Imperial College London

ProfessorJoannaMorgan

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Geophysics
 
 
 
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Contact

 

+44 (0)20 7594 6423j.v.morgan

 
 
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Location

 

2.38BRoyal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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102 results found

Christeson GL, Morgan JV, Gulick SPS, 2021, Mapping the Chicxulub Impact Stratigraphy and Peak Ring Using Drilling and Seismic Data, Journal of Geophysical Research: Planets, ISSN: 2169-9097

Journal article

Heath BA, Hooft EEE, Toomey DR, Paulatto M, Papazachos CB, Nomikou P, Morgan JVet al., 2021, Relationship Between Active Faulting/Fracturing and Magmatism Around Santorini: Seismic Anisotropy From an Active Source Tomography Experiment, Journal of Geophysical Research: Solid Earth, Vol: 126, ISSN: 2169-9313

Journal article

Zhao J, Xiao L, Xiao Z, Morgan JV, Osinski GR, Neal CR, Gulick SPS, Riller U, Claeys P, Zhao S, Prieur NC, Nemchin A, Yu S, IODP 364 Science Partyet al., 2021, Shock-deformed zircon from the Chicxulub impact crater and implications for cratering process, Geology, Vol: 49, Pages: 755-760, ISSN: 0091-7613

Large impact structures with peak rings are common landforms across the solar system, and their formation has implications for both the interior structure and thermal evolution of planetary bodies. Numerical modeling and structural studies have been used to simulate and ground truth peak-ring formative mechanisms, but the shock metamorphic record of minerals within these structures remains to be ascertained. We investigated impact-related microstructures and high-pressure phases in zircon from melt-bearing breccias, impact melt rock, and granitoid basement from the Chicxulub peak ring (Yucatán Peninsula, Mexico), sampled by the International Ocean Discovery Program (IODP)/International Continental Drilling Project (IODP-ICDP) Expedition 364 Hole M0077A. Zircon grains exhibit shock features such as reidite, zircon twins, and granular zircon including “former reidite in granular neoblastic” (FRIGN) zircon. These features record an initial high-pressure shock wave (>30 GPa), subsequent relaxation during the passage of the rarefaction wave, and a final heating and annealing stage. Our observed grain-scale deformation history agrees well with the stress fields predicted by the dynamic collapse model, as the central uplift collapsed downward-then-outward to form the peak ring. The occurrence of reidite in a large impact basin on Earth represents the first such discovery, preserved due to its separation from impact melt and rapid cooling by the resurging ocean. The coexistence of reidite and FRIGN zircon within the impact melt–bearing breccias indicates that cooling by seawater was heterogeneous. Our results provide valuable information on when different shock microstructures form and how they are modified according to their position in the impact structure, and this study further improves on the use of shock barometry as a diagnostic tool in understanding the cratering process.

Journal article

Cockell CS, Schaefer B, Wuchter C, Coolen MJL, Grice K, Schnieders L, Morgan JV, Gulick SPS, Wittmann A, Lofi J, Christeson GL, Kring DA, Whalen MT, Bralower TJ, Osinski GR, Claeys P, Kaskes P, de Graaff SJ, Déhais T, Goderis S, Hernandez Becerra N, Nixon Set al., 2021, Shaping of the present-day deep biosphere at chicxulub by the impact catastrophe that ended the cretaceous, Frontiers in Microbiology, Vol: 12, Pages: 1-16, ISSN: 1664-302X

We report on the effect of the end-Cretaceous impact event on the present-day deep microbial biosphere at the impact site. IODP-ICDP Expedition 364 drilled into the peak ring of the Chicxulub crater, México, allowing us to investigate the microbial communities within this structure. Increased cell biomass was found in the impact suevite, which was deposited within the first few hours of the Cenozoic, demonstrating that the impact produced a new lithological horizon that caused a long-term improvement in deep subsurface colonization potential. In the biologically impoverished granitic rocks, we observed increased cell abundances at impact-induced geological interfaces, that can be attributed to the nutritionally diverse substrates and/or elevated fluid flow. 16S rRNA gene amplicon sequencing revealed taxonomically distinct microbial communities in each crater lithology. These observations show that the impact caused geological deformation that continues to shape the deep subsurface biosphere at Chicxulub in the present day.

Journal article

Boddupalli B, Minshull TA, Morgan J, Bayrakci G, Klaeschen Det al., 2021, Comparison of 2-D and 3-D full waveform inversion imaging using wide-angle seismic data from the Deep Galicia Margin, Geophysical Journal International, Vol: 227, Pages: 228-256, ISSN: 0956-540X

