Sedimentology and Geochemistry of the 2930 Ma Red Lake–Wallace Lake Carbonate Platform, Western Superior Province, Canada

Abstract

Chemical sedimentary rocks in the Red Lake-Wallace Lake area of the Canadian Shield form the Earth's oldest known carbonate platform and, as such, provide a unique opportunity to explore the floor of a 2930 Myr old warm, shallow sea. Peritidal depositional features dominate the platform top, ranging from colloform crusts, teepee structures, and evaporate pseudomorphs in the supratidal; pseudomorph crystal fans and laterally linked domal stromatolites, associated with stromatactis-like structures, sheet cracks and liminoid fenestral fabrics extending from the lower supratidal through the intertidal; and herringbone cross-stratification, isolated domal stromatolites and herring-bone calcite cement in tidal channels. These lithofacies indicate a low energy, restricted evaporitic environment. Limited subtidal platform top deposits are characterized by laterally linked domal stromatolites and pseudomorph crystal fans on a larger scale than those found in the intertidal areas. A transitional lithofacies to deeper water were deposited further offshore. It consists of ribbon rock (mixed laminae and beds of carbonate, slate and iron oxide sediments), slump structures composed of intraclastic carbonate lithoclasts in a marl matrix and carbonate-associated iron formation. Basinal deposits consist of chert and chert-oxide facies iron formation. Peritidal lithofacies are composed of ferroan dolomite, whereas deep subtidal to upper slope lithofacies are composed of calcite. The dolomites have O and Sr isotopic ratios which were probably reset during dolomitization, whereas only O is altered in the limestones. The d 13 C values for all the carbonate samples were 0 AE 1Á1& V-PDB , with samples formed in deeper water having lighter d 13 C values, suggesting the deeper open ocean had a lighter d 13 C budget than water in the platform interior. Post Archean Australian Shale normalized rare earth element patterns for the carbonate samples have positive La and Eu anomalies, suprachondritic Y/Ho ratios and slight heavy rare earth element enrichment in most samples. Basin lithofacies are characterized by heavy rare earth element enrichment and positive Eu anomalies. One sample had a significant negative Ce anomaly. These data probably indicate restricted circulation in the supra and intertidal areas and possibly the development of spatially limited areas where oxygen production could move the redox boundary out into the water column.

Geochemistry of the Neoarchean Dodguni carbonates of Chitradurga greenstone belt, Dharwar Craton, India: Implications on depositional environment

“…Several Archean carbonate rocks are well preserved in various cratons and their study is important in understanding the oxygenation process during the Precambrian time (Allwood et al, 2006, 2010; Bolhar et al, 2004; Kamber et al, 2004; Kamber & Webb, 2001; McIntyre & Fralick, 2017; Ravindran et al, 2020; Siahi et al, 2018; Van Kranendonk et al, 2003). The present study deals with the geochemistry and stable isotopes (C and O) of carbonate rocks from the Dodguni area of the Chitradurga greenstone belt of the Dharwar Craton to understand the (1) chemical and isotopic signatures of Archean sea‐water; (2) influence of diagenetic and metamorphic processes and (3) to reconstruct the palaeo‐depositional conditions of the Archean carbonates.…”

Facies Control on Geochemistry of the Mesoarchean Carbonate Platform at Woman Lake (Canada)

“…The Mesoarchean carbonate platform at Woman Lake, Ontario, Canada, presents a unique opportunity to fill a 130 million year knowledge gap on early carbonate sedimentology and ocean chemistry evolution between similar occurrences at Steep Rock Lake (2.80Ga) [1] and Red Lake (2.93Ga) [2]. Stromatolitic carbonates have previously been recognized at Woman Lake [3] and is among one of the first thick carbonate platforms to develop in the Precambrian at 2857±5 Ma (this study).…”