Introduction
The Paleogene Period (66.00–23.04 Ma) is the opening interval of the Cenozoic Era and the tenth period of the Phanerozoic Eon, encompassing 43 million years of Earth history. It is formally divided into three successive epochs—Paleocene, Eocene, and Oligocene—each recording distinct phases of environmental and biotic change within the 66–23.04 Ma span.
Nomenclatural variants include Paleogene, Palaeogene, and Palæogene; it is commonly abbreviated “Pg” (rendered “Pe” on some USGS maps). The older, informal term “Tertiary” once included the Paleogene together with the Neogene but is no longer used in formal stratigraphy.
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Biologically, the Paleogene immediately follows the Cretaceous–Paleogene (K–Pg) mass extinction. The elimination of non‑avian dinosaurs, pterosaurs, marine reptiles and several fish clades created extensive ecological opportunities that precipitated rapid diversification among surviving lineages. Mammals, which survived the end‑Cretaceous biota as generally small and generalized forms, underwent a major adaptive radiation during the Paleogene, expanding in body size and taxonomic breadth and, by the Eocene, occupying a wide array of niches including aerial and marine habitats. Birds, as the sole surviving dinosaur clade, likewise radiated quickly from a few surviving neognath and paleognath lineages into numerous orders with broad morphological and ecological disparity. Among fishes, percomorph teleosts experienced a rapid Paleogene diversification that produced much of their modern order‑ and family‑level diversity and a wide range of body plans.
Climatically, the Paleogene records dramatic change: an early, short‑term warming pulse exemplified by the Paleocene–Eocene Thermal Maximum (PETM) was followed by sustained cooling through the Eocene. This long‑term decline culminated in the Oligocene transition and the first persistent glaciation of Antarctica at the Paleogene–Neogene boundary (23.04 Ma), a fundamental shift that reorganized ocean circulation and global climate regimes.
Stratigraphy
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The Paleogene System is formally subdivided into three chronostratigraphic series—Paleocene, Eocene, and Oligocene—that serve as standardized units for organizing rock successions and the early Cenozoic time scale. These epoch names denote formal stratigraphic intervals rather than informal time labels and are used to delimit successive portions of the rock record.
Definition of these units operates at two scales. Regionally, stages or local chronostratigraphic units are delineated within individual basins or areas on the basis of lithology, fossil assemblages, or tectonostratigraphic history and thus retain utility for detailed, area-specific interpretation. Globally, stages are established to permit correlation of time and rock across different continents and depositional environments, requiring an internationally consistent framework.
The International Commission on Stratigraphy (ICS) formalizes global stages through a ratification process that fixes stage boundaries by reference to a single, precisely located physical horizon. That horizon is the Global Boundary Stratotype Section and Point (GSSP), situated within a designated stratotype formation; the GSSP marks the lower boundary of a stage in the rock record. By anchoring each globally ratified stage to a single GSSP/stratotype, the ICS provides a consistent international standard for stage limits and facilitates worldwide chronostratigraphic correlation while recognizing the continuing need for regional stages and local lithostratigraphic detail.
Paleocene
The Paleocene Epoch (66.0–56.0 Ma) is the inaugural epoch of the Paleogene Period and the earliest interval of the Cenozoic Era. It is formally divided into three stages with calibrated ages: Danian (66.0–61.6 Ma), Selandian (61.6–59.2 Ma), and Thanetian (59.2–56.0 Ma).
The stratigraphic base of the Paleocene — which simultaneously defines the base of the Paleogene System and the Cenozoic Era — is fixed at a Global Boundary Stratotype Section and Point (GSSP) near Oued Djerfane, west of El Kef, Tunisia. The boundary is lithologically expressed by the rusty-colored basal surface of a ~50 cm clay layer that sedimentological evidence indicates was deposited in a matter of days; this horizon serves as the local marker for the global boundary.
That clay horizon carries a worldwide geochemical and petrographic signature attributable to a large extraterrestrial impact. A pronounced iridium enrichment is reproducibly recorded in marine and continental sequences worldwide and is accompanied by impact-derived particulates such as microtektites, nickel-rich spinel crystals, and shocked quartz. The co-occurrence of these independent lines of evidence identifies an impact origin for the boundary ejecta.
