This study directly links iridium anomalies to mass extinction events across the Cretaceous-Paleogene boundary in New Jersey. High-resolution iridium analyses of sediment cores from eight localities confirm a previous report of an iridium anomaly 20 cm below the extinction horizon at Tighe Park, Freehold. Iridium anomalies also correlate with extinctions at three other clay-rich sections. These data reaffirm the link between the Chicxulub impact and mass extinction and attribute the iridium anomaly at Freehold to downward movement of iridium.
3. 868 GEOLOGY, October 2010
and Sea Girt) also provide constraints on the relationship of extinctions to
impact ejecta (Figs. 1 and 2).
METHODS
Iridium analyses at high spatial resolution are necessary to elucidate
the K-Pg boundary in detail. This requires Ir analysis on small samples
(1 g), which we accomplished using a NiS fire-assay technique modified
after Ravizza and Pyle (1997). Low procedural blanks (7 pg g–1
) combined
with high-sensitivity sector field inductively coupled plasma–mass spec-
trometry provide the detection limits (10 pg g–1
= 0.01 ppb) essential for
the quantification of Ir in 1 g sediment core samples. Standardization by
isotope dilution yields excellent procedural reproducibility (±5%, 2σ) for
even the lowest Ir concentrations (40–100 pg g–1
) found in background
samples. We used the resultant high-fidelity Ir data to quantify and locate
the Ir anomaly with respect to other stratigraphic features associated with
the K-Pg boundary.
RESULTS
Results from previous drilling at downdip (~60–100 m paleodepth)
Bass River, New Jersey, show a 6-cm-thick spherule (altered microtek-
tite) layer with common shocked quartz grains and carbonate accretionary
lapilli (Yancey and Guillemette, 2008) that separates uppermost Creta-
ceous from Paleogene sediments (Figs. 1 and 2; Olsson et al., 1997, 2002).
Uppermost Cretaceous sediments underlie the spherules based on plank-
tonic foraminifera and assignment to the Palynodinium grallator dinocyst
and Micula prinsii nannofossil zones. Sediments immediately above the
spherule layer are assigned to lowermost Danian planktonic foraminiferal
zone P0 and include the first occurrence of the Danian dinoflagellate index
fossil Senoniasphaera inornata (Olsson et al., 1997, 2002; Norris et al.,
1999). The basal Danian contains a layer (~3 cm thick) of white clay rip-
up clasts containing uppermost Cretaceous foraminifera and dinocysts.
There is a modest Ir anomaly (~0.5 ppb) immediately above the spherule
bed associated with the clast layer and a large Ir anomaly (2.5 ppb) at its
base (Fig. 2). The global Ir anomaly is a result of stratospheric fallout and
should occur above ballistic deposits, as it does at ODP Site 1049 at Blake
Nose in the western North Atlantic (Norris et al., 1999), where the ejecta
also occur immediately above the marine mass extinction. Thus, the Ir
anomaly at the base of the spherule bed is interpreted as resulting from
displacement of Ir down section 6 cm by postdepositional processes (Ols-
son et al., 1997, 2002).
Other onshore New Jersey ODP sites have recovered less complete
K-Pg sections, though a clay clast layer is found in most New Jersey
coastal plain sites above the K-Pg boundary. Hole A at Ancora (Miller et
al., 1999b) recovered white clay clasts and reworked spherules; a distinct
spherule layer is absent. By contrast, Ancora Hole B contains a spherule
layer, though the original microtektites have been redeposited. Although
biostratigraphically complete, the ODP Leg 174AX Site Millville (Sug-
arman et al., 2005) K-Pg boundary lacks impact spherules and shocked
UpperCretaceousNewEgyptFormationPaleogeneHornerstownFm.
ClayeyglauconitesandClayeyglauconitesand
veryheavilyburrowed
ClayeyglauconitesandClayeyglauconitesand
(Pinnalayerequivalent)
Meirs Farm 1
Iridium
Fecal pellets
(#/gram)
Iridium (ppb)
13
12
10 20 30
(m) (ft)
44
Spherule
bed
Burrowedglauconiticclay,richlyfossiliferous
Lithology
NewEgyptFormation
UppermostMaastrichtian
Glauconiticsiltyclay,
poorlyfossiliferous
HornerstownFm.
