Dryland dunes and other dryland environmental archives as proxies for Late Quaternary stratigraphy and environmental and climate change in southern Africa

2021 ◽  
Author(s):  
A. Stone
Keyword(s):  
Southern Africa ◽  
Late Quaternary ◽  
Sand Dunes ◽  
Geographic Area ◽  
Global Scale ◽  
Namib Desert ◽  
The Past ◽  
The North ◽  
Quaternary Stratigraphy ◽  
Environmental Responses

Abstract The Namib Desert and the Kalahari constitute the drylands of southern Africa, with the current relatively humid portions of the latter having experienced periodically drier conditions during the Late Quaternary. This study explores the range of dryland archives and proxies available for the past ~190 ka. These include classic dryland geomorphological proxies, such as sand dunes, as well as water-lain sediments within former lakes and ephemeral fluvial systems, lake shorelines, sand ramps, water-lain calcrete and tufa sediments at the interface of surface hydrological and hydrogeological, speleothems and groundwater hydrogeological records, and hyrax middens. Palaeoenvironmental evidence can also be contained within geoarchaeological archives in caves, overhangs and rockshelters. This integration of records is undertaken with the aim of identifying a (or a number of) terrestrial regional chronostratigraphic framework(s) for this time period within southern Africa, because this is missing from the Quaternary stratigraphy lexicon. Owing to a lack of long, near-continuous terrestrial sequences in these drylands, the correspondence between nearby terrestrial records are explored as a basis for parasequences to build this chronostratigraphy. Recognising the modern climatological diversity across the subcontinent, four broad spatial subdivisions are used to explore potential sub-regional parasequences, which capture current climatic gradients, including the hyper-arid west coast and the decrease in aridity from the southwest Kalahari toward the north and east. These are the Namib Desert, the northern Kalahari, the southern Kalahari and the eastern fringes of the southern Kalahari. Terrestrial chronostratigraphies must start from premise that climate-driven environmental shifts may have occurred independently to those in other terrestrial locations and may be diachronous compared to the marine oxygen isotope stratigraphy (MIS), which serves as a global-scale master climatostratigraphy relating to global ice volume. The fragmented nature of preserved evidence means that we are still some way from producing unambiguous parasequences. There is however, a rich record to consider, compile and compare, within which seven broad wetter intervals are identified, with breaks between these inferred to be relatively drier, and some also have proxy evidence for drying. The onset and cessation of these wetter intervals does not align with MIS: they occur with greater frequency, but not with regular periodicity. Precession-paced insolation forcing is often invoked as a key control on southern African climate, but this does not explain the pacing of all of the identified events. Overall, the pattern is complex with some corresponding wetter intervals across space and others with opposing west-east trends. The evidence for drying over the past 10 ka is pronounced in the west (Namib Desert), with ephemerally wet conditions in the south (southern Kalahari). The patterns identified here provide a framework to be scrutinised and to inspire refinements to proposed terrestrial chronostratigraphies for southern Africa. Considering changes across this large geographic area also highlights the complexity in environmental responses across space as we continue to test a range of hypotheses about the nature of climatic forcing in this region.

Late Quaternary Spatio-temporal Limnological Variations in the Altiplano of Bolivia and Peru

1995 ◽  
Vol 43 (3) ◽  
pp. 344-354 ◽  
Author(s):  
Denis Wirrmann ◽  
Philippe Mourguiart
Keyword(s):  
Late Quaternary ◽  
Present Condition ◽  
Dry Period ◽  
Lake Titicaca ◽  
The Past ◽  
The North ◽  
Gypsum Precipitation ◽  
Salt Crust ◽  
Spatio Temporal ◽  
Large Decline

