Megamonsoons Were Present in Tibet Multiple Times From the Late Permian Through the Middle Triassic

Mesozoic litho- and magneto-stratigraphic evidence from the central Tibetan Plateau for megamonsoon evolution and potential evaporites

Authors:

Fang et al

Abstract:

The megamonsoon was a striking event that profoundly impacted the climatic environment and related mineral sources (salts, coals and oil-gases) in the Mesozoic. How this event impacted Asia is unknown. Here, we firstly reported a Mesozoic stratigraphic sequence in the northern Qiangtang Basin, in the central Tibetan Plateau, based on lithofacies and chronologies of paleontology and magnetostratigraphy. How the planetary and megamonsoon circulations controlled the Asian climate with time has been recorded. Using the basic principles of physical geography, present analogs and a newly developed model, the evolution of the stratigraphic sequence was interpreted to demonstrate that the Qiangtang Basin has been subjected to a megamonsoon climate with heavy precipitation during its northward movement since the Latest Permian but has been subjected to a dry environment due to moving into the northern hemisphere subtropic high zone in the Middle Triassic and monsoonal retreat in the early Late Jurassic (early Oxfordian) approximately 161 Ma. The coupling of the hot-dry climate and the close of the Meso-Tethys, along with sea retreat in the Late Jurassic, ensured a large potential time window for evaporite (potash) formation in the Qiangtang Basin, while the tropic megamonsoon rain forest in the Late Permian to the Early Triassic and in the Late Triassic to Middle Jurassic favored the formation of coal and hydrocarbon source rocks.

Tournaisian Mississipian Tetrapods of Scotland Lived in a Seasonal Mosaic Tropical Forest

The terrestrial landscapes of tetrapod evolution in earliest Carboniferous seasonal wetlands of SE Scotland

Authors:

Kearsey et al

Abstract:

The Lower Mississippian (Tournaisian) Ballagan Formation in SE Scotland yields tetrapod fossils that provide fresh insights into the critical period when these animals first moved onto land. The key to understanding the palaeoenvironments where they lived is a detailed analysis of the sedimentary architecture of this formation, one of the thickest and most completely documented examples of a coastal floodplain and marginal marine succession from this important transitional time anywhere in the world. Palaeosols are abundant, providing a unique insight into the early Carboniferous habitats and climate.

More than 200 separate palaeosols are described from three sections through the formation. The palaeosols range in thickness from 0.02 to 1.85 m and are diverse: most are Entisols and Inceptisols (63%), indicating relatively brief periods of soil development. Gleyed Inseptisols and Vertisols are less common (37%). Vertisols are the thickest palaeosols (up to 185 cm) in the Ballagan Formation and have common vertic cracks. Roots are abundant through all the palaeosols, from shallow mats and thin hair-like traces to sporadic thicker root traces typical of arborescent lycopods.

Geochemical, isotope and clay mineralogical analyses of the palaeosols indicate a range in soil alkalinity and amount of water logging. Estimates of mean annual rainfall from palaeosol compositions are 1000–1500 mm per year. The high mean annual rainfall and variable soil alkalinities contrast markedly with dry periods that developed deep penetrating cracks and evaporite deposits. It is concluded that during the early Carboniferous, this region experienced a sharply contrasting seasonal climate and that the floodplain hosted a mosaic of closely juxtaposed but distinct habitats in which the tetrapods lived. The diversification of coastal floodplain environments identified here may link to the evolution and movement of tetrapods into the terrestrial realm.

Were the Exposed Continental Shelves Important Refugia for the Neotropical Rainforests During the Last Ice Age?

Neotropical forest expansion during the last glacial period challenges refuge hypothesis

Authors:

Leite et al

Abstract:

The forest refuge hypothesis (FRH) has long been a paradigm for explaining the extreme biological diversity of tropical forests. According to this hypothesis, forest retraction and fragmentation during glacial periods would have promoted reproductive isolation and consequently speciation in forest patches (ecological refuges) surrounded by open habitats. The recent use of paleoclimatic models of species and habitat distributions revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity is associated with historically stable forest areas. However, the role of the emerged continental shelf on the Atlantic Forest biodiversity hotspot of eastern South America during glacial periods has been ignored in the literature. Here, we combined results of species distribution models with coalescent simulations based on DNA sequences to explore the congruence between scenarios of forest dynamics through time and the genetic structure of mammal species cooccurring in the central region of the Atlantic Forest. Contrary to the FRH predictions, we found more fragmentation of suitable habitats during the last interglacial (LIG) and the present than in the last glacial maximum (LGM), probably due to topography. We also detected expansion of suitable climatic conditions onto the emerged continental shelf during the LGM, which would have allowed forests and forest-adapted species to expand. The interplay of sea level and land distribution must have been crucial in the biogeographic history of the Atlantic Forest, and forest refuges played only a minor role, if any, in this biodiversity hotspot during glacial periods.

