Schieber Juergen, Southard John, Thaisen Kevin
Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA.
Science. 2007 Dec 14;318(5857):1760-3. doi: 10.1126/science.1147001.
Mudstones make up the majority of the geological record. However, it is difficult to reconstruct the complex processes of mud deposition in the laboratory, such as the clumping of particles into floccules. Using flume experiments, we have investigated the bedload transport and deposition of clay floccules and find that this occurs at flow velocities that transport and deposit sand. Deposition-prone floccules form over a wide range of experimental conditions, which suggests an underlying universal process. Floccule ripples develop into low-angle foresets and mud beds that appear laminated after postdepositional compaction, but the layers retain signs of floccule ripple bedding that would be detectable in the rock record. Because mudstones were long thought to record low-energy conditions of offshore and deeper water environments, our results call for reevaluation of published interpretations of ancient mudstone successions and derived paleoceanographic conditions.
泥岩构成了地质记录的大部分。然而，在实验室中很难重现泥质沉积的复杂过程，比如颗粒聚集成絮状体。通过水槽实验，我们研究了黏土絮状体的推移质输运和沉积，发现这一过程发生在能搬运和沉积沙子的流速条件下。在广泛的实验条件下都会形成易于沉积的絮状体，这表明存在一个潜在的普遍过程。絮状体波纹会发展成低角度前积层和泥床，这些泥床在沉积后压实作用下会呈现出层状，但这些层仍保留着絮状体波纹层理的特征，而这些特征在岩石记录中是可以检测到的。由于长期以来人们一直认为泥岩记录了近海和更深水环境的低能状况，我们的研究结果要求重新评估已发表的关于古代泥岩序列及其推导的古海洋学条件的解释。
