Large impact events excavate mid- to lower-crustal rocks, offering a unique perspective on the interior composition and tectonic history (if any) of planetary bodies. On the Yucatán Peninsula, Mexico, the surface geology mainly consists of sedimentary rocks, with a lack of exposure of crystalline basement in many areas. Consequently, current understanding of the Yucatán subsurface is largely based on impact ejecta and drill cores recovered from the ∼200-km-diameter Chicxulub impact structure. In this study, we present the first apatite and titanite U-Pb ages for pre-impact dacitic, doleritic, and felsitic magmatic dikes preserved in Chicxulub’s peak ring sampled during the 2016 IODP-ICDP Expedition 364. Dating yielded two age groups, with Carboniferous-aged dacites (326–317 Ma) and a felsite (342.5 ± 4.3 Ma) overlapping in age with most of the granitoid basement sampled in the Expedition 364 drill core, as well as Jurassic dolerites (168–158 Ma) and a felsite (152.2 ± 11.4 Ma) that represent the first in-situ sampling of Jurassic-aged magmatic intrusions for the Yucatán Peninsula. The Nd, Sr, and Hf isotopic compositions of the pre-impact lithologies and impact melt rocks suggest that dolerites generally contributed to up to ~10 vol% of the Chicxulub impact melt that locally can exceed 40 vol%. This percentage implies that the dolerites comprised a large part of the Yucatán subsurface by volume, representing a hitherto unsampled pervasive Jurassic magmatic phase. We interpret this magmatic phase to be related to the opening of the Gulf of Mexico, representing the first physical sampling of lithologies associated with the southern extension of the opening of the Gulf of Mexico and likely constraining its onset to the Late Middle Jurassic.
Abstract. Bivalves record seasonal environmental changes in their shells, making them excellent climate archives. However, not every bivalve can be used for this end. The shells have to grow fast enough so that micrometre- to millimetre-sampling can resolve sub-annual changes. Here, we investigate whether the bivalve Angulus benedeni benedeni is suitable as a climate archive. For this, we use ca. 3-million-year-old specimens from the Piacenzian collected from a temporary outcrop in the Port of Antwerp area (Belgium). The subspecies is common in Pliocene North Sea basin deposits, but its lineage dates back to the late Oligocene and has therefore great potential as a high-resolution archive. A detailed assessment of the preservation of the shell material by micro-X-ray fluorescence, X-ray diffraction, and electron backscatter diffraction reveals that it is pristine and not affected by diagenetic processes. Oxygen isotope analysis and microscopy indicate that the species had a longevity of up to a decade or more and, importantly, that it grew fast and large enough so that seasonally resolved records across multiple years were obtainable from it. Clumped isotope analysis revealed a mean annual temperature of 13.5 ± 3.8 ∘C. The subspecies likely experienced slower growth during winter and thus may not have recorded temperatures year-round. This reconstructed mean annual temperature is 3.5 ∘C warmer than the pre-industrial North Sea and in line with proxy and modelling data for this stratigraphic interval, further solidifying A. benedeni benedeni's use as a climate recorder. Our exploratory study thus reveals that Angulus benedeni benedeni fossils are indeed excellent climate archives, holding the potential to provide insight into the seasonality of several major climate events of the past ∼ 25 million years in northwestern Europe.
<p>The youngest time interval of the Cretaceous Period is known as the Maastrichtian, a reference to the marine strata exposed in the area surrounding the city of Maastricht, in the Netherlands-Belgium border region. The stratigraphic succession at the original type-locality of the Maastrichtian (ENCI quarry, NL) only covers the upper part of the Maastrichtian Stage as it is nowadays defined. However, in combination with similar rock sequences in several other quarries (e.g. Hallembaye, Curfs) in the region, a substantial part of the Maastrichtian Stage is represented.</p><p>While the type-Maastrichtian strata have provided a wealth of paleontological data, comparatively little geochemical work has been carried out on this succession. So far, the age assessment of, and stratigraphic correlation with, the type-Maastrichtian has been largely based on biostratigraphy and preliminary attempts at cyclostratigraphy, techniques that are hampered by bioprovincialism and the presence of stratigraphic gaps in the succession. In recent years, stable carbon isotope stratigraphy has been proven to be a powerful tool for correlating Upper Cretaceous strata on a global scale. When calibrated with biostratigraphic events, carbon isotope stratigraphy can be used to test the synchroneity of bio-events and reconcile inter-regional biostratigraphic schemes. Therefore, we have generated the first high-resolution stable carbon isotope stratigraphy for the type-Maastrichtian, using the extensive sample set acquired in the context of the Maastrichtian Geoheritage Project. In combination with elemental data generated using &#181;XRF (e.g. Ca, Si, Al, Ti, Fe wt%), our record presents the first high-resolution chemostratigraphy for the type-Maastrichtian. This new chemostratigraphic framework enables us to refine the age-model for studied strata, and allows a better regional and global correlation with the type-Maastrichtian successions, placing the paleontological records from the type-Maastrichtian in a global context. &#160;</p>
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.
