The OED lists it as a conjunction; etymology is:
being, present participle of be v. (compare be v. 3).
- It being the case that, seeing that, since. Now regional and nonstandard.
However, there are examples over centuries. Google Ngram provides a variety, although there are many false hits.
According to the OED:
It can immediately begin a clause, or is used with that:
b. With that.
a1642 H. Best Farming & Memorandum Bks. (1984) 126
They wente all for halfe gates, beinge that they coulde not bee
1780 Mirror No. 75 (1781) 3 1 For this, you must answer
to yourself, being that you are able to write printed papers.
1813 J. Austen Let. 11 Oct. (1952) 86, I am tired of Lives of Nelson,
being that I never read any.
1815 Scott Guy Mannering I. ix. 138 With whom he himself had no delight in > associating, ‘being that he was addicted unto profane and scurrilous jests’.
1855 C. Kingsley Westward Ho! xiv. 270 It goes sorely against my
conscience, Sir; but being that he is your cousin, of course—.
1942 A. Lewis Last Inspection 159, I sent him to clean your kit, sir,
being that Thomas your batman isn't available.
1994 Rolling Stone 2 June 20/1 Being that I had been out since I was 17,
nothing has changed.
2003 ‘Zane’ Nervous xvii. 100 She also needs to improve her computer
science grade and being that you're a programmer, I would think you could help
her out with that.
Also "being as" or "being as how."