Evidence of Extreme Aridification Across the Jurassic/Cretaceous Boundary From North China

Jurassic–Cretaceous terrestrial transition red beds in northern North China and their implication on regional paleogeography, paleoecology, and tectonic evolution

Authors:

xu et al

Abstract:

Craton are associated with a number of major geological issues that remain controversial, such as paleogeography, biotic transition, and tectonic evolution. Based on previous studies and new progress related to stratigraphy, sedimentology, provenance, biotas, and tectonics, this paper performs a comprehensive review of the red beds in the northern North China Craton represented by the Tuchengzi/Houcheng/Daqingshan Formation (ca. 154–137 Ma) and offers some new perspectives. Based on the 15 measured sections, five facies units including alluvial fan, fluvial, delta, lacustrine, and eolian facies have been recognized and described in detail. Provenance analysis indicates that the red beds were derived from local sources. Deposits in the basins in the eastern Yinshan–Yanshan orogenic belt were derived mainly from volcanic rocks of the Middle–Late Jurassic Tiaojishan Formation and the Mesoproterozoic–Early Paleozoic carbonate, siliceous, and clastic rocks present around the basin, especially in the north. In contrast, sediments in the basins in the western Yinshan–Yanshan orogenic belt were provided predominantly by the Neoarchean–Paleoproterozoic metamorphic rocks exposed mainly in the north of the basin. Paleocurrent features in different regions show characteristics of a localized convergent paleo-drainage system, suggesting that a series of relatively independent small- to mid-scale basins developed in the northern North China Craton. The east–west-trending Yinshan–Yanshan orogenic belt, formed in the late Middle Jurassic, uplifted successively and constituted a paleogeographic highland in northern North China during the Jurassic–Cretaceous transition time. The presence of eolian deposits in the early Early Cretaceous indicates degradation of the severe arid and hot environment, which may have been an essential factor in the dying out of the Yanliao Biota. Combined with regional Late Jurassic–Early Cretaceous A-type granites, mafic dykes, and metamorphic core complexes and rift basins, this suggests that the Jurassic–Cretaceous transition red beds were formed in an extensional tectonic setting controlled by the post-orogenic collapse of the Mongol–Okhotsk orogenic belt.

Increasing Aridity Negatively Impacts Soil Microbes in Global Drylands

Increasing aridity reduces soil microbial diversity and abundance in global drylands

Authors:

Maestre et al

Abstract:

Soil bacteria and fungi play key roles in the functioning of terrestrial ecosystems, yet our understanding of their responses to climate change lags significantly behind that of other organisms. This gap in our understanding is particularly true for drylands, which occupy ∼41% of Earth´s surface, because no global, systematic assessments of the joint diversity of soil bacteria and fungi have been conducted in these environments to date. Here we present results from a study conducted across 80 dryland sites from all continents, except Antarctica, to assess how changes in aridity affect the composition, abundance, and diversity of soil bacteria and fungi. The diversity and abundance of soil bacteria and fungi was reduced as aridity increased. These results were largely driven by the negative impacts of aridity on soil organic carbon content, which positively affected the abundance and diversity of both bacteria and fungi. Aridity promoted shifts in the composition of soil bacteria, with increases in the relative abundance of Chloroflexi and α-Proteobacteria and decreases in Acidobacteria and Verrucomicrobia. Contrary to what has been reported by previous continental and global-scale studies, soil pH was not a major driver of bacterial diversity, and fungal communities were dominated by Ascomycota. Our results fill a critical gap in our understanding of soil microbial communities in terrestrial ecosystems. They suggest that changes in aridity, such as those predicted by climate-change models, may reduce microbial abundance and diversity, a response that will likely impact the provision of key ecosystem services by global drylands.

Europe Suddenly Became Much Drier 13,000 Years ago

Molecular-based moisture indicators, remains of midges and climate simulations have provided climate scientists with the final piece to one of the most enduring puzzles of the last Ice Age.

For years, researchers have struggled to reconcile climate models of the Earth, 13,000 years ago, with the prevailing theory that a catastrophic freshwater flood from the melting North American ice sheets plunged the planet into a sudden and final cold snap, just before entering the present warm interglacial.

Now, an international team of scientists, led by Swedish researchers from Stockholm University and in partnership with UK researchers from the Natural History Museum (NHM) London, and Plymouth University, has found evidence in the sediments of an ancient Swedish lake that it was the melting of the Scandinavian ice sheet that provides the missing link to what occurred at the end of the last Ice Age. The study, published in Nature Communications, today, examined moisture and temperature records for the region and compared these with climate model simulations.

Francesco Muschitiello, a PhD researcher at Stockholm University and lead author of the study, said: "Moisture-sensitive molecules extracted from the lake's sediments show that climate conditions in Northern Europe became much drier around 13,000 years ago."

link.

