Tracing Ediacaran δ ¹³ C anomalies across southwestern Gondwana: new stratigraphic insights from the Sete Lagoas Formation, central Brazil

The Cryogenian–Ediacaran interval records widespread carbonate sedimentation along the margins of the São Francisco Craton (SFC), with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 13 C carb values that enable stratigraphic correlation across the sedimentary basin. In the Brasília region, the Ediacaran Sete Lagoas Formation (SLF) unconformably overlies Mesoproterozoic carbonate and siliciclastic rhythmites of the Paranoá Group, making a major hiatus and the absence of Cryogenian glacial diamictites. The SLF is subdivided into two distinct stratigraphic sequences. Sequence 1 comprises deep- to shallow-water carbonates, with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 13 C carb values ranging from −3 to +3‰. Sequence 2 begins with a transgressive siltstone and grades into interbedded limestone and lime-shales, showing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 13 C carb values between +5 and +14‰, a pattern consistently observed across the basin. Despite the contrasting carbon isotope trends, 87 Sr/ 86 Sr ratios remain relatively stable throughout the Ediacaran succession. A comparable positive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 13 C carb excursion is recorded in coeval strata of the Otavi Group (northern Namibia) and the Schisto-Calcaire Subgroup (western Congo Belt), supporting a potential regional basin-wide chemostratigraphic correlation across the southwestern margin of Gondwana.