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Evidence for a Major Meteorite Impact on the Earth 34 Million Years Ago: Implication for Eocene Extinctions
Abstract
A deep-sea core from the Caribbean contains a layer of sediment highly enriched in meteoritic iridium. This layer underlies a layer of North American microtektites dated at 34.4 million years ago and coincides with the extinction of five major species of Radiolaria. It is suggested that a massive, chemically undifferentiated meteorite collided with the earth, producing the tektites and leading to extinctions 34 million years ago.
... 70°48.6′W) is located in 3548 m water depth (Saito et al., 1974) with a late Eocene paleo water depth >1000 m (Baker and Glass, 1974). Core RC9-58 displays 25 cm of separation between the North American microtektite layer and the cpx spherule layer, with its coupled Ir anomaly ( Fig. 3) (Ganapathy, 1982;Glass et al., 1982). The equivalent age separation equals ~25 k.y. ...
... (1) Glass (1989) (2) Glass et al. (1982) (3) Ganapathy (1982) (4) Kyte and Liu (2002) (5) Glass and Koeberl (1999) (Vonhof et al., 2000), and equatorial Pacifi c ODP Site 1218 (Lear et al., 2004) negative δ 13 C anomaly. One possible source is the dissociation of ~310 Gt of methane hydrates stored on continental margins, which are thought to be capable of abruptly releasing massive amounts of readily oxidized 12 C-rich carbon (δ 13 C = −60‰) into the ocean-atmosphere system (e.g., Dickens et al., 1995Dickens et al., , 1997Katz et al., 1999Katz et al., , 2001, perhaps through slope failure triggered by an impact. ...
... As noted herein, it is diffi cult to explain a whole-ocean δ 13 C excursion of ~0.5‰ magnitude and <10 k.y. onset using standard (7) (1) Glass (1989) (2) Glass et al. (1982) (3) Ganapathy (1982) (4) Kyte and Liu (2002) (5) Glass and Koeberl (1999) carbon budgets. The observation that the δ 13 C excursion coincident with the Popigai impact was a rapid (< 10 k.y.) whole-ocean event is therefore of interest for more general understanding of the carbon cycle. ...
Two of the three largest impact craters found on Earth since 200 Ma (Popigai and the Chesapeake Bay Impact Structure or CBIS) are late Eocene (~35.4-35.5 Ma based on radiometric ages) and are well preserved, yet the environmental response to these near synchronous and large impacts is poorly understood. No extinction events are recorded in coccolithophorids, planktonic or benthic foraminifera at this time, and terrestrial biota appear unaffected. The late Eocene global temperature history and carbon budget are poorly constrained because of sparsely sampled delta18O and delta13C records. We present new microfauna and nannoplankton evidence and stable isotopic data that show: 1) minimal biotic and temperature response associated with the impacts; and 2) a large and transient carbon isotope excursion associated with the impacts that reflect a major change in the global carbon budget. Southern Ocean ODP Site 1090 provides an exceptional record to test if a carbon isotopic anomaly is associated with the late Eocene impacts because benthic foraminifera are well preserved, the identified ejecta horizon is marked by an Ir anomaly (~950pg/g; Kyte and Liu, 2002), and the magnetostratigraphic age control is excellent (Channell et al., 2003). A first-order correlation to the geomagnetic polarity time scale at Site 1090 places the impact ejecta horizon in Chron C16n.1n (279.01 mbsf) with a corresponding age of ~35.4 Ma, consistent with published radiometric ages. We generated a high-resolution carbon and oxygen stable isotope record of benthic foraminifera across the impact ejecta layer from 34.6-35.8 Ma (8 kyr sampling) and 33.7-36 Ma (16 kyr sampling). Our results show that a transient carbon isotope decrease (277-278 mbsf) of 0.4-0.5% is associated with the impact horizon. The delta13C anomaly persists for ~250 kyr; then the signal returns to `pre-impact' values. Following recovery from the transient excursion there were no long-term changes in global carbon isotopic values associated with the impacts. Our results show no significant changes in benthic foraminifera oxygen isotope values across the impact ejecta layers, implying that no major changes in deep-water temperatures occurred. Coeval benthic foraminiferal records also show the carbon isotopic excursion: 1) new benthic data from New Jersey slope Site 612 show a 0.5% change, though this record is partially truncated due to a hiatus; 2) Southern Ocean Site 689 shows a larger excursion (1.0%) (Vonhof et al., 2000); and 3) Pacific Ocean Site 1218 shows a smaller anomaly (0.4%) (Lear et al., 2004). We suggest this delta13C perturbation was global and directly related to the late Eocene impactor(s).
... 70°48.6′W) is located in 3548 m water depth (Saito et al., 1974) with a late Eocene paleo water depth >1000 m (Baker and Glass, 1974). Core RC9-58 displays 25 cm of separation between the North American microtektite layer and the cpx spherule layer, with its coupled Ir anomaly ( Fig. 3) (Ganapathy, 1982;Glass et al., 1982). The equivalent age separation equals ~25 k.y. ...
... (1) Glass (1989) (2) Glass et al. (1982) (3) Ganapathy (1982) (4) Kyte and Liu (2002) (5) Glass and Koeberl (1999) (Vonhof et al., 2000), and equatorial Pacifi c ODP Site 1218 (Lear et al., 2004) negative δ 13 C anomaly. One possible source is the dissociation of ~310 Gt of methane hydrates stored on continental margins, which are thought to be capable of abruptly releasing massive amounts of readily oxidized 12 C-rich carbon (δ 13 C = −60‰) into the ocean-atmosphere system (e.g., Dickens et al., 1995Dickens et al., , 1997Katz et al., 1999Katz et al., , 2001, perhaps through slope failure triggered by an impact. ...
... As noted herein, it is diffi cult to explain a whole-ocean δ 13 C excursion of ~0.5‰ magnitude and <10 k.y. onset using standard (7) (1) Glass (1989) (2) Glass et al. (1982) (3) Ganapathy (1982) (4) Kyte and Liu (2002) (5) Glass and Koeberl (1999) carbon budgets. The observation that the δ 13 C excursion coincident with the Popigai impact was a rapid (< 10 k.y.) whole-ocean event is therefore of interest for more general understanding of the carbon cycle. ...
We evaluated the age of two Upper Eocene impact ejecta layers (North American microtektites linked to the Chesapeake Bay impact structure and clinopyroxene (cpx) spherules from the Popigai crater) and the global effects of the associated impact events. The reported occurrence of cpx spherules from the Popigai impact structure at South Atlantic ODP Site 1090 within the middle of magnetochron C16n.1n yields a magnetochronologic age of 35.4 Ma. We generated high-resolution stable isotope records at Sites 1090, 612 (New Jersey slope), and Caribbean core RC9-58 that show: (1) a 0.5‰ δ 13 C decrease in bulk-carbonate at Site 1090 coincident with the Popigai cpx spherule layer; and (2) a 0.4‰-0.5‰ decrease in deep-water benthic foraminiferal δ 13 C values across the Popigai impact ejecta layer at Site 612 and core RC9-58. We conclude that the δ 13 C excursion associated with Popigai was a global event through- out the marine realm that can be correlated to magnetochron C16n.1n. The ampli- tude of this excursion (~0.5‰) is within the limits of natural variability, suggesting it was caused by a decrease in carbon export productivity, potentially triggered by the impact event(s). North American microtektites associated with the Chesapeake Bay impact occur stratigraphically above the Popigai cpx spherules at Site 612 and core RC9-58. We found no defi nite evidence of a δ 13 C anomaly associated with the North American microtektite layer, though further studies are warranted. High-resolution bulk-carbonate and benthic foraminiferal δ 18 O records show no global temperature change associated with the cpx spherule or North American microtektite layers.
... Geochemical analysis determined the Caribbean microtektites are part of the NASF (John and Glass, 1974). A clinopyroxene-bearing microspherule layer is located 20 cm (John and Glass, 1974) to 30 cm (Ganapathy, 1982) below the peak abundance of microtektites in core RC9-58. Additional work (Ganapathy, 1982) identified an Ir anomaly of 4.1 ppb located at 279.5 cm in the core, which is in close proximity to the stratigraphically lower microkrystite layer. ...
