 So the sedimentary structures in deltas vary from the delta plane to the delta slope to the pro-delta. And I'm going to talk in this video about different processes that transport the sediment from the mouth of the river to the deeper water and how that affects the accumulation of sediment and how we see that in the rock record. So I'm going to start off with delta where the water, the lake water, or the ocean has very few storms and very few tides. So this is going to be a river-dominated delta, which means that the fluvial processes are the ones that are predominantly shaping the characteristics of the delta. So I've started with a profile and a bunch of sedimentary structures that we're going to be talking about. On the delta plane, the facies are mostly the fluvial facies, and particularly meandering river facies. So we often have sandstones that are deposited by the migration of those channels with erosional surfaces at the bottom with planar lamination trough cross stratification ripples as the point bars migrate with the channel. Between those deposits, we can have a flood plain deposits or lake deposits, and those reflect the delta plane facies as well as meandering river facies. So when the river reaches the lake or the ocean here, the flow speed decreases very, very quickly, and you deposit a lot of sediment very fast. That typically produces climbing ripples. Those are ripples where there's very little erosion on the upstream side, and instead you're accumulating sediment very quickly. So if there aren't storms or tides transporting the sediment elsewhere, you end up accumulating a wedge of sediment schematically shown here right at the river mouth. So the sediment, the slope there gets steeper and steeper, never as steep as I've shown it here, but it gets steep enough that you end up with a slope failure. And that triggers a turbidity current which produces a turbidite in terms of deposits. So if you just have sediment being deposited here, you end up triggering turbidity flows, and those will flow down the slope, depositing some sand on the slope depending on how steep it is and how fast the flow is. And they will extend out into the pro-delta area here. So what you see in this particular case, I drew a stratigraphic column in here, is you'd accumulate mud between flows, then you'd have a turbidite, and then you'd accumulate mud again. And so this lower part would be massive, and then you'd have the upper planar lamination, so the massive part is the Bulma A sequence, the planar lamination's Bulma B. And then you'd get the current ripples, and then the faint lamination at the top, and go back to your deposition here. So this would be in an area where you accumulate a fair amount of sand, but you're not eroding away all the shale. If you came out here, what you would see in the pro-delta is maybe just a little bit of sand or maybe between shale, maybe you'd have some of these finding upward normally graded beds, maybe occasionally a ripple. So when the only way sediment is transported from the river mouth to the basin is by the salt failure, you end up with turbidites. Some parts of the ocean have a significant number of waves, which helps transport the sediment brought in to rivers, to other places on the shoreline, or into deeper water. And some large lakes also have waves that redistribute that sediment, and that process of redistributing the sediment creates distinctive sedimentary structures that record that influence of waves. And so one of the things that happens is in the zone near shore, the waves create beaches, and so you get the climbing ripples right at the mouth of the river, but those can be reworked into a planar lamination that dip towards the ocean that represent the beach deposits. Almost always when you have waves, you see evidence of beaches from that activity and that transport of sand along the shore. So the waves will also produce wave ripples and transport the sand down to these depths. So in here, you end up with wave ripples, and with storm wave base, out at this zone you end up with typical storm deposits, where you're accumulating mud between storms, you have erosion at peak storm, deposition of the storm deposits, so this can have some conglomerate in it, and hammocky cross stratification is really common, and you can get some of the wave ripples at the top. So between storm wave base and normal wave base, you typically get these deposits, and then out in the deep basin, normally accumulating mudstone, but sometimes you get these little finding upward beds that represent storm deposits that get all the way out to this zone here. So the main difference between a river dominated delta and a river influenced delta is that the storm deposits are common offshore instead of turbidites, and you have a lot more wave ripples in the shallower environments. There are deltas that have both storms and turbidites in them, and so there are end members of the two of them. Tides can be a very important process, transporting sediment from rivers offshore and along the shoreline as well. In the case of tide influenced deltas, the river mouth and that junction between the river mouth and the ocean has very high tidal flows. So in this particular zone, depending on the flow of the tide, there's a lot of sedimentary characteristics typical of tides. So for example, herringbone cross stratification is one of those where you have deposition in one direction during the tide coming in and going the other way as the tide goes out. Mud drapes, reactivation surfaces are also common. A lot of times these, on the delta top, these tidal currents are within channels, so they can end up looking quite a bit like the meandering river facies. And as you go further inland, it is dominated by the meandering river facies, and as you get closer and closer to the edge of the delta, you get more and more of these tidal influences. So sometimes you can see their places in between those two where you can see the fluvial deposits, but occasionally you might see a ripple migrating, or ripple cross lamination showing flow in the upstream direction. So as you go offshore, you still have those strong tidal currents, and so you end up with the herringbone ripple and cross stratification going further offshore. When you go far enough out here, it's mostly mud, and so you typically get tidal influences to the depth where the tidal currents interact with the bottom. Sediments still need to be transported farther offshore, and so sometimes out here you'll see a few sand beds in the mud, maybe from a lot of tidal erosion, but it's pretty common to also get turbidites below the zone where you have a lot of the tidal transport, because the sediment will accumulate above this zone here, and the slopes can be steep enough to produce the turbidites as well, and the tide influence delta. You know that to identify that tides are important, you look for the very distinctive sedimentary structures that indicate tides, like the herringbone cross stratification, the reactivation surfaces, and the mud drapes. Thanks for watching.