Reconstructing the oceanic carbon cycle gradient for the

end-Cretaceous mass extinction: insights from El Kef, Tunisia

Siri Ofstad

A dissertation submitted on the 1st of June 2015 for the degree of

Master of Oceanography

Supervisor: Dr. Jessica H. Whiteside

Word Count: 7888

Abstract

There is general agreement in the scientific community that the end-Cretaceous mass extinction at the K/Pg boundary (~66 Ma) was triggered by a bolide impact. Up to 76% of all species at the time went extinct, among them were calcifying plankton (>90% of species), including planktic foraminifera and calcareous nannoplankton. However this was not the fate for non-calcifying pelagic organisms such as diatoms, radiolarians, dinoflagellates, benthic foraminifera, and ostracodes. The K/Pg boundary is characterized by a sudden 1-3‰ negative excursion in δ13C. This can be interpreted as a collapse of the surface-to-bottom δ13C gradient, indicative of a major alteration in marine primary productivity levels and the biological pump. The δ13C gradient did not fully recovery for hundreds of thousands to a few million years after the extinction event. However, plankton-dependent benthic foraminifera did not suffer mass extinction, meaning there must have been a sufficient level of export production to support their community. The lack of extinction of benthic foraminfera, but the persistent collapse of the δ13C gradient must be explained. A bulk δ13C record will be used in concert with compound specific δ13C, calcium carbonate (CaCO3), δ13C of benthic foraminifera and carbon isotopic photosynthesis fractionation (εp) to test the hypothesis that there was a rapid resurgence in primary production. The bulk δ13C records and biomarkers show contrasting duration and magnitude of the perturbation. The biomarker data show initially subdued levels of primary production but recovery after ~1-2 kyr. These data imply a transient perturbation, the significance of the sustained negative shift in bulk δ13C remains in doubt. Bulk δ13C records reflect multiple and complex signals, and may be dominated by other influences besides primary and export production, mainly ‘vital effects’ as a result of change in assemblages from the Cretaceous to the Paleogene. The drastic reduction of sediment CaCO3 content highlights the loss of calcifying organisms. The Lower Danian is market by unstable conditions and low productivity. However, non-calcifying primary producers may have sustained the benthic community by forming the base of the marine foodchain.

Contents

1. Introduction............................................................................................................1

1.1 The End-Cretaceous Mass Extinction.................................................................1

1.2 The Biological Pump...........................................................................................3

1.3 The Isotopic Gradient..........................................................................................4

1.4 The Strangelove Ocean and Living Ocean..........................................................7

1.5 The Benthic Community......................................................................................9

1.6 Heterogeneous Response...................................................................................11

1.7 The El Kef Coring Program...............................................................................13

2. Materials and Methods.........................................................................................14

2.1 El Kef, Tunisia..................................................................................................14

2.2 Sampling Strategies...........................................................................................15

2.3 Carbon Isotopic Analysis...................................................................................17

2.4 Bulk Nitrogen isotopic Analysis........................................................................17

2.5 δ13C of Anomalinoides acuta and CaCO3..........................................................18

2.6 Cleaning Protocol and Sample Preparation for organic geochemistry work.....18

2.7 Lipid Extraction and Separation........................................................................19

2.8 Compound-specific Carbon isotopes.................................................................19

3. Results.....................................................................................................................20

3.1 Bulk Carbon Isotopes.........................................................................................21

3.2 δ15N....................................................................................................................21

3.3 CaCO3................................................................................................................21

3.4. δ13CBenthic...........................................................................................................21

3.5 Compound-specific Carbon isotopes.................................................................22

4. Discussion...............................................................................................................22

4.1 Interpretation......................................................................................................22

4.2 Factors influencing bulk δ13C.............................................................................26

4.3 Further Research.................................................................................................27

5. Conclusions........................................................................................................28

Acknowledgements………………………..………………………..………....….29

Appendix A Outcrop figure………………………..………………….…30

Appendix B Data tables………………………..………………………...30

References………………………..………………………..…………………..…..34

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1. Introduction

1.1 The End-Cretaceous Mass Extinction

Throughout Earth’s history there have been a number of mass extinction events that

decimated more than half of the species alive at that time (Takashima et al., 2006) (Fig

1). A mass extinction event is defined as “any substantial increase in the amount of

extinction (i.e., lineage termination) suffered by more than one geographically wide-

spread higher taxon during a relatively short interval of geologic time, resulting in an at

least temporary decline in their standing diversity” (Sepkoski, 1986). These events

induced substantial biotic and environmental change (Kump, 2003). The end-Cretaceous

extinction at the Cretaceous-Paleogene (K/Pg) boundary is the most recent and

intensively studied of the “big five” (Wilson, 2013) mass extinction events of the

Phanerozoic and occurred 66 million years (Myr) ago (Gradstein et al., 2012).

Figure 1. Percentage extinction of marine genera (Raup and Sepkowski, 1986) during mass extinction events through the Phanerozoic. The end-Cretaceous is indicated by the red arrow. Modified from Takashima et al. 2006. The K/Pg was historically regarded as the Cretaceous-Tertiary (K/T) boundary, but

“Tertiary” is an informal term as it is not included in the Geologic Time Scale edited by

Gradstein et al. (2012). It is also the most well known due to it causing the demise of

nonavian dinosaurs (D’Hondt, 2005; Hsu et al., 1982), but also up to 76% of all species at

the time (Vilhena et al., 2013). Among them were calcifying plankton (>90% of species),

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including planktic foraminifera (Smit, 1982; Stott and Kennett, 1990; Liu and Olsson,

1992; Berggren and Norris, 1997; Molina et al., 1998) and calcareous nannoplankton

(Pospichal and Wise, 1990; Bown, 2005; Fuqua et al., 2008). However, this was not the

fate for non-calcifying pelagic organisms such as diatoms, radiolarians (Harwood, 1988;

Hollis et al., 2003), dinoflagellates (Brinkhuis et al., 1998), benthic foraminifera (e.g.,

Thomas, 1990a,b; Alegret and Thomas, 2005), and ostracodes (e.g., Majoran et al., 1997;

Boomer, 1999; Elewa, 2002), which did not suffer significant extinction over background

level (Culver, 2003). The return to pre-extinction levels of biodiversity took hundreds of

thousands to millions of years (Barnosky et al., 2012).