AbstractBetween the western and eastern Andean cordilleras in Peru and Bolivia, there are three main lacustrine basins: Lake Titicaca, Lake Poopó, and the group of Coipasa-Uyuni. For the past few millennia, highly variable environmental conditions have been recorded in their sediments. Today a latitudinal meteorological gradient influences the lakes' status, leading to specific deposits and ostracod communities. Lake Titicaca in the north is oligohaline, whereas Lake Poopó further south is polyhaline. In the south, the Coipasa-Uyuni depression is characterized by a 12,000-km2 surficial salt crust. During the Late Pleistocene (ca. 40,000 to 25,000 yr B.P.), the water depth and salinity in paleolake Poopó fluctuated widely and paleolake Titicaca was slightly larger than at present. Sedimentation was mostly biocarbonate in the shallower areas and it was detrital-organic in the deepest zones. During the Holocene, a dry period transformed Lake Poopó into a "salar" with evaporite precipitation. Lake Titicaca registered a large decline in water level (8100-3600 yr B.P.) initially inducing gypsum precipitation followed by short influxes of water, with an ostracod faunal composition similar to that of the modern brines of Lake Poopó. Lake Titicacas' present condition only appeared between 2200 and 1500 yr B.P.

scholarly journals Bidrag til Læsøs geologi. Lithologi, biostratigrafi og geofysik

1986 ◽  
Vol 6 ◽  
pp. 1-72
Author(s):  
Henner Bahnson ◽  
Karen Luise Knudsen ◽  
Jens Morten Hansen
Keyword(s):  
Late Quaternary ◽  
Border Zone ◽  
Normal Faulting ◽  
Marine Deposits ◽  
The North ◽  
Tectonic Events ◽  
Quaternary Stratigraphy ◽  
Late Weichselian ◽  
Sea Cliff ◽  
Southeasterly Direction

Seven wells have been performed on the island of Læsø in the Northern Kattegat Sea in order to clarify the Quaternary stratigraphy and structure of the island. All wells have been gamme-logged and five wells have been test-pumped. In addition, geoelectrical and electromagnetic (georadar) profiles have been measured. The lithostratigraphy and biostratigraphy of the seven wells show, that the late Quaternary of Læsø can be divided into four units: 1) a lower clay unit, which biostratigraphically is nearly identical with the type-section of the marine late Eemian - early Weichselian Skærumhede Series of Vendsyssel, 2) a sandy unit, which on the basis of reworked Foraminifera is believed to be a Weichselian melt-water deposit, 3) a clayey and silty unit, which biostratigraphically and lithologically corresponds to the marine socalled Younger Yoldia Clay of Vendsyssel, and 4) Holocene, marinesands and beachridges. Unit 3 and 4 is separated by an almost horizontal abrasion surface, which in three wells is developed into a soil profile demonstrating that Læsø was elevated above sea level before the onset of the Flandrian transgressions. In other wells and outcrops the boundary between unit 3 and 4 is covered by a conglomerate of boulders derived from the underlying deposits of various age. Six of the wells have been performed within a distance of a few hundred meter enabling a structural interpretation of the· area of investigation. A correlation of the six wells demonstrate, that the pre-Holocene of Læsø is disturbed by tectonic events, since the same stratigraphical units are found at surprisingly different levels. In three wells the Younger Yoldia Clay is even missing. Thus, the pre-Holocene, including the late Weichselian, marine deposits, may be dipping as much as 4 percent towards the north or northeast. A glacio-tectonical interpretation of this structure would anticipate a new glaciation of Læsø after the deposition of the Younger Yoldia Clay. However, more likely the northward tilting of late Weichselian and older strata is related to a Fennoscandian Border Zone fault, which is crossing Læsø in northwest-southeasterly direction immediately south of the area of investigation. Normal faulting in this fault during late Weichselian and Holocene times would cause northeastwards tilting of the strata within the magnitude as actually found. Moreover, from the georadar profiles the same fault is seen also to affect the almost horizontal boundary between unit 3 and 4, since a four meter jump in the level of the abrasion surface is coincident with the above mentioned fault and an app. 3000 years old sea cliff parallel with the fault. This may explain previous observations on the topography of Læsø, which showed that Læsø is divided in 8 shore-terraces, which after their formation during the last app. 3000 years have been slightly tilted, sometimes slowly towards southwest, and sometimes comparatively rapid towards northeast. Since the general late Weichselian and Holocene isostatic recovery of Scandinavia in this area would result in gradual southwesterly tilting of ancient shore-lines, it is reasonable to suggest the southwestwards tilting of the shore-terraces to be caused by the general isostatic upheaval of Denmark, while the north or northeastwards tilting fases may be caused by normal faulting activity.

