Stratigraphic Gaps and Stratigraphic Traps

If you heard that oil is located in underground pools or lakes then you are misinformed. Most oil is found in minute spaces in sedimentary rocks like sandstone and course-grained limestone. Think of the sandstone as a sponge. The sponge has holes that can contain liquid or gas. Though limestone and sandstone are hard rocks, they are very porous.

The holes are very small. Oil and gas are trapped in these holes.

One of the most common sedimentary rocks is fine-grained shale. Layers of shale in the earth’s crust four miles thick are common. That is, shale is the majority of the rock in said layers. As time passed in the earth’s history these layers of shale were deposited in the oceans. Continents were flooded over with water for eons and huge mounds of sediment were formed, which contain large amounts of shale and sandstone.

But what happened to the oil and gas deposits? Many microscopic sea creatures—trillions

of them have fallen—plant and animal alike and they became a speck each of the shale sediment on the ocean floor. Of course, larger sea animals like fish, sharks and whales have died contributed to this deposit, but their portion is small compared to the tiny plants and animals contribution—only because there have been trillions and trillions of them.

In the beginning oil and gas deposits are really small, but as the earth’s humongous pressure squeezed these deposits they traveled horizontally and they run into other roaming oil. Eventually these moving spots of gas and oil are trapped in a rock formation of sandstone or limestone. Their roaming days are over. They can’t detach from these sponge-like rocks.

The two elementary types of traps are the structural trap and the strategic trap. A structural trap occurs when the earth has been bent or deformed. These structures may be in the form of a dome or a crease in the earth. It could also be caused by a more complex action like a vertical movement of the earthen layers. There are three types of structural trap: the salt dome trap, the anticline and the fault.

Stratigraphic Traps are formed when sandstone gets closed up in shale. The shale stops the oil and gas from roaming away. Otherwise, they would move when the earth exerted enough pressure on them again.

Stratigraphic Gaps are missing divisions in the standard geographic column of the earth’s sedimentary layers. These gaps are common. There is a problem in determining age or length of time involved in these gaps. Layers found in the surrounding area are missing in the gap. Those areas are dated with characteristic fossil types and radiometric dating.

Many times there are stratigraphic gaps in the fossil record. Actually they are not the exception, but they are the norm. There is a new view that says that these gaps don’t represent an incomplete ness of the fossil record. In this view the stratigraphic data should be evaluated to determine if a phylogenetic relationship exists.

Whereas, traditionally this relationship has been assumed, therefore it has been thought that the fossil record is incomplete.