university of copenhagen
Nano particles as the primary cause for long-term sunlight suppression at high
southern latitudes following the Chicxulub impact - evidence from ejecta deposits in
Belize and Mexico
Vajda, Vivi; Ocampo, Adriana; Ferrow, Embaie; Bender Koch, Christian
Published in:
Gondwana Research
DOI:
10.1016/j.gr.2014.05.009
Publication date:
2015
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Citation for published version (APA):
Vajda, V., Ocampo, A., Ferrow, E., & Bender Koch, C. (2015). Nano particles as the primary cause for long-term
sunlight suppression at high southern latitudes following the Chicxulub impact - evidence from ejecta deposits in
Belize and Mexico. Gondwana Research, 27(3), 1079-1088. DOI: 10.1016/j.gr.2014.05.009
Download date: 19. Jun. 2017
Gondwana Research 27 (2015) 1079–1088
Contents lists available at ScienceDirect
Gondwana Research
journal homepage: www.elsevier.com/locate/gr
Nano particles as the primary cause for long-term sunlight suppression at
high southern latitudes following the Chicxulub impact — evidence from
ejecta deposits in Belize and Mexico☆
Vivi Vajda a,⁎, Adriana Ocampo b, Embaie Ferrow a, Christian Bender Koch c
a
b
c
Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden
NASA HQ, Science Mission Directorate, Washington, DC 20546, USA
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
a r t i c l e
i n f o
Article history:
Received 31 December 2013
Received in revised form 17 May 2014
Accepted 20 May 2014
Available online 19 June 2014
Keywords:
Mass extinction
Cretaceous
Impact-winter
Belize
a b s t r a c t
Life on Earth was sharply disrupted 66 Ma ago as an asteroid hit the sea-floor in what is today Yucatan Peninsula,
Mexico. Approximately 600 km3 of sedimentary rock were vapourized, ejected into the atmosphere and
subsequently deposited globally as an ejecta apron and fallout layer. Proximal ejecta deposits occur in Belize
and southern Mexico where the so called Albion island spheroid bed is superimposed on the target rock (the
Barton Creek Formation). We analysed the spheroid bed via Mössbauer spectroscopy, petrology, XRD, and
palynology at several sites ~350–500 km distance from the crater centre. Our results show that the relative concentrations of Fe in nano-phase goethite (α-FeOOH) are very high in the spheroid bed samples from Albion Island
(Belize) and from Ramonal South (Mexico), but are low to absent in the spheroid bed at Ramonal North, and in
the Cretaceous target rock. Moreover, our study shows that goethite and haematite are the dominant Fe-oxide
nano-phases and the XRD results show that the target rock consists of both calcite and dolomite. We suggest
that the heterogeneous composition of the spheroid bed between the various sites reflects the different types of
target rocks that were dispersed within the rapidly expanding vapour plume and the complex sorting processes
involved in the formation of the ejecta blanket. The distribution of the vapourized target rock strongly influenced
life on Earth at the close of the Mesozoic. However, the comparatively thin K–Pg boundary clay in high-latitude
Gondwanan successions combined with evidence of catastrophic changes to the biota in this region implies that
the long-term sunlight suppression in the Southern Hemisphere was mainly governed by the large quantities of hydrous aerosols nucleated around sulphuric acid droplets or nano-sized particles, such as the nano-phase Fe-oxides.
© 2014 The Authors. Published by Elsevier B.V. on behalf of International Association for Gondwana Research.
This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
1. Introduction
The discovery of a crater buried beneath the town of Chicxulub on
the Yucátan Peninsula (Penfield and Camargo, 1981) provided the
pivotal evidence supporting the assertion that the end-Cretaceous
mass extinction was indeed caused by the impact of an asteroid or
comet (Hildebrand and Boyton, 1990; Hildebrand et al., 1991; Pope
et al., 1991) as proposed by Alvarez et al. (1980). The extinction of
over 70% of species, including the dominant dinosaurs on land, is now
attributed to this asteroid impact (Schulte et al., 2010 and references
therein). The impact site has been well preserved from erosion by burial
beneath more than 1000 m of younger strata (Pope et al., 1991). Thus,
expensive drilling programmes are required to access the sedimentary
successions within the crater. After more than 30 years of investigations
☆ This article belongs to the Special Issue on Gondwanan Mesozoic biotas and bioevents.
⁎ Corresponding author.
by multiple research groups, well-founded geochemical and mineralogical data have been generated that support the extra-terrestrial cause of
the end-Cretaceous event. Such data include the presence of anomalous
concentrations of iridium, the presence of high-temperature and highpressure phases in shocked quartz, and the presence of Ni-rich spinel
in the clay layer separating the Cretaceous from the Paleogene
(Schulte et al., 2010 and references therein). The presence of metal
oxides and hydroxides in nano-phases in the ferruginous layer within
the K–Pg boundary clay at Mimbral in Mexico (Wdowiak et al., 2001)
and mid-Waipara and Compressor Creek in New Zealand (Ferrow
et al., 2011), has been presented as additional mineralogical evidence
of the precise position of the ejecta layer.
