At https://anthropology.net/2019/09/10/80000-year-old-le-rozel-footprints-i… … French archaeologists have unearthed 257 Neanderthal footprints and 8 hand prints from a layer of fine dark sand deposited around 80,000 years ago, it is believed. The site is at Le Rozel in Normandy. They appear to represent evidence Neanderthals lived in groups much like modern day hunter gatherers …
the same story is at https://phys.org/news/2019-09-neanderthals-footsteps.html … again, the explanation is on them living in groups (which we may take as now established as fact). It is assumed the sand was wind driven and part of a dune system, even though, at the time, Normandy was joined to southern England and the Channel was dry land. Alternatively, the sand may have covered the muddy soil more dramatically – in a catastrophist manner. The footprints were made in a muddy environment – possibly a marsh or river location, and not necessarily a sea shore. The water to make it muddy may have been dumped out of the sky – heavy rainfall. Apparently, tons of metres of sand were extracted with mechanical shovels in order to reach the layers of interest. Presumably some part of the inter face had become visible hence the desire to excavate more fully.