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.