Yanhong Pan

Triassic-Jurassic climate in continental high-latitude Asia was dominated by obliquity-paced variations (Junggar Basin, Ürümqi, China).

Significance Geological records of paleoclimate provide the only constraints on Solar System orbital solutions extending beyond the ∼50-Ma limit imposed by chaotic diffusion. Examples of such constraints are coupled high and low latitude, Triassic–Jurassic (∼198–202 Ma) sedimentary cyclicity in coal-bearing outcrops from the ∼60° N-paleolatitude Junggar Basin (Western China), and contemporaneous tropical basins. Analysis reveals climate variability dominated by obliquity-scale cyclicity in the Junggar Basin and precession-scale cyclicity in the tropics. Together, these geological records empirically constrain orbital solutions by providing joint g4 − g3 and s4 − s3 secular frequency estimates of the Earth–Mars orbital resonance. These results demonstrate the opportunity for developing a new class of solutions grounded by geological data extending hundreds of millions of years into the geologic past. Empirical constraints on orbital gravitational solutions for the Solar System can be derived from the Earth’s geological record of past climates. Lithologically based paleoclimate data from the thick, coal-bearing, fluvial-lacustrine sequences of the Junggar Basin of Northwestern China (paleolatitude ∼60°) show that climate variability of the warm and glacier-free high latitudes of the latest Triassic–Early Jurassic (∼198–202 Ma) Pangea was strongly paced by obliquity-dominated (∼40 ky) orbital cyclicity, based on an age model using the 405-ky cycle of eccentricity. In contrast, coeval low-latitude continental climate was much more strongly paced by climatic precession, with virtually no hint of obliquity. Although this previously unknown obliquity dominance at high latitude is not necessarily unexpected in a high CO2 world, these data deviate substantially from published orbital solutions in period and amplitude for eccentricity cycles greater than 405 ky, consistent with chaotic diffusion of the Solar System. In contrast, there are indications that the Earth–Mars orbital resonance was in today’s 2-to-1 ratio of eccentricity to inclination. These empirical data underscore the need for temporally comprehensive, highly reliable data, as well as new gravitational solutions fitting those data.

A MODEL FOR ORGANIC FOSSILIZATION OF THE EARLY CRETACEOUS JEHOL LAGERSTÄTTE BASED ON THE TAPHONOMY OF “EPHEMEROPSIS TRISETALIS”

ABSTRACT The taphonomic pathways of “Ephemeropsis trisetalis” nymphs (mayfly larvae) were systematically investigated based on fossils of different preservational types, collected during three high–stratigraphic-resolution (mm to cm) excavations in the Lower Cretaceous Yixian Formation in the Sihetun area of western Liaoning, China. All fossils studied are fully articulated either in three or two dimensions, which indicates that decay was terminated at a stage before the exoskeleton became disarticulated. We conclude that the Jehol organic skeletons represent at least two general types of preservation produced by pyritization and collapse/compression, respectively. The two-dimensional compressions show no evidence for authigenic minerals, but the three-dimensionally preserved fossils are wholly or partially pyritized. Our study also indicates that aluminosilicate clay and pyrite mineralization are closely associated with fossil “Ephemeropsis trisetalis” nymphs, suggesting that both clay and pyrite played important roles in lacustrine fossil preservations, as in some marine fossil Lagerstätten. We propose a general model for organic tissue fossilization in the Jehol Lagerstätte based on study of taphonomy of “Ephemeropsis trisetalis” nymphs.

Diagenesis of bivalves from Jurassic and Lower Cretaceous lacustrine deposits of northeastern China

In contrast to the numerous excellently preserved arthropods, vertebrates and plants from the Mesozoic lacustrine fossil lagerstatten of northeastern China, which have calcium phosphate or organic skeletons, the preservation of taxa with a calcareous skeleton is fairly poor. Here we investigate, using a scanning electron microscope and energy dispersive X-ray spectrometer, the preservational modes of bivalves from the Jurassic Daohugou Fossil Beds of Inner Mongolia and the Lower Cretaceous Yixian Formation of eastern Liaoning. The Jurassic bivalve Ferganoconcha sibirica is preserved as strongly compressed composite moulds which contain remains of the organic periostracum. In the Yixian Formation, the bivalves Sphaerium anderssoni and Arguniella ventricosa occur as compacted internal, external or composite moulds or are preserved with a silicified shell, and rarely with a shell consisting of iron hydroxides, which had replaced pyrite during late diagenesis/weathering. Silicification produced partly fabric-replacive microcrystalline quartz and partly void-filling megaquartz crystals after the carbonate shell had been dissolved. Films of authigenic aluminosilicate minerals, partly secondarily silicified, cover the exterior and interior shell surfaces. Occasionally, early diagenetic pyrite crystals, now oxidized to iron hydroxides, filled shell cavities forming internal moulds and rarely replaced the bivalve shell. The poor preservation of the bivalves reflects the environment and water chemistry of these lakes, which were heavily influenced by volcanic processes. Frequent ash deposition and decomposition of volcanic glass particles created acidic and alkaline lake and interstitial waters, which led to early diagenetic formation of authigenic aluminosilicate minerals, ferruginous internal moulds, dissolution of shell carbonate and silicification of shells.

Exceptional preservation of clam shrimp (Branchiopoda, Eucrustacea) eggs from the Early Cretaceous Jehol Biota and implications for paleoecology and taphonomy

Abstract. Fossil eggs of clam shrimps (Spinicaudata) are rare and little attention has been paid to the study of their shape and microstructures. Here, we report the discovery of exceptionally preserved three-dimensional eggs from numerous specimens of Eosestheria elliptica Chen, 1976 from the lacustrine Early Cretaceous Yixian Formation in western Liaoning, China. These three-dimensionally preserved fossil eggs display a spherical shape with smooth surface, part of the tertiary envelope, and possibly the first embryonic cuticle, which were previously unknown or ambiguous. The eggs are abundant and assumed to be attached to the exopod as in extant Spinicaudata. Moreover, the exceptional three-dimensional preservation and delicate preparation of slices of the eggs allowed us to document the microstructures and elemental composition of fossil eggs of clam shrimps from the Jehol Biota. Energy dispersive spectroscopy of the fossilized envelope revealed a calcium phosphate composition. However, the egg contents display two completely different elemental compositions. Some exhibit the same elemental composition as the envelope, whereas others has been replaced by alumino-silicate. The taphonomic process is also briefly discussed in this paper.

Lower Cretaceous Stratigraphy of Eastern Asia: Nonmarine and Marine Correlations

There are abundant nonmarine Cretaceous deposits around the globe, but it is difficult to correlate the nonmarine strata within the international chronostratigraphic framework chart, which was established based on marine rocks and fossils. Fortunately, in the Lower Cretaceous of eastern Asia, there are both alternating nonmarine–marine sections and complete nonmarine sections. The approaches for dating the nonmarine Cretaceous rocks and fossils, and the nonmarine and marine correlation of Lower Cretaceous strata in eastern Asia, are summarized in this paper.