Physicochemical and biological influences on sedimentary‐fabric formation in a salinity and oxygen‐restricted semi‐enclosed sea: Gotland Deep, Baltic Sea
Physicochemical and biological influences on sedimentary‐fabric formation in a salinity and oxygen‐restricted semi‐enclosed sea: Gotland Deep, Baltic Sea
复制标题
盐度和限氧半封闭海中沉积织物形成的物理化学和生物影响：哥特兰深海、波罗的海
DOI：
10.1111/j.1365-3091.2010.01166.x
复制
发表时间：
2011
期刊：
影响因子：
3.5
通讯作者：
A. Kotilainen
中科院分区：
文献类型：
--
作者：
J. Virtasalo;T. Leipe;M. Moros;A. Kotilainen
通过数字图像、X射线照片和扫描电子显微镜-能量色散X射线矿物学分析，研究了来自波罗的海中央次盆地哥特兰深海的两个约8000年长的沉积物岩心，以了解现代和古代海洋中沉积组构形成的物理化学和生物学影响，这些海洋具有高通量的有机碳，以及相关的氧应力和沉积遗迹动物群。识别出四种岩相：（i）明显的层压泥;（ii）生物变形泥;（iii）洞穴斑驳泥;和（iv）沉积事件床。强烈的层状和洞穴斑驳相以交替的长间隔为主，而生物变形和沉积事件相则以薄夹层的形式出现在强烈的层状间隔内。明显的层压泥包括交替的富含硅藻和岩屑的薄层，偶尔有锰碳酸盐薄层。纹层内的纹层不连续层位（规则纹层被平缓倾斜的纹层急剧覆盖）挑战了悬浮液沉降导致泥浆堆积的传统观点，但表明颗粒捕获微生物垫以及推移质运输导致泥浆快速侧向加积可能导致局部堆积。生物变形夹层记录了短暂（几年到几十年）的缺氧-缺氧条件，打断了缺氧背景条件，并允许沉积物表面放牧和仅限于表面混合层的非常不成熟的底栖生物群落进食。可能的生物变形者是小型底栖生物和浮游底栖先驱，它们是随洋流被动输入的。沉积事件夹层是由浊流沉积的远端泥浊积岩，浊流可能是由邻近沿海地区的强烈风暴引发的。缺氧背景条件有利于浊积岩的保存。长的洞穴斑驳间隔的特征是强烈的生物扰动织物与离散的Planatrium，罕见的Areniculum/Polykladichnus和非常罕见的Lockeia痕迹化石，以及双壳生物变形结构，代表浅穿透底栖动物的进食和放牧策略和永久住所。这些挖洞的间隔代表了较长时期（几年到几个世纪）的缺氧-缺氧条件，通过机会性蠕虫状大型动物和双壳类的幼虫定居，使底栖生物成熟，导致过渡层的发展。这些观测结果表明，哥特兰深水区的动态和氧化沉积条件比以前认为的要多。与该地区以前的底栖动物研究进行比较，可以讨论底栖动物动态，并确定可能的生物变形和微量生产物种。目前的生物相和微量化石模型的影响进行了讨论。
Two ca 8000 year long sediment cores from the Gotland Deep, the central sub‐basin of the Baltic Sea, were studied by means of digital images, X‐radiographs and scanning electron microscopy–energy‐dispersive X‐ray mineralogical analysis to gain understanding of the physicochemical and biological influences on sedimentary‐fabric formation in modern and ancient seas with a high flux of organic carbon, and associated oxygen stress and depauperate ichnofauna. Four lithofacies were recognized: (i) sharply laminated mud; (ii) biodeformed mud; (iii) burrow‐mottled mud; and (iv) sedimentation‐event bed. The sharply laminated and burrow‐mottled facies dominate the cores as alternating long intervals, whereas the biodeformed and sedimentation‐event facies occur as thin interbeds within the sharply laminated intervals. The sharply laminated mud comprises alternating diatom‐rich and lithic laminae, with occasional Mn‐carbonate laminae. Lamination discontinuity horizons within the laminites, where the regular lamination is overlain sharply by gently inclined lamination, challenge the traditional view of mud accumulation by settling from suspension, but indicate localized accumulation by particle‐trapping microbial mats and, potentially, by the rapid lateral accretion of mud from bedload transport. The biodeformed interbeds record brief (few years to few decades) oxic–dysoxic conditions that punctuated the anoxic background conditions and permitted sediment‐surface grazing and feeding by a very immature benthic community restricted to the surface mixed tier. The likely biodeformers were meiofauna and nectobenthic pioneers passively imported with currents. The sedimentation‐event interbeds are distal mud turbidites deposited from turbidity currents probably triggered by severe storms on the adjacent coastal areas. The turbidite preservation was favoured by the anoxic background conditions. The long burrow‐mottled intervals are characterized by intensely bioturbated fabrics with discrete Planolites, rare Arenicolites/Polykladichnus and very rare Lockeia trace fossils, as well as bivalve biodeformational structures which represent shallowly penetrating endobenthic feeding and grazing strategies and permanent dwellings. These burrowed intervals represent longer periods (several years to few centuries) of oxic–dysoxic conditions that permitted maturation in the benthos by means of larval settling of opportunistic worm‐like macrofauna and bivalves, resulting in the development of a transition tier. These observations imply more dynamic and oxic depositional conditions in Gotland Deep than previously thought. Comparison to previous zoobenthic studies in the area allowed discussion of the benthic dynamics, and the identification of probable biodeforming and trace‐producing species. Implications for current biofacies and trace‐fossil models are discussed.