Well-known is an adjective but author is a noun. Well-known author isn't a compound noun and therefore have two different parts of speech.
Cape Cod.
Yes ! The phenomenon of chemoluminescence is wellknown.
No.
she was a teacher in Mississippi before she became a wellknown journalist.
It is probably most known for its kookaburra.
It is a wellknown, largely used explosive from approx. 150 years.
Steaua Bucharest is a wellknown Romanian club for sports.
No, it is a noun, except as a noun adjunct (author list, author biography).The past participle (authored) might be used as an adjective, or more rarely authorial.
The island Krakatoa (with the wellknown volacano) is in Indonesia, not in the Iberian Peninsula !
A wellknown example is bakelite.
Adjective
The musical group, Within Temptation are from the Netherlands.There are many famous people in the Netherlands. We call them BNer's. It means Bekende Nederlanders( Wellknown Dutchmen )