Seams, as broken by cutting upward (6)
I believe the answer is:
strata
'seams' is the definition.
The definition and answer can be both locations as well as being plural nouns.
Perhaps you can see a link between them that I can't see?
'as broken by cutting upward' is the wordplay.
'broken by' is an insertion indicator (inserted letters break into the word).
'cutting' becomes 'tart' (both can mean sharp or sarcastic).
'upward' says the letters should be written backwards (in a down clue, letters go up).
'as' enclosing 'tart' is 'atarts'.
'atarts' in reverse letter order is 'STRATA'.
Can you help me to learn more?
(Other definitions for strata that I've seen before include "hard beds" , "Geological levels" , "Tiers of thicknesses" , "Levels, grades or social classes" , "Layers of sedimentary rock" .)