<jats:title>SUMMARY</jats:title> <jats:p>Full waveform inversion (FWI) is a data-fitting technique capable of generating high-resolution velocity models with a resolution down to half the seismic wavelength. FWI is applied typically to densely sampled seismic data. In this study, we applied FWI to 3-D wide-angle seismic data acquired using sparsely spaced ocean bottom seismometers (OBSs) from the Deep Galicia Margin west of Iberia. Our data set samples the S-reflector, a low-angle detachment present in this area. Here we highlight differences between 2-D, 2.5-D and 3-D-FWI performances using a real sparsely spaced data set. We performed 3-D FWI in the time domain and compared the results with 2-D and 2.5-D FWI results from a profile through the 3-D model. When overlaid on multichannel seismic images, the 3-D FWI results constrain better the complex faulting within the pre- and syn-rift sediments and crystalline crust compared to the 2-D result. Furthermore, we estimate variable serpentinization of the upper mantle below the S-reflector along the profile using 3-D FWI, reaching a maximum of 45 per cent. Differences in the data residuals of the 2-D, 2.5-D and 3-D inversions suggest that 2-D inversion can be prone to overfitting when using a sparse data set. To validate our results, we performed tests to recover the anomalies introduced by the inversions in the final models using synthetic data sets. Based on our comparison of the velocity models, we conclude that the use of 3-D data can partially mitigate the problem of receiver sparsity in FWI.</jats:p>

Journal article

Ormö J, Gulick SPS, Whalen MT, King DT, Sturkell E, Morgan Jet al., 2021, Assessing event magnitude and target water depth for marine-target impacts: Ocean resurge deposits in the Chicxulub M0077A drill core compared, Earth and Planetary Science Letters, Vol: 564, Pages: 1-14, ISSN: 0012-821X

The rim wall of water formed from even a modestly-sized marine impact may be kilometers in height.Although modeling has shown that this wave swiftly breaks and relatively rapidly loses energy duringoutwards travel from the impact site, the portion of the rim wall that collapses inwards may generatea resurge flow with tremendous transport energy. Here we compare the deposits generated by thisocean resurge inside one of the largest marine-target craters on Earth, the 200-km wide Chicxulubcrater, Yucatán Peninsula, México, with resurge deposits (breccias) in eight drill cores from five othermarine-target craters in Sweden and the United States. Examination of the wide range of cored locationswithin the craters, and target water depths (H) relative to modeled projectile diameters (d) reveal a highcorrelation between location, average clast frequency (N ), and d/H from which any of the four variablescan be obtained. The relationship shown here may provide an important tool for diagnosing marineimpact cratering processes where there is limited understanding of crater size and/or paleobathymetry

Journal article

Schulte FM, Wittmann A, Jung S, Morgan JV, Gulick SPS, Kring DA, Grieve RAF, Osinski GR, Riller Uet al., 2021, Ocean resurge-induced impact melt dynamics on the peak-ring of the Chicxulub impact structure, Mexico, International Journal of Earth Sciences, ISSN: 1437-3254

Core from Hole M0077 from IODP/ICDP Expedition 364 provides unprecedented evidence for the physical processes in effect during the interaction of impact melt with rock-debris-laden seawater, following a large meteorite impact into waters of the Yucatán shelf. Evidence for this interaction is based on petrographic, microstructural and chemical examination of the 46.37-m-thick impact melt rock sequence, which overlies shocked granitoid target rock of the peak ring of the Chicxulub impact structure. The melt rock sequence consists of two visually distinct phases, one is black and the other is green in colour. The black phase is aphanitic and trachyandesitic in composition and similar to melt rock from other sites within the impact structure. The green phase consists chiefly of clay minerals and sparitic calcite, which likely formed from a solidified water–rock debris mixture under hydrothermal conditions. We suggest that the layering and internal structure of the melt rock sequence resulted from a single process, i.e., violent contact of initially superheated silicate impact melt with the ocean resurge-induced water–rock mixture overriding the impact melt. Differences in density, temperature, viscosity, and velocity of this mixture and impact melt triggered Kelvin–Helmholtz and Rayleigh–Taylor instabilities at their phase boundary. As a consequence, shearing at the boundary perturbed and, thus, mingled both immiscible phases, and was accompanied by phreatomagmatic processes. These processes led to the brecciation at the top of the impact melt rock sequence. Quenching of this breccia by the seawater prevented reworking of the solidified breccia layers upon subsequent deposition of suevite. Solid-state deformation, notably in the uppermost brecciated impact melt rock layers, attests to long-term gravitational settling of the peak ring.

Journal article

Goderis S, Sato H, Ferrière L, Schmitz B, Burney D, Kaskes P, Vellekoop J, Wittmann A, Schulz T, Chernonozhkin SM, Claeys P, de Graaff SJ, Déhais T, de Winter NJ, Elfman M, Feignon J-G, Ishikawa A, Koeberl C, Kristiansson P, Neal CR, Owens JD, Schmieder M, Sinnesael M, Vanhaecke F, Van Malderen SJM, Bralower TJ, Gulick SPS, Kring DA, Lowery CM, Morgan JV, Smit J, Whalen MT, IODP-ICDP Expedition 364 Scientistset al., 2021, Globally distributed iridium layer preserved within the Chicxulub impact structure., Science Advances, Vol: 7, Pages: 1-14, ISSN: 2375-2548

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.

