Jurassic period

Most commercial marine diatomite deposits exploit accumulations resulting from large blooms of diatoms that occurred ia the oceans during the Miocene geological epoch. Diatomite sediments older than the Jurassic period are rare in the fossil record. Commercial deposits of diatomite are accumulations of the fossil skeletons, which can occur in beds as thick as 900 m in some locations (5). Marine deposits must have been formed on the bottom of protected basins or other bodies of quiet water, undisturbed by strong currents, in an environment similar to the existing Santa Barbara Channel or Gulf of California (3,6). 

Jurazeitalter, n. Jurassic period, just, adv. just, just now exactly. — a. right, saje. 

Conway (1942) and Smulikowski (1954) have interpreted the potassium-distribution data to indicate that there is a potassium deficiency in Tertiary and Recent seas. However, Spiro and Gramberg (1964) made analyses of the composition of cations adsorbed on argillaceous rocks of northern Siberia and concluded that ... the highest content of potassium is inherent in marine water of the Permian Period. In Triassic seas the content of the potassium dropped significantly, and reached a minimum in seas of the Jurassic Period. Beginning with Cretaceous, the amount of potassium in sea water increased again, and during the Quaternary Period its level approached that of the Permian seas. These ideas are extremely speculative. 

Bob passes other exhibits in the distance. In one huge pool swim icthyosaurs. They resemble dolphins but are actually aquatic reptiles that swam in the Jurassic Period and became extinct on Earth long before humans evolved. 

Jurassic Period Middle period of the Mesozoic Era, between 185-135 million years ago. Characterized by the (possible) origin of angiosperms and the continued split of the worldwide supercontinent of Pangaea. 

Several more island arcs struck western North America since the middle Jurassic period. The granite mountains of the Sierra Nevada are the roots of one of these island arcs. Landmasses created on the Pacific Plate have been scraped off it like the roof of the sports coupe mentioned earlier would be scraped off as it crammed itself under the rear bumper of a tractor-trailer. This mechanism is the origin of the west coast s ranges, the Cascades, and much of British Columbia and Alaska s southern coast. 

Birds evolved from a group of reptiles known as the dinosaurs (order Dinosauria), which first appeared during the late Triassic period (which ended about 210 million years ago). The earliest bird known in the fossil record is Archaeopteryx, from the mid-Jurassic period about 160 million years ago. These extremely early birds had many typical avian characteristics, such as feathers and a homy beak, and were very likely warm-blooded, but they also had reptilian features, such as teeth. In fact, modem birds and dinosaurs still have many characteristics in common, and some biologists and paleontologists believe that birds should be viewed, and classified, as living dinosaurs. ... 

Fig. 4. Seismic and geoseismic cross-section through the 30/9-3A and -4S wells, illustrating the sedimentary growth across faults in the Oseberg Syd area. Note the dramatic thickness increase of the Brent Group of ca. 100% from the Gamma to the Omega North structure, and an -i-additional 30 ms increase to the westernmost fault block. The growth observed in the Dunlin Group and StatQord Fm indicate that most of the faults were active through most of the Jurassic period.

Some of the trends visible in Figure 3 are a relatively slow decrease in Sr/ "Sr ratios from the Cambrian to the Jurassic period, upon which are superimposed a number of relatively large fluctuations. The sharp decline and following rise at the Permian/Triassic boundary are spectacular, and are thought to reflect either an extreme climate and weathering change, or the sudden mixing of a... 

Joint is a discontinuity, fracture or parting in a rock, involving no displacement. Jurassic limestone was deposited in the Jurassic period 135 to 180 million years ago. 

During the Jurassic period large parts of the Northern Hemisphere were covered by sea. The coastal areas consisted of flood and delta plains, which were covered with vegetation. In the middle of this period, the tectonic uphft resulted in parts of the basin being elevated above sea level. Later, the land was again inundated by a rise in the sea level. 

Prof Yangqi confirmed that these coals got the ranks in Jurassic Period. Groundwater stopped convectional flow because heat consumed out. The materials in the columns become too compacted to... 

Fig. 8.4 The granitic plutons of the nunataks located in a belt in West Antarctica between the Thiel Mountains and the Ellsworth Mountains were intruded during the Jurassic Period. The dates of these plutons are listed in Appendix 8.6.5 (Adapted from Vennum and Storey 1987a)...

These considerations remind us that the Transantarctic Mountains did not exist during the Permian glaciation of the East Antarctic craton and that the eventual uplift of the mountains may have between initiated by large-scale rifting of Gondwana which was accompanied by the eruption of flood basalts during the Jurassic Period. 

Fig. 9.1 The supercontinent Pangea was composed of Laurasia and Gondwana during the Jurassic Period when it began to disintegrate into the continents and islands we know today. The gap between Laurasia and Gondwana was occupied by the Tethys Sea which evolved into the Mediterranean Sea. Note that Antarctica was not located at the Geographic South Pole at that...

The break-up of Gondwana started during the Jurassic Period and proceeded in a series of steps that were outlined by Lawver et al (1991) in Fig. 15.8a-d ... 

Fig. 15.12 According to a proposal by Schmidt and Rowley (1986), the Antarctic plate was split by a rift that developed during the Jurassic Period. This rift caused the eruption of basalt flows and the intrusion of dolerite sills of the Ferrar Group in the Transantarctic Mountains along the raised margin of the rift valley. Marie Byrd Land, which was originally located adjacent to northern Victoria Land, moved to its present position in West Antttfctica by right-lateral motion along the Transantarctic rift system tmd the EUsworth Mountain block was rotated clockwise out of alignment with the Transantarctic Mountains at about the same time. These displacements of blocks of continental crust were caused by transform faults that developed in the spreading ridge that separated Africa from Queen Maud Land of East Antarctica (Adapted from Fig. 1 of Schmidt and Rowley (1986))...

Starting during the Jurassic Period, the supercontinent of Gondwana which had sheltered the East Antarctic craton, began to break up into large crustal fragments that slowly moved away and became the continents of the southern hemisphere. East Antarctica... 

The flipside of speeding up evolution in response to stress is that it can slow down in the absence of stress. Fossils of ferns found in Sweden from the early Jurassic period, about 200 million years old, are preserved well enough to see the species genome size. As far as we can tell, it is exactly the same now as it was then. These ferns are truly hving fossils. ... 

Fossils of ferns found in Sweden from the early Jurassic period,. .B. Bomfleur et al. Fossilized nuclei and chromosomes reveal 180 million years of genomic stasis in royal ferns. 2014. Science 343(6177), p. 1376. DOl 10.1126/science.l249884. 

The evolution of grasses is summarized in Brown and Smith (1972) and Jones (1991). The grasses probably appeared during the Jurassic period (Mesozoic), in the wet tropics. The Centothecoideae, Bambusoideae, and Arundinoideae with C3 type of photosynthesis are supposed to be the most primitive. Their descendants, the subfamilies Chloridoideae and Panicoideae developed C4 photosynthetic pathways and thus acquired competitive advantage in warmer regions. 

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