Multiple factors in the origin of the Cretaceous/Tertiary boundary: the role of environmental stress and Deccan Trap volcanism

Abstract

A review of the scenarios for the Cretaceous/ Tertiary (K/T) boundary event is presented and a coherent hypothesis for the origin of the event is formulated. Many scientists now accept that the event was caused by a meteorite impact at Chicxulub in the Yucatan Peninsula, Mexico. Our investigations show that the oceans were already stressed by the end of the Late Cretaceous as a result of the long-term drop in atmospheric CO2, the long-term drop in sea level and the frequent development of oceanic anoxia. Extinction of some marine species was already occurring several million years prior to the K/T boundary. The biota were therefore susceptible to change. The eruption of the Deccan Traps, which began at 66.2 Ma, coincides with the K/T boundary events. It erupted huge quantities of H2SO4, HCl, CO2, dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature. The result was a major reduction in oceanic productivity and the creation of an almost dead ocean. The volcanism lasted almost 0.7 m.y. Extinction of biological species was graded and appeared to correlate with the main eruptive events. Elements such as Ir were incorporated into the volcanic ash, possibly on soot particles. This horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the K/T boundary. An oxidation front penetrated this horizon leading to the redistribution of elements. The eruption of the Deccan Traps is the largest volcanic event since the Permian-Triassic event at 245 Ma. It followed a period of 36 m.y. in which the earth's magnetic field failed to reverse. Instabilities in the mantle are thought to be responsible for this eruption and therefore for the K/T event. We therefore believe that the K/T event can be explained in terms of the effects of the Deccan volcanism on an already stressed biosphere. The meteorite impact at Chicxulub took place after the onset of Deccan volcanism. It probably played a regional, rather than global, role in the K/T extinction.

Atmospheric halogen and acid rains during the main phase of Deccan eruptions: Magnetic and mineral evidence

“…Glass analyses recently demonstrated that Deccan basalts were responsible for a huge HCl input into the atmosphere (4 × 10 12 g SO 2 and 1 × 10 12 g HCl released into the atmosphere per cubic kilometer of lava; Self et al, 2008b), confi rming former scenarios (Glasby and Kunzendorf, 1996). The volume of lavas extruded during Deccan phase 2 is ~80% of the total lava volume, i.e., ~10 6 km 3 (Self et al, 2006).…”

Environmental change prior to the K–T boundary inferred from temporal variation in the morphology of cheilostome bryozoans

“…The shift to the production of smaller zooids just prior to the boundary may, however, be indicative of changes in oxygen conditions that are not driven by temperature. Anoxic events have been inferred to occur on a global scale prior to the boundary as a result of environmental perturbations from Deccan volcanism (see Glasby and Kunzendorf, 1996), and indeed the boundary clay in the Danish Basin has been suggested to represent an anoxic event (Kajiwara and Kaiho, 1992;Hart et al, 2005). What's more, alternating bioturbated and laminated chalks in other parts of the Danish basin imply the regular occurrence of dysoxic events during the Maastrichtian (Damholt and Surlyk, 2004), although no laminations were observed at Nye Kløv.…”

Barium anomaly preceding K/T boundary: possible causes and implications on end Cretaceous events of K/T sections in Cauvery basin (India), Israel, NE-Mexico and Guatemala

“…As Deccan volcanism impacted the sedimentary record of the Cauvery basin through inducing greenhouse effect, rise in atmospheric temperature and sea level and initiation of carbonate deposition, which are recorded only at or after the end of the Cretaceous (Niniyur Formation), which in turn are much younger than the Ba anomaly. On the contrary, based on the suggestion of Hallam (1987), Glasby and Kunzendorf (1996) noted that extensive Deccan volcanism itself might have caused sea level fall by up to $100 m and sea level fall may have taken place during latest Maastrichtian. Thus, it is concluded that the impact of Deccan volcanism on sedimentation in the Cauvery basin, if any, postdates the Ba anomaly.…”

“…However, as the Ir anomalies occur in intertrappean beds, it is inferred that Deccan volcanism predates meteoritic impact (Venkatesan et al 1993;Bhandari et al 1993;Khadkikar et al 1999). In view of the enormity of Deccan volcanism (Glasby and Kunzendorf 1996) and its proximity to the study area, it could be assumed that it would have influenced the sediments of the study area more readily than the meteoritic impact in the Gulf of Mexico region. Furthermore, owing to the sampling interval of this study, lack of Ir data for the analyzed samples, the occurrence of a Ba anomaly far below the perceived K/T boundary and the occurrence of Ir anomaly at the K/T boundary, meteoritic impact and its relevance to Ba anomaly can be excluded from discussion.…”

“…Thierstein (1981) noted that prior to the Deccan volcanism, global ecological stability prevailed. Many authors, namely McLean (1985), Bhandari et al (1993;1995), Venkatesan et al (1993) and Glasby and Kunzendorf (1996) have examined the timing of the Deccan volcanism and its effect on global climate. Based on their observations, the following can be inferred with reference to the Ba anomaly.…”