滦河三角洲潮坪环境现代生物遗迹组合及其分布特征*

现代生物遗迹的特点、分布和组合特征及其与沉积环境、沉积物性质的关系,对遗迹化石及古环境研究具有重要的实证价值,但现代生物遗迹研究起步较晚,国内研究成果较少。文中论述了滦河三角洲潮坪环境中现代生物遗迹的组成、组合与分布特征,并分析了遗迹组合与沉积环境的关系。研究表明: (1)层面遗迹以节肢动物、环节动物、腹足动物的爬行迹和拖迹为主; 层内遗迹包括垂直或高角度倾斜于层面的潜穴、平行于层面的潜穴,以居住迹为主,丰度高,类型多样。(2)建立了3种生物遗迹组合: 遗迹组合I以Y形和垂直管状潜穴为特征,局部丰度较高,表层潜穴和层面拖迹不发育,造迹生物主要为沙蚕和螃蟹,沉积物底层具有砂含量较高、水动力强、有机质含量低的特点,显示其出现于三角洲潮坪砂质沉积环境;遗迹组合Ⅱ以各种形态的层内潜穴和大量的层面爬行拖迹为特征,层内潜穴包括垂直管状、J形、U形、Y形和分枝形潜穴,丰度高,造迹生物主要是沙蚕和螃蟹,层面遗迹常见爬行拖迹和足辙迹,造迹生物主要为沙蚕、螃蟹、扁玉螺、寄居蟹,沉积物底层具有高泥质含量、高含水率和高有机质含量的特点,形成于三角洲潮坪中低潮区;遗迹组合Ⅲ以与层面近似垂直和与层面近似平行的层内潜穴以及大量的层面运动迹为特征,与层面近似垂直的潜穴包括垂直管状、J形、U形、Y形和复杂分枝形潜穴,造迹生物主要是螃蟹、泥甲虫及其幼虫, 与层面平行的表层潜穴主要是蝼蛄、泥甲虫及其幼虫营造的,层面上的运动迹常见为螃蟹足辙迹和鸟类足迹,沉积物底层具泥质含量高、含水率低、有机质含量高、底质固结程度较高的特点,产生于三角洲潮坪高潮区。(3)基于对遗迹组合和分布特征及其与底层性质和沉积环境关系的分析,建立了三角洲潮坪生物遗迹组合的沉积环境分布模式。该研究成果既可作为古代三角洲潮坪沉积环境的判识依据,也可为相似遗迹化石组合的沉积环境恢复提供佐证。

Assemblages of lebensspuren and distribution characteristics in tidal flat of Luanhe delta

The characteristics,distribution and assemblage of lebensspuren and their relationships with sedimentary environment and sediment properties are significant for the study of trace fossils and palaeoenvironment. However,the research on lebensspuren started late and few related work is found in China. The paper discussed the composition,assemblage and distribution characteristics of lebensspuren in tidal flat of Luanhe delta,and analyzed the relationship between the biological assemblage and the sedimentary environments. The results are as follows: (1)The lebensspuren at the surface of bedding mainly include the repichnia and trails made by arthropoda,annelida and gastropods,and the lebensspuren in the bedding include the burrows approximately perpendicular and parallel to bedding plane,in which the domichnia is dominant with high abundance and various types. (2)Three kinds of biological assemblages are established. Type I is characterized by Y-shaped and vertical tubular burrows with locally high abundance. The epigenic burrows and trails on the bedding plane are less,and the trace makers mainly include Nereis succinea and Brachyura. The bottom of the sediments are characterized as high sand content,high intensity hydrodynamics and low organic matter content,indicating the sandy delta tidal flat sedimentary environment. Type II is characterized as various burrows in the substrate and numerous trails on the surface of bedding. The burrows in the substrate include vertical tubular,J-shaped,U-shaped,Y-shaped and branched burrows with high abundance,and the trace makers mainly include Nereis succinea and Brachyura. The lebensspuren on the formation surface mainly include repichnia and trackways,e.g., Nereis succinea,Brachyura,Glossaulax didyma and Paguridae. The substrate sediments are characterized as high muddy content,high water content and high organic matter content,forming in the middle and lower tidal area of delta tidal flat. Type Ⅲ is characterized by the burrows approximately perpendicular and parallel to the bedding plane and motion traces on the bedding surface. The burrows in the substrate include vertical tubular,J-shaped,U-shaped,Y-shaped and complex branched burrows,which are mainly made by Brachyura,mud beetles and their larvaes. The burrows parallel to bedding plane are mainly made by Cryllotalpa,mud beetles and their larvaes. The motion traces on the bedding surface include the trackways made by Brachyura and footprint made by birds. The substrate sediments for type Ⅲ assemblage showed the characteristics of high muddy content,low water content,high organic matter content and high degree of consolidation,indicating the high tidal area of delta tidal flat. (3)Based on the analyses of lebensspuren assemblage,distribution characteristics and the relationship with the substrate sediments properties and sedimentary environment,a sedimentary environment distribution model of lebensspuren in deltaic tidal flat was established. The research results can not only acted as a basis for the identification of the sedimentary environment of the ancient delta tidal flat,but also provide evidence for the sedimentary environment restoration of similar relic fossil assemblages.