Abstract
Pre- and syn-glacial low-latitude carbonate sediments of the Elbobreen
Formation, NE Svalbard, preserve evidence for dramatic climate changes
associated with Cryogenian glaciations (720–635 Ma). We combine
carbonate stable (δ13C, δ18O) and clumped isotope (Δ47) geochemistry
with petrographic observations to assess the source of carbonate within
glacial facies of the Petrovbreen Member and their environmental
significance. Calcite Δ47 temperatures reflect solid-state reordering
under burial temperatures, whereas dolomites record lower temperatures
that vary with depositional facies. Pre-glacial dolomites have Δ47
temperatures from 48–73°C, with a reconstructed fluid δ18O value of
+0.6‰ (VSMOW) in the coldest sample. Glacial dolomites comprise: (1)
detrital carbonate clasts similar to pre-glacial strata in stable
isotope composition, Δ47 temperature, and petrographic textures; and (2)
autochthonous dolomicrite and re-worked dolomicrite clasts with heavier
δ18O values and colder Δ47 temperatures of 19–44 °C. Measured dolomite
temperatures likely include a component of diagenetic alteration that
elevated the sample temperature above that imparted at deposition. The
statistically significant difference in temperatures between
precipitated matrix and re-worked detrital clasts in diamictite
indicates that matrix samples preserve some component of carbonate that
records early temperature differences either reflecting the primary
sediments or early dolomitization and shallow lithification. The higher
source fluid δ18O values in glacial carbonates is consistent with an
active hydrological cycle, either through local evaporation or growth of
continental ice sheets sourced from evaporation of seawater. Continued
hydrological cycling and 20–30 °C offsets in temperature between
glacial and non-glacial conditions constrain carbonate depositional
environments in this first Cryogenian glaciation.