Direct evidence of intense chemical weathering induced by volcanism is rare in sedimentary successions. Here, we undertake a multiproxy analysis (including organic carbon isotopes, mercury (Hg) concentrations and isotopes, chemical index of alteration (CIA), and clay minerals) of two well-dated Triassic–Jurassic (T–J) boundary sections representing high- and low/middle-paleolatitude sites. Both sections show increasing CIA in association with Hg peaks near the T–J boundary. We interpret these results as reflecting volcanism-induced intensification of continental chemical weathering, which is also supported by negative mass-independent fractionation (MIF) of odd Hg isotopes. The interval of enhanced chemical weathering persisted for ~2 million years, which is consistent with carbon-cycle model results of the time needed to drawdown excess atmospheric CO₂ following a carbon release event. Lastly, these data also demonstrate that high-latitude continental settings are more sensitive than low/middle-latitude sites to shifts in weathering intensity during climatic warming events.

Ashicaulis macromedullosus sp. nov. (Osmundaceae) is described on the basis of one silicified rhizome, collected from the Middle Jurassic Tiaojishan Formation in Hebei, China. This specimen consists of a small, upright stem surrounded by frond bases, and adventitious roots. The stem consists of pith, xylem cylinder, a two-layered cortex and petiole bases. In cross section, the stem has a dictyoxylic xylem cylinder composed of 24–32 xylem strands separated by many leaf gaps with some incomplete leaf gaps. This species is characterized by continuous cylindrical phloem, absence of medullary traces in the pith, no sclerenchyma in leaf trace concavity, homogeneous cortical sclerenchyma, and one mass of sclerenchyma in each stipular wing. This is the third structurally preserved rhizome of Ashicaulis from the Mesozoic in northern China and adds to the knowledge of fern diversity in China. Northern Hemisphere species from the Jurassic have a tendency to larger stele diameter than comparable Mesozoic spe...