FOSSIL ALGAE

A new occurrence of fossil brown alga from the Orida tuffaceous sandstone and mudstone Member of the Sawatari Formation assumed to be middle Middle Miocene
in Nakanojo Town, Gunma Prefecture, Japan, is reported. The specimen GMNH-PB-2632 and its counterpart NHFM-KHDS-0002 has round-shaped single pneumacyst in some bases of branches and twigs or short rod-like leaves, and is identified as Cystoseira sp. This alga is also the second recorded fossil of the genus from Japan.
Three living species of Cystoseira are distributed in coastal areas of Japan and are dominantly between cool-temperate and frigid regions of the Northern hemisphere. They prefer cool-temperate marine conditions. Through the basis of the distribution mentioned above, it is suggested that some cold currents also influenced surface water of northeast Japan, including Gunma, in the middle to late Middle Miocene, not only warm currents. The mixing of the biota that preferred cool- and warm-temperate marine conditions in the Sawatari Formation might be the result of climate oscillation
 between warming and cooling, after the Middle Miocene Climatic Optimum. And on the basis of the occurrence of Cystoseira and some fish fossils, it is also suggested that there were rocky shores, reefs or some hard substrates near the sedimentary environment of the Sawatari Formation.

Despite the crucial role of epibenthic primary producers (cyanobacteria, green and red algae), no diversity curves for calcimicrobes and calcareous algae are available to assess the pyramiding paleoecology characterizing the Ordovician biodiversifica-tion episode. A total of 24 taxa of calcimicrobes and calcareous algae are identified from a Dapingian to lower Katian succession of carbonate sedimentary rocks exposed at the Leyayilitag ridge, Bachu Uplift, Tarim Basin, northwest China. Calcimicrobes (14 taxa), Dasycladales (seven taxa), Bryopsidales (one taxon), and Cyclocrinales (two taxa) contribute to five distinct taphocoenoses characterizing a suite of carbonate mounds. In stratigraphic order, these are calathid sponge mounds, algal calcimicrobial mounds, algal mounds, algal reefs, and calcimicrobial mounds. Within the lower Katian Belodina confluens Zone, the diversity increases substantially from around 5 to more than 20 taxa per 2 Ma. This increase in diversity is based on new calcimicrobes (Bija, Ortonella, Garwoodia, Hedstroemia, Rothpletzella, Phacelophyton, Rauserina) and the diversification of Dasycladales and Cyclocrinales. By comparison, the global diversity of calcimicrobes and calcareous algae (derived from literature data) started to increase earlier, namely within the late Darriwilian Pygodus serra Zone (offset of about 4 Ma). This offset might be due to the peculiar lithology of the Sandbian Tumuxiuke Formation (condensed section of red nodular limestones bounded by disconformities). However, a similar temporal offset is recorded for calathid sponge mounds; therefore, the Tarim tectonic microplate (Tarim Block) might display an endemic–anachronistic character. The diversity curves of Ordovician benthic primary producers (calcimicrobes, calcareous algae) are similar to those recorded by some fossil groups, in particular eleutherozoan echinoderms. Résumé : Malgré le rôle clé des producteurs primaires épibenthiques (cyanobactéries, algues vertes et rouges), aucune courbe de diversité pour les calcimicrobes et les algues calcaires n'est disponible pour évaluer la paléoécologie pyramidale qui caractérise l'épisode de biodiversification ordovicienne. Un total de 24 taxons de calcimicrobes et d'algues calcaires sont identifiés dans une séquence allant du Dapingien au Katien inférieur de roches sédimentaires carbonatées exposée sur la crête de Leyayilitag, dans la zone de soulèvement de Bachu du bassin du Tarim (nord-ouest de la Chine). Des calcimicrobes (14 taxons), dasycladales (sept taxons), bryopsidales (un taxon) et cyclocrinales (deux taxons) font partie de cinq thanatocoenoses distinctes qui caractérisent une suite de monticules carbonatés. En ordre stratigraphique, il s'agit de monticules d'éponges calathides, de monticules algaires et calcimicro-biens, des monticules algaires, des récifs algaires et des monticules calcimicrobiens. Dans la zone a ` Belodina confluens du Katien inférieur, la diversité augmente considérablement d'environ 5 a ` plus de 20 taxons chaque 2 Ma. Cette augmentation de la diversité repose sur de nouveaux calcimicrobes (Bija, Ortonella, Garwoodia, Hedstroemia, Rothpletzella, Phacelophyton, Rauserina) et la diversification des dasycladales et cyclocrinales. En comparaison, la diversité planétaire des calcimicrobes et des algues calcaires (tirée de données publiées) a commencé a ` augmenter plus tôt, soit dans la zone a ` Pygodus serra du Darriwilien tardif (un décalage d'environ 4 Ma). Ce décalage pourrait être le fait de la lithologie particulière de la Formation sandbienne de Tumuxiuke (séquence condensée de calcaires nodulaires rouges limités par des discordances érosionnelles). Cependant, un décalage temporel semblable est observé pour des monticules d'éponges cathalides, de sorte que la microplaque tectonique du Tarim (bloc du Tarim) pourrait présenter un caractère endémique–anachronistique. Les courbes de diversité des producteurs primaires benthiques (calcimicrobes et algues calcaires) de l'Ordovicien sont semblables a ` celles enregistrées par certains groupes de fossiles, en particulier les échinodermes éleuthérozoaires. [Traduit par la Rédaction]

