This Mudstone has a thin layer of sand, less than 2mm, causing the fracture of otherwise continuous core. Why this thin layer existed during the formation?
Climate played a major role in such formation. Mudstone and Shale were generally former alluvial and shallow sea deposits which later converted to rock due to pressure and temperature. The materials were brought down from highlands through erosion and water flow. Water flow is associated with climate. Along the rivers, plains and sea, there are zones of the various sizes of particles. In general, if the climate is uniform, nearer to the hill will be boulders, cobbles, and gravels. Further downstream, the gradient is lesser and less rapid water flow, the particles are of smaller sizes, sands would be the major constituents. Towards the plains and the lake/sea, water flow is much slower due to flatness and very slow flow, silt and clay will be deposited. But weather is never constant, sometimes you have storm and sometimes drought. That was the time different materials would be deposited at the supposed gravels, sand. silt and clay areas. The mud area obviously experienced a heavy storm which resulted larger particles, the sand, to deposit at the silt/clay site.
Therefore, if we can drill this whole rock formation and study the distribution of particles sizes, we can probably study the climate conditions throughout the depositing period. But dating may be difficult if fossils are not found.
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