The end-Cretaceous extinction was likely triggered by an asteroid impact to the

Yucatán Peninsula in Mexico (Alvarez et al., 1981; Hildebrand et al., 1991;

Mukhopadhyay et al., 2001). The evidence for an extraterrestrial trigger is overwhelming

(Schulte et al., 2010). The most notable evidence is the prominent global spikes in the

platinum group element iridium found in the sediment record (Alvarez et al., 1980), and

the physical evidence of the temporally coincident 180-200-km-diameter Chicxulub

crater and impact ejecta (Hildebrand et al., 1991).But the specific mechanisms involved

with how an asteroid impact caused an abrupt mass extinction on both land and sea is

poorly understood. The discovery of extraterrestrial material at the boundary by Alvarez

et al. in 1980 fueled the formulation of new hypotheses and theories attempting to explain

the mass extinction. Three decades later different mechanisms are still widely debated by

scientists. Some suggest that the bolide impact triggered a bevy of secondary effects

(Vilhena et al., 2013). For example: (i) global darkness inhibiting photosynthesis a.k.a

‘impact winter’ (Pope, 2002), (ii) initial temperature spikes (Robertson et al., 2004), (iii)

acid rain (Schulte et al., 2010), (iv) metal poisoning of the surface ocean (Jiang et al.,

2010), and (v) ocean acidification (Alegret et al., 2012). When combined, these

secondary effects caused the cascade of extinction. Others suggest additional events,

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particularly, the Deccan flood basalt volcanism in India, which may have enhanced the

effects of the bolide impact by releasing large amounts of sulfur and carbon dioxide into

the atmosphere (Stuben et al., 2003; Arens and West, 2008; Schulte et al., 2010; Tobin et

al., 2012; Keller, 2014). The main problem with Deccan volcanism as a trigger is that its

main eruptive phase preceded the K/Pg boundary (Robinson et al., 2009). Not only is the

cause of extinction unclear, but also the extinction pattern, which is key to resolving the

cause. The two proposed scenarios are either instantaneous or a gradual extinction which

started below or just above the boundary (Bernaola and Monechi, 2007). A gradual

extinction pattern may suggest that a natural climatic variation was at play; it is also

inline with the Deccan flood basalt hypothesis. However, recent studies suggest the mass

extinction could have occurred on a timescale as short as a human lifetime (Barnosky et

al., 2012).

Although the scientific community is in general agreement of the existence of a

bolide impact, it is unclear whether or not it was the principle cause of mass extinction.

The end-Cretaceous mass extinction event caused lasting effects that can be seen today in

the evolutionary and biogeographic structure of modern biotas (Krug, et al., 2009).

In the marine realm, the fate and recovery of the biological pump following the

end-Cretaceous is particularly well studied, yet still poorly constrained. What complicates

the situation further is that the global terrestrial and marine response was not homogenous

(Vilhena et al., 2013, Silbert et al., 2014; Alegret and Thomas 2013; Hull and Norris,

2011; Jiang et al., 2010) (Fig. 4).

1.2 The Biological Pump

The biological pump is a set of processes in which inorganic carbon (e.g. carbon dioxide)

is fixed into organic matter by primary producers via photosynthesis in the euphotic zone,

and then sequestered away from the atmosphere, generally by transport into the deep

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ocean (De La Rocha, 2014). This transport into the deep ocean is called export

production, and is facilitated by the passive sinking of particulate organic matter, through

the vertical migration of zooplankton, or downwelling of surface waters (De La Rocha,

2014). The biological pump affects not only the distribution of carbon, but also a host of

associated chemicals (e.g. oxygen, nitrogen and phosphorus) and trace metals in the

ocean (Archer, 2006). Simply put, it is the flux of organic matter from the surface ocean

to the deep ocean, and is a major term in the global carbon cycle. One of the most studied

aspects of the end-Cretaceous mass extinction event is how primary production and

export production, i.e. the biological pump changed at this boundary and the following

recovery. The physical environment, the type of phytoplankton present, the activities of

zooplankton, the presence of biominerals and clay minerals and the structure of the food

web all play a role in determining the efficiency and capacity of the biological pump (De

La Rocha, 2014).

1.3 The Isotopic Gradient

The end-Cretaceous mass extinction had ecological and biological effects on the carbon

isotopic values (δ13C) of the surface and deep water, and perhaps related to a collapse in

the marine food chain (Silbert et al., 2014; Belcher and Mander, 2012). Fossils provide

the prima facie evidence of mass extinction events, but the forensic evidence for causes

and environmental consequences lie primarily in the geochemical signature of sediment

cores (Kump, 2003). The δ13C values of planktonic and benthic foraminifera following

the end-Cretaceous extinction have been intensively studied. δ13C is a proxy for

palaeoproductivity (Cooke and Rohling, 2001), and the collapse of the planktic to benthic

δ13C gradient (i.e. the difference in carbon isotope values between the tests of planktic

and benthic organisms) is a key feature of the K/Pg sedimentary record (see Fig. 2). In the

modern ocean δ13C is controlled by the amount of atmospheric exchange of CO2 and by a

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balance between the amount of CO2 removed from and returned to the system. If

inorganic carbon is no longer removed from the system by primary producers and

transferred to the deep sea-floor then δ13C becomes more negative (Hsü et al., 1982).

Because the biological pump has a first order impact on the concentration of CO2 in the

atmosphere, it also has a first order impact on Earth’s climate (Archer, 2006).

.

Figure 2. K/Pg δ13C records from the Central Pacific DSDP site 577. The red circles represent δ13C differences between bulk δ13C and the benthic foraminifera Nuttalides. The other symbols represent differences between the benthic and various planktic foraminifera. The planktic foraminifera are as follows: Morozovella species (blue triangles), Praemurica uncinata (light green triangles), Praemurica taurica (yellow triangles), Rugoglobigerina rotundata (green squares), Parasubbotina pseudobulloides (blue diamond), Subbotina triloculinoides (pink diamond), and Pseudotextularia ultimatumida (purple square). All values are in parts per million. Figure modified from D’Hondt et al. 1998.

The creation of the surface-to-bottom marine isotopic gradient stems from the formation

of new organic matter facilitated by photosynthesis. Primary producers are strongly

discriminative against 13C in favour of the lighter carbon isotope 12C. This strong

preferential uptake of 12C causes the euphotic layer of the ocean to become depleted in

12C relative to 13C, resulting in an enriched δ13C value (D’Hondt et al., 1998). In the

present Atlantic Ocean surface waters are enriched in 13C of up to 2‰ relative to

underlying waters at depths 200-1000m (Hsü et al., 1982). Phytoplankton form organic

matter that is -20‰ to -23‰ relative to ambient water (Cooke and Rohling, 2001). When

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organic matter is remineralised, the δ13C depletion is ‘released’ into the water column. If

this remineralisation occurs within the euphotic layer, it offsets the enrichment effect due

to photosynthesis by resupplying 12C; i.e. decreasing the δ13C (Cooke and Rohling, 2001).

