Initial growth of the Northern Lhasaplano, Tibetan Plateau in the early Late Cretaceous (ca. 92 Ma)

Constraining the growth of the Tibetan Plateau in time and space is critical for testing geodynamic models and climatic changes at the regional and global scale. The Lhasa block is a key region for unraveling the early history of the Tibetan Plateau. Distinct from the underlying shallow-marine limestones, the Jingzhushan and Daxiong formations consist of conglomerate and sandstone deposited in alluvial-fan and braided-river systems. Both units were deposited at ca. 92 Ma, as constrained by interbedded tuff layers, detrital zircons, and micropaleontological data. Provenance and paleocurrent analyses indicate that both units were derived from the same elevated source area located in the central-northern Lhasa block. These two parallel belts of coeval conglomerates record a major change in paleogeography of the source region from a shallow seaway to a continental highland, implying initial topographic growth of an area over 160,000 km2, named here the Northern Lhasaplano. The early Late Cretaceous topographic growth of the Northern Lhasaplano was associated with the demise of Tethyan seaways, thrust-belt development, and crustal thickening. The same paleogeographic and paleotectonic changes were recorded earlier in the Northern Lhasaplano than in the Southern Lhasaplano, indicating progressive topographic growth from north to south across the Bangong-Nujiang suture and Lhasa block during the Cretaceous. Similar to the Central Andean Plateau, the Northern Lhasaplano developed by plate convergence above the oceanic Neo-Tethyan subduction zone before the onset of the India-Asia collision

Loess plateau storage of northeastern Tibetan plateau-derived Yellow River sediment

Marine accumulations of terrigenous sediment are widely assumed to accurately record climatic- and tectonic-controlled mountain denudation and play an important role in understanding late Cenozoic mountain uplift and global cooling. Underpinning this is the assumption that the majority of sediment eroded from hinterland orogenic belts is transported to and ultimately stored in marine basins with little lag between erosion and deposition. Here we use a detailed and multi-technique sedimentary provenance dataset from the Yellow River to show that substantial amounts of sediment eroded from Northeast Tibet and carried by the river’s upper reach are stored in the Chinese Loess Plateau and the western Mu Us desert. This finding revises our understanding of the origin of the Chinese Loess Plateau and provides a potential solution for mismatches between late Cenozoic terrestrial sedimentation and marine geochemistry records, as well as between global CO2 and erosion records

Phylogenetic Analysis of Seven WRKY Genes across the Palm Subtribe Attaleinae (Arecaceae) Identifies Syagrus as Sister Group of the Coconut

BACKGROUND:The Cocoseae is one of 13 tribes of Arecaceae subfam. Arecoideae, and contains a number of palms with significant economic importance, including the monotypic and pantropical Cocos nucifera L., the coconut, the origins of which have been one of the "abominable mysteries" of palm systematics for decades. Previous studies with predominantly plastid genes weakly supported American ancestry for the coconut but ambiguous sister relationships. In this paper, we use multiple single copy nuclear loci to address the phylogeny of the Cocoseae subtribe Attaleinae, and resolve the closest extant relative of the coconut. METHODOLOGY/PRINCIPAL FINDINGS:We present the results of combined analysis of DNA sequences of seven WRKY transcription factor loci across 72 samples of Arecaceae tribe Cocoseae subtribe Attaleinae, representing all genera classified within the subtribe, and three outgroup taxa with maximum parsimony, maximum likelihood, and Bayesian approaches, producing highly congruent and well-resolved trees that robustly identify the genus Syagrus as sister to Cocos and resolve novel and well-supported relationships among the other genera of the Attaleinae. We also address incongruence among the gene trees with gene tree reconciliation analysis, and assign estimated ages to the nodes of our tree. CONCLUSIONS/SIGNIFICANCE:This study represents the as yet most extensive phylogenetic analyses of Cocoseae subtribe Attaleinae. We present a well-resolved and supported phylogeny of the subtribe that robustly indicates a sister relationship between Cocos and Syagrus. This is not only of biogeographic interest, but will also open fruitful avenues of inquiry regarding evolution of functional genes useful for crop improvement. Establishment of two major clades of American Attaleinae occurred in the Oligocene (ca. 37 MYBP) in Eastern Brazil. The divergence of Cocos from Syagrus is estimated at 35 MYBP. The biogeographic and morphological congruence that we see for clades resolved in the Attaleinae suggests that WRKY loci are informative markers for investigating the phylogenetic relationships of the palm family

