scholarly journals Early Pleistocene climate-induced erosion of the Alaska Range formed the Nenana Gravel

Geology ◽  
2021 ◽  
Author(s):  
Rachel N. Sortor ◽  
Brent M. Goehring ◽  
Sean P. Bemis ◽  
Chester A. Ruleman ◽  
Marc W. Caffee ◽  
...  
Keyword(s):  
Foreland Basin ◽  
Early Pleistocene ◽  
Alaska Range ◽  
Climate Signal ◽  
Oxygen Isotope Stage ◽  
Tectonic History ◽  
Pleistocene Climate ◽  
Tectonically Active ◽  
Initial Deposition ◽  
Cordilleran Ice Sheet

The Pliocene-Pleistocene transition resulted in extensive global cooling and glaciation, but isolating this climate signal within erosion and exhumation responses in tectonically active regimes can be difficult. The Nenana Gravel is a foreland basin deposit in the northern foothills of the Alaska Range (USA) that has long been linked to unroofing of the Alaska Range starting ca. 6 Ma. Using 26Al/10Be cosmogenic nuclide burial dating, we determined the timing of deposition of the Nenana Gravel and an overlying remnant of the first glacial advance into the northern foothills. Our results indicate that initial deposition of the Nenana Gravel occurred at the onset of the Pleistocene ca. 2.34 Ma and continued until at least ca. 1.7 Ma. The timing of initial deposition is correlative with expansion of the Cordilleran ice sheet, suggesting that the deposit formed due to increased glacial erosion in the Alaska Range. Abandonment of Nenana Gravel deposition occurred prior to the first glaciation extending into the northern foothills. This glaciation was hypothesized to have occurred ca. 1.5 Ma, but we found that it occurred ca. 0.39 Ma. A Pleistocene age for the Nenana Gravel and marine oxygen isotope stage 10 age for the oldest glaciation of the foothills necessitate reanalysis of incision and tectonic rates in the northern foothills of the Alaska Range, in addition to a shift in perspective on how these deposits fit into the climatic and tectonic history of the region.

scholarly journals Supplemental Material: Early Pleistocene climate-induced erosion of the Alaska Range formed the Nenana Gravel

2021 ◽  
Author(s):  
Rachel Sortor ◽  
et al.
Keyword(s):  
Early Pleistocene ◽  
Alaska Range ◽  
Pleistocene Climate ◽  
Sample Data

Expanded methods, discussion of outliers, sample data and supplemental figures.<br>

scholarly journals Supplemental Material: Early Pleistocene climate-induced erosion of the Alaska Range formed the Nenana Gravel

2021 ◽  
Author(s):  
Rachel Sortor ◽  
et al.
Keyword(s):  
Early Pleistocene ◽  
Alaska Range ◽  
Pleistocene Climate ◽  
Sample Data

Expanded methods, discussion of outliers, sample data and supplemental figures.<br>

Emergence of critical climate states during the Pleistocene

2021 ◽  
Author(s):  
Nicholas Golledge
Keyword(s):  
Dynamical Systems ◽  
Late Pleistocene ◽  
Dominant Frequency ◽  
Climate System ◽  
Ice Age ◽  
Early Pleistocene ◽  
Glacial Cycles ◽  
Pleistocene Climate ◽  
System Nodes ◽  
Systems Framework