However, any loss from the surface layer through export productivity will cause a

decrease in the δ13C depleted marine organic matter from the surface layer. When organic

matter remineralises at depth, there is a transfer of 12C from surface to deep water. Hence,

enhanced export productivity will cause increasing gradients between δ13C enrichment in

surface waters and δ13C depletion in deep waters, which is recorded in calcareous fossils

(Cooke and Rohling, 2001). Given the above, the collapse of this gradient can be

interpreted as a switching off of the biological pump. This small gradient between

planktic and benthic signatures persisted for several hundred thousand years – shorter

than previously thought, but full pelagic ecosystem recovery required up to 3 Myr

(D’Hondt et al., 1998), indicating that Earth’s biogeochemical cycles were significantly

perturbed, while shelf seas recovered much quicker (Hsü and McKenzie, 1985). The

recovery took place over two steps, within 300 kyr the gradient stabilized, this sequential

recovery indicates that organic flux to shallow sediment recovered far before organic flux

to the deep ocean (Hull et al., 2011; Sepúlveda et al., 2009)

This study aims to develop a high resolution δ13C record from a bulk carbon

isotope analysis of a marine sediment core in El Kef, Tunisia. A collapse in the surface-

to-bottom marine isotopic gradient would be reflected in the bulk δ13C record as a

negative excursion, which has been shown in several other sites around the world

(Alegret et al., 2012). The record will be used to test the hypothesis that there was a rapid

resurgence in primary production by combining the bulk carbon isotope record with

previously extracted or published data of compound specific δ13C, calcium carbonate

(CaCO3), δ13C of benthic foraminifera and carbon isotopic photosynthesis fractionation

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(εp) from El Kef, Tunisia. This rapid resurgence hypothesis is an alternative to the

Strangelove and Living Ocean models, and has been previously suggested by Alegret et

al., 2013, Hull and Norris, 2011, and Sepúlveda et al., 2009.

1.4 The Strangelove Ocean and Living Ocean

The two main interpretations of the δ13C gradient collapse and interval of low organic

flux were the models: Strangelove Ocean and Living Ocean. The Strangelove Ocean first

proposed by Hsü and McKenzie (1985), suggests the impact caused a suppression of

photosynthesis and heavy environmental pollution. This resulted in the surface ocean

becoming mostly devoid of phytoplankton and degassing of CO2 into the atmosphere that

caused global warming, due to no uptake by photosynthesis. Also, the extinction of fecal

pellet producing zooplankton that were thought to be an important food source for

benthics supported this ‘dead ocean’ scenario went on for several hundred thousand years

(Alegret and Thomas, 2009).

The alternative model, the Living Ocean suggests there was a rapid recovery of

primary production on the basis of carbonate proxies (D’Hondt et al., 1998). There were

non-calcifying phytoplankton present in the surface ocean performing photosynthesis, but

most organic matter was recycled in the upper ocean, due to a more efficient cycling

meaning there was very little export production (Alegret and Thomas, 2009). This was

thought to be a natural consequence of mass extinction; due to the absence of large

pelagic grazers and smaller phytoplankton, the packaging of biomass into large particles

that sink to the deep seafloor is greatly reduced (D’Hondt et al., 1998). The collapse of

the biological pump was hypothesized to have persisted for several hundred thousand

years after the mass extinction (Alegret and Thomas, 2009).

Both of these hypotheses have been falsified. Both the Living Ocean and

Strangelove Ocean suggest that a prolonged (3–4 Myr) global decline in export

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production is responsible for the collapse of the surface‐to‐bottom δ13C gradients (Hsü

and McKenzie, 1985; Zachos et al., 1989; D’Hondt et al., 1998; D’Hondt, 2005). The

lack of significant extinction among benthic foraminifera argues strongly against both

models, because life on the deep-sea floor is dependent on the flux of organic matter from

the surface ocean. There would have been a severe extinction of benthic foraminifera if

there were a prolonged lack of food. In addition, the rapid resurgence of primary

production in terms of biomass is supported by organic biomarker data (Sepúlveda et al.,

2009) and Ba/Ti ratios, which is a proxy for export production (Hull and Norris, 2011).

Furthermore, models have concluded that there were no physical consequences of the

impact that would have caused a multi-million year collapse of production. There was a

very brief global darkness – ‘impact winter’, which saw low light levels and colder water

(Belcher and Mander, 2012) resulting from the atmosphere being filled with dust and

sulfate aerosols. Based on modeling experiments, this lasted for less than a year

(D’Hondt, 2005), and with phytoplankton typically doubling their biomass on timescales

of hours to days, maintaining a Strangelove ocean once light levels recovered is unlikely

(Hull and Norris, 2011; Alegret and Thomas, 2013). Collapse of primary production

during a minimum period of 3 months is to be expected – laboratory tests on modern

species subjected to low light levels reveal a 2-8 week survival timescale, however it took

a few thousand years for production levels to be sufficient enough to support abundant

small zooplankton (Belcher and Mander, 2012). Furthermore, there is no global response

as hypothesized by the two models.

The alternative emerging hypothesis is one of a heterogeneous response rather

than a global response. It suggests a very rapid full recovery, and no prolonged collapse

in primary production (Fig. 3). Ultimately, other factors besides a collapse in the

biological pump altered the isotopic signature of the K/Pg oceans.

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Figure 3. Depictions of previous end-Cretaceous mass extinction conceptual models Strangelove and Living Ocean proposed by Hsü and McKenzie (1985) and D’Hondt et al. (1998), and the more recent Rapid Recovery model notably suggested by Alegret et al., (2013), Hull and Norris (2011), and Sepúlveda et al., (2009), among others.

1.5 The Benthic Community

Following the end-Cretaceous extinction there was a restructuring of the agglutinated and

calcareous benthic foraminifera community (Thomas, 2007). Most scientists suggest that

this is due to the collapse of the pelagic food web, especially because deep-sea ocean

temperatures were largely unaffected due to its large thermal mass (Schulte et al., 2010).

The presence of benthic foraminifera in addition to biogenic Barium records suggests

there was no global decline in export production (Hull and Norris, 2011). The bentho-

pelagic and dominant supply of food to the benthos may have been different in the K/Pg

oceans (Thomas, 2007; Alegret and Thomas, 2005). Also, the formation of sticky

polysaccharides by cyanobacteria and diatoms – which is a mechanism that forms large

aggregates of rapidly-sinking organic material (Thomas, 2007), could have aided the

recovery of the biological pump. This makes the fact that the size of the primary

producers decreased post-impact (D’Hondt, 2005) and the absence of fecal pellet

producing zooplankton (Alegret and Thomas, 2009) less meaningful. Benthic

foraminifera live for a few months to years, meaning export production could not have

been lacking for more than several years, if it did benthic extinction would likely have

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occurred (Thomas, 2013). Shallow-water species did not suffer more extinction compared

to deeper dwelling species, which was the consensus for two decades (Culver, 2003).

