Paul Eric Olsen

Triassic-Jurassic Lagerstätten in eastern North America record biotic and environmental changes that set the stage for the era of dinosaurian ecological dominance that lasted 136 million years. This paper describes the morphologic, systematic, stratigraphic, temporal, and environmental context of these extraordinary fossil assemblages within strata of the vast, paleotropical eastern North American Newark Supergroup. Formed during the initial rifting of the supercontinent of Pangea, these mostly lacustrine and fluvial deposits combine a super-abundance of tetrapod footprints, particularly those of dinosaurs, with a physical stratigraphy that reflects orbitally paced climate cyclicity, which in turn provides a high-resolution stratigraphy for most of the record. Some Newarkian footprint Lagerstätten are exceptional, displaying detailed scale patterns, associated body impressions, and, plausibly, feather homologues. These strata contain other Lagerstätten that yield superbly preserved insects, fishes, and reptiles. More conventional assemblages of skeletal remains, tracks, fishes, and plants also abound. Most Lagerstätten and other assemblages occur in sedimentary cycles that reflect the expansion and contraction of perennial lakes in monsoonal climates. Newark Supergroup faunal and floral assemblages, and the strata they come from, document consequential events during the early Mesozoic, most notably those surrounding the continental end-Triassic mass extinction and the ensuing Jurassic recovery.

Discovery of abundant lake ice-rafted debris (L‑IRD) coeval with dinosaurs in continental strata of the Late Triassic to middle Jurassic of northwestern China (Junggar Basin) led to reevaluation of paleolatitude for that region (1). The basin was inferred to lie north of the Arctic Circle during the Late Triassic/Early Jurassic, along with much of Northeast Asia, consistent with paleomagnetic reference frame data (2–4). Similarities in facies transitions through the Triassic and Jurassic in both the North and South China blocks, together with recent paleomagnetic interpretations, suggest amalgamation with the Siberian plate by the Late Triassic (5, 6), implying a giant Early Mesozoic Arctic continent dwarfing present-day Antarctica.The L‑IRD shows that the southern margin of the Arctic had freezing winters despite high pCO₂, consistent with climate models (7), and the outsized Arctic continent would have had an enhanced continental climate with even colder winters. With lowlands freezing in winter in the southern Arctic, there were presumably significant mountain glaciers, perhaps even a small ice cap, as a background condition, consistent with glacioeustatic Triassic–Jurassic sea-level fluctuations (8).The end-Triassic sea-level drop stands out in particular: a ∼10⁵‑year event on a multimillion-year rise, broadly coincident with the end-Triassic mass extinction (ETE) (9). This sea-level drop is coincident with the onset of the Central Atlantic Magmatic Province (CAMP), but modeling suggests that CAMP-related uplift would have had relatively local effects (10). An increase in glacial ice triggered by CAMP volcanic winters provides a possible mechanism (11). Perhaps enhanced via ice–albedo feedback and a consequent increase in Earth System sensitivity to polar orbital forcing, ice-sheet growth may have triggered a recently identified ~400 kyr switch in tropical orbital pacing from expected precession dominance to obliquity dominance and back (12), a temporary transition resembling the onset of the “40 kyr world” at the mid-Miocene transition, plausibly caused by growth of the Antarctic Ice Sheet to near-modern size (13).This giant Arctic continent may have primed the Earth System to switch from a hothouse to a transient icehouse world during CAMP volcanic winters, causing an abrupt sea-level drop. The same cold perturbations may also have driven the extinction of all large non-insulated land animals, paving the way for dinosaur ecological dominance, as these insulated reptiles were already living in the freezing Arctic beforehand.1) Olsen et al. 2022. Sci. Adv. 8, eabo6342; 2) Marcilly et al. 2021. http://www.earthdynamics.org/climate/exposed_land.zip; 3) van Hinsbergen et al. 2014. paleolatitude.org; 4) Leonard et al. 2025. Commun. Earth Environ. 6, 508. 5) Yi et al. 2023. Earth Planet. Sci. Lett. 118143; 6) Olsen et al. 2024. Geol. Soc. Lond. Spec. Publ. 538, SP538–2023–2089; 7) Landwehrs et al. 2022. Proc. Natl. Acad. Sci. 119, e2203818119; 8) Wang et al. 2022. Glob. Planet. Change 208, 103706; 9) Fox et al. 2020. Proc. Natl. Acad. Sci.; 10) Austermann et al. 2015. EGU Gen. Assem. Abstr. 3073; 11) Schoene. 2010. Geology 38, 387–390; 12) Olsen et al. 2024. AGU24, Abstr. V22A-05; 13) Westerhold et al. 2020. Science 369, 1383.

