【摘要】 在天津蓟县剖面古元古界串岭沟组下部的环潮坪相粉砂质泥页岩细粒沉积中,发育许多粉砂岩岩墙。由于该粉砂岩岩墙在层面上和层内具有特别的形态,因而对其成因具有多种解释:在层面上呈纺锤状粉砂岩裂缝以及在层内呈砂质充填管形态,从而被认为是最古老的后生动物遗迹化石;在层内呈弯弯曲曲的粉砂岩岩墙以及明显的流体化作用特点,所以又被解释为地震振荡作用形成的液化砂岩脉。显微镜下,这种岩墙具有明显的富残余有机质构成的边界,以及由粉砂颗粒相对聚集所显示出的明显的流体化作用特征;再加上与这种粉砂岩岩墙共生的沉积构造主要是皱饰构造,局部还发育变余波痕,由此表明沉积面上曾经发育过微生物席。因此,这种粉砂岩岩墙应该解释为沉积面在曾经被微生物席封闭的情况下,相对富含有机质的细粒沉积物在早期成岩作用过程中所发生的脱气作用和脱水作用的产物,最终可以归为由微生物形成的沉积构造的一种类型。更多还原

【Abstract】 There are many silty dykes in peritidal silty muddy shales of the lower part of the Paleoproterozoic Chuanlinggou Formation at Jixian section in Tianjin.Particular configurations on bedding planes and on the surface perpendicular to the bedding planes lead to different explanations for the genesis of these silty dykes:(1)they are considered as the oldest trace fossils of metazoan according to the spindle-crack of siltstones on the bedding plane and the sand-filling tube configurations on the surface perpendicular to the bedding plane;(2)they are considered as the liquefied sand-veins induced by earthquake according to the sinuous configuration of siltstone dykes on the surface perpendicular to the bedding plane and the obvious liquation feature.Several features indicate that these silty dykes were generated by the degassing and dewatering processes in the early diagenesis under the condition that the sedimentary surface was sealed by microbial mats,and can further be grouped into the microbial induced sedimentary structure(MISS).These features include:(1)the clear boundary being enriched with residue organic substance and the obvious fluidization feature shown by the relative accumulation of silty grains under the petrographic microscope;(2)the accompanied wrinkle structure and the palimpsest ripples which indicate the development of microbial mats on the sedimentary surface.更多还原