The correct answer is - the ocean animals deposited in its layers.
The sedimentary rock on the image is clearly an organic sedimentary rock because it contains fossils of marine animals. This type of sedimentary rocks form when sediments and organic matter come in contact, are merged, or rather naturally cemented so they are stuck together, and the end result is a sedimentary rock with organic matter involved in its composition. The organic sedimentary rocks are much more common in places where there was once a marine life, and much rarer with organic matter from terrestrial animals in it, though there are some rich deposits from that type in certain places as well.
