ABSTRACT Recently, a set of mercury (Hg) anomalies in Valanginian sediments recovered from European sections demonstrated that an important magmatic pulse occurred at the onset of the Weissert episode. In this study, we report the distribution of Hg contents near the onset of the Weissert episode from localities outside of Europe, in the proto–Atlantic Ocean (Blake Bahama and Cap Hatteras Basins, Deep Sea Drilling Project [DSDP] Holes 534A and 603B) and southern Tethys Ocean (Argo Abyssal Plain, Ocean Drilling Program [ODP] Hole 765C), in order to evaluate the global impact of volcanism during the Valanginian. In addition, we also reinvestigated the Orpierre and Angles sections of the Vocontian Basin at a very high time resolution, to examine the potential impact of regional volcanic activity during that time interval. The onset of the Weissert episode in the proto-Atlantic and in the southern Tethyan cores is marked by significant increases in Hg contents. The persistence of the Hg anomaly in Hg/total organic carbon and Hg/Al ratios suggests that Hg enrichments were not primarily controlled by runoff processes and/or redox conditions, but instead indicate an increase in volcanic activity. The Hg enrichments recorded from localities outside of Europe at different latitudes were correlated to those previously observed in European sections, thereby confirming the presence of a global Hg peak at the onset of the Weissert episode. This peak was probably related to the emplacement of the Paraná-Etendeka large igneous province, suggesting a key role for volcanic activity during the Valanginian global environmental perturbations. In coeval intervals in the Vocontian Basin, Hg records show abrupt and short-lived enrichments, which correspond in the sedimentary successions to a goethite-rich ocher-colored layer. Two regional processes could explain Hg deposition and sequestration in this region: increased Hg sequestration by organic matter production in an oxygen-depleted environment, and/or the presence of regional volcanic activity, which is also indicated by the occurrence of a distal volcanic ash layer.

ABSTRACT The Guerrero-Morelos carbonate platform (southwestern Mexico) is one of the rare platforms that persisted throughout the Cenomanian–Turonian oceanic anoxic event 2 (OAE 2). Two sections from this carbonate platform exhibit the typical δ 13 C positive excursion characterizing the OAE 2. This enables the precise distribution of larger benthic foraminifers and their biotic response to paleoenvironmental changes to be characterized during this event. At Axaxacualco, oligotrophic conditions prevailed during the δ 13 C positive excursion in the distal part of the carbonate platform. In the more proximal part, at Barranca del Cañon, OAE 2 impact was more significant and is marked by thick laminated microbialite deposition, indicating mesotrophic conditions. Low phosphorus and trace-element contents confirm the persistence of oligotrophic to mesotrophic conditions throughout OAE 2 in the Central Mexico carbonate platform despite the proximity of the Caribbean-Colombian oceanic plateau. Before the δ 13 C positive excursion, which characterizes the OAE 2, the microfauna assemblage was well diversified, including corals, rudists, and large benthic foraminifera ( Pseudorhapydionina chiapanensis , Pseudorhapydionina dubia , Cuneolina parva , Dicyclina sp., Chrysalidina gradata , and large miliolids). During the δ 13 C positive excursion, significant biotic changes occurred, with increasing dominance of organisms adapted to high-stress conditions. Endobenthic assemblages such as Nezzazatinella sp. and Nezzazata sp. were still present. The green symbiotic benthic foraminifera nearly disappeared, except C. parva and Dicyclina sp. During the basal Turonian, the carbonate platform returned to a more open and oxygenated environment, with the reappearance of pre-OAE microfauna, but without the large benthic foraminifera, which did not survive. The definitive drowning of the Guerrero-Morelos carbonate platform took place after the early Turonian, well above the end of the δ 13 C shift. The deposition of black shale and turbidites, which indicate deeper, anoxic environments, precluded large benthic foraminifera reestablishment. Correlation with the pelagic environments of the Eastbourne section (UK) reveals a synchronicity of biotic responses between basin and platform environments. Low-oxygen conditions are marked by multiple blooms of Heterohelix species in the basin, corresponding to an assemblage dominated by ? Decastronema , Thaumatoporella , and Istriloculina on the carbonate platforms.