The Chicxulub structure on the Yucatán Peninsula is the recognized impact crater associated with this ejecta layer and thus the primary source of the boundary materials. The physical and chemical impact record coincides with major biotic turnover — most notably the abrupt disappearance of non-avian dinosaurs and ammonites and extensive reorganization of marine plankton and numerous other taxa — providing complementary biostratigraphic markers used for global correlation.
The Eocene Epoch spans the middle portion of the Paleogene, extending from 56.0 Ma to 33.9 Ma and thus encompasses an interval of approximately 22.1 million years within Cenozoic stratigraphy. It is formally divided into four internationally ratified stages—Ypresian (56.0–47.8 Ma), Lutetian (47.8–41.2 Ma), Bartonian (41.2–37.71 Ma) and Priabonian (37.71–33.9 Ma)—providing a high-resolution chronostratigraphic framework for correlating regional stratigraphic, palaeoclimatic and biotic records.
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The base of the Eocene is fixed by a Global Boundary Stratotype Section and Point (GSSP) at Dababiya, near Luxor, Egypt, where the boundary is defined principally by a chemostratigraphic signal rather than by a unique lithologic horizon. This marker corresponds to an abrupt, globally recognisable negative carbon-isotope anomaly—a rapid input of 13C‑depleted carbon into the ocean–atmosphere system—which coincides with the onset of the Paleocene–Eocene Thermal Maximum (PETM). The PETM represents a geologically brief but intense greenhouse episode; the leading explanation for the associated carbon and temperature perturbations is rapid venting of methane from seafloor hydrates, mobilising a large marine-sediment carbon reservoir and producing the observed global geochemical and climatic consequences.
Oligocene
The Oligocene is the third and youngest epoch of the Paleogene, lasting from 33.9 Ma to 23.03 Ma. It is formally subdivided into two chronostratigraphic stages: the lower Rupelian (33.9–27.82 Ma) and the upper Chattian (27.82–23.03 Ma).
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The global base of the Oligocene is defined by a GSSP at Massignano near Ancona, Italy. The Eocene–Oligocene boundary is principally recognized in marine sequences by the abrupt extinction of hantkeninid planktonic foraminifera, a biostratigraphic event widely used to correlate this transition.
The onset of the Oligocene marks a pronounced climatic cooling that precipitated extensive ecological and biogeographic reorganization. Changes in oceanography and terrestrial climates during 33.9–23.03 Ma drove major turnovers in both marine and terrestrial biotas, making the Oligocene a key interval of global environmental change within the Paleogene.
Palaeogeography (Paleogene)
During the Paleogene the terminal separation of Pangaea continued under sustained continental rifting and seafloor spreading, fundamentally reconfiguring plate boundaries and ocean basins and establishing much of the framework for modern continental arrangement. North Atlantic rifting propagated northward, progressively severing North America from Eurasia and enlarging the Atlantic basin, while contemporaneous rifting along Antarctica’s margins detached Australia and South America, generating new oceanic crust and opening the circum‑Antarctic seaway that evolved into the Southern Ocean.
Convergent processes simultaneously reshaped other regions: the northward motions of Africa and the Indian plate led to successive collisions with southern Eurasia, producing extensive crustal shortening and the Alpine–Himalayan orogenic belt that dominates southern Eurasian topography. At the same time the western Pacific margin experienced a tectonic polarity reversal from spreading to subduction, converting an extensional ocean edge into a subduction‑dominated margin and driving trench development, arc magmatism, and mountain building around the Pacific rim. These interacting extensional and compressional regimes during the Paleogene thus produced enduring changes to global paleogeography.
Alpine orogeny (Paleogene)
The Alpine orogeny during the Paleogene represents a broad, arcuate mountain‑building system produced by convergence between the African and Eurasian plates during closure of the Neotethys and contemporaneous reorganization of the Atlantic realm. Extending from the Tell‑Rif‑Betic arc in the western Mediterranean through the Alps, Carpathians, Apennines, Dinarides and Hellenides to the Taurides, this zone forms the western segment of the Alpine–Himalayan belt that dominates present tectonics of southern Europe, North Africa and the Middle East.
Tectonic inheritance and plate‑boundary geometry strongly controlled deformation style and segmentation. North‑projecting promontories of the African plate (notably the Adriatic/Adria microplate) and other irregular continental margins prevented development of a single continuous convergent margin and instead fostered several short, contemporaneous subduction systems. These discrete subduction cells concentrated deformation into arcuate orogens rather than a uniform orogenic front.
