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Albian

The Albian is a and age of the , representing the uppermost subdivision of the Lower Series, which spans approximately 113.2 to 100.5 million years ago and lasted about 12.7 million years. It is defined by the Global Boundary Stratotype Section and Point (GSSP) at the lowest occurrence of the planktonic foraminifer Microhedbergella renilaevis in the Vocontian Basin of , with its base dated via U-Pb zircon analysis at around 113.2 Ma. Named after the Aube region (ancient ) in northeastern where characteristic clays were first studied, the stage is bounded below by the and above by the , marking a transition to the Upper . During the Albian, experienced warm conditions with high sea levels, leading to widespread transgressions and the deposition of diverse lithologies including glauconitic sands, mudstones, marls, and carbonates across continents. In , particularly the Anglo-Paris Basin and , key formations such as the Gault Clay, Upper Greensand, and Folkestone Beds record sequences of shallow to deltaic environments, often featuring phosphatic nodules, bioturbation, and sequence boundaries tied to eustatic cycles. Globally, Albian rocks are significant reservoirs, as seen in mixed siliciclastic-carbonate ramps offshore and the Kwanza Basin, where evaporites like the Loeme Salt formed during major incursions. The stage is renowned for its rich fossil record, which provides critical biostratigraphic zonations primarily based on ammonites such as Leymeriella regularis, Hoplites dentatus, and Mortoniceras rostratum, divided into Lower, Middle, and Upper substages. Associated fauna include belemnites like Neohibolites minimus, bivalves such as Birostrina sulcata and Actinoceramus, and microfossils including , nannofossils (e.g., Seribiscutum primitivum in NAL2 zone), and dinoflagellates, enabling precise global correlations from Tethyan realms to the . Notable paleoenvironmental events encompass rifting along continental margins, transpressional deformation (e.g., in the margin), and the diversification of ecosystems, including early angiosperms and ammonoid biogeographic networks that highlight connectivity across paleocontinents. These features underscore the Albian's role in understanding evolution, sea-level dynamics, and resource geology.

Stratigraphy

Definition and Naming

The Albian Stage represents the youngest or uppermost division of the Lower Series within the System. This stage is formally recognized in the international chronostratigraphic framework established by the (). The name "Albian" originates from "," the Latin term for the River in northeastern , where the stage's type area features prominent white chalk exposures that inspired the . The term was first introduced in by naturalist Alcide d'Orbigny, who developed it as part of his pioneering work on , drawing from observations of the Basin's sedimentary sequences. Early adoption by geologists in the 19th century reflected regional mapping efforts, with the stage initially defined based on lithological characteristics like the "" clays and chalks around the valley. Over time, the Albian was integrated into global through comparative and correlation with European and North American sections, solidifying its status as a standard unit by the mid-20th century. A ceremony was held on June 29, 2024, at the GSSP site to commemorate its ratification. The ICS ratified the precise definition of the Albian's base in 2016, with official publication in 2017, establishing the Global Stratotype Section and Point (GSSP) at the Col de Pré-Guittard section near Arnayon in the Department of southeastern . This boundary is demarcated by the first occurrence of the planktonic foraminifer Microhedbergella renilaevis at 37.4 meters above the section base, within the Marnes Bleues Formation. Earlier proposals relying on ammonite taxa, such as Leymeriella tardefurcata, were abandoned due to their limited geographic distribution and biostratigraphic inconsistencies. The Albian thus follows the Stage below and precedes the Stage above.