The topographic evolution of the Tibetan Region as revealed by palaeontology

The Tibetan Plateau was built through a succession of Gondwanan terranes colliding with Asia during the Mesozoic. These accretions produced a complex Paleogene topography of several predominantly east–west trending mountain ranges separated by deep valleys. Despite this piecemeal assembly and resultant complex relief, Tibet has traditionally been thought of as a coherent entity rising as one unit. This has led to the widely used phrase ‘the uplift of the Tibetan Plateau’, which is a false concept borne of simplistic modelling and confounds understanding the complex interactions between topography climate and biodiversity. Here, using the rich palaeontological record of the Tibetan region, we review what is known about the past topography of the Tibetan region using a combination of quantitative isotope and fossil palaeoaltimetric proxies, and present a new synthesis of the orography of Tibet throughout the Paleogene. We show why ‘the uplift of the Tibetan Plateau’ never occurred, and quantify a new pattern of topographic and landscape evolution that contributed to the development of today’s extraordinary Asian biodiversity

Uplift-driven climate change at 12 Ma: a long delta O-18 record from the NE margin of the Tibetan plateau

Carbonates from fluvial and lacustrine sediments were sampled from multiple measured sections in the Linxia basin of western China. Based on textural and mineralogical evidence, lacustrine carbonates are primary precipitates from lake water. A 29 million year record of the oxygen isotope composition of meteoric water is inferred from the delta(18)O values of these carbonates. This inference is based on the most negative delta(18)O values in the lake carbonates, which represent lake waters that have experienced the least evaporative enrichment. Carbonate delta(18)O values, a proxy for rainfall delta(18)O, are similar to -10.5 parts per thousand throughout the interval of 29-12 Ma. At 12 Ma there is a shift to -9 parts per thousand, a value that remains into the Pliocene. This implies a major reorganization of atmospheric circulation patterns and a shift to more and conditions at the NE margin of the Tibetan plateau with the post-12 Ma system similar to that of today. The 12 Ma event may represent the time at which the Tibetan plateau achieves sufficient elevation to block the penetration of moisture from the Indian Ocean or south Pacific into western China. The period of greatest aridity is from 9.6 to 8.2 Ma, a time interval which agrees well with other climate records. (C) 2003 Elsevier B.V. All rights reserved

Magnetostratigraphy of Cenozoic deposits in the western QaidamBasin and its implication for the surface uplift of the northeasternmargin of the Tibetan Plateau

Thick Cenozoic deposits in the northwestern Qaidam Basin record erosion of the Altyn Tagh and high terrain west of that basin and presumably the concurrent growth of the northeastern Tibetan Plateau. A detailed magnetostratigraphic study of the Huatugou section, northwestern Qaidam basin, reveals that this section spans the period from ∼30 to ∼11 Ma. Magnetostratigraphic and sedimentological studies indicate that the accumulation rate abruptly increased near ∼15 Ma. The acceleration in sedimentation rate suggests enhanced tectonic deformation in the Qaidam basin since 15 Ma that may have begun simultaneously with accelerated deformation along the Altyn Tagh, Kunlun, and Haiyuan faults, which contributed to the growth history of the Qaidam basin and its surroundings since ∼15 Ma

Qaidam Basin and northern Tibetan Plateau as dust sources for the Chinese Loess Plateau and paleoclimatic implications

The Chinese Loess Plateau of central Asia is composed of interbedded loess and paleosol layers, deposited during glacial and interglacial cycles, respectively, during the past similar to 2.5 m.y. Understanding the provenance of loess is fundamental to reconstructing wind patterns during Quaternary glacial periods. We determined and compared U-Pb ages on zircon crystals from Loess Plateau strata and potential source areas. The results indicate that the loess was largely derived from the Qaidam Basin and the northern Tibetan Plateau to the west, both of which exhibit spatially extensive geomorphic landforms indicative of past (interpreted as pre-Holocene) wind erosion and/or deflation by westerly winds. This challenges the current paradigm that the loess of the Chinese Loess Plateau was largely sourced from deserts located to the northwest, as observed in the modern interglacial climate. We propose that during glacial periods, the mean annual positions of the polar jet streams were shifted equatorward, resulting in more southerly tracks for dust-generating storms and suppression of the East Asian monsoon by inhibiting the subtropical jet from shifting northward across the Tibetan Plateau.</p