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This paper discusses the geometrical properties of a radiolarian skeletal structure, namely, that of genus Didymocyrtis. We characterized the evolution of skeletal structures and analyzed the structures using geometry. We defined two ratios in order to quantify the geometrical properties of Didymocyrtis and verified that the two ratios changed with their phylogenic evolution. We also used the 3D skeletal data of a specimen of species D. tetrathalamus, which were obtained through micro X-ray CT. The cortical shell obtained in the 3D data was projected onto a spherical surface, and we determined the centers of the pores. Our analysis revealed that the number of pores is approximately 200 and their distribution is not regular. We also determined that the column-like parts of the skeleton, which connect the inner and upper parts of the specimen, do not lie on a plane and their intervals are not equal. [ABSTRACT FROM AUTHOR]

The aim of this report is to 1) to formally describe Austral and Subtropical Gyre Radiolaria recovered from ODP Hole 123-765C), 2) to compare them with published records of Southern Hemisphere "non-Tethyan" assemblages and 3) to discuss radiolarian paleobiogeography of the Southern Hemisphere and its implications for global climate change during the Jurassic-Cretaceous transition. The Tithonian to Aptian/early Albian radiolarian record recovered from Hole 765C, Cores -62R to -36R in the Argo Abyssal Plain (AAP) is unique in its density of well-preserved samples and in its faunal contents. Radiolaria recovered from claystones yielded the low diversity, ecologically tolerant "Crypto-Archaeo" Assemblage, (chiefly cryptocephalic and cryptothoracic nassellarians and Archeodictyomitra spp.) interpreted herein as originated in the Subtropical Gyre (STG). In contrast, assemblages extracted from radiolarite layers, interpreted as pelagic turbidites derived from the deeper Australian margin, are dominated by Austral taxa. Neotethyan taxa are very rare to absent before the late Hauterivian/Barremian, when they gradually gain in diversity and abundance. Described Austral and STG taxa include 10 families, of which Fusitanellidae n. fam. and Windaliinae n. subfam. are new. Of 18 genera 7 are new (Nodosphaera, Praewindalia, Pachycingula, Archaeotanella, Morchella, Fusitanella, Argofusus) and of 55 species 30 new ones are formally described and 14 new ones are left in open nomenclature. The southern hemisphere Late Jurassic to Early Cretaceous radiolarian biogeography is defined from low- to high latitude: 1. the Neotethyan (NT) and 2. the Central Panthalassan (CP) realms, 3. Eastern Boundary Current (EBC) realm, 4. the Subtropical Gyre (STG) and the Austral (A) circum south-polar realm. Radiolarian biogeography and plate tectonic models support a scenario of palaeoceanographic and global climatic change during the Jurassic-Cretaceous transition related to progressive Pangea break-up with the following consequences: 1. an increased heat transfer to the Southern hemisphere which caused cooling of Neotethyan regions during the Late Tithonian dry event. 2. Anorthward shift of the southern summer Intertropical Convenience Zone reduced the Neotethyan monsoon area and allowed the establishment of a southern Neotethyan subtropical gyre documented by the "Crypo-Archaeo" Assemblage. 3. The south-polar West Wind Drift may have forced a circum Antarctic-Australian cold current through the epicontinental rift between India and Antarctica-Australia since the Berriasian (140 my), transporting Austral Radiolaria into the AAP where they accumulated in radiolarite layers. [ABSTRACT FROM AUTHOR]

