TY - JOUR

T1 - Testing models of pre-GOE environmental oxidation

T2 - a Paleoproterozoic marine signal in platform dolomites of the Tongwane Formation (South Africa)

AU - Warke, Matthew R.

AU - Schröder, Stefan

AU - Strauss, Harald

N1 - MRW was supported by a NERC-studentship through the University of Manchester. SS was supported through a Strategy Grant of the Faculty of Engineering and Physical Sciences at the University of Manchester.

PY - 2018/8

Y1 - 2018/8

N2 - Carbonate facies of the upper Tongwane Formation preserve a largely overlooked record of pre-GOE Paleoproterozoic seawater. This inventory has survived despite a complex paragenetic history involving both diagenetic and contact metamorphic processes. BIF mineral assemblages are dominated by a medium-grade grunerite overprint and the formation of prograde and retrograde riebeckite. The massive dolomite member, a platform top carbonate which caps the succession, is characterized by marine REYSN patterns lacking significant negative CeSN anomalies (<10%) and δ13Ccarb values of between +1.83 and +2.95 ‰VPDB that are slightly elevated above Paleoproterozoic ‘normal marine’ values. Systematically decreasing δ13Ccarb values measured in monotonously recrystallized, talc bearing, slope carbonates reflect interaction with devolatilization fluids during contact metamorphism caused by the intrusion of the Bushveld Igneous Complex; slope carbonates offer no insight into marine paleoredox conditions. Thus, despite contact metamorphism, Paleoproterozoic marine signals are retained in platform-top dolomites, however they do not support claims for widespread oxygen accumulation in shallow depositional environments of the Transvaal Basin on the eve of the GOE.

AB - Carbonate facies of the upper Tongwane Formation preserve a largely overlooked record of pre-GOE Paleoproterozoic seawater. This inventory has survived despite a complex paragenetic history involving both diagenetic and contact metamorphic processes. BIF mineral assemblages are dominated by a medium-grade grunerite overprint and the formation of prograde and retrograde riebeckite. The massive dolomite member, a platform top carbonate which caps the succession, is characterized by marine REYSN patterns lacking significant negative CeSN anomalies (<10%) and δ13Ccarb values of between +1.83 and +2.95 ‰VPDB that are slightly elevated above Paleoproterozoic ‘normal marine’ values. Systematically decreasing δ13Ccarb values measured in monotonously recrystallized, talc bearing, slope carbonates reflect interaction with devolatilization fluids during contact metamorphism caused by the intrusion of the Bushveld Igneous Complex; slope carbonates offer no insight into marine paleoredox conditions. Thus, despite contact metamorphism, Paleoproterozoic marine signals are retained in platform-top dolomites, however they do not support claims for widespread oxygen accumulation in shallow depositional environments of the Transvaal Basin on the eve of the GOE.

KW - Tongwane Formation

KW - Transvaal Supergroup

KW - Great Oxidation Event

KW - Cerium anomalies

KW - Carbon isotopes

U2 - 10.1016/j.precamres.2018.04.015

DO - 10.1016/j.precamres.2018.04.015

M3 - Article

VL - 313

SP - 205

EP - 220

JO - Precambrian Research

JF - Precambrian Research

SN - 0301-9268

ER -