ABSTRACT We conducted a detailed rock magnetic and mineralogical study of bole beds from the Deccan magmatic province, India. Magnetic susceptibility of 15 bole beds showed two contrasting patterns, with susceptibility values either increasing or decreasing up the profile. We then focused on two representatives red boles located in the Western Ghats, the RBB and RBAN profiles, to unravel the nature and origin of these contrasting magnetic susceptibility patterns. The presence of smectite argues against significant secondary thermal alterations. Major-elemental compositions obtained by X-ray fluorescence spectrometry of RBB and RBAN red boles are comparable to the parent basalt and show significant and typical depletion of mobile elements such as sodium and calcium compared to the parent basalt. The Ti/Al ratio of both the red boles and their overlying clay layers is close to the typical value of Deccan basalt (0.2), suggesting that the material of the red boles has been derived from weathering of the parent basalt. The chemical index of alteration varies from 40–50 in the parent basalt to 80–90 at the top of the bole beds, consistent with moderate to intense weathering of the bole beds. However, similar to other Deccan bole beds, indices of lateritization below 50 suggest that the state of lateritization has not been reached. Although the RBB and RBAN profiles share similar mineralogical signatures, their magnetic mineral assemblages are distinctly different. In the RBB profile, magnetic susceptibility decreases up-profile as a result of oxidation/dissolution of primary titanomagnetite inherited from the parent basalt, with subsequent formation of pedogenic hematite and superparamagnetic particles. In contrast, magnetic susceptibility in the RBAN profile, which contains magnetite, some hematite, and goethite, increases up-profile. The increase in the magnetic signal is mainly due to the increasing amounts of phyllosilicate and goethite, while the content of magnetite and hematite remains constant along the profile. We attribute the variation in the magnetic mineral assemblage to contrasting humid and dry environments during weathering, leading to the preferential formation of goethite or hematite, respectively. The combined mineralogical and rock magnetic data suggest the existence of a single weathering profile involving soil formation in the two studied red boles, with few or no contributions from an external source.

ABSTRACT The Cretaceous-Paleocene (K/P) boundary intervals are rarely preserved in successions of shallow-water limestones. Here, we describe a shallow rocky shore on the active orogenic wedge of the eastern Alps (Austria) fringed by a carbonate platform that was largely cannibalized by erosion. We compared this succession with similar nearshore environments globally, as well as the deep sea, to gain a better understanding of the environmental response to the K/P boundary transition. In the eastern Alps, Cretaceous and Paleocene lithofacies across the K/P boundary transition are separated by a hardground that formed during subaerial exposure and that terminates Upper Maastrichtian limestone with planktic foraminiferal assemblages deposited at neritic depth during zone CF3 (ca. 66.500 Ma). Above the hardground, there are beachrocks with early Danian zone P1a(1) assemblages, which indicate the hardground spans about ~600 k.y. of nondeposition and/or erosion. During the early Danian, the marine transgressive fringe fluctuated between “shoreface to emersion” environments, depositing limestones rich in bryozoans, rhynchonellids, coralline algae, and rare planktic foraminifera along with abraded, bored, and/or encrusted clasts eroded from older rocks. Repeated short subaerial exposure is marked by vadose diagenesis and hardgrounds, including an ~1.5 m.y. interval between magnetochrons C29n to C28n and planktic foraminiferal zones P1b to P1c(2). Comparison with platform carbonate sequences from Croatia, Oman, Madagascar, Belize, and Guatemala, as well as nearshore siliciclastic environments of southern Tunisia, Texas, and Argentina, across the K/P boundary transition revealed surprisingly similar deposition and erosion patterns, with the latter correlative with sea-level falls and repeated subaerial exposure forming hardgrounds. Comparison with deep-sea depositional patterns revealed coeval but shorter intervals of erosion. This pattern shows a uniform response to the K/P boundary transition linked to climate and sea-level changes, whether in shallow nearshore or deep-sea environments, with climate change tied to Deccan volcanism in magnetochrons C29r-C29n.