The Chicxulub ejecta layer is amongst the best preserved proximal
ejecta deposit of any large-scale crater on Earth, and it provides an
ideal opportunity to study impact processes. In 1995 and 1996, beds
containing spherules related to the Chicxulub ejecta blanket were
found at two sites in Belize: at Albion Island in the northern part of
http://dx.doi.org/10.1016/j.gr.2014.05.009
1342-937X/© 2014 The Authors. Published by Elsevier B.V. on behalf of International Association for Gondwana Research. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
1080
V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
Chicxulub
Crater
Yucatan
Peninsula
Mexico
Ramonal
Albion Island
Belize
Armenia
Maya Mountains
100 km
Guatemala
Honduras
Fig. 1. Map showing the Chicxulub crater and the four sampled impact ejecta exposures in
Mexico and Belize. Black dots mark locations of Albion Formation ejecta in Belize, and light
gray dots show localities in Quintana Roo, Mexico.
the country and at Armenia, in the foothills of Maya Mountain in the
Cayo district of the central region (Fig. 1), at distances of 365 and
470 km from the crater centre, respectively (Ocampo et al., 1996).
Since this initial discovery, further outcrops have been identified and
described in detail in several studies (e.g., Ocampo et al., 1996; Vega
et al., 1997; Pope et al., 1999; Fouke et al., 2002; Keller et al., 2003a,b;
King and Petruny, 2003; Pope et al., 2005). Significant differences
expressed in the mineralogy and texture of the ejecta layer at the various sites have prompted an ongoing dispute concerning the causal
mechanisms behind the heterogeneity of the ejecta deposits. The
two dominant hypotheses raised to explain this heterogeneity invoke:
(1) different depositional processes following the impact (Ocampo
et al., 1996; Wdowiak et al., 2001; Bauluz et al., 2004; Ocampo et al.,
2006; Wigforss-Lange et al., 2007; Schulte et al., 2010 and references
therein), and (2) multiple impact events (Keller et al., 2007).
This study aims to examine the Fe-bearing phases of the ejecta
deposits focussing on the spheroid bed of the Albion Formation, which
is exposed at several sites in Belize and Mexico within a 500 km radius
of the crater centre. Results from petrography, Mössbauer spectroscopy,
powder X-ray diffraction (XRD) and palynology, are used to assess differences and similarities between the different parts of the spheroid bed, and
between samples from the spheroid bed at various sites along the Mexican/
Belize border. Additionally, we compare these data with one sample from
the underlying Cretaceous Barton Creek dolomite. Further, the global distribution of the ejecta is discussed and linked to the end-Cretaceous biotic
turnover with particular focus on the Gondwanan vegetation.
2. Geological setting
Belize is situated on the east coast of the Yucatan Peninsula in
Central America, southeast of the Chicxulub crater (Fig. 1). The geology
of northern Belize is not well documented due to the paucity of natural
outcrops in this tropical, low relief region and because dissolutioninduced collapse and recrystallization of carbonates and evaporites
have destroyed many of the original textures, bedding and fossils.
However, quarrying activities on Albion Island in Rio Hondo (Hondo
River), northern Belize, provides excellent bedrock exposures in this
particular region (Figs. 1–3).
Proximal ejecta deposits were first recognized in a quarry on Albion
Island, northern Belize, approximately 365 km southeast of the centre
of the Chicxulub impact structure; the geographical name was subsequently employed to name the Albion Formation (Ocampo et al.,
1996). The deposits are now known to be exposed at several places
along the Mexico–Belize–Guatemala border, e.g., in Ramonal North,
Ramonal South, Agua Dulce, Alvaro Obregón, the Albion Island Quarry,
Armenia and Santa Teresa (Fig. 1). The deposits incorporate the basal
spheroid bed containing carbonate accretionary lapilli and altered
impact glass, overlain by a diamictite bed consisting of coarser material
including displaced carbonate boulders up to 8 m in diameter and associated sparse dolomite spheroids.
The target rock consists of a 3-km-thick succession of limestones,
marls, dolomites, evaporites and sandstones overlying a crystalline
basement. The ejecta deposits rest directly on the fractured and
karstified Maastrichtian Barton Creek Formation. This dolomitic unit
was formed on a carbonate platform and has been interpreted to represent the deposits of a shallow, back-reef lagoon environment (Flores,
1952a,b; Vega et al., 1997).
The impactor, inferred to be a carbonaceous chondrite (Shukolyukov
and Lugmair, 1998) approximately 10 km in diameter (Alvarez et al.,
1980), excavated a 180–200 km diameter crater in the volatile-rich
carbonate platform and the underlying crystalline basement down to
the base of the crust (Kring, 2007). The globally distributed ejecta and
fallout deposits generated by this event are recognized by the presence
of shocked quartz, tektites and geochemical anomalies, such as iridium
enrichment (Alvarez et al., 1980).
3. Material and methods
3.1. Material
Samples from four sections in Belize and Mexico were studied for
petrology, geochemistry and palynology. The samples were collected
by A. Ocampo between 1994 and 2005, and represent mainly the ejecta
deposits (spheroid bed), together with one sample from the underlying
Cretaceous Barton Creek Formation for comparison. The base of the
Albion Formation and its contact with the underlying Barton Creek Formation are well exposed at Ramonal South. Eight samples were selected
for Mössbauer analysis, three samples for XRD, and four samples for
palynology and, petrographic analyses were carried out on thin sections
from three samples (Figs. 4, 5).