Climates Changes During the Early to Middle Triassic

Climate changes during the Early–Middle Triassic transition in the E. Iberian plate and their palaeogeographic significance in the western Tethys continental domain

Authors:

Borruel-Abadía et al

Abstract:

Until recently the climate of the Early–Middle Triassic at low latitudes was broadly considered as generally temperate-warm with no major climate oscillations. This work examines the climate of this period through a detailed study of the sedimentary, plant, soil and mineral records of continental rocks (Buntsandstein facies) in eastern Iberian basins. Our findings indicate temporal climate variations for these near equator (10°–14°N) regions and unveil the significance of such variations in the southern Laurasian domain.

The climate of Iberia's Early Triassic was mainly dominated by alternating brief (< 0.4 ma) arid and semi-arid climate periods, with two main arid periods documented at the end of the Smithian and middle Spathian. However, an initial short subhumid to semi-arid period was also observed in the late Spathian. Remarkably, this latter period appears just after an unconformity related to the tectonically induced Hardegsen Event in western Europe. It is also of interest that this short subhumid climate period is concurrent with the beginning of faunal and floral recovery in the basins examined. The Early Triassic ended again with a short very arid period. Although the beginning of the Anisian (Aegean) was represented by alternating arid and semi-arid to subhumid intervals, during the Bithynian and Pelsonian clearly wetter climates are recorded by the succession consisting of alternating semi–arid to semi-humid intervals. This general tendency was interrupted by three short but marked intervals, two humid intervals in the late Bithynian, and one arid period near the Bithynian/Pelsonian boundary. Iberia was crossed by prominent irregular highs separating marked corridors or isolated areas. This palaeogeography, prevailing since Variscan tectonics, clearly conditioned dominant climates and their geographical distribution. No clear climate belts developed in these conditions. However, isolated internal climate zones separated by elevated areas are identified. This palaeogeographic configuration and the low latitudinal position of Iberia determined central Iberia highs in the southernmost border of Laurasia, beyond which more humid conditions clearly extended towards the equator reaching the present-day Moroccan Meseta and Argana Basin.

New Study Predicts Horn of Africa to Become More Arid due to Global Warming

he Horn of Africa is becoming drier in step with global warming, researchers said on Friday, contradicting some climate models predicting rainier weather patterns in a region that has suffered frequent food crises linked to drought.

A new study using a sediment core extracted from the Gulf of Aden found the East African region covering Somalia, Djibouti and Ethiopia has dried at an unusually fast rate over the past century.

Lead author Jessica Tierney, an associate professor at the University of Arizona, told the Thomson Reuters Foundation the research team was confident the drying was linked to rising emissions of climate-changing greenhouse gases, and was expected to continue as the region heats up further.

"If the region becomes dry, like we think it might get, that completely changes your models for food security and agriculture," she said.

Study co-author Peter deMenocal of Columbia University's Lamont-Doherty Earth Observatory warned that many aid groups are expecting "a wetter, greener future for the Horn of Africa". But the new findings show "the exact opposite is occurring".

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Central Asia Became More Arid Across the Eocene-Oligocene Boundary

Onset of aridification by 34 Ma across the Eocene-Oligocene transition in Central Asia

Authors:

Sun et al

Abstract:

Cenozoic climate has changed markedly from a warm, wet climate to the present cool, dry glacial-interglacial cycles. The largest of these cooling steps is thought to have taken place across the Eocene-Oligocene transition. Terrestrial airborne eolian loess is a direct result of land aridification; therefore, the prolonged formation of thick eolian loess deposits provides a key to aridification history in the geological past. However, the oldest eolian loess in the Asian interior has been dated to only 25–22 Ma. Here we present new sedimentological, geochemical, and magnetostratigraphic data from Cenozoic sections in southwestern Mongolia to show that the earliest eolian dust accumulation occurred by 34 Ma, ∼10 m.y. earlier than currently believed. We suggest that this oldest eolian dust accumulation provides direct evidence for enhanced aridification across the Eocene-Oligocene transition in Central Asia; this is explicable by reduced moisture transport caused by prevailing westerlies during retreat of the Neotethys Ocean. These climatic changes were related to the changing regional plate configuration as well as to global cooling and ice-sheet growth in Antarctica.

The Link Between Tectonics & Climate in Miocene Neogene Asian Interior's Aridification

Late Miocene stepwise aridification in the Asian interior and the interplay between tectonics and climate

Authors:

Sun et al

Abstract:

The mid-latitudinal central Asian continent is characterized by large sand deserts and Gobi (stony desert). In this context, it is of interest to study the timing and forcing mechanisms of aridification in the region. Here we present multiple geochemical climatic proxies from late Cenozoic strata in the Tarim Basin of northwestern China, a region sensitive to climatic change. The results yield long-term climatic records covering a time interval of 13.3 to 2.5 Ma. We find that a general trend towards a dry climate was superimposed by two stepwise aridification events, the first lesser aridity phase occurred at ~ 7–5.3 Ma and the second extreme aridity episode was initiated at ~ 5.3 Ma. Based on the correlation between climatic change and regional tectonic events, we propose a mechanism to explain the climatic variations. The general long-term drying trend since the mid-Miocene was a response to global climatic cooling, while the stepwise aridification since the latest Miocene was controlled mainly by regional tectonic uplift.