137-11 Embracing Enigmas: Why is Carbonate Production in Geologic History so Challenging to Interpret?

Session: Joint SGD-SEPM-IAS Focus on the Sedimentary Record of Climate Change

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Limestones and related carbonate rocks have been recognized for their value to humans for millennia. Besides providing shelter, building stones, and sources of water from springs and aquifers, they have been recognized as key reservoirs for fossil fuels for more than 150 years. Yet for geologists and paleontologists, understanding and interpreting carbonate production and preservation is rife with challenges because linear thinking commonly leads to seemly unresolvable conundrums. One basic problem is that carbonate chemistry is inherently counterintuitive, as it is largely controlled by CO₂ chemistry rather than Ca²⁺ concentrations. For example, because CaCO₃ is more soluble at cooler temperatures and higher pressures, pelagic carbonate accumulation is highly dependent on rates of ocean circulation. Another challenge is that precipitation, resulting minerals, and subsequent diagenetic processes are quite diverse, while most carbonate production since the Neoproterozoic has been associated with evolutionary processes that have responded to changes and events through Earth history. An important enigma that has perplexed some geologists is “Why should rising atmospheric CO₂ concentrations imperil the persistence of coral reefs? Weren’t rates of carbonate production much higher during times of high atmospheric CO₂?” For example, Cretaceous carbonates are so widespread that the period name means “chalk terrains”. Another enigma that was articulated by Stan Frost in the 1970s is: “Why did shallow-water coral reefs, which are warm-water ecosystems, emerge as dominant carbonate factories as the Earth transitioned from the Greenhouse World of the Cretaceous and Paleogene to the Icehouse World of the Neogene?” Recalling the origins and proliferation of major carbonate-producing organisms through more than 4 Ga of Earth history, in response to physical and chemical changes, both gradual and abrupt, can provide insights into regional and local responses by both fossil assemblages and modern producers of CaCO₃ sediments. Enhanced insights may also be useful in predicting future assemblages and the potential for both production and preservation in the anthropogenically altered ecosphere.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7659

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