The assemblages following the end-Cretaceous extinction were much less diverse

but there is no agreement on an environmental interpretation which caused these small

changes in the community structure. In the Pacific, diversity and heterogeneity of benthic

foraminifera rapidly decreased across the boundary, yet food supply was high, suggesting

a stressed environment (Alegret and Thomas, 2009). One hypothesis that explains how

benthic foraminifera survived across the K/Pg is that they can tolerate oligotrophic

conditions (Alegret and Thomas, 2005).

The collapse of the δ13C gradient may not reflect a collapse in the biological

pump. Three different scenarios may explain the negative carbon isotope anomaly.

Firstly, it may have been caused by an injection of isotopically light carbon into the

ocean-atmosphere system, either by biomass burning, or methane liberation caused by

dissociation of gas hydrates due to continental slumping (Thomas, 2007). Secondly, the

negative anomaly may be due to ‘vital effects’ (Alegret and Thomas, 2009). The carbon

isotope values measured pre- and post-extinction are derived from different species owing

to the severe extinction of calcareous nannoplankton and planktic foraminifera. Post-

extinction calcareous nannoplankton species such as the calcareous dinoflagellate cyst

Thoracosphaera naturally have very light carbon isotope signatures (Alegret et al., 2012),

i.e. depleted in 13C. In addition, planktonic foraminifera had relatively light δ13C

signatures compared to late Cretaceous species, so this alone could account for some if

not all of the negative shift in δ13C (Hull and Norris, 2011). It is possible that these

species had different primary sources of carbonate that fractionate differently compared

to Cretaceous carbonate. Lastly, in some sites the carbon isotope signal may be affected

by diagenesis, which is common in low carbonate sediments (Alegret and Thomas, 2009).

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1.6 Heterogeneous Response

The effect on export production and timing of recovery varies greatly among different

oceanic sites (Fig. 4). The Pacific Ocean and New Zealand experienced increased rates of

export production, while export production decreased in the Indian Ocean, Tethys Ocean

and Atlantic Ocean, with some Atlantic sites showing no changes (Hull and Norris, 2011;

Sibert et al., 2014). Pacific sites show sharp increases in benthic foraminiferal

accumulation rates and infaunal taxa in the earliest Paleocene (Alegret et al., 2012).

Restructuring of the benthic foraminifera community also varied geographically and

bathymetrically (Thomas, 2007). At some locales, benthic foraminiferal community

structure indicates increases in food supply to the deep ocean (Pacific Ocean), even in

cases where δ13C gradients or sedimentation rates imply decreased productivity and

export (Alegret and Thomas, 2009). A hypothesis regarding these different responses is

that it is related to different habitat types (Hull and Norris, 2011).

The biological response to the impact has, over time, shown itself to be much

more complex than previous sweeping generalizations. There was no uniformly dead

ocean that was hypothesized by the Strangelove and Living Ocean models.

Mid-trophic level species were sustained or even increased regionally. Pelagic fish

exhibit a geographically varied response (Sibert et al., 2014). Increases in ichthyoliths

were found in the Pacific sediment record, and a decrease in Tethys and South Atlantic

(Sibert et al., 2014). Although there was a marked extinction of primary producers in the

Pacific, some species must have been present in order to support mid-trophic level fish –

the link between primary producers and top predators (Sibert et al., 2014). It seems non or

poorly fossilized primary producers sustained the food web as primary production in the

Pacific did not fall after the end-Cretaceous mass extinction event (Sibert et al., 2014).

Bivalve extinction patterns indicate less extinction away from the tropics (Vilhena

et al., 2013). This suggests that either high latitude species were more resistant to

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extinction, or the intensity of the extinction mechanism decreased away from the tropics,

or both (Vilhena et al., 2013). In the past, bivalve records were interpreted as showing

globally uniform extinction intensities (Raup and Jablonski, 1993), which was in

agreement with the Strangelove hypothesis. In the marine realm, there are some taxon-

specific cases where survivorship is linked to ecological traits – for instance, the reliance

on photosymbiosis among scleractinian corals severely reduced survivorship (Kiessling et

al., 2004) and sea urchin feeding strategy correlates positively with survivorship (Smith

and Jeffery, 1998).

Not only did the biological effects vary, but also the pace at which ecosystems and

communities recovered (Sibert et al., 2014; Alegret and Thomas, 2005). A latitudinal

extinction gradient was found for calcareous nannoplankton; extinction rates were higher

in the Northern Hemisphere ocean basins, with low levels of diversity for 310 kyr, while

in the Southern Hemisphere extinction rates were lower in addition to an almost

immediate return to pre-K/Pg population numbers (Jiang et al., 2010).

Studying the different patterns of extinction and recovery bring scientists closer to

determining the killing mechanism and above all; ecosystem resilience, climate

thresholds and sensitivity to catastrophic events.

These variations in extinction intensity and dynamics of recovery exemplify the

complexity of the system following the end-Cretaceous. Lastly, Hull and Norris (2011)

not only illustrated the global heterogeneous response, they also showed that different

proxies display diverse responses of export production at the same site (see Fig. 4). This

is a strong argument against the global decrease in export production and a globally

synchronous event. It also advocates the need for a multiproxy approach, and to not

generalise the response of the ocean or even an ocean basin when studying the carbon

cycle of the K/Pg oceans.

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Figure 4. Map depicting heterogeneous response in export production across the K/Pg boundary based on different proxies. Modified from Hull and Norris, 2011.

1.7 The El Kef Coring Program

The Upper Cretaceous and Lower Paleogene sediments that bracket the K/Pg are among

the most studied deposits in the geological record (Schulte et al., 2010). More than 350

K/Pg sites are known, and as the GSSP site El Kef has been in the center of the K/Pg

debate for the past three decades. The El Kef Coring Program has brought together an

international team of scientists who share a common interest; exploring ecosystem

responses to Earth’s most recent mass extinction event (El Kef Coring Program 2014).

This study investigates the collapse of the marine surface-to-bottom δ13C gradient,

and whether or not it reflects a sustained extinction. The persistent collapse of the

surface-to-bottom δ13C gradient coupled with a lack of extinction of benthic foraminifera

must be explained. It is clear that the end-Cretaceous mass extinction event is complex

and variable in nature – both spatially and temporally, and for that reason has puzzled

scientists for three decades. As part of the El Kef Coring Program, this study aims to

contribute to the growing body of literature suggesting a rapid resurgence in primary

production, which seemingly contradicts the collapse of the δ13C gradient, a main feature

of the K/Pg oceans.

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2. Materials and Methods

2.1 El Kef, Tunesia

El Kef is the Global Stratotype Section and Point (GSSP) for the base of the Danian

stage. The black Boundary Clay is characterised by a 1-3 mm thick rust coloured layer at

the base. This is where the “golden spike” was placed and marks the precise definition of

the K/Pg boundary. The thickness of the boundary clay is ~1m, and spans 10 kyr

(Mukhopadhyay et al., 2001). It is characterised by a number of geochemical anomalies,

e.g. iridium (Hsü et al., 1982) and shocked quartz, and is underlain by a Maastrichtian

stage grey marl (Molina et al., 2006).

