This formation forms the striking, massive, m high vertical cliffs along the south side of the San Juan River on the south side of the city of Farmington in the west-central part of the basin Figure 1. The Ojo Alamo is a coarse-grained, conglomeratic sandstone that crops out around the periphery of most of the New Mexico part of the San Juan Basin but is absent in the northern part mostly in Colorado, Figure 1. The Ojo Alamo was deposited on a basin-wide erosion surface in early, but not quite earliest, Paleocene time by south-to-southeasterly flowing, high energy, braided streams Fassett , Fassett et al. A hiatus of nearly 8 m. The Ojo Alamo is a multi-storied conglomeratic sandstone with highly varied internal architecture and thicknesses throughout the basin Fassett et al. Conglomerate clasts range from near-boulder size in the northwest part of the basin to small pebbles and grit in the southeast part. The rock-stratigraphic definition and age of the formation have been characterized differently by various workers over the years as discussed in numerous papers; those discussions are summarized and referenced in Fassett et al. Figure 2 shows the principal differences in the ways the Ojo Alamo has been characterized in its type area and the way the name is used in this report. The so-called middle, “shaly” part of the Ojo Alamo in the type area of the Ojo Alamo Sandstone is a mischaracterization of this interval because it contains multiple sandstone beds, and these sandstones represent a significant part of the interval. In the type area, the sandstones of the middle part of the Ojo Alamo are white and relatively friable rather than having the rusty-brown color of the harder lower and upper benches, thus these beds do not typically form cliffs or ledges.
This boundary layer is well marked and recognized world-wide and has been long known to mark one of the largest mass extinctions in the fossil record. What has always clearly marked this boundary layer is the fossils above and below. In the younger, Tertiary sediments, there are only tiny, less ornate foraminifera. Other creatures, prominently the ammonites, the fish of the oceans except they are cephalopods like the octopus and the chambered nautilus in the Paleozoic and Mesozoic Eras, some to 65 million years ago, abruptly disappeared.
And of course, the terrible reptiles, the dinosaurs, disappeared from the face of the Earth.
Shocked quartz and more: Impact signatures in K-T boundary clays and U-Pb isotopic dating of single 1 – 3 micrograms zircons from K/T distal ejecta from a.
All rights reserved. New insights about the asteroid thought to have killed off the dinosaurs suggest it may have just been the final blow, and that the reptiles were already suffering from a finicky climate prompted by volcanic eruptions long before the meteorite struck. The research, detailed in the February 8 issue of the journal Science , adds to the ongoing scientific debate over what exactly killed off the dinosaurs. That debate, which once revolved around the question of whether the culprit was an asteroid or volcano-induced climate changes, has evolved to consider the possibility that perhaps multiple environmental factors were involved.
Using a high-precision dating technique on tektites—pebble-sized rocks formed during meteorite impacts—from Haiti that were created during the event, the team concluded that the impact occurred 66,, years ago—slightly later than previously thought. When error limits are taken into account, the new date is the same as the date of the extinction, the team says, making the events simultaneous.
Renne said the new findings should lay to rest any remaining doubts about whether an asteroid was a factor in the dinosaurs’ demise. That is not to say, however, that the asteroid—which carved out the so-called Chicxulub crater—was the sole cause of the dinosaurs’ extinction. Evidence now suggests massive volcanic eruptions in India that predated the asteroid strike also played a part, triggering climate changes that were already killing off some dinosaur groups.
For example, “nobody has ever found a non-avian dinosaur fossil exactly at the impact layer,” Renne said in an email. The idea that volcanism was responsible for the dinosaurs’ demise actually predates the impact theory, and it fits well with what is known about Earth’s other mass extinction events. But in the s, father-son team Luis and Walter Alvarez, a physicist and planetary scientist, respectively, presented a bold new theory.
After discovering that a layer of clay that’s found throughout the world and that coincided with the end of the Cretaceous period is enriched in iridium—an element rare on Earth but common in space rocks—they proposed that a meteorite wiped out the dinosaurs. An asteroid of that size striking the Earth would have had devastating consequences, including destructive pressure waves, global wildfires, tsunamis, and a “rain” of molten rock reentering the atmosphere.
Scientists from the Berkeley Geochronology Centre University of California , in co-operation with colleagues from Glasgow University and Vrije University Amsterdam, Holland , have concluded that an asteroid, meteorite or possibly even an object such as a comet collided with the Earth approximately Although this single event may not have been the cause of the mass extinction, the scientists conclude that if the extraterrestrial impact was not wholly responsible, it would have contributed significantly to the global extinction event.
