I had a quick look. It's not ZIP, not GZIP, not PKWare DCL.
First longword (little endian) seems to match the unpacked size (corresponding O1CHAOS.CAS file of the CD32 version has roughly the same size as the first longword found in O1CHAOS.DAT (maybe you figured out this already).
There are not that much packers/unpackers that work on streams/single files (as opposed to archivers).
maybe it's RNC but header is little endian...
Tried Powerpacker, IMP/ATN, no luck... We lack PC culture. Good for us
I figured out some stuff of LEVSDAT.BIN. It seems to confirm that this is a general data file for all game
So far, I have sorted the values just before ENDS marker, and decoded the chunks at the given offsets, size = next offset - current offset (hence the sort without which it would not work)
The offsets make sense. Most of the time I notice a change in the data. I examined the chunk 0x2168 (60 bytes), and it is values starting at 7000, 14000, 21000 ... and ending at 98000. AFAIR you got extra life at 7000 right? then 14000 ... see what I mean?
Edit: I suggest that some mod renames this thread to something like "hacking through Bitmap Bros games". I've got some info on Cadaver level format and some level writer too...