastic products are described based on reef complexes from the Nama Group, Namibia (ca547 Ma), and the first three‐dimensional numerical models are constructed to parametrize these dynamics. These reefs are observed to form large domal mounds and columns neighbouring locally high rates of bioclastic sediment accumulation, and commonly evolve to flat‐topped surfaces overlain by sediment. This model is parsimonious, embodying a single dynamic rule:metazoans attach to microbialite mounds which grow radially into free space shedding bioclasts in proportion to metazoan production. Models evolve mounds into columns due to spatial competition, and produce an oscillating interplay between mound expansion and smothering that results in an inter‐fingering of microbialite mound and detrital sediment. This dynamic is shown to be non‐linear in the proportion of bioclastic sediment produced. Smothering by bioclastic sediment is also demonstrated to both reduce the rate (by volume) of subsequent mound growth, and to overwhelm the growing mat surfaces of stromatolites: after a threshold is reached in the rate of bioclastic sediment deposition, sediment terminates all stromatolite growth. These models show that the general characteristics of field observations can be explained by a single dynamic rule, and that reef‐sourced bioclasts may make an important local contribution to Ediacaran to Cambrian microbial–metazoan reef dynamics – a contribution that remains important throughout the Phanerozoic.