&lt;p&gt;During the Pleistocene (approximately 2.6 Ma to present) glacial to interglacial climate variability evolved from dominantly 40 kyr cyclicity (Early Pleistocene) to 100 kyr cyclicity (Late Pleistocene to present). Three aspects of this period remain poorly understood: Why did the dominant frequency of climate oscillation change, given that no major changes in orbital forcing occurred? Why are the longer glacial cycles of the Late Pleistocene characterised by a more asymmetric form with abrupt terminations? And how can the Late Pleistocene climate be controlled by 100 kyr cyclicity when astronomical forcings of this frequency are so much weaker than those operating on shorter periods? Here we show that the decreasing frequency and increasing asymmetry that characterise Late Pleistocene ice age cycles both emerge naturally in dynamical systems in response to increasing system complexity, with collapse events (terminations) occuring only once a critical state has been reached. Using insights from network theory we propose that evolution to a state of criticality involves progressive coupling between climate system 'nodes', which ultimately allows any component of the climate system to trigger a globally synchronous termination. We propose that the climate state is synchronised at the 100 kyr frequency, rather than at shorter periods, because eccentricity-driven insolation variability controls mean temperature change globally, whereas shorter-period astronomical forcings only affect the spatial pattern of thermal forcing and thus do not favour global synchronisation. This dynamical systems framework extends and complements existing theories by accomodating the differing mechanistic interpretations of previous studies without conflict.&lt;/p&gt;

Early Pleistocene climate changes in the central Mediterranean region as inferred from integrated pollen and planktonic foraminiferal stable isotope analyses

2007 ◽  
Vol 67 (2) ◽  
pp. 264-274 ◽  
Author(s):  
Sébastien Joannin ◽  
Frédéric Quillévéré ◽  
Jean-Pierre Suc ◽  
Christophe Lécuyer ◽  
François Martineau
Keyword(s):  
Mediterranean Region ◽  
Climate Changes ◽  
Environmental Changes ◽  
Early Pleistocene ◽  
Subtropical Climate ◽  
Central Mediterranean ◽  
Globigerina Bulloides ◽  
Riparian Trees ◽  
Pleistocene Climate ◽  
Anoxic Events

AbstractVegetation inherited from a Pliocene subtropical climate evolved through obliquity oscillations and global cooling leading to modern conditions. An integrated, highly time-resolved record of pollen and stable isotopes (δ18O and δ13C of Globigerina bulloides) was obtained to understand vegetation responses to Early Pleistocene climate changes. Continental and marine responses are compared in the Central Mediterranean region with a particular consideration of environmental changes during anoxic events.Pollen data illustrate vegetation dynamics as follows: [1] development of mesothermic elements (warm and humid conditions); [2] expansion of mid- and high-altitude elements (cooler but still humid conditions); and [3] strengthening of steppe and herb elements (cooler and dry conditions). These successions correlate with precession. δ18O variations recorded by Globigerina bulloides define two cycles (MIS 43-40) related to obliquity. At northern low- to mid-latitudes, the pollen signal records temperature and wetness changes related to precession even during global climate changes induced by obliquity. This may result in unexpected increasing wetness during glacial periods, which has to be considered specific to the Central and Eastern Mediterranean region. Lastly, an analysis of anoxic events reveals that enhanced runoff is indicated by increasing frequency of the riparian trees Liquidambar and Zelkova.

scholarly journals Petrography of the Siwalik sandstones, Amlekhganj-Suparitar area, central Nepal Himalaya

2003 ◽  
Vol 28 ◽  
Author(s):  
Naresh Kazi Tamrakar ◽  
Shuichiro Yokota ◽  
Suresh Das Shrestha
Keyword(s):  
Middle Miocene ◽  
Foreland Basin ◽  
Early Pleistocene ◽  
Nepal Himalaya ◽  
Central Nepal ◽  
Present Study Area ◽  
Mean Grain Size ◽  
Siwalik Group ◽  
Variation Trends ◽  
The Himalaya

Middle Miocene to early Pleistocene sedimentary sequence deposited in the foreland basin of the Himalaya is represented by the Siwalik Group. In the present study area the Siwalik Group extends in a NW-SE direction and well-exposed. Forty­four sandstone samples were studied for texture, fabric and composition in order to assess their petrographic properties and variation trends of these properties in stratigraphic levels. Sandstones were classified into sublitharenite, subarkose, lithic arenite, arkosic arenite and feldspathic graywacke and further thirteen sub-clans. Mean grain size (M) and Trask sorting coefficient (So) increase up-section. Recalculated quartz, matrix, modified maturity index (MMI), total cement (Ct), cement versus matrix index (CMI) and ratio of strong cement over total cement ((Cfc/Cs)/Ct) also increase, whilst packing proximity (PP), packing density (PD) and consolidation factor (Pcc) decrease up-section showing distinct trends, and therefore, these properties are promising in recognizing the older sandstones from the younger ones.