Chronostratigraphic Extent

The Albian stage, the youngest subdivision of the Lower Cretaceous series, encompasses an absolute age range of approximately 113.0 ± 1.0 Ma at its base to 100.5 ± 0.5 Ma at its top, according to the International Chronostratigraphic Chart of the International Commission on Stratigraphy (ICS) 2023. This interval corresponds to a duration of about 12.5 million years, calibrated through integration of radiometric dating and stratigraphic correlations across global sections. These numerical ages provide a framework for understanding the timing of key geological and biological events during this period of significant paleoenvironmental change. The lower boundary of the Albian falls within the Normal Superchron (C34n), coinciding with the first occurrence of the planktonic foraminifer Microhedbergella renilaevis in the Global Stratotype Section and Point (GSSP) located at Col de Pré-Guittard, Arnayon, Drôme, . This boundary level, situated 37.4 m above the base of the Marnes Bleues Formation, also aligns with the base of the Leymeriella ammonite zonation (approximately 30 m above), serving as the primary biostratigraphic marker, while the ammonite datum facilitates global correlation within the standard Tethyan zonation. The upper boundary is marked by the first appearance of the foraminifer Rotalipora globotruncanoides at the Cenomanian GSSP in the Mont Risou section, , , with Mantelliceras mantelli appearing as a secondary ammonite marker nearby. This level, approximately 36 m below the top of the Marnes Bleues Formation, is further corroborated by the initial occurrence of Cenomanian taxa, with the foraminifer providing robust biostratigraphic linkage across marine sequences. Correlation of the Albian's chronostratigraphic extent relies on multiple methods, including to identify polarity chrons such as M0r, cyclostratigraphy for detecting Milankovitch-band cycles in sedimentary records, and U-Pb dating of volcanic ash layers to anchor absolute timescales. For instance, U-Pb zircon ages from ash beds near boundary sections have refined the base to 113.2 ± 0.3 Ma, enhancing precision in integrating these approaches.

Subdivisions and Biostratigraphy

The Albian Stage is traditionally subdivided in into four substages based primarily on ammonite biozonations, reflecting progressive faunal changes in the Anglo-Paris Basin and Vocontian Trough. The Lower Albian, sometimes referred to locally as the Substage in northern contexts, corresponds to the Douvilleiceras mammillatum , marked by the of Douvilleiceras mammillatum and associated taxa like Otohoplites auritiformis in its subzones (raulinianus, bulliensis, and steinmanni). This substage spans the early part of the stage and is characterized by hypernodose ammonites indicative of shallow environments. The Albian aligns with the Hoplites dentatus , defined by the of Hoplites dentatus and subdivided into the Lyelliceras lyelli and Hoplites spathi subzones, followed by the Euhoplites loricatus (with subzones such as intermedius, , and subdelaruei). The Upper Albian encompasses the Anahoplites daviesi Subzone within the Euhoplites lautus and extends into the Mortoniceras inflatum , featuring taxa like Anahoplites daviesi and Dipoloceras cristatum. The uppermost Vraconian Substage, recognized particularly in sequences, is equated with the Mortoniceras rostratum (a subzone of the Stoliczkaia dispar ), where Mortoniceras (Subschloenbachia) rostratum serves as the index fossil, signaling the transition toward the . Globally, biostratigraphic schemes for the Albian rely on integrated fossil groups for correlation beyond , with ammonites providing the primary framework in marine sections. Key ammonite zones include the Lower Albian Leymeriella tardefurcata and Leymeriella regularis zones in the Boreal Realm, transitioning to the widespread Hoplites dentatus Zone in the Middle Albian, and Upper Albian zones such as attenuatus (correlative with Hoplites dentatus in transitional settings) and the Mortoniceras inflatum to Stoliczkaia dispar sequence. Planktonic offer complementary zonation, particularly in Tethyan and open-ocean settings, with the Rotalipora appenninica Zone defining the latest Albian, bounded below by the last occurrence of Rotalipora ticinensis and above by the Albian-Cenomanian ; this zone is characterized by abundant Rotalipora appenninica alongside Hedbergella delrioensis and Planomalina buxtorfi. nannofossils provide high-resolution subdivision, as outlined in the NAL scheme: Lower Albian zones include NAL1 (Repagulum parvidentatum, marked by the last abundant occurrence of Rhagodiscus asper) and NAL2 (Acaenolithus viriosus total range); Middle Albian features NAL4 (Braloweria boletiformis) to NAL6 (Ceratolithina bicornuta); and Upper Albian spans NAL7 (Ceratolithina hamata) to NAL13 (Gartnerago praeobliquum), with Nannoconus truittii (including variants like truittschleensis) appearing as a common component in mid-to-upper Albian assemblages for refined correlation. These schemes enable worldwide tying of sections, though integration with cysts and ostracods enhances precision in marginal marine deposits. Biozonation challenges arise from provincialism, particularly between the warm-water Tethyan and cooler realms, complicating direct correlations. In the Tethyan Province, diverse cosmopolitan ammonites like Cleoniceras and Oxytropidoceras dominate zones such as the Douvilleiceras mammillatum Superzone, with higher speciation rates and periodic incursions into European basins; foraminiferal and nannofossil assemblages are similarly rich, supporting zones like Rotalipora appenninica. Conversely, the Province features endemic taxa (e.g., Arcthoplites in the Leymeriella tardefurcata Zone), with limited Tethyan influence due to paleogeographic barriers, leading to asynchronous zone boundaries and reliance on shared markers like Leymeriella for linkage. Nannofossil distributions show bipolar patterns, with cool-water indicators like Axopodorhabdus albianus aiding -Tethyan ties, but hiatuses and facies variations often require chemostratigraphy (e.g., carbon isotopes) for resolution. Recent refinements to Albian zonations, coordinated through the International Chronostratigraphic Chart of the , incorporate quantitative and astrochronology for enhanced precision, though major updates since the 2020 GSSP definition at the Col de Pré-Guittard section remain incremental. Studies in the , including the 2022 Kilian Group meeting, have proposed adjustments to Middle Albian hoplitid zones (e.g., elevating Lyelliceras lyelli to zonal status) and integrated non-marine correlations using and charophytes, with preliminary calibrations from terrestrial vertebrates aiding ties to marine schemes in ; however, full adoption of molecular data for Albian non-marine biochronology is pending further validation.

