Regarding phosphates:
some older sources but available ...
articles by Eidt (1973) in American Antiquity 38:206-210
Woods (1977) American Antiquity 42:248-252
Eidt, Robert C., 1985 Theoretical and Practical Considerations in the
Analysis of Anthrosols. In Archaeological Geology pp. 155-190. Edited by G.
Rapp, Jr. and J. A. Gifford. Yale University Press, New Haven, Conn.