Based on the dateline evidence that the team established, the impact of a large extraterrestrial object in the Gulf of Mexico area could have proved to have been the final blow that saw off the Dinosauria, marine reptiles and Pterosaurs. It was father and son Luis and Walter Alvarez who first published a theory , stating that a thin layer of clay enriched with the rare Earth element iridium found at the boundary between Uppermost Cretaceous strata and younger Cenozoic deposits marked the impact of a large, extraterrestrial object.
It was these two American scientists who first claimed that this was evidence of a meteorite or some other object from outer space colliding with the Earth. Although the American scientists did not know where the impact actually occurred.
Cambridge Core – Plant Sciences – Plants and the K-T Boundary – by Douglas J. Publisher: Cambridge University Press; Online publication date: August
Scientists determine most precise dates yet for dinosaur extinction 66 million years ago. Rock strata in northeastern Montana; they span the time of the dinosaur extinction. This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts. In an attempt to resolve the issue, scientists at the Berkeley Geochronology Center BGC at the University of California, Berkeley, and at universities in the Netherlands and the United Kingdom, have determined that an impact event occurred at about the same time as the mass extinction of the dinosaurs.
Using a recalibrated technique for dating Earth minerals, the researchers hypothesize that impact happened 66,, years ago, and that it produced the final atmospheric conditions needed to wipe out the dinosaurs. The newly determined date of the impact is the same, within error limits, as the date for the mass extinction event, which also occurred about 66 million years ago, according to Paul Renne, BGC director. The dates are so close, the researchers say, that it was likely that a comet or asteroid that, if not wholly responsible for the global extinction, at least dealt the death blow.
But it probably wasn’t just the impact. The revised date clears up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures, Renne said. Renne decided to recalculate the date of the boundary between the Cretaceous and Tertiary periods–the KT boundary–after recalibrating the argon-argon method used to date rocks, which relies on the decay rate of a radioactive isotope of potassium.
The impact in question left a mile-wide crater in the Caribbean off the Yucatan coast of Mexico. Called Chicxulub cheek’-she-loob , the crater was excavated by an object some six miles across.
Scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have pinpointed the date of the dinosaurs’ extinction more precisely than ever thanks to refinements to a common technique for dating rocks and fossils. The argon-argon dating method has been widely used to determine the age of rocks, whether they’re thousands or billions of years old. Nevertheless, the technique had systematic errors that produced dates with uncertainties of about 2.
Renne and his colleagues in Berkeley and in the Netherlands now have lowered this uncertainty to 0. As a result, argon-argon dating today can provide more precise absolute dates for many geologic events, ranging from volcanic eruptions and earthquakes to the extinction of the dinosaurs and many other creatures at the end of the Cretaceous period and the beginning of the Tertiary period. That boundary had previously been dated at
40Ar/39Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and.
Plants and the K—T Boundary. Its impact on plant life appears to have been of a much lesser magnitude. The authors, both on the staff of the Denver Museum of Nature and Science, have published extensively on fossil plants of Tertiary and Cretaceous age. Nichols has been mainly concerned with the palynology the microfossil record , while Johnson has concentrated on leaf assemblages megafossils of this age span. The Alvarez father-and-son team argued that the cause of the peak occurrence of that element was the result of the impact of an extra-terrestrial body.
The diverse and disastrous consequences of such an impact were, they claimed, the most likely cause for the extinctions occurring at the close of the Cretaceous Period the K—T boundary. This thesis has subsequently become widely, but not universally, accepted. The most likely site for the impact is generally agreed to be close to Chicxulub, on the Yuccatan Peninsula of Mexico. While the effect of the end-Cretaceous event is very evident in the fossil record of animal life, both marine and terrestrial, the extent to which plant life was significantly affected has been less generally agreed.
The information from these two types of plant fossils microfossils and fossil leaves seemed at first to be in conflict. In this book the authors set out to review the entire field of fossil plant evidence, both palynological and macrofossil, for the nature and causality of events at the K—T boundary. The authors record that some papers making reference to changes in the flora through the K—T sequence have been published over the last 50 years.
A large part of the book is a detailed survey of the record of these two principal types of plant fossils across the K—T boundary, mainly from western North America, but including a review of published material from Europe and Asia, and also including a number of Gondwanan sites.
The Yacoraite Formation corresponds to a mixed carbonate-siliciclastic lacustrine sedimentary system, deposited during the sag phase post-rift and also records the K-T boundary. An integrated S2S approach was applied using sedimentary, geochronology, geochemical and isotopic datasets at basin scale ca. These data are used here to discuss the high-resolution time step ca. Results show that the Yacoraite Formation recorded major climate changes that can be documented in terms of catchment dynamic, erosion processes, carbonate accumulation trends, lacustrine dynamic and source rock quality.
The K-T boundary was the climax of a climate change initiated ca.
Ar Dating of the Manson Impact Structure: A Cretaceous-Tertiary Boundary Crater Geochemical data on material from the K-T boundary interval in marine.