Geographic and Lithologic Features

Key Formations and Localities

The Albian stage is represented by several key formations across , particularly in the Anglo-Paris Basin, where the in the consists primarily of clay-rich mudstones and serves as a reference for middle to upper Albian strata. The type section of the is exposed in the cliffs at Copt Point, , , where it overlies the Lower and underlies the Upper , providing critical data for defining the Albian-Cenomanian boundary through its ammonite zonation. In southeastern , the Marnes Bleues Formation in the Vocontian Trough comprises hemipelagic marls that span the late to Albian, with the Col de Pré-Guittard section near Arnayon designated as the Global Boundary Stratotype Section and Point (GSSP) for the base of the Albian stage at 37.4 meters above the formation base, marked by the first occurrence of the planktonic foraminifer Microhedbergella renilaevis. This locality underscores the formation's role in global chronostratigraphic correlation. North American Albian deposits are prominently featured in the Washita Group of , which includes alternating shales and limestones that record shallow marine to lagoonal environments across the middle to late Albian. This group, encompassing formations such as the Georgetown Limestone and Del Rio Clay, exhibits widespread distribution along the Comanche Shelf and contributes to biostratigraphic frameworks through its rudist and ammonite assemblages. Further north, the Dakota Sandstone in the region represents a fluvial-marine transitional sequence from late Albian time, with sandstone-dominated units interfingering with shales across states like and , marking the initial inundation by the seaway and aiding in regional sequence stratigraphic correlations. Beyond these continents, the Sergipe Basin in hosts Albian evaporites within the Muribeca Formation, which includes and deposits indicative of restricted marine conditions during early Albian rifting in the South Atlantic. In the Neuquén Basin of , Albian volcaniclastic sequences occur within units like the lower Huitrín Formation, reflecting arc-related sedimentation in a back-arc setting during Andean margin evolution.

