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The Middle Triassic Luoping biota represents a full recovery of marine ecosystem after the Permian-Triassic mass extinction, yet the temporal duration and exceptional preservation mechanism of the Luoping biota remain uncertain. Here, zircon geochronology and cyclostratigraphy analysis are carried out on an Anisian (Middle Triassic) Guanling Formation succession yielding the Luoping biota at the Xiangdongpo section in Yunnan Province, South China. The sensitive high-resolution ion microprobe (SHRIMP) zircon U Pb dating of a tuff bed (bed 15) in the strata confirmed an age of 244.5 ± 2.2 Ma for the Luoping biota. Spectral analyses on the elemental proxies for terrestrial flux (K, Ti, Si, Al, and K/Ti) reveal significant sedimentary cycles. The cyclostratigraphy analysis shows persistent cycles of ca. 4.4–5.1 m, 1.7–2.0 m, 0.9–1.2 m, ∼0.5 m, 0.33–0.37 m, and ∼ 0.23 m cycles, which may correspond to the orbitally forced sedimentary cycles caused by short-eccentricity (∼100 kyr), obliquity (∼32.9 kyr), precession (∼20 kyr), and sub-Milankovitch cycles (∼10 kyr, ∼8.3 kyr, and ∼ 5 kyr). Based on these results, we estimate the duration of the Luoping biota to be ∼340 ± 71 kyr. The intensified monsoonal climate during eccentricity maxima modulated large amplitude of variations of ∼5 kyr quarter precession, ∼10 kyr half precession, and ∼ 20 kyr precession cycles, led to high terrigenous discharge and strengthened upwelling, which fueled the primary productivity in surface water due to high nutrient input into the Luoping area. We propose that this process enhanced oxygen consumption in the water column, triggered anoxia of bottom water, and promoted the exceptional preservation of the Luoping biota. • Zircon U Pb SHRIMP dating of a tuff bed reveals the formation age of the Luoping biota in the Middle Triassic. • The 100 ka-tuned floating astronomical age scale provides new constraints on the duration of the Luoping biota. • Our results illustrate the relationship between orbital scale variability of monsoon and preservation of the Luoping biota. [ABSTRACT FROM AUTHOR]

Late Paleozoic deglaciation is Earth's first icehouse-to-greenhouse transition with extensive vegetation, but the response of tropical climate to this transition has not yet been fully addressed. Here, cyclostratigraphic analysis was conducted on the magnetic susceptibility (MS) record of a deep marine carbonate succession in South China to construct the astrochronology of late Cisuralian (Early Permian), and decipher the evolutionary response to the climate transition in the MS and δ13C carb time series. The constructed astronomical time scale indicates an age of 272.83 ± 0.2 Ma for the Cisuralian–Guadalupian boundary in South China. Synchronizing global records demonstrates a complicated linkage between low and high latitudes, involving secular changes in atmospheric p CO 2 , ice volume, tropical climate and carbon cycling. In the final stage of the Early Permian icehouse (~290–288.2 Ma), the delivery of moisture from low to high latitudes was reduced in comparison with that in the icehouse apex. A more humid climate facilitated the development of tropical coal forests and more storage of 12C on land. In a full greenhouse condition (~281–272 Ma), the tropical responses to a rise in atmospheric p CO 2 involved continental drying and ocean stagnation. On a shorter time scale, the nodes of 1.36 Myr obliquity cycles triggered ice-sheet expansion and enhanced tropical precipitation during an icehouse condition. With the gradual transition to an arid greenhouse, the insolation-climate relationship began to change at ~285.1 Ma, and the obliquity nodes became associated instead with terrestrial aridity and marine anoxia. These results bring into a focus pattern of shifting dynamics involving Earth's astronomical parameters and climate change for icehouse and greenhouse worlds in the Late Paleozoic Era. • The Cisuralian–Guadalupian boundary were dated as 272.83 ± 0.2 Ma. • Obliquity nodes triggered ice sheet expansion and enhanced tropical precipitation during a subhumid icehouse (290–285.1 Ma). • Obliquity nodes resulted in the terrestrial aridity and marine anoxia during an arid greenhouse (285.1–272 Ma). [ABSTRACT FROM AUTHOR]

The early Middle Triassic (Anisian) Luoping biota is representative of marine ecosystems following their full recovery after the Permian-Triassic mass extinction; however, its exceptional preservation remains poorly understood. In this paper, we report multiple geochemical proxies (TOC, TN, P/Al, Cu xs , Ni xs , Ba xs , δ13C carb , and δ13C org) from Member II of the Middle Triassic Guanling Formation at the Xiangdongpo section in Luoping County, Yunnan Province, China, to assess the relationship between primary productivity and exceptional preservation of the Luoping biota. Variations in TOC, TN, P/Al, Cu xs , and Ni xs values show that exceptional preservation coincides with two intervals of high productivity. Relatively low C/N ratios and distributed Δ13C carb-org values indicate that primary productivity was dominated by eukaryotic algae and prokaryotic microbes. Based on geochemical analyses and regional correlations, we conclude that, following sea level rise, nutrients were supplied to the Luoping area by upwelling from the open ocean and facilitated the blooming of marine communities in an open platform setting. In the intra-platform depression, increased nutrients supply also fueled high primary productivity in surface waters and oxygen consumption in the water column, causing bottom water anoxia. The lack of oxygen in the bottom water reduced the rate of biomass degradation and bioturbation, promoting growth of microbial mats, leading to the exceptional preservation of macrofauna. This study highlights the important role of elevated primary productivity in exceptional fossil preservation by triggering anoxia of bottom waters. Our findings confirm the widespread development of anoxic conditions during the middle Anisian (Pelsonian), from the eastern Tethys to the Panthalassa, and also reveal the interactions between organisms and the environment after Permian-Triassic mass extinction. • The exceptional preservation of the Luoping biota is related to two anoxic intervals with high productivity. • The source of productivity is derived from a mixture of eukaryotic algae and prokaryotic microbes. • A updated model is proposed for the exceptional preservation of the Luoping biota. [ABSTRACT FROM AUTHOR]