Figure 5. Location of the El Kef section (modified after Stuben et al., 2003)

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The Ir anomaly is the main method of correlation with other sites. Lastly, the site has

excellent preservation of calcareous micro- and nannofossils and dinoflagellates that

allow for further global correlation (Molina et al., 2006).

Because El Kef is a shallow marine section – between the mesopelagic and

epipelagic zone at 200m (see Fig. 5), it is more complete stratigraphically and with higher

rates of sedimentation. The data presented in this paper represents conditions of the outer

shelf or continental platform of the Tethyan Sea (Keller and Lindinger, 1989).

The El Kef site has continuous sedimentation over the K/Pg, and the Boundary

Clay is considerably thicker than the other locations considered for the K/Pg boundary

GSSP (Molina et al., 2006). Brazos in USA, Stevens Klint in Denmark and Zumaya in

Spain have boundary clay/shale thicknesses of 10- to 25-cm (Schulte et al., 2006), 5- to

10-cm (Surlyk et al., 2006), and 10 cm (Molina et al., 2009), respectively. The Boundary

Clay at El Kef has a sedimentation rate of 7.96 ± 1.30 cm kyr-1 (Giron, 2013). Although it

is a small drop from the average Maastrichtian sedimentation rate, it provides a high-

resolution record of the K/Pg interval, which is ideal when studying how this event

effected the shelf sea environment (Giron 2013). In deep-sea sections the clay layer is

only a few mm to a few cm thick (Keller and Lindinger, 1989), meaning that El Kef

provides a unique opportunity to study the end-Cretaceous mass extinction event.

2.2 Sampling Strategies

The El Kef Coring Program is based on four holes that were drilled in December 2013

and January 2014. This particular location was chosen as it has the best exposure and

minimal erosion. Cores at all four holes were recovered: Hole A, Hole B, Hole C, and

Hole D (Fig. 6). The cores were processed in November 2014 at the Bremen Core

Repository, MARUM - Center of Marine Environmental Sciences, University of Bremen,

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where the science team convened for 5 days to carry out data collection and sampling

protocols similar to International Ocean Drilling Program projects.

Figure 6. Location of the four holes (A-D) drilled in El Kef. The coordinates of this location is 36°09’13.63”N 8°38’57.33”E and the scalebar is 104 m across.

The samples analysed for this paper are from Hole A, Core 16 (Fig. 7). Based on

biostratigraphy and lithology, the K/Pg boundary was determined to be between 85 and

115 cm downcore. The samples are 1 cm wide. 30 samples were taken at fine resolution

(1 cm) at the boundary, and 38 samples above the boundary at a lower resolution (2 cm).

Samples were taken from the surface down to 116 cm, this interval represents

approximately 15 kyr. After mechanical crushing and powdering using a pestle and

mortar, with careful cleaning in between samples, the samples were dried using a LyoDry

Compact freeze dryer (Mechatech Systems Ltd).

Figure 7. LineScan image of Core 16 from Hole A. The core is in total 150 cm long. The location of the boundary is denoted by the red arrow, and is at approximately 110 cm below the surface. The transition from marl to clay is evident by the decrease in sediment lightness following the K/Pg boundary.

  17  

The outcrop data from the site has been plotted for core correlation purposes, and it

shows an overall -3.6‰ excursion in the δ13C of carbonate following the impact (see

Appendix A).

2.3 Carbon Isotopic Analysis

Stable isotope values of sediment samples were measured in the Rutgers University

Stable Isotope Laboratory. Measurements were made on a VG Prism II mass

spectrometer using a Multiprep automated carbonate preparation system. Samples were

reacted in 100% phosphoric acid at 90°C. Oxygen and carbon isotopic values are reported

in per mille difference (‰) from the Vienna Pee Dee belemnite (VPDB) by normalization

to NSB-19 (limestone) and NSB-18 (carbonatite) standards. Differences in isotope ratios

are expressed in conventional delta (δ) notation, defined by:

𝛿!"# =  𝑅!"# −  𝑅!"#

𝑅!"#  ×  1000

Where sam is the sample value, std is the standard value, and R is an isotopic ratio. The

typical deviations (1σ) of the standards (minimum of 6 standards measured with each run

of 25 samples) are 0.05‰ and 0.04‰ for δ18O and δ13C, respectively.

2.4 Bulk Nitrogen isotopic Analysis

For nitrogen isotopic analyses, a subsample of approximately 10 g was selected for a lack

of visible fracture fills and surface alteration, and cleaned by sonication in ethanol for 1

hour, and in ultrapure deionized water (>18 MΩ) three consecutive times. Samples were

then powdered using an agate ball mill. Powders were acidified overnight in an excess of

20 % HCl solution at 40° C to remove carbonates, then rinsed three times with deionized

water before being dried overnight at 40° C. Nitrogen isotopes were measured via

  18  

elemental-analyzer continuous-flow isotope ratio mass spectrometry (EA-CF-IRMS) at

Brown University. Decalcified powders in quantities of 25-45 mg were weighed into tin

capsules and combusted in a Costech 4010 elemental analyzer system coupled to a

Thermo Finnigan Delta-V-Plus Isotope Ratio Mass Spectrometer through a

ThermoFinnigan CONFLO III gas interface. Measurements were corrected using

calibrated internal laboratory standards. The standard for nitrogen isotope measurements

was atmospheric air. Analytical precision based on repeated measurement of standards

was 0.32 ‰.

2.5 δ13C of Anomalinoides acuta and CaCO3

The δ13C of benthic foraminifera Anomalinoides acuta and CaCO3 concentrations in the

El Kef boundary clay layer was copied from data tables in Keller and Lindinger (1989).

(See corresponding references for details on collection methods and sample preparation

procedures).

2.6 Cleaning Protocol and Sample Preparation for organic geochemistry work

Weathered edges were removed using a rock saw, followed by rinses with B-Pure water

and acetone, and later sonicated in B-Pure water for 30 min to remove surface

contamination. Samples were dried, crushed with a metal press, and pulverized to a fine

power using an agate mortar and pestle. All laboratory equipment was rinsed with high-

purity acetone, methanol (MeOH), and dichloromethane (DCM) between samples to

avoid cross contamination. Powdered samples were then split for bulk elemental analysis

and lipid extraction All glassware, aluminum foil, silica, quartz wool and quartz sand

were combusted at 500ºC for at least 12 hours to remove organic contamination; metal

tools were rinsed in MeOH and DCM.