Journal article

Bralower TJ, Cosmidis J, Fantle MS, Lowery CM, Passey BH, Gulick SPS, Morgan JV, Vajda V, Whalen MT, Wittmann A, Artemieva N, Farley K, Goderis S, Hajek E, Heaney PJ, Kring DA, Lyons SL, Rasmussen C, Sibert E, Rodríguez Tovar FJ, TurnerWalker G, Zachos JC, Carte J, Chen SA, Cockell C, Coolen M, Freeman KH, Garber J, Gonzalez M, Gray JL, Grice K, Jones HL, Schaefer B, Smit J, Tikoo SMet al., 2020, The habitat of the nascent chicxulub crater, AGU Advances, Vol: 1, Pages: 1-27, ISSN: 2576-604X

An expanded sedimentary section provides an opportunity to elucidate conditions in the nascent Chicxulub crater during the hours to millennia after the Cretaceous‐Paleogene (K‐Pg) boundary impact. The sediments were deposited by tsunami followed by seiche waves as energy in the crater declined, culminating in a thin hemipelagic marlstone unit that contains atmospheric fallout. Seiche deposits are predominantly composed of calcite formed by decarbonation of the target limestone during impact followed by carbonation in the water column. Temperatures recorded by clumped isotopes of these carbonates are in excess of 70°C, with heat likely derived from the central impact melt pool. Yet, despite the turbidity and heat, waters within the nascent crater basin soon became a viable habitat for a remarkably diverse cross section of the food chain. The earliest seiche layers deposited with days or weeks of the impact contain earliest Danian nannoplankton and dinocyst survivors. The hemipelagic marlstone representing the subsequent years to a few millennia contains a nearly monogeneric calcareous dinoflagellate resting cyst assemblage suggesting deteriorating environmental conditions, with one interpretation involving low light levels in the impact aftermath. At the same horizon, microbial fossils indicate a thriving bacterial community and unique phosphatic fossils including appendages of pelagic crustaceans, coprolites and bacteria‐tunneled fish bone, suggesting that this rapid recovery of the base of the food chain may have supported the survival of larger, higher trophic‐level organisms. The extraordinarily diverse fossil assemblage indicates that the crater was a unique habitat in the immediate impact aftermath, possibly as a result of heat and nutrients supplied by hydrothermal activity.

Journal article

Whalen MT, Gulick SPS, Lowery CM, Bralower TJ, Morgan JV, Grice K, Schaefer B, Smit J, Ormö J, Wittmann A, Kring DA, Lyons S, Goderis Set al., 2020, Winding down the Chicxulub impact: The transition between impact and normal marine sedimentation near ground zero, Marine Geology, Vol: 430, Pages: 1-18, ISSN: 0025-3227

The Chicxulub impact led to the formation of a ~ 200-km wide by ~1-km deep crater on México's Yucatán Peninsula. Over a period of hours after the impact the ocean re-entered and covered the impact basin beneath several hundred meters of water. A suite of impactites were deposited across the crater during crater formation, and by the resurge, tsunami and seiche events that followed. International Ocean Discovery Program/International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub crater, and recovered ~130 m of impact deposits and a 75-cm thick, fine-grained, carbonate-rich “Transitional Unit”, above which normal marine sedimentation resumed. Here, we describe the results of analyses of the uppermost impact breccia (suevite) and the Transitional Unit, which suggests a gradual waning of energy recorded by this local K-Pg boundary sequence.The dominant depositional motif in the upper suevite and the Transitional Unit is of rapid sedimentation characterized by graded bedding, local cross bedding, and evidence of oscillatory currents. The lower Transitional Unit records the change from deposition of dominantly sand-sized to mainly silt to clay sized material with impact debris that decreases in both grain size and abundance upward. The middle part of the Transitional Unit is interrupted by a 20 cm thick soft sediment slump overlain by graded and oscillatory current cross-laminated beds. The uppermost Transitional Unit is also soft sediment deformed, contains trace fossils, and an increasing abundance of planktic foraminifer and calcareous nannoplankton survivors. The Transitional Unit, as with similar deposits in other marine target impact craters, records the final phases of impact-related sedimentation prior to resumption of normal marine conditions. Petrographic and stable isotopic analyses of carbon from organic matter provide insight into post-impact processes. δ13Corg values are bet

Journal article

Smith V, Warny S, Grice K, Schaefer B, Whalen MT, Vellekoop J, Chenot E, Gulick SPS, Arenillas I, Arz JA, Bauersachs T, Bralower T, Demory F, Gattacceca J, Jones H, Lofi J, Lowery CM, Morgan J, Nuñez Otaño NB, O'Keefe JMK, O'Malley K, Rodríguez-Tovar FJ, Schwark Let al., 2020, Life and death in the Chicxulub impact crater: a record of the Paleocene–Eocene Thermal Maximum, Climate of the Past, Vol: 16, Pages: 1889-1899, ISSN: 1814-9324