Lithology and Depositional Environments

The Albian stage is characterized by a diverse array of sedimentary lithologies, predominantly including clays, marls, chalks, sandstones, and limestones, which reflect varying degrees of marine influence and clastic input across global basins. Clays and marls, often calcareous and fossiliferous, dominate in fine-grained, low-energy settings such as the in , where they form thick sequences indicative of hemipelagic deposition. Chalks, composed primarily of coccolith-derived micrite, appear in more open marine areas like the upper Albian of the Anglo-Paris Basin, transitioning from underlying marls as a result of increased pelagic carbonate productivity. Sandstones, typically glauconitic and quartz-rich, occur in coarser clastic intervals, such as the Upper Greensand of the , representing shallow shelf sands reworked during transgression. Limestones, including bioclastic and oolitic varieties, are prevalent in carbonate-dominated regions, as seen in the Edwards Formation of , where they form thick platform successions. Regional variations in are pronounced, with black shales emerging in oxygen-restricted basins during episodes of enhanced organic preservation, such as the late Albian sequences at Site 530 in the southeastern Basin, where organic-carbon-rich mudrocks up to 170 meters thick accumulated under anoxic conditions. These black shales contrast with the more oxygenated, carbonate-rich deposits in epicontinental settings, highlighting the role of local oceanographic restrictions in modulating sediment composition. In tectonically active margins, interbedded sandstones and shales reflect higher siliciclastic fluxes, while carbonates show purer development. Depositional environments during the Albian were largely , encompassing shallow shelves, epicontinental seas, deltaic systems, and reef platforms, each tied to specific lithological assemblages. Shallow shelves, with slow sedimentation rates, favored the accumulation of glauconite-rich sands and marls, as evidenced by Albian strata in the Eastern Black Sea region, where winnowing concentrated authigenic minerals in condensed sections. Epicontinental seas, such as the of , hosted broad, low-gradient shelves that deposited alternating shales and limestones under fluctuating salinity and nutrient conditions. Deltaic systems, including braid deltas in the Basque-Cantabrian Basin, produced progradational sandstones and heterolithic muds, with coarsening-upward sequences marking fluvial-marine transitions. Reef platforms, built by and corals, generated boundstone and grainstone limestones on carbonate ramps, as in the Aitzgorri platform of northern , where high-energy margins transitioned to lagoonal muds basinward. Albian sedimentation occurred within diverse basin types, including passive margins along , foreland basins in the Andean , and rift basins in , each influencing the scale and character of depositional systems. Passive margins, such as those fringing the opening South Atlantic, accumulated thick clinoform sequences of shales and sandstones in subsiding depocenters, transitioning from rift-related fluvio-lacustrine fills to fully marine shelves. Foreland basins adjacent to the proto-Andes, exemplified by the closing Rocas Verdes marginal in southern , featured compressive subsidence that trapped Albian marine shales and turbidites in peripheral troughs. Rift basins in , like the Rio Muni , recorded syn-rift faulting with restricted marine incursions depositing organic-rich mudstones and algal limestones in depocenters. Sedimentological features of Albian deposits, such as glauconite-rich sands, provide key indicators of depositional dynamics, particularly slow sedimentation rates under high sea-level stands that allowed prolonged mineral at the sediment-water interface. These green, peloidal grains, often comprising up to 50% of matrices in shelf settings like the Zanda in , formed in low-oxygen, nutrient-enriched waters with minimal burial, signaling transgressive conditions and reduced clastic supply. Such features underscore the interplay between eustatic rise and basin in shaping Albian .

