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The Nama Group (Kalahari Craton) is an archetypal stratigraphic record of the Ediacaran–Cambrian transition. The upper Schwarzrand Subgroup preserves key biostratigraphic markers of this interval, including erniettomorphs, cloudinomorphs, and trace fossils, yet has a complex stratigraphic architecture due to deposition in a foreland basin. Here, we describe the stratigraphy of the upper Schwarzrand Subgroup of the Nama Basin, and collate sedimentologic, geochronologic, carbon isotope chemostratigraphic, and biostratigraphic data. We argue that strata previously identified as the Nomtsas Formation in the Witputs Subbasin are lithostratigraphically and tectonostratigraphically distinct from those in the type area (Farm Nomtsas) in the Zaris Subbasin. Therefore, we introduce the Swartkloofberg Formation as a new name for the terminal Schwarzrand Subgroup in the Witputs Subbasin. While carbonates of the underlying Urusis Formation were deposited within shallow marine environments, the Swartkloofberg Formation records a transition to dominantly siliciclastic deposition, mostly below fair-weather wave base, and with extensive evidence of slope instability. High-relief stromatolite reefs formed diachronously at different localities within both the Urusis and Swartkloofberg formations due to laterally variable accommodation space within the foreland basin. Strata of the Swartkloofberg Formation are interpreted as flysch deposits within an underfilled basin. We propose that the distinct deltaic peritidal and shoreface strata that—in some localities—were previously assigned to the upper Nomtsas Formation, are placed within the unconformably overlying molasse deposits of the Fish River Subgroup. These strata contain the stratigraphically lowest identified occurrences ofTreptichnus pedumwithin the Nama Group, and thus the base of the Cambrian Period. This stratigraphic revision solves several longstanding issues with regional correlation and revises the position of the Ediacaran–Cambrian boundary in the Witputs Subbasin. Accordingly, the Swartkloofberg Formation in the Witputs Subbasin (538.5–<537.6 Ma) is Ediacaran in age, as defined by biostratigraphy, supporting recent interpretations that the base of the Cambrian Period may be younger than 537.6 Ma. With increasingly refined age-stratigraphic models for the Nama Group, the upper Schwarzrand Subgroup provides a high-resolution record of the evolution of increasingly complex benthic invertebrate behaviors in the terminal Ediacaran lead-up to the classical Cambrian radiation of biomineralized invertebrate phyla. 

Abstract The upper Ediacaran stratigraphic record hosts fossil assemblages of Earth’s earliest communities of complex, macroscopic, multicellular life. Tubular fossils are a common and diverse, though frequently undercharacterized, component of many of these assemblages. Gaojiashania cyclus is an enigmatic tubular fossil and candidate index fossil found in upper Ediacaran strata globally and is best known from the Gaojiashan Lagerstätte of South China. Here we describe a recently discovered assemblage of Gaojiashania fossils from the Ediacaran Dunfee Member of the Deep Spring Formation of Nevada, USA. Both body and trace fossil affinities have been proposed for Gaojiashania; we present morphological and biostratinomic evidence for a body fossil affinity for the Dunfee specimens. Additionally, previous studies have highlighted that Ediacaran tubular fossils are characterized by a wide range of preservational modes, including association with pyrite, apatite, or clay minerals and preservation as carbonaceous compressions. Petrographic, SEM, and EDS data indicate that the Dunfee Gaojiashania specimens are preserved as ‘Ediacara-style’ external, internal and composite molds, in siltstone and sandstone with a clay mineral-rich matrix of both aluminosilicates and non-aluminous Mg- and Fe-rich silicate minerals that we interpret as authigenic clays. Authigenic clay-mediated fossilization of unmineralized tissues, including moldic preservation in heterolithic siliciclastic strata, as indicated by the Dunfee Gaojiashania, may be linked to the prevalence of both silica-rich and ferruginous seawater conditions prior to both the radiation of silica-biomineralizing organisms and the rise of ocean and atmospheric oxygen to modern levels. In this light, clay authigenesis may have played a critical role in facilitating multiple modes of Ediacaran and Cambrian exceptional fossilization, thus shaping the stratigraphic distribution of a range of Ediacara macrofossil taxa. 

Abstract The terminal Ediacaran Period is signaled worldwide by the first appearance of skeletonizing tubular metazoan fossils, e.g.,CloudinaGerms, 1972 andSinotubulitesChen, Chen, and Qian, 1981. Although recent efforts have focused on evaluating the taxic composition and preservation of such assemblages from the southwestern United States, comparable forms reported in the 1980s from Mexico remain to be re-examined. Here, we reassess the latest Ediacaran skeletal materials from the La Ciénega Formation of the Caborca region in Sonora, Mexico, using a combination of analytical methods: optical microscopy of extracted fossils, thin-section petrography, scanning electron microscopy and energy dispersive X-ray spectroscopy, and X-ray tomographic microscopy. From our examination, we conclude that the La Ciénega hosts a polytaxic assemblage of latest Ediacaran tubular organisms that have been preserved through two taphonomic pathways: coarse silicification and calcareous recrystallization preserving finer details. Further, these fossils show signs that their shells might not have been inflexible or completely mineralized in vivo, and that they might also record tentatively interpreted predation traces in the form of drill holes or puncture marks. This work, along with ongoing efforts around the world, helps to provide a framework for biostratigraphic correlation and possible subdivision of the Ediacaran Period, and further shapes our view of metazoan evolution and ecology in the interval directly preceding the Cambrian explosion. 

The geologically rapid appearance of fossils of modern animal phyla within Cambrian strata is a defining characteristic of the history of life on Earth. However, temporal calibration of the base of the Cambrian Period remains uncertain within millions of years, which has resulted in mounting challenges to the concept of a discrete Cambrian explosion. We present precise zircon U–Pb dates for the lower Wood Canyon Formation, Nevada. These data demonstrate the base of the Cambrian Period, as defined by both ichnofossil biostratigraphy and carbon isotope chemostratigraphy, was younger than 533 Mya, at least 6 My later than currently recognized. This new geochronology condenses previous age models for the Nemakit–Daldynian (early Cambrian) and, integrated with global records, demonstrates an explosive tempo to the early radiation of modern animal phyla. 

Paleomagnetic, rock magnetic, or geomagnetic data found in the MagIC data repository from a paper titled: Paleomagnetic Records From Pulsed Magmatism in the Southwestern Laurentia Large Igneous Province and Cardenas Basalt Support Rapid Late Mesoproterozoic Plate Motion