Stenian

Stenian is the third and final period of the Mesoproterozoic Era within the Proterozoic Eon. It spans roughly from 1,200 to 1,000 million years ago, following the Ectasian and preceding the Neoproterozoic. The name derives from the Greek stenēs, meaning narrow, a term used to distinguish this interval in early Mesoproterozoic stratigraphy.

Stratigraphically, the base of the Stenian is placed around 1,200 million years ago, defined by radiometric ages and shifts in sedimentation observed in fragmented cratons. The upper boundary lies near 1,000 million years ago, marking the transition to the Neoproterozoic. There is no universally ratified Global Boundary Stratotype Section and Point (GSSP) for the Stenian base, and absolute ages are approximate, reflecting the limited fossil record of this time.

Geologically, the Stenian record reflects continued crustal growth and stabilization, with tectonic activity associated with the early stages of supercontinent assembly, notably the growth of Rodinia. Continental cratons experienced orogenic events and the development of extensive sedimentary basins during this interval, contributing to regional geological diversification.

Biologically, the period shows sparse macroscopic fossil evidence compared with later intervals, but isotope data and microfossil records indicate ongoing biological activity and evolving biosignatures in Proterozoic oceans. The Stenian set the stage for the environmental and evolutionary complexity that characterizes the succeeding Neoproterozoic.

See also: Proterozoic, Mesoproterozoic, Rodinia.