Shape evolution of ooids: a geometric model
Shape evolution of ooids: a geometric model
复制标题
鲕粒的形状演化：几何模型
作者：
A. Sipos;G. Domokos;D. Jerolmack
自然界中引人注目的形状已经被证明是化学沉淀的结果--例如梯田温泉和叠层石--通常是通过表面正常的生长进行的。另一类被研究的物体是那些通过物理磨损来进化形状的物体--主要的例子是河流和海滩上的鹅卵石--这会导致形状相关的表面侵蚀。虽然形状可能会以自相似的方式进化，但无论是生长还是侵蚀，表面都不可能保持不变。在这里，我们研究了一个罕见而美丽的地球物理问题，它结合了这两个过程：碳酸盐颗粒的形状演变，也就是众所周知的椭圆形。我们假设，矿物沉淀和波流输运引起的侵蚀，竞相产生新的和不变的几何形式。我们表明，建立在这一前提下的平面(2D)数学模型预测了由沉淀和磨损之间的平衡产生的时不变(平衡)形状。这些模型结果产生了与自然界中发现的成熟卵母相一致的不平凡的形状。
Striking shapes in nature have been documented to result from chemical precipitation — such as terraced hot springs and stromatolites — which often proceeds via surface-normal growth. Another studied class of objects is those whose shape evolves by physical abrasion — the primary example being river and beach pebbles — which results in shape-dependent surface erosion. While shapes may evolve in a self-similar manner, in neither growth nor erosion can a surface remain invariant. Here we investigate a rare and beautiful geophysical problem that combines both of these processes; the shape evolution of carbonate particles known as ooids. We hypothesize that mineral precipitation, and erosion due to wave-current transport, compete to give rise to novel and invariant geometric forms. We show that a planar (2D) mathematical model built on this premise predicts time-invariant (equilibrium) shapes that result from a balance between precipitation and abrasion. These model results produce nontrivial shapes that are consistent with mature ooids found in nature.