Some sedimentary structures also help you determine which side of the rock was originally facing upwards, called way-up indicators. Sedimentary structures provide a lot of information about the environment in which they formed, including processes that were occurring when sediment was deposited, the environment of deposition, the direction sediment was traveling, and/or the mechanism for transporting the sediment (wind, water, or ice). You can figure out the scale of the image by looking for trees or other vegetation. Figure 4.3 – Cross-bedding in sandstone seen on a cliff face in Zion National Park, Utah. This rock is Permian in age from Nomgon, Mongolia. This is a view from the top surface and not the side. Thicker layers are most likely sandstone, and thinner layers are shale. Figure 4.1 – Titled sedimentary beds from Morro Solar near Lima, Peru. Structures can be more complex like the wavy pattern seen in ripple marks (Figure 4.2) or chaotic looking patterns in cross-bedding (Figure 4.3). Laminations are typically composed of fine-grained silt and clay-sized sediment. Layers of sediment that are thicker than 1 cm are called beds and layers thinner than 1 cm are called laminations. The simplest sedimentary structure is stratification, which is layering that can be observed in sedimentary rocks (Figure 4.1). Read your descriptions to your classmates and see if they can identify which samples you are talking about. Now put your observational and descriptive skills to the test. If it helps, pretend you are describing what the structure looks like to someone who can not see it. Then, in full sentences, describe the structure you just sketched. Create a sketch of each sedimentary structure in the blank space below, focusing on what you think are the most important characteristics of the sample. Look at the samples closely and use a hand lens if necessary. For this exercise, your instructor will provide you with a set of sedimentary structures.

Sandstone depositional environment