Modern vs. Ancient Marine Evaporite Environments

Compare and contrast modern and ancient marine evaporite environments.

The mineral makeup of the earth has changed over time. Aside from mineral evolution, atmospheric and climate changes also impact what type of sediments are produced. In the era of a reducing atmosphere, sulfur precipitates as pyrite, while in an oxidizing atmosphere, that same sulfur will instead precipitate as gypsum. In the period of changing over from a reducing to oxidizing atmosphere, iron precipitated out of the oceans as banded iron formations.

Climate plays a role that is most easily recorded in the type of limestone produced. In Greenhouse conditions (like most of the Phanerozoic), a lack of polar ice caps and high sea levels are recorded by extensive high-Mg calcite limestone deposits. In Icehouse conditions (Permo-Triassic, late Cenozoic, and the present day), polar ice caps and a low sea level in a stratified ocean are producing few low-Mg calcite and aragonite limestone deposits.

Approximately 1.2 billion years ago, hot, arid climate paired with broad, stable landmasses, such that episodic thin films of evaporating seawater produced massive evaporite deposits. Modern evaporite environments are relatively small and contained — hypersaline coastal lagoons, an isolated lake, maybe even an extensive saltflat. Ancient environments had these localized evaporites, but also large, extensive deposits from isolated shallow or barred deep marine basins. Ancient deposits have been identified in the interior of Australia and underneath the Mediterranean Sea.

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