Ramonal North is located at ~340 km from the crater centre and is
close to the village of Ramonal, Quintana Roo, Mexico (Fig. 1), where a
road-cut exposes 3.6 m of the spheroid bed incorporating calcitic silty
matrix with abundant green altered glass clasts 2–40 mm in diameter.
The bed also contains abundant spherical to slightly oblate pink carbonate lapilli 5–25 mm in diameter. One sample (RN-68) was selected from
this deposit for Mössbauer analysis (Fig. 2).
Ramonal South locality is situated a few hundred metres south of
Ramonal North (Fig. 1). The Barton Creek Formation is exposed at this
site and has been affected by extensive karst weathering. This heavily
recrystallized limestone with iron oxide staining, caliche deposits,
solution cavities and travertine deposits has a local surface relief of
3–5 m. Overlying the Barton Creek Formation at Ramonal South is a
2-m-thick spheroid bed. At Ramonal South, this basal unit is overlain
by a 5-m-thick diamictite bed incorporating limestone cobbles and
boulders (up to 3 m in diameter) supported in a calcitic silt matrix
(Fig. 2). Samples selected for Mössbauer analysis from this unit were
taken from the spheroid bed at 1.60 m above the contact with the
underlying Barton Creek Formation (sample RS-160) and from the topmost part of the spheroid bed, approximately 2 m above the contact
(sample RS-SPH).
V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
Mexico
Mexico
1081
Belize
Belize
Armenia
Diamictite bed
Ramonal South
10
8
8
6
6
RS-SPH
m
12
10
m
8
2
AI-97a
RS-160
AI-97b
AI-SB
RN-68
Barton Creek Fm
Dolomite
0
Cretaceous
m
m
Ramonal North
Spheroid bed
Paleogene
Albion Formation
Albion Island
4
4
6
AR-104
AI-143
AR-118
4
2
2
2
0
0
340 km
0
365 km
470 km
Distance from the Chicxulub crater
Diamictite bed
Spherules
Spheroid bed
Barton Creek
Formation
Impact glass
Roots in palaeosol
Caliche
Clay
Fig. 2. Stratigraphical columns of the four profiles with the exposed spheroid bed along the Mexico–Belize–Guatemala border with increasing distance from the Chicxulub crater. Sample
numbers indicate the sampled levels at the various sites (modified from Ocampo et al., 1996; Wigforss-Lange et al., 2007).
Albion Island locality is situated in Belize at a distance of 365 km from
the crater's centre (Figs. 1, 2). The succession exposed in Albion Quarry
(Fig. 3) incorporates the Cretaceous Barton Creek Formation and the
Paleogene Albion Formation. Immediately overlying the Barton Creek
Formation is the spheroid bed, which at this site contains carbonate accretionary lapilli and altered impact glass. The spheroid bed is overlain
Fig. 3. Albion Island quarry with the contact between the Maastrichtian Barton Creek Formation and the Paleogene Albion Formation exposed. The Barton Creek Formation is overlain by
the Albion Formation, which consists of the spheroid bed, and the diamictite bed. The K–Pg boundary is marked by the spheroid bed extending horizontally through the quarry.
1082
V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
Fig. 4. Photographic enlargements of samples from the spheroid bed (Albion Formation) showing the erratic distribution of yellowish-brown material implying the presence of iron oxides
from three localities at increasing distance from the crater centre; spheroid bed at: A) Ramonal North located at 340 km from the Chicxulub crater; B) Albion Island at 365 km distance,
fragment of spherulitic glass with relic vesicules; and C) Armenia at 470 km distance, sample with well-rounded accretionary lapilli with rim.
by a coarse diamictite bed hosting carbonate boulders up to 8 m in diameter, associated with sparse dolomite spheroids (Fig. 2). One sample
from the topmost part of the Barton Creek Formation (sample AI-143)
was analysed for Mössbauer spectroscopy and XRD (Fig. 2). Two samples were further selected from the spheroid bed for Mössbauer analysis
(AI-97 and the “saddle breccia” AI-SH), and XRD analysis was also
carried out on sample AI-97.
The Armenia section is located at a distance of 470 km from the crater
centre, and south of the Belizean capital Belmopan (Fig. 1). An approximately 17-m-thick succession spanning the Cretaceous–Paleogene
boundary is exposed here along the Hummingbird Highway. The
basal part of the succession comprises the uppermost part of the
Maastrichtian Barton Creek Formation and is composed mainly of a
5-m-thick indurated regolith deposit. This is overlain by a deep red–
green calcitic clay (0.5–1.5 m thick) hosting small angular to rounded
pebbles and granules. At the top of this clay, and immediately underlying the basal contact of the lowermost Paleocene spheroid bed, fossil
roots are present suggesting that it represents soil formed on the weathered surface of the Barton Creek Formation at the end of the Cretaceous.
A 5-m-thick spheroid bed consisting of altered glass and accretionary
lapilli overlies the palaeosol. Overlying the spheroid bed at Armenia
is a 5-m-thick portion of the diamictite bed consisting of matrixsupported limestone pebble and cobble conglomerate (Fig. 2). The
contact with the underlying spheroid bed is sharp and lacks evidence
of mixing or weathering. One sample (AR-118) from the red–green
clay layer was selected for Mössbauer analysis (Fig. 2) and one sample
(AR-104) for XRD derives from the spheroid bed.