SUMMARY: Basaltic flows and sills of the Central Atlantic Magmatic Province (CAMP) along the eastern North American seaboard have been proposed to be present in buried Mesozoic basins. Their offshore distribution is poorly constrained, yet the strong magnetic and gravity signature produced by basaltic rocks means it should be possible to map them using magnetic and gravity surveys. We conducted forward modelling using existing magnetic and gravity data to identify Mesozoic basins and basaltic units offshore. Onshore and offshore basins containing CAMP basalts in forward models generally predict the best fit with observed magnetic and gravity data. A positive magnetic anomaly over the New York Bight Basin suggests it may contain multiple basalt flows at depths > 2500 m, and scenario testing indicates the Long Island Basin possibly hosts at least one flow. The newly identified Central Bight Basin is unlikely to contain basaltic units, although the adjacent East Coast Magnetic Anomaly may be overwhelming potential basalt signatures within the basin. Deeper basement structures and/or possible interbasinal basalt likely influence existing data, therefore higher resolution aeromagnetic and marine gravity surveys are needed to constrain CAMP basalt presence in offshore basins.

A half-century of investigations in deep-lake and littoral facies have produced a wealth of fossils, illuminating the trophic structure of the latest Triassic and Early Jurassic rift ecosystems in the Hartford and Deerfield Basins (Connecticut and Massachusetts, USA). Fossil assemblages include representatives of all fundamental levels of the food chain: bacteria, algae, plants, mollusks, crustaceans, insects, fishes, and tetrapods. The superabundance of large theropod dinosaur footprints in near-shore lake environments, as exemplified at Dinosaur State Park, Rocky Hill, Connecticut, and the rarity of herbivore tracks in the same facies suggest that the aquatic food web was critically important to apex dinosaurian carnivores. We clarify the stratigraphy and elucidate the monsoonal expansion and contraction of perennial lakes at Dinosaur State Park, highlighting the importance of microbial mats that blanketed trackway surfaces. At basin scale, we document the facies-dependent distribution of large carnivorous dinosaur tracks (Eubrontes) in lake-margin strata. In contrast, large herbivorous dinosaur tracks (Otozoum) primarily occur in fluvial facies, more proximal to upland environments. The rarity of herbivorous tetrapod footprints in lake-margin environments may indicate that herbivores lived in dry-land, upland habitats, spent most of their time foraging along streams and rivers, or intentionally avoided lake shores frequented by large carnivores. Large theropods were opportunistic apex predators in littoral habitats, with a diet of fishes and the smaller tetrapods that also frequented lake margins. Rather than tearing through coniferous forests displaying a fierce raptorial lifestyle, as typically portrayed, the large carnivores of the Triassic-Jurassic circum-Atlantic rift valleys likely spent most of their days at the beach, fishing.

Solar system gravitational interactions are embedded in Earth’s record of climate, providing a way to bypass the 60 Myr limit imposed by chaos. Presently with a 2.4 Myr period, the Mars–Earth beat cycle of orbital perihelion frequencies is particularly sensitive to chaotic diffusion, potentially varying by more than a million years. Early Mesozoic (252 to 145 Ma) strata provide some constraints on this cycle, with evidence of a swing through most of the solution space from 1.8 Myr at 210 Ma to 2.5 Myr at 190 Ma and back to 1.6 Myr at 180 Ma. However, only the 1.8 Myr cycle is corroborated by geochronologic data and the 1.6 Myr period is disputed. Here, we show that variations in land-plant-dominated stable carbon isotopic ratios (δ ¹³ C _org ) from the lacustrine, paleo-high-latitude Sangonghe Formation (Junggar Basin, northwestern China), reveal at least three 1.6 Myr Mars–Earth beat cycles centered at 183 Ma, tracking atmospheric CO ₂ isotopic composition in Earth’s exchangeable carbon reservoirs. Furthermore, the middle cycle includes the famous Jenkyns Event, expressed here by poleward migration of cheirolepidaceous conifers driven by CO ₂ warming from the Karoo-Ferrar large igneous province (LIP). Our data do not, however, support major, LIP-triggered input of isotopically light carbon and instead support CO ₂ amplification of local processes via warming and ecosystem change. Although requiring additional independent geochronological support, Sangonghe data help provide empirical constraints for filtering orbital solutions, tightening initial conditions, and testing gravitational models, as well as showing how extrinsic cyclical processes interact with a tectonic event, the Karoo-Ferrar LIP.

