Steno’s law of lateral continuity states that strata or rock layers extend in all directions until they meet a barrier, tappers (or pinch-out), or grade into adjacent sedimentary rocks or thin.
This principle indicates that rock layers on either side of the valley or outcrop will match up as they were once continuous before some events like erosion or Earth movements displaced or broke them apart. However, this applies in the same depositional basin.
Learn more about the law or principle of lateral continuity, including its significance. We will also give you an example to help explain it and some areas where you can notice this law.
Historial background
The law of lateral continuity is one of the four basic laws in geology by Steno, especially in stratigraphy, up to date. The others are the principle of superposition, original horizontality, and cross-cutting relationships. These laws, like inclusion and fossil succession, are important in determining the relative age of rock layers.
Nicolaus Steno (1638-1686) was a Danish anatomist and a pioneering geologist who later became a priest. He was born Niels Stensen but later Latinized his name to Nicolaus Steno.
Steno proposed his ideas in a dissertation known as Prodromus or De Solido Intra Solidum Naturaliter Contento Dissertationis Prodromus or simply Prodromus. These laws are based on his simple observations by looking at exposed rock strata; not until many years later did they become popular.
Later, an Englishman named John Strachey used this superposition principle to decipher coal-bearing rock layer formation in Northern and Southern English Counties.
Lastly, before officially recognizing Steno’s principle of continuity, many people assumed that rock outcrops did not have a relationship.
What is the principle of lateral continuity?
The law or principle of lateral continuity states that rock layers or strata will continuously extend outwards in all directions until they meet a barrier, thin out, or grade into a different rock layer.
This law implies sedimentary rock layers were originally deposited as continuous lateral layers or sheets only terminated by thinning, barriers, or grading to other rocks. However, erosion and Earth Movements, including faulting, tectonic drift, etcetera, tore or displaced them.
Therefore, going by this law of original lateral continuity, it is true that rock layers on either side of outcrops, valley walls, river banks, road cuts, mines, quarries, or drill cores were once part of continuous strata. And you can establish their correlation or match them up by looking at the strata, especially their lithology.
This principle came from something Steno noticed by observing separated rock adjacent rock layers. Their position, sequence, and lithology matched, meaning they were once continuous. And indeed, most sedimentary rocks span a much larger area than their lateral thickness.
Steno’s law of lateral continuity makes a lot of sense, considering how deposition occurs from fluids (wind or water) that carry them. They will spread horizontally in all directions until they reach an edge or barrier due to gravity.
Monument Valley Navajo Tribal Park, i.e., is a classic example that even beginner geologists can see lateral continuity of the Cedar Mesa sandstone on the two outcrops.
Here is a video of lateral continuity that will further clarify everything:
Example to explain the law of lateral continuity
To help you further understand the law of lateral continuity, assume you have liquids of different colors, such as red, blue, yellow, etc., which solidify after some time. Solidifying is like lithification, which happens to sediments deposited in basins.
Now, pour the first red liquid into a fish aquarium or transparent basin. The water will spread in all directions, i.e., laterally inside your container, just as sediments in a fluid would. Let it solidifier and add the second liquid, i.e., blue.
Go on until you have several layers. You will notice that each layer spreads outwards in all directions until it meets the container wall, i.e., a barrier.
Let us say you remove a vertical section on your solidified colored layers. You can still notice the various colors and conclude that the layers were initially continuous, which is what this law of original lateral continuity notes.
Why is lateral continuity law important?
The law states that rock layers were originally deposited continuously outward in all directions within the same depositional basin. Although Earth’s movement, erosion, or human activities may have eaten or displaced some parts, they were continuous before. Therefore, we can piece together or correlate (locally or globally) rock bodies and know more about the sequence of past events and spatial relationships.
For instance, we know that 300-200 million or in the late Paleozoic Era to late Triassic, North America was a continuous continent with Africa, Europe, and South America, known as Pangea.
Lateral continuity may help predict mineral resources by correlating rock bodies. For instance, if you find coal in strata separated by a valley, it may likely occur on the other side of the valley if the strata were continuous.
Things to note
One potential challenge will be correlating rock bodies in different depositional basins. To avoid this issue, remember that rock layers don’t run indefinitely but are restricted within certain basins, meaning you need to study the shape of depositional basins to correlate rock bodies. Also, the type and quantities of sediments available may control depositional areas.
Secondly, beware that Earth’s movements, like faulting, may break, overturn, or displace rock layers that were originally laterally continuous. Such a case needs careful study to locate rock layers that match up.
Lastly, you may notice a lateral variation of sediments in a stratum from rough to smooth. This occurrence is due to current (wind or water) power. As a currency goes further, its energy may reduce, meaning heavier sediments will first settle, and lighter ones may move further. It will create a variation along stratum or sedimentary facies.
References
- Levin, H. L., & King, D. T. (2016). The Earth through time, 11th edition (11th ed.). Wiley.
- Wicander, R., & Monroe, J. S. (2010). Historical geology: Evolution of the earth and life through time (6th ed.). Books-Cole.
- Burbank, D. W., & Anderson, R. S. (2012). Tectonic geomorphology (2nd ed.). Wiley-Blackwell.
- Principle of lateral continuity. (2021, September 8). In Wikipedia. https://en.wikipedia.org/w/index.php?title=Principle_of_lateral_continuity&oldid=1043038053