latitudes, with sea surface temperatures at some localities exceeding the 35 ∘C at which marine organisms experience heat stress. Relatively few equivalent terrestrial sections have been identified, and the response of land plants to this extreme heat is still poorly understood. Here, we present a new record of the PETM from the peak ring of the Chicxulub impact crater that has been identified based on nannofossil biostratigraphy, an acme of the dinoflagellate genus Apectodinium, and a negative carbon isotope excursion. Geochemical and microfossil proxies show that the PETM is marked by elevated TEXH86-based sea surface temperatures (SSTs) averaging ∼37.8 ∘C, an increase in terrestrial input and surface productivity, salinity stratification, and bottom water anoxia, with biomarkers for green and purple sulfur bacteria indicative of photic zone euxinia in the early part of the event. Pollen and plants spores in this core provide the first PETM floral assemblage described from Mexico, Central America, and the northern Caribbean. The source area was a diverse coastal shrubby tropical forest with a remarkably high abundance of fungal spores, indicating humid conditions. Thus, while seafloor anoxia devastated the benthic marine biota and dinoflagellate assemblages were heat-stressed, the terrestrial plant ecosystem thrived.

Journal article

Bralower TJ, Cosmidis J, Heaney PJ, Kump LR, Morgan J, Harper DT, Lyons SL, Freeman KH, Grice K, Wendler JE, Zachos JC, Artemieva N, Chen SA, Gulick SPS, House CH, Jones HL, Lowery CM, Nims C, Schaefer B, Thomas E, Vajda Vet al., 2020, Origin of a global carbonate layer deposited in the aftermath of the Cretaceous-Paleogene boundary impact, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 548, ISSN: 0012-821X

Journal article

Lyons SL, Karp AT, Bralower TJ, Grice K, Schaefer B, Gulick SPS, Morgan JV, Freeman KHet al., 2020, Organic matter from the Chicxulub crater exacerbated the K-Pg impact winter., Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 25327-25334, ISSN: 0027-8424

An asteroid impact in the Yucatán Peninsula set off a sequence of events that led to the Cretaceous-Paleogene (K-Pg) mass extinction of 76% species, including the nonavian dinosaurs. The impact hit a carbonate platform and released sulfate aerosols and dust into Earth's upper atmosphere, which cooled and darkened the planet-a scenario known as an impact winter. Organic burn markers are observed in K-Pg boundary records globally, but their source is debated. If some were derived from sedimentary carbon, and not solely wildfires, it implies soot from the target rock also contributed to the impact winter. Characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Chicxulub crater sediments and at two deep ocean sites indicate a fossil carbon source that experienced rapid heating, consistent with organic matter ejected during the formation of the crater. Furthermore, PAH size distributions proximal and distal to the crater indicate the ejected carbon was dispersed globally by atmospheric processes. Molecular and charcoal evidence indicates wildfires were also present but more delayed and protracted and likely played a less acute role in biotic extinctions than previously suggested. Based on stratigraphy near the crater, between 7.5 × 1014 and 2.5 × 1015 g of black carbon was released from the target and ejected into the atmosphere, where it circulated the globe within a few hours. This carbon, together with sulfate aerosols and dust, initiated an impact winter and global darkening that curtailed photosynthesis and is widely considered to have caused the K-Pg mass extinction.

Journal article

Chiarenza A, Farnsworth A, Mannion PD, Lunt DJ, Valdes P, Morgan JV, Allison PAet al., 2020, Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction, Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 17084-17093, ISSN: 0027-8424

The Cretaceous/Paleogene mass extinction, 66 Ma, included the demise of non-avian dinosaurs. Intense debate has focused on the relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms for this event. Here, we combine fossil-occurrence data with paleoclimate and habitat suitability models to evaluate dinosaur habitability in the wake of various asteroid impact and Deccan volcanism scenarios. Asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats. Conversely, long-term forcing from Deccan volcanism (carbon dioxide [CO2]-induced warming) leads to increased habitat suitability. Short-term (aerosol cooling) volcanism still allows equatorial habitability. These results support the asteroid impact as the main driver of the non-avian dinosaur extinction. By contrast, induced warming from volcanism mitigated the most extreme effects of asteroid impact, potentially reducing the extinction severity.

Journal article

Zhao J, Xiao L, Gulick SPS, Morgan JV, Kring D, Fucugauchi JU, Schmieder M, de Graaff SJ, Wittmann A, Ross CH, Claeys P, Pickersgill A, Kaskes P, Goderis S, Rasmussen C, Vajda V, Ferrière L, Feignon J, Chenot E, Perez-Cruz L, Sato H, Yamaguchi Ket al., 2020, Geochemistry, geochronology and petrogenesis of Maya Block granitoids and dykes from the Chicxulub Impact Crater, Gulf of México: Implications for the assembly of Pangea, Gondwana Research, Vol: 82, Pages: 128-150, ISSN: 1342-937X