Convergence began in the Late Cretaceous and continued into the early Paleocene; early collision of Adria with the Eurasian margin occurred in the early Paleocene and was followed by an approximately 10 Myr reduction in Africa–Eurasia convergence coincident with initial North Atlantic opening and Greenland rifting. Convergence resumed and accelerated in the early Eocene, reactivating subduction and driving progressive closure of remaining oceanic basins between Adria and Europe, with renewed orogenic growth across southern Europe.
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From roughly 40 to 30 Ma, subduction beneath the western Mediterranean produced volcanically and tectonically active arcs (Tell, Rif, Betic, Apennines). Because trenchward retreat of the dense subducting lithosphere (slab roll‑back) outpaced plate convergence, these arcs developed strongly curved planforms. Subduction polarity varied east–west: in the west the European plate was driven beneath Africa, whereas in the east African/Adria elements dipped northwards beneath Eurasia. This polarity contrast contributed to different structural architectures along the belt and to localized orogeny such as the Pyrenees (Iberia–Europe convergence) and the growth of the Alps and Carpathians as Adria impinged on Eurasia.
In the eastern Mediterranean, from about 35 Ma the Anatolide–Tauride platform and associated passive‑margin successions entered trench systems and were detached and accreted onto Eurasia. Combined processes — slab roll‑back, variable subduction versus convergence rates, and accretion of trench sediments — generated arcuate mountain chains, spatially variable uplift, and development of foreland basins along different segments of the orogen. The cumulative effect of segmented subduction, episodic convergence (including the Paleocene lull), Eocene reactivation and Miocene–Oligocene roll‑back and accretion produced the present mosaic of curved orogens that underpins the complex tectonic and topographic patterns of the region.
Zagros Mountains (Paleogene context)
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The Zagros mountain belt extends roughly 2,000 km from the eastern border of Iraq east-southeast to the Makran coast of southern Iran, forming a continuous orogenic system along the northern margin of the Arabian Plate. Its present geometry and orientation record long-lived convergence between the Arabian and Eurasian plates as the intervening Neotethys Ocean narrowed and closed.
Structurally, the Zagros is dominated by an accretionary prism and a folded-thrust belt composed largely of sedimentary rocks that were sheared off the descending Arabian margin during subduction and progressively accreted onto the Eurasian margin. Concurrently, subduction of Neotethys oceanic lithosphere beneath Eurasia produced sustained arc volcanism from the Late Cretaceous onward, leaving a volcanic-arc record along the Eurasian margin. In addition, intra-oceanic subduction within the Neotethys generated obduction events from the Late Cretaceous into the Paleocene, emplacing slices of oceanic crust onto the Arabian continental edge and complicating the margin architecture.
Tectonic evolution in the Paleogene was punctuated by a slab break-off in the Eocene, when a detached piece of subducted oceanic plate altered stress transmission and influenced subsequent deformation patterns. Continental collision between Arabia and Eurasia began in the Eocene at about 35 Ma and progressed through the Oligocene until roughly 26 Ma; this interval marks the principal phase of uplift and structural consolidation that produced the modern Zagros orogenic belt.
Himalayan orogeny
During the Late Cretaceous–Paleogene interval the Indian continental block separated from Madagascar (c. 83 Ma) and migrated rapidly northward toward southern Eurasia. Paleocene plate reconstructions indicate very high Indian plate speeds of roughly 18 cm/yr, followed by a pronounced deceleration to about 5 cm/yr in the early Eocene; this slowdown is temporally linked to initiation of collision along the southern margin of Eurasia. The first contact between the approaching Indian margin (the leading edge of “Greater India”) and the Lhasa terrane of Tibet is recorded along the Indus–Yarlung–Zangbo suture and is commonly placed near 55 Ma, although parts of the Indian plate remained to the south at that time.
The emerging Himalayan range south of the suture is dominantly composed of metasedimentary sequences that were tectonically accreted during progressive collision and underthrusting. These rocks record derivation from Indian continental crust and, in places, from subducted lithosphere, indicating both scraping-off (accretion) and involvement of material removed from the downgoing plate. Paleomagnetic and stratigraphic data imply that a substantial portion of the northernmost Indian plate—termed Greater India—occupied a more southerly paleolatitude before collision and may now be either subducted beneath Eurasia or incorporated into the Himalayan orogenic wedge. Greater India is inferred to have formed by extension along India’s northern margin during Neotethys opening; its leading edge in many reconstructions is represented by the Tethyan (Tibetan) Himalaya block, which originally lay seaward of the Eurasian margin across the Neotethys Ocean.