ABSTRACT Deccan volcanism likely triggered environmental stress that controlled biotic transformations and Cretaceous/Paleogene (K/Pg) boundary mass extinction in the Indian subcontinent, but these revelations still remain inconclusive. Thus, we conducted high-resolution organo-molecular studies on a marine Um-Sohryngkew River K/Pg boundary succession. The results were used as standard reference for comparison with biotic attributes of the brackish water (Jhilmili) to freshwater (Anjar) intertrappean sediments and bole beds of the Deccan Traps. Organo-molecular compounds of the former section show strong correlation with the global stratotype section and point. High amounts of short-chain n -fatty acids and n -alkanes derived from autochthonous marine algal remains were observed in this section. However, the dominance of mid- and long-chain n -alkanes over short-chain n -alkanes in the Jhilmili intertrappean and intravolcanic bole beds of the eastern Deccan volcanic province suggested a terrestrial origin from higher plants under semiarid climatic conditions. The prolific abundance of n -alkanes in the Um-Sohryngkew River succession implies a mixture of terrestrial input from emergent and submerged/floating aquatic macrophytes. Low-molecular-weight aromatic hydrocarbon markers peak in biozone CF2 of the Um-Sohryngkew River succession. Possibly, this corresponds to greenhouse effects linked to the second phase of Deccan volcanism in the latest Maastrichtian, chron 29r. Abundant n -fatty acids found in the eastern Deccan bole beds suggest an origin from bacteria developed in a terrestrial environment. Depleted δ 13 C bulk values recorded from Jhilmili intertrappean and eastern Deccan bole beds are indicative of low primary productivity and burning of terrestrial biomass. Total organic carbon (TOC) maxima observed in the lowermost Danian P1a foraminiferal biozone of the Um-Sohryngkew River succession are also linked to late Deccan phase-two eruptions. The presence of three low-molecular-weight aromatic hydrocarbon markers in the eastern Deccan bole bed implies incomplete combustion of organic compounds in a terrestrial environment. Moreover, the dominance of high-molecular-weight aromatic hydrocarbon markers in biozone CF3 of the Um-Sohryngkew River succession is akin to that reported from other well-established K/Pg boundary successions, suggestive of their possible derivation from regional fire induced by the heat supplied by Deccan volcanism, which has been linked to the K/Pg boundary transition. Thus, regional wildfire played a significant role and affected the ecosystem, which perhaps accounts for the mass extinction.

ABSTRACT Fluid release structures resulting from the interaction of igneous intrusions with sedimentary basins form an important part of the evolution of large igneous provinces. Hydrothermal breccia pipes formed in the Karoo Basin in South Africa during emplacement of igneous sills in the Karoo large igneous province represent one of the best-exposed expressions of such venting structures. Earlier work has shown that degassing of thermogenic CO 2 and CH 4 through the breccia pipes may have contributed to the Early Jurassic environmental changes. Here, we present the first detailed analysis of the distribution of breccia pipes in the western parts of the Karoo Basin. We mapped 431 pipes in a 650 km 2 area using outcrop data. The pipes are rooted in contact aureoles around four sills emplaced in organic-rich Ecca Group shale, and thermal modeling of sill cooling and contact metamorphism gives a maximum temperature of 675 °C near the sill contacts, sufficient to convert a significant fraction of the organic carbon to gas. Model estimates indicate that metamorphism in the 650 km 2 area generated 75–88 Gt of CO 2 , depending on actual sill thicknesses and emplacement levels. When further up-scaled, an area of 7400–8700 km 2 (i.e., less than 2% of the area in the Karoo Basin intruded by sills) would be required to generate 1000 Gt of CO 2 . In order to characterize the degassing pipes, their geographical positions and diameters were analyzed using several point-pattern methods. The results showed that the pipes (1) have diameters in the 11–177 m range (average 44 m), (2) are spaced with an average nearest-neighbor distance of 452 m, and (3) are overall randomly spaced but with weak overdispersion at very small scales (<50 m) and weak clusters at larger scales (400–3000 m). In contrast to studies of volcanic pipe spacing, this study on breccia pipes does not indicate that the pipe spacing is controlled by any large-scale geophysical parameters such as crustal or basin thicknesses. Conclusions point to the pipes being formed following sill emplacement and pressure increase in the low-permeability organic-rich shale, followed by rapid carbon degassing, emphasizing their important role in the Early Jurassic climate change and oceanic anoxic event.