... A clinopyroxene-bearing microspherule layer is located 20 cm (John and Glass, 1974) to 30 cm (Ganapathy, 1982) below the peak abundance of microtektites in core RC9-58. Additional work (Ganapathy, 1982) identified an Ir anomaly of 4.1 ppb located at 279.5 cm in the core, which is in close proximity to the stratigraphically lower microkrystite layer. Previous work (Alvarez et al., 1982) of DSDP Caribbean core 149 identified the presence of an Ir anomaly coinciding with the highest abundance of microtektites in upper Eocene sediments. ...
... Finally, we note that uncritical acceptance of these younger age estimates for the Eocene-Oiigocene boundary have led to what we consider to be a premature misreading of the geohistorical record (Ganapathy 1982;Alvarez et al. 1982). These authors have suggested a cause and effect relationship between a bolide impact (c.34 Ma), the termination of five 'major' (sic I) radiolarian species (Ganapathy 1982: 885) (which were said to constitute over 70% of the total Radiolaria) and an iridium anomaly at supposedly correlative levels in DSDP Site 149 and RC9-58 in the Caribbean. ...
... The interpretation of the geohistoric record at the Eocene-Oligocene boundary in a framework of 'catastrophism' (Ganapathy 1982;Alvarez et al. 1982) similar to that postulated for the Cretaceous-Tertiary boundary (AIvarez et al. 1979; is quite unwarranted by presently available data. ...
We present a revised Paleogene geochronology based upon a best fit to selected high temperature radiometric dates on a number of identified magnetic polarity chrons (within the late Cretaceous, Paleogene and Neogene) which minimizes apparent accelerations in sea-floor spreading. An assessment of first order correlations of calcareous plankton biostratigraphic datum events to magnetic polarity stratigraphy yields the following estimated magnetobiochronology of major chrono- stratigraphic boundaries: Cretaceous-Tertiary boundary (Chron C29R), 66.4 Ma; Paleocene-Eocene (Chron C24R), 57.8 Ma; Eocene-Oligocene (Chron C13R), 36.6 Ma; Oligocene-Miocene (Chron C6CN), 23.7 Ma.
The Eocene is seen to have expanded chronologically (- 21 m.y.) at the expense of the Paleocene (- 9 m.y.) and is indeed the longest of the Cenozoic epochs. In addition, magnetobio- stratigraphic correlations require adjustments in apparent correlations with standard marine stage boundaries in some cases (particularly in the Oligocene). Finally, we present a correlation between standard Paleogene marine and terrestrial stratigraphies.
... cyclic extinction events was proposed by Raup and Sepkoski (1984) to fall at the Eocene/Oligocene boundary. A number of authors (e.g., Alvarez et al., 1982;Asaro et al., 1982;Ganapathy, 1982) attributed the Eocene/Oligocene extinctions to extraterrestrial causes, a hypothesis that has engendered considerable debate (Keller et al., 1983;Keller, 1986). ...
... The discovery of an iridium anomaly at the Cretaceous/ Tertiary boundary in a number of sections led Alvarez et al. (1980) to suggest that the Cretaceous/Tertiary mass extinc- tions were the result of an extraterrestrial impact. Similarly, the simultaneous deposition of the North American tektites field and the extinction of five radiolarian species at the Eocene/Oligocene boundary (Glass and Zwart, 1979) led some authors (e.g., Alvarez et al., 1982;Asaro et al., 1982;Ganapathy, 1982) to suggest that a bolide event caused mass extinctions at the Eocene/Oligocene boundary. The Eocene-Oligocene extinctions have been prominently figured in the discussions of extinction periodicity, first proposed by Fischer and Arthur (1977) and Raup and Sepkoski (1984). ...
An Eocene-Oligocene calcareous nannofossil biostratigraphic framework for ODP Site 748 in the southern Indian Ocean is established, which enables a reinterpretation of the preliminary magnetostratigraphy and a new placement for magnetic Subchron C13N in the lowermost Oligocene. Calcareous nannofossil species diversity is low at Site 748 relative to lower latitude sites. There is, however, no apparent mass extinction at any stratigraphic level. Similarly, no mass extinctions were recorded at or near the Eocene/Oligocene boundary at Site 711 in the equatorial Indian Ocean. Species diversity at the equatorial site is significantly higher than at Site 748. The abundance patterns of nannofossil taxa are also quite different at the two sites, and indicated a significant latitudinal biogeographic gradient between the equatorial site and the high-latitude site in the Indian Ocean for the middle Eocene-Oligocene interval. The abundance change of warm-water taxa is similar to that of species diversity at Site 711. There is a general trend of decreasing abundance of warm-water taxa from the middle Eocene through the early Oligocene at Site 711, suggesting a gradual cooling of the surface waters in the equatorial Indian Ocean. The abundance of warm-water taxa increased in the late Oligocene, in association with an increase in species diversity, and this may reflect a warming of the surface waters in the late Oligocene. -from Authors
... My (crater diameters >10 km across: Alvarez and Muller, 1984 (Glass and Burns, 1987). The micro-tektites have very similar composition to tektites strewn across the North American continent (Koeberl and Glass, 1988); their fission track ages of 34 My agree with a time of diverse extinctions (Ganapathy, 1982). Both microtektites and spherules are considered to be impact melts, the former produced from loess or greywacke material, the latter from more mafic terrestrial material. ...
Three of the more dramatic events in natural history - extinction of species, meteoritic impacts and volcanic outbursts have come together in a scientific controversy. One school favours an extraterrestrial impact for the "catastrophe' marker bed, another violent volcanic discharges from the earth's core. The evidence is conflicting. This paper sorts through these scenarios and seeks a solution. Australian evidence is rarely considered in the balance of the arguments. New concepts on Australia's past volcanism will be discussed, as they seem to suggest vigorous volatile volcanism 65 million years ago. -from Author
... Una forma de extinción masiva en nuestro planeta se acredita al impacto de objetos extraterrestres de enormes tamaños en una variedad de ocasiones (Hodych and Dunning, 1992;Claeys et al., 1992;Benton and Twitchett, 2003;White and Saunders, 2005;Benton, 2015). De los impactos de asteroides en la Tierra, los más significantes ocurrieron en tiempos arcaicos, finales de tiempos de Permiano, como en finales del Cretácico (Ganapathy, 1980;1982;Smit, 1990;Kaiho et al., 2001;Schulte et al., 2010;Lowe, 2013). Muchos mitos y leyendas están asociadas con la apariencia de un objeto espacial como el Cometa Halley, o de un objeto que traspasó la atmósfera y posteriormente impactó. ...
Lo que muchas personas temen, y consideran como el fin de la humanidad, es un impacto de un asteroide colisionando con nuestro planeta. En el pasado de la Tierra se han impactado varios asteroides y meteroides, pero la mayoría de estos choques se erosionaron, y hoy por hoy se encuentran solamente a veces unos indicios directos como indirectos, como extinciones masivas de unas especies en forma de fósiles, o capas con contenido de material extraterrestre entre otros. En la superficie actual de la Tierra sí hay unas claras evidencias de estos impactos, y debido a un reconocimiento en el campo, se ha encontrado una más el 12 de Marzo de 2017, en el Parque Nacional Cajas, muy cerca del centro de interpretación. Este descubrimiento del impacto sobre una roca volcánica podrá ser muy pronto un atractivo turístico principal del país debido a su accesibilidad, e importancia por ser único en el Ecuador.
What many people fear and consider as the end of the humanity is an impact of an asteroid colliding with our planet. In the past of the earth several asteroids and meteroids have been impacted, but most of these collisions have been eroded and today there are only sometimes direct and indirect indications, such as massive extinctions of species in the form of fossils, layers with content of extraterrestrial material among others. On the present surface of the earth there are clear evidence of these impacts, and due to a reconnaissance in the field, one more was found on March 12, 2017, in the Cajas National Park, very close to the interpretation center. This discovery of the impact on a volcanic rock may soon be a major tourist attraction of the country due to its accessibility and importance for being unique in Ecuador.
... For example, Glass and Zwart (1979) have suggested that an extinction at the end of the Eocene is syn-chronous with abundant microtektites found in deep sea cores in the Caribbean and Gulf of Mexico, which may belong to the North American tektite strewnfield. The tektite horizon has subsequently been tested, and an iridium anomaly detected in two of the cores examined (Ganapathy, 1982;Alvarez and others, 1982). A discrepancy of 30 cm of sediments between the tektite horizon and the iridium anomaly is explained as being due to bioturbation. ...
