The image below shows typically laterally adjacent depositional environments.īy Mikenorton - Own work, CC BY-SA 3.0, WikimediaĬhanges in depositional environments are driven by changes in base level, or the elevation of the terminal body of water (often, but not always sea level!). The kitchen and the yard are not laterally adjacent. Can you get from your kitchen to the grassy backyard without encountering something else? Nope, you have to cross the porch to get the yard. That means your kitchen and the porch are laterally adjacent. You can walk from the kitchen to the porch without encountering the grassy backyard. (If there IS something in between, that something is the laterally adjacent environment!) Imagine that your kitchen has a door to an outside porch, and your porch is just one step above your grassy back yard. So what are laterally adjacent depositional environments? Two depositional environments are considered laterally adjacent if you can walk from one to the next without anything in between. ![]() Some examples of depositional environments include meandering river, delta, beach, lake, swamp, shallow marine, and deep marine. Different types of sedimentary rock form in different depositional environments, so geologists can often figure out what existed at a particular place millions of years ago. A depositional environment is simply a place sediment can be deposited. If two things are right next to each other, they are laterally adjacent. Let’s break it down, starting with laterally adjacent and depositional environments. If there is something missing, there is missing time, or an unconformity. Walther’s law states that depositional environments that are laterally adjacent on the surface of the earth will also appear in succession in a stratigraphic sequence. Instead of dealing only with relative time, Walther’s law deals with relative space through time. ![]() Walther’s law is a little different from the previously discussed geologic principles, but it is justĪs important. Image of rocks: three are cut, the rocks on top are not Walther's Law By carefully examining which rock units are cut by faults or intrusions, or which rock units have been weathered, geologists can further determine the relative ages of rocks. Similarly to the principle of superposition, a rock must already be in place to be cut by a fault, igneous intrusion or erosion. A, b, c, d, e, f Cross-Cutting Relationships Knowing this, geologists can figure out the relative ages of rocks on top of each other. ![]() In order to deposit a sandstone on top of a limestone, the limestone has to already be there. If the table isn’t already there and you put the book down, it falls to the floor (and note! The floor had to be there for the book to land on it.). A simple way to think about this is that for something to be on top of something else, for example in order to put a book on top of a table, the table has to be there. This principle states that a sequence of rocks in their original orientation will have the oldest rock on the bottom and the youngest rock on the top. The rocks remain horizontal until a force acts on them, pushing (or pulling) them out of their original orientation. More sediment is deposited on top, and over time the whole sequence lithifies (sort of like the jello did in the fridge). As water moves sediment from high regions, like mountains, to low regions, like the ocean, the energy of the system decreases until the sediments are deposited in a basin, like a lake or an ocean. This is similar to how sedimentary rocks form. ![]() Now imagine that you have a jello mixture in the bowl - if you chill it and it solidifies, and then pour a different color on top, You have the two flat layers of jello, one on top of the other. If you dump that water into a bowl, the surface remains flat. The surface of the water is perfectly flat - horizontal. This is sometimes easier to envision with liquids: imagine pouring water into a cup. The principle of original horizontality states that sediment is deposited horizontally. Nooreen Meghani 2015 Original Horizontality
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