Tropical Deforestation has Global Impacts

A new study released today presents powerful evidence that clearing trees not only spews carbon into the atmosphere, but also triggers major shifts in rainfall and increased temperatures worldwide that are just as potent as those caused by current carbon pollution. Further, the study finds that future agricultural productivity across the globe is at risk from deforestation-induced warming and altered rainfall patterns.

The report, "Effects of Tropical Deforestation on Climate Change and Agriculture," published today in Nature Climate Change and released in collaboration with Climate Focus provides the most comprehensive analysis to date of the climate impacts of tropical forest destruction on agriculture in the tropics and thousands of miles away. Specifically, the study finds that deforestation in South America, Southeast Asia and Africa may alter growing conditions in agricultural areas in the tropics and as far away as the US Midwest, Europe and China.

The study is also the only global synthesis of research based on cutting-edge climate models and empirical data on the direct local, regional and global impacts of cutting down tropical forests, which regulate interactions between the earth and the atmosphere. It predicts that atmospheric impacts resulting from complete tropical deforestation could lead to a rise in global temperature of 0.7 degrees Celsius (on top of the impact from greenhouse gases), which would double the observed global warming since 1850. Currently, climate change negotiators are shaping policies that focus on greenhouse gases, in particular carbon. To date, they have overlooked policy responses that address other ways that forests affect climate.

"Tropical deforestation delivers a double whammy to the climate--and to farmers," said Deborah Lawrence, Professor of Environmental Sciences at the University of Virginia, the study's lead author. "Most people know that climate change is a dangerous global problem, and that it's caused by pumping carbon into the atmosphere. But it turns out that removing forests alters moisture and air flow, leading to changes--from fluctuating rainfall patterns to rises in temperatures--that are just as hazardous, and happen right away. The impacts go beyond the tropics--the United Kingdom and Hawaii could see an increase in rainfall while the US Midwest and Southern France could see a decline."

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Is the Amazon Rain Forest Only 2,000 Years Old?

Swathes of the Amazon may have been grassland until a natural shift to a wetter climate about 2,000 years ago let the rainforests form, according to a study that challenges common belief that the world’s biggest tropical forest is far older.

The arrival of European diseases after Columbus crossed the Atlantic in 1492 may also have hastened the growth of forests by killing indigenous people farming the region, the scientists wrote in the U.S. journal Proceedings of the National Academy of Sciences (PNAS).

"The dominant ecosystem was more like a savannah than the rainforest we see today," John Carson, lead author at the University of Reading in England, said of the findings about the southern Amazon.

The scientists said that a shift toward wetter conditions, perhaps caused by natural shifts in the Earth’s orbit around the sun, led to growth of more trees starting about 2,000 years ago.

The scientists studied man-made earthworks, uncovered by recent logging in Bolivia, that included ditches up to about a kilometer (1,100 yards) long and up to 3 meters deep and 4 meters wide.

They found large amounts of grass pollen in ancient sediments of nearby lakes, suggesting the region had been covered by savannah. They also found evidence of plantings of maize, pointing to farming.

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The Forests of SE Asia Have Been Undergoing Anthropic Modification Since at Least the Beginning of the Holocene

New research from Queen's University Belfast shows that the tropical forests of South East Asia have been shaped by humans for the last 11,000 years.

The rain forests of Borneo, Sumatra, Java, Thailand and Vietnam were previously thought to have been largely unaffected by humans, but the latest research from Queen's Palaeoecologist Dr Chris Hunt suggests otherwise.

A major analysis of vegetation histories across the three islands and the SE Asian mainland has revealed a pattern of repeated disturbance of vegetation since the end of the last ice age approximately 11,000 years ago.

The research, which was funded by the Arts and Humanities Research Council and the British Academy, is being published in the Journal of Archaeological Science. It is the culmination of almost 15 years of field work by Dr Hunt, involving the collection of pollen samples across the region, and a major review of existing palaeoecology research, which was completed in partnership with Dr Ryan Rabett from Cambridge University.