The stratigraphic record is punctuated by episodes of mass extinction; these must be accounted for by major changes in the evolution of the Earth. Three groups of forces have acted on the Earth through time and may be adduced as the ultimate causes of many geological phenomena—including extinctions. These are: internal Earth changes, solar-system changes, and astronomical accidents. Immediate causes are many and may stem from more than one ultimate cause. Among astronomical accidents, asteroid or cometary impacts by bodies ranging up to 10 km in diameter or more occur at a known rate and must be accepted as an ongoing phenomenon. Evidence for large-body impacts exists locally in the presence of craters and ejecta, but regional or worldwide evidence is harder to assess. It is probable that geochemical, sedimentological, and biological effects will prove the most reliable indicators, although each involves difficulties in preservation and interpretation.
Mass extinctions and animal or plant diversity are commonly demonstrated by plotting numbers of taxa that disappeared against an interval of time, for example, genera or families per Stage or Series. A better measure of the real effect on life of an extinction event is to estimate changes in the biomass, a measure of the number or volume of organisms, and their extent. The difference in biomass between two taxa of equal rank can be, and frequently is, many orders of magnitude. Changes in the physical environment are seen as the driving force of evolution and may be slow acting or sudden. Only accurate biochronological and sedimentological studies can determine how sudden an event has been. Evidence for some extinctions is found by changes at a bedding plane in each section examined. If the possibility of gaps in sedimentation in such sections can be eliminated and the horizon accurately correlated, then this constitutes strong evidence for a sudden event, and an astronomical accident must be considered. The Phanerozoic record contains at least five major extinctions: Late Ordovician, Late Frasnian (mid-Late Devonian), Late Permian, Late Trias, and Late Cretaceous. Detailed evidence on the time of disappearance of the taxa affected is hard to come by, and much more work is required before any hypotheses of extinction can be substantiated. Although the Cretaceous-Tertiary extinction is marked by noble metal anomalies at many sections, the reason for such anomalies remains controversial; there appears to be a substantial extinction of biomass at the same horizon. In considering the five mass extinctions, the likelihood that a large body impact has contributed to each extinction event is assessed as follows: probability high enough to take seriously: Late Frasnian, Late Cretaceous; possibility: Late Ordovician, Late Trias; least likely: Late Permian.
... Además, el hallazgo de una anomalía de iridio llevó a algunos autores a proponer un impacto hace 34 Ma. y relacionarlo con la extinción del Eoceno terminal (Ganapathy, 1982;Alvarez et al., 1982). Las microtectitas se extienden por el Atlántico Norte como pusieron de manifi esto numerosos sondeos del DSDP-ODP Molina et al., 1993). ...
A comparative synthesis of the fi ve main Paleogene events from the Cretaceous/Paleogene boundary to the Eocene/Oligocene boundary is given. This synthesis integrates the results gained from the study of the foramini- feral assemblages with other paleontological and geological data. Different surviving strategies are described and the duration of the different extinction, survival and recovery stages are estimated. The models and patterns of foraminiferal extinction are described. Different evidence and paleoenvironmental factors related to those events are pointed out and the possible causes of extinction are analysed.
Despite several, sometimes prominent propagators, meteorite impact research had a long period of peripheral status until the 1980s. Since then, there has been an intense search for impact-extinction pairs, driven by the rapid acceptance of Alvarez’s hypothesis of a catastrophic Chicxulub impact at the end of the Mesozoic era.
However, substantial errors have occurred for incompletely identified and/or indirectly dated impact craters in the context of purportedly coeval mass extinctions. For example, supposed giant craters based only on geophysical studies, such as those alleged as evidence of impact-driven end-Permian and Late Ordovician extinctions, are not supported by any real impact evidence (e.g., catastrophic sedimentation) in adjacent areas.
The updated three-step methodology presents an accurate approach to cause-effect inference in impact catastrophism. It begins with (1) conclusive recognition of impact craters and ejecta, followed by (2) their precise radiometric or biostratigraphic dating, and concludes with (3) assessing the impact’s “kill” potential. The impact contribution to widely defined mass extinctions has been falsified based on the latest crater information from the global database and the updated ages of stratigraphic boundaries. In the Phanerozoic, two contrasting collision phenomena occurred: the Chicxulub asteroid mega-impact and a prolonged asteroid shower from a shattered
chondritic body in the Middle to Late Ordovician. Accordingly, a distinction has been proposed between steady background conditions (impacts occurring singly and rarely in clusters) and perturbation (bombardment) intervals. Current evidence for an impact trigger has been reviewed in detail for the other four Big Five mass extinctions, but no confirmation has been found. The probability of a prolonged impact-enhanced Late Eocene to
Early Oligocene crisis, caused by an asteroid shower, is considered, as well as biotic changes accompanying other
major cratering events: the mid-Norian Manicouagan and the end-Jurassic Morokweng structures. In particular, for the Popigai asteroid swarm, implied from paired 100-km-sized craters, and the possible Morokweng-Mjølnir coincidence, the relationships between impact signatures and likely stepwise biotic events are far from conclusive. Even if medium-sized bolide impacts, recorded in ~40-km-diameter craters, may have initiated near-global climatic hazards, the killing effect is unpredictable due to the diversity of cataclysm severity controls. Also the Ordovician cosmic bombardment did not have any negative influence on the great biodiversification. However, the asteroid swarms may have (by unusual dustiness of the inner Solar System) ultimately triggered or accelerated ice ages in the Late Ordovician and Oligocene, respectively. Overall, this implies a continuum in the
biosphere’s response to extraterrestrial stimuli.
Furthermore, a first attempt was made to explain the hidden record of predicted additional Chicxulub-type mega-events. ‘Lost’ oceanic impacts in the Middle Ordovician, Late Devonian, and Late Triassic were traced in the context of previously suggested records of mega-tsunamis and seismicity. The Frasnian-Famennian transition seems to be the most likely case of such a cryptic cataclysm, manifested in the worldwide “top-Frasnian
reworking event.” In summary, of the 18 extinctions, one confirmed impact-induced mass extinction and 3–4 possible impact-enhanced biotic crises can now be considered in terms of extraterrestrial forcing. This tentative conclusion is only superficially consistent with the simplistic assertion in recent literature of four ‘mass extinctions’ associated with the four largest impacts, as much substantial evidence is still needed. In fact, well-documented volcanic cataclysms currently shape the mainstream neocatastrophic geology.
Many proposals, mostly by non-geologists, of periodic causal connections between extraterrestrial factors and biosphere turnovers are shown once more to be totally inconclusive. In this context, the future of actualistic impact catastrophism and Alvarez’s ‘bolide theory’ remains open to many fascinating topics. In contrast, ‘nonbolide’ catastrophic concepts, such as the triggering role of intergalactic dark matter, are too questionable to
provide real evidence in the fossil record for these ‘invisible’ phenomena.
The Florida Platform, and its associated subsurface geology and surface landforms, is clearly a child of the sea. The geologic formations from the latter part of the Mesozoic through the Cenozoic were laid down in shallow seas and periodically reworked by marine, near-shore, and fluvial erosion/ deposition processes numerous times. The subsurface lithologies are complex and difficult to correlate due to limited data availability and lithologic similarity. Information is compiled in the form of water well cuttings, stratigraphic core tests, geophysical wire line logs, seismic reflection data, groundwater geochemistry, and limited surface exposures. Further, it is painstakingly difficult to understand and decipher the environmental changes that occurred throughout the geologic past, as the platform grew and was built by the various sedimentary processes.
The authors of The Geology of the Everglades and Adjacent Areas have done an outstanding job of compiling decades of data collected by their own field reconnaissance and other geoscientists. They have described the Cenozoic rock sequence units, both formally and informally, to establish the overall lithologic character, paleontology, age, and map extent of the various units. Their sequential paleoenvironmental interpretations and graphical figure representations are a significant contribution to the chronologic understanding of the development of the Florida Platform. They are to be congratulated for the innovative use of modern satellite technology and digital graphics to present their sequential paleogeography interpretations. This represents a significant contribution to the understanding of the development of the Florida carbonate platform, and it will assist other disciplines as they strive for better understanding of our groundwater resources, aquifer characterizations, paleoenvironmental interpretations, and historical/educational geology programs.
