晚震旦世灯影组叠层石中微生物的排列方式和降解序列

ARRANGEMENT PATTERN AND DEGRADATION SEQUENCES OF MICROORGANISMS WITHIN THE STROMATOLITES FROM THE TONGYING FORMATION (UPPER SINIAN)

在江苏丹徒县黄墟乡灯影组下部,分布黑色燧石质叠层石,经切片研究,发现叠层石纹层中保存大量隶属于Eomycetopsis sp.,Siphonophycus sp.和?Animikiea sp.等管状衣鞘类微化石。从这些衣鞘化石排列规律中,可以看出组成叠层石原始藻丝的生长节律和趋光性的生长方式以及这些衣鞘类微化石从保存至降解过程中形态变化的序列。

Well-preserved tubular sheaths have been found from the cherty stromatolites of the Tongying Formation in the Huangxu area, Dantu County, jiangsu Province. The Tongying Fm. is mainly composed of grey alloehem (intraclast andoolite) dolomite intercalated with stromatolite- and oncoid-bearing lime-dolomite and siliceous rocks. Three microfossil forms have been discovered in thin sections, of the stromatolites, namely, Eomycetopsis sp., Siphonophycus sp, and ? Animikiea sp.Vertical sections of the domical (Collenia-like) stromatolites show a cyclothemic sequence of light, thick, silica-filled layers alternating with dark, thinner, organism-rich layers (PI.Ⅱ, fig. 1).The tubular sheaths exhibit a distinct pattern of horizontally and vertically oriented populations in alternating layers. The light layers composed of erect or slant tubular sheaths are interpreted as recording phototactic daytime algal growth, whereas the dark ones composed of prostrate tubular sheaths reflect nocturnal layering (P1.Ⅲ, fig. 2). The writer believes that the cyclothemic sequence represents a probable nocti-diurnal growth rhythm of the original filamentous cyanobacteria. On these grounds, the writer determined the average thickness produced daily of the stromatolitie lamina to be 128 μm (in light layer 87μm, dark layer 41μm). In vertical thin sections of conical (Conophyton-like) stromatolites, dark layers in cone flanks, which show nets of tubular sheaths combining both horizontal and vertical arrangements (Pl.Ⅲ, fig. 3, 4), ares several times as thick as light layers in which tubular sheaths are generally not preserved, At the cone tips, tubular sheaths tend to stand vertically, forming tufts or thickenings within the laminae (P1.Ⅱ,fig. 3). Similar phototactic responses have been observed by Monty (1976) and Walter et al. (1976) in modern stromatolitas, which have provided physiological data for the reconstruction of microorganisms before 600 Ma.The dagradatiou sequences of microorganisms can be observed in thin sections of the present-day stromatolites (P1.Ⅳ, figs, 1—4), Comparative studies between degradation remnants and microstructures of carbonate stromatolites would lead to a better understanding and interpretation of the origin of the microstructures.