Multiple impacts across the Cretaceous–Tertiary boundary
Introduction
The Chicxulub structure in Yucatan, Mexico, is generally considered the K/T boundary impact that caused one of the major mass extinctions in the Earth's history. Impact ejecta layers have now been widely recognized in numerous localities around the Gulf of Mexico (see review by Smit, 1999) and linked to the Chicxulub impact based on their geographic distribution, 39Ar/40Ar ages close to the K/T boundary Sigurdsson et al., 1991, Swisher et al., 1992, Dalrymple et al., 1993 and chemical similarity to Chicxulub melt rock Izett et al., 1991, Blum et al., 1993, Koeberl et al., 1994, Chaussidon et al., 1996. Controversies persist with respect to the stratigraphic position of the ejecta layer at or near the K/T boundary, and the nature and tempo of emplacement, whether by tsunami (Smit et al., 1996) or gravity flows and sea level changes Adatte et al., 1996, Bohor, 1996, Stinnesbeck et al., 1996, Keller et al., 1997, and the presence of multiple altered impact glass spherule layers in the Late Maastrichtian and Early Danian Keller et al., 2001, Keller et al., 2002a, Keller et al., 2002b, Soria et al., 2001. A better understanding of these events may reconcile the two divergent K/T mass extinction hypotheses. The impact–extinction hypothesis calls for sudden mass extinctions due to a single large impact (Alvarez et al., 1980) now considered to be the Chicxulub structure. Paleontologists have long argued that the fossil record does not support a single cause for the mass extinction and, therefore, proposed multievent scenarios that include major volcanism, rapid climate and sea level changes Archibald, 1996, Keller, 1996, MacLeod et al., 1997 and one or more impacts Keller et al., 1997, Keller et al., 2002a, Keller, 2001.
These controversies have remained unsolved, in part, because most impact-related investigations have been geographically limited to a narrow region surrounding Chicxulub, and temporally limited to an interval spanning the K/T boundary clay, the ejecta layer and a few samples above and below. No significant effort has been made to examine older or younger sediments for additional impact ejecta or other environmental signals. The wider context of the mass extinction event, including the half million years before and after the K/T boundary, is well studied based on fossil assemblages, climate and sea level changes, all of which show major changes preceding the K/T boundary (see review in Keller, 2001). Only recently have investigations of impact ejecta in Haiti and Mexico included the upper part of the Late Maastrichtian and Early Danian and revealed the presence of multiple impact ejecta layers (microtektites and microkrystites) in both Late Maastrichtian and Early Danian sediments, as well as Ir and Platinum group element (PGE) anomalies in the Early Danian Keller et al., 2001, Keller et al., 2002a, Stinnesbeck et al., 2001, Stinnesbeck et al., 2002, Odin et al., 2001, Stüben et al., 2002.
In this paper, we review the stratigraphy and biochronology of the K/T boundary ejecta deposits and provide new evidence of multiple ejecta deposits from sections in central and southern Mexico, southern Belize and eastern Guatemala (Fig. 1). The first part introduces the biostratigraphic scheme of the K/T boundary, the globally recognized boundary markers and the age and biozonation control of the Late Maastrichtian and Early Danian based on which the age and continuity of the sedimentary record is evaluated. In the second part, we review and document the stratigraphy and age of thick microtektite and microkrystite ejecta deposits from Mexico, Guatemala, Belize, Haiti and deep-sea sites, and provide new mineralogical (Cheto smectite) analyses that suggest a common glass origin. Finally, we provide a regional synthesis of the age of spherule deposition in Central America and the Caribbean and propose a multievent scenario for the K/T transition that is consistent with current impact, climate and fossil data.
Field sections were examined, measured and sampled based on standard methodologies. Biostratigraphic analysis was based on planktic foraminifera processed following the standard method of Keller et al. (1995). The smaller (36–63 μm) size fraction was examined for the first occurrence of tiny Early Danian species. Individual clasts from breccias, conglomerates and spherule layers were processed separately and analyzed for planktic foraminifera in order to determine the biostratigraphic ages of these sediments prior to erosion and redeposition.
Clay mineral analyses were conducted at the University of Neuchatel, Switzerland, based on XRD (SCINTAG XRD 2000 Diffractometer, Geological Institute) and ESEM (Phillips environmental microprobe equipped with EDEX analyzer, Institute of Microtechnique) following the procedures outlined by Kübler (1987) and Adatte et al. (1996). Platinum group elements (PGE) were analyzed at the Institute for Mineralogy and Geochemistry, University of Karlsruhe, by isotope dilution HR-ICP-MS after preconcentration and matrix reduction by Ni-fire assay Kramar et al., 2001, Stüben et al., 2002.
