scholarly journals Geomorphology, Stratigraphy and 14C-Chronology of Ancient Tufas at Louie Creek, Northwest Queensland, Australia

2007 ◽  
Vol 48 (3) ◽  
pp. 285-295 ◽  
Author(s):  
Russell Drysdale ◽  
John Head
Keyword(s):  
Stream Flow ◽  
Humid Tropics ◽  
Sediment Supply ◽  
Karst Spring ◽  
Fluvial System ◽  
Contact Points ◽  
River Incision ◽  
Eastern Edge ◽  
The Last Glacial Maximum ◽  
The Last Glacial

ABSTRACT Louie Creek is a karst spring-fed stream situated in the seasonally humid tropics of northwest Queensland, Australia. It rises as a series of small exsurgences along the eastern edge of the Barkly Tableland. As it enters the lowlands of the Carpentaria plain, the creek deposits tufa which produces a series of cascades. This modern tufa extends discontinuously for about 1.5 km. A series of ancient tufas, in places lying adjacent to sites of modern deposition, extends discontinously for about 8 km downstream. At least two ancient tufa units are preserved at one location, Little lndarri site. The older unit comprises a sequence of well-preserved barrages with an orientation transverse to present-day stream flow. In places, erosion has reduced these barrages to their calcrete substrate. The older tufa is overlain in places by sediment which has become cemented to form a second calcrete unit. This sediment is in turn succeeded by the younger ancient tufa. Subsequent river incision has removed part of the sediment from the older unit and exposed several contact points between the ancient tufa and calcrete units. Radiocarbon dating of the Little lndarri site tufas, as well as other ancient Louie Creek units, yielded apparent ages ranging from ~ 30 to ~ 14 ka BP, suggesting that conditions were sufficiently wet during the period immediately preceding and throughout the Last Glacial Maximum for tufa depostion to occur. However, ancient tufa formation occurred during a phase of net river aggradation. There is geomorphic evidence that such aggradation was a result of an increased sediment supply to the fluvial system, most likely in response to conditions drier than present. Results from studies elsewhere in the region support such a Late Pleistocene trend. Incision of Louie Creek, which postdates the youngest of the dated ancient tufas, is most likely to have resulted from a shift to wetter conditions during the early Holocene,

scholarly journals High-Resolution Marine Record of Climatic Change in Mid-latitude Chile during the Last 28,000 Years Based on Terrigenous Sediment Parameters

1999 ◽  
Vol 51 (1) ◽  
pp. 83-93 ◽  
Author(s):  
Frank Lamy ◽  
Dierk Hebbeln ◽  
Gerold Wefer
Keyword(s):  
Sediment Cores ◽  
Climatic Conditions ◽  
Sediment Supply ◽  
Size Distributions ◽  
Terrigenous Sediment ◽  
Latitudinal Position ◽  
Grain Size Distributions ◽  
The Last Glacial Maximum ◽  
Southern Westerlies ◽  
The Last Glacial

AbstractMarine sediment cores from the continental slope off mid-latitude Chile (33°S) were studied with regard to grain-size distributions and clay mineral composition. The data provide a 28,000-yr14C accelerator mass spectrometry-dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland. These variations can be interpreted in terms of the paleoclimatic evolution of mid-latitude Chile and are compared to existing terrestrial records. Glacial climates (28,000–18,000 cal yr B.P.) were generally cold–humid with a cold–semiarid interval between 26,000 and 22,000 cal yr B.P. The deglaciation was characterized by a trend toward more arid conditions. During the middle Holocene (8000–4000 cal yr B.P.), comparatively stable climatic conditions prevailed with increased aridity in the Coastal Range. The late Holocene (4000–0 cal yr B.P.) was marked by more variable paleoclimates with generally more humid conditions. Variations of rainfall in mid-latitude Chile are most likely controlled by shifts of the latitudinal position of the Southern Westerlies. Compared to the Holocene, the southern westerly wind belt was located significantly farther north during the last glacial maximum. Less important variations of the latitudinal position of the Southern Westerlies also occurred on shorter time scales.