Reconciling the observed Himalayan shortening, the change in Indian plate velocity, and the inferred paleogeography of Greater India remains a central geological challenge and has led to several competing models. A “narrow Greater India” model envisages a relatively small Indian northern margin (<900 km) separated from Eurasia by Late Cretaceous–Paleocene subduction of Neotethyan lithosphere and a middle‑Eocene terminal collision. An alternative model treats Greater India as a very wide plate (thousands of kilometres) but posits a microcontinental Tethyan Himalaya isolated from the Indian main mass by an intervening oceanic basin; in that scenario the microcontinent collided with Eurasia in the late Paleocene (~58 Ma) while overall plate slowdown occurred later (c. 50 Ma) as younger oceanic crust entered the trench. A third model invokes extended continental crust 2,000–3,000 km wide within Greater India, allowing much of the required shortening to be accommodated by pre‑existing extension rather than extreme crustal shortening during orogenesis.
Taken together, stratigraphic, structural and paleomagnetic evidence favors a multi‑stage collision history in which different parts of Greater India—oceanic basins, microcontinental slivers and extended continental domains—were successively consumed or accreted between roughly 58 and 50–55 Ma. This complex temporal and spatial mosaic explains the abrupt Paleogene deceleration of the Indian plate and the composite nature of the Himalayan orogen, which integrates accreted metasediments, underplated and subducted lithosphere.
The Alpine–Himalayan orogenic system in Southeast Asia constitutes a continuous tectono-orogenic corridor that links continental collision zones and island-arc domains from the Himalaya eastward through the West Burma block and along the Sunda arc (Sumatra, Java) to West Sulawesi. Throughout the Late Cretaceous into the Paleogene, northward motion of the Indian plate produced markedly oblique Neotethyan subduction beneath the western margin of Southeast Asia. This obliquity favored the development of a major strike-parallel, north–south transform system along the southern margin of the region, which accommodated significant lateral displacement between converging plates.
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Around 60–50 Ma the leading northeastern margin of Greater India directly impinged on the West Burma block, generating a pulse of intense crustal shortening, deformation and regional metamorphism as continental lithosphere overprinted the preexisting margin. Following this early collision phase, plate dynamics shifted in the middle Eocene: north-dipping subduction was reestablished along the southern edge of the Southeast Asian margin from west Sumatra to West Sulawesi, driven in part by the slower northward drift of the Australian plate. This reactivation renewed trench-related magmatism and accretionary processes along that segment.
By the late Oligocene the principal collisional emplacement between Greater India and the West Burma block had largely concluded. Continued India–Eurasia convergence thereafter was increasingly accommodated not by further frontal underthrusting but by lateral extrusion of crustal material away from the main suture. Preexisting strike-slip systems were lengthened and reactivated to absorb this ongoing convergence, producing an evolved tectonic regime dominated by major transcurrent faulting and lateral escape tectonics.
During the Paleogene the locus of North Atlantic plate divergence migrated northward and reorganized the plate architecture of the Arctic–northeast Atlantic region. Seafloor spreading initiated along the Mid‑Atlantic Ridge in the Central Atlantic propagated into the Labrador Sea by ~62 Ma and into Baffin Bay by ~57 Ma, reaching the northeastern Atlantic between Greenland and Eurasia by the early Eocene (c. 54 Ma). Early Eocene extension between North America and Eurasia opened the Eurasian Basin across the Arctic; this nascent oceanic domain was kinematically linked southward to the Baffin Bay Ridge and the Mid‑Atlantic Ridge by major strike‑slip fault systems that transferred deformation between ridge segments.
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From the Eocene into the early Oligocene Greenland behaved as an independent plate, translating northward with anticlockwise rotation. That motion produced regional compression across the Canadian Arctic Archipelago, Svalbard and northern Greenland and drove the Eureka orogeny. From about 47 Ma the Reykjanes Ridge propagated along Greenland’s eastern margin, migrating north and progressively isolating the Jan Mayen microcontinent. After ~33 Ma spreading in the Labrador Sea and Baffin Bay waned as the spreading focus shifted to the northeast Atlantic. By the late Oligocene the plate boundary between North America and Eurasia was effectively established along the Mid‑Atlantic Ridge, Greenland had become reattached to the North American plate, and the Jan Mayen microcontinent was incorporated into the Eurasian plate, with its remnant crust displaced eastward and potentially buried beneath SE Iceland.