ABSTRACT Large igneous provinces and associated silicic magmatism can have a significant global climatic effect, so we explored the relationship between the large igneous province record and the ca. 580 Ma Gaskiers glaciation. The late Ediacaran glaciation exists on at least 14 different paleocontinental blocks, and assuming synchroneity, this Gaskiers glaciation was likely of short duration, with estimates ranging from 1.6 m.y. to 340 k.y. The Central Iapetus magmatic province event found in Laurentia, Baltica, and West Africa consists of multiple pulses in the range 620–520 Ma, with the ca. 580 Ma pulse particularly well developed in North Africa. Based on the age matches of 580–570 Ma Central Iapetus magmatic province pulses and the Gaskiers glaciation, and taking into consideration that there is no robust evidence for a major meteorite impact at the time of the Gaskiers onset, we propose that: (1) the initial silicic ca. 580 Ma pulse of the Ouarzazate event (Anti-Atlas of Morocco) helped to trigger the Gaskiers glaciation, and (2) global warming associated with the subsequent ca. 579–570 Ma continental flood basalts, marking the second stage of the Ouarzazate event, helped to end the ice age.

ABSTRACT The latest Cretaceous (Maastrichtian) through earliest Paleogene (Danian) interval was a time marked by one of the five major mass extinctions in Earth’s history. The synthesis of published data permits the temporal correlation of the Cretaceous-Paleogene boundary crisis with two major geological events: (1) the Chicxulub impact, discovered in the Yucatán Peninsula (Mexico), and (2) eruption of the Deccan Traps large igneous province, located on the west-central Indian plateau. In this study, environmental and biological consequences from the Chicxulub impact and emplacement of the Deccan continental flood basalts were explored using a climate-carbon-biodiversity coupled model called the ECO-GEOCLIM model. The novelty of this study was investigation into the ways in which abiotic factors (temperature, pH, and calcite saturation state) acted on various marine organisms to determine the primary productivity and biodiversity changes in response to a drastic environmental change. Results showed that the combination of Deccan volcanism with a 10-km-diameter impactor would lead to global warming (3.5 °C) caused by rising carbon dioxide (CO 2 ) concentration (+470 ppmv), interrupted by a succession of short-term cooling events, provided by a “shielding effect” due to the formation of sulfate aerosols. The consequences related to these climate changes were the decrease of the surface ocean pH by 0.2 (from 8.0 to 7.8), while the deep ocean pH dropped by 0.4 (from 7.8 to 7.4). Without requiring any additional perturbations, these environmental disturbances led to a drastic decrease of the biomass of calcifying species and their biodiversity by ~80%, while the biodiversity of noncalcifying species was reduced by ~60%. We also suggest that the short-lived acidification caused by the Chicxulub impact, when combined with eruption of the Deccan Traps, may explain the severity of the extinction among pelagic calcifying species.