The Late Paleozoic tectono–magmatic history and basement of the Maya block are poorly understood due to the lack of exposures of coeval magmatic rocks in the region. Recently, IODP–ICDP Expedition 364 recovered drill core samples at borehole M0077A from the peak ring of the Chicxulub impact crater, offshore of the Yucatán peninsula in the Gulf of México, have been studied comprehensively. In the lowermost ~600 m of the drill core, impact–deformed granitoids, and minor felsite and dolerite dykes are intercalated with impact melts and breccias. Zircon U-Pb dating of granitoids yielded ages of around 326 ± 5 Ma, representing the first recovery of Late Paleozoic magmatic rocks from the Maya block, which could be genetically related to the convergence of Laurentia and Gondwana. The granitoids show the features of high K2O/Na2O, LaN/YbN and Sr/Y ratios, but very low Yb and Y contents, indicating an adakitic affinity. They are also characterized by slightly positive ԑNd(326Ma) of 0.17–0.68, intermediate initial 87Sr/86Sr(326Ma) of 0.7036–0.7047 and two–stage Nd model age (TDM2) of 1027–1069 Ma, which may indicate a less evolved crustal source. Thus, the adakitic granitoids were probably generated by partial melting of thickened crust, with source components similar to Neoproterozoic metagabbro in the Carolina block (Pan–African Orogeny materials) along Peri–Gondwana. Felsite dykes are shoshonitic with typical continental arc features that are sourced from a metasomatic mantle wedge by slab–fluids. Dolerite dykes display OIB–type features such as positive Nb and Ta anomalies and low ThNpm/NbNpm. In our interpretation, the Chicxulub adakitic granitoids of this study are formed by crustal anatexis due to asthenospheric upwelling resulting from slab breakoff. Through comparing sources and processes of Late Paleozoic magmatism along the Peri–Gondwanan realm, a tearing slab breakoff mode

Journal article

Kring DA, Tikoo SM, Schmieder M, Riller U, Rebolledo-Vieyra M, Simpson SL, Osinski GR, Gattacceca J, Wittmann A, Verhagen CM, Cockell CS, Coolen MJL, Longstaffe FJ, Gulick SPS, Morgan J, Bralower TJ, Chenot E, Christeson GL, Claeys P, Ferriere L, Gebhardt C, Goto K, Green SL, Jones H, Lofi J, Lowery CM, Ocampo-Torres R, Perez-Cruz L, Pickersgill AE, Poelchau MH, Rae ASP, Rasmussen C, Sato H, Smit J, Tomioka N, Urrutia-Fucugauchi J, Whalen MT, Xiao L, Yamaguchi KEet al., 2020, Probing the hydrothermal system of the Chicxulub impact crater, Science Advances, Vol: 6, ISSN: 2375-2548

The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.

Journal article

Collins G, Patel N, Davison T, Rae A, Morgan J, Gulick S, IODPICDP Expedition 364 & Third-Party Scientistset al., 2020, A steeply-inclined trajectory for the Chicxulub impact, Nature Communications, Vol: 11, Pages: 1-10, ISSN: 2041-1723

The environmental severity of large impacts on Earth is influenced by their impact trajectory. Impact direction and angle to the target plane affect the volume and depth of origin of vaporized target, as well as the trajectories of ejected material. The asteroid impact that formed the 66 Ma Chicxulub crater had a profound and catastrophic effect on Earth’s environment,but the impact trajectory is debated. Here we show that impact angle and direction can be diagnosed by asymmetries in the subsurface structure of the Chicxulub crater. Comparison of 3D numerical simulations of Chicxulub-scale impacts with geophysical observations suggests that the Chicxulub crater was formed by a steeply-inclined (45 -60° to horizontal) impact from the northeast; several lines of evidence rule out a low angle (< 30°) impact. Asteeply-inclined impact produces a nearly symmetric distribution of ejected rock and releases more climate-changing gases per impactor mass than either a very shallow or near-vertical impact.

Journal article

Artemieva N, Morgan J, 2020, Global K‐Pg layer deposited from a dust cloud, Geophysical Research Letters, Vol: 47, Pages: 1-8, ISSN: 0094-8276

Although it is widely agreed that the distal K‐Pg clay layer contains ejecta from the Chicxulub impact site, no current models can explain how these ejecta travel from the impact site around the globe. A widely accepted hypothesis is that impact spherules and shocked minerals in the layer were ejected from an expanding impact plume and traveled to their final destination on a ballistic path. Shocked minerals, however, are ejected at too low a velocity to reach distal sites, and plausible ballistic ejection models cannot explain the observed ejecta distribution. Using a suite of numerical simulations, we find that intense interactions between the ejecta curtain and atmosphere generate a fast‐moving dust cloud traveling at speeds of a few kilometers per second, which carries a substantial fraction of ejecta, including shocked minerals, to distal sites. We conclude that ejecta curtain material must make a major contribution to the formation of the distal K‐Pg layer.

