The CM and CI carbonaceous chondrites and C-type asteroids hosted abundant liquid water and organic compounds in the past. Studies of meteorites indicate that a diverse array of water-rich environments existed early in solar system history, and the chemistry of secondary minerals produced by this alteration record the physiochemical conditions and timescales under which fluid alteration occurred. In-situ studies of carbonate minerals found in these meteorites, which precipitate directly from the fluid and can be dated using the 53Mn-53Cr chronometer, can provide strong constraints on the timing and chemistry of aqueous activity. However, a lack of appropriate analytical standards may have affected the accuracy of in-situ measurements, particularly measurements of carbonate formation ages. In this work, I developed standards designed to facilitate accurate measurements of the Mn-Cr age of carbonates and used them to measure the ages of carbonates from extensively altered meteorites, as well as samples returned from the Cb-type asteroid 162173 Ryugu by JAXA’s Hayabusa2 mission. I combine measurements of the carbonate formation age with carbon and oxygen stable isotopic measurements on the same carbonates to connect the sequence and timing of alteration with the source of the fluids and the relevant carbon reservoirs present during alteration. Using the new standards, I found that the CI chondrites (and the CI-like material returned from Ryugu) formed earlier than previously inferred and attribute this difference to the use of the improved standards. I also identified signatures of impact resetting in measurements of CM carbonate.