Paleoenvironment and Climate

Climatic Conditions

The Albian stage was characterized by a pronounced greenhouse climate, with global mean surface temperatures estimated at 21–28°C, approximately 6–13°C warmer than modern values. This warmth resulted in equatorial sea surface temperatures reaching up to 35°C, as inferred from oxygen (δ¹⁸O) analyses of well-preserved planktonic using paleotemperature equations. Polar regions were ice-free, evidenced by the absence of glendonites and tillites typical of earlier cold snaps, indicating a transition to fully ice-free conditions and supporting the overall hothouse state. Paleotemperature reconstructions from δ¹⁸O in belemnites and reveal short-term fluctuations, including a mid-Albian cooling episode followed by late Albian warming. During the middle Albian, bulk carbonate δ¹⁸O values indicate a cooling trend to around 21°C in mid-latitude settings, based on analyses from the Clay Formation. This was succeeded by a brief warming event of 6–7°C, reaching up to 30°C in the early late Albian, corroborated by negative δ¹⁸O excursions in calcareous nannofossils and foraminiferal tests. These isotopic shifts highlight dynamic temperature regimes within the broader context. Atmospheric CO₂ concentrations during the Albian are estimated at 800–1500 ppm, significantly elevated compared to pre-industrial levels, based on stomatal indices from fossil conifer leaves such as Pseudofrenelopsis. These proxies, calibrated against modern analogs, show values around 1200 ppm in the late Albian, with pedogenic carbonates providing supporting evidence of high CO₂ from carbonate isotopes in Early Cretaceous sections. Such elevated CO₂ levels drove the intensified , contributing to the observed warmth and high sea levels. Regional climate variations included humid conditions in the , arid belts in the , and evidence of across latitudes. Palynological records from high latitudes indicate a shift toward drier conditions in subtropical , with increasing Cheirolepidiaceae pollen suggesting hot and arid environments, while tropical regions maintained higher as evidenced by diverse thermophilic floras. is documented through growth rings in bivalve shells, such as Late Albian and pectinids from the Lusitanian Basin, where stable isotope and profiles reveal cyclic growth patterns tied to and fluctuations, implying annual environmental contrasts even in settings.

Sea Level Changes and Paleogeography

During the Albian stage of the , sea levels were markedly elevated compared to the present day, with long-term eustatic highstands reaching approximately +200 m above modern levels, primarily driven by of seawater and minimal polar ice volumes associated with conditions. These high sea levels facilitated widespread inundations across interiors, forming extensive epicontinental seas that connected distant basins and altered terrestrial connectivity. Warmer temperatures, as evidenced in contemporaneous paleoclimate records, further amplified this through enhanced . Paleogeographic reconstructions indicate that the Albian world featured accelerating continental fragmentation, particularly the ongoing breakup of with the progressive opening of the between and , which began in the and intensified during the Albian. In contrast, remained relatively stable, dominated by the expansive that extended from the proto-Mediterranean to the western Pacific, serving as a major conduit for equatorial currents and marine dispersal. Key paleogeographic features included the nascent in , an elongate embayment initiated by flexural subsidence and high sea levels along the western margin of the continent; the Basin in , a shallow intracratonic depression flooded by Tethyan waters; and the expansive Saharan platforms in northern , where vast shallow carbonate platforms emerged under the influence of the Trans-Saharan Seaway linking the Tethys to the . Sequence stratigraphic analyses reveal dynamic eustatic fluctuations during the Albian, with a prominent mid-Albian regression linked to a relative sea level fall of up to 50 m, followed by a late Albian transgression that restored highstand conditions and expanded marine realms. These curves, derived from global correlations of third-order cycles across multiple basins, underscore the role of eustasy in shaping depositional patterns, with the mid-Albian lowstand exposing continental shelves and the subsequent rise promoting renewed flooding of epicontinental areas. Such variations influenced paleogeographic connectivity, temporarily isolating landmasses before re-establishing seaways that facilitated biotic exchange.

Tectonic and Oceanic Events

During the Albian stage, the ongoing breakup of the Pangea continued to drive major tectonic reconfiguration, particularly through rifting in the South Atlantic between and , which initiated around 110 Ma in the early Albian. This rifting marked a transition from continental extension to formation, with the Equatorial Atlantic gateway beginning to open and facilitating initial marine connections. Concurrently, the initiation of in the progressed as India separated further from and , contributing to the dispersal of eastern fragments and the establishment of new oceanic pathways. Volcanic activity during the Albian was prominent in the , where the had undergone main emplacement around 122 Ma in the late , with a later pulse around 90 Ma in the ; recent (as of 2023) indicates a protracted formation with ages ranging from ~128 to ~119 Ma, suggesting limited minor activity into the earliest Albian but no significant mid-Albian phases. This massive submarine volcanism released substantial CO₂, influencing global ocean chemistry and contributing to the onset of oceanic anoxic conditions through enhanced greenhouse forcing and nutrient input. Two key oceanic anoxic events punctuated the Albian: OAE1b at the Aptian-Albian boundary around 113 Ma and OAE1d in the late Albian around 104 Ma, both characterized by widespread deposition of organic-rich shales across epicontinental seas and basins. These events featured positive carbon excursions in carbonates and organic matter, with δ¹³C shifts of up to +2‰ for OAE1b and approximately +1‰ for OAE1d, reflecting perturbations in the global driven by increased burial of organic carbon under low-oxygen conditions. Changes in ocean circulation during the Albian were influenced by evolving tectonic gateways, notably the progressive widening of connections between the and the proto-Atlantic, which enhanced intermediate water exchange and led to shifts in basin by the late Albian around 100 Ma. These developments promoted more dynamic flow patterns, altering deep-water renewal and contributing to the stratification patterns observed in sedimentary records.