Danian
P0Pα
PF
Fecal pellets
(#/gram)
0 0.5 1 1.5 2 2.5
0 2 4 6 8 10
Depth
(cm above/below
K/Pg boundary)
Shocked
minerals
few many
Iridium (ppb*)
Iridium
Epifaunal echinoid
fecal pellets
*Note scale change
Bass River
P1aA.mayaroensiszone
0
+10
-10
40
Quartzsand
Indurated
zone
Red
clay
GlauconiticgreenclayGlauconiticclaytoclayeyglauconitesand
UpperCretaceous?TintonFormationPaleogeneHornerstownFormation
Buck Pit 1
Senoniasphaerainornata
5
6
(m) (ft)
Depth
14
15
16
17
18
19
0.1 0.3
40
41
42
43
Depth 0.3 0.5
22
21
23
24
25
26
27
(m)(ft)
7
8
Depth 0.1 0.3
Iridium (ppb)
Search Farm 1
Iridium
Epifaunal echinoid
fecal pellets
VerydarkgreenclayeyglauconitesandBlack,bioturbatedclayeyglauconitesand
PaleogeneHornerstownFormationUpperCretaceousNewEgyptFormation
0 2 4 6 8
Fecal pellets
(#/gram)
Clast
Unnamed
Iridium (ppb)
0.10.5
10
0.5
0
Epifaunal echinoid
fecal pellets
Figure 2. Other subsurface sections. Ir in parts per billion (ppb), fecal pellets in number/g of sediment, core photographs, lithology, and
formational assignment for Buck Pit 1 (40°14′18.79″N, 74°24′45.85″W), Search Farm 1 (40°05′29.20″N, 74°32′16.10″W), and Meirs Farm 1
(40°06′15.48″N, 74°31′37.48″W) coreholes. Note that scale for Ir at Bass River (Olsson et al., 1997) is greatly compressed relative to other
locations. Lowest occurrence of Senoniasphaera inornata is at base of green clay in adjacent Buck Pit outcrop (E. Rudolph, 1994, personal
commun.). K-Pg—Cretaceous-Paleogene.
on September 30, 2010geology.gsapubs.orgDownloaded from
4. GEOLOGY, October 2010 869
minerals. ODP Leg 174AX Site Sea Girt, spot cores from Parvin, New
Jersey, and outcrops at Sewell, New Jersey (Fig. 1), recovered clay clasts
but no spherules (Miller et al., 1999b, 2006). These findings reflect the
heterogeneity of preservation of spherules on the New Jersey coastal
plain. The pervasive white clay clasts are interpreted as rip-ups result-
ing from a tsunami that eroded the outer continental shelf and upper
slope (Olsson et al., 1997, 2002; Norris et al., 2000). The clasts contain
Maastrichtian planktonic foraminifera and a diverse outer neritic benthic
foraminiferal assemblage; this contrasts with inner neritic environments
in the enveloping Hornerstown Formation, supporting tsunami erosion
of the outer shelf. This tsunami was due to slope failure triggered by
earthquakes generated by the Chicxulub impact (Norris et al., 2000; Ols-
son et al., 2002) and is distinct from the impact-generated mega-tsunami
that reworked sediments in the Gulf of Mexico but was blocked from the
open Atlantic (Norris et al., 2000).
We compare our new outcrop and corehole studies with previous
results from outcrop and the Bass River corehole (Figs. 1 and 2). The
Tighe Park 1 corehole is adjacent to (~190 m) the Agony Creek type sec-
tion of the Pinna bed and faithfully reproduces the stratigraphy in the out-
crop (Fig. 1; Table DR1 in the GSA Data Repository1
). Meirs Farm 1,
Buck Pit 1, and Search Farm 1 cores (Fig. 2) provide a slightly different
physical stratigraphy, with generally finer-grained sediments than Tighe
Park I (Table DR1). Local lithologic variations are complex spanning the
boundary: a basal Danian burrowed glauconite sand of the Hornerstown
Formation overlies various lithologies, including clayey glauconite sands
and glauconitic clays (Navesink and New Egypt Formations) and mostly
indurated quartz sands (Tinton Formation)(Table DR1). Biostratigraphic
control on the shallow coreholes is limited because of the absence of cal-
careous microfossils, though dinocyst and macrofossil data allow confi-
dent placement of the K-Pg boundary (Table DR1). Downdip cores from
Bass River and Ancora allow firm identification of the K-Pg boundary
using calcareous and dinocyst microfossils (Fig. 2). The contrasting litho-
facies spanning the K-Pg boundary at these sites allows us to test the rela-
tionships among Ir, lithology, and impact-related features.