3.2. Analytical methods
3.2.1. Mössbauer spectroscopy and powder X-ray diffraction
Seven samples were selected for Mössbauer spectroscopy (Figs. 2,
6–8) and three of these were powdered and analysed by powder
X-ray diffraction (XRD). Mössbauer spectra were recorded at 20 K and
300 K (room temperature) using a constant-acceleration Mössbauer
spectrometer with a 57Co in Rh source. This type of spectroscopy is element specific and was employed to study the Fe-containing minerals.
The spectrometers were calibrated using a thin foil of natural iron, and
isomer shifts are given with respect to the centre of the calibration
spectrum. Thin absorbers were prepared by mixing the sample with a
Fig. 5. Thin sections of the spheroid bed in the Yucatan–Belize region. A) Thin section from the spheroid bed at Ramonal North showing clay shards with relic vesicles formed by diagenetic
alteration of glass, with slightly larger spherules of dolomite formed by re-crystallization of limestone in response to shock-melting. B) Thin section from the spheroid bed at Albion Island
with vesicular accretionary lapilli, composed mainly of carbonates. Lapilli with lithic cores, some of which are composed of altered glass and carbonate clasts with alteration rinds. Black
clasts comprise thermally altered organic particles. C) Thin section from the red–green clay, Armenia locality. Calcitic clay with rounded limestone clasts. Organic matter representing root
fragments appears as black dots (scale bar = 1 cm).
V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
-0.5
0.0
A bsorption (% )
0.5
1
1.0
1.5
2
3
5
-10
Spheroid bed
A bsorption (% )
-0.5
10
0.0
AI-SB
-5
0
5
v (mm/s)
10
0.0
0
v (mm/s)
0.5
AI-143
1.0
4
1.5
2
-12
6
A bsorption (% )
Barton Creek Formation
AI-143
-8
-4
-8
-4
0
4
8
12
0
4
8
12
v (mm/s)
-1
0
v (mm/s)
0
-2
1
-4
-1
-6
0
A bsorption (% )
1.5
1.0
Goethite
1
Barton Creek Fm
Dolomite
-5
0.5
A bsorption (% )
-10
AI-SB
Cretaceous
AI-97
20 K
Goethite
Albion Formation
Spheroid bed
Paleogene
AI-97
Saddle breccia
0
A bsorption (% )
Albion Island
-1
300 K
Northern Belize
1083
-12
4
3
3
2
2
Haematite
-8
-4
0
4
8
12
-12
v (mm/s)
v (mm/s)
Fig. 6. Mössbauer spectra measured at 300 and 20 K of selected samples from Albion Island, northern Belize. Note different velocity scales in the spectra. Iron oxides have been identified
based on the hyperfine parameters of the magnetically ordered sextets (see text).
petroleum jelly in a 5 mm thick and 10 mm diameter sample support
(Rancourt, 1994). The spectra were fitted using the Lorentzian site
analysis software programme in the Recoil package.
X-ray powder diffraction was used to study mineral phases in the
samples. Data were obtained using a PW 1710 Philips diffractometer
equipped with a Cu tube and a diffracted beam monochromator.
mounted in epoxy resin on glass microscopy slides. As the organic recovery was very low, all palynomorphs in the residue were identified.
3.2.2. Petrology
Hand specimens representing the Barton Creek Formation and the
spheroid bed (Fig. 4) from all four localities were studied and described.
Additionally, thin sections from the spheroid bed and the red–green
clay from Ramonal North, Albion Island and Armenia were studied by
transmitted light microscopy for petrographic constituents (Fig. 5).
Petrological analysis of the red–green clay, underlying the spheroid
bed at Armenia shows that the red clay is calcitic and contains ~ 10%
0.2–3 mm diameter, rounded limestone clasts. The red–green clay is
topped by a palaeosol containing lenticular clay clasts in sharp contact
with the overlying spheroid bed. The organic matter recovered from
the red clay (sample AR-118) via palynological processing shows sparse
occurrences of tricolpate angiosperm pollen, fern spores and the alga
Botryococcus. The presence of fossil root fragments show that these
deposits are terrestrial lateritic palaeosols, representing land when
covered by the ejecta from the impact.
Highly vesicular glass fragments comprise about 20–30% of the overlying spheroid bed at Armenia. These glass fragments enclose some zonal
altered glass cores that are possibly the products of shock-melted quartz.