Climate warming and related drivers of soil thermal change in the Arctic are expected to modify the distribution and dynamics of carbon contained in perennially frozen grounds. Thawing of permafrost in the Mackenzie Delta region of northwestern Canada, coupled with increases in river discharge and coastal erosion, trigger the release of terrestrial organic matter (OMt) from the largest Arctic drainage basin in North America into the Arctic Ocean. While this process is ongoing, well-established, and its rate is accelerating, the fate of the newly-mobilized organic matter, as it transits from the watershed through the delta and into the marine system, remains poorly understood. In the framework of the European Horizon 2020 Nunataryuk programme, and as part of theWork Package 4 (WP4) CoastalWaters theme, four field expeditions were conducted in the Mackenzie Delta region and southern Beaufort Sea from April to September 2019. The temporal sampling design allowed the survey of ambient conditions in the coastal waters under full ice cover prior to the spring freshet, during ice break-up in summer, as well as anterior to the freeze-up period in fall. To capture the fluvial-marine transition zone, and with distinct challenges related to shallow waters and changing seasonal and meteorological conditions, the field sampling was conducted in close partnership with members of the communities of Aklavik, Inuvik and Tuktoyaktuk, using several platforms: helicopters, snowmobiles and small boats. Water column profiles of physical and optical variables were measured in situ, while surface water, groundwater and sediment samples were collected and preserved for the determination of the composition and sources of OMt, including particulate and dissolved organic carbon (POC, DOC), and chromophoric dissolved organic matter (CDOM), as well as a suite of physical, chemical and biological variables. Here we present an overview of the standardized datasets, including hydrographic profiles, remote sensing reflectance, temperature and salinity, particle absorption, nutrients, dissolved organic carbon, particulate organic carbon, particulate organic nitrogen, colored dissolved organic matter absorption, fluorescent dissolved organic matter intensity, suspended particulate matter, total particulate carbon, total particulate nitrogen, stable water isotopes, radon in water, bacterial abundance, and a string of phytoplankton pigments including total chlorophyll. Datasets and related metadata can be found in Juhls et al. 2021. https://doi.pangaea.de/10.1594/PANGAEA.937587. [ABSTRACT FROM AUTHOR]

Defining the Jurassic-Cretaceous boundary is a controversy in stratigraphic study of the world. It has been widely accepted that this boundary can be defined at the bottom of Berriasian in Tethys, with the appearance of the ammonite Berriasella jacobi dating to ca. 145 Ma. However, it is difficult for the widespread terrestrial deposits in China to correlate with the international standard of marine facies. The Somanakamura Group in Japan is represented by a succession of marine-continental transitional strata. It provides a bridge of marine and nonmarine stratigraphic correlation. The ammonite and radiolarian fossils preserved in this group suggest an age from Bajocian to early Valanginian. The J-K boundary was defined in or atop the Tomizawa Formation of the group according to the ammonite data. The present authors study the fossil spores and pollen newly found from the Tomizawa and Koyamada formations. Three assemblages have been recognized. They are Assemblage 1 (Cyathidites-Classopollis) from the upper part of the Tomizawa Formation, Assemblage 2 {Cyathidites-Jiaohepollis) from the lower part of the Koyamada Formation, and Assemblage 3 {Cyathidites-Spheripollemtes-Ephedripites) from the middle to upper part of the Koyamada Formation. With the reference of ammonite evidence, the J-K boundary can be defined between Assemblage 1 and Assemblage 2. This palynological J-K boundary can be correlated with that of terrestrial sequence in China. However, local biostratigrapby imply that the continental J-K boundary in China is of 135 or 137 Ma age. It has a considerable discrepancy from the marine standard. Biogeographically, the distribution pattern of spores and pollen in southern China is in accordance with that in the Somanakamura Group, which parallels the Tuchengzi Formation in northeastern China. By the palynological correlation between the Somanakamura Group and the strata in southern China, and then with the sequence in northeastern China, it is suggested that the continental J-K boundary is located in the Tuchengzi Formation. [ABSTRACT FROM AUTHOR]

The Gujingling (古井岭) Section in Xiaodong (小董), Guangxi (广西) Zhuang Autonomous Region, China, consists of cherts and siliceous siltstones, which belongs to the Bancheng (板城) Formation of the Qinzhou (钦州) allochthon. Three successive radiolarian assemblage-zones related to the Guadalupian (Middle Permian) appear in the section in the following ascending order: Pseudoalbaillella sp. aff. Pseudoalbaillella longicornis-Pseudoalbaillella fusiformis, Follicucullus monacanthus, and Follicucullus scholasticus-Follicucullus porrectus. The radiolarian content in this section is generally greater than that of sponge spicules. The radiolarian fauna commonly consists of abundant Albaillellaria and spherical radiolaria with minor Latentifistularia and Entactinaria. The sponge fauna is composed mainly of hexactinellids with minor demosponges. These siliceous fossil faunal features, comparable with those in a deep basin of the western belt of the Phosphoria Basin in the western United States, indicate that the Bancheng Formation in the Gujingling Section was deposited in a basin deeper than 1 000 m. The siliceous siltstones in the section are characterized by inclusion of silt-sized quartz and no inclusion of sand-sized materials, suggesting that the Gujingling Section was located at least a few hundred kilometers from the South China Block in the Guadalupian. [ABSTRACT FROM AUTHOR]