Freshwater control of ice-rafted debris in the last glacial period at Mono Lake, California, USA

2011 ◽  
Vol 76 (2) ◽  
pp. 264-271 ◽  
Author(s):  
Susan R. H. Zimmerman ◽  
Crystal Pearl ◽  
Sidney R. Hemming ◽  
Kathryn Tamulonis ◽  
N. Gary Hemming ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Warm Season ◽  
Glacial Maximum ◽  
Sediment Supply ◽  
Mono Lake ◽  
Last Glacial ◽  
Type Section ◽  
High Lake Level ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractThe type section silts of the late Pleistocene Wilson Creek Formation at Mono Lake contain outsized clasts, dominantly well-rounded pebbles and cobbles of Sierran lithologies. Lithic grains > 425 μm show a similar pattern of variability as the > 10 mm clasts visible in the type section, with decreasing absolute abundance in southern and eastern outcrops. The largest concentrations of ice-rafted debris (IRD) occur at 67–57 ka and 46–32 ka, with strong millennial-scale variability, while little IRD is found during the last glacial maximum and deglaciation.Stratigraphic evidence for high lake level during high IRD intervals, and a lack of geomorphic evidence for coincidence of lake and glaciers, strongly suggests that rafting was by shore ice rather than icebergs. Correspondence of carbonate flux and IRD implies that both were mainly controlled by freshwater input, rather than disparate non-climatic controls. Conversely, the lack of IRD during the last glacial maximum and deglacial highstands may relate to secondary controls such as perennial ice cover or sediment supply. High IRD at Mono Lake corresponds to low glacial flour flux in Owens Lake, both correlative to high warm-season insolation. High-resolution, extra-basinal correlation of the millennial peaks awaits greatly improved age models for both records.

scholarly journals Changes in detrital sediment supply to the central Yellow Sea since the Last Glacial Maximum

2020 ◽  
Author(s):  
Hyo Jin Koo ◽  
Hyen Goo Cho
Keyword(s):  
Last Glacial Maximum ◽  
Yellow Sea ◽  
Clay Mineralogy ◽  
Glacial Maximum ◽  
Sediment Supply ◽  
Last Glacial ◽  
Sea Mud ◽  
Detrital Sediment ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The sediment supply to the central Yellow Sea since the Last Glacial Maximum was uncovered through clay mineralogy and geochemical analysis of core 11YS-PCL14 in the Central Yellow Sea mud (CYSM). The core can be divided into four units: Unit 4 (700–520 cm; 15.5–14.8 ka), Unit 3 (520–280 cm; 14.8–12.1 ka), Unit 2 (280–130 cm; 12.1–8.8 ka), and Unit 1 (130–0 cm;

The Timing and Environmental Significance of Late Quaternary Linear Dune Development in Western Zambia

1999 ◽  
Vol 52 (1) ◽  
pp. 44-55 ◽  
Author(s):  
Peter W. O'Connor ◽  
David S. G. Thomas
Keyword(s):  
Late Quaternary ◽  
River System ◽  
Sediment Supply ◽  
Environmental Significance ◽  
Optical Luminescence ◽  
Forcing Mechanisms ◽  
Dune Activity ◽  
The Last Glacial Maximum ◽  
The Last Glacial ◽  
Zambezi River

Optical luminescence dates for 19 samples from the degraded linear dune field of western Zambia indicate multiple periods of regional dune building for the late Quaternary, 32,000–27,000, 16,000–13,000, 10,000–8000, and 5000–4000 yr ago. These dates show that the last glacial maximum was not the only time when dune construction, commonly linked to marked aridity, occurred in central-southern Africa during the late Quaternary. Whereas rainfall significantly less than today's ca. 1400 mm yr−1 is a prerequisite for dune construction in the area, adequate sediment supply also determines dune construction and preservation, so that dune building cannot be simply and singularly linked to marked aridity. The Zambezi River system is proposed as an important source of dune sediments, with the nature of linear dune activity explaining why stacked sediments preserve several phases of dune formation. Chronologies of dune construction in western Zimbabwe and the southwest Kalahari are in broad agreement with our Zambian chronology and support a model of rainfall shifts along a SW–NE gradient, with some notable disparities. These are probably a function of interregional sediment supply differences, the number of samples used to delimit constructional periods, and the multicausal nature of forcing mechanisms.