Accretionary lapilli, mainly composed of carbonates, comprise approximately 10–20% of the spheroid bed sample from this site. These lapilli
range from b1 mm to 6 cm in diameter and possess lithic cores, some
of which are composed of altered glass (Figs. 4, 5). The unit also contains
3.2.3. Palynology
As part of a pilot study, since carbonaceous ejecta deposits would not
normally be a target for palynological analyses, five samples were processed according to standard palynological procedures at Global GeoLab
Ltd, Canada: Albion Island Cretaceous dolomite (AI-143); Albion Island
spheroid bed (AI-97a, AI-97b); Armenia Cretaceous red–green clay (AR118) and Armenia spheroid bed, (AR-104). Fifteen grams of sediment
were first treated with dilute hydrochloric acid (HCl) to remove calcium
carbonate, and subsequently macerated by immersion in 45% hydrofluoric
acid (HF). The organic residue was sieved using a 10 μm mesh and
4. Results and interpretation
4.1. Petrology and palynology
1084
V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
1
1
0
AR-104
-1
20 K
A bsorption (% )
-1
300 K
Spheroid bed
2
2
Paleogene
Albion Formation
Spheroid bed
Armenia
0
A bsorption (% )
Central Belize
3
-2
4
6
Red green clay
-12
A bsorption (% )
-1
2
AR-118
-8
-4
-8
-4
0
4
8
12
0
4
8
12
v (mm/s)
1
0
2
5
3
4
3
2
2
A bsorption (% )
0
v (mm/s)
-1
-4
0
-6
AR-118
1
Barton Creek Fm
Red green clay
Cretaceous
3
AR-104
-6
-4
-2
0
v (mm/s)
2
4
6
-12
v (mm/s)
Fig. 7. Mössbauer spectra measured at 300 and 20 K of selected samples from Armenia, central Belize. Note different velocity scales in spectra. Arrows 2 and 5 in the 300 K spectrum of the
red–green clay indicate lines 2 and 5 in a magnetically ordered sextet assigned to haematite. Iron oxides have been identified based on the hyperfine parameters of the magnetically ordered sextets (see text).
carbonate clasts that range from b1 mm to 8 cm in diameter (clasts
N1 cm constitute about 1–3% of the unit), many of which have alteration
rinds. These rinds are composed of a vesicular calcite, in which the vesicles are filled with sparry calcite. In sample AI-104 from the spheroid
bed, the organic content consists of dark foraminiferal linings and the
alga Botryococcus but is otherwise barren of palynomorphs. The presence
of microfossils in this sample is interpreted to be the result of reemplacement of Cretaceous target rock and shows that some organic
matter survived the general heat of the impact process.
The samples from the spheroid bed at Albion Island (Fig. 5) contain
clay shards with relic vesicles formed by diagenetic alteration of glass,
an interlocking mosaic of spherulites, and larger spherules of dolomite
formed by re-crystallization of limestone in response to shock-melting.
Additionally, the palynological sample from the Barton Creek Formation
at Albion Island (AI-143; Fig. 2), contains sparse occurrences of
tricolporate angiosperm pollen, fern spores, foraminiferal linings and a
few dinoflagellate cysts. As organic matter combusts in the atmosphere
at approximately 250 °C, we argue that the temperature within the clasts
bearing these organic particles did not exceed this temperature.
4.2. Mössbauer spectroscopy and powder X-ray diffraction
The powder X-ray diffractograms confirm the dominance of carbonate minerals (dolomite and calcite) and, additionally, provide evidence
of large amounts of dioctahedral smectite (asymmetric diffraction
peaks at 4.5 and 2.5 Å combined with a basal 001 peak close to 16 Å
and a 060 peak at 1.50 Å) in the spheroid bed samples from the
Armenia and Albion Island sections. Bulk chemical analyses (WigforssLange et al., 2007) indicate that the smectite is a montmorillonite type
formed from the weathering of glass. The absence of a broad peak in
the diffractogram typical of glass indicates that the glass to clay conversion is almost complete. No indications of the presence of iron oxides
are evident from the XRD measurements, most likely due to low relative
concentrations in the samples.
The Mössbauer spectra reveal simple combinations of paramagnetic
doublets and magnetically ordered sextets or more complex superpositions of paramagnetic doublets and spectral components exhibiting
magnetic relaxation. Sample RS-SPH from the Ramonal South spheroid
bed (Fig. 8) exhibits no typical magnetically ordered components at 300
K but a clear sextet can be identified at 20 K. This sextet has a magnetic
hyperfine field of 49.6 T and quadrupole shift of −0.1 mm/s indicating
the presence of goethite (α-FeOOH).
The lower sample from Ramonal South (RS-160, Fig. 8) exhibits a
magnetically ordered sextet and a doublet having the same relative
spectral areas at 300 and 20 K. The hyperfine parameters of the
sextet (magnetic hyperfine field of 52.7 T and quadrupole shift of
− 0.04 mm/s) identifies this component as an impure haematite
(α-Fe2O3) with a crystallite size of several nanometres. At 300 K, the
doublet has an isomer shift (0.36 mm/s), quadrupole splitting
(0.55 mm/s) and linewidth (0.35 mm/s) typical of smectites.
Sample RN-68 from Ramonal North only exhibits a paramagnetic
component at both 300 K and 20 K indicating the absence of iron oxides
in this sample (i.e., below detection level). The behaviours of the two
samples from the spheroid bed at the Albion Island section (AI-SB, AI97) are similar to that of the sample from the Ramonal South spheroid
bed, again indicating the occurrence of goethite (Fig. 6). At high resolution, the 300 K spectrum of the spheroid bed sample AI-SB exhibits a
very broad relaxation component that combines with the paramagnetic
doublet due to ferric iron in the smectite. This feature indicates that the
goethite has a crystallite size for which magnetic relaxation at room
temperature is significant — such goethite crystals are often referred
to as nano-sized.