North Atlantic Large Igneous Province (NAIP)
The Paleogene coastal cliffs of the Isle of Staffa provide a compact, vertically continuous record of NAIP volcanism: a basal volcaniclastic unit grades upward into a single, compositionally homogeneous basaltic flow that is internally zoned. This flow preserves contrasting cooling histories — a mid-section of well-formed columnar jointing produced by relatively slow cooling, overlain by a cap of irregular, closely spaced joints indicative of more rapid quenching — and thus records the local transition from explosive/fragmental deposition to effusive basalt emplacement and variable thermal regimes within the same emplacement event. The human-scale exposure of these features makes Staffa a useful field example of how joint morphology records cooling and emplacement processes.
Regionally, these outcrops are part of the North Atlantic Igneous Province, a widespread Paleogene magmatic episode extending across the Greenland and northwest European margins and spatially linked to the inferred ascent of a proto‑Icelandic mantle plume. Geochronology indicates plume-related activity began around 65 Ma and that the province experienced two principal volcanic pulses near 60 and 55 Ma. However, NAIP magmatism is temporally and spatially heterogeneous: volcanism in the British Isles and the northwest Atlantic is concentrated in the early Paleocene (with northwest Atlantic activity contemporaneous with an increased Labrador Sea spreading rate), whereas much northeast Atlantic magmatism is concentrated in the early Eocene and coincides with changes in spreading direction and the northward translation of Greenland.
The locus of NAIP magmatism commonly coincides with intersections between propagating rift systems and pre‑existing lithospheric fabrics; these inherited structures appear to have acted as preferential channels for magma ascent, focusing surface volcanism at structural weak points. The broader tectonic interpretation remains contested. While a rising mantle plume beneath Greenland offers a parsimonious source for voluminous melting, several observations complicate a simple plume‑driven rift model: rift initiation and initial seafloor spreading in parts of the North Atlantic predate the proposed plume arrival, major magmatism sometimes occurs far from synchronous rifting, and rifting episodes propagated toward rather than away from the plume locus. These lines of evidence support an alternative view in which plate‑tectonic forces that propagated rifting across the basin played a primary role, with plume activity and attendant magmatism potentially emerging as a consequence of, rather than the initial cause of, the evolving plate configuration.
Paleogene — North America
During the Paleogene the continued subduction of the Farallon plate beneath North America governed long‑lived Cordilleran deformation. A progressive shallowing of the downgoing slab produced a flat‑slab segment beneath the continent, increasing mechanical coupling at the plate interface and transmitting compressive stress far inboard of the trench. As a consequence, the locus of deformation shifted eastward from the earlier Sevier contractional belt, whose crustal shortening diminished after the Cretaceous–Paleocene interval.
This change in subduction geometry triggered the Laramide orogeny, which built the Rocky Mountain province through thick‑skinned, basement‑involved uplift rather than near‑surface thin‑skinned thrusting. Deformation during the Laramide comprised reverse and thrust faults that cut into mid‑crustal levels and elevated continental basement blocks at distances in excess of 700 km from the plate margin. The orogeny markedly reorganized continental drainage and marine connections, fragmenting the Western Interior Seaway and driving its progressive retreat.
By the mid to late Eocene (≈50–35 Ma) plate convergence rates declined and the formerly shallow Farallon slab began to steepen. That change coincided with the cessation of major Laramide uplift and extensive planation of uplifted terrain by erosional processes. In the Oligocene the tectonic regime transitioned from convergence‑dominated shortening to extensional behavior: rifting and voluminous magmatism affected the former Laramide belt, marking a fundamental shift in deformation style and magmatic activity across western North America.
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The Paleogene tectonic evolution of the South American margin was governed by persistent eastward-dipping subduction of the Farallon plate beneath the continent, a long-lived convergent regime that underpinned Andean orogenesis. Superimposed on this steady driver were temporal changes in plate motions and episodic modifications of slab geometry — notably alternating intervals of regional slab flattening and steepening — which produced pronounced along-strike variability in crustal shortening, deformation style, and the timing, volume and locus of magmatism.
