** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its 50 society members.
Gallery View of PEPS Articles
Research
Interdisciplinary research
202308202308
K-feldspar enrichment in the Pacific pelagic sediments before Miocene
Yoichi Usui, Toshitsugu Yamazaki
X-ray diffraction, Grain size, Minamitorishima, Site U1366, Ice nucleating particles
Relative abundances of feldspars, quartz, glass and clinoptilolite after chemical digestions, based on analyses of pelagic clay around Minamitorishima Island. K-feldspar abundance is indicated by red hatching and showed high abundance prior to the Early Oligocene.
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.
