Aspidella Research Articles

Towards a glacial subdivision of the Ediacaran Period, with an example of the Boston Bay Group, Massachusetts

After the Elatina glaciation of Snowball Earth, at least four distinct glacial advances and sea-level retreats punctuated Ediacaran time: Gaskiers glaciation (580 Ma), Fauquier glaciation (571 Ma), Bou-Azzer glaciation (566 Ma) and Hankalchough glaciation (551 Ma). Tillites or diamictites are commonly controversial, but periglacial paleosols with distinctive physical structure and degree of chemical weathering offer supporting evidence of glaciation and sea-level change useful for stratigraphic correlation. This paper reviews glacial advances of the Ediacaran stratotype and other sequences, and also reveals the value of paleosols and chemical index of alteration to understand the upper Squantum and Brookline members of the Roxbury Conglomerate near Boston, Massachusetts. The Boston Bay ice wedges are periglacial paleosols, and evidence of maritime glacial climate like that of modern coastal Greenland and Arctic Canada. Simple discoidal vendobiont fossils (Aspidella terranovica) in the Dorchester Member of the Roxbury Conglomerate and in the Cambridge Argillite are in heterolithic shale–siltstone facies that are interpreted as intertidal to shallow marine environments. Local marine transgressions and other paleosols showing significant chemical weathering represent temperate interglacial paleoclimates. Short glacial advances affecting climate and sea-level enable subdivision of the Ediacaran Period. KEY POINTS Four distinct glacial advances and sea-level retreats punctuated Ediacaran time: Gaskiers (580 Ma), Fauquier (571 Ma), Bou-Azzer (566 Ma), Hankalchough (551 Ma). Paleosols with distinctive structures such as ice wedges were periglacial. Squantum Member diamictites near Boston, Massachusetts are Gaskiers age.

SYSTEMATICS OF THE NON-SKELETON FAUNA OF THE VENDIAN DEPOSITES OF THE PODILLYA’S TRANSNISTRIA

The paper presents the systematic composition of the soft-bodied fauna and trace fossils found throughout the long history of study in the Podillya’s Transnistria. Mainly fauna is common in the Mogyliv-Podilsky series, in the lower part of it. In the Kanylivska series, the number of finds of imprints of animals is negligible, but numerous traces of their life are known. Literary data and L.I. Konstantinenko's collection were used to write the work. The samples were selected from the Lomozivsky layers (Mogyliv-Podilsky series) in the outcrop near the village Vinozh. In the study of remains, a comparative and morphometric method was used to analyze the morphology of animal elements; as well as comparative-morphological and analysis and synthesis for the establishment of taxa. In the work, the species are presented in alphabetical order without determination of over-generic categories because of the uncertainty of the systematic position. Probably the younger synonyms of Aspidella terranovica were removed from the list. It was shown that on this territory there were also three different age associations of fossil non-skeleton organisms: the Avalon-type, Ediacara-type and Nama-type, and the genera which are characteristic for them.

Vendian Macrofossils of the Yudoma Group, Southeast of the Siberian Platform

An assemblage of Late Precambrian macrofossils consisting of five species (Aspidella terranovica, Beltanelliformis brunsae, Nenoxites curvus, Palaeopascichnus renarius, and Suvorovella aldanica), was discovered in the type sections of the Yudoma Group of the Siberian Platform. A unique feature of the assemblage is the presence of carbonate discoidal remains of Suvorovella, formed as a result of secondary incrustation of basal structures, similar to Aspidella. The accumulations of redeposited fragments of Suvorovella formed the rock resembling the Phanerozoic shell beds. Except for this taxon, all members of the Yudoma assemblage have a wide geographic distribution. Their stratigraphic distribution tends to occur in the youngest deposits of the Upper Vendian, directly underlying the beds with small shelly fauna (SSF) of the Nemakit-Daldynian Stage, Cloudina tubes, and traces of the Treptichnus pedum Zone.

Finds of Ediacaran-type fossils in Vendian deposits of the Yudoma Group, Eastern Siberia

It has been established that terrigenous units of mainly carbonate deposits of the Yudoma Group in the Uchur–Maya Region of the Siberian Platform contain an assemblage of Late Vendian Ediacaran-type macrofossils. The assemblage contains species such as Aspidella terranovica, Beltanelliformis brunsae, Nenoxites curvus, and Palaeopascichnus sp., which had widespread geographic distribution. Finds of Ediacaran fossils in fossil-rich deposits of the Yudoma Group have expanded the possibilities of using the classic biostratigraphic approach applied for subdivision and global correlation of carbonate deposits in Late Precambrian paleobasins.

