 Welcome to Open Geology. This is a project by a group of Salt Lake Community College professors to share geology with everybody. It's creative commons and these videos are partly funded by Salt Lake Community College, though the views and ideas expressed in them doesn't necessarily reflect that at the college. This goes with the textbook OpenGeology.org. Today, we will be talking about depositional environments. Environments of deposition. What is a depositional environment? A depositional environment is the environment or scenario that deposits a sedimentary rock. So, you look for different clues to tell you about that environment. For example, sedimentary structures or the what is in the rock, the composition, the size and types of grains you see in the rock, all of these provide clues as to what type of environment deposited that rock. And this is all based on the premise of this concept of uniformitarianism, which is the idea that the present is the key to the past. Processes, depositing rocks now in modern environments should be very similar to the processes that were depositing rocks 200 million years ago or 50 million years ago, right, or in the past in general. So you start to look for clues that tell you about the environment that deposited each one of these rocks. We separate these environments of deposition into three broad categories, continental, transition, and marine. Continental is probably the deposition environment we all are most familiar with because this is essentially where we live. These include rivers, dunes, deserts, right, lakes. Transition is that boundary area between the continental and the marine. Transition includes deltas, beaches, coastal environments, tidal flats, things like that. Shallow marine in some cases, areas where you have that are exposed to both the marine and the continental. And then finally the marine is probably by far where a lot of the deposition is occurring. Depending on how you look at it, this is shallow marine, offshore, deep marine, where there's tons of sea critters living. And here is a cartoon depiction of those different depositional environments, those major ones. So here's your continental environments here, glaciers, leaving moraines and alluvial planes and big alluvial fans and colluvial fans. And then you have these areas of desert, lakes, evaporite basins, rivers, right? And then your transitional environment. Here's your beach, your reef, your delta. And then you get into your marine environments. So you have a slope, an abyssal plane, shelf, and some reefs. So let's talk about the continental environments. Continental environment streams are kind of the main agents that are shaping the landscape and depositing things. And this will commonly create redbeds. It can create imbricated pebbles, which are pebbles that are kind of lined up. Glaciers will make big unsorted mixtures of sediments. So you get tills, which is unsorted mixtures of sediment. And then wind type depositional environments. Those will create well-sorted and fine sediments. I mean, we have examples here in Utah of all of these environments. We have mineral fork tillite that represents ancient glaciers. It's a dark rock with big pieces of rock floating around and in it finer pieces. And then for streams, you can have all types of formations have some evidence of stream channels. The wind, we have the Navajo sandstone. It has these big giant crossbeds. We looked at those when we talked about sedimentary structures. Here's an example of a modern-day river environment. And this would be your depositional environment. And here is the rock that could represent that depositional environment. Nice, well-rounded cobbles in this conglomerate, right? Here's a continental type depositional environment laying down this wild mixture, everything from very large boulders to very, very fine rock flower. And here's a picture of a glacier as it melts since leaving behind a marine which is made of till, which forms a tillite. Depositional environments, these transitional environments, these are your shoreline. I think deltas might be the most significant or most important of these transitional environments, but that's fairly subjective. You can also have beaches, tidal flats, and lagoons. Here's a nice inviting photo of a transitional environment. A lagoon is a very common transitional environment. You can see sediment floating around in this lagoon. And this can create for some very interesting features, structures, including raindrop imprints and mud cracks and evaporites, which we talked about when we were talking about chemical sedimentary rocks. Here's a delta. And with deltas, that's where your river meets the water, the ocean in many cases. And when it hits that still water, it starts to deposit sediment. You get these areas of massive amounts of sediment deposition over a decent-sized area, and it's just piling on top of itself over time. Marine environments, shallow marines are the most exciting for me because you get a lot of fossils and living things, create these fossils. In deep marine, you can start to get things like chert and shale. These are areas that are more still and less macroscopic, living things more tiny, shells and stuff accumulate in these deep marine environments, like radiolarens, which go on to create chert. And then you can get these sedimentary facies where you kind of know what typifies these different environments and how they're related to each other. And these can represent changes in the sea level, where the sea level can be rising and lapping on to a shore or lowering and lapping off of a shore and leaving behind these patterns, these facies of change in those depositional environments. And that is it for depositional environments. Here's some farves to leave you off with. I hope you learned something and follow these videos if you enjoyed it.