Walt Schmidt, Ph.D., PG #1
Florida State Geologist & Chief
Florida Geological Survey
(Florida State Geologist 1987-2008)
Central Italy has been a cradle of geology for centuries. For more than 100 years, studies at the Umbria and Marche Apennines have led to new ideas and a better understanding of the past, such as the Cretaceous-Paleogene (K-Pg) boundary event, or the events across the Eocene-Oligocene transition from a greenhouse to an icehouse world. The Umbria-Marche Apennines are entirely made of marine sedimentary rocks, representing a continuous record of the geotectonic evolution of an epeiric sea from the Early Triassic to the Pleistocene. The book includes reviews and original research works accomplished with the support of the Geological Observatory of Coldigioco, an independent research and educational center, which was founded in an abandoned medieval hamlet near Apiro in 1992.
More than three decades have passed since the discovery of anomalies in the abundance of platinum group elements (PGEs) across sections of Cretaceous/Paleogene (K/Pg) strata from Gubbio (Italy) and Caravaca (Spain), which have been attributed to a bolide impact. This remains one of the most significant findings in the field of Earth science. After the discovery, the PGE anomaly at the K/Pg boundary has been confirmed from more than 120 sites. Bolide impacts are not limited to the K/Pg boundary, but occurred throughout Earth's history. Pelagic deep-sea sediments, such as bedded chert, are repositories of information regarding impact events over geologic time, because they preserve long-duration continuous records with low sedimentation rates. This paper reviews geochemical studies reporting evidence for a large impact event in the Triassic bedded chert sequences from a Jurassic accretionary complex in Japan. Geochemical data on PGEs and radiogenic osmium (Os) isotope ratios (¹⁸⁷Os/¹⁸⁸Os) in the bedded chert provide information regarding the type and size of impactor.
By focusing on impact-triggered phenomena having occurred synchronously
with or shortly prior to formation boundaries, two glass sand pits (Upper
Maastrichtian) located near Uhry, North Germany have been studied in regard
to the K/T boundary throughout the last 40 years during progressive exploitation
of glass sand. However, a clastic sequence of sand, mass flow and
pelite deposited in a deep channel of about 10 - 12 m in depth, eroded into the
glass sand, surprisingly shows an Upper Eocene/Lower Oligocene age, well
defined by a Dinocyst assemblage (Chiripteridium c. galea, Enneado cysta arcuata,
Areoligera tauloma = D 12na - D 14na) from a 0.5 meter thick pelite
that marks the Rupelian transgression within an estuarian system running
northwest/southeastward. The section exposes a high energy mass flow and
formerly solid frozen angular glass sand blocks of up to a meter-size embedded
in fluvial sand of the channel base. Furthermore, erratic clastics of up to
0.4 meter in diameter appear at the pelite base. The “unusual” Dinocyst assemblage
is of autochthonous origin and comprises the fresh water alga Pediastrum
Kawraiskyias indicator for cold climate, hitherto only known from
Quaternary. Missing pollen indicate a vegetation-less hinterland. Thus, there
cannot be any doubt that around the E/O b. at least one “rare event” has happened
as verified by short tremendous flooding and significant temperature
fall (“cosmic winter”). According to the attitude of the global impact scientific
community, these phenomena belong to the spectrum of “indirect effects” of
major impacts. Radiometric ages of relevant major impact events underline
that both impact craters of Popigai, Russia (100 Kilometer in diameter, 35.7
Ma) and Chesabreake, USA (85 Kilometer in diameter, 35.5 Ma) happened
How to cite this paper: Schneider, W. and
Salameh, E. (2018) How to Trace out Impact-
Triggered Effects Globally Scattered
around Formation Boundaries: Case Uhry,
North Germany (Eocene/Oligocene Boundary).
Open Journal of Geology, 8, 9-32.
https://doi.org/10.4236/ojg.2018.81002
Received: November 16, 2017
Accepted: January 12, 2018
Published: January 15, 2018
Copyright © 2018 by authors and
Scientific Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY 4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access
W. Schneider, E. Salameh
DOI: 10.4236/ojg.2018.81002 10 Open Journal of Geology
shortly before the E/O b.(33.75 Ma). In addition, a tektite strewn field along
the eastern coast of the USA and micro-tektites (Gulf of Mexico, Caribbean
Sea, Barbados) yield an age of ~34.4 Ma, close to the E/O b. Consequently,
there does exist an extremely high probability that Uhry site hosts impact-
triggered products at the E/O b. It should be stressed that the Upper Eocene
Epoch comprises an amazingly high number of impact events during the
time-span 34.2 - 37.0 Ma.
Calcium carbonate accumulation rate patterns for the late Eocene-early Oligocene interval in 12 DSDP sites show inter- and intra-basin variations. Significant increases in calcium carbonate accumulation at the Eocene/Oligocene boundary are seen at Sites 77B, 292, 289 (Pacific Ocean), and Sites 214 and 219 (Indian Ocean), whereas a decrease is observed at Site 516F (South Atlantic). In contrast, no major changes are seen at Sites 73 and 277 (Pacific Ocean) or at Sites 363, 366 and 360 (Atlantic Ocean). Intra-oceanic variation in the accumulation records from the Pacific is observed as well. In comparison to Sites 292, 289 and 77B, Sites 73 and 277 show no change at the boundary. Instead increases are observed in Site 277 during the late Eocene and in Site 73 at the early/late Oligocene boundary.
Late Eocene microtektites, belonging to the North American tektite strewn field, have been found in the Gulf of Mexico, Caribbean Sea, on Barbados, and in the western Atlantic. The North American microtektite layer does not appear to be associated with any major extinctions or climatic changes; however, a slightly older layer (∼10,000 yrs. older) of clinopyroxene-bearing spherules appear to be associated with an iridium anomaly and the extinction of several radiolarian species. The clinopyroxene-bearing spherules have been found in the eastern Indian Ocean and equatorial Pacific, as well as, the Gulf of Mexico and Caribbean Sea. The North American tektites and microtektites have K-Ar, Ar-40/Ar-39, and fission-track ages of 34 to 35 m.y. Extrapolation from the microtektite layer to the overlying Eocene/Oligocene boundary indicates an age of 33–34 m.y. for the Eocene/Oligocene boundary.
Late Eocene extinctions are neither catastrophic nor mass extinctions, but occur stepwise in a sequence of 4 steps over a period of 3.4Ma. Closely associated with 2 of the stepwise extinction events are 3 microtektite horizons; one in the upper part of Globigerapsis semiinvoluta Zone at 38.2Ma, and 2 closely spaced layers in the lower part of Globorotalia cerroazulensis Zone at 37.3 and 37.2Ma. Species extinctions and relative species abundance declines are closely associated with microtektite layers and suggest, but do not prove, a cause-effect relationship between impact events and some of the stepwise mass extinctions.-Author
Sea-level change is known to have influenced the evolution of marine life. It is examined here how faunal diversity and rates of taxic evolution are related to change in sea-level and stability of the sea-level cycles. Evolutionary metrics of Palaeogene larger foraminifera are calculated and stability of sea-level cycles are determined using number and average duration of third order cycles in each stratigraphic interval. Generic diversity and the rates of origin and extinction individually do not show one to one correspondence either with transgression-regression or with the stability of the sea-level cycles. The rate of extinction relative to the rate of origination, however, is found to be significantly affected by the stability of the sea-level cycles. The rate of extinction exceeds the rate of origin during the periods of low stability. Regression, assisted by unstable sea-level cycles and possibly sharp climatic deterioration caused extinction maxima of larger foraminifera in Late Eocene.
Diversity and faunal turnover of North American land mammals are calibrated against the magnetic polarity time scale for million-year intervals for the latest Eocene through late Oligocene. A major, gradual Late Eocene decline in diversity, caused mostly by an extended period of extinction of archaic forms, seems to be related to the worldwide crisis known as the “Terminal Eocene Event.” Along with other evidence of gradual changes in deep-sea microfossils, this evidence argues against a catastrophic explanation for late Eocene extinctions.
