Impact of astronomical forcing on sea-level changes and peat-swamp development in the Late Paleozoic of North China

Abstract

The Late Paleozoic Ice Age represents a critical phase of coal accumulation in the North China Basin. Coal was primarily deposited in marine-terrestrial transitional environments, where coal seams display distinct cyclicity closely associated with cyclic marine transgressions. Astronomical cycles are believed to play a crucial role in the evolution of climate and environmental changes during the Late Paleozoic Ice Age. To explore the impact of astronomical cycles on sea-level changes and peat swamp development, and to clarify the relationship between astronomically forced transgressions and the termination of peat swamp development, a time-series and cyclostratigraphic analysis were conducted on the Taiyuan Formation gamma ray (GR) data from well H-2 in Juye, Shandong. A floating astronomical time scale of ∼4.55 Myr for the Taiyuan Formation is constructed by astronomical tuning of GR data to the robust ∼405 kyr eccentricity cycle. Sea-level changes of the Taiyuan Formations are recovered based on the sedimentary noise model. Cyclostratigraphic analysis indicates that the high-frequency, cyclic deposition of limestone transgressive layers and coal seams was impacted by astronomical forcing. During periods of high orbital eccentricity with low precession, the Northern Hemisphere summer solstice at perihelion, resulting in warm and humid climatic conditions, enhanced precipitation, and promoting vegetation growth and peat swamp development. In contrast, high precession aligned the Southern Hemisphere summer solstice with perihelion, creating a warm summer orbit that maximized insolation and temperatures, thereby accelerating the deglaciation and collapse of Gondwana and triggering sea-level rise. Following the accumulation of glacial melt from multiple high-precession phases, rising sea-levels eventually surpassed the strait heights, leading to seawater intrusion, which submerged the peat swamps and terminated their development. The peat was preserved and subsequently formed coal seams. An ideal model was established to illustrate how astronomical forcing influences sea-level changes and the development and termination of peat swamps.