Small carbonaceous fossils (SCFs) from North Greenland: new light on metazoan diversity in early Cambrian shelf environments

Abstract

The Sirius Passet Lagerstätte of North Greenland is one of the oldest records of soft‐bodied metazoan‐dominated ecosystems from the early Cambrian. The Lagerstätte site itself is restricted to just a single c. 1‐km‐long outcrop located offshore from the shelf margin, in an area affected by metamorphic alteration during the Ellesmerian Orogeny (Devonian – Early Carboniferous). The recent recovery of small carbonaceous fossils (SCFs) to the south, in areas that escaped the effects of this deformation, has substantially expanded the known coverage of organic preservation into shallower water depositional settings in this region. Here, we describe additional SCF assemblages from the siliciclastic shelf succession of the Buen Formation (Cambrian Series 2, stages 3–4; c. 515 Ma), expanding the previously documented SCF biota. Newly recovered material indicates a rich diversity of non‐mineralizing metazoans, chiefly represented by arthropod remains. These include the filtering and grinding elements of a sophisticated crustacean feeding apparatus (the oldest crustacean remains reported to date), alongside an assortment of bradoriid sclerites, including almost complete, 3D valves, which tie together a number of SCFs previously found in isolation. Other metazoan remains include various trilobite cuticles, diverse scalidophoran sclerites, and a range of metazoan fragments of uncertain affinity. This shallower water assemblage differs substantially from the Sirius Passet biota, which is dominated by problematic euarthropod stem‐group members and sponges. Although some of these discrepancies are attributable to taphonomic or temporal factors, these lateral variations in taxonomic composition also point to significant palaeoenvironmental and/or palaeoecological controls on early Cambrian metazoan communities.

Vertically migrating Isoxys and the early Cambrian biological pump

“…[47,57,58]). The first macroscopic nektonic suspension feeders, such as the radiodont Tamisiocaris, also appear at this time [59], while the first centimetre-scale phytoplanktivores are identified close to the Stage 3–4 boundary (figure 5) [12]. These data suggest that there was an increase in the diversity of millimetre-scale zooplankton at or close to the base of Stage 3, very close in time to the appearance of the first vertical migrants.…”

An outer shelf shelly fauna from Cambrian Series 2 (Stage 4) of North Greenland (Laurentia)

“…The Aftenstjernesø Formation documents the initial establishment of carbonate deposition following the siliciclastic shelf sediments of the Buen Formation (Ineson and Peel, 1997;Peel and Willman, 2018;Wallet et al, 2020), which crop out extensively across central and eastern North Greenland (Ineson and Peel, 1997;Peel and Willman, 2018). The formation is dominated by cliff-forming dolostone grainstones.…”

“…Assemblages of small carbonaceous fossils described by Slater et al (2018) and Wallet et al (2020) Valkov, 1983. Phosphatized spheres are known from the Ediacaran (Xiao et al, 2014;Cunningham et al, 2017;Anderson et al, 2019) and Cambrian and Early Ordovician (Donoghue et al, 2006) in Canada, China, Siberia, Australia, and USA.…”

“…Assemblages of exceptionally preserved small carbonaceous fossils have been described from the Mount Cap Formation (Cambrian Series 2-3), Northwest Territories (Butterfield, 1994;Harvey and Butterfield, 2011;Fig. 2.1, locality 12), but cannot be compared closely to the fauna of the Aftenstjernsø Formation, as is the case also with material from the Buen Formation of southern Peary Land described by Slater et al (2018) and Wallet et al (2020).…”

“…1.4), yields a rich biota dominated by trilobites and hyoliths in southern Peary Land (Peel and Willman, 2018), but the lack of carbonates precludes sampling for small shelly fossils that might be compared to the Navarana Fjord assemblages. Digestion of Buen mudstones in hydrofluoric acid has yielded abundant small carbonaceous fossils (Slater et al, 2018;Wallet et al, 2020), but these show little similarity with the carbonate-derived small shelly fossils of the basal Aftenstjernesø Formation.…”