Premise of research. Although largely neglected by the paleobotanical literature, the Early Devonian genus Sphondylophyton Schultes and Dorf is on record as the oldest sphenophyte. Given current understanding of the fossil record, a revised interpretation of the depositional environment at the fossil locality, and the discovery of new specimens, reconsideration of the taxonomic affinities of Sphondylophyton is necessary.
Methodology. All known Sphondylophyton specimens were examined for morphological comparison with plant and algal lineages exhibiting a similar whorled architecture.
Pivotal results. Sphondylophyton is characterized by sparsely branched, flexuous axes bearing whorled, simple, terete appendages with dimorphic apical morphology. Sphenophyte affinities are ruled out, as whorled taxis does not appear in vascular plants until the Late Devonian. Evidence for marine influences in the depositional environment of Sphondylophyton warrants consideration of algal affinities. Although dasycladalean and charophycean green algae share superficial morphological similarities with Sphondylophyton, they can be excluded upon detailed comparison (e.g., branching, lateral appendage dimensions and complexity).
The combination of characters of Sphondylophyton falls within the morphospace of the Rhodophyta. Among these, Sphondylophyton is most similar to rhodomelacean taxa in overall habit, appendage morphology, and thallus durability. Generic and specific emended amplified diagnoses are provided.
Conclusions. Sphondylophyton is not a sphenophyte as previously suggested; dasycladalean and charophycean
affinities are not supported. We demonstrate that Sphondylophyton is a red alga most comparable to Rhodomelaceae, although no taxonomic placement below the phylum rank is proposed; as such, it contributes to the limited fossil record of the Rhodophyta.

The Devonian Period experienced many changes within the environmental and biological realms and terminated with one of the largest mass extinctions of the Phanerozoic. The Appalachian Basin of western New York contains several alternating successions of gray and black shale, many of which mark marine crises culmination in the end-Devonian mass extinction. The causes for the formation (e.g., anoxia, flooding, biological production changes) of the black shale sequences has long been debated within the basin. This period was characterized by major changes in both the terrestrial and marine biospheres and terminated with one of the largest mass extinctions of the Phanerozoic Era (Kaiser et al., 2016). Middle Devonian terrestrial environments saw tremendous increases in biomass and complexity with the evolution of vascular and seed-producing plants, trees, and the formation of deeply weathered and thicker soils (Beerbower et al., 1992). The Devonian marine realm has long been suspected to have been heavily affected by bottom water anoxia, enhanced organic carbon burial rates, dramatic shifts in primary production, and an extended biotic crisis. The biotic crises and related marine extinction events have been attributed to many factors including bolide impacts (McLaren, 1982), tectonism and climate change (Ettensohn et al., 1988), oceanic overturn and/or euxinic conditions (Kelly et al., 2019; Haddad et al., 2016; Boyer et al., 2021), cold water oceans and dysaerobic conditions (Copper, 1986), marine ecosystem collapse (McGhee, 2013), eustatic change (Johnson and Sandberg, 1988), and more recently linking the marine phenomena to coeval developments in the terrestrial realm (Algeo et al., 1995; Algeo and Scheckler, 1998; Algeo et al., 2000).
Algeo et al. (1995) presented the hypothesis that the Middle-to-Late Devonian marine biotic crisis and mass extinction of benthic communities were precipitated by the evolutionary development of vascular land plants; terrestrial floras appeared in the Middle Ordovician, and these land plants were small, either non-rooted or shallowly rooted, and ecologically limited to moist lowland habitats (Cascales-Miñana, 2016). Evolutionary innovations of these floras in the Devonian allowed them to interact with substrates and strongly influence weathering processes, hydrologic cycling that would have changed the amount of run-off and peak discharge (Schumm, 1977; Algeo and Scheckler, 1998), and has been suspected by some researchers to have resulted in geochemical fluxes and the formation of carbon-rich black shale beds within the Appalachian Basin. While flooding events in the Appalachian Basin have received much attention recently (Kelly et al., 2019; Haddad et al., 2016; Lash, 2019; Bartlett et al., 2021 (in press)), by no means is there a consensus on the causes of formation of black shale sequences and other major shifts in lithology during this global event (see Kaiser et al., 2016).
Over 100 years of research of the Devonian Appalachian Basin has led to the construction of one of the most detailed litho-stratigraphic frameworks of a Paleozoic foreland system that has allowed for detailed interpretations of sea level history and shifts in sedimentation rates (Dana, 1894; Wanless, 1947; Brett and Baird, 1986; House and Kirchgasser, 1993; Brett, 1995; Ver Straeten and Brett, 1995; Brett et al., 2011; Ver Straeten et al., 2011). As a result, a tremendous amount of geochemical proxy data from these gray and black shale sequences has shown that the perception that the Devonian black shales were deposited under anoxic conditions holds true, thus far, for only one black shale unit (Werne et al., 2002), the Oatka Creek Shale, and that intervals of terrestrial fresh water flux were not as prevalent as previously thought and that primary production plays a strong role in many, if not all black shale beds of the Appalachian Basin (Arthur and Sageman, 2005).
More recent research on intercalcated deposits described in ancient and modern marine settings (e.g., Cretaceous Western Interior Seaway and Eastern Atlantic Ocean, Pleistocene North Atlantic, Neogene Mediterranean, modern Black Sea) has focused on eutrophic conditions and the effects of organic input, climate variations, primary production changes and seasonal riverine input and has made clear that the formation of carbonaceous and organic-carbon-deficient layers is anything but straightforward. The same is true of investigations attempting to derive the mechanisms behind the gray and black sequences in the Devonian Appalachian Basin (Werne et al., 2002; Sageman et al., 2003; Arthur and Sageman, 2005; Ver Straeten et al., 2011; Wilson and Schieber, 2015; Kelly et al., 2019; Smith et al., 2019; Haddad et al., 2016; Lash, 2019; Boyer et al., 2021; Bartlett et al., 2021 (in press)).