This variability manifests in distinct segmental responses. In the Northern Andes, latest Cretaceous–Paleocene accretion of an oceanic plateau that carried a volcanic arc onto the margin reconfigured crustal architecture, promoting crustal growth and localized deformation. The Central Andes, by contrast, largely recorded continuous subduction of “normal” oceanic lithosphere; this steady regime controlled the segment’s characteristic pattern of crustal shortening and arc-related magmatism. In the Southern Andes, subduction of a Farallon–East Antarctic ridge introduced further complexity: ridge subduction locally perturbed slab geometry and the tectonic regime, producing tectonic and magmatic consequences distinct from those in the central and northern segments.
In sum, the interplay of sustained east-dipping Farallon subduction, changing plate motions during the Paleogene, and spatially variable slab behavior (flat versus steep segments and ridge versus normal-oceanic crust subduction) accounts for the along-strike heterogeneity in shortening and magmatism observed across the Northern, Central, and Southern Andes.
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Caribbean
The Caribbean Plate is underlain predominantly by oceanic crust of the Caribbean Large Igneous Province (CLIP), a voluminous magmatic construction formed in the Late Cretaceous that provides the principal lithospheric framework for the region. During the Late Cretaceous into the Paleocene, subduction of adjacent Atlantic oceanic lithosphere became established along the plate’s northern margin, producing a northerly-oriented subduction regime. At the same time, tectonic convergence to the southwest involved collision of an island arc with the northern Andes; this interaction inverted subduction polarity regionally and drove portions of Caribbean lithosphere eastward beneath northern South America, establishing an east-dipping subduction system along that margin.
A major reorganization occurred by the Eocene (≈45 Ma). Along the western margin, subduction of the Farallon Plate was (re)established beneath Central America, restoring trench-parallel convergence along the plate’s western/northwestern flank. Nearly contemporaneously, collision of the Bahamas carbonate platform with Cuba terminated subduction along the northern segment of the Caribbean volcanic arc and converted the northern boundary to dominantly strike‑slip motion. This transform system, extending toward the Mid‑Atlantic Ridge, became the principal kinematic link at the plate’s north. With the northern margin transmuted to strike‑slip, active subduction was routed southward and concentrated on the intra‑oceanic southern volcanic arc—now expressed by the Lesser Antilles—which became the main locus of arc volcanism and trench development.
By the Oligocene the intra‑oceanic Central American arc began to impinge on and collide with the northwestern South American margin, initiating progressive accretion of arc terranes and sustained tectonic interaction between Central American volcanic arcs and the continental margin.
During the Paleogene the Pacific basin evolved from a multi‑plate oceanic system to a configuration dominated by a single, actively convergent Pacific plate. Early in the interval four major oceanic plates—the Pacific, Farallon, Kula and Izanagi—governed seafloor production and subduction dynamics. Continued spreading in the southern Pacific along the Pacific–Antarctic, Pacific–Farallon and Farallon–Antarctic ridges sustained oceanic lithosphere generation and lateral divergence in that sector, while the central Pacific plate expanded by seafloor spreading as its neighbors were progressively consumed at trenches.
A key transformation occurred as the Izanagi–Pacific spreading ridge, oriented nearly parallel to the East Asian subduction zone, began to be overridden between about 60 and 50 Ma. By ~50 Ma the Pacific plate was no longer ringed by spreading centers but instead developed a pronounced western subduction margin. This loss of surrounding ridges and the newly established western trench system changed the balance of plate forces across the basin, producing a major reorganisation of relative motions and stress fields. The altered stress regime between the Pacific and Philippine Sea domains facilitated the initiation of persistent intra‑oceanic subduction systems and volcanic arcs, notably the Izu–Bonin–Mariana and Tonga–Kermadec chains.
To the east and north, continued subduction of the Farallon plate beneath the Americas persisted from the Late Cretaceous. A northern segment of the Farallon system separated around the Eocene (c. 55 Ma) to form the ancestor of the Vancouver/Juan de Fuca plate. Subsequent interactions between the Pacific–Farallon spreading ridge and the North American margin—first entering the subduction zone near Baja California in the Oligocene (c. 28 Ma)—induced large‑scale strike‑slip deformation along the continental margin and set the tectonic conditions that ultimately produced the San Andreas fault system. Across the Paleogene–Neogene boundary (early Neogene, c. 23 Ma) spreading between the Pacific and Farallon ceased and the residual Farallon lithosphere fragmented, giving rise to the modern Nazca and Cocos plates. Meanwhile, spreading between the Kula, Pacific and Farallon plates ended by ~40 Ma; the Kula plate was progressively accreted to the Pacific as its independent spreading terminated and it was subducted beneath the Aleutian region.