To fully assess the resilience and recovery of life in response to the Cretaceous-Paleogene (K-Pg) boundary mass extinction ~ 66 million years ago, it is paramount to understand biodiversity prior to the Chicxulub impact event. The peak ring of the Chicxulub impact structure offshore the Yucatán Peninsula (México) was recently drilled and extracted a ~ 100 m thick impact-generated, melt-bearing, polymict breccia (crater suevite), which preserved carbonate clasts with common biogenic structures. We pieced this information to reproduce for the first time the macrobenthic tracemaker community and marine paleoenvironment prior to a large impact event at the crater area by combining paleoichnology with micropaleontology. A variable macrobenthic tracemaker community was present prior to the impact (Cenomanian-Maastrichtian), which included soft bodied organisms such as annelids, crustaceans and bivalves, mainly colonizing softgrounds in marine oxygenated, nutrient rich, conditions. Trace fossil assemblage from these upper Cretaceous core lithologies, with dominant Planolites and frequent Chondrites, corresponds well with that in the overlying post-impact Paleogene sediments. This reveals that the K-Pg impact event had no significant effects (i.e., extinction) on the composition of the macroinvertebrate tracemaker community in the Chicxulub region.
Abstract. Repeated carbon isotope excursions and widespread organic-rich shale deposition mark the Middle and Late Devonian series. Various explanations such as extensive volcanism and land plant evolution have been given for these perturbations and the general sensitivity of the Devonian to oceanic anoxia, but their repeated nature suggests that astronomical forcing may have controlled their timing. Here, a cyclostratigraphic study of the Kellwasser Crisis at the Frasnian-Famennian stage boundary (ca. 372 Ma) is carried out. The Kellwasser Crisis was one of the most ecologically impactful of the Devonian perturbations and is ranked among the ‘Big Five’ Phanerozoic mass extinctions. The studied site is the Winsenberg Road Cut section in the Rhenish Massif, Germany, which represents a quiet tropical shelf basin setting. Centimetre-scale elemental records, generated by portable X-Ray scanning, allow for testing of the hypothesis that a 2.4 Myr eccentricity node preceded the Upper Kellwasser event. The study’s results are supportive of this hypothesis. We find enhanced chemical weathering (K2O/Al2O3) during the period leading up to the Upper Kellwasser, and a peak in distal detrital input (SiO2/CaO) and riverine runoff (TiO2/Al2O3) just prior to the start of the Upper Kellwasser. We interpret this pattern as the long-term eccentricity minimum facilitating excessive regolith build-up in the absence of strong seasonal contrasts. The Earth’s system coming out of this node would have rapidly intensified the hydrological cycle, causing these nutrient-rich regoliths to be eroded and washed away to the oceans where they resulted in eutrophication and anoxia. An astronomical control on regional climate is observed beyond this single crisis. Wet-dry cycles were paced by 405-kyr eccentricity, with both the Lower and Upper Kellwasser events taking place during comparatively drier times. A precessional-forced monsoonal climate system prevailed on shorter timescales. Intensification of this monsoonal system following the node may have caused the widespread regolith erosion. We estimate the total duration of the Kellwasser Crisis at ca. 900 kyr, with the individual events lasting for ca. 250 and 100 kyr, respectively. If astronomical control indeed operated via regolith build up in monsoonal climates, land plants may have played an important role. Not by certain evolutionary steps triggering specific perturbations, but by permanently strengthening the climatic response to orbital forcing via soil development – creating soils thick enough to meaningfully respond to orbital forcing – and intensifying the hydrological cycle.
Abstract The IODP‐ICDP Expedition 364 drilling recovered a 829 m core from Hole M0077A, sampling ˜600 m of near continuous crystalline basement within the peak ring of the Chicxulub impact structure. The bulk of the basement consists of pervasively deformed, fractured, and shocked granite. Detailed geochemical investigations of 41 granitoid samples, that is, major and trace element contents, and Sr–Nd isotopic ratios are presented here, providing a broad overview of the composition of the granitic crystalline basement. Mainly granite but also granite clasts (in impact melt rock), granite breccias, and aplite were analyzed, yielding relatively homogeneous compositions between all samples. The granite is part of the high‐K, calc‐alkaline metaluminous series. Additionally, they are characterized by high Sr/Y and (La/Yb) N ratios, and low Y and Yb contents, which are typical for adakitic rocks. However, other criteria (such as Al 2 O 3 and MgO contents, Mg#, K 2 O/Na 2 O ratio, Ni concentrations, etc.) do not match the adakite definition. Rubidium–Sr errorchron and initial 87 Sr/ 86 Sr t =326Ma suggest that a hydrothermal fluid metasomatic event occurred shortly after the granite formation, in addition to the postimpact alteration, which mainly affected samples crosscut by shear fractures or in contact with aplite, where the fluid circulation was enhanced, and would have preferentially affected fluid‐mobile element concentrations. The initial (ɛ Nd ) t =326Ma values range from −4.0 to 3.2 and indicate that a minor Grenville basement component may have been involved in the granite genesis. Our results are consistent with previous studies, further supporting that the cored granite unit intruded the Maya block during the Carboniferous, in an arc setting with crustal melting related to the closure of the Rheic Ocean associated with the assembly of Pangea. The granite was likely affected by two distinct hydrothermal alteration events, both influencing the granite chemistry: (1) a hydrothermal metasomatic event, possibly related to the first stages of Pangea breakup, which occurred approximately 50 Myr after the granite crystallization, and (2) the postimpact hydrothermal alteration linked to a long‐lived hydrothermal system within the Chicxulub structure. Importantly, the granites sampled in Hole M0077A are unique in composition when compared to granite or gneiss clasts from other drill cores recovered from the Chicxulub impact structure. This marks them as valuable lithologies that provide new insights into the Yucatán basement.
