Possible trilobozoans with internal structures from the Late Ediacaran Nama Group, Northern Cape, South Africa

• Sedimentary rocks of the classic Nama Group extend for over 1000 km from southern Namibia across the Orange River and into northwestern Republic of South Africa. We report on fossils from the Nama Group deposited in the southern part of the Witputs sub-basin exposed in the Northern Cape Province of the RSA between Vioolsdrif and Springbok. This succession begins with the shallow marine and fluvial siliciclastics and platform carbonates of the Dabis and Zaris formations. Carbonates of the Zaris Fm. yield the late Ediacaran skeletal fossils Cloudina and Namacalathus. The Nudaus Fm. begins with sandstone of the Niederhagen Mbr., followed by the shale-dominated Vingerbreek Mbr. The Vingerbreek Mbr. in southern Namibia has been interpreted as a muddy tidal deposit in places with strong microbial mat signature whereas the upper part of the member in the Springbok-Vioolsdrif area has been interpreted as storm-influenced shallow marine deposits. The Vingerbreek Mbr. near Springbok measures c.100 m and is constrained by radiometric ages in over- and underlying rocks elsewhere in the Nama Basin to between 547 and 545 Ma. The succession in the Vioolsdrif-Springbok area terminates with the Urusis Fm., comprising quartzarenites of the Nasep Mbr. and the carbonate-dominated Huns Mbr. In late 2016, four discoidal fossils were collected from a fine-grained silciclastic interval within the Vingerbreek Mbr. to the north of Springbok. The fossils occur in an assemblage with abundant vendotaenids, textured organic surfaces (TOS), scratch circles, various skeletal tubes, several types of small dimples and horizontal trace fossils. Micro-CT scans were made of all four discs, and in the case of the largest disc (diam. 4 cm), complex internal structures are visible. There are three distinct central “pouches” with no apparent connection to each other. Each central pouch appears to be connected by tubes to five smaller pouches. These clusters of five outer pouches form a peripheral ring of 15 circular chambers at the inferred “base” of the disc and become more irregular towards the “top”. The wrinkled outer surface, distinct margin and tripartite symmetry suggest a trilobozoan body plan with possible affinities with Rugoconites and Skinnera. Most trilobozoan taxa are known only from simple external moulds. The more complex mineralogy and taphonomy exhibited by these specimens, offers a unique taphonomic window that may help unravel the paleobiology of this enigmatic group.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Annan geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Other Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Ediacaran

problematica

trilobozoan

South Africa

Nama Group

Earth Science with specialization in Historical Geology and Palaeontology

Geovetenskap med inriktning mot historisk geologi och paleontologi

Publikations- och innehållstyp

vet (ämneskategori)

kon (ämneskategori)