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The Cretaceous has been considered a "high-fire" world accompanied by widespread by-products of combustion in the rock record. The mid-Cretaceous oceanic anoxic event 1b (OAE1b) is marked by one of the major perturbations in the global carbon cycle characterized by deposition of organic-rich sediments in both marine and terrestrial settings. However, our understanding is still limited on changes in wildfire activity during OAE1b period. Here, we carried out a comprehensive analysis, including organic carbon isotope (δ13C org), total organic carbon (TOC), coal petrology, trace elements, and pyrolytic polycyclic aromatic hydrocarbons (pyroPAHs), of coal seams of the middle Aptian to early Albian Shahezi Formation from borehole SK-2 in Songliao Basin, Northeast China. Two negative δ13C org excursions in the Shahezi Formation can be corresponded with the 113/Jacob and Kilian sub-events of OAE1b. Moreover, the intensive peatland wildfires have been identified during the sub-event periods of OAE1b based on the co-occurrence of high abundance of charcoal and pyroPAHs at that time. In addition, Sr/Ba, Sr/Cu and Sr/Rb ratios demonstrate that enhanced peatland wildfires were controlled by dryer climate conditions owing to episodic northward migration of arid zones in East Asia related with rising global temperature during the sub-events of OAE1b. The climate-driven extensive wildfire activity in the mid-latitude terrestrial ecosystems can be a contributing factor for OAE1b through the increased flux of nutrients fuelling primary producers in the lake and marine environments and leading to more speculative anoxia to allow the deposition of organic-rich sediments. Our results provide essential understanding of the importance of wildfires in driving mechanism of oceanic anoxic events (OAEs) in Earth's history. [ABSTRACT FROM AUTHOR]

Abstract: The micromorphology of trichomes of the leaves of 17 taxa (including two varieties) of the genus Chelonopsis Miq. and of six species representing four additional genera (Bostrychanthera deflexa Benth., Colquhounia coccinea Wall. var. coccinea, Co. seguinii Vaniot. var. seguinii, Gomphostemma chinense Oliv. var. chinense, G. crinitum Wall. ex Benth. and Physostegia virginiana (L.) Benth.) was surveyed by light and scanning electron microscopy. Two basic types of trichomes can be identified: non-glandular and glandular trichomes. The non-glandular trichomes can be subdivided into two subtypes: simple unbranched and branched trichomes. Based on the cell number, simple unbranched trichomes are further divided into four shapes (unicellular, two-celled, three-celled, and more than three cells), whilst branched trichomes are separated into three shapes (biramous, stellate, and dendroid trichomes). The glandular trichomes can in turn be subdivided into four subtypes: subsessile, capitate, clavate, and sunken. Non-glandular trichomes with two cells (NGTW) and subsessile glandular trichomes (GSU) are most widespread in all taxa examined. The indumentum shows considerable variation among different sections or species. Consequently, trichome micromorphology and distribution have high taxonomic value for Chelonopsis at both infrageneric and interspecific levels. The presence of capitate glandular trichomes (GCA) provides an additional morphological character to clarify the boundaries between subgenus Chelonopsis and Aequidens Wu and Li. Within subgenus Aequidens, non-glandular trichomes with more than three cells (NGMT) and clavate glandular trichomes (GCL) are important characters for sectional division between sect. Aequidens Wu and Li and sect. Microphyllum Wu and Li. Again, three forms of three-celled trichomes can be used as a distinctive taxonomic character at specific level between C. albiflora Pax et K. Hoffm. ex Limpr., C. forrestii J. Anthony, and C. souliei (Bonati) Merr. in sect. Aequidens. This study supports Wu''s delimitation of subgenus and sections and the subsequent review work by Xiang et al. Additionally, distribution of trichome types is correlated with the altitudinal distribution and habitats of some species in Chelonopsis. [Copyright &y& Elsevier]