The Sirius Passet Lagerstätte of North Greenland—A geochemical window on early Cambrian low‐oxygen environments and ecosystems

Abstract

The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional water‐column chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (Fe HR /Fe T ), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ 15 N). These data, together with Mo/Al and the preservation of organic carbon ( TOC ), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones ( OMZ s), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2–0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with sea‐level change, and where this early Cambrian biota was established in conditions with very low oxygen.

On the edge of exceptional preservation: insights into the role of redox state in Burgess Shale-type taphonomic windows from the Mural Formation, Alberta, Canada

“…Overall, these data point toward 'suboxic' to anoxic (but non-sulfidic) conditions during deposition of the Chengjiang BST deposits. Echoing these results, a detailed multi-proxy study of the Series 2 Sirius Passet deposit in North Greenland reported transiently anoxic (ferruginous) conditions during the interval of highest soft-bodied fossil abundance and diversity [45].…”

The Sirius Passet Lagerstätte of North Greenland: a remote window on the Cambrian Explosion

“…The highest diversity of animal species recorded in the interval between 3.0 and 7.7 m in the Sirius Passet succession corresponds to an interval where the water column appears to have contained very low concentrations of dissolved oxygen (Fig. 10); there is a significant positive correlation (P = 5.3 × 10 −7 ) between diversity and Fe HR /Fe T values (Hammarlund et al 2019). The intervals of low-oxygen water-column conditions thus directly correlate with preserved biodiversity.…”

“…Although optimal conditions for preservation were associated with fluctuations in water-column chemistry and sea-level, we envisage that a substantial component of the Sirius Passet animal community also lived at or near the site, tolerating conditions of low watercolumn oxygen concentrations. The geochemical analysis indicates that the Sirius Passet Lagerstätte represents an early Cambrian biota that, in terms of oxygen, lived at concentrations that we today consider extremely low (Hammarlund et al 2019).…”

“…Our high-resolution geochemical exploration of palaeoenvironmental conditions in the Sirius Passet Lagerstätte has involved, to date, the analysis of 144 samples through 12 m of the Buen Formation (Hammarlund et al 2019;Fig. 10).…”

“…Proposed intervals of periodic anoxia in blue with horizontal ruling. Modified from Hammarlund et al 2019.…”