K-feldspar enrichment in the Pacific pelagic sediments before Miocene

Abstract

The mineralogy of atmospheric silicate dust controls its interaction with clouds. K-feldspar has a remarkably high ice-nucleating activity, and its distribution may have influenced the global climate throughout Earth's history. However, long-term archives of past atmospheric feldspar are not known. Here, we investigate feldspar mineralogy, content, and grain size in pelagic clay cores. Sediments around Minamitorishima Island contain > 10 wt% of K-feldspar before ~ 35 Ma, which is five times more than the younger sediments. This distribution does not resemble other volcanic minerals or geochemically estimated volcanic input, suggesting that the K-feldspars are not associated with volcanic ash. The K-feldspars are present as isolated grains as well as pseudorhombohedral microcrystals indicative of authigenic overgrowth. On the other hand, they contain some Na, arguing against a purely authigenic origin. Grain size distributions of chemically separated quartz and feldspars show stratigraphic variation analogous to other North Pacific sites, further suggesting a link to eolian materials. Sediments from a South Pacific site also show K-feldspar enrichment over plagioclase before ~ 44 Ma, although the content relative to bulk sediment does not change much. We propose that the K-feldspar may be enriched in the wide area of the Pacific before ~ 30 to 40 Ma.