Evidence of human activity in rainforests is extremely difficult to find and traditional archaeological methods of locating and excavating sites are extremely difficult in the dense forests. Pollen samples, however, are now unlocking some of the region's historical secrets.

Dr Hunt, who is Director of Research on Environmental Change at Queen's School of Geography, Archaeology and Palaeoecology, said: "It has long been believed that the rainforests of the Far East were virgin wildernesses, where human impact has been minimal. Our findings, however, indicate a history of disturbances to vegetation. While it could be tempting to blame these disturbances on climate change, that is not the case as they do not coincide with any known periods of climate change. Rather, these vegetation changes have been brought about by the actions of people.

"There is evidence that humans in the Kelabit Highlands of Borneo burned fires to clear the land for planting food-bearing plants. Pollen samples from around 6,500 years ago contain abundant charcoal, indicating the occurrence of fire. However, while naturally occurring or accidental fires would usually be followed by specific weeds and trees that flourish in charred ground, we found evidence that this particular fire was followed by the growth of fruit trees. This indicates that the people who inhabited the land intentionally cleared it of forest vegetation and planted sources of food in its place.

"One of the major indicators of human action in the rainforest is the sheer prevalence of fast-growing 'weed' trees such as Macaranga, Celtis and Trema. Modern ecological studies show that they quickly follow burning and disturbance of forests in the region.

"Nearer to the Borneo coastline, the New Guinea Sago Palm first appeared over 10,000 years ago. This would have involved a voyage of more than 2,200km from its native New Guinea, and its arrival on the island is consistent with other known maritime voyages in the region at that time – evidence that people imported the Sago seeds and planted them."

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Late Triassic to Jurassic Paleoclimate Data From Western-Central Mediterranean Alpine Mountains Were Tropical Rain Forest

Palaeoclimatic conditions and palaeoweathering processes on Mesozoic continental redbeds from Western-Central Mediterranean Alpine Chains

Authors:

Perri et al

Abstract:

Chemical and mineralogical analyses of the Triassic to lowermost Jurassic mudstones from continental redbeds outcropping in the Internal Domains of the Betic-Rifian and Calabria-Peloritani chains have been used to infer the relationships between palaeoclimatic conditions and palaeoweathering processes during rifting of a continental crust block that finally detached from adjoining western Tethyan realms to form an independent microplate (Mesomediterranean Microplate) from Jurassic to lower Miocene time. The studied mudstone samples come from Middle Triassic and Upper Triassic beds of the Saladilla Formation (both in the Betic Cordillera and in the Rif), whereas the Calabria-Peloritani Arc studied mudstones come from Upper Triassic to lowermost Jurassic beds (both in the Sila and Longi Taormina Units). Major and trace element concentrations, based on the mass-balance calculation relative to the upper continental crust, show negative values both in Gibraltar and Calabria-Peloritani Arcs, implying that mudstone formation in the Early Mesozoic involved moderate to intense continental palaeoweathering of the crust. In particular, CaO, Na2O, MgO, Sr, Ba, Fe2O3, MnO and transition metal elements (V, Cr, Co and Ni) are more depleted in the Triassic to Upper Jurassic samples of the Calabria-Peloritani samples than in the Middle to Upper Triassic Betic-Rifian samples, and suggest an increase of continental palaeoweathering in the Mediterranean region from the Triassic to the Jurassic. In addition enrichment in SiO2, TiO2, Al2O3, K2O and incompatible elements in the Calabria-Peloritani Arc mudstones indicates sediment recycling effects that gradually increase from the Triassic to Jurassic time. The hinterland palaeoweathering and sediment recycling effects have been mathematically distinguished using principal component analysis (PC1 is a measure of palaeoweathering rate mainly due to humidity (positive values) against aridity (negative values), whereas PC2 corresponds to the extent of sediment recycling). The results strongly indicate that humidity had increased from the Triassic to the Jurassic and that the depositional environments in Calabria-Peloritani Arc were probably more suitable for sediment recycling. These seasonal climate alternations corresponding to an increase in palaeoclimatic humidity that favored palaeoweathering conditions and recycling processes. These results are also confirmed by the mineralogical data, which show a higher abundance of kaolinite, typical of warm-humid conditions, in the Calabria-Peloritani mudstones than in those of the Betic Cordillera and the Rif. Furthermore, the comparison among geochemical weathering index values of the studied samples and of recent soils from different climatic zones likely suggests a tropical rainforest climate in the studied area during the Triassic to the lowermost Jurassic.