Periods of records covering old church (6)
I believe the answer is:
epochs
'periods' is the definition.
(I have seen 'Historical periods ' mean 'epochs' so perhaps 'periods' could also mean 'epochs')
'records covering old church' is the wordplay.
'records' becomes 'EPs' (EP is a type of record).
'covering' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'church' becomes 'ch' (common abbreviation).
'o'+'ch'='och'
'eps' placed around 'och' is 'EPOCHS'.
'of' acts as a link.
(Other definitions for epochs that I've seen before include "Periods, ages" , "Eras, subdivisions of time" , "Remarkable period of time" , "Divisions of geological periods" , "Geological ages" .)