The red–green clay from the Armenia section (Figs. 1, 7) is dominated by a paramagnetic doublet that can be assigned to ferric iron in smectite. In addition, a weak-intensity sextet pattern is evident in the 20 K
(lines 1, 2, 5 and 6 are resolved) and in the 300 K spectra (lines 2 and
5 are resolved). The magnetic hyperfine field of the sextet (52.5 T at
20 K) identify this as due to a small amount of haematite.
V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
1085
Mexico
Ramonal South
0
2
A bsorption (% )
RS-SPH
0
A bsorption (% )
Spheroid bed
20 K
2
Goethite
6
4
4
8
6
Spheroid bed
10
-10
RS-160
-5
0
5
10
0
5
10
v (mm/s)
-2
5
0
0
v (mm/s)
8
6
Haematite
6
4
4
2
0
A bsorption (% )
-5
A bsorption (% )
-10
2
RS-160
8
RS-SPH
Fm
Albion Formation
Spheroi d bed
Diamictite
m
Dolomite
Barton Creek
Cretaceous
Paleogene
300 K
-10
-5
0
5
10
-10
-5
v (mm/s)
v (mm/s)
Mexico
0
A bsorption (% )
-2
0
RN-68
2
A bsorption (% )
m
Spheroid bed
5
Haematite
10
RN-68
6
4
2
0
-10
15
10
8
Albion Formation
Spheroi d bed
Paleogene
Ramonal North
-5
0
v (mm/s)
5
10
-10
-5
0
5
10
v (mm/s)
Fig. 8. Mössbauer spectra measured at 300 and 20 K of selected samples from Ramonal South and Ramonal North, Mexico. Iron oxides have been identified based on the hyperfine
parameters of the magnetically ordered sextets (see text).
In summary, the Mössbauer results show the presence of goethite
and haematite within the spheroid bed (Figs. 6–8). However, the two
oxides do not co-occur in any of the samples, i.e., samples contain either
haematite or goethite possibly indicating that a single factor controls
which mineral precipitates. A further possibility is that some exposures
have been more weathered and that the haematite is a weathering
product of goethite, as suggested by Brooks et al. (1985).
5. Discussion and conclusion
The results of this study of the spheroid bed at Albion Island,
Ramonal South and Ramonal North are consistent with studies at
Mimbral, Mexico, by Wdowiak et al. (2001), which revealed that the
spheroid bed is characterised by the presence of goethite in nanophase. Comparisons between our low-temperature (20 K) Mössbauer
data from the spheroid bed at Albion Island and Ramonal South, and
that from the spheroid bed at Mimbral investigated by Wdowiak et al.
(2001), show that the latter contains finer particles probably reflecting
that site's more distal location from the crater. Moreover, our study
confirms the observation that goethite is the dominant Fe-oxide nanophase associated with the K–Pg boundary spheroid bed in Yucatan.
Whilst goethite dominates in the North American K–Pg clay layer
(Moscow Landing, Madrid East, Berwind Canyon, Starkville South),
haematite dominates the European K–Pg boundary clays (Caravaca,
Contessa, Petriccio and Stevns Klint; Wdowiak et al., 2001).
The elevated levels of iridium, chromium, nickel and gold from the
impactor, and arsenic and carbonate from the evaporitic target rock,
reveal contributions from Chicxulub even at very remote New Zealand
K–Pg sites, such as Moody Creek Mine (Vajda et al., 2001; Vajda and
McLoughlin, 2004). In the marine K–Pg boundary section at Woodside
Creek, New Zealand, the boundary clay is 8 mm thick with an iridiumenriched 2 mm basal layer also containing grains of shocked quartz
and three types of spheroids (A–C; Brooks et al., 1985). Spheroid types
A and B primarily comprise microcrystalline goethite, whereas type C
includes significant amounts of haematite. Brooks et al. (1985) suggested that spheroids of types A and B are weathering products of pyrite. This was also suggested by Bauluz et al. (2004) where Fe and O
were identified at Woodside Creek and considered to be “alteration
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V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
products of diagenetic pyrite”. We suggest that the goethite in these
spherules more likely represents Fe nano-phase oxide. We propose
that the goethite formed by the processes initiated by the impact in
Yucatan but further studies of the minerogenesis sequence are needed.
It is possible that the difference in the Fe-oxides between the
European and North American sites is related to proximity to the impact
site; those sites close to the impact containing goethite and more remote sites containing haematite. If this is the case, then the variation
in the Fe-bearing phases could reflect fundamental differences in
depositional mechanisms whereby goethite was deposited during the
expansion of the vapour plume cloud in the atmosphere and haematite
was crystallized during re-entry of particles ejected from the atmosphere. However, it is also possible that the variance in the Fe-phases
evident at the various K–Pg boundary sites in Europe, North America
and the Gondwanan continents simply reflects the different types of target rocks that were disseminated within the rapidly expanding vapour
plume. This is supported by the presence of goethite within the New
Zealand K–Pg boundary clay (Ferrow et al., 2011). It is further supported
by the geochemical composition of glass shards from various parts of
the world showing that two types of impact glasses occur; one dark
and Si-rich and another, yellow and Ca-rich. The Si-rich glass represents
the crystalline deeper part of the target rock and the Ca-rich glass represents the upper evaporitic part of the target (Bauluz et al., 2004) as the
impactor excavated a crater penetrating the 3-km-thick succession of
carbonates, evaporites, sandstones and the underlying crystalline basement (Morgan et al., 1997). Both types of glass are present in Mexico
(Mimbral) and Haiti (Beloc) (Kring and Boynton, 1991; Koeberl and
Sigurdson, 1992), whilst the K–Pg boundary clay in Denmark (Stevns
Klint) contains only Si-rich glass (Bauluz et al., 2000). Geochemical
studies of glass shards from Southern Hemisphere sites, such as
Woodside Creek and the nearby locality at Flaxbourne River in South
Island, New Zealand (Bauluz et al., 2004), show that these shards are
smaller than those identified from Stevns Klint (Denmark) and that
they have high values of Ca (25%), making them geochemically similar
to the Ca-rich impact glass found at Mimbral, Mexico (Keller et al.,
2003a). Although the palaeontological evidence indicates severe disruption to the biota globally (Vincent et al., 2013), these observations
do not negate the possibility of a low-angle impact hypothesis, in
which the Northern Hemisphere would have received greater amounts
of impact debris.