Paleobiology and Evolutionary Developments

Marine Biota

During the Albian stage of the , marine plankton communities underwent significant evolutionary developments, particularly among nannoplankton and dinoflagellates, while experiencing notable turnovers in . nannoplankton exhibited radiations, with the Watznaueria biota, including species such as Watznaueria barnesiae, becoming dominant and comprising up to 14% of assemblages near the Albian-Cenomanian boundary, reflecting adaptations to varying nutrient conditions. Dinoflagellates reached a peak in during the Albian, with an estimated 584 species, marking a major radiation that contributed to the modernization of marine . Planktonic showed a turnover across the Aptian-Albian boundary, characterized by the decline and of large Tethyan forms, leading to lower dominated by smaller, opportunistic taxa like Hedbergella and Planoheterohelix moremani. Nektonic communities in Albian oceans were dominated by cephalopods and early ray-finned fishes, highlighting high rates of speciation amid expanding epicontinental seas. Ammonites, particularly from the families Hoplitidae and Douvilleiceratidae, achieved peak diversity in the late Albian, with genera like Douvilleiceras displaying varied ornamentation and contributing to rapid evolutionary turnover through high speciation rates. Belemnites, such as Neohibolites and Parahibolites, were common in shallow to outer shelf environments, with regional extinctions noted in the North Pacific by the late Albian. Early teleost fishes diversified, with otolith assemblages from North American formations revealing at least ten taxa, including clupeomorphs like Armigatus, indicating the onset of modern teleost radiations in marine settings. Benthic communities reflected shifts toward bivalve dominance in shallow marine habitats, with declining brachiopod presence. Inoceramid bivalves expanded significantly, with early Albian species like Mytiloides serving as pioneers for later diversification, adapting to soft substrates in nutrient-enriched basins. Rudist bivalves formed reefs in tropical shallow waters, constructing bioherms up to 25 meters thick in regions like the Trough, often alongside corals and during transgressive phases. Brachiopods experienced a terminal decline, with records ceasing by the Albian in areas like the Northern Caucasus, overshadowed by rising bivalve and rudist abundances. Adaptations to episodic during Oceanic Anoxic Events (OAEs), such as OAE1d, favored opportunistic planktonic taxa. Radiolarians bloomed in nutrient-rich, low-oxygen waters, with like Holocryptocanium barbui reaching abundances up to 85% during late Albian transgressions, thriving as disaster opportunists amid black deposition triggered by enhanced . These events briefly disrupted surface productivity but promoted resilient, r-selected in the and sediments.

