A review of the geologic history of the Himalayan-Tibetan orogen suggests that at least 1400 km of north-south shortening has been absorbed by the orogen since the onset of the Indo-Asian collision at about 70 Ma. Significant crustal shortening, which leads to eventual construction of the Cenozoic Tibetan plateau, began more or less synchronously in the Eocene (50–40 Ma) in the Tethyan Himalaya in the south, and in the Kunlun Shan and the Qilian Shan some 1000–1400 km in the north. The Paleozoic and Mesozoic tectonic histories in the Himalayan-Tibetan orogen exerted a strong control over the Cenozoic strain history and strain distribution. The presence of widespread Triassic flysch complex in the Songpan-Ganzi-Hoh Xil and the Qiangtang terranes can be spatially correlated with Cenozoic volcanism and thrusting in central Tibet. The marked difference in seismic properties of the crust and the upper mantle between southern and central Tibet is a manifestation of both Mesozoic and Cenozoic tectonics. The form...

Geologic Evolution of the Himalayan-Tibetan Orogen

Assembly, configuration, and break-up history of Rodinia: A synthesis

The gradual discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum. Was the Earth’s orbital obliquity > 60� (making the tropics colder than the poles) for 4.0 billion years following the lunar-forming impact, or did climate cool globally for some reason to the point at which runaway ice-albedo feedback created a ‘snowball’ Earth? The high-obliquity hypothesis does not account for major features of the Neoproterozoic glacial record such as the abrupt onsets and terminations of discrete glacial events, their close association with large (> 10&) negative d 13 C shifts in seawater proxies, the deposition of strange carbonate layers (‘cap carbonates’) globally during post-glacial sea-level rise, and the return of large sedimentary iron formations, after a 1.1 billion year hiatus, exclusively during glacial events. A snowball event, on the other hand, should begin and end abruptly, particularly at lower latitudes. It should last for millions of years, because outgassing must amass an intense greenhouse in order to overcome the ice albedo. A largely ice-covered ocean should become anoxic and reduced iron should be widely transported in solution and precipitated as iron formation wherever oxygenic photosynthesis occurred, or upon deglaciation. The intense greenhouse ensures a transient post-glacial regime of enhanced carbonate and silicate weathering, which should drive a flux of alkalinity that could quantitatively account for the world-wide occurrence of cap carbonates. The resulting high rates of carbonate sedimentation, coupled with the kinetic isotope effect of transferring the CO2 burden to the ocean, should drive down the d 13 C of seawater, as is observed. If cap carbonates are the ‘smoke’ of a snowball Earth, what was the ‘gun’? In proposing the original Neoproterozoic snowball Earth hypothesis, Joe Kirschvink postulated that an unusual preponderance of land masses in the middle and low latitudes, consistent with palaeomagnetic evidence, set the stage for snowball events by raising the planetary albedo. Others had pointed out that silicate weathering would most likely be enhanced if many continents were in the tropics, resulting in lower atmospheric CO2 and a colder climate. Negative d 13 C shifts of 10–20& precede glaciation in many regions, giving rise to speculation that the climate was destabilized by a growing dependency on greenhouse methane, stemming ultimately from the same unusual continental distribution. Given the existing palaeomagnetic, geochemical and geological evidence for late Neoproterozoic climatic shocks without parallel in the Phanerozoic, it seems inevitable that the history of life was impacted, perhaps profoundly so.

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The snowball Earth hypothesis: testing the limits of global change

http://www2.ess.ucla.edu/~yin/05-Publications/papers/091-Yin-2006-ESR.pdf

Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation

The Himalaya and Tibet provide an unparalleled opportunity to examine the complex ways in which continents respond to collisional orogenesis. This paper is an attempt to synthesize the known geology of this orogenic system, with special attention paid to the tectonic evolution of the Himalaya and southernmost Tibet since India-Eurasia collision at ca. 50 Ma. Two alternative perspectives are developed. The first is largely historical. It includes brief (and necessarily subjective) reviews of the tectonic stratigraphy, the structural geology, and metamorphic geology of the Himalaya. The second focuses on the processes that dictate the behavior of the orogenic system today. It is argued that these processes have not changed substantially over the Miocene–Holocene interval, which suggests that the orogen has achieved a quasi–steady state. This condition implies a rough balance between plate-tectonic processes that lead to the accumulation of energy in the orogen and many other processes (e.g., erosion of the Himalayan front and the lateral flow of the middle and lower crust of Tibet) that lead to the dissipation of energy. The tectonics of the Himalaya and Tibet are thus intimately related; the Himalaya might have evolved very differently had the Tibetan Plateau never have formed.

Tectonics of the Himalaya and southern Tibet from two perspectives

The evolution of the great river systems of southern Asia during the Cenozoic India-Asia collision: rivers draining southwards

Three orders of aeolian bounding surface are arranged in a hierarchy based on their extent and regularity.



First order surfaces are the most extensive. They are flat-lying bedding planes cutting across all other aeolian structures and are attributed to the passage of the largest aeolian bedforms—draas—across an area. First order surfaces cut across second order surfaces, which are gentle to moderately dipping surfaces bounding sets of cross-strata. Second order surfaces are attributed to the passage of dunes across draas, or to longitudinal dunes migrating across the lower ice slopes of draas. Third order surfaces bound bundles of laminae within coscts of cross laminae and are due either to local fluctuations in wind direction and velocity or to changes in airflow patterns caused by configurational changes in dune patterns. All these bounding surfaces could be explained by wind variations and dune migration, but the rates of dune migration relative to probable sediment deposition rates are incompatible with this general explanation of the form and spacing of the bounding surfaces. The concept of climbing bedforms of different hierarchical order together with subsidence provides a better explanation. Analogous bounding surfaces in aqueous bedforms have already been attributed to climbing bedforms of differing hierarchical order.

The origin of bounding surfaces in ancient aeolian sandstones

The Himalayan passive margin from Precambrian to Cretaceous times

Pyrite framboid evidence for oxygen-poor deposition during the Permian-Triassic crisis in Kashmir

Papers cover the entire spectrum of eolian investigations, ranging from the microscopic level to regional synthesis as well as ancient eolian deposits and their interpretation.

Michael E. Brookfield

Papers

The evolution of the great river systems of southern Asia during the Cenozoic India-Asia collision: rivers draining southwards

The origin of bounding surfaces in ancient aeolian sandstones

The Himalayan passive margin from Precambrian to Cretaceous times

Pyrite framboid evidence for oxygen-poor deposition during the Permian-Triassic crisis in Kashmir

Eolian sediments and processes