Section snippets
Continuous K/T records
Our understanding of the Cretaceous–Tertiary boundary events largely depends on two critical factors: (1) the quality and continuity of the stratigraphic record that holds evidence for impacts, mass extinctions, climate and sea level changes, and (2) the age resolution that can be achieved for these events based on biostratigraphy, cyclostratigraphy and magnetostratigraphy. To evaluate the temporal distribution of impact ejecta, it is essential to understand the stratigraphy of the K/T boundary
Impact ejecta database
The most diagnostic and easily recognized impact ejecta within <1000 km of Chicxulub are layers of tiny altered glass spherules (0.3–4 mm) characterized by abundant internal vesicles. These altered glass spherules have been identified as tektites or microtektites produced by melting and quenching of terrestrial rocks during a hypervelocity impact Izett et al., 1991, Sigurdsson et al., 1991, Blum and Chamberlain, 1992, Blum et al., 1993, Koeberl, 1993, or microkrystites, a product of impact
Guatemala
At El Caribe, Guatemala, Cretaceous limestone breccias with altered glass spherules underlie Early Danian Pla(l) sediments enriched with iridium, similar to Bochil-1, Chiapas Stinnesbeck et al., 1997, Fourcade et al., 1998, Fourcade et al., 1999, Keller and Stinnesbeck, 2000. Thick deposits of altered vesicular spherules, similar to the microtektite and microkrystite deposits in northeastern Mexico, have recently been discovered at Actela located 30-km southeast of San Luis, El Peten, near the
Belize
Most investigations in Belize have focused on the Albion Island quarry and its unusual spheroid and diamictite deposits that overlie the Barton Creek Formation Ocampo et al., 1996, Pope et al., 1999, Fouke et al., 2002, and similar deposits are also present at Armenia in central Belize along the Hummingbird Highway (Fig. 13, Keller et al., in preparation). The absence of age diagnostic fossils in these deposits has prevented age determination or stratigraphic correlation to the impact ejecta
Haiti
The biostratigraphy of the Beloc sections has been previously reported in several studies including Maurasse and Sen (1991), Sigurdsson et al. (1991), Jéhanno et al. (1992), Leroux et al. (1995) and Lamolda et al. (1997). Most of these studies focused on roadside outcrops which have a prominent spherule layer that is folded, faulted and slumped. Stinnesbeck et al. (2000) and Keller et al. (2001) reported on several new and undisturbed sections that contain expanded K/T transitions with spherule
Caribbean ODP Sites 999 and 1001
Caribbean ODP Leg 165 cored several localities with the expectation of recovering an undisturbed and complete K/T transition to complement the MM deposits in Beloc, Haiti, 350 km to the north. The K/T boundary was recovered in two localities. At Site 999, located on Kogi Rise in the Colombian Basin at 2828-m depth, an incomplete K/T transition was recovered in a 2-cm-thick clayey layer in a calcareous limestone (Sigurdsson et al., 1997). At Site 1001, located on the Hess Escarpment at 32,600-m
Early Danian Ir and Pd anomalies
There is widespread evidence for an Early Danian P. eugubina subzone Pla(l) Ir anomaly in Haiti, Guatemala and Mexico (Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15; Keller et al., 2001, Stinnesbeck et al., 2002, Stüben et al., 2002). This Ir anomaly is generally above the altered microtektite and microkrystite deposits of the Early Danian and represents a unique unrelated event. In contrast, no spherule deposits are directly associated with Ir enrichments above
K/T impact at Chicxulub
All spherules originated from the Chicxulub impact at the K/T boundary and their stratigraphic emplacement in Late Maastrichtian and Early Danian sediments is the result of slumps, gravity flows, mass wasting, margin collapse due to seismic shaking, tsunamis and reworking into younger sediments as a result of current activity.
This is the standard K/T impact scenario. It gains some support from slumps on the slope of Blake Nose, off Florida Klaus et al., 2000, Norris et al., 2000, and
Conclusion
A multiimpact scenario is most consistent with current evidence of altered impact glass (microtektites, microkrystites), Ir anomalies, PGEs, volcanic activity and climate change during the Late Maastrichtian to Early Danian as summarized in Fig. 20. Current evidence supports three impact events over a period of about 400 ky. The first impact, marked by the oldest deposit of altered microtektites and microkrystites (MM) occurred at about 65.27±0.03 Ma nearly coincident with major Deccan
Acknowledgements
We thank Andrew Glikson for a tremendously helpful review and for liberally sharing his knowledge with us. We also thank Robert Hargraves for his many stimulating discussions and his untiring pursuit of impacts. This study has benefited from various student projects in Mexico over the past 6 years and we gratefully acknowledge the contributions by W. Affolter, C. Ifrim, M. Lindinger, L. Schilli and P. Schulte. We also thank Brian Holland, Belize Minerals, and Jorge de la Cruz and Carlos de
Gerta Keller is Professor in the Geosciences Department of Princeton University. She received her Ph.D. in Paleontology and Geology from Stanford University and worked at the U.S. Geological Survey in Menlo Park, CA before accepting her present position in 1984. Her main research interests focus on evolution and mass extinctions, biotic effects of catastrophic events (e.g. impacts, volcanism, ocean anoxia), and global climate and environmental changes.
