Home | Session 3 | Sedimentary Rock Pg 1, 2, 3, 4, 5, 6, 7, 8, 9
What's in a Sedimentary Rock?
Presented
by Carol Tang
California Academy of Sciences
This next set of slides use one fossil occurrence--an oyster boundstone from the Jurassic Carmel Formation of southern Utah--to show how one can use evidence from different spatial scales to learn something about biology, ecology, and geology.
This is affectionately referred to as an "oysterball" (technically called an oyster boundstone in the scientific literature). The surface of this is covered with oysters which are growing next to each other.
Here is a polished surface cut through one of the fossils. What we see is that there are layers upon layers of oysters grown on top of one another on each side of this cobble. The story we can tell is that one layer of oysters would grown on the upperside of this "ball" and then, it would get overturned, and another layer would grown on the other side. Then, the whole thing would get flipped again and another generation of oysters would grow once again. Here is a photo of a "thin section" under the microscope. A "thin section" is a slice of rock which is cut so thin that light can penetrate through it. You can look at it under a petrographic microscope and identify the shape, type, texture and orientation, etc. of the grains. Here, the long horizontal features are the oyster shells. The clear and pastel grains are quartz sand grains. This is a photo of the oysterballs in their original orientation within the sedimentary rock. As you can see, there are several of them within this large boulder. These oysterballs get buried in carbonate muds and preserved in this manner.
updated February 11, 2002
UCMP Home | What's new | About UCMP | History of Life | Collections | Subway
