R.L. HAY'S CONTRIBUTIONS TO SEDIMENTARY MINEROLOGY, GEOCHEMISTRY AND HYDROLOGY

For those of us devoted to the study of water-rock interaction under field conditions, Dick Hay's name has been synonymous with diagenesis of volcanoclastic sediments and related mineral authigenesis, especially zeolites, clays and carbonates. Examples of topics on which he provided seminal understanding include:1) recognition and timing of differential weathering in pyroclastic deposits and the importance of physical properties (particle size and surface area), as well as chemical compostion; 2) distribution and sequence (zoning) in zeolitic alteration of silicic tephra; 3) delineation of relative roles of major cation solution chemistry (as well as pH and alkalinity) in sedimentary silicate authigenesis; 4) silicate leaching and secondary mineralization, including pedogenic calcretes; and 5) mineralogic indicators of hydrologic sources, such as groundwater versus surface water. At Amboseli (Kenya), Amargosa (Nevada), and Olduvai (Tanzania) Mg, K clay stratigraphy and oxygen isotope chemistry were used to interpret detailed depositional environment and paleoclimate, Pliocene to present. Dick's clear definition of “open” versus “closed” systems successfully contrasted Searles Lake deposits, where static saline fluids control mineralogic alteration, with Lake Olduvai, where complex hydrology was reflected in highly variable mineralogy.