ABSTRACT In recent models of earth-system crises, the correlation between the major Phanerozoic mass extinctions and large igneous provinces has been well established. Specifically, pulsed massive exhalations of large amounts of volcanogenic CO 2 transformed Earth’s atmosphere, leading to an excessive greenhouse effect and global warming, combined with slowed oceanic circulation, oxygen deficiency, and seawater acidification. In a historical context, however, the path leading to this neocatastrophic doctrine, traced by way of ever-more-convincing proofs (in recent years, via mercury anomalies), was convoluted for many objective and notional-personal reasons. From the late eighteenth century to the revolutionary 1980s, the reception of this conceptual route in the English-language mainstream science was determined principally by the rise and fall of the orthodox nonprogressive (steady-state) paradigm of the Lyellian uniformitarian. The main cognitive steps, pioneered frequently in continental Europe, included such principal conclusions as: (1) volcanic eruptions are a natural process, consisting of heat being vented from a central incandescent core, itself a relic of an initial nebular state; (2) cataclysmic phenomena were far more intense in the geologic past, both in orogenic and nonorogenic time intervals, with a dominant nonactualistic style of fissure-type effusive activity in intraplate settings, recorded in vast trap-type basalt successions (= large igneous provinces); (3) volcanogenic gaseous emanations, dominated by carbon dioxide and water vapor, had a strong impact on the global climate in the geological past toward the global warmth mode; and (4) this “volcanic greenhouse” was deleteriously augmented by several forms of immanent stress feedback (resulting in anoxia, acidification, hypercapnia, acid rains, ultraviolet radiation, etc.). Overall, diverse global ecosystem interactions, combined with the updated large igneous province scenario, can elucidate all major destructive factors in the biosphere, such as regressive versus transgressive sea-level changes and cooling versus warming climatic responses. Notwithstanding the particularity of each major biodiversity crisis in the Phanerozoic, however, a greenhouse/icehouse volcanism-driven catastrophe is a well-confirmed key toward better understanding these biotic turnovers over a variety of time scales and feedbacks. The holistic volcanic “press-pulse” model involves the joint action of two different types of stress factors: long-lived (“press”) large igneous provinces and a variety of critically sudden (“pulse”) disturbances. Therefore, the killing effectiveness of volcanic cataclysm should be viewed not only by the large igneous province size but also by their host geology, magma plumbing system, and eruption dynamics, determining the magnitude and composition of disastrous thermogenic outgassing. In search of possible pulse signals, emphasis has recently been placed on large igneous province–related, volatile-rich, mafic-ultramafic intrusions (owing to the great fluid-bearing capacity of their magmas) and sill-type intrusions (resulting in the most-effective devolatilization of sedimentary rocks). A simultaneous burst of arc magmatism and coeval impact of arc-continent collisions (especially in tropical domain) on global weatherability are additional cumulative cataclysmic stimuli awaiting more rigorous numerical simulations.

This volume covers new developments and research on mass extinctions, volcanism, and impacts, ranging from the ancient Central Iapetus magmatic province linked with the Gaskiers glaciation to thermogenic degassing in large igneous provinces, the global mercury enrichment in Valanginian sediments, and the Guerrero-Morelos carbonate platform response to the Caribbean-Colombian Cretaceous large igneous province. This section is followed by a series of end-Cretaceous studies, including the implications for the Cretaceous-Paleogene boundary event in shallow platform environments and correlation to the deep sea; the role of wildfires linked to Deccan volcanism on ecosystems from the Indian subcontinent; rock magnetic and mineralogical study of Deccan red boles; and factors leading to the collapse of producers during Deccan Traps eruptions and the Chicxulub impact.

The geological record represents the only source of data available for documenting long-term historical patterns of extinction intensity and extinction susceptibility. Such data are critical for testing hypotheses of extinction causality in the modern world as well as in deep time. The study of extinction is relatively new. Prior to 1800, extinctions were not accepted as a feature of the natural environment. Even after extinctions were recognized to have occurred in Earth's geological past, they were deemed to have played a minor role in mediating evolutionary processes until the 1950s. Global extinction events are now recognized as having been a recurring feature of the history of life and to have played an important role in promoting biotic diversification. Interpretation of the geological extinction record is rendered complex as a result of several biasing factors that have to do with the spatial and temporal resolutions at which the data used to study extinctions have been recorded: fluctuations in sediment accumulation rates, the presence of hiatuses in the stratigraphic sections/cores from which fossils are collected, and variation in the volumes of sediments that can be searched for fossils of different ages. The action of these factors conspires to render the temporal and geographic records of fossil occurrences incomplete in many local stratigraphic sections and cores. In some cases, these stratigraphic and sampling uncertainties can be quantified and taken into account in interpretations of that record. However, their effects can never be eliminated entirely. Testing hypotheses of global extinction causality requires acknowledgment of the uncertainties inherent in extinction data, the search for unique predictions of historical patterns of variation or associations that can, in principle, be preserved in the fossil record and tied logically to the operation of specific causal processes, and to adoption of an explicitly comparative approach that establishes the presence of multiple instances of the predicted cause-effect couplets within a well-documented chronostratigraphic context.