Luminescence-dated aeolian deposits of late Quaternary age in the southern Tibetan Plateau and their implications for landscape history

2009 ◽  
Vol 72 (3) ◽  
pp. 421-430 ◽  
Author(s):  
ZhongPing Lai ◽  
Knut Kaiser ◽  
Helmut Brückner
Keyword(s):  
Tibetan Plateau ◽  
Late Quaternary ◽  
Age Distribution ◽  
Sediment Accumulation ◽  
Global Scale ◽  
The Tibetan Plateau ◽  
Last Deglaciation ◽  
Aeolian Deposits ◽  
The Last Deglaciation ◽  
Environmental Responses

AbstractAeolian deposits are widely distributed in the interior of the Tibetan Plateau, and their chronology is poorly known. It is not yet clear whether they accumulated only after the last deglaciation, or over a longer time. We applied quartz OSL dating to aeolian samples from the Lhasa area with OSL ages ranging from 2.9 ± 0.2 to at least 118 ± 11 ka. The probability density frequency (PDF) distribution of 24 ages reveals age clusters at about 3, 8, 16–21, 33, and 79–83 ka, indicating enhanced sediment accumulation then. The results show that aeolian deposition occurred throughout most of the last 100 ka. This implies that: 1) an ice sheet covering the whole Tibetan Plateau during the last glacial maximum (LGM) could not have existed; and 2) erosion during the last deglaciation was not as strong as previously proposed, such that not all pre-Holocene loess was removed. The age distribution shown in the PDF indicates that aeolian accumulation is episodic. Sand-formation events revealed by age clusters at 3, 8, and 16–21 ka imply roughly synchronous environmental responses to corresponding global-scale arid events.

Productivity and life history of sockeye salmon in relation to competition with pink and sockeye salmon in the North Pacific Ocean

2015 ◽  
Vol 72 (6) ◽  
pp. 818-833 ◽  
Author(s):  
Gregory T. Ruggerone ◽  
Brendan M. Connors
Keyword(s):  
North Pacific ◽  
Sockeye Salmon ◽  
North Pacific Ocean ◽  
Pink Salmon ◽  
Geographic Area ◽  
Oncorhynchus Gorbuscha ◽  
Fraser River ◽  
The Past ◽  
The North ◽  
Key Factor

Sockeye salmon (Oncorhynchus nerka) populations from Southeast Alaska through British Columbia to Washington State have experienced similar declines in productivity over the past two decades, leading to economic and ecosystem concerns. Because the declines have spanned a wide geographic area, the primary mechanisms driving them likely operate at a large, multiregional scale at sea. However, identification of such mechanisms has remained elusive. Using hierarchical models of stock–recruitment dynamics, we tested the hypothesis that competition between pink (Oncorhynchus gorbuscha) and sockeye salmon for prey has led to reduced growth and productivity and delayed maturation of up to 36 sockeye populations spanning the region during the past 55 years. Our findings indicate the abundance of North Pacific pink salmon in the second year of sockeye life at sea is a key factor contributing to the decline of sockeye salmon productivity, including sockeye in the Fraser River where an increase from 200 to 400 million pink salmon is predicted to reduce sockeye recruitment by 39%. Additionally, length-at-age of Fraser River sockeye salmon declined with greater sockeye and pink salmon abundance, and age at maturity increased with greater pink salmon abundance. Our analyses provide evidence that interspecific competition for prey can affect growth, age, and survival of sockeye salmon at sea.

Archaeology in the Brooks Range of Alaska

1951 ◽  
Vol 17 (1Part1) ◽  
pp. 52-52 ◽  
Author(s):  
William Irving
Keyword(s):  
Small Groups ◽  
Bering Sea ◽  
Organic Materials ◽  
Sand Dunes ◽  
Mountain Region ◽  
The Past ◽  
The North ◽  
Academy Of Sciences ◽  
Hunting And Fishing ◽  
Sea Coast

A cursory survey of the archaeology of parts of the Endicott mountains was made by the writer during 1950. It served to confirm a belief that the mountain region is and in the past has been hospitable to small groups of people dependent on hunting and fishing. Ten sites near the Anaktuvuk and Killik rivers were examined, and the probable locations of several others were obtained from local Eskimos. Recognizable culture phases encountered include types comparable with the modern and recent-prehistoric Eskimo, and Denbigh Flint complex, as described by Giddings (J. L. Giddings, “Early Flint Horizons on the North Bering Sea Coast,” Journal of the Washington Academy of Sciences, Vol. 39, No. 3, March 15, 1949, pp. 85-90). In addition, a number of flint implements which are not readily identifiable were found in the sand dunes along the Killik River (Fig. 34). No evidence of ground slate or jade was found anywhere, and implements of organic materials were preserved only in the most recent sites.