Faunal stability characterized the rest of the Oligocene except for a wave of extinctions in the mid-Oligocene (Chadronian-Orellan boundary, about 32.4 ma). This mid-Oligocene event is sudden and severe, occurring in less than 200,000 yr, based on estimates from sedimentation rates calibrated from magnetic polarity interval boundaries. The mid-Oligocene event is found in many paleoclimatic records, but not in all of them. It may be related to the completion of the Circum-Antarctic Current and to increased mid-Oligocene glaciation.
Late Eocene foraminiferal extinction shows diverse patterns of selective morphologic and latitudinal extinction. Taxa with discoidal shape, calcareous tests, and narrow and low-latitudinal ranges are at significantly greater risk of extinction. Elevated extinction intensities in calcareous tests are mainly due to the presence of larger benthic foraminifera that evolved in late Paleocene and diversified through the lower to middle Eocene. Selectivity of late Eocene foraminiferal extinction indicates that this extinction event was not a globally uniform event. Although this result does not verify an extraterrestrial impact or any other proposed cause of extinction, it does constrain the causes of late Eocene extinction. Furthermore, the geography of late Eocene foraminiferal extinction, and previously studied Cenomanian/Turonian extinction, demonstrates that mass extinctions exhibit different patterns of selectivity.
The past one hundred years of ocean science have been distinguished by dramatic milestones, remarkable discoveries, and major revelations. This book is a clear and lively survey of many of these amazing findings. Beginning with a brief review of the elements that define what the ocean is and how it works-from plate tectonics to the thermocline and the life within it-Wolf H. Berger places current understanding in the context of history. Essays treat such topics as beach processes and coral reefs, the great ocean currents off the East and West Coasts, the productivity of the sea, and the geologic revolution that changed all knowledge of the earth in the twentieth century.
In order to better defi ne the late Eocene clinopyroxene-bearing (cpx) spherule layer and to determine how the ejecta vary with distance from the presumed source crater (Popigai), we searched for the layer at 23 additional sites. We identifi ed the layer at six (maybe seven) of these sites: Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) Holes 592, 699A, 703A, 709C, 786A, 1090B, and probably 738B. The cpx spherule layer occurs in magnetochron 16n.1n, which indicates an age of ca. 35.4 ± 0.1 Ma for the layer. We found the highest abundance of cpx spherules and associated microtektites in Hole 709C in the northwest Indian Ocean, and we found coesite and shocked quartz in the cpx spherule layer at this site. We also found coesite in the cpx spherule layer at Site 216 in the northeast Indian Ocean. This is the first time that coesite has been found in the cpx spherule layer, and it provides additional support for the impact origin of this layer. In addition, the discovery of coesite and shocked quartz grains (with planar deformation features [PDFs]) supports the conclusion that the pancake-shaped clay spherules associated with quartz grains exhibiting PDFs are diagenetically altered cpx spherules. An Ir anomaly was found associated with the cpx spherule layer at all four of the new sites (699A, 709C, 738B, 1090B) for which we obtained Ir data. The geometric mean of the Ir fluence for the 12 sites with Ir data is 5.7 ng/cm2, which is ̃10% of the fluence estimated for the Cretaceous-Tertiary boundary. Based on the geographic distribution of the 23 sites now known to contain the cpx spherule layer, and 12 sites where we have good chrono stratigraphy but the cpx spherule layer is apparently absent, we propose that the cpx spherule strewn field may have a ray-like distribution pattern. Within one of the rays, the abundance of spherules decreases and the percent microtektites increases with distance from Popigai. Shocked quartz and coesite have been found only in this ray at the two sites that are closest to Popigai. At several sites in the Southern Ocean, an increase in δ8O in the bulk carbonate occurs immediately above the cpx spherule layer. This increase may indicate a drop in temperature coincident with the impact that produced the cpx spherule layer.
From the immense amount of geochronologically relevant literature, the attempt was made in this book to survey, on the one hand, the primary literature, on the other hand, the most recent publications. Some of the reviewers, quite correctly, criticized that this has resulted in neglecting important publications that reflect the development of the individual methods. We have attempted to avoid this in the following compilation, which also includes secondary literature that seems to us to give a particularly valuable presentation or contain an extensive compilation of references. We hope that we have found an acceptable compromise.
Tektites are small, generally rounded, silicate glass bodies found in several widely separated areas of the Earth's surface called strewn fields. Four strewn fields are recognized: (1) Australasian, (2) Ivory Coast, (3) Czechoslovakian, and (4) North American. Tektites from the four known strewn fields were formed approximately 0.7, 1, 15 and 35 million years (m.y.) ago, respectively. Tektites are generally black, but those from Czechoslovakia and Georgia are translucent green or brown in color. Most tektites occur as splash forms, but some are blocky with a layered structure (Muong Nong-type); and some of the splash forms have been remelted or ablated by high velocity flight down through the Earth's atmosphere. Although they superficially resemble obsidian, they can be distinguished from obsidian by their petrography and compositions. Tektites, unlike obsidians, contain ubiquitous lechatelierite (SiO2 glass) particles and are generally completely devoid of microlites or crystallites. Tektites are drier than obsidians and have higher FeO/Fe2O3 ratios. Although some researchers favor a lunar volcanic origin for tektites, most of the chemical, isotopic, and petrographic studies seem to support a terrestrial impact origin. The presence of lechatelierite, coesite, shock relict inclusions, and NiFe spherules favors an impact origin; and chemical and isotopic data indicate that the parent material was a terrestrial sedimentary deposit. The Czechoslovakian and Ivory Coast tektites have been associated with the Ries crater (in Germany) and the Bosumtwi crater (in Ghana), respectively.
Environmental change, including changes in biogeochemical cycles, climate, and sea level, is the primary cause of extinctions that result from mechanisms external to evolutionary dynamics. Evidence that extraordinary tectonism, including volcanism, sea—floor spreading, and eustatic sea level changes, took place prior to and at the Cretaceous–Tertiary boundary (K–TB) is sufficient to account for the environmental changes that led to mass extinctions. A coincident impact of an extraterrestrial object cannot be conclusively ruled out. Some mineralogic evidence suggests a scenario that includes impacts, but this does not rule out tectonism. The K–TB is certainly the best studied and most often discussed extinction boundary, but study of other extinction episodes and other potential extinction causes will now shed more light on mechanisms than continued study of the K–TB. See full-text article at JSTOR
We review the four main extinction events in the Paleogene, from the Cretaceous/Paleogene boundary to the Eocene/Oligocene boundary, integrating the results obtained from a study of foraminiferal assemblages with other paleontological and geological data. Different survival strategies followed by the species are described and the duration of the phases of extinction, survival, and recovery is estimated. The models and patterns of extinction of the foraminifera are highlighted. We present a range of evidence and paleo-environmental factors and analyze the possible causes of extinction. A new terminology for mass extinction events is proposed: sudden mass extinction would have happened virtually instantaneously and the process would have taken a few years or decades (Cretaceous/Paleogene boundary). Rapid mass extinction is defined as that which occurred in relatively short events, around 100 kyr (Paleocene/Eocene and Eocene/Oligocene boundaries). Slow mass extinctions are suggested to have lasted around 1 Myr (Bartonian/Priabonian transition) and may even have lasted for several million years.
New biostratigraphic evidences from a core drilled in the central part of the 40 km diameter submarine Mjølnir meteorite crater on the Barents Shelf are presented. The data suggest a stratigraphical age for the meteorite impact approximating the Volgian - Ryazaman boundary. This age corresponds to the later pan of the Early Berriasian (Berriasella jacobi Zone) of the Tethyan Realm. A similar age for the impact is further documented from the macro- and microfaunas and microfloras found in the ejecta-bearing strata in an additional borehole located 30 km northeast of the crater. Iridium anomalies found in the Volgian-Ryazaman boundary strata on central Spitsbergen - Svalbard and Nordvik Peninsula in northern Siberia appear also to be related to the Mjølnir impact, providing additional support for a Volgian-Ryazanian boundary age of the impact.
Late Eocene-early Oligocene (42-35 Myr) sediments cored at two DSDP
sites in the south-west Pacific contain evidence of a pronounced
increase in local volcanic activity, particularly in close association
with the Eocene-Oligocene boundary. This pulse of volcanism is coeval
with that in New Zealand and resulted from the development of an Indo-
Australian / Pacific Plate boundary through the region during the late
Eocene. The late Eocene / earliest Oligocene was marked by widespread
volcanism and tectonism throughout the Pacific and elsewhere, and by one
of the most important episodes of Cenozoic climatic cooling.
