SEPM Strata


*shale*
igneous rocks metamorphic rocks minerals sedimentary rocks	Ternary Composition Description Fine grained rock composed of lithified clay making the rock shale. Pure clays (such as kaolinite) tend to be white or tan, although varying amounts of other components are usually present. Other components may be iron oxides or organic matter. The dark color of this specimen respresents the presence of incompletely decayed organic matter (humus) making the rock dark gray (the rock looks light colored because of the way light is reflected; the Detail Picture shows its true coloration). shales normally have a fine lamination structure. This image is looking at the side of the rock, and you will note no layering orlaminations visible. Technically that makes this a mudstone. mudstone is made of the same stuff as shale, but it has been distrupted by something that destroyed the laminations. Often the disruption is caused by bioturbation; organisms burrowing through the sediment and ingesting it to extract food. Tectonic Association From the shale alone no tectonic interpretations are possible. shale shows up in many environments in many tectonic situations, but out of context of other rocks with which it was deposited nothing can be confidently said about tectonic associations. Formation & Environments shale = quiet water deposition. Aside from this it is hard to say anything definitive about the environment of a shale since most environments have periods and places of quite water deposition. For example, shales are common in basins, shelves, deltas, Meandering rivers, flood plains, etc. The dark gray of this specimen indicates a low oxygen environment. From its geologic context we know it was a relatively deep water, quiet, marine basin. See Color Link for further description. Detail QFL Composition Description Fine grained rock composed of lithified clay making the rock shale. In this close up image we can easily note the fine grained nature; no visible particles can be seen. Furthermore, if you rub this rock across your finernail it will not scratch, typical shale behavior, but not siltstone behavior. The dark gray to black color of the rock can be easily seen here, but if you look at the Next Image the rock looks much lighter. It is just the way the light is reflecting. Further Detail QFL Composition Description Fine grained rock composed of lithified clay making the rock shale. In this close up, taken at the same distance as the last closeup, the rock looks much lighter in color. The only difference is the angle of the reflected light. On the other hand, it is easier to see in this image that there is no "grit," sand or coarse silt in the rock.