We measured Ir and compared it to the basic stratigraphy outlined
earlier herein and to counts of echinoid fecal pellets. The appearance
of epifaunal echinoid fecal pellets is a distinct lowermost Danian strati-
graphic horizon that is used to correlate Tighe Park outcrops to Meirs
Farm 1, Search Farm 1, Buck Pit 1, and Bass River coreholes (Fig. 2).
We suggest that the dramatic decrease in export production following the
extinction event (D’Hondt, 2005) resulted in increased burrowing and
benthic bulldozing.
The Tighe Park 1 corehole (Fig. 1) shows an Ir anomaly below the
sandy Pinna bed (i.e., it occurs in uppermost Cretaceous sediments),
confirming the relationship observed between Ir and the Pinna bed in
the adjacent outcrop (Landman, et al., 2007) and apparently predating
the extinctions. At Meirs Farm 1, the Ir anomaly occurs in clay-rich sedi-
ments containing a white clay clast layer correlated to the interval above
the extinctions at Bass River (Fig. 2). At Buck Pit 1, the Ir anomaly also
occurs in clay-rich sediments and is associated with the lowest occur-
rence of Senoniasphaera inornata, a marker for the base of the Danian.
At Search Farm 1, the anomaly occurs just above a Cucullaea vulgaris
layer, an abundant species in the Pinna bed at Tighe Park, and is associ-
ated with an increase in fecal pellets. Thus, Meirs Farm 1, Buck Pit 1,
and Search Farm 1 show that the Ir anomaly is basal Danian and that it
immediately postdates the extinctions. At Bass River, the Ir anomaly is
at the base of the spherule layer, 8 cm below the white clay clast layer,
but it clearly still postdates the extinctions of Cretaceous planktonic
foraminifera.
Comparisons of these sections show that in clay-rich sections, the Ir
anomaly correlates with the extinctions, but in sandier sections, the Ir is
found 6 cm (Bass River) to 20 cm (Tighe Park) lower. The Ir anomaly at
Tighe Park 1 is a sharp peak at a redox boundary that occurs 20 cm below
the appearance of Danian dinocysts; this is similar to Bass River, where
the anomaly occurs 6 cm below the appearance of Danian foraminifera
and dinocysts. This differs from the other three sites, where broader Ir
peaks are associated with the appearance of Danian dinocysts (Buck Pit 1)
or the up-section increase in fecal pellets (Search Farm 1, Meirs Farm 1)
that correlates with the appearance of Danian foraminifera and dinocysts.
Originally considered relatively immobile, postdepositional mobi-
lization/focusing of Ir and other platinum group elements is now well
established. Nonimpact Ir (terrestrial) associated with authigenic Fe-Mn
can be reduced, solubilized, mobilized (20 cm), and deposited at redox
boundaries (Colodner et al., 1992). Modest Ir anomalies at the Devonian-
Carboniferous boundary are attributed to focusing of terrestrial Ir by redox
conditions during deposition and/or early diagenesis (Wang et al., 1993).
Although Ir may be mobilized and redeposited up to 1 m from its origi-
nal location, evidence for an extraterrestrial source can be provided by
chondritic Ir/Pt ratios associated with the K-Pg Ir anomaly (Norris et al.,
2000; Robinson et al., 2009). As an example of this, Ir at Bass River was
mobilized after initial deposition at the top of the permeable spherule layer
and concentrated at the base of the spherule layer at an aquiclude. We
suggest that this explanation similarly applies to the type section of the
Pinna bed at Tighe Park, where the Ir was mobilized, percolated through
the sandy Pinna bed, and accumulated in a 2-cm-thick zone at a distinct
contact on top of the indurated Tinton Formation, also an aquiclude. The
mobilization and redeposition of Ir were likely due to differences in redox
potential (Colodner et al., 1992). Ir is likely mobilized up and down sec-
tion, but accumulates only where the sediments become more oxidizing
(e.g., at the base of the spherule layer at Bass River and Pinna bed at Tighe
Park 1). Thus, our studies strongly suggest that the Ir has been mobilized
at Tighe Park and Bass River, weakening the case for the hypothesis that
the extinctions postdate impact. We cannot refute the alternate hypothesis
that the Pinna bed could be a unique survivor layer. However, considering
that the Ir anomaly at Tighe Park/Agony Creek is displaced, as it is at Bass
River, there is no evidence to support this hypothesis. We suggest that the
mobility of Ir requires caution when using the Ir anomaly alone as a pre-
cise means of global correlation.