Ediacaran fossils in thin-section

Retallack, G.J., June 2016. Ediacaran fossils in thin-section. Alcheringa 40, xx–xx. ISSN 0311-5518Megafossils from the Ediacaran Period (635–541 Ma) have been controversial in part because many are mere impressions in coarse-grained rocks. New examination of these fossils in petrographic thin-sections reveals various features that inform understanding of the biological affinities of these problematic fossils. Material examined includes Dickinsonia costata from the Ediacara Member of the Rawnsley Quartzite in South Australia, Ernietta plateauensis from the Kliphoek Member of Namibia, Ivesheadia lobata from the Drook Formation of Newfoundland, Charnia antecedens and Charniodiscus spinosus from the Mistaken Point Formation of Newfoundland, Aspidella terranovica from the Fermeuse Formation of Newfoundland, and Nemiana simplex from the Mogilev Formation of Ukraine and the Verkovka Formation of Russia. Three characteristics stand out for all but Nemiana. First, these fossils were remarkably resistant to burial compaction, as originally inferred from depth gauge measurements of overlying moulds, and here confirmed by thin-sections perpendicular to bedding planes. Second, thin-sections reveal a construction of micrometric branching elongate structures forming millimetric hollow elongate structures in fractal arrangements. Third, some of the fossils are asymmetric bifacial or unifacial, with a thick finished upper wall but lower wall thin or non-existent and attached to elongate structures downward into sediment. Compaction-resistant fossils with asymmetric histological layering are most like crustose and fruticose lichens fortified with chitin. In contrast, non-resistant impressions in the tops of beds filled by overlying cross-bedded sediment, as in Nemiana, preserve no informative histology and are similar to lake balls and microbial colonies.Gregory J. Retallack [gregr@uoregon.edu], Department of Geological Sciences, University of Oregon, Eugene, OR 97403-1272, USA.

Evidence for Cnidaria-like behavior in ca. 560 Ma Ediacaran Aspidella: COMMENT

[Menon et al. (2013)][1] regard wrinkles at the base of discoid fossils ( Aspidella terranovica ) and deformation of laminae in cut slabs as evidence for upward migration of a cnidarian polyp in marine shales, but their observations are better explained by a sessile-growing organism with growth

Evidence for Cnidaria-like behavior in ca. 560 Ma Ediacaran Aspidella

The first appearance of animals in the geological record is a matter of continuing debate: how deep were the roots of the Cambrian explosion? Molecular clock estimates indicate that the deepest divergences of the Metazoa had occurred by the Ediacaran Period (635–541 Ma), yet evidence of animal activity from well below the Ediacaran-Cambrian boundary has been rare and often questionable. Meanwhile, the Ediacaran macrobiota has remained enigmatic, as emphasized by recent controversial claims that South Australia Ediacaran forms were not marine animals at all, but land-based lichens and microbial colonies. Here we report evidence for animal-like behavior in a submerged setting in a key Ediacaran form, Aspidella terranovica Billings 1872, a discoidal fossil from the ca. 560 Ma Fermeuse Formation of Newfoundland (Canada). We describe sedimentary fabrics indicating progressive vertical movement of an organism through sediment in response to an aggrading sediment-water interface. Such equilibrium traces are familiar from the Phanerozoic and are observed in partially buried marine animals such as tube anemones today. Furthermore, horizontal trails closely comparable to trails previously described from ∼565 m.y. old Mistaken Point (Newfoundland) are now linked to Aspidella . Our findings constitute evidence of both vertical and horizontal movement in a key Ediacaran taxon, consistent with an animal of cnidarian grade. Moreover, because Aspidella is also reported from the Rawnsley Quartzite of South Australia, our evidence conflicts with the proposed radical interpretation of that Ediacaran fossil assemblage. We demonstrate that at least some Ediacaran forms were probably early animals, and that they lived underwater.

The first named Ediacaran body fossil, Aspidella Terranovica

Aspidella terranovica Billings, 1872 was first described from the late Neoproterozoic Fermeuse Formation (St. John's Group) on the Avalon Peninsula of eastern Newfoundland, approximately 1km stratigraphically above the famous Ediacaran biota at Mistaken Point, and several kilometres below the base of the Cambrian. Aspidella has been reinterpreted perhaps more than any other Precambrian taxon, and has variously been regarded as a fossil mollusc or ‘medusoid’, a gas escape structure, a concretion, or a mechanical suction mark. Our studies indicate that Aspidella includes a wide variety of preservational morphs varying from negative hyporeliefs with a raised rim and ridges radiating from a slit (Aspidella‐type preservation), to flat discs with a central boss and sharp outer ring (Spriggia preservation), to positive hyporeliefs with concentric ornamentation (Ediacaria preservation). Specimens occur in a continuum of sizes, with preservational styles dependent on the size of the specimen and the grain size of the host lithology; the elongation of specimens is tectonic. Aspidella is confirmed as a body fossil from observations of complex radial and concentric ornamentation, mutually deformed borders in clusters of specimens, and occurrence on the same bedding planes as certain distinctive Ediacaran taxa. Aspidella is indistinguishable from, and has priority over, several of the most common genera of late Neoproterozoic discoidal body fossils worldwide. Similar fossils from Australia are interpreted as holdfasts of frond‐like organisms. The density of specimens in the Aspidella beds suggests levels of benthic biomass in the Neoproterozoic that could rival those of modern marine communities. The serial growth forms, PalaeopascichnusIntrites, Neonereites renariusYelovichnus, associated with Aspidella, are interpreted as body fossils of unknown affinities rather than trace fossils. A new, trilobed, Ediacaran body fossil, Triforillonia costellae gen. et sp. nov., is described from the Aspidella beds of the Fermeuse Formation.