Paleotropical lacustrine strata of eastern North America are only known place where vertebrate and floral records of the end-Triassic extinction (ETE) (1) are directly interbedded with U-Pb zircon CA-TIMS-dated lavas of the CAMP (2) and a high-resolution, orbitally paced, lacustrine cyclostratigraphy (3, 4). New, continuous XRF elemental scans of Newark and Hartford rift basin cores (5) confirm previous work in showing expected climatic-precession-dominance modulated by eccentricity for most of the section (6, 7), but an emerging major surprise is that the 500 kyr interval around the Triassic-Jurassic transition is very strongly obliquity-dominated. Tied by sub-Milankovitch magnetic polarity stratigraphy [chron E23r (3)] to rich outcrop-based biostratigraphy, this new Mn/Fe, K/Al, Zr/Rb, S and Na chemostratigraphy requires a revision of environmental interpretations of the proximal cause of the continental ETE. We argue that despite the clear record of pulsed massive pCO2 increases tied to CAMP emplacement, CAMP eruptions produced extreme, sulfur-driven, mega-volcanic winters that were proximal drivers of extinction on land (8) — not the giant hyperthermal itself. We hypothesize that these extreme cold events, superimposed on a background of polar latest Triassic-earliest Jurassic cooling (9) and wintertime freezing (10, 11), enhanced polar ice-albedo feedback and possibly glaciation (12). This amplified Earth System sensitivity to obliquity forcing, perhaps not unlike the initiation of the “40 kyr” world of the Late Neogene [e.g. (13)]. Onset of this Triassic-Jurassic obliquity pacing modality marked the continental phase of the ETE, but in light of these competing radiative balance forcings, interpretations of end-Triassic sea-level drop (12) and marine extinctions require reevaluation as well, considering factors beyond global warming alone (14).1, Olsen+ 2002 Science 296:1305. 2, Blackburn+ 2013 Science 340:941–945. 3, Kent & Olsen 1999 JGR 104:12831-12841. 4, Olsen & Kent 1996 PPP 122:1-26. 5, Kinney+ 2002 Abstract PP25D-0899, AGU Fall Meeting. 6, Van Houten 1962 AJS 260:561. 7, Olsen 1986 Science 234:842. 8, Kent+ 2024 PNAS 121:e2415486121. 9, Judd+ 2024 Science 385:eadk3705. 10, Olsen+ 2022 Science Adv. 8:eabo6342. 11, Chang+ 2024 GSL Spec Pap. 538:114. 12, Schoene+ 2010 Geology 38:387. 13, Westerhold+ 2020 Science 369:1383-1387. 14, Funded by NSF & the Heising-Simons Foundation.