Journal article

McVey BG, Hooft EEE, Heath BA, Toomey DR, Paulatto M, Morgan J, Nomikou P, Papazachos CBet al., 2020, Magma accumulation beneath Santorini volcano, Greece, from P-wave tomography, GEOLOGY, Vol: 48, Pages: 231-235, ISSN: 0091-7613

Journal article

Schaefer B, Grice K, Coolen MJL, Summons RE, Cui X, Bauersachs T, Schwark L, Böttcher ME, Bralower TJ, Lyons SL, Freeman KH, Cockell CS, Gulick SPS, Morgan JV, Whalen MT, Lowery CM, Vajda Vet al., 2020, Microbial life in the nascent Chicxulub crater, Geology, Vol: 48, Pages: 328-332, ISSN: 0091-7613

The Chicxulub crater was formed by an asteroid impact at ca. 66 Ma. The impact is considered to have contributed to the end-Cretaceous mass extinction and reduced productivity in the world’s oceans due to a transient cessation of photosynthesis. Here, biomarker profiles extracted from crater core material reveal exceptional insights into the post-impact upheaval and rapid recovery of microbial life. In the immediate hours to days after the impact, ocean resurge flooded the crater and a subsequent tsunami delivered debris from the surrounding carbonate ramp. Deposited material, including biomarkers diagnostic for land plants, cyanobacteria, and photosynthetic sulfur bacteria, appears to have been mobilized by wave energy from coastal microbial mats. As that energy subsided, days to months later, blooms of unicellular cyanobacteria were fueled by terrigenous nutrients. Approximately 200 k.y. later, the nutrient supply waned and the basin returned to oligotrophic conditions, as evident from N2-fixing cyanobacteria biomarkers. At 1 m.y. after impact, the abundance of photosynthetic sulfur bacteria supported the development of water-column photic zone euxinia within the crater.

Journal article

Bell R, Gray M, Morgan J, Warner M, Fagereng A, McNeill L, Jacobs K, Henrys S, Fry B, Watkins S, Lacey H, Black J, Victoria L, Daly D, Lindsay D, Bangs N, Arai R, Kodaira S, and the NZ3D teamet al., 2019, New Zealand 3D full waveform inversion (NZ3D-FWI) 2017-2018 field acquisition report

Report

Paulatto M, Moorkamp M, Hautmann S, Hooft E, Morgan J, Sparks Set al., 2019, Vertically extensive magma reservoir revealed from joint inversion and quantitative interpretation of seismic and gravity data, Journal of Geophysical Research. Solid Earth, Vol: 124, Pages: 11170-11191, ISSN: 2169-9356

Recent advances in our understanding of arc magmatic systems indicate that melt is stored for long periods in low‐melt fraction crystal mushes and that eruptible magma reservoirs are short‐lived and are assembled rapidly by buoyancy‐induced instabilities and draining of the crystal mush. Many aspects of their architecture remain unclear, particularly in relation to their geometry and shallow melt distribution. We investigate the storage of melt below the active Soufrière Hills Volcano (SHV), Montserrat, using joint geophysical inversion combined with a quantitative interpretation approach based on rock physics. We jointly inverted active‐source P‐wave traveltimes and gravity anomalies to derive coincident 3‐D models of P‐wave velocity and density to a depth of 8 km. Comparative analysis of the active SHV and extinct Centre Hills volcano and effective elastic medium computations allow us to constrain temperature, melt fraction, and melt geometry. A continuous column of partial melt is inferred beneath SHV, at 4–8 km depth. Melt fraction is ~6% (ranging from 3 to 13% depending on melt geometry) and is maximum at 5–6 km depth. When under‐recovery of the low‐vP volume is taken into account, the melt fraction is revised to ~17% (ranging from 11 to 28%). Analysis of vP/density cross plots indicates that the melt distribution is best represented by low‐aspect ratio geometries. These likely span a multiscale spectrum ranging from grain‐scale inclusions and fractures to 100‐m‐scale dykes and sills. Our results confirm the concept of vertically extensive crystal mush including one or multiple more melt‐rich layers.

Journal article

Rasmussen C, Stockli DF, Ross CH, Pickersgill A, Gulick SP, Schmieder M, Christeson GL, Wittmann A, Kring DA, Morgan JVet al., 2019, U-Pb memory behavior in Chicxulub's peak ring - Applying U-Pb depth profiling to shocked zircon, Chemical Geology, Vol: 525, Pages: 356-367, ISSN: 0009-2541

The zircon U-Pb system is one of the most robust geochronometers, but during an impact event individual crystals can be affected differently by the passage of the shock wave and impact generated heat. Unraveling the potentially complex thermal history recorded by zircon crystals that experienced variable levels of shock and heating, as well as additioanl pre- and post-impact thermal events, has been difficult using classical geochronological methods. The existing high-precision 40Ar/39Ar age constraints for the K-Pg Chicxulub event, and the previous U-Pb dating of the basement rocks from the impact site, make Chicxulub an ideal location to study impact-induced effects on the zircon U-Pb systematics and to evaluate potential 'memory effects' of pre-impact U-Pb signatures preserved within those individual zircon crystals. Recent IODP-ICDP drilling of the Chicxulub impact structure recovered 580 m of uplifted shocked granitoid and 130 m of melt and suevite, providing an unprecedented opportunity to study zircon crystals subjected to a range of shock pressures, thermal, and deformational histories. Zircon morphologies were classified using scanning electron microscopy (SEM) imaging and then samples were depth profiled using laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) to document the range of preserved age domains from rim-to-center within individual crystals. The results show U-Pb ages range from 66 to 472 Ma, which are consistent with both inherited Carboniferous and Late Paleozoic basement ages as well as Pb loss ages in response to the K-Pg impact event. While the bulk of the zircon grains preserve Paleozoic ages, high U (metamict) zones within fractured zircon crystals exhibited an age within uncertainty (66 ± 6.2 Ma) of the impact age (66.038 ± 0.049 Ma), indicating that inherited intragrain U-Pb kinetics and/or hydrothermal fluid flow may have controlled age resetting those zircon crystals rather than impact-induced shock