The GSSP for the K–Pg boundary is located on a Gondwanan continent, at Oued Djerfane, west of El Kef, Tunisia, where it is marked by a
N50-cm-thick, dark boundary clay with a rusty iridium-enriched layer
at the base and a significant faunal and floral turnover (Molina et al.,
2006). The paleo-position of Tunisia places it relatively close to the
impact site, which possibly explains the substantial thickness of the
boundary clay.
5.1. Implications for the end-Cretaceous biota
The end-Cretaceous event is undoubtedly the best-studied impactinduced global mass-extinction and, as such, serves as a model for biotic
responses to extremely abrupt events throughout Earth's geological history and the fundamental scenario for such an event is summarized in
Fig. 9. Although the instantaneous effects of the impact caused local to
regional destruction of biological communities by various high-energy
processes (e.g., heat release, wildfires, shock waves, tsunamis and
earthquakes), global communities were affected mainly by the longer
term (years–decades) consequences, such as global cooling induced
by aerosols formed in the atmosphere.
The local biota within the Yucatan Peninsula, both those organisms
inhabiting the shallow marine environment and terrestrial settings at
the time of impact, were evidently instantaneously exterminated. The
Barton Creek Formation hosts a range of foraminiferal taxa including
miliolides and rotaliids (Flores, 1952a) and macrofossils include rudist
bivalves, gastropods and crabs (Vega et al., 1997), but well-preserved
fossils are otherwise scarce due to recrystallization (dolomitization).
Our results show that algal groups, such as Botryococcus, and dinoflagellates, were present in the Late Cretaceous lagoons and in the sea covering the carbonate platform at Yucatan. The presence of fossil algae both
in the target rock and in the matrix of the spheroid bed indicate that
some microfossils were reworked from the underlying Barton Creek
Formation and resisted the high temperatures, pressures and transport
processes following the Chicxulub impact.
Sparse paleontological data are available from terrestrial settings
close to the impact site. The only available fossils are roots preserved
in palaeosols that indicate the presence of vegetation growing on thin
soils developed on the Late Cretaceous carbonates/evaporates. The
local vegetation may have been adapted to arid conditions (Craggs
et al., 2012) and was inevitably devastated by the impact and covered
by vast deposits of molten rock and ejecta debris excavated from the
crater. The ejecta deposits thin with distance from the crater, and
other factors controlled extinctions at locations remote from the impact
site. Whilst ejecta deposits may attain thicknesses up to 45 m at the localities studied herein, the thinnest layer identifiable by an iridium
anomaly on a global basis is only a few millimetres thick and occurs
in terrestrial Southern Hemisphere high-latitude settings, such as in
New Zealand (Moody Creek Mine; Vajda et al., 2001; Vajda and
McLoughlin, 2004; Vajda, 2012).
The target rock represented a shallow sea to slope setting with water
depths ranging from 100 m to as deep as 2.5 km on the eastern flank according to Gulick et al. (2008) implying that a larger quantity of water
vapour was produced than previously contended. Some studies have
proposed that the ejecta deposits were chiefly directed towards North
America based on the crater shape combined with palaeontological
Ruling mechanisms
High energy release
triggered by an impacting
extraterrestrial body
Extremely rapid
killing mechanisms
Rapid normalization of
environmental conditions
Biotic recovery and
diversification
Implications for K-Pg boundary biota
Diverse Cretaceous fauna
and flora
Mass extinction of fauna,
die back of vegetation
Proliferation of pioneer
organisms.
Fern spike on land
and algal blooms
in sea
Long term recovery,
mammals replacing
reptiles on land and in sea
Fig. 9. Schematic illustration of the scenario following an asteroid impact induced extinction, and how it was manifested for the Cretaceous–Paleogene event.
V. Vajda et al. / Gondwana Research 27 (2015) 1079–1088
data from the North American interior that imply that the asteroid
impacted from the southeast to the northwest at a 20–30° angle and
mainly affected the Northern Hemisphere biota (Schultz and D'Hondt,
1996). However, later high-resolution studies across the K–Pg boundary
in New Zealand have revealed that a major disruption to the biota also
occurred in Gondwanan high-latitude settings.
It might be argued that this difference in ejecta distribution should
also be reflected in the magnitude of the biotic response. The low quantities of clay (devitrified glass) at some remote sites, combined with the
evidence of catastrophic changes to the vegetation (Vajda et al., 2001;
Vajda and McLoughlin, 2004; Schulte et al., 2010), imply that the
long-term sunlight suppression was probably caused by aerosols
formed from the vast amount of H2O and S-containing vapour injected
into the atmosphere. Recent studies have shown that sulphur trioxide
(SO3) dominated over sulphur dioxide in the vapour cloud and that
SO3 enhanced the formation of sulphuric aerosol particles following
the asteroid impact (Ohno et al., 2014). Both sulphuric acid and
nanoparticles may have acted as cloud condensation nuclei (CNN) for
water in the atmosphere.