THE discovery of high concentrations of iridium in Cretaceous/Tertiary
boundary sediments engendered the hypothesis1 that a
meteorite collided with the Earth 65 million years ago, coincident with
the mass extinction that occurred at that time. Iridium spikes of
various magnitudes have subsequently been reported at more than 10 other
extinction horizons2-11. It has been suggested, on the other
hand, that geochemical processes might create or modify many of these
spikes5, 11-4, but a critical evaluation of these suggestions
has been hindered by incomplete understanding of low-temperature iridium
geochemistry. Other platinum-group elements (Ru, Rh, Pd, Re, Os, Pt, Au)
are often found to be associated with Ir spikes, and inter-element
ratios have been used to assess the cosmic or terrestrial nature of the
enrichments5,7,9,28,29; but the geochemical influences on
these relative abundances are also poorly constrained. Here we describe
analyses of recent abyssal marine sediments which allow us to
characterize the behaviour of Pt, Re and Ir during early diagenesis.
These elements are redistributed by changes in sedimentary redox
conditions. Such changes can probably account for many of the small
platinum-group-element spikes found in the geological record, and may
render ambiguous attempts to interpret inter-element ratios.
It is proposed to regard the terminal Cretaceous event as similar to the radiolarian extinction event in the late Eocene: the result of a volcanic eruption or series of eruptions on the moon. Some glassy ash, lapilli and blocks from these eruptions fell to the earth; some, in geocentric orbit, formed clouds around the earth. In accordance with current theory, it is found that the clouds in orbit would evolve into sets of rings, which would last a few hundred thousand to a few million years, and would perturb the climate of the earth. One such eruption apparently included iridium-bearing material, perhaps from the deep interior of the moon.The hypothesis permits a reconciliation between the evidence for the catastrophic intervention of extra-terrestrial masses in the earth environment, and the evidence for gradual (though rapid) change of flora and fauna at the Cretaceous/Tertiary boundary. The formation of the E-ring of Saturn by ejecta from the Saturnian satellite Enceladus may have been analogous. The theory might be tested by studies of diurnal layering in molluscan shells.
At the end of the Cretaceous Period, 65 million years ago, the dinosaurs and many other forms of life disappeared suddenly. The agency which destroyed them has recently shown to be the same as the agency which, at intervals of millions or tens of millions of years, scatters glass pebbles and dust (called tektites and microtektites) over huge areas of the earth's surface. After almost a century of study and discusion, it has become clear that the agency involved is either the impact of giant meteorites (asteroids or comets) on the earth's surface, or the eruption of lunar volcanoes. One of the best approaches to this question is through the kinetics of glassmaking. Is it possible that ordinary soil or rock could be converted to a high-silica glass, sometimes of good quality (homogeneous and free of bubbles), during a meteorite impact (in which the heating period is a few tens of seconds at most?). Calculations of the rate of bubble movement and the rates of homogenization make it appear hopeless. A recent study by E. Luft furnishes data confirming these conclusions. The alternative is lunar volcanism. A cloud of ash and pebbles from a lunar volcano, if directed toward the earth, would organize itself into rings like those of Saturn, shadowing the winter hemisphere and so destroying some forms of life. R. Sheldon may have geological confirmation of these ideas.
The influx of extraterrestrial matter to the Earth is dominated by two size-fractions: sub-millimeter interplanetary dust and impacting asteroids and comets. Over geologic time the major contribution of extraterrestrial matter is from the largest impactors. Interplanetary dust is largely vaporized by atmospheric entry, but some surviving material is found in sediments as cosmic spherules. Impacting asteroids and comets can produce fallout layers either regionally or globally which may contain a significant fraction of meteoritic material as well as shock-metamorphosed and shock-melted terrestrial material. Iridium is a sensitive tracer of extraterrestrial matter. Although high concentrations of Ir in marine sediments probably have an extraterrestrial origin, they do not necessarily indicate the presence of a major impact event. Of the thousands of impact horizons which must be resolvable in the sedimentary record, to date only seven probable impact horizons have been identified in the entire Phanerozoic. The marine geochemistry and occurrence of Ir is still poorly understood, but the thousands of Ir analyses performed in the last several years have demonstrated that the global occurrence high Ir (>10 ng/g) concentrations in Cretaceous-Tertiary boundary sediments is a truly anomalous phenomenon.
Several theoretical and laboratory studies suggest that some large impact events are capable of inserting material into space depending on mechanics of the impact. This material would quickly coalesce to form a temporary debris ring in orbit around the equator, which would cast its shadow on the winter hemisphere. The results of an atmospheric general circulation model (GCM) simulation where an orbiting equatorial debris ring is applied as a boundary condition to the model show how the longer-term effects of a major impact could affect the climate system. The primary effect is a severe cooling in the tropics and the subtropics, especially under the seasonally migrating ring shadow. The globe cools and becomes drier, with the exception of monsoonal regions that become wetter. The Hadley cell is weakened resulting in drier tropics and weaker subtropical high-pressure cells in the winter hemisphere. Because the tropics cool more than middle latitude regions, the equator-to-pole temperature gradient becomes shallower resulting in weaker tropospheric winds and less high-latitude storminess. We suggest that the late Eocene impact(s) (35.5 Ma) could have generated a geologically temporary orbiting debris ring based on the global distribution of tektites associated with these events and patterns of climate change immediately above the iridium/microtektite layer. The Cretaceous-Tertiary boundary event, while larger, did not produce a debris ring. We also suggest that an opaque debris ring could have acted as the trigger to at least one episode of global glaciation during the Neoproterozoic.
Iridium has proven to be a useful fingerprint of extraterrestrial material, and neutron activation analysis is the method of choice for its determination because of the high thermal cross section (910 b) of 191Ir (37.3% natural abundance) and the favorable decay characteristics of the product nuclide. However, radiochemical separations are frequently required for the determination of iridium at low concentrations (in the ppb range). The present work describes a precise, nondestructive neutron-activation procedure that is capable of analyzing samples of both high (ppm) and low (ppb) Ir content. Advantage is taken of the fact that the principal gamma lines of 73.8-d 192Ir are in various coincidences with one another. Instead of conventional gamma-gamma coincidence spectrometry with two Ge detectors, we utilize the 784.6- and 920.9-keV sum peaks which are generated when an iridium containing sample is placed in the well of a highly-efficient HPGe detector. The well-type detector is positioned centrally in a large annular NaI(Tl) detector which is operated in an anticoincidence mode. This improves the quality of the gamma spectra by suppressing the Compton backgrounds due to nuclides such as 60Co by a factor of 4-6 in the regions of interest without affecting the intensities of the two sum peaks. The sensitivity of this method under our experimental conditions (20-mg sample irradiated at 1.5 × 1014 n cm-2 s-1 for 5 min and counted 3-4 weeks after irradiation) is ~5 ppb Ir in a relatively unfavorable matrix such as peridotite.
The size distribution of comets and asteroids that move through the Solar System on Earth-crossing orbits, and the record of impact craters on the terrestrial planets can be used to determine the average intervals among impacts of various sizes. The apparent coincidence of the impact (or impacts) with the abrupt extinctions, including that of the dinosaurs, and the possibility that climatic and environmental changes caused by the impact led to the extinctions, revived interest in the physical effects of large impact events. The carbon cycle involves the transfer of carbon between the solid Earth and the ocean/atmosphere system. Carbon dioxide releases associated with metamorphic decarbonation of sediments at subduction zones, mantle out gassing at mid-ocean ridges and the chemical weathering of carbonate rocks, represent the primary sources of carbon dioxide to the oceans and atmosphere. The mix of species can be quite variable from one site to another, and thus differences in the depth zone in which calcification takes place among calcareous plankton and species-specific vital effects in isotope fractionation, can affect the isotopic composition of bulk material.