The Late Devonian oceans were susceptible to the development of anoxic conditions, as evidenced by repeated widespread organic-rich shale deposition. Understanding how these anoxic facies were deposited will provide insight into Devonian climatic modes. To this end, we constructed a high-resolution cyclostratigraphic model based on portable XRF-generated elemental ratio records from a Frasnian-Famennian (~372 Ma) black shale section. These black shales are associated with the Kellwasser Crisis, one of the largest mass extinctions of the Phanerozoic, which is not fully understood to this day. The studied section at Winsenberg is located in the Rhenish Massif in Germany and represents a basinal setting at southern low paleolatitudes. Spectral analysis was carried out on the Si/Ca ratios generated by XRF, which is interpreted as the detrital (distal) vs carbonaceous (local) input. The resulting astrochronology suggests a duration of ca. 1 Myr from the base of the Lower Kellwasser to the F-F boundary at the top of the Upper Kellwasser level. This corresponds to an average sedimentation rate of 0.9 cm/kyr. Both the Lower and Upper Kellwasser shales occur at the onset of a 405 kyr eccentricity cycle. We further interpret the Ti/Al record as a riverine runoff signal, as Ti is associated with the coarse-grained fraction, and K/Al as a chemical weathering signal, as K is leached easier than Al. Both tuned records exhibit eccentricity-modulated precession cycles. On precession and short eccentricity timescales, Ti/Al and K/Al are positively correlated, suggesting an orbitally forced wet/dry monsoonal climate in the region where the section was deposited. On longer timescales, the weathering signal becomes decoupled from the riverine runoff signal, highlighting that K/Al (chemical weathering) decreased even during wetter periods. This decoupling is linked to soil maturation in the hinterland, as potassium leaching from mature soils became increasingly limited. Soil build-up and maturation forms a potential mechanism for nutrient storage and subsequent release into the ocean, potentially triggering eutrophication and anoxia.
Abstract The mid-Maastrichtian carbon isotope event (MME), dated at ∼69 Ma, reflects a perturbation of the global carbon cycle that, in part, correlates with the enigmatic global extinction of ‘true’ (i.e., non-tegulated) inoceramid bivalves. The mechanisms of this extinction event are still debated. While both the inoceramid extirpation and MME have been recorded in a variety of deep-sea sites, little is known about their expression in epicontinental chalk seas. In order to study the shallow-marine signature of the MME in this epicontinental shelf sea, we have generated quantitative foraminiferal assemblage data for two quarries (Hallembaye, NE Belgium; ENCI, SE Netherlands) in the Maastrichtian type area, complemented by a species-specific benthic δ 13 C record. In contrast to deep-sea records, no significant changes in benthic foraminiferal assemblages and benthic foraminiferal accumulation rates are observed across the MME in the type-Maastrichtian area. At the Hallembaye quarry, the otherwise rare endobenthic species Cuneus trigona reaches a transient peak abundance of 33.3% at the onset of the MME, likely caused by a local transient change in organic matter flux to the seafloor. Nevertheless, high and near-constant species evenness shows that neither oxygen nor organic matter flux was limited across the extinction level or during the MME. Benthic foraminiferal data from the uppermost part of the studied section, above the MME, indicate a significant increase in food supply to the seafloor. Decreased amounts of terrigenous elements across this interval document a lesser riverine or aeolian influx, which means that the increased benthic productivity is linked to a different origin. Potentially, the continuous precipitation of chalk under nutrient-poor conditions in the Late Cretaceous chalk sea was enabled by efficient nutrient recycling in the water column. In shallower depositional settings, nutrient recycling took place closer to the seafloor, which allowed more organic matter to reach the bottom. These results provide insights in the importance of nutrient cycling for biological productivity in the NW-European chalk sea.
