Long-period astronomical forcing of climatic and biological evolution during the late Paleozoic icehouse-to-greenhouse transition.

Termination of the late Paleozoic icehouse (LPI) serves as the Earth's first icehouse-to-greenhouse transition when the continents were covered by extensive vegetation. However, low-latitude climatic and biological responses to this climate transition remain unclear. In this study, we conducted a cyclostratigraphic analysis of a shallow marine succession of the Tieqiao section in South China. Variations in gamma rays that reflect continental weathering strength in the source regions are paced by Milankovitch cycles, including 405-kyr long eccentricity, 31.7-kyr obliquity, and ∼ 20-kyr (20.1 kyr and 18.7 kyr) precession. Based on the 405-kyr-scale cyclostratigraphic correlation between the Tieqiao section and the deep marine succession of Naqing, a floating astronomical time scale for the late Early Permian was constructed, and the base of the Kungurian stage was estimated as 284.83 ± 0.40 Ma. Climatic and astronomical variations were synchronized to this refined timescale and further compared with a geochronologically independent marine invertebrate biodiversity time series to interpret the dynamics of marine biological evolution during the late Paleozoic icehouse-to-greenhouse transition. The impacts of low-frequency obliquity forcing (with a period of ∼1.35 Myr) on climatic and biotic systems have differentiated in the changing climate backgrounds. When Gondwana land was minimally glaciated during the Artinskian, increased marine speciation was associated with elevated climatic humidity, nutrient inputs, linkage to glacial building at low-amplitude obliquity oscillation intervals (obliquity nodes). This cause-and-effect relationship gradually changed from ∼285.1 Ma, along with the termination of Gondwanan glaciation and tropical aridification over the long term. In an arid greenhouse, continental aridity and marine transgression at obliquity nodes led to a low nutrient level that the suppressed marine biodiversity. Our results show differential dynamics involving the Earth's astronomical parameters, climate change, and marine invertebrate biodiversity between icehouse and greenhouse conditions in the late Paleozoic Era. • The constructed astronomical time scale yields an age for the basal Kungurian stage of 284.83 ± 0.40 Ma. • Obliquity nodes led to climate humidity and marine speciation during the partially glaciated period. • Obliquity nodes led to aridity, marine transgression and reduced biodiversity in an ice-free world. [ABSTRACT FROM AUTHOR]