Dating Early and Middle (Reid) Pleistocene Glaciations in Central Yukon by Tephrochronology

2001 ◽  
Vol 56 (3) ◽  
pp. 335-348 ◽  
Author(s):  
John A. Westgate ◽  
Shari J. Preece ◽  
Duane G. Froese ◽  
Robert C. Walter ◽  
Amanjit S. Sandhu ◽  
...  
Keyword(s):  
Gulf Of Alaska ◽  
Supporting Evidence ◽  
Pleistocene Glaciations ◽  
Late Cenozoic ◽  
Aeolian Sand ◽  
Oxygen Isotope Stage ◽  
Aleutian Arc ◽  
Dawson City ◽  
Cordilleran Ice Sheet ◽  
Tephra Beds

AbstractThe late Cenozoic deposits of central Yukon contain numerous distal tephra beds, derived from vents in the Wrangell Mountains and Aleutian arc–Alaska Peninsula region. We use a few of these tephra beds to gain a better understanding on the timing of extensive Pleistocene glaciations that affected this area. Exposures at Fort Selkirk show that the Cordilleran Ice Sheet advanced close to the outer limit of glaciation about 1.5 myr ago. At the Midnight Dome Terrace, near Dawson City, exposed outwash gravel, aeolian sand, and loess, related to valley glaciers in the adjacent Ogilvie Mountains, are of the same age. Reid glacial deposits at Ash Bend on the Stewart River are older than oxygen isotope stage (OIS) 6 and likely of OIS 8 age, that is, about 250,000 yr B.P. Supporting evidence for this chronology comes from major peaks in the rates of terrigeneous sediment input into the Gulf of Alaska at 1.5 and 0.25 myr B.P.

scholarly journals A multidisciplinary study of ecosystem evolution through early Pleistocene climate change from the marine Arda River section, Italy

2018 ◽  
Vol 89 (2) ◽  
pp. 533-562 ◽  
Author(s):  
Gaia Crippa ◽  
Andrea Baucon ◽  
Fabrizio Felletti ◽  
Gianluca Raineri ◽  
Daniele Scarponi
Keyword(s):  
Climate Change ◽  
Integrated Approach ◽  
Early Pleistocene ◽  
Tectonic Activity ◽  
Delta Front ◽  
Multidisciplinary Study ◽  
Sedimentary Evolution ◽  
Pleistocene Climate ◽  
Pleistocene Climate Change ◽  
Uplift And Erosion

AbstractThe Arda River marine succession (Italy) is an excellent site to apply an integrated approach to paleoenvironmental reconstructions, combining the results of sedimentology, body fossil paleontology, and ichnology to unravel the sedimentary evolution of a complex marine setting in the frame of early Pleistocene climate change and tectonic activity. The succession represents a subaqueous extension of a fluvial system, originated during phases of advance of fan deltas affected by high-density flows triggered by river floods, and overlain by continental conglomerates, indicating a relative sea level fall and the establishment of a continental environment. An overall regressive trend is observed through the section, from prodelta to delta front and intertidal settings. The hydrodynamic energy and the sedimentation rate are not constant through the section, but they are influenced by hyperpycnal flows, whose sediments were mainly supplied by an increase in Apennine uplift and erosion, especially after 1.80 Ma. The Arda section documents the same evolutionary history of coeval successions in the Paleo-Adriatic region, as well as the climatic changes of the early Pleistocene. The different approaches used complement quite well one another, giving strength and robustness to the obtained results.

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