I live on the South Coast of England on a bit of geology called chalk
Snap Though given by your choice of photo, I think you're a fair bit further east than me
They're single celled algae - phyloplankton, with a calcium carbonate 'skin'. The inhabit the seas in vast qualities and fall onto the ocean floor when they die. The then fossilise and form chalk. They can be seen in the chalk cliffs - that's what they're made of, billions and billions of single celled organisms living and dying over millions of years.
Now how does a flood create that?
My favourite calculation around this is the number of Coccolithophores required to make our observed chalk deposits, and dividing this into the creationist's available volume of water on Earth between Genesis 1 and the flood, to give a density of Coccolithophores per cubic meter of sea water that can only be described as white and gloopy
I must run these figures to make sure I'm not pulling this out of my backside!