References (123)
- et al.
High stress late Maastrichtian paleoenvironment in Tunisia: inference from planktic foraminifera
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2002) - et al.
Age and paleoenvironment of the Maastrichtian–Paleocene of the Mahajanga Basin, Madagascar: a multidisciplinary approach
Mar. Micropaleontol.
(2003) - et al.
Micropaleontology and sedimentology across the Cretaceous/Tertiary boundary at La Ceiba (Mexico): impact-generated sediment gravity flows
J. South Am. Earth Sci.
(2001) - et al.
Coexisting altered glass and Fe–Ni oxides at the Cretaceous–Tertiary boundary, Stevns Klint (Denmark): direct evidence of meteorite impact
Earth Planet. Sci. Lett.
(2000) - et al.
Sedimentological evolution of the Cretaceous carbonate platform of Chiapas (Mexico)
J. South Am. Earth Sci.
(1998) - et al.
Age of the Guatemala breccias around the Cretaceous–Tertiary boundary: relationships with the asteroid impact on the Yucatan
C. R. Acad. Sci., Ser. 2, Sci. Terre Planetes
(1998) - et al.
Cretaceous stratigraphy and palaeoenvironments of the Southern Petén Basin, Guatemala
Cretac. Res.
(1999) The astronomical connection of terrestrial evolution: crustal effects of post-3.8 Ga mega-impact clusters and evidence for major 3.2±0.1 Ga bombardment of the Earth–Moon system
J. Geodyn.
(2001)- et al.
Electron spin resonance of 65 million year old glasses and rocks from the Cretaceous–Tertiary boundary
J. Non-Cryst. Solids
(1999) - et al.
Magnetostratigraphy of the Cretaceous–Tertiary boundary at Agost (Spain)
Earth Planet. Sci. Lett.
(1989)
Processional climate cyclicity in Late Cretaceous–Early Tertiary marine sediments: a high resolution chronometer of Cretaceous–Tertiary boundary events
Earth Planet. Sci. Lett.
Geochemical markers of the Cretaceous–Tertiary boundary event at Brazos River, Texas, USA
Geochim. Cosmochim. Acta
The Cretaceous–Tertiary boundary at Beloc, Haiti: no evidence for an impact in the Caribbean area
Earth Planet. Sci. Lett.
The role of komatitic and picritic magmatism and S-saturation in the formation of ore deposits
Lithos
The end-cretaceous mass extinction: year 2000 assessment
J. Planet. Space Sci.
Stable isotope, TOC and CaCO3 record across the Cretaceous/Tertiary Boundary at El Kef, Tunisia
Palaeogeogr. Palaeoclimatol. Palaeoecol.
High-stress paleoenvironment during the late Maastrichtian to early Paleocene in Central Egypt
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Are Ir anomalies sufficient and unique indicators for cosmic events?
Planet. Space Sci.
Terminal Cretaceous warming event in the mid-latitude South Atlantic Ocean: evidence from poleward migration of Contusotruncana contusa (planktonic foraminifera) morphotypes
Palaeogeogr. Palaeoclimatol. Palaeoecol.
The K/T boundary of Beloc (Haiti): compared stratigraphic distributions of boundary markers
Earth Planet. Sci. Lett.
Maastrichtian climate, productivity and faunal turnovers in planktic foraminifera in South Atlantic DSDP Site 525A and 21
Mar. Micropaleontol.
The late Campanian and Maastrichtain in northwestern Tunisia: paleoenvironmental inferences from lithology, macrofauna and benthic foraminifera
Cretac. Res.
Planktonic foraminiferal turnover across the Cretaceous–Tertiary boundary in the Vajont valley (southern Alps, northern Italy)
Cretac. Res.
High resolution planktonic foraminiferal analysis from the Cretaceous–Tertiary boundary at Ain Settara (Tunisia): evidence of an extended mass extinction
Palaeogeogr. Palaeoclimatol. Palaeoecol.
K–Ar d'un neveau volcanoclastique maastricthien de Haiti
Chicxulub impact ejecta from Albion Island, Belize
Earth Planet. Sci. Lett.
Iridium and other platinum-group elements as geochemical markers in sedimentary environments
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Decline of the Maastrichtian pelagic ecosystem based on planktic foraminiferal assemblage change: implications for the terminmal Cretaceous faunal crisis
Geology
Lithostratigraphic and mineralogical correlations of near-K/T boundary clastic sediments in northeastern Mexico: implications for mega-tsunami or sea level changes?
