First, beach sand gets deposited on a slight upslope. Second the Flood water is what rose over the land carrying the sediments. Stir sediments into a vessel of water and let them settle out. They will settle out in layers.
I'm doing my best with the facts as I understand them, both from the Bible and from the observed strata and fossils. Fountains of the deep whatever they were or are, would certainly have stirred up the water, mixing sediments that were both from the ocean and running off the land due to forty days and nights of rain plus the rising of the water caused by that. Once you've got water full of sediments rising over the land you've got the ingredients for the sorting into layers that we see. You can't debunk the Bible, it isn't going to happen.
Floods don't move tectonic plates and floods don't create mountains -- they erode them.
Of course "floods" don't do either of those things, what a silly straw man. But THE Flood built sedimentary strata which was full of dead things which became fossils, and some mountains are strata that was tectonically pushed up into mountains. And I happen to think this all occurred at the end of Noah's Flood in a great tectonic cataclysm that had something to do with causing the Flood water to recede. It also caused the separation of the continents and other interesting phenomena. Not the Flood, but geological processes connected with it.
Horseshoe crabs, some of them anyway, do look quite a bit like trilobites. And I guess I'd think of them as I think of the other "living fossils" as evidence against the ToE because the changes they show are just variations within the Kind over hundreds of millions of years. Funny how the creatures that don't show such a lengthy fossil history, where there is no evidence of evolution that is, are assumed to have evolved from one thing into another, such as reptiles into mammals, whereas when there is actual evidence from one time period to another of the changes to a creature -- like trilobites, horseshoe crabs and coelecanths, the differences are obviously the expected changes within the Kind.
Haven't mentioned prokaryotes, but gave plenty of reasoning on the trilobites and coelecanths, and more recently added the horseshoe crabs. Don't even you with your odd way of laughing at Nothing recognize that these creatures are found in a great many "time periods" up the Geological Time Scale, adding up to hundreds of millions of years, without changing to any degree that would suggest something other than a trilobite, coelacanth or horseshoe crab, while some creatures that are found in only one or two "time periods" are assumed to have evolved into something dramatically different in a time period above them?
I mean even you ought to stop and ponder how, when we have actual evidence we see no evolution whatever, just the usual changes within the Species creationists expect to see, while when there is no evidence at all, great leaps are made to assume evolution between dramatically different creatures, such as from reptiles to mammals.
I know the ToE and the OE have an iron grip on your brain, but break the shackles, man, and see what's really going on here.