Sunspot cycles recorded in Mesoproterozoic carbonate biolaminites

• Mesoproterozoic carbonate biolaminites show annual laminar couplets.
• Couplet thickness and geochemical variations show ∼11 and ∼22 yr solar cycles.
• Mesoproterozoic microbial life was sensitive to subtle solar-induced climate changes.

Well-preserved carbonate biolaminites from the early Mesoproterozoic Wumishan Formation (ca. 1.5–1.45 Ga) of North China show submillimeter-scale yearly couplets that consist of alternating dark and light laminae, and are texturally similar to those reported from Holocene tufas. Power spectrum and wavelet transform analyses of laminar couplet thickness variations and geochemical series (Ca, Fe, Co/Ti, Cr/Ti, and Br) reveal a prominent periodicity at 9.0–11.7 and a less prominent periodicity at 19.7–21.4 couplets. These coherent periodic modes match well with the 11-yr Schwabe sunspot cycle and 22-yr solar Hale cycle. The observed layering pattern is thus interpreted as recording solar induced climate changes that may have modulated microbial growth rate and biomass production in restricted subtidal environments on a broad epicontinental platform. The documented example represents the first reported solar signature in Mesoproterozoic marine carbonates and implies the sensitivity of microbial life to environmental changes prior to metazoan evolution.