Jurassic period what was it like

The weight of this overlying sediment has been pushing down on Alabama's Jurassic deposits for million years. Present-day Alabama's economy benefits from this geology. The structure of Alabama's Jurassic rocks, combined with the pressure and temperature of deep long-term burial, has generated significant deposits of oil and gas from organic material in the Jurassic sediment. In fact, Alabama ranks fifteenth among the states in crude oil production. The Smackover Formation is Alabama's most important oil-producing unit and is responsible for a significant portion of the state's income.

The state ranks eleventh in natural gas production, roughly half of which comes from the Jurassic Norphlet Formation. Red Sea Environment As noted earlier, the Gulf of Mexico began to open during the Triassic, sometime between and million years ago. Initially, narrow rift valleys opened in the Earth as Mexico and the United States were torn apart. The rocks dating to this period consist of complex mixtures of river, floodplain, lake, and other terrestrial deposits, as well as some near-shore marine units.

Although these Triassic rocks are not exposed anywhere in Alabama, similar Triassic valley fills occur on the surface in many Atlantic states. Alabama's Eagle Mills Formation, which formed at this time, is buried deep below the surface of south Alabama. Some of these valley fill deposits may be as young as the Early Jurassic. By sometime in the Middle Jurassic, the valleys had expanded and merged to form the early Gulf of Mexico. During this time, the Gulf occasionally became isolated from the oceans, and intense evaporation in the hot dry climate caused the sea water to become highly concentrated.

Each time the Gulf opened, fresh seawater diluted the concentrated seawater. At a certain level of concentration, the minerals commonly found in seawater began to crystallize, and anhydrite, salt, and sometimes other minerals were deposited. These deposits, some as much as a mile thick in places, are now called the Werner Anhydrite, the Louann Salt, and the Pine Hills Anhydrite. Norphlet Formation Sandstone By the early Late Jurassic, the salt deposits began to become buried by the sands of a coastal desert that formed what is now the Late Jurassic Norphlet Sandstone.

These deposits are typical of desert environments, displaying thick bands composed of thin, even layers that are parallel to one another but steeply inclined. These dune deposits are associated with horizontal layers that were laid down between the dunes, including some that formed in small temporary ponds. Coastal marine deposits are widespread but thin in the uppermost part of the Norphlet. During this time, rising waters filled the Gulf and formed a shallow tropical sea that covered the sand deposits of the Norphlet and remained subject to significant evaporation in the arid climate.

The deposits of this period are made up primarily of limestone and dolomite of the Smackover Formation. The best-known Smackover deposits consist of ooids: tiny spheres of limestone that form in warm, agitated salt water.

The Haynesville Formation, which overlies the Smackover, was deposited in a system of salty lagoons, shallow seas, and associated coastal environments and combines characteristics of all three underlying units. It consists of layers of rock salt, limestone, mudstone, and sandstone that reflect the shifting coastline and varying degrees of evaporation in waters of the Gulf margin. Image credit: gadigal yilimung shield made by Uncle Charles Chicka Madden.

This website uses cookies to ensure you get the best experience on our website. Learn more. The Jurassic was warm and wet with flourishing plant life supporting a diverse fauna. Toggle Caption A typical landscape of the Jurassic Period, - million years ago. Cambrian: to Explore This Park. Article Jurassic Period— Significant Jurassic events The Jurassic Period was a golden time for dinosaurs, which flourished for million years.

For instance, Brachiosaurus was the largest known dinosaur for many decades. Recently, several giant titanosaurians e. Elmer S. The type species of Brachiosaurus is known from two partial skeletons recovered in Colorado and Utah. Brachiosaurus lived from to million years ago.

Some consider the predators that preyed on these giants to be even more spectacular. For example, Tyrannosaurus rex is so well-known that it seems to be one of the first tongue twisters that children master. Modern research has disproved the old concept that dinosaurs were slow-moving, dim-witted, solitary creatures, forced to wade about in swamps because their great bulk could not be supported on land. In fact, many dinosaurs were very agile even the large ones.

Many species apparently roamed the land easily despite their size, and some were quite social, traveling in herds, building nests, and caring for their young Macdougall With the discovery of many new species since the s, scientists have divided the Dinosauria into two major groups: the Ornithischia and the Saurischia, with the distinction based on the construction of the pelvis.

Allosaurus was a bit smaller with a longer jaw and heavier forelimbs. They relied on the stronger hind limbs for a running gait, but it is unclear how fast they could move. It is unlikely to have been common for an Allosaurus to take on a healthy large adult herbivore like a Brachiosaurus or even a Stegosaurus.

They were likely opportunistic, consuming young, sick, aged or injured prey. They were probably able to grasp such prey with their heavily muscled forelimbs, tearing it to pieces with large claws and then swallowing the pieces whole. Dinosaurs may have been the dominant land animals, but they were not alone. Early mammals were mostly very small herbivores or insectivores and were not in competition with the larger reptiles.

Adelobasileus , a shrew-like animal, had the differentiated ear and jaw bones of a mammal and dates from the late Triassic. In August , scientists in China announced discovery of Juramaia. This tiny animal of the mid-Jurassic has caused excitement among scientists because it is clearly a eutherian, an ancestor of placental mammals , indicating that mammals evolved much earlier than previously thought.

Marine life of the Jurassic period was also highly diversified. The largest marine carnivores were the Plesiosaurs.