Terrestrial Biota

The terrestrial of the Albian featured a diversifying array of land ecosystems, particularly in non-marine depositional environments such as river valleys and floodplains, where evidence reveals the coexistence of archaic and emerging plant and animal groups. during this interval showed the continued diversification of early angiosperms, including basal lineages such as (e.g., Archaeanthus linked to ) and chloranths (e.g., inflorescences), which coexisted with persistent gymnosperms like and pteridophytes such as ferns. Leaf impressions and from the Potomac Group in the provide key evidence of this radiation, with tricolpate indicating the influx of eudicot-like forms by the middle to late Albian, marking a shift toward angiosperm dominance in some local . Invertebrate communities included exhibiting early signs of social complexity, such as the Albian cockroach Sociala perlucida, which displays morphological adaptations suggestive of eusocial behavior, predating the full evolution of eusociality in . Freshwater mollusks, primarily bivalves of the Unionida, are recorded in Albian fluvial and lacustrine deposits across , including northeastern Brazil and , where they inhabited riverine environments alongside early angiosperms. Vertebrate faunas were dominated by dinosaurs in continental settings, with ornithopods such as Iguanodon and related styracosternans thriving in floodplain habitats of Europe and North America. Theropod predators like Acrocanthosaurus, a large carcharodontosaurid reaching lengths of up to 11.5 meters, occupied apex roles in North American ecosystems, preying on herbivores in coastal plain environments. Sauropods, including titanosauriforms like Sauroposeidon, represented long-necked herbivores adapted to browsing in forested floodplains of the western United States. Among non-dinosaurian reptiles, early turtles such as Isisfordia and crocodylomorphs including goniopholids appear in Albian fluvial deposits of Australia and North America, indicating adaptation to riverine niches. The last temnospondyl amphibians, exemplified by the giant brachyopoid Koolasuchus cleelandi from Australian deposits, persisted into the late Albian, reaching lengths of 5 meters and occupying predatory roles in cooler, high-latitude freshwater systems before their final extinction.

Biotic Turnovers and Extinctions

The Albian stage witnessed several notable turnovers, though no mass events comparable to the end-Cenomanian or end-Cretaceous crises. A prominent mid-Cretaceous crisis, dated to approximately 116–114 Ma in the late to early Albian transition but extending influences into the mid-Albian around 108 Ma, was driven by Atlantic cooling of about 5 °C over 2 million years, coinciding with sea-level regression and a positive carbon isotope excursion of ~2‰. This event triggered significant turnover in communities, including declines in planktonic abundance and nannoconid , as surface productivity increased but favored opportunistic taxa. Ammonite faunas experienced major family- and genus-level turnover during this interval, with the late –early Albian marking a peak in evolutionary replacement, affecting groups like the Deshayesitidae and Douvilleiceratidae. Rudist bivalves, key reef-builders, also underwent diversification and selective turnover linked to these environmental shifts, with early Albian recovery following declines but mid-Albian regression limiting shallow-water habitats. In the late Albian, around 104–100 , another pulse of turnover occurred in planktonic foraminifera, prefiguring the oceanic (OAE 2), with elevated rates estimated at –25% for in open-ocean assemblages. This crisis involved the decline of deeper-dwelling taxa like the Rotalipora lineage, driven by transient anoxia and thermal stratification during OAE 1d (~101 ), which reduced oxygenation in intermediate waters and favored surface-dwellers. Calcareous nannoplankton similarly showed accelerated speciation- rates, with ~20% loss tied to black deposition and fertility shifts. These contributed to broader genus-level in mollusks, including ammonites and bivalves, at rates of –20% per stage boundary interval, reflecting heightened sensitivity to eustatic and climatic fluctuations without reaching mass thresholds. (OAEs), briefly referenced from tectonic contexts, acted as key triggers by amplifying . Amid these turnovers, evolutionary radiations marked adaptive successes. Angiosperms expanded into higher latitudes during the mid- to late Albian, with leaf fossils from Antarctica (~70°S paleolatitude) indicating seven species in diverse riparian and floodplain settings, signaling their ecological versatility in cooler, seasonal climates. This poleward migration, from equatorial origins in the Barremian–Aptian, accelerated by ~110–100 Ma, outpacing gymnosperm declines through superior nutrient uptake and growth rates. On land, dinosaur faunas in Gondwana exhibited increasing provincialism, with Albian assemblages in South America, Africa, and Australia showing distinct theropod and ornithischian clades (e.g., megaraptorans in Patagonia), isolated by widening seaways and climatic barriers that limited intercontinental dispersal. Overall, Albian biotic dynamics prepared the stage for diversification, as turnover rates elevated without catastrophic loss—e.g., molluscan genera saw 15–20% but rapid opportunistic replacement—fostering in post-turnover ecosystems. This period's cumulative impacts, blending minor crises with radiations, underscored the interplay of cooling, , and OAEs in shaping mid-Cretaceous life, transitioning from disruptions to more stable conditions.