Geol. Soc. Am. Spec. Pap.
Paleoenvironment across the Cretaceous-Tertiary transition in eastern Bulgaria
Geol. Soc. Am. Spec. Pap.
Extraterrestrial cause for the Cretaceous–Tertiary extinction
Science
Testing extinction theories at the Cretaceous–Tertiary boundary using the vertebrate fossil record
Extinción de foraminı́feros en el lı́mite Cretácico/Terciario de Coxquihui (México) y su relación con las evidencias de impacto
Rev. Esp. Micropaleontol.
Hazard due to giant comets: climate and short-term catastrophism
Global environmental changes preceding the Cretaceous–Tertiary boundary: early–late Maastrichtian transition
Geology
A revised Cenozoic geochronology and chronostratigraphy
Oxygen isotope constraints on the origin of impact glasses from the Cretaceous–Tertiary boundary
Science
Isotopic comparison of K–T boundary impact glass with melt rock from the Chicxulub and Manson impact structures
Nature
A sediment gravity flow hypothesis for siliciclastic units at the K/T boundary, northeastern Mexico
Geol. Soc. Am. Spec. Pap.
The Cretaceous–Tertiary boundary cocktail: Chicxulub impact triggers margin collapse and extensive sediment gravity flows
Geology
Multiple impacts at the KT boundary and the death of the dinosaurs
Sulfur and boron isotope study of high-Ca impact glass from the K/T boundary: constraints on source rocks
Geol. Soc. Am. Spec. Pap.
Evolutionary Catastrophes: The Science of Mass Extinction
Stratigraphic Commission accelerates progress, 1984–1989
Episodes
40Ar/39Ar age spectra and total fusion ages of tektites from Cretaceous–Tertiary boundary sedimentary rocks in the Beloc formation, Haiti
Les argiles de la transition Cretace–Tertiaire au Guatemala, temoins d'un impact d'asteroide
Bull. Soc. Geol. Fr.
Ichnology of Cretaceous–Tertiary (K/T) boundary beds in northeastern Mexico
Palaios
Origin of the Mg smectite at the Cretaceous/Tertiary (K/T) boundary at Stevns Klint, Denmark
Clays Clay Miner.
The origin of clay minerals at the Cretaceous/Tertiary boundary in Denmark
Geol. Soc. Amer. Bull.
Cited by (121)
End-Cretaceous to middle Eocene events from the Alpine Tethys: Multi-proxy data from a reference section at Kršteňany (Western Carpathians)
2021, Palaeogeography, Palaeoclimatology, PalaeoecologyChronostratigraphy
2020, Encyclopedia of Geology: Volume 1-6, Second EditionThe genesis of oceanic impact craters and impact-generated tsunami deposits
2020, Tsunamiites: Features and ImplicationsTsunamiites-conceptual descriptions and a possible example at the Cretaceous-Paleogene boundary in the Pernambuco Basin, Northeastern Brazil
2020, Tsunamiites: Features and Implications
Gerta Keller is Professor in the Geosciences Department of Princeton University. She received her Ph.D. in Paleontology and Geology from Stanford University and worked at the U.S. Geological Survey in Menlo Park, CA before accepting her present position in 1984. Her main research interests focus on evolution and mass extinctions, biotic effects of catastrophic events (e.g. impacts, volcanism, ocean anoxia), and global climate and environmental changes.
Wolfgang Stinnesbeck is Professor in the Geological Department of Karlsruhe University, Germany. He received his Ph.D. in Paleontology and Geology from the University of Bonn and was professor at the Autonomous University of Nuevo León, Mexico before accepting his current position as Professor for Geology at Karlsruhe University in 1996. His main research interests include biostratigraphy, Cretaceous ecosystems and mass extinctions, with research activities centered in Latin America.
Thierry Adatte is Assistant Professor and Research Associate at the Geological Institute of the University of Neuchâtel, Switzerland, where he received his Ph.D. in Mineralogy and Sedimentary Geology. His research interests focus on global change associated with mass extinction events, high resolution bio-, chemo- and sequence stratigraphy. geochemistry (stable isotopes, organic carbon, speciation of major elements) and mineralogy (whole rock and clay-mineralogy).
Doris Stüben is Professor and Director of the Mineralogy and Geochemistry Institute at the University of Karlsruhe, Germany. She received her Ph.D. in geochemistry from the University of Clausthal-Zellerfeld, and was a Research Associate at the Geological Institute of the University of Kiel, before accepting her current position in 1995. Her main research interests focus on environmental and applied geochemistry, isotopes, marine ore deposits and sediment geochemistry.