The Hawaiian–Emperor seamount chain preserves the history of interaction between a mantle plume and the overlying Pacific plate, recording relative motions in the Paleogene. Revising the classical fixed-hotspot model, current syntheses show that the plume itself migrated southward during the Paleocene–early Eocene while the Pacific plate moved northward, so the chain’s geometry reflects both hotspot drift and plate translation. At approximately 47 Ma the plume’s southward migration ceased and the Pacific plate rotated from a predominantly northward to a northwestward trajectory; this change is linked to a major reorganization of plate boundaries. The onset of subduction along the western margin of the Pacific plate is implicated in forcing the plate-motion pivot, and the combined effects of hotspot drift and the plate-direction change produced the abrupt ~60° bend that separates the older Emperor segment from the younger Hawaiian segment. Similar contemporaneous orientation changes in other South Pacific hotspot tracks corroborate a basin-scale plate-motion reorganization rather than a strictly local phenomenon.
During the Paleogene, persistent seafloor spreading between Australia and East Antarctica progressively separated these continental blocks and widened the intervening ocean basin. Shallow-water channels south of Tasmania likely developed in the Eocene and initiated a proto-Tasmanian Passage; these connections were deepened in the mid‑Oligocene when true deep-ocean routes formed and altered regional bathymetry and circulation. Rifting between the Antarctic Peninsula and southern South America opened the Drake Passage and, together with the Tasmanian opening, established a continuous oceanic gateway encircling Antarctica and thereby created the Southern Ocean.
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The emergence of these circumpolar gateways permitted the development of the Antarctic Circumpolar Current (ACC). By isolating the Antarctic continent from lower-latitude waters, the ACC exerted a strong thermal and dynamic control that favored cooling of the high southern latitudes. This geographic and oceanographic isolation promoted the growth of continental-scale ice sheets on Antarctica and marks a fundamental shift of the global climate system from warmer “greenhouse” conditions toward cooler “icehouse” conditions during the late Paleogene.
These tectonic reconfigurations and the consequent reorganization of ocean circulation were major mechanisms driving global temperature decline. Contemporaneous Paleogene tectono-magmatic activity elsewhere—illustrated by extensive flood basalts on the Ethiopian Plateau and the Afar Depression—underscores that rifting and volcanic outpourings were regionally widespread expressions of the plate‑tectonic processes operating during this interval.
Extensional deformation driven by subduction along the northern Neotethys produced lithospheric stretching that rifted Africa from Arabia, culminating in the opening of the Gulf of Aden in the late Eocene. Early Oligocene impingement of the Afar mantle plume beneath the African lithosphere generated extensive flood‑basalt volcanism across Ethiopia, northeast Sudan and southwest Yemen; the voluminous magmatism thermally weakened the lithospheric mantle and thereby enhanced extension. Continental breakup and nascent sea‑floor separation then migrated into the Red Sea realm: rifting commenced in the southern Red Sea in the mid‑Oligocene and propagated northward into the central and northern Red Sea during the late Oligocene, continuing into the early Miocene. Together, subduction‑related extension and plume‑driven magmatism controlled the timing and spatial progression of continental breakup in this region.
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The Paleogene climate record begins with a brief post‑impact “winter” following the end‑Cretaceous Chicxulub impact, then proceeds through a Late Cretaceous–Early Paleogene cool interval punctuated by transient warming (the Latest Danian Event, ~62.2 Ma) and a pronounced sequence of Early Paleogene hyperthermals. The most extreme of these, the Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma), raised reconstructed global mean surface temperature to ≈31.6 °C; land‑site reconstructions (2018) indicate mid‑latitude annual mean air temperatures of roughly 23–29 °C (±4.7 °C) between ~56 and 48 Ma—some 10–15 °C warmer than present in those regions. Smaller subsequent spikes (ETM2 at ~53.69 Ma and ETM3 at ~53 Ma) followed the PETM.
Rapid greenhouse gas release appears to have driven the PETM: emplacement of magmatic sills into organic‑rich strata of the North Atlantic Igneous Province during intense volcanism (~56–54 Ma) liberated large amounts of CO2 and thermally induced secondary methane release from destabilized continental‑slope hydrates. Extreme warmth amplified hydrological and geochemical feedbacks—accelerated chemical weathering (reflected by increased kaolinite), higher atmospheric humidity, and poleward expansion of tropical/subtropical forests that added water vapour to the atmosphere—while elevated temperatures also reduced organic‑carbon burial through faster microbial decomposition, further elevating atmospheric CO2.