The element iridium was brought into the public view with the discovery of a subsurface layer which was greatly enriched in iridium compared with its normal abundance. This layer was found many places around the globe and came to be associated with the boundary between the Cretaceous and Tertiary Periods, referred to as the K-T Boundary on the geological age scale. The fact that a layer like this has been found at several locations scattered around the world suggests a large-scale atmospheric suspension of the material, such as would occur upon the impact of a sizable asteroid.
Coupled with the presence of dinosaur fossils below this layer, but not above, this evidence has led to the asteroid model for the extinction of the dinosaurs. This cross-section of the strata containing the iridium-rich layer is on display at the Smithsonian Museum of Natural History. The thickness of the layer appeared to be cm. Iridium-Rich Layer The element iridium was brought into the public view with the discovery of a subsurface layer which was greatly enriched in iridium compared with its normal abundance.
Index Frankel, “The End of the Dinosaurs”.
Maybe the global climate changed, maybe they were killed by disease, volcanoes, or the rise of mammals. It was this event that pushed the dinosaurs over the edge into extinction. A thin dark line found in layers of sediment around the world; evidence that something devastating happened to the planet 65 million years ago. This line is known as the K-T boundary.
not at) the K-T boundary (dated at about Ma). Hofmann et al.  collected and analyzed samples from close to the bottom and top of the main lava pile in.
You may print out a copy for personal or educational use, and you may link to this site. Illustrations are missing from this Web version of the chapter. Cowen, R. History of Life. Blackwell Scientific Publications, Cambridge, Massachusetts. This is a freshman-level textbook published by Blackwell Science. Copyright Richard Cowen Information and updates on the 3rd edition. See also a separate essay devoted to the general topic of major extinctions , and for an outline of Richard Cowen’s oral presentation.
The beginning of the end started with violent shaking that raised giant waves in the waters of an inland sea in what is now North Dakota. Then, tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills. The heaving sea turned into a foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of fresh-water fish — sturgeon and paddlefish — onto a sand bar and temporarily reversing the flow of the river.
Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud.
The K-T boundary is a geological signature, usually a thin band, dated to Few researchers support Keller’s dating of the impact crater. .
Whether the platinum group elements PGE can be taken as the indicators of extraterrestrial materials is a very important and interesting scientific problem. It is discussed on the basis of systematic investigation and study of a great amount of related literature. The following conclusions can be obtained: i extraterrestrial impact event can cause the PGE anomaly; conversely, the PGE anomaly may not represent the existence of extraterrestrial impact event, because the PGE anomaly can be caused by many terrestrial events e.
This is a preview of subscription content, log in to check access. Alvarez, L. Hildebrand, A.
All available evidence is consistent with an impact into oceanic crust terminating the Cretaceous Period. The commonly cited evidence for a large impact stems from delicate clay layers and their components and the impact site has not yet been found. Impact sites have been suggested all over the globe. The impact is felt to have occurred near North America by: the occurrence of a 2 cm thick ejecta layer only at North American locales, the global variation of shocked quartz grain sizes peaking in North America, the global variation of spinel compositions with most refractory compositions occurring in samples from the Pacific region and possibly uniquely severe plant extinctions in the North American region.
PHYSICAL STRATIGRAPHY OF K-T BOUNDARY STRATA model would effectively be disproved if precise dating of Kirtland strata proved that a substantial.
The Cretaceous—Paleogene K—Pg boundary , formerly known as the Cretaceous—Tertiary K-T boundary , [a] is a geological signature , usually a thin band of rock. K , the first letter of the German word Kreide chalk , is the traditional abbreviation for the Cretaceous Period and Pg is the abbreviation for the Paleogene Period. Its age is usually estimated at around 66 Ma million years ago ,  with radiometric dating yielding a more precise age of The K—Pg boundary is associated with the Cretaceous—Paleogene extinction event , a mass extinction which destroyed a majority of the world’s Mesozoic species, including all dinosaurs except for birds.
Strong evidence exists that the extinction coincided with a large meteorite impact at the Chicxulub crater and the generally accepted scientific theory is that this impact triggered the extinction event. In , a team of researchers consisting of Nobel Prize -winning physicist Luis Alvarez , his son, geologist Walter Alvarez , and chemists Frank Asaro and Helen Michel discovered that sedimentary layers found all over the world at the K—Pg boundary contain a concentration of iridium many times greater than normal 30 times the average crustal content in Italy and times at Stevns on the Danish island of Zealand.
As iridium remains are abundant in most asteroids and comets, the Alvarez team suggested that an asteroid struck the earth at the time of the K—Pg boundary. Shocked quartz granules and tektite glass spherules, indicative of an impact event, are also common in the K—Pg boundary, especially in deposits from around the Caribbean.