The Ir anomaly at Tighe Park, Buck Pit 1, Search Farm 1, and Meirs
Farms 1 is significantly lower (~0.5 ppb) than at Bass River (~2.5 ppb)
or other locations (Smit, 1999). Because the input of Ir was due to rapid
atmospheric fallout, the lower values observed are not due to dilution by
sedimentation rate differences, but must be due to bioturbation, vertical
mixing, or pore-water mobility of the signal. Baseline Ir concentrations
tend to have different values below and above the anomaly, suggesting dif-
ferential up/down mobility of impact Ir over approximately a meter scale.
CONCLUSION
The end Cretaceous mass extinction was predated by a large cool-
ing and sea-level fall at the Campanian-Maastrichtian boundary (71.5 Ma)
(e.g., Miller et al., 1999a), a latest Cretaceous warming ~0.5 m.y. before
the boundary, a minor cooling just prior to (tens of thousands of years) the
extinction (Olsson et al., 2002), and massive volcanism associated with
the Deccan Traps (e.g., Keller, et al., 2008). Sea level fell slowly during
the Maastrichtian, with a gradual fall across the boundary and a major
fall ~0.5 m.y. after the boundary. These tumultuous Maastrichtian climatic
events undoubtedly contributed to a decline in species diversity prior to the
K-Pg boundary, but the evidence is clear: impact-related spherules and an
Ir anomaly are associated with the mass extinction of the marine plankton
1
GSA Data Repository item 2010244, Table DR1 (lithologies and age in-
formation from the boreholes discussed in the text), is available online at www
.geosociety.org/pubs/ft2010.htm, or on request from editing@geosociety.org or
Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
on September 30, 2010geology.gsapubs.orgDownloaded from
5. 870 GEOLOGY, October 2010
(Fig. 2) and, by extension, the shallow-water invertebrates, marine verte-
brates, and terrestrial vertebrates.
ACKNOWLEDGMENTS
We thank G. Ravizza for advice about Ir extraction, E. Boyle for the enriched
Ir spike, E. Rudolph for dinocyst data, S. Esmeray for discussions, R. Norris and
two anonymous reviewers for comments, the New Jersey Geological Survey, the
U.S. Geological Survey Eastern Region Mapping Team drillers for collecting the
cores, L. Campo, D. Meirs, W. Search, W. Stone, and the staff of Tighe Park for
access, and funding by National Science Foundation grant EAR-070778. We thank
N. Landman and R. Johnson for comments.
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![GEOLOGY, October 2010 867
ABSTRACT
We directly link iridium (Ir) anomalies in New Jersey to the
mass extinction of marine plankton marking the Cretaceous-Paleo-
gene (K-Pg) boundary. We confirm previous reports of an Ir anomaly
20 cm below the extinction of Cretaceous macrofauna (the “Pinna”
bed) with new results from a muddy sand section from Tighe Park,
Freehold, New Jersey (United States), but we also show that Ir anom-
alies correlate with marine mass extinctions at three other clay-rich
New Jersey sections. Thus, we attribute the anomaly at Freehold to
the downward movement of Ir and reaffirm the link between impact
and mass extinction.
INTRODUCTION
Most scientists have accepted the hypothesis that a large bolide
impact caused the Cretaceous-Paleogene (K-Pg) boundary mass extinction
(Alvarez et al., 1980). A key to this debate is the detection of a large (>1
parts per billion [ppb]) Ir anomaly at the precise level of mass extinction
in planktonic foraminifera and calcareous nannoplankton (Alvarez et al.,
1980; Smit, 1999). The impact hypothesis is supported by identification
of altered impact glass and impact-derived shocked quartz (Smit, 1999;
Bohor et al., 1987) and the finding and dating of the ~180-km-diameter
Chicxulub crater (Hildebrand et al., 1991). The leading counter-hypothe-
sis to impact invokes hotspot volcanism of the Deccan Traps in India (e.g.,
Officer and Drake, 1985; Courtillot et al., 1988; Keller, et al., 2008). This
large igneous province consists of ~3–4 × 106
km3
of flood basalts (Coffin
and Eldholm, 1994). However, other studies have shown that the Deccan
Trap volcanism began in early chron C29r, predating the K-Pg boundary
by ~0.5 m.y., and was associated with sharp Sr-isotope and Os-isotope
excursions and a global warming event (e.g., Olsson et al., 2002; Ravizza
and Peucker-Ehrenbrink, 2003). Nevertheless, recent studies have re-
emphasized the role of Deccan volcanism, claiming that the main pulse of
volcanic outpouring occurred at the K-Pg boundary (Keller et al., 2008).
