Annual growth bands in the late Carboniferous reef-building colonial rugose coral Ivanovia and their environmental significance

Abstract

Annual growth bands featuring with high- and low-density bands of massive reef-building corals are considered to be physiological response to seasonal changes in environment and have been widely used as environmental and climatic proxies. Here, we conduct paleontological and geochemical analysis on the late Carboniferous massive coral (Ivanovia) with distinct density bands from Houchang area, South China. Four Ivanovia species including Ivanovia cf. manchurica, I. podolskiensis, I. guizhouensis, Ivanovia sp. have been found in the study area. Aluminum (Al) content and oxygen isotope (δ¹⁸O) of the annual growth bands in Ivanovia sp. suggest that high-density bands are probably formed during hot and rainy seasons with high temperature and more terrestrial input. In contrast, low-density bands are generally constructed during cooler periods with optimal environmental conditions, consistent with the modern tropical reef-building coral density bands. Spectral analysis of the Al and δ¹⁸O series from the Ivanovia sp. reveals significant 2–7 yr cycles close to the cyclicality (2–7 yr) of modern El Niño–Southern Oscillation (ENSO). This study highlights the coral annual growth bands and ENSO-like variability during the late Carboniferous.