Journal article

Heath BA, Hooft EEE, Toomey DR, Papazachos CB, Nomikou P, Paulatto M, Morgan V, Warner MRet al., 2019, Tectonism and Its Relation to Magmatism Around Santorini Volcano From Upper Crustal P Wave Velocity, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 124, Pages: 10610-10629, ISSN: 2169-9313

Journal article

Gulick SPS, Bralower T, Ormö J, Hall B, Grice K, Schaefer B, Lyons S, Freeman KH, Morgan J, Artemieva N, Kaskes P, de Graaff SJ, Whalen M, Collins G, Tikoo SM, Verhagen C, Christeson GL, Claeys P, Coolen M, Goderis S, Goto K, Grieve R, McCall N, Osinski G, Rae A, Riller U, Smit J, Vajda V, Wittmann A, and the Expedition 364 Scientistset al., 2019, The first day of the Cenozoic, Proceedings of the National Academy of Sciences of the United States of America, Vol: 116, Pages: 19342-19351, ISSN: 0027-8424

Highly expanded Cretaceous–Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP)–International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by <1 m of micrite-rich carbonate deposited over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to form a peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarse-grained suevite, including clasts possibly generated by melt–water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting. Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impact-induced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms.

Journal article

Gray M, Bell R, Morgan J, Henrys S, Barker D, IODP Expedition 372 scientists, IODP Expedition 375 scientistset al., 2019, Imaging the shallow subsurface structure of the North Hikurangi subduction zone, New Zealand, using 2-D full-waveform inversion, Journal of Geophysical Research. Solid Earth, Vol: 124, Pages: 9049-9074, ISSN: 2169-9356

The northern Hikurangi plate boundary fault hosts a range of seismic behaviors, of which the physical mechanisms controlling seismicity are poorly understood, but often related to high pore fluid pressures and conditionally stable frictional conditions. Using 2D marine seismic streamer data, we employ full-waveform inversion (FWI) to obtain a high-resolution 2D P-wave velocity model across the Hikurangi margin down to depths of ~2 km. The validity of the FWI velocity model is investigated through comparison with the pre-stack depth migrated seismic reflection image, sonic well data, and the match between observed and synthetic waveforms. Our model reveals the shallow structure of the overriding plate, including the fault plumbing system above the zone of SSEs to theoretical resolution of a half seismic wavelength. We find that the hanging walls of thrust faults often have substantially higher velocities than footwalls, consistent with higher compaction. In some cases, intra-wedge faults identified from reflection data are associated with low-velocity anomalies, which may suggest they are high-porosity zones acting as conduits for fluid flow. The continuity of velocity structure away from IODP drill site U1520 suggests that lithological variations in the incoming sedimentary stratigraphy observed at this site continue to the deformation front and are likely important in controlling seismic behavior. This investigation provides a high-resolution insight into the shallow parts of subduction zones, which shows promise for the extension of modeling to 3D using a recently-acquired, longer-offset, seismic dataset.

Journal article

Rae ASP, Collins G, Morgan J, Salge T, Christeson GL, Leung J, Lofi J, Gulick SPS, Poelchau M, Riller U, Gebhardt C, Grieve RA, Osinski GRet al., 2019, Impact-induced porosity and micro-fracturing at the Chicxulub impact structure, Journal of Geophysical Research: Planets, Vol: 124, Pages: 1960-1978, ISSN: 2169-9097

Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave-speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small scale petrographic and petrophysical measurements with larger scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock-induced micro-fracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak-ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak-ring formation, can accurately predict the distribution and orientation of impact-induced micro-fractures in large craters which plays an important role in the geophysical signature of impact structures.

Journal article

Hooft EEE, Heath BA, Toomey DR, Paulatto M, Papazachos CB, Nomikou P, Morgan JV, Warner MRet al., 2019, Seismic imaging of Santorini: subsurface constraints on caldera collapse and present-day magma recharge, Earth and Planetary Science Letters, Vol: 514, Pages: 48-61, ISSN: 0012-821X