Iceberg discharge to the Chukchi shelf during the Younger Dryas

2010 ◽  
Vol 74 (1) ◽  
pp. 57-62 ◽  
Author(s):  
Jenna C. Hill ◽  
Neal W. Driscoll
Keyword(s):  
Radiocarbon Dating ◽  
Discrete Event ◽  
Younger Dryas ◽  
Sediment Supply ◽  
Geological Data ◽  
Northern Alaska ◽  
Chukchi Shelf ◽  
The Last Glacial Maximum ◽  
Age Estimates ◽  
The Last Glacial

AbstractThe extent of glaciation in northwestern Alaska, the source of sediment supply to the Chukchi shelf and slope, and the movement of sea ice and icebergs across the shelf during the last glacial maximum (LGM) remain poorly constrained. Here we present geophysical and geological data from the outer Chukchi margin that reveal a regionally extensive, heavily ice-scoured surface ∼ 5–8 m below the modern seafloor. Radiocarbon dating of this discrete event yields age estimates between 10,600 and 11,900 14C yr BP, indicating the discharge event occurred during the Younger Dryas. Based on mineralogy of the ice-rafted debris, the icebergs appear to be sourced from the northwestern Alaskan margin, which places important constraints on the ice extent in northern Alaska during the LGM as well as existing circulation models for the region.

scholarly journals Ice-stream demise dynamically conditioned by trough shape and bed strength

2019 ◽  
Vol 5 (4) ◽  
pp. eaau1380 ◽  
Author(s):  
Tom Bradwell ◽  
David Small ◽  
Derek Fabel ◽  
Rachel K. Smedley ◽  
Chris D. Clark ◽  
...  
Keyword(s):  
Stream Flow ◽  
Three Dimensional ◽  
Step Change ◽  
Ice Streams ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Ice sheet mass loss is currently dominated by fast-flowing glaciers (ice streams) terminating in the ocean as ice shelves and resting on beds below sea level. The factors controlling ice-stream flow and retreat over longer time scales (>100 years), especially the role of three-dimensional bed shape and bed strength, remain major uncertainties. We focus on a former ice stream where trough shape and bed substrate are known, or can be defined, to reconstruct ice-stream retreat history and grounding-line movements over 15 millennia since the Last Glacial Maximum. We identify a major behavioral step change around 18,500 to 16,000 years ago—out of tune with external forcing factors—associated with the collapse of floating ice sectors and rapid ice-front retreat. We attribute this step change to a marked geological transition from a soft/weak bed to a hard/strong bed coincident with a change in trough geometry. Both these factors conditioned and ultimately hastened ice-stream demise.

scholarly journals A late Quaternary paleoenvironmental record in sand dunes of the northern Atacama Desert, Chile

2018 ◽  
Vol 90 (1) ◽  
pp. 127-138 ◽  
Author(s):  
Kari M. Finstad ◽  
Marco Pfeiffer ◽  
Gavin McNicol ◽  
Michael Tuite ◽  
Kenneth Williford ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Late Quaternary ◽  
Sand Dunes ◽  
Atacama Desert ◽  
Glacial Maximum ◽  
Sediment Supply ◽  
Steady Increase ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractThis paper reports a previously unidentified paleoenvironmental record found in sand dunes of the Atacama Desert, Chile. Long-term aeolian deflation by prevailing onshore winds has resulted in the deposition of sand on the irregular surface of a Miocene-aged anhydrite outcrop. Two deposits ~25 km apart, along the prevailing wind trajectory, were hand excavated then analyzed for vertical (and temporal) changes in physical and chemical composition. Radiocarbon ages of organic matter embedded within the deposits show that rapid accumulation of sediment began at the last glacial maximum and slowed considerably after the Pacific Ocean attained its present post-glacial level. Over this time period, grain sizes are seen to increase while accumulation rates simultaneously decrease, suggesting greater wind speeds and/or a change or decrease in sediment supply. Changes in δ34S values of sulfate in the sediment beginning ~10 ka indicate an increase in marine sources. Similarly, δ2H values from palmitic acid show a steady increase at ~10 ka, likely resulting from aridification of the region during the Holocene. Due to the extreme aridity in the region, these sand dunes retain a well-preserved chemical record that reflects changes in elevation and coastal proximity after the last glacial maximum.

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