  19  

2.7 Lipid Extraction and Separation

About 5-10 g of powdered rock were extracted with DCM: MeOH (9:1 v/v) using a

Dionex ASE 250 accelerated solvent extraction system. Cells were packed with quartz

filters and quartz sand. Before extraction, samples were spiked with 1 mg of d4 C29 ααα

(20R)-ethylcholestane. The total lipid extract (TLE) was then concentrated, mixed with

activated copper powder for 12 hours to remove elemental sulfur, and filtered through a

pipette column packed with quartz wool to remove impurities. Copper was activated

using 4N HCl for 1 hour, then rinsed with water to neutrality, and finally rinsed with

MeOH and DCM (10x). Asphaltenes were precipitated from TLEs in 10-40 mL of hexane

overnight at ~4ºC and by centrifugation at 2,500 rpm for 30 minutes. The maltene

fraction (supernatant) was pipetted out and collected, and the entire process of asphaltene

precipitation was repeated three times. Maltenes (<5 mg) were then separated into three

fractions using glass pipette columns filled with silica gel. The dead volume (DV) of each

column was calculated by the addition of n-hexane. Aliphatic hydrocarbons, aromatic

hydrocarbons, and polar compounds were eluted in n-hexane (3/8 DV), n-hexane:DCM

(8:2 v:v, 4 DV), and DCM:MeOH (4:1 v:v, 4 DV), respectively. After separation, the

aromatic fraction was spiked with d4 C29 ααα (20R)-ethylcholestane, after ensuring a

complete separation from the aliphatic fraction previously spiked as a TLE.

2.8 Compound-specific Carbon isotopes

Carbon isotopic analysis of kerogen and the compound-specific isotope analyses on the

isoprenoid phytane and carbon isotopic fractionation (εp), were determined by isotope

ratio monitoring-gas chromatography/mass spectrometry using a Thermo DeltaVPlus MS

coupled to an Agilent 6890 GC via a GCC-III combustion interface at Brown University.

The δ 13C values for individual compounds were determined based on introduction of

reference CO2 gas pulses. The gas pulses were previously and subsequently calibrated

  20  

with a series of well-characterised standard materials. Values are expressed in ‰ relative

to the Pee Dee belemnite (PDB). The value of εp represents several terms, it is defined

by:

𝜀! =   𝜀! −𝜇𝜈!

𝜅[𝐶𝑂!]

where 𝜀! is the isotopic shift associated with carbon fixation (≃ 25–30‰), 𝜅 is

proportional to the permeability of the algal cell wall, 𝜈! is the volume-to-surface-area

ratio of the cell, 𝜇 is the specific growth rate, and [CO2] is the concentration of dissolved

carbon dioxide (Rothman 2001).

3. Results

All curves are illustrated in Fig. 8.

Figure 8. Geochemical parameters from El Kef showing affects of the bolide impact at the K/Pg boundary. The 1m shaded interval is the clay layer which starts at the K/Pg boundary, set at 0 cm. The plotted interval represent ~15 kyr, and the clay layer is ~10 kyr (Mukhopadhyay et al., 2001). The Figure shows bulk δ13C of carbonate (see Fig. 5-6 for location) compared with previously analysed, published, and in preparation data from El Kef. An image of core 16 is shown on the left side. The planktic foraminifera Zones are from Keller 1988, and correlated to the δ13C of carbonate curve by comparison with lower resolution outcrop data generated previously. (See Appendix B for data tables)

  21  

3.1 Bulk Carbon Isotopes

Throughout the record, δ13C values range between -1.76‰ and 1.50‰. The peak

Cretaceous bulk δ13C level of 1.50‰ is followed by a sudden negative shift that marks

the K/Pg boundary. This negative trend continues across P1a reaching a minimum of

-1.76‰ 89 cm above the boundary. There is an overall negative shift of 3.26‰, and there

is no sign of recovery in the ~15 kyr time interval (inferred from cosmogenic dust 3He

dating of Mukhopadhyay et al., 2001, and backed up by the sedimentation rate of Giron

2013).

3.2 δ15N

The δ15N values ranges between 3.55‰ and 5.79‰ throughout the record. The minimum

value occurs in the Cretaceous just below the boundary, then followed by a positive

excursion reaching a peak of 5.79‰, 101 cm above the boundary. The δ15N record does

not revert back to Cretaceous values or show any sign of recovery in the ~15 kyr time

interval.

3.3 CaCO3

Calcium carbonate (CaCO3) shows a large range of values in this record, ranging between

0.89% and 48.82%. The peak value of 48.82% appears 5 cm below the K/Pg boundary

and decreases dramatically at the boundary to 0.89%. These low CaCO3 levels above the

boundary – ranging from 0.89% to 10.5%, are sustained in the entire ~15 kyr interval.

3.4. δ13CBenthic

The δ13C of the low oxygen tolerant epifaunal benthic foraminifera Anomalinoides acuta

values ranges between 0.045‰ and 0.84‰ throughout the record. Across the boundary

there is a positive excursion of 0.54‰, following this peak value at 22cm, the

  22  

measurements gradually become more negative, tending towards pre-extinction values.

At 97cm above the boundary δ13CBenthic is 0.34‰ more negative than the pre-extinction

value.

3.5 Compound-specific Carbon isotopes

δ13Ckerogen values range between -27.28‰ and -25.3‰, and δ13Cphytane range between -

33.83‰ and -30.72‰ throughout the record. At the boundary, both δ13Ckerogen and

δ13Cphytane experience a sudden decrease of 1.67‰ and 1.17‰ respectively. This negative

excursion continues until 8 and 4 cm above the boundary, respectively. There is an

overall negative δ13Ckerogen excursion of 1.95‰, while δ13Cphytane has an overall negative

excursion of 3.06‰. Carbon isotopic fractionation (εp) values range between 28.32‰ and

24.35‰ throughout the record. There is a sharp increase in εp of 2.3‰ at the boundary,

after which it quickly starts to recover. At 8 cm above the boundary – equivalent to ~1

kyr, εp has fully recovered. All three of these parameters show recovery to pre-K/Pg

values, or near that, by 16 cm above the boundary, which corresponds to only ~2 kyr.

4. Discussion

4.1 Interpretation

Isotopic evidence from carbonate and biomarkers show a contrasting duration and

magnitude of the negative carbon isotopic excursion. The sudden decrease in bulk δ13C of

carbonate may reflect a collapse in the biological pump and more C12 in the system due to

inefficient uptake by primary producers. This decrease in bulk δ13C has been shown in

several other sites around the globe, including the Pacific, Southeast Atlantic, and

Southern Ocean, although the pattern of change may vary geographically (Alegret et al.,

2012). Constrastingly, δ13Ckerogen and δ13Cphytane, and εp show a fast recovery in the order

  23  

of 1-2 kyr. This suggests that the perturbation associated with the end-Cretaceous was

very short lived, although the bulk δ13C shows no sign of recovery and becomes

increasingly more negative over the ~15 kyr interval.