This has rejuvenated the hypothesis that the mass extinction postdates the
Chicxulub impact, though a recent review (Schulte et al., 2010) reaffirms
the direct relationship between a single impact and extinctions.
A key to understanding the relationship among extinctions, impact(s),
and large igneous province volcanism is the location of the Ir anomaly rela-
tive to the fossil record. Recent studies in New Jersey have suggested that
extinction of shallow shelf Cretaceous macrofossils may have postdated
the Ir anomaly (Landman et al., 2004, 2007). A 20-cm-thick fossil bed (the
Pinna bed) from Tighe Park, Freehold, New Jersey (United States), is asso-
ciated with the K-Pg boundary (Fig. 1); it contains a diverse latest Creta-
ceous fauna including the ammonite Discoscaphites iris and bivalve Pinna
laqueata (Landman et al., 2007). It is assigned to the uppermost Cretaceous
Palynodinium grallator dinocyst zone. A modest Ir anomaly of ~0.5 ppb
occurs at the base of the Pinna bed, suggesting two hypotheses (Landman
et al., 2007): (1) the diverse Cretaceous fauna survived the impact; or (2)
the Ir is displaced 20 cm down section. A third hypothesis, that the Ir is in
place but the Pinna layer is a reworked tsunamite, was rejected based on
the observation of P. laqueata in life position (Landman et al., 2007).
To test the relationship between Ir and the mass extinction event,
we conducted a campaign of shallow coring (<25 m) at eight New Jersey
localities in 2008 and 2009 adjacent to outcrops of the K-Pg boundary
(Fig. 1). Data from deeper coreholes drilled onshore by Ocean Drilling
Program (ODP) Legs 150X (Bass River) and 174AX (Ancora, Millville,
Geology, October 2010; v. 38; no. 10; p. 867–870; doi: 10.1130/G31135.1; 2 figures; Data Repository item 2010244.
© 2010 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org.
Relationship between mass extinction and iridium across the
Cretaceous-Paleogene boundary in New Jersey
Kenneth G. Miller1
, Robert M. Sherrell1,2
, James V. Browning1
, M. Paul Field2
, W. Gallagher3
, Richard K. Olsson1
,
Peter J. Sugarman4
, Steven Tuorto2
, and Hendra Wahyudi1
1
Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA
2
Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey 08903, USA
3
Department of Geological, Environmental, and Marine Sciences, Rider University, Lawrenceville, New Jersey 08468, USA
4
New Jersey Geological Survey, P.O. Box 427, Trenton, New Jersey 08625, USA
0.1 0.3 0.5
(m)
Depth
Iridium (ppb)
clayeyglauconitesand
Veryheavilybioturbated
clayeyglauconitesandquartzoseglauconitesand
PaleogeneHornerstownFormationUpperCretaceousTintonFormation
Iridium
Tighe Park 1
12
13
14
15
16
(ft)
4
5
20 30
74°W
40°N
39°N
Ancora
Millville
Bass River
Parvin
Sewell
Sea Girt
Fecal pellets
(#/gram)
infaunal echinoid
fecal pellets
0 10
Damassadiniumcalifornicum
WeatheredPinnalayerIndurated
0 20 mi
0 20 km
“Agony Creek”
75°W See inset
below
Fort Monmouth
Tighe Park
Buck Pit
Meirs Farm
Lowe Meadow
Search Farm
5cm
0 10 mi
0 10 km
Figure 1. Freehold, New Jersey, sections. Ir in parts per billion
(ppb), fecal pellets in number/g of sediment, core photographs, li-
thology, and formational assignment for Tighe Park 1 corehole
(40°12′51.42″N, 74°17′17.79″W). First occurrence of Danian dino-
cyst index fossil Damassadinium californicum is after Landman
et al. (2007). Also shown is outcrop photograph (from Landman et
al., 2007) from an adjacent (~190 m east) tributary (“Agony Creek”)
of Manasquan River. Asterisk indicates level of Ir anomaly in this
section. Inset location map shows outcrop of post-Campanian Cre-
taceous (dark-green Red Bank and light-green Tinton Formations)
and Paleocene (brown Hornerstown and mustard/yellow Vincentown
Formations) strata; pre-Maastrichtian strata are in dark gray; post-
Paleocene strata are light gray.
on September 30, 2010geology.gsapubs.orgDownloaded from](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)