The temporal link between mass extinctions and large igneous provinces is well known. Here, we examine this link by focusing on the potential climatic effects of large igneous province eruptions during several extinction crises that show the best correlation with mass volcanism: the Frasnian-Famennian (Late Devonian), Capitanian (Middle Permian), end-Permian, end-Triassic, and Toarcian (Early Jurassic) extinctions. It is clear that there is no direct correlation between total volume of lava and extinction magnitude because there is always sufficient recovery time between individual eruptions to negate any cumulative effect of successive flood basalt eruptions. Instead, the environmental and climatic damage must be attributed to single-pulse gas effusions. It is notable that the best-constrained examples of death-by-volcanism record the main extinction pulse at the onset of (often explosive) volcanism (e.g., the Capitanian, end-Permian, and end-Triassic examples), suggesting that the rapid injection of vast quantities of volcanic gas (CO 2 and SO 2 ) is the trigger for a truly major biotic catastrophe. Warming and marine anoxia feature in many extinction scenarios, indicating that the ability of a large igneous province to induce these proximal killers (from CO 2 emissions and thermogenic greenhouse gases) is the single most important factor governing its lethality. Intriguingly, many voluminous large igneous province eruptions, especially those of the Cretaceous oceanic plateaus, are not associated with significant extinction losses. This suggests that the link between the two phenomena may be controlled by a range of factors, including continental configuration, the latitude, volume, rate, and duration of eruption, its style and setting (continental vs. oceanic), the preexisting climate state, and the resilience of the extant biota to change.

The recent discovery of the direct link between Deccan volcanism and the end-Cretaceous mass extinction also links volcanism to the late Maastrichtian rapid global warming, high environmental stress, and the delayed recovery in the early Danian. In comparison, three decades of research on the Chicxulub impact have failed to account for long-term climatic and environmental changes or prove a coincidence with the mass extinction. A review of Deccan volcanism and the best age estimate for the Chicxulub impact provides a new perspective on the causes for the end-Cretaceous mass extinction and supports an integrated Deccan-Chicxulub scenario. This scenario takes into consideration climate warming and cooling, sea-level changes, erosion, weathering, ocean acidification, high-stress environments with opportunistic species blooms, the mass extinction, and delayed postextinction recovery. The crisis began in C29r (upper CF2 to lower CF1) with rapid global warming of 4 °C in the oceans and 8 °C on land, commonly attributed to Deccan phase 2 eruptions. The Chicxulub impact occurred during this warm event (about 100–150 k.y. before the mass extinction) based on the stratigraphically oldest impact spherule layer in NE Mexico, Texas, and Yucatan crater core Yaxcopoil-1. It likely exacerbated climate warming and may have intensified Deccan eruptions. The reworked spherule layers at the base of the sandstone complex in NE Mexico and Texas were deposited in the upper half of CF1, ~50–80 k.y. before the Cretaceous-Tertiary (K-T) boundary. This sandstone complex, commonly interpreted as impact tsunami deposits of K-T boundary age, was deposited during climate cooling, low sea level, and intensified currents, leading to erosion of nearshore areas (including Chicxulub impact spherules), transport, and redeposition via submarine channels into deeper waters. Renewed climate warming during the last ~50 k.y. of the Maastrichtian correlates with at least four rapid, massive volcanic eruptions known as the longest lava flows on Earth that ended with the mass extinction, probably due to runaway effects. The kill mechanism was likely ocean acidification resulting in the carbonate crisis commonly considered to be the primary cause for four of the five Phanerozoic mass extinctions.