The concept of periodic mass extinctions by extraterrestrial impacts has contributed very strongly to the current revival of interest in the problem of mass extinctions. In this context, several radical claims have been made, asserting that the newly emerging picture of mass extinctions as a separate class of biological phenomena, caused by a separate class of processes, demands a far-reaching revision of the neodarwinian paradigm of evolution and implies a vindication of the Cuvierian perspective on Earth's history. The validity of these claims, however, is questionable at all levels: from the interpretation of particular events, to the concept of mass extinctions as a special class of phenomena, to their proposed causation by impacts, and to their alleged historical pedigree and implications for current evolutionary theory. Mass extinctions may actually be clusters of more or less accidentally aggregated-in-time but causally distinct extinction episodes. -Author
A significant iridium enrichment has been found in a Jurassic marine sequence, about 180 million years old, outcropping in the Alps of the Venetian region. The maximum iridium concentration of 3.2±0.2 ng g-1 occurs in a brown crust 2 - 3 mm thick, containing essentially iron hydroxide. This crust, characterized by a nearly total absence of detritic components, lies on top of upper Lias limestones, and is overlaid with Bajocian-Bathonian limestones. The origin of the Ir anomaly is not clearly understood yet but could be explained by either a drop in the sedimentation rate resulting in the concentration within a thin sediment layer of the normally infalling cosmic dust and/or by an increase of cosmic material infall following an asteroid or comet impact(s).
In a previous publication, an iridium anomaly was reported in core RC9--58 from the Caribbean Sea, about 30 cm below the peak abundance of North American microtektites. In order to determine more precisely the relationship between the iridium anomaly and the North American microtektite layer, we searched for microtektites in the samples that were used for the iridium studies. We found that the North American microtektite layer is actually two layers, with the peak abundances separated by 25 cm. The upper layer consists of 'normal' North American microtektites and the lower layer consists of previously described clinopyroxene-bearing spherules. The iridium anomaly was found to correlate with the lower layer. Although the two layers appear to be the result of two separate events, several lines of evidence suggest that they were produced by a single event. The separation into two layers may have been produced by differential settling in the sediment due to density variations. The correlation between the iridium anomaly and the North American microtektite layer supports the terrestrial impact origin for tektites.
Magnetic spherules and spheroids are found in association with Ir anomalies at the Cretaceous/Tertiary (K/T) boundary and near to the Eocene/Oligocene (E/O) boundary. Detailed magnetic analyses have been performed on these particles, and on bulk K/T boundary clay from marine and continental sections. Coercivity spectra, and blocking and Curie temperatures of the spheroids and K/T boundary clays have been determined, and natural remanence and susceptibility measured for the bulk clay and associated strata.Marine K/T boundary clays are strongly magnetic, with remanent coercivities similar to those of the spheroids. In contrast, the continental clays are diamagnetic, except for the thin, overlying “impact layer”, which contains abundant paramagnetic jarosite, along with shocked quartz and feldspar.The morphologies, mineralogies, and magnetic properties of the K/T magnetic spheroids are closely analogous to magnetic fly ash spherules. This similarity may be related to the presence of carbonaceous “soot” particles in some marine K/T boundary clays, and the recent identification of plerospheres and cenospheres in continental boundary clay. In contrast, tektites and microtektites differ from the K/T magnetic spherules in a number of fundamental ways. The late Eocene particles are magnetically distinct from the K/T spheroids, both in their coercivity and thermal spectra.INAA results on Upper Cretaceous combustible shales indicate that the anomalous abundances of certain chalcophile and lithophile elements at the K/T boundary may be explained in terms of the natural combustion of bituminous sediments.
The documented presence of two large (∼100-km diameter), possibly coeval impact craters of late Eocene age, requires modification of the impact-kill curve proposed by David M. Raup. Though the estimated meteorite size for each crater alone is large enough to have produced considerable global environmental stress, no horizons of mass mortality or pulsed extinction are known to be associated with either crater or their ejecta deposits. Thus, either there is no fixed relationship between extinction magnitude and crater diameter, or a meteorite that would produce a crater of >100-km diameter is required to raise extinction rates significantly above a ∼5% background level. Both impacts took place ∼1-2 m.y. before the "Terminal Eocene Event"( =early Oligocene pulsed extinction). Their collective long-term environmental effects, however, may have either delayed that extinction pulse or produced threshold conditions necessary for it to take place.
Three sedimentary sequences in New York State (Dunkirk Beach, Walnut
Creek Gorge, and Mills Mills) and one sedimentary sequence in Belgium
(Sinsin), that cross the Devonian Frasnian-Famennian boundary, were
examined for an iridium (Ir) anomaly to determine whether the biotic
extinctions at the end of the Cretaceous could have been caused by an
asteroidal impact. The sampling at three of the four areas was on 2-cm
center points, and 15 to 20 g of sample were collected. The instrumental
neutron activation method required 5 g samples, and consequently the
distance between samples was less than 1 cm. Though the Devonian samples
studied had a high probability of locating an Ir anomaly, none was
found. The highest Ir values were between 0.2 and 2 percent of those
reported for the marine and terrestrial Ir analyses at the
Cretaceous-Tertiary boundary, and Devonian pyrite-rich sediments did not
exhibit high Ir concentrations.
The theory of evolution involving episodic terrestrial catastrophism predicts that the Oort cloud is disturbed by close encounters with massive nebulae. Each disturbance generates bombardment pulses of a few million years duration, the pulse frequencies being determined by the Sun's passage through the spiral arms and central plane of the Galaxy where nebulae concentrate. The structure within a pulse is shown here to be dominated by a series of "spikes" of ≡0.01 - 0.1 Myr duration separated by ≡0.1 - 1.0 Myr, each caused by the arrival in circumterrestrial space of the largest comets followed by their disintegration into short-lived Apollo asteroids. Evidence is presented that a bombardment pulse was induced 3 - 5 Myr ago and that a "spike" in the form of debris from a Chiron-like progenitor of Encke's comet has dominated the terrestrial environment for the last 0.02 Myr. Among the predicted consequences are 14C modulations, climatic variations including the last major glaciation and observable zodiacal light phenomena.
Drilling at Site 549, located on the Goban Spur in the northern Bay of Biscay (Irish continental margin), penetrated an apparently continuous section of upper Eocene lower Oligocene nannofossil chalks. The Eocene-Oligocene boundary as identified by nannofossils does not coincide with that recognized using planktonic foraminifers. Regardless of which biostratigraphic criteria are used, no dramatic nannofloral or planktonic foraminiferal change occurred at the boundary. There was a gradual transition from warm-water to cool-water assemblages through the late Eocene, with more intense cooling indicated by low-diversity assemblages in lower Oligocene sediments. A bottom-water temperature drop occurred in the late Eocene through early Oligocene as indicated by an 18O enrichment in benthic foraminifers, although some of this enrichment may have been caused by increased ice volume. A major benthic foraminiferal faunal change, from a Nuttallides truempyi dominated assemblage to one dominated by wide- and long-ranging taxa, occurred in the early late Eocene. No major benthic assemblage changes occurred at the Eocene-Oligocene boundary.
Part 1 Foundations of a Contary View: Paradox and puzzles. Radioactivity of continental crust. Radioactivity of upper mantle. The heat flow paradox. Sub-continent upwelling and heat transfer. Seismic and petrographic structure. Part 2 Clues to Direction of Mantle Flow: Heat dissipation in mobile belts and oceanic regions. Viscous flow and its surface expression. Regional and structure-controlled stress. Uplifted old rocks on the Oceanic Range. The Coriolis effect. Crestward change and the spreading hypothesis. Geodetic surveys. Block tilting. Gravity anomalies over upward and downward mantle flow. Seismic indicators of rising and sinking mantle. Crestal structure. Collapse model of a rift. Rift structure. Part 3 Convection, Subsidence and Geologic Age: Experimental convection. Proposed mantle convection. Origin of Fracture Zones and Transforms. Relative motion on Transforms. Near-axial structure and magnetic stripes. Ocean depth control and ages on the Oceanic Ridge. Part 4 Recycling Model of Volcanism: Melting of heterogeneous mantle. Recycling and igneous diversity. Mid-ocean volcanism. Recycling and the flux of helium and neon. Inclined subduction, andesites and the calc-alkaline trend. Return flow and upwelling. Part 5 Evolution and Reversal of Convection: Archean. Archean-Proterozoic transition. Early Proterozoic stability. Continental growth. Part 6 Disruption and Mantle Surge: Indicators of times of mantle surge. Pacific structure and Mesozoic disruption. Circum-Pacific and world-wide surge of mantle flow. Part 7 Revolution in the Earth Sciences.
