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Johan Vellekoop MSc
J.Vellekoop@uu.nl
PhD Candidate
Earth Sciences
Gegenereerd op 2014-07-29 14:41:44


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The Cretaceous – Paleogene (K-Pg) boundary is characterized by a mass extinction event. This was one of the most devastating events in the history of life, as many biological groups went extinct, including the dinosaurs, flying reptiles, many marine reptiles, ammonites, belemnites and many others were seriously effected, such as calcareous nannoplankton and planktonic foraminifera (MacLeod et al., 1997; Alroy, 2008). After decades of research, an overwhelming amount of evidence points towards the impact of a large asteroid as the cause for the mass extinction. As a result, international scientific focus shifted from the reality of such impacts to the effects of impacts on the global environmental system and ecological and biological recovery of a major environmental crisis (e.g., Brinkhuis et al., 1998; Galeotti et al., 2004; Kring, 2007).

A key element in most K-Pg boundary impact scenarios and models is the blocking of sunlight by stratospheric dust and aerosol loading (Alvarez et al., 1980). All models predict a resulting short-lived severe drop in global surface temperatures, the so-called ‘impact winter’. The various scenarios suggest that the period of reduced solar radiation may have lasted anywhere between six months to more than a decade. When the dust-veil had lifted, an increase of CO2 in the atmosphere led to a longer period of pronounced warming (e.g. Kring 2007). This post impact greenhouse phase may have lasted several thousands of years and the KTB extinctions likely caused rearrangements of the pelagic oceanic ecosystems leading to sustained, long term (> 3 million years) reduced/different carbon delivery to the ocean floor and the so-called ‘Strangelove/Living Ocean’ (e.g., D’Hondt et al., 1998; Adams et al., 2004; D’Hondt et al., 2005).

Although decades of K-Pg boundary studies have brought important information, studies detailed and quantified enough to elucidate possible impact-provoked global environmental change mechanisms, or to test various proposed aftermath scenarios are still lacking (Kring, 2007). In contrast to calcareous (phyto)plankton, organic-walled cyst producing dinoflagellates were hardly affected by the K-Pg crisis (e.g., Brinkhuis and Zachariasse, 1988). Brinkhuis et al. (1998) demonstrated that quantitative analysis of organic-walled cysts of temperature-sensitive dinoflagellates may be applied in testing models of the environmental effects of the K-Pg impact. Furthermore, the long term eustatic sea level history was reconstructed at many K-Pg boundary sites, showing conspicuous lowering of sea level across the boundary, and marked transgression shortly after. This long term (~800 Kyr) sea level motion resulted in varying expression and completeness of notably marginal marine K-Pg sections worldwide, but the degree of completeness is resolvable using dinocyst biostratigraphy (Brinkhuis et al., 1998).

The above makes clear that quantitative marine palynology can serve to recognize and document K-Pg boundary environmental perturbations, as well as ongoing ‘background’ environmental change, including the global sea level history across K-Pg boundary. It is particularly effective when dealing with the critical, high accumulation rate, relatively nearshore settings which likely yield most relevant information pertaining to e.g., sea level dynamics and surface salinity, temperature and productivity, and potential leads and lags between them.

Although dinocyst analysis will and has revealed distinct trends in environmental parameters, quantification of such trends and values is not possible using only palynology. Recently, however, novel techniques have been developed for reconstructing absolute mean annual sea surface temperature and mean annual air temperature based on distributions of organic biomarkers: TEX86 and MBT/CBT respectively (Schouten et al., 2002; Weijers et al., 2007). These proxies have been successfully applied in deep time, integrated with marine palynology (e.g., Sluijs et al., 2006; Jenkyns et al., 2004; Forster et al., 2007).

We are carrying out high-resolution studies to reconstruct millennial-scale dynamics of climate and carbon cycling across the K-Pg boundary. For this, I am investigating a large selection of K-Pg deep to marginal marine and even continental sedimentary sequences. Our published and pilot studies show that the combination of biomarker based paleothermometers with quantitative dinocyst analysis is a powerful and innovative tool in the analysis of the environmental consequences of the K-Pg impact in the marginal marine realm. These tools are applied on sediments deposited at different paleo-latitudes and sedimentary settings, from both hemispheres, in order to contribute to (1) documenting regional and global climate and carbon cycle changes across the critical ~50 Kyr following the impact, (2) assessing the timing, magnitude and areal extent of these events, (3) providing an accurate database of background environmental change and the effects of the catastrophic event(s) to (4) test and improve model predictions.

Expertise
Cretaceous-Paleogene organic-walled dinoflagellate cysts - Cretaceous-Paleogene palaeoclimatology and palaeoceanography

Gegenereerd op 2014-07-29 14:41:44
Last updated 31.10.2013