Volcanic calderas are surface depressions formed by roof collapse following evacuation of magma from an underlying reservoir. The mechanisms of caldera formation are debated and predict differences in the evolution of the caldera floor and distinct styles of magma recharge. Here we use a dense, active source, seismic tomography study to reveal the sub-surface physical properties of the Santorini caldera in order to understand caldera formation. We find a ∼3-km-wide, cylindrical low-velocity anomaly in the upper 3 km beneath the north-central portion of the caldera, that lies directly above the pressure source of the 2011-2012 inflation. We interpret this anomaly as a low-density volume caused by excess porosities of between 4% and 28%, with pore spaces filled with hot seawater. Vents that were formed during the first three phases of the 3.6 ka Late Bronze Age (LBA) eruption are located close to the edge of the imaged structure. The correlation between older volcanic vents and the low-velocity anomaly suggests that this feature may be long-lived. We infer that collapse of a limited area of the caldera floor resulted in a high-porosity, low-density cylindrical volume, which formed by either chaotic collapse along reverse faults, wholesale subsidence and infilling with tuffs and ignimbrites, phreatomagmatic fracturing, or a combination of these processes. Phase 4 eruptive vents are located along the margins of the topographic caldera and the velocity structure indicates that coherent down-drop of the wider topographic caldera followed the more limited collapse in the northern caldera. This progressive collapse sequence is consistent with models for multi-stage formation of nested calderas along conjugate reverse and normal faults. The upper crustal density differences inferred from the seismic velocity model predict differences in subsurface gravitational loading that correlate with the location of 2011-2012 edifice inflation. This result supports the hypothesis th

Journal article

Timms NE, Pearce MA, Erickson TM, Cavosie AJ, Rae ASP, Wheeler J, Wittmann A, Ferriere L, Poelchau MH, Tomioka N, Collins GS, Gulick SPS, Rasmussen C, Morgan JV, Gulick SPS, Morgan JV, Chenot E, Christeson GL, Claeys P, Cockell CS, Coolen MJL, Ferriere L, Gebhardt C, Goto K, Green S, Jones H, Kring DA, Lofi J, Lowery CM, Ocampo-Torres R, Perez-Cruz L, Pickersgill AE, Poelchau MH, Rae ASP, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tikoo SM, Tomioka N, Urrutia-Fucugauchi J, Whalen MT, Wittmann A, Xiao L, Yamaguchi KEet al., 2019, New shock microstructures in titanite (CaTiSiO5) from the peak ring of the Chicxulub impact structure, Mexico, Contributions to Mineralogy and Petrology, Vol: 174, ISSN: 0010-7999

Accessory mineral geochronometers such as apatite, baddeleyite, monazite, xenotime and zircon are increasingly being recognized for their ability to preserve diagnostic microstructural evidence of hypervelocity-impact processes. To date, little is known about the response of titanite to shock metamorphism, even though it is a widespread accessory phase and a U–Pb geochronometer. Here we report two new mechanical twin modes in titanite within shocked granitoid from the Chicxulub impact structure, Mexico. Titanite grains in the newly acquired core from the International Ocean Discovery Program Hole M0077A preserve multiple sets of polysynthetic twins, most commonly with composition planes (K1) = ~  {1¯11} , and shear direction (η1) = < 110 > , and less commonly with the mode K1 = {130}, η1 = ~ <522 > . In some grains, {130} deformation bands have formed concurrently with the deformation twins, indicating dislocation slip with Burgers vector b = < 341 > can be active during impact metamorphism. Titanite twins in the modes described here have not been reported from endogenically deformed rocks; we, therefore, propose this newly identified twin form as a result of shock deformation. Formation conditions of the twins have not been experimentally calibrated, and are here empirically constrained by the presence of planar deformation features in quartz (12 ± 5 and ~ 17 ± 5 GPa) and the absence of shock twins in zircon (< 20 GPa). While the lower threshold of titanite twin formation remains poorly constrained, identification of these twins highlight the utility of titanite as a shock indicator over the pressure range between 12 and 17 GPa. Given the challenges to find diagnostic indicators of shock metamorphism to identify both ancient

Journal article

Urrutia-Fucugauchi J, Pérez-Cruz L, Morgan J, Gulick S, Wittmann A, Lofi J, Morgan JV, Gulick SPS, Chenot E, Christeson G, Claeys P, Cockell C, Coolen MJL, Ferrière L, Gebhardt C, Goto K, Jones H, Kring DA, Lofi J, Lowery C, Mellett C, Ocampo-Torres R, Perez-Cruz L, Pickersgill A, Poelchau M, Rae A, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tikoo-Schantz S, Tomioka N, Urrutia-Fucugauchi J, Whalen M, Wittmann A, Xiao L, Yamaguchi KE, Bralower T, Collins GSet al., 2019, Peering inside the peak ring of the Chicxulub Impact Crater—its nature and formation mechanism, Geology Today, Vol: 35, Pages: 68-72, ISSN: 0266-6979

© 2019 John Wiley & Sons Ltd, The Geologists' Association & The Geological Society of London The IODP-ICDP Expedition 364 drilled into the Chicxulub crater, peering inside its well-preserved peak ring. The borehole penetrated a sequence of post-impact carbonates and a unit of suevites and clast-poor impact melt rock at the top of the peak ring. Beneath this sequence, basement rocks cut by pre-impact and impact dykes, with breccias and melt, were encountered at shallow depths. The basement rocks are fractured, shocked and uplifted, consistent with dynamic collapse, uplift and long-distance transport of weakened material during collapse of the transient cavity and final crater formation.

Journal article

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