The terrestrial impact craters are mostly recognized not by their
morphology but by the occurrence of the characteristic shock metamorphic
effects. The recognition of the diagnostic shock metamorphic effects and
the signature of the projectile contamination through geochemical
anomalies in impact lithologies provide the basis for recognizing the
impact signature in K/T boundary samples and for testing hypothesis of
periodic cometary showers. It is emphasized, however, that, in
evaluating and making interpretations based on the overall cratering
record, it is important to realize that one of the basic characteristics
of the terrestrial impact record is its bias to geologically young
craters on the better known cratonic areas and the fact that the sample
of the currently known (about 130) terrestrial craters is deficient in
small (D less than 20 km) craters.
The major element composition of microspherules from all three late
Eocene stratigraphic layers was analyzed using an electron microprobe.
The results indicate a major element compositional overlap beween
individual microspherules of different microtektite layers or strewn
fields. However, multivariate factor analysis shows that the
microtektites of the three late Eocene layers follow recognizably
different compositional trends. The microtektite population of the North
American strewn field is characterized by high concentrations of SiO2,
Al2O3, and TiO2; the microspherules of an older layer, the Gl.
cerroazulensis Zone, are relatively enriched in FeO and MgO and
impoverished in SiO2 and TiO2; while those of the oldest layer in the
uppermost G. semiinvoluta Zone are relatively enriched in CaO and
impoverished in Al2O3 and Na2O.
The stratigraphy, faunal changes, and geochemistry of deep-sea sediments
associated with late Eocene microtektite and microspherule layers are
reported. Microprobe analyses of major element compositions of
microspherules show that, although there is some compositional overlap
in all three late Eocene layers as well as with the Pleistocene
Australasian and Ivory Coast microtektites, each microspherule
population has characteristic compositional features. All three
microspherule layers are associated with decreased carbonate, possibly
due to a sudden productivity change, increased dissolution as a result
of sea-level and climate fluctuations, or impact events. A discovery of
microtektites in the Gl. cerroazulensis Zone off the New Jersey coast
extends the North American strewn field from the Caribbean to the
northwest Atlantic.
Several thousand microtektites (125 to 1,000 μm in diameter) have been found in cores from two Deep Sea Drilling Project sites: site 94 in the Gulf of Mexico and site 149 in the Caribbean Sea. The microtektites occur in upper Eocene sediments associated with the last occurrence of at least five species of Radiolaria. X-ray diffraction data, energy dispersive X-ray analysis, and petrographic studies indicate the presence of inclusions of quartz, cristobalite, and lechatelierite. Major-element compositions were determined for 57 of the microtektites using energy-dispersive X-ray analysis. The geographical location, age, petrography, and chemistry of the microtektites indicate that they belong to the North American tektite strewn field (∼34 m.y. old). Calculations indicate that there may be as much as 109 t (metric tons) of microtektites in this strewn field.
Crystallite-bearing glass spherules (
Iridium and osmium concentrations were measured in dated deep-sea sediments by neutron activation analysis to attempt to set limits on the influx rate of cosmic matter. Twentyone measurements on five cores from the central Pacific gave Ir and Os contents from 0·06 to 0·4 ppb, with an observed precision of ±15 percent. The Ir and Os contents were correlated with each other: Ir = (1·2 ± 0·2) Os . Both tended to increase with decreasing sedimentation rate. The Ir content can be represented by the expression: Ir ( ppb ) = (0·07 ± 0·08) + (0·094 ± 0·047)1/ r s where r s is the sedimentation rate in mm per 1000 years from Th 230 / Th 232 ratios. If the first term is interpreted as an average terrestrial component and the second term, as an exclusively cosmic component which is diluted in proportion to the sedimentation rate, an upper limit to the influx rate of cosmic matter may be established on the basis of the average Ir content of some representative meteoritic material. With an assumed Ir content of 0·42 ppm, the value in Type I carbonaceous chondrites, the influx rate for the entire earth becomes (6 ± 3) × 10 4 tons/yr. This value represents an average over the last 10 5 to 10 6 years; the mass range effectively sampled by this method is ~10 -14 to ~10 12 g. A firm upper limit on the influx rate can be obtained by assuming that all the Ir and Os in deep-sea sediments is of cosmic origin. The value obtained is between 0.5 × 10 5 and 1.5 × 10 5 tons/yr. It is more than an order of magnitude lower than other estimates based on the Ni content of deep-sea sediments or particles counts by satellites.
Elgygytgyn crater (lat. 67–30 N, long. 172–00 E) in remote northeastern Siberia is proposed as the meteorite impact site from which the Australasian tektite strewnfield was splashed. The following points support this interpretation: 1, Elgygytgyn very likely is an impact crater and is of adequate size, 18 km across, to generate tektites; 2, the apex of the strewnfield points towards this crater; 3, the terrane is Mesozoic which fits the age of the tektite parental material from Sr/Rb data; 4, compositional and specific gravity lineations within the strewnfield are directed, in part, toward this crater; 5, the high velocity tektites, australites, are distal with respect to this crater while the low velocity tektites, splash forms and Muong Nong tektites, are proximal; 6, the loess deposits and mixed acid/basic rocks of the impact site provide a suitable subgraywacke-type source material; 7, the erosional state of Elgygytgyn suggests that its age may well be in accordance with that of the Australasian tektite event, i.e., 700,000 years.
The most profound climatic event of the Tertiary was the terminal Eocene event at −34 Myr (ref. 1). Botanical data indicate that winters became much more severe, while summer temperatures were little affected. An explanation in terms of a change in the space direction of the Earth's axis is not dynamically acceptable. On the other hand, an ecological disaster of some kind apparently struck the Radiolaria at this time2; the latter event is accurately correlated (to a few tens of thousands of years) with the formation of the greatest known tektite strewn field, the so-called North American strewn field, which has recently been shown to extend at least half-way around the Earth3. It is suggested here that tektites and microtektites which accompanied this fall, but missed the Earth, organized themselves into a ring system like that of Saturn. The shadow of the rings fell on the winter hemisphere and so produced the observed cooling. The ring lasted between one and several million years.
Over 6000 microscopic glass spherules between 125 μm and 1 mm in diameter were found in a sediment core (RC9-58) from the Caribbean Sea. These glassy objects are mostly confined to a zone ∼ 40 cm thick at a depth of ∼ 250 cm. We believe that the microscopic glass objects are microtektites belonging to the North American strewnfield, based on their geographical location, appearance, physical properties, stratigraphic age (middle Upper Eocene), fission track age (∼34.6 my) and major element compositions. The occurrence of North American microtektites in the Caribbean Sea indicates that the North American strewnfield is two to three times larger than previously indicated. An estimate on the abundance of microtektites in core RC9-58 indicates that the North American strewnfield may contain greater than 1017 g of tektite material.
SOME fifteen years ago, I suggested that tektites were produced by collisions of comets with the Earth1-3. Many detailed investigations of these objects have added much to our knowledge, and these, together with the lunar investigations, have proved this hypothesis to be very probably correct. I have also suggested that the geological periods were terminated by such collisions, but this was published in the Saturday Review of Literature, and no scientist except me, so far as I know, reads that magazine. The energy of such collisions and their frequency was roughly estimated at that time, and the number of these collisions has been reviewed again by Durrani4.
Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium observations. Impact of a large earth-crossing asteroid would inject about 60 times the object's mass into the atmosphere as pulverized rock; a fraction of this dust would stay in the stratosphere for several years and be distributed worldwide. The resulting darkness would suppress photosynthesis, and the expected biological consequences match quite closely the extinctions observed in the paleontological record. One prediction of this hypothesis has been verified: the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 +/- 4 kilometers.
Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the "fish clay" from Denmark representing the Cretaceous-Tertiary boundary. Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of 10(4) to 10(2) relative to cosmic abundances, are enriched in this boundary clay by factors of 5 to 100 over the expected abundances. With the exception of rhenium, all the enriched noble metals in the clay are present in cosmic proportions, indicating that the impacting celestial body had not undergone gross chemical differentiation. The major extinction of life on the earth at the end of the Cretaceous Period may be related to the meteorite impact.
Seratigraphic Micropaleontology of Atlantic Basin and Borderlands
- B P Glass