Podcasts about paleogeography

Ever since Alfred Wegener proposed the theory of continental drift in 1912, we have been aware that blocks of the Earth's lithosphere are moving with respect to each other. With the advent of plate tectonics in the 1960s, these moving blocks became identified with the tectonic plates that tile the Earth's surface. We now have accurate measurements of plate motion speeds, which range from about ½ a cm per year to 10 cm per year. But there is still no general consensus as to what makes plates move. Broadly speaking, there are two competing explanations. In the first, the plates ride on top of convection cells of a vigorously convecting mantle. In the second, it is the forces acting on plate boundaries, principally the pull of dense lithospheric slabs subducting into a less dense mantle that drive the plates. Douwe van Hinsbergen is a Professor of Global Tectonics and Paleogeography at the University of Utrecht. He has reconstructed the history of plate motions in various locations around the world with the primary goal of using this history to understand the dynamics of the mantle. And his latest research is directed to shedding light on the long-standing question as to what drives tectonic plates.

Outcrops of Cretaceous Cedar Mountain Formation in Grand County, Utah contain dinosaur fauna found nowhere else in the world. We talk with Dr. James Kirkland, state paleontologist for the Utah Geological Survey about his discoveries of these unique dinosaur species and how the salt tectonics of the area is key to preserving these rare fauna from the Cretaceous time.

Today we’re going back about 280 million years, to what is now Uruguay in South America. 280 million years ago puts us in the early part of the Permian Period. Gondwana, the huge southern continent, was in the process of colliding with North America and Eurasia to form the supercontinent of Pangaea. South America, Africa, Antarctica, India, and Australia had all been attached to each other in Gondwana for several hundred million years, and the extensive glaciers that occupied parts of all those continents were probably still present in at least in highlands in southern South America and South Africa, as well as Antarctica. But the area that is now in Uruguay was probably in cool, temperate latitudes, something like New Zealand or Seattle today. The connection between southern South America and South Africa was a lowland, partially covered by a shallow arm of the sea or perhaps a broad, brackish lagoon at the estuary of a major river system that was likely fed in part by glacial meltwater from adjacent mountains. We know the water was shallow because the rocks preserve ripple marks produced by wave action or currents. The basin must have been near the shore because delicate fossils such as insect wings and plants are among the remnants. It looks like this shallow sea or lagoon became cut off from the ocean, allowing the waters to become both more salty, even hypersaline, and anoxic, as the separation restricted inflows of water, either fresh or marine, that could have continued to oxygenate the basin. In the absence of oxygen, excellent preservation of materials that fell to the basin floor began, and there were few or no scavenging animals to disrupt the bodies.The rocks of the Mangrullo Formation, as it’s called today, include limestones and siltstones, but the most important for fossil preservation are probably the extremely fine-grained claystones and oil shales. These rocks contain some of the best preserved fossil mesosaurs known anywhere. That’s mesosaurs, not the perhaps more well-known mosasaurs, which are large whale-like marine reptiles that lived during Cretaceous time. Here, we’re in the Permian, well before the first dinosaurs. Mesosaur by Nobu Tamura (Creative Commons license & source) Mesosaurs were aquatic reptiles, and they are the earliest known. They evolved from land reptiles and were among the first to return to the water to adopt an aquatic or amphibious lifestyle. They were once thought to be part of a sister group to reptiles, a separate branch of amniotes, which are animals that lay their eggs on land or bear them inside the mother, like most mammals do. In that scheme, mesosaurs and reptiles would have diverged from a common, earlier ancestor. But more recent studies categorize them as reptiles that split off from the main genetic stem early in the history of the class, so they’re pretty distant cousins to dinosaurs and all modern reptiles, but they’re still reptiles. There is ongoing debate among evolutionary paleontologists as to exactly where mesosaurs fit.The fossils in Uruguay are so well preserved that we can identify the gut materials of mesosaurs, and we know they mostly ate crustaceans, aquatic invertebrates related to crabs, shrimp, and lobsters. The preservation is so exceptional that in some cases, soft body parts are preserved including major nerves and blood vessels in mesosaurs and stomachs and external appendages in the crustaceans. The earliest known amniote embryos also come from these fossil beds. Mesosaurs had a short run in terms of their geologic history, only about 30 million years. They were extinct about 270 million years ago, well before the great extinction event at the end of the Permian, 250 million years ago. But the presence of coastal-dwelling mesosaurs in both South America and Africa was a contributing idea in the early development of the theory of continental drift, since it was presumed that they could not have crossed the Atlantic Ocean as it is today. —Richard I. GibsonLinks:Piñeiro et al. 2012 Environmental conditions Paleogeography from Ron Blakey 