The total fractionation of carbon associated with photosynthesis is represented by

εp, and can therefore be used as an indicator of photosynthetic activity. A decline in the

algal growth rate may have caused the increase in εp, if this is indeed what the data

suggests then photosynthesis fully recovered after only ~1 kyr. It may also indicate higher

atmospheric CO2 conditions, although to prove this one would require knowledge of both

εp and phytoplankton growth rate (Laws et al., 1995). A spike in atmospheric CO2

supports the possibility of a brief warming event following the bolide impact, and ocean

acidification. Ocean acidification as a kill mechanism would explain why non-cacifying

organisms suffered considerably less extinction than calcifyers.

Kerogen is insoluable organic matter that represents the remains of a wide variety

of organisms, both terrestrial and marine, and is responsible for accumulation of oil and

gas (Eglinton et al., 1991). Isotopically lighter δ13Ckerogen suggests that carbon is not being

efficiently removed from surface waters. The δ13Ckerogen values recovered to near pre-

boundary levels after only ~2 kyr, indicating that photosynthesis had recovered. Phytane

is an organic molecule derived from phytol, the esterified side chain of most chlorophylls

and consequently characteristic for all primary producers using photosynthesis (Schoon et

al., 2011). Phytane has been the subject of compound-specific carbon isotopic analysis

since the advent of the technique. Much like δ13Ckerogen, δ13Cphytane displays a brief

negative excursion, followed by a rapid recovery to more enriched values – although not

to pre-boundary levels. Like the δ13Ckerogen record, this suggests that factors controlling

isotopic fractionation in primary producers such as the δ13C of the carbonate source, CO2,

growth rates, etc. – so-called ‘vital effects’, were changed for a relatively short period of

  24  

time. The fact that δ13Cphytane and δ13Ckerogen values remained only slightly more depleted

than pre-boundary values might point to fact that real change in δ13C of DIC pool was not

more than 1-2‰, compared to 3.26‰ which the bulk δ13C record shows. Both δ13Ckerogen,

and δ13Cphytane suggest a rapid resurgence in primary production, but there is a possibility

that export production levels remained slightly suppressed, or unstable. Higher resolution

biomarker data from the boundary layer at Kulstirenden, Denmark has shown primary

production recovering in less than 100 years – once optimal solar radiation levels returned

(Sepúlveda et al., 2009).

The Maastrichtian marl is rich in CaCO3 (~50%), and the drastic decrease in

CaCO3 following the K/Pg boundary highlights the loss of calcifying organisms. This

heavily reduced CaCO3 content continued for 230 kyr at El Kef (Berggren et al., 1985).

All parameters, with the exception of bulk δ13C, CaCO3, and δ15N show recovery to near

pre-K/Pg levels. However, the system could have recovered without the presence of

calcifying organisms. Non-calcifying primary producers may have sustained the benthic

community by forming the base of the marine foodchain. Non-calcifying haptophytes,

diatoms, and organic walled and calcareous dinoflagellates did not suffer a severe

extinction like calcareous nannoplankton and planktic foraminifera (Alegret et al., 2012).

The importance and resilience of prokaryote primary producers has been demonstrated in

Danish sections (Sepúlveda et al., 2009), and diatoms and radiolarians in New Zealand

(Hollis et al., 2003). A molecular clock study showed non-calcifying haptophytes having

high diversity before and after the K/Pg boundary, with no bottlenecking associated with

the event (Medlin et al., 2008). The presence of non-calcareous primary producers would

explain the lack of extinction of benthic foraminifera. It is often assumed that

photosynthesis is necessary for the survival of benthic communities due to the biological

pump. In the modern ocean the bentho-pelagic link appears to be strong; benthic

communities are dependent on surface production as a food supply (Thomas, 2013).

  25  

However, chemosynthesis may have played a larger role in a much warmer ocean

compared to the modern ocean where it only accounts for ~1.5% of total oceanic primary

production (Middelburg 2011).

The enrichment in the δ13C of A. acuta following the boundary may be interpreted

as a decrease in the organic carbon oxidation at the sediment-water interface as a result of

the decrease in primary production in the surface ocean, which in turn decreases export

production (Keller and Lindinger, 1989). This enrichment in benthic δ13C was sustained

for ~12 kyr. Again, these values may be the result of ‘vital effect’ following the change of

assemblages with different physiological characteristics compared to Cretaceous forms.

The positive excursion in δ15N above the boundary suggests a decrease in the nitrate

availability (a macronutrient), and a nutrient starved environment. The δ15N values do not

recover in the ~15 kyr record, but it shows near pre-boundary values at 66 cm (~8 kyr),

where it was 4.29‰ compared to 3.55‰ below the boundary. There may have been other

periods with “normal” nitrate levels; it is hard to tell due to the low-resolution record, but

it may suggest a fluctuating food supply. There is evidence that suggests that the early

Paleocene oceans were unstable and variable environments (Alegret and Thomas, 2007),

and changes in the benthic community structure have been interpreted as being a result of

a drop in food supply to the benthos (Alegret and Thomas, 2004). However, certain

epifaunal benthic foraminifera that lived close to the sediment surface were tolerant of

oligotrophic conditions (Alegret and Thomas, 2005). Additionally, the food supply may

have differed in nature due to the change in phytoplankton composition. In the modern

ocean few organisms consume dinoflagellates (e.g. Thoracosphaera), therefore benthic

organisms may have lived in a stressed environment because of this change (Alegret and

Thomas, 2005).

In concert, data generated for this thesis argue against a prolonged collapse in

marine primary productivity. These results oppose the once credited Strangelove Ocean

  26  

model that suggested suppressed levels of primary production persisting for hundreds of

thousands of years.

4.2 Factors influencing bulk δ13C

There are a number of factors besides primary and export production that may influence

bulk δ13C. The carbon isotopic signal measured from bulk sediments is the net result of a

highly complex interplay of sedimentological, physico-chemical and biological processes

that have affected the rock record (Wendler, 2013). The major influencing components

are (i) the δ13C dissolved inorganic carbon (DIC) of the ambient water, (ii) the type of

carbonate grains and taxonomic composition of calcareous shells with their specific

habitat and vital effects and (iii) diagenetic alterations (syn-depositional and burial)

(Minoletti et al. 2005) (Wendler, 2013).

The change in assemblages from the Cretaceous to the Paleogene introduced

forms that may have had different sources of carbonate. The new sources would

fractionate differently causing lighter δ13C signatures. Other factors that may have caused

the shift in δ13C include atmospheric CO2 levels, growth rate, and cell geometry. For

instance the calcareous dinoflagellate cyst Thoracosphaera which bloomed

opportunistically worldwide (Thomas, 2007). Smaller forms, particularly nonsymbionts

are generally isotopically lighter (Alegret et al., 2012). Physiological parameters vary

substantially across phytoplankton species, which is why they fractionate differently

(Popp et al., 1998).

