The Zumaia cliffs are identified by an extraordinary section of strata that reveals the geological history of the Earth in the period of 115-50 million years back (Ma). Credit: University of Barcelona/ IUCA– University of Zaragoza
A study published in the journal Geology rules out that severe volcanic episodes had any impact on the huge extinction of species in the late Cretaceous. The outcomes confirm the hypothesis that it was a huge meteorite effect that caused the great biological crisis that ended up with the non-avian dinosaur family trees and other marine and terrestrial organisms 66 million years earlier.
The study was performed by the scientist Sietske Batenburg, from the Faculty of Earth Sciences of the University of Barcelona, and the experts Vicente Gilabert, Ignacio Arenillas and José Antonio Arz, from the University Research Institute on Environmental Sciences of Aragon (IUCA-University of Zaragoza).
K/Pg limit: the great extinction of the Cretaceous in Zumaia coasts
The situation of this study was the Zumaia cliffs (Basque Country), which have an extraordinary section of strata that reveals the geological history of the Earth in the period of 115-50 million years ago (Ma). In this environment, the team analyzed sediments and rocks that are abundant in microfossils that were transferred between 66.4 and 65.4 Ma, a time interval that consists of the known Cretaceous/Paleogene limit (K/Pg). Dated in 66 Ma, the K/Pg limit divides the Cenozoic and mesozoic ages and it corresponds with one of the five large extinctions of the world.
This study analyzed the climate modifications that took place prior to and after the huge extinction marked by the K/Pg limit, as well as its possible relation to this big biological crisis. For the first time, scientists analyzed whether this environment modification corresponds on the time scale with its prospective causes: the Deccan enormous volcanism (India)– one of the most violent volcanic episodes in the geological history of the world– and the orbital variations of the Earth.
The experts Sietske Batenburg, from the Faculty of Earth Sciences of the University of Barcelona, and ¡ Vicente Gilabert, from the University Research Institute on Environmental Sciences of Aragon (IUCA-University of Zaragoza). Credit: University of Barcelona/ IUCA– University of Zaragoza
” The particularity of the Zumaia outcrops lies in that 2 kinds of sediments accumulated there– some richer in clay and others richer in carbonate– that we can now identify as strata or marl and limestone that alternate with each other to form rhythms,” keeps in mind the scientist Sietske Batenburg, from the Department of Earth and Ocean Dynamics of the UB. “This strong rhythmicity in sedimentation is connected to cyclical variations in the orientation and disposition of the Earth axis in the rotation movement, as well as in the translational movement around the Sun”.
These astronomic setups– the recognized Milankovitch cycles, which duplicate every 405,000, 100,000, 41,000, and 21,000 years– regulate the amount of solar radiation they receive, modulate the worldwide temperature of our planet and condition the kind of sediment that reaches the oceans. “Thanks to these periodicities identified in the Zumaia sediments, we have had the ability to figure out the most precise dating of the weather episodes that happened around the time when the last dinosaurs lived,” states PhD trainee Vicente Gilabert, from the Department of Earth Sciences at UZ, who will present his thesis defense by the end of this year.
Planktonic foraminifera: exposing the climate of the past
Carbon-13 isotopic analysis on the rocks in combination with the study of planktonic foraminifera– microfossils used as high-precision biostratigraphic indicators– has made it possible to rebuild the paleoclimate and chronology of that time in the Zumaia sediments. More than 90% of the Cretaceous planktonic foraminiferal types from Zumaia ended up being extinct 66 Ma earlier, accompanying a huge interruption in the carbon cycle and a build-up of effect glass spherules originating from the asteroid that struck Chicxulub, in the Yucatan Peninsula (Mexico).
In addition, the conclusions of the research study reveal the presence of 3 extreme weather warming occasions– understood as hyperthermal occasions– that are not associated with the Chicxulub impact. The very first, referred to as LMWE and prior to the K/Pg limit, has been dated to in between 66.25 and 66.10 Ma. The other 2 events, after the mass termination, are called Dan-C2 (in between 65.8 and 65.7 Ma) and LC29n (between 65.48 and 65.41 Ma).
In the last years, there has been intense argument over whether the hyperthermal events discussed above were caused by an increased Deccan volcanic activity, which gave off large amounts of gases into the environment. “Our results indicate that all these occasions remain in sync with severe orbital setups of the Earth referred to as eccentricity maxima. Only the LMWE, which produced an estimated worldwide warming of 2-5 ° C, seems temporally associated to a Deccan eruptive episode, suggesting that it was triggered by a mix of the effects of volcanism and the most current Cretaceous eccentricity optimum”, the professionals add.
Earths orbital variations around the Sun
The international environment changes that occurred in the late Cretaceous and early Palaeogene– in between 250,000 years before and 200,000 years after the K/Pg limit– were due to eccentricity maxima of the Earths orbit around the Sun.
The orbital eccentricity that influenced environment modifications before and after the K/Pg limit is not related to the late Cretaceous mass extinction of types. The weather modifications triggered by the eccentricity optimums and enhanced by the Deccan volcanism occurred gradually at a scale of numerous thousands of years.
” These information would validate that the termination was caused by something totally external to the Earth system: the impact of an asteroid that happened 100,000 years after this late Cretaceous environment modification (the LMWE),” the research study team says. “Furthermore, the last 100,000 years prior to the K/Pg boundary are characterized by high ecological stability with no obvious perturbations, and the large mass extinction of species took place instantaneously on the geological timescale,” they conclude.
Referral: “Contribution of orbital forcing and Deccan volcanism to international weather and biotic modifications throughout the Cretaceous-Paleogene limit at Zumaia, Spain” by Vicente Gilabert, Sietske J. Batenburg, Ignacio Arenillas and José A. Arz, 30 August 2021, Geology.DOI: 10.1130/ G49214.1.
The scenario of this study was the Zumaia cliffs (Basque Country), which have an exceptional area of strata that reveals the geological history of the Earth in the period of 115-50 million years ago (Ma). In this environment, the group analyzed sediments and rocks that are rich in microfossils that were transferred in between 66.4 and 65.4 Ma, a time period that includes the known Cretaceous/Paleogene border (K/Pg). Dated in 66 Ma, the K/Pg limit divides the Cenozoic and mesozoic periods and it corresponds with one of the five large terminations of the world.
The other 2 events, after the mass termination, are called Dan-C2 (in between 65.8 and 65.7 Ma) and LC29n (in between 65.48 and 65.41 Ma).
“Our results suggest that all these occasions are in sync with extreme orbital setups of the Earth known as eccentricity maxima.
