Ive got a tape here from what I believe to be a VM
system.  The
 structure is unknown to me, although I can possibly take a stab at
 it.  Lots of data between tapemarks that seems to consist of a number
 of records that start out something like this (translated from
 EBCIDC): 
I think this might be the older VMFPLC (not VMFPLC2) format, used by IBM
for software distribution and other things.  The format seems fairly
simple: Five character block header (x'02' 'CMS' 'N' or
'0'), 800 bytes
of contents.  First block is the FST for the file.
https://www.garlic.com/~lynn/2003b.html#42
Old VMFPLC may be just CMS TAPE DUMP under the covers.
De