Eruptions of the Central Atlantic Magmatic Province (CAMP) at 201.6 Ma are linked to the end-Triassic extinction (ETE) on land via competing radiative forcings, which caused extreme alternations in warming and cooling and humidity and aridity (climatic whiplash) [c.f., (1)]. Although ETE effects on land-plant diversity are often described as minor, tropical flora exhibit significant changes in plant physiognomy, paralleling pCO2 and hydrological variations recorded from the same strata.Most dramatic is the extirpation of the vesicate pollen group exemplified by Patinasporites and Enzonalosporites, known to have low latitudinal preferences. In the Late Triassic Pangean tropics, this likely voltzialian conifer group remained a major component of the palynoflora up to the ETE and the time of the earliest known CAMP lavas, whereas it is progressively rarer or absent in older, more northerly Late Triassic strata, and virtually absent in the paleoarctic. This trend is consistent with the northward drift of central Pangea, but the diachronous last appearances have resulted in some biostratigraphic mischief, if other markers are ignored. Also dramatic is the tropical expansion of the dipteridaceous fern Clathropteris meniscoides. This tough-leaved fern is abundant at mid- to high-latitudes in Late Triassic and Early Jurassic continental units of Pangea but absent from tropical Late Triassic-Early Jurassic assemblages except during the earliest to peak CAMP eruptive interval, where it becomes common or even dominant. In fact, its spores (Granulatisporites and Converrucosisporites) comprise the "fern spike" in the Newark Basin at the ETE (2, 3).Both of these floral phenomena are inconsistent with warming as an extinction driver during the CAMP episode and instead are consistent with CAMP-driven mega-volcanic winters. A similar pattern is seen among continental tetrapods, where insulated forms (e.g., pterosaurs, dinosaurs, mammals) preferentially survive while all large non-insulated pseudosuchians perish (4).Cheirolepidaceous conifer leaf and stomatal morphology from deposits show trends related to CAMP events (5). These include short, scale-like leaves with thickened cuticle and sunken stomata that are traditionally interpreted as adaptations to heat and evaporative stress, but are also seen in cold-adapted conifers, suggesting these traits are "poly-tolerance" (6) adaptations. In fact, tropical conifer assemblages directly associated with the ETE have the thickest and shortest leaves of all tropical forms, suggesting adaptations to freezing.Further, hydrological conditions based on hydrogen isotope data captured in n-alkanes suggest amplified precession and obliquity pacing (7). This observation is consistent with both amplification of the hydrological system during times of CAMP-driven high pCO2 seen in pedogenic carbonates, molecular proxies from chlorophyll degradation products, and volcanic winters reflected in the floral disruption patterns. From these collective observations, we suggest that "climatic whiplash" at seasonal- and Milankovitch-timescales was a critical driver of the continental ETE and associated floral responses, and that such processes may have panned out elsewhere in Earth history.References:1, Swain+ 2025 Nature Rev Earth Env 6:35-50. 2, Olsen+ 2002 Science 296:1305. 3, Fowell+ 1994 GSA Spec Pap 288:197. 4, Olsen+ 2022 Sci Adv 8:eabo6342. 5, Cornet 1977 PhD thesis, PA State. 6, McCulloh+ 2022Tree Phys 43:1-15. 7, Landwehrs+ 2022 PNAS 119:e2203818119.

Northeast China’s Early Cretaceous Yixian Formation preserves spectacular fossils that have proved extraordinarily important in testing evolutionary hypotheses involving the origin of birds and the distribution of feathers among nonavian dinosaurs. These fossils occur either flattened with soft tissue preservation (including feathers and color) in laminated lacustrine strata or as three-dimensional (3D) skeletons in “life-like” postures in more massive deposits. The relationships of these deposits to each other, their absolute ages, and the origin of the extraordinary fossil preservation have been vigorously debated for nearly a half century, with the prevailing view being that preservation was linked to violent volcanic eruptions or lahars, similar to processes that preserved human remains at Pompeii. We present high-precision zircon U-Pb geochronology from cores and outcrops, demonstrating that Yixian Formation accumulation rates are more than an order of magnitude higher than usually estimated. Additionally, we provide zircon provenance and sedimentological data from 3D dinosaur fossils, which imply that their death and burial occurred in collapsed burrows, rather than via a catastrophic volcanogenic mechanism. In the studied area, the three principal fossil-rich intervals of the Yixian occur as a cyclic sequence that correspond to periods of high precipitation. Using Bayesian–Markov Chain Monte Carlo approaches, we constrain the total duration of the sequence to less than ~93,000 y and suggest that climatic precession paced the expression of these cyclic sediments. Rather than representing multiple, Pompeii-like catastrophes, the Yixian Formation is instead a brief snapshot of normal life and death in an Early Cretaceous continental community.

The end-Triassic extinction (ETE) on land was synchronous with the initial lavas of the Central Atlantic Magmatic Province (CAMP) and occurred just after the brief 26 thousand year (kyr) reverse geomagnetic polarity Chron E23r that can be used for global correlation. Lava-by-lava paleomagnetic secular variation data, previously reported from Morocco and northeastern United States combined with our data for the North Mountain Basalt from the Fundy Basin of Canada show that the initial phase of CAMP volcanism occurred in only five directional groups or pulses each occupying less than a century. The first four directional groups occur during a ~40 kyr period based on available astrochronology and U-Pb geochronology. The coincidence of the initial major pulse of CAMP volcanism with the ETE points to short-lived volcanic winters albedo-induced by sulfate aerosols as a plausible key agent of the extinctions in the tropical continental realm, whereas looser correlations allow prolonged CO ₂ emissions to contribute to more long-ranging effects in the marine realm via ocean acidification and longer-term warming.