The Central Asian Orogenic Belt (CAOB) is one of the world's largest accretionary orogens, which was active during most of the Paleozoic. In recent years it has again moved into focus of the geological community debating how the acrreted lithospheric elements were geographical arranged and interacting prior and/or during the final amalgamation of Kazakhstania. In principal two families of competing models exist. One possible geodynmaic setting is based on geological evidence that a more or less continuous giant arc connecting Baltica and Siberia in the early Paleozoic was subsequently dissected and buckled. Alternatively an archipelago setting, similar to the present day south west Pacific was proposed. This thesis collates three studies on the paleogeography of the south western part of the CAOB from the early Paleozoic until the latest Paleozoic to earliest Mesozoic. It is shown how fragments of Precambrian to early Paleozoic age are likely to have originated from Gondwana at high southerly paleolatitudes (~500 Ma), which got then accreted during the Ordovician (~460 Ma), before this newly created terrane agglomerate (Kazakhstania) migrated northwards crossing the paleo-equator. During the Devonian and the latest Early Carboniferous (~330 Ma) Kazakhstania occupied a stable position at about ~30°N. At least since this time the area underwent several stages of counterclockwise rotational movements accompanying the final amalgamation of Eurasia (~320 - ~270 Myr). This overall pattern of roughly up to 90° counterclockwise bending was replaced by internal relative rotational movements in the latest Paleozoic, which continued probably until the early Mesozoic or even the Cenozoic. In Chapter 2 a comparison of declination data acquired by a remagnetization process during folding in the Carboniferous and coeval data from Baltica and Siberia lead to a documentation and quantification of rotational movements within the Karatau Mountain Range. Based on this results it is very likely that the rotational reorganization started in the Carboniferous and was active until at least the early Mesozoic. Additionally, the data shows that maximal declination deviation increases going from the Karatau towards the Tianshan Mountains (i.e. from North to South). This observation supports models claiming that Ural mountains, Karatau and Tianshan once formed a straight orogen subsequently bent into a orocline. The hinge of this orocline is probably hidden under the sediments of the Caspian basin. In chapter 3 we show that inclination shallowing has affected the red terrigenous sediments of Carboniferous age from the North Tianshan. The corrected inclination values put this part of the Tianshan in a paleolatitude of around 30°N during Carboniferous times. These results contradict previously published paleopositions of the area and suggest a stable latitudinal position between the Devonian and the Carboniferous. Chapter 4 presents paleomagnetic data from early Paleozoic rocks from within the North Tianshan. They imply a second collisional accretion event of individual terranes in the Ordovician. To further constrain the dimensions of these early Paleozoic terranes, chapter 5 presents a compilation of all available paleomagnetic data from the extended study region of southern Kazakhstan and Kyrgyzstan. Apart from a broad coherence of paleolatitudes of all studies at least since the Ordovician and the exclusive occurrence of counterclockwise declination deviations, no areas with the same rotational history can be detected. Also a clear trend caused by oroclinal bending can not be observed. We conclude that first order counterclockwise oroclinal bending, shown in chapter 2, resulted in brittle deformation within the mountain belt and local block rotations. In order to improve our understanding of intra-continental deformation a study combining the monitoring of recent deformation (Global Positioning System, GPS) with a paleomagnetic study of Cenozoic age in the greater vicinity of the Talas-Ferghana fault has been undertaken in chapter 6. The major task was to distinguish between continuous versus brittle deformation. As it turned out the GPS signal indicates rather continuous and consistent counterclockwise rotational movements of the order of ~2° per Myr. This is in contrast to our paleomagnetic results, where even within fault bounded areas the error intervals of the rotations do always overlap. This indicates that a pure block model seems not appropriate even to explain Cenozoic paleomagnetic data. If this means that also Paleozoic rocks have been affected by complex recent deformation, and that the Paleozoic rotational pattern has been obscured by this, can not be decided based on the present data set. It means, however, that interpreting Paleozoic rotational data from this area has to be done with great caution.

Ron Blakey summarizes his pioneering work in this AAPG Distinguished Lecture series. By being a congealer of disparate forms of data, and a visionary, his is able to explain his science to the public, both professional and layperson alike.

A lecturer explains what is involved in environmental field work; aims, objectives and the assessment of a field study.

Transcript -- A lecturer explains what is involved in environmental field work; aims, objectives and the assessment of a field study.

A lecturer explains what is involved in environmental field work; aims, objectives and the assessment of a field study.

Transcript -- A lecturer explains what is involved in environmental field work; aims, objectives and the assessment of a field study.