Late Miocene

Late Miocene
Name	Late Miocene
Color	#a0c0ff
Time start	11.63
Time end	5.333
Unit	epoch
Era	Neogene
Period	Miocene
Preceding	Middle Miocene
Following	Pliocene

Late Miocene The Late Miocene is the youngest subdivision of the Miocene, spanning from about 11.63 to 5.333 million years ago and bridging the transition to the Pliocene. This interval witnessed major shifts in Plate tectonics-driven geography, global climate change toward cooler and drier conditions, and faunal turnovers that shaped modern lineages such as Hominidae, Canidae, Bovidae, and Equidae. Key tectonic episodes including the uplift of the Himalayas, reorganization of the Mediterranean Sea, and closure events in the Central American Seaway had profound biogeographic consequences.

Definition and Chronology

The Late Miocene is formally recognized within the International Commission on Stratigraphy timescale and subdivided into the Tortonian and Messinian stages, framed by magnetostratigraphy and biostratigraphic markers such as planktonic foraminifera events and calcareous nannofossil turnovers. Chronostratigraphic correlation uses reference sections in regions like the Gibraltar Arc, Mediterranean Basin, and the Siwalik Group of the Indian subcontinent. Radiometric constraints derive from K–Ar dating and 40Ar/39Ar dating of volcanic ash layers intercalated with fossiliferous strata documented at classic sites such as Laetoli, Chesapeake Bay, and the Tortonian stratotype.

Paleogeography and Tectonics

Plate motions during the Late Miocene reconfigured ocean gateways and continental margins: continued convergence at the Alps-Apennines junction affected the Mediterranean Basin; collision between the Arabian Plate and the Eurasian Plate uplifted the Zagros Mountains; and northward drift of the African Plate modified the Red Sea–Gulf of Aden rift system. The progressive closure of the connection between the Atlantic Ocean and the Mediterranean Sea culminated in the Messinian salinity crisis, while tectonic shoaling in the Central American Seaway influenced equatorial circulation, as inferred from sedimentary records in the Caribbean Plate and the Panama Isthmus region. Regional uplift of the Eastern African Rift and the Tibetan Plateau altered drainage patterns recorded in basins like the Turkana Basin and the Siwalik fluvial archives.

Climate and Environmental Changes

Global climate in the Late Miocene trended toward cooling and increased aridity, linked to declining atmospheric CO2 and orbital forcings observed in marine isotope records, including multiple stages of the Messinian salinity crisis and expanded polar ice in the Antarctic Ice Sheet. These climatic shifts drove vegetational transitions from subtropical woodlands to open grassland-dominated biomes across parts of Eurasia, Africa, and North America, documented by isotopic excursions in tooth enamel from sites like Bighorn Basin and by palynological assemblages in the Paratethys deposits. Monsoon systems, notably the South Asian Monsoon and the East Asian Monsoon, underwent reorganization influenced by uplift of the Himalaya and sea-surface temperature changes in the Indian Ocean.

Flora and Fauna

Late Miocene ecosystems saw radiation and turnover among key clades: expansion of C4 grasses fostered diversification in Bovidae and influenced browsers-to-grazers transitions in Equidae and Rhinocerotidae; proboscideans such as Gomphotheres and early Elephantidae dispersed across continents; carnivore assemblages including primitive Canidae and Felidae adapted to open habitats. Hominid lineages, including members attributed to Australopithecus and possible early Homo ancestors, emerged in East African sites like Laetoli and Hadar. Avian groups such as Accipitriformes and Anseriformes adjusted ranges, while plant macrofossils and phytolith records show expansion of grass-dominated savannas in regions including the East African Rift System, the Iberian Peninsula, and the Central Asian steppes.

Marine Changes and Oceanography

Oceanography during the Late Miocene experienced major reorganizations: the Messinian salinity crisis in the Mediterranean Sea produced evaporite deposition and near-desiccation, impacting marine biogeography, faunal extinctions, and subsequent reflooding at the Zanclean flood. Cooling of deepwater sources and changes in thermohaline circulation occurred as gateways such as the Tethys Seaway closed and the Bering Strait and Panama Seaway migrated, altering nutrient delivery and plankton communities including diatoms, calcareous nannoplankton, and foraminifera. Oceanic anoxic events were absent at the scale of Mesozoic crises but regional hypoxic episodes and upwelling shifts shaped marine vertebrate communities documented in the Peru-Chile Trench and the Mediterranean basin.

Human and Hominin Context

The Late Miocene provides the backdrop for divergence events within the Hominidae; molecular clock estimates and fossil evidence from East African localities such as Laetoli, Hadza region sites, and the Hadar Formation indicate diversification of australopiths and possible pan-human-chimpanzee split timing hypotheses. Paleoenvironmental reconstructions from the Turkana Basin, Omo Group, and Afar Triangle link hominin evolution to savanna expansion and resource landscapes shaped by rift-related hydrology and monsoon variability. Comparative analyses with Old World faunal exchanges highlight dispersal corridors across the Levant and Gibraltar regions.

Paleontological and Geological Evidence

The Late Miocene fossil record is rich and geographically widespread, preserved in formations such as the Siwalik Group, Apetun Formation, Tortonian stratotype, Marrakesh Basin, Chapadmalal Formation, and the Gelasian sections that record stage boundaries. Key proxies include mammalian megafauna assemblages, isotopic compositions of tooth enamel (δ13C, δ18O), magnetostratigraphy, calcareous nannofossils, and detrital zircon U–Pb ages that constrain depositional histories. Marine evaporites, fluvial conglomerates, and lacustrine diatomites provide evidence for the Messinian salinity crisis, basin isolation events, and long-term climatic trends, enabling integration of paleoclimatic, tectonic, and biotic datasets from institutions such as the International Union of Geological Sciences and research programs like the IODP.

Category:Miocene epochs