Trace element variations across Middle-Upper Cambrian carbonates: Implications for the paleoenvironment of eastern Laurentia

The investigated Middle-Upper Cambrian carbonates span, from bottom to top, the uppermost Hawke Bay (40 m), the March Point (similar to 83 m thick), and the lowermost Petit Jardin (similar to 47 m) formations of the Port au Port Group (western Newfoundland, Canada). A multi-technique evaluation of the preservation of carbonates was applied by using several petrographic and chemical screening tools. The variations in several proxies of bioproductivity (e. g., P, Ni, and Cu), input of weathering products (Mn, Fe, Al, and n-ary Sigma REE), and paleoredox (e.g., Th/U) have been utilized to study the paleoenvironmental conditions during the investigated time interval. Distinct positive shifts in the profiles of Al, n-ary Sigma REE, Mn, and Fe have been associated with the negative shifts recorded by the delta C-13 profile and correlated with the DICE (Middle Cambrian) and base of the SPICE (lowermost Upper Cambrian) events. They reflect contributions from detrital weathered material during sealevel falls. Similar correlated positive shifts are also documented by the P, Ni, and Cu profiles, thus suggesting an increase in the riverine inputs of nutrients associated with the drop of sealevel and increase of weathering activities. In addition, the changes in the bio-productivity and weathering proxies were associated with relative rising in the Th/U ratios (0.1-8.3), which reflects variations in the redox state towards relatively more oxidizing conditions.

Automated summary

The study utilized multiple proxies to analyze the productivity, weathering products input, and paleoredox conditions of the Middle-Upper Cambrian carbonates. Positive shifts in certain geochemical profiles were associated with sea level falls and increased weathering activities, indicating changes in redox state.