Your post is somewhat confusing but I assume you are working on a genealogy. If you are looking for the parents of Nathaniel Fields and his wife then you should track down their marriage record as their names may be there. As these dates are from the RevWar period they will likely have their marriage recorded in church records rather than civil records. I would try to find out where they were located at the time and check a local historical society.
The National Archives has muster rolls of the 6th Virginia on microfilm roll #246 pp.103-104. If you just want to track down a bit of Nathaniel's military record. I would also look at the archives to see if he applied for a Revolutionary War Pension. Pension files seem to have the most genealogical information.
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