通过微生物垫中剪切诱导的不稳定性形成Kinneyia
Formation of Kinneyia via shear-induced instabilities in microbial mats
摘要：
Kinneyia是一类微生物介导的沉积化石。Kinneyia的特征是明显的波纹结构，通常发现于正式的沿海栖息地和微生物垫覆盖的地区。到目前为止，还没有对这些化石形成过程的结论性解释。微生物垫表现得像粘弹性流体。我们建议，Kinneyia的形成所涉及的关键机制是一个Kelvin-Helmholtz型不稳定性在流动的水的粘弹性膜诱导。在薄膜中自发地诱发波纹，并且随着时间的推移，波纹的振幅增大。理论预测表明，波纹不稳定性的波长成正比的膜的厚度。使用粘弹性薄膜进行的实验证实了这一预测。形成的波纹图案的波长大约是薄膜厚度的三倍。这种行为与膜的粘度和流动条件无关。通过玻璃珠的沉淀形成类似于Kinneyia的波纹，玻璃珠优先沉积在波纹的槽中。良好有序的图案形式，与蜂窝状和平行的脊被观察到，这取决于流速。这些模式与Kinneyia中发现的模式相对应，观察到类似的形态，波长和振幅。
英文摘要：
Kinneyia are a class of microbially mediated sedimentary fossils. Characterised by clearly defined ripple structures, Kinneyia are generally found in areas that were formally littoral habitats and covered by microbial mats. To date there has been no conclusive explanation of the processes involved in the formation of these fossils. Microbial mats behave like viscoelastic fluids. We propose that the key mechanism involved in the formation of Kinneyia is a Kelvin-Helmholtz type instability induced in a viscoelastic film under flowing water. A ripple corrugation is spontaneously induced in the film and grows in amplitude over time. Theoretical predictions show that the ripple instability has a wavelength proportional to the thickness of the film. Experiments carried out using viscoelastic films confirm this prediction. The ripple pattern that forms has a wavelength roughly three times the thickness of the film. This behaviour is independent of the viscosity of the film and the flow conditions. Laboratory-analogue Kinneyia were formed via the sedimentation of glass beads, which preferentially deposit in the troughs of the ripples. Well-ordered patterns form, with both honeycomb-like and parallel ridges being observed, depending on the flow speed. These patterns correspond well with those found in Kinneyia, with similar morphologies, wavelengths and amplitudes being observed.
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