As the nanoparticles partly form by cooling of the plume, they are
available almost immediately, and for as long as they are in the atmosphere they will be expected to scatter the sunlight relatively effectively. The sulphuric acid nuclei will form following a photochemical
reaction between water and sulphur dioxide depending on the sunlight.
The hydrous aerosols may have nucleated around nano-sized particles,
such as the nano-phase Fe-oxides described from the ejecta deposits in
this study and from other K–Pg boundary layers globally.
As excavated material, together with the remnants of the asteroid,
was vapourized and ejected ballistically into the stratosphere, a global
heat pulse was generated by ejecta re-entering the troposphere. Several
studies have concluded that the atmosphere was heated globally to
temperatures where only organisms with abilities/possibilities to shelter from the heat were able to survive (Melosh et al., 1990; Kring and
Durda, 2002; Robertson et al., 2004 and references therein), although
the existence and extent of the global heat pulse is still intensely debated. After this initial phase (time-frame of hours) with intense infra-red
radiation, the principal lethal factor became the effects of dust-loading
on climate and photosynthesis (Toon et al., 1982, 1997; Pope, 2002)
with the large quantities of atmospheric sulphur aerosols prolonging
the cooling. This process had devastating effects on the biota as far
away as remote Gondwanan settings. The major killing agent would
have been related to the massive drop in primary productivity induced
by the suppressed light levels.
This is manifested by the presence of a fern-spike in New Zealand
K–Pg boundary successions revealing a mass-kill of vegetation and initial recovery of pioneer plants in southern high latitudes after a
prolonged time of darkness (Vajda et al., 2001, 2004; Vajda and
McLoughlin, 2004; Ferrow et al., 2011). Long-term effects persisted in
New Zealand as evidenced by Araucariaceae conifers (dominant elements of the Late Cretaceous flora in large areas of the pre-impact
Gondwanan continents) being replaced by Podocarpaceae upon recovery of the seed-plant communities (Pole and Vajda, 2009; Vajda and
Bercovici, 2012). A similar long-term vegetation turnover has been described from Argentinean K–Pg boundary deposits where the treesized conifers (Cheirolepidiaceae) briefly dominated the post-impact
floras that later saw the recovery of Podocarpaceae and Araucariaceae
(Barreda et al., 2012). Although the palaeontological evidence indicates
severe disruption to the biota globally, these observations do not negate
the possibility of a low-angle impact hypothesis, in which the Northern
Hemisphere would have received greater amounts of impact debris. The
paleo-position of Tunisia places it relatively close to the impact site,
which possibly explains the substantial thickness of the boundary clay
at the K–Pg GSSP.
In Antarctica, a K–Pg boundary layer has been detected based on an
iridium anomaly within a layer of the nearshore marine succession
on Seymour Island (Askin and Jacobson, 1996) and subsequent
1087
palynological studies have shown that the succession indeed spans
the boundary. However, high-resolution studies are required to
decipher the details of the biological turnover on Antarctica. Likewise,
a sedimentary succession on Campbell Island on the southern fringe of
the Zealandia continent, which during the Late Cretaceous was still possibly attached to West Antarctica, appears to include the K–Pg boundary
(Wanntorp et al., 2011). However, geochemical studies are needed to
confirm its position.
Several IODP drill-cores from the Pacific region show the presence of
a K–Pg boundary layer based on the presence of iridium, shocked quartz
and spherules (Zinsmeister et al., 1989; Schulte et al., 2010) but micropaleontological studies have yet to be performed in order to evaluate
the biotic consequences at these sites. Although we have only glimpses
into the Southern Hemisphere record of biotic extinction and recovery,
there is sufficient evidence to show that the extinction event was genuinely global. Several authors have invoked catastrophic heating and
wildfires following the Chicxulub impact (Melosh et al., 1990; Kring
and Durda, 2002; Robertson et al., 2004 and references therein), but
the existence and extent of the global heat pulse are still intensely
debated. After this initial phase (time-frame of hours) with intense
infra-red radiation, the principal lethal factor became the effects of
dust-loading on climate and photosynthesis (Toon et al., 1982, 1997;
Pope, 2002).
The low quantities of clay (devitrified glass) at some sites, combined
with the evidence of catastrophic changes to the vegetation (Vajda et al.,
2001; Schulte et al., 2010), implies that long-term sunlight suppression
was probably caused by aerosols formed from the vast amount of H2O
and S vapour injected into the atmosphere. These aerosols may have nucleated around nano-sized particles, such as the nanophase Fe described
in this study.
Acknowledgements
This work was supported by the Royal Swedish Academy of Sciences
through the Knut and Alice Wallenbergs foundation. VV acknowledges
support from LUCCI (Lund University Centre for Studies of Carbon Cycle
and Climate Interactions), a Linnaeus centre funded by the Swedish
Research Council. AO acknowledges the support from the National
Aeronautics and Space Administration Exobiology Program, California
Institute of Technology, Jet Propulsion Laboratory and the European
Space Agency. We further thank the two anonymous referees for providing constructive critisism and comments improving this paper.
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