Bulk δ13C records reflect multiple and complex signals, a part of the negative shift

may come from the change in the carriers of the isotopic signal before and after the

extinction (Alegret et al., 2012). Furthermore, the effects of the solubility pump on the

δ13C of DIC, which works in the opposite direction of the biological pump becomes more

  27  

pronounced during periods of reduced export production. Therefore it may also have

contributed to the negative shift (Cameron et al., 2005).

4.3 Further research

Following this high-resolution bulk δ13C study, the faunal turnover and evolutionary rates

will be determined by quantitative analysis of benthic foraminifera assemblages from the

same sediment samples. This will give more insight into how benthic foraminifera were

affected by the impact. The species present in the samples will provide also

paleoecological and paleoenvironmental information based on the niches they occupy in

the modern ocean. In addition, specific foraminifera-based proxies will be used to

determine export production, giving an alternative and more specific record compared to

the bulk δ13C record from the same core. These studies will bring the El Kef group closer

to achieving their overreaching goal to investigate a number of key questions surrounding

the end-Cretaceous mass extinction. One of which is the persistent collapse of the

surface-to-bottom δ13C gradient and the survivorship of benthic foraminifera. Due to the

high sedimentation rate and excellent preservation during this interval the El Kef section

provides a unique opportunity to study the end-Cretaceous mass extinction.

There are several up and coming proxies that are showing great potential. One of

which is the application of novel tracers (molybdenum, cadmium and zinc isotopes) to

shallow marine sediments as a way to quantify biogenic activity. Furthermore,

atmospheric CO2 levels during this interval are poorly constrained, independent controls

on CO2 using the boron isotope-pH proxy are being developed. It is important to

understand the relationship between the biological pump and climate change. This will

provide valuable data for model projections of biological feedbacks in the high CO2

world we are entering.

  28  

5. Conclusions

The compound-specific organic δ13C suggests a very transient perturbation (1-2 kyr), this

is not in agreement with the δ13C measurements of bulk carbonate from the same site.

The significance of the sustained negative shift in bulk δ13C remains in doubt. There are

several potential influences over bulk δ13C that could explain the shift that took millions

of years to recover. The negative excursion of the bulk measurements may be related to a

change in the microfossil assemblages and ‘vital effects’, and not a collapse in the

biological pump. The dramatic decrease in the CaCO3 content of the sediment highlights

the extinction of calcifying organisms. Non-calcifying primary producers may have

sustained the benthic community by forming the base of the marine foodchain.

It is clear that the two existing conceptual models – Strangelove and Living Ocean

are out-dated. Compound-specific isotopic proxies are consistent with the benthic

foraminifera records, and call for a new rapid recovery model. This rapid recovery is

unlike any other mass extinction events that have adequately high-resolution records.

Productivity following the Permian-Triassic (~252 Ma) and the Triassic-Jurassic (~201.3

Ma) both took significantly longer to recover from their perturbations. For the K/Pg it is

thought that a brief kill mechanism could have occurred on a timescale as short as a

human lifetime, making it a unique mass extinction event.

This study highlights the importance of a multiproxy approach and challenges the

meaning of the paleoproductivity proxy δ13C. All proxies have limitations in preservation

and interpretive power associated with them. Separate proxies may tell different stories,

but when used together they could potentially point to the same conclusion and allow for

a more robust interpretation.

Studies of the end-Cretaceous act as bridges between potential future conditions

and ancient environments, which can be used as a way to predict how the Earth will

  29  

change. Overall these studies contribute to our understanding of ecosystem resilience,

climate thresholds and sensitivity to catastrophic events.

6. Acknowledgments

I would like to thank my supervisor Dr. Jessica H. Whiteside for her continued support

and being a source of inspiration. Also, Rutgers University for running the sediment

samples and providing the δ13C measurements.

  30  

Appendix A

Figure 1: Outcrop data from El Kef, Tunisia.

Appendix B

Distance from boundary (cm) δ13Cbulk (‰) 108 -1.55 106 -1.58 102 -1.13 100 -1.56 98 -1.37 89 -1.76 87 -1.03 85 -0.99 80 -0.80 78 -0.99 75 -1.02 73 -0.95 71 -1.02 69 -1.03 67 -0.55 65 -0.72 63 -0.72 59 -0.54

  31  

57 -0.72 55 -0.51

52.75 -0.42 50 -0.17 48 -0.37 46 0.15 44 -0.24 42 0.13 40 -0.01 38 0.58 36 -0.01 34 0.36 32 0.75 30 0.00 28 0.61 26 0.01 23 0.34 22 0.06 21 0.13 20 -0.07 19 0.17 18 -0.08 17 0.30 16 -0.08 15 0.06 14 -0.03 13 0.10 11 0.91 10 0.13 9 0.16 8 0.17 7 0.74 6 0.60 5 0.54 3 1.24 2 1.25 1 1.41 0 1.50 -1 1.47 -2 1.38 -3 1.39 -4 1.43 -6 1.38

Table 1: K/Pg δ13Cbulk from core 16, hole A.

  32  

Distance from boundary (cm)

δ13Ckerogen(‰) εp(‰) δ13Cphytane(‰) δ15N(‰)

116 -26.05 24.35 -31.98 5.32 101 -26.42 24.75 -31.37 5.79 66 -26.33 24.93 -32.13 4.29 16 -26.41 25.1 -31.38 5.78 8 -27.28 26.32 -31.58 4.78 4 -27.27 27.8 -33.83 4.72 0 -27 28.32 -31.94 4.5 -4 -25.33 26.2 -30.77 3.55 -16 -25.3 26.21 -30.72 3.55

Table 2: K/Pg δ13Ckerogen, εp, δ13Cphytane and δ15N data from El Kef, Tunisia. Sepúlveda et al. (In preparation).

Table 3: K/Pg CaCO3(%) data from El Kef, Tunisia (Keller and Lindinger 1989).

Distance from boundary (cm)

CaCO3(%)

107 7.6 102 8.74 97 9.75 92 9.75 87 8.03 82 8.7 77 7.36 72 6.67 67 4.8 62 10.5 57 7.67 52 7.18 47 8.58 42 5.61 37 5.76 32 5.62 27 5.07 22 3.3 17 2.1 12 2.55 7 4.47 0 0.89 -2 6.04 -5 48.82

  33  

Table 4: K/Pg δ13C benthic of the low oxygen tolerant epifaunal benthic foraminifera Anomalinoides acuta from El Kef, Tunisia (Keller and Lindinger 1989).

Distance from boundary (cm)

δ13C benthic(‰)

102 0.328 97 0.045 92 0.29 87 0.438 82 0.281 77 0.523 72 0.423 67 0.637 62 0.375 57 0.523 52 0.627 47 0.496 42 0.737 37 0.71 32 0.839 27 0.556 22 0.92 17 0.558 7 0.783 -2 0.388 -5 0.061

  34  

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