Biotic and sea‑level responses to these hyperthermals were profound. Marine ecosystems suffered severe turnover (for example, ~70% loss of deep‑sea foraminiferal species with Arctic warming), while terrestrial faunas diversified and reorganized, including the radiation of many modern mammal lineages and early primates. Sea‑level fluctuations produced low stands that exposed a Bering land bridge, facilitating interchange between North America and Eurasia.
By ~48.5 Ma a massive freshwater bloom of the fern Azolla sequestered substantial CO2, initiating a long‑term cooling trend through the Middle and Late Eocene until about 34 Ma. High‑latitude proxy evidence records progressive cooling: cold‑water diatoms and indicators of seasonal sea ice appear in the Arctic, and by the late Eocene (~37 Ma) multiple lines of geological data mark the onset of Antarctic glaciation. At the Eocene–Oligocene transition, glacially derived marine sediments document an Antarctic ice sheet reaching the continental margin.
Plate tectonic reorganizations—the northward drift of Australia and South America away from Antarctica and the opening of the Tasmanian and Drake passages—permitted development of a cold Antarctic Circumpolar Current (ACC). Circumpolar isolation promoted sinking of dense polar water, enhanced upwelling of cold deep water and increased primary productivity, which together improved organic‑carbon preservation, fostered methane hydrate growth in sediments, and drew down atmospheric CO2. These oceanographic feedbacks constituted a reinforcing cooling loop, and the reorganization of deep ocean circulation may have driven major cooling and attendant marine extinctions on timescales shorter than 100,000 years.
The transition into cooler, more seasonal climates altered continental moisture budgets: reduced ocean evaporation lowered atmospheric humidity and expanded aridity on land. Throughout the Oligocene, tropical and subtropical forests in North America and Eurasia contracted, giving way to dry woodlands and extensive grasslands as precipitation regimes shifted. Glacial history in the Oligocene includes an Early Oligocene Glacial Maximum lasting ~200 kyr, continued temperature decline during the Rupelian, a mid‑Oligocene sea‑level fall consistent with major Antarctic ice growth, and a modest Late Oligocene warming; nevertheless conditions after the Eocene remained substantially cooler than Paleogene thermal maxima, with persistent polar ice cover heralding the onset of the Late Cenozoic icehouse.
Flora and fauna
The Paleogene witnessed rapid biotic restructuring in the wake of the Cretaceous–Paleogene (K–Pg) extinction. Tropical lineages diversified more quickly than those at higher latitudes, producing a steep latitudinal diversity gradient with disproportionately greater species richness and clade proliferation toward the equator. Vertebrate faunas underwent extensive adaptive radiations: mammals radiated from a few small, generalized ancestors into most modern orders and ecological roles, evolving large terrestrial dominants, multiple aquatic lineages (including the origins of cetaceans and sirenians), numerous specialized terrestrial forms, and arboreal primates. Birds, already the surviving dinosaurian clade, similarly diversified to fill aerial niches vacated by pterosaurs while several flightless avian groups (e.g., penguins, ratites, phorusrhacids) occupied terrestrial and marine roles formerly held by Mesozoic avifauna.
Marine fish also show notable Paleogene patterns: myctophid fishes first appear in the Late Paleocene–Early Eocene fossil record, persisting mainly on continental shelves through the Eocene and much of the Oligocene before expanding into the open ocean during a late-Oligocene warm interval. On land, a marked cooling in the Oligocene initiated a broad floristic reorganization. Many plant lineages characteristic of modern temperate and open habitats originated or rose to prominence at this time, signaling a shift away from predominantly tropical assemblages. Grasses and other herbaceous taxa—including Artemisia and similar genera—expanded substantially during and after this cooling, replacing formerly widespread tropical communities, while montane zones became focal areas for the establishment and expansion of coniferous forests under cooler, drier conditions.
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This overall cooling trajectory intensified in the Oligocene and, with major fluctuations, continued through subsequent epochs to the end of the Pleistocene, driving repeated biome shifts, range adjustments, and ecosystem reorganization. Palynological records of fossil pollen and spores provide stratigraphic and temporal evidence for these long-term vegetational turnovers and for the timing and nature of the Oligocene floral transition.