The late Quaternary stratigraphy of coastal dunes and associated deposits in southern Africa

2021 ◽  
Author(s):  
J. Knight
Keyword(s):  
Sea Level ◽  
Southern Africa ◽  
Sand Dune ◽  
Late Quaternary ◽  
Sand Dunes ◽  
Coastal Sand Dunes ◽  
Coastal Sand Dune ◽  
African Coast ◽  
Coastal Sand ◽  
And Sea Level

Abstract Coastal sand dune sediments with associated intraformational aeolianite, palaeosols and beachrock are found throughout much of the southern African coast, and have important roles as both Quaternary environmental archives and in recording the interplay of sediment supply, coastal processes and sea-level change. This paper examines the stratigraphy and palaeoenvironmental significance of coastal sand dunes and associated sediments, using examples mainly from South Africa but also with reference to the sandy coasts of Namibia and southern Mozambique. Based on morphological, sedimentary and dating evidence reported in the diverse literature, the stratigraphic relationship of coastal sand dune sediments to Marine Isotope Stages (MIS) is summarized, and a chronostratigraphic diagram for the period MIS 6 to 1 along the South African coast is used to identify spatially coherent sedimentary units that correspond to different regional climatic and sea-level phases. This framework provides a stratigraphic context to better examine the relationship between coastal sand dunes and external forcing during the late Quaternary in southern Africa, and to guide future field studies.

An Environmental History of Southern Africa

2020 ◽  
Author(s):  
Jasper Knight
Keyword(s):  
Environmental History ◽  
Southern Africa ◽  
Land Surface ◽  
Environmental Changes ◽  
Late Quaternary ◽  
Global Scale ◽  
Time Intervals ◽  
Ecological Processes ◽  
Environmental Controls ◽  
Proxy Indicators

Southern Africa has experienced significant environmental changes since the breakup of the Gondwana supercontinent, starting around 180 million years ago. These environmental changes broadly reflect the interplay between tectonic and global-scale climatic drivers, which in combination result in changes to the properties and dynamics of land surface physical and ecological processes. The preserved record of such processes can be used as proxy indicators to reconstruct past environments and climates. In southern Africa, different types of proxy indicators have formed and are preserved in different geographical areas, broadly corresponding to their individual climatic and geomorphic contexts. Three significant time intervals over which landscape evolution have taken place are the Phanerozoic, the late Quaternary, and the last 200 years. A critical outcome of this analysis is that the record of environmental change in southern Africa is highly variable and only partly preserved, and that there are spatial and temporal gaps which mean that it is difficult to construct a continuous or unambiguous environmental history either for all areas of the region or for all time intervals. Changing physical drivers and environmental controls over time, including land surface feedbacks, are now being supplanted by a stronger imprint of human activity in the Anthropocene.

scholarly journals Response of an Afro-Palearctic bird migrant to glaciation cycles

2021 ◽  
Vol 118 (52) ◽  
pp. e2023836118
Author(s):  
Kasper Thorup ◽  
Lykke Pedersen ◽  
Rute R. da Fonseca ◽  
Babak Naimi ◽  
David Nogués-Bravo ◽  
...  
Keyword(s):  
Global Scale ◽  
Seasonal Migration ◽  
Migratory Species ◽  
Effective Population ◽  
Long Distance ◽  
Climate Conditions ◽  
The Past ◽  
The North ◽  
Population Sizes ◽  
Glacial Periods

Migration allows animals to exploit spatially separated and seasonally available resources at a continental to global scale. However, responding to global climatic changes might prove challenging, especially for long-distance intercontinental migrants. During glacial periods, when conditions became too harsh for breeding in the north, avian migrants have been hypothesized to retract their distribution to reside within small refugial areas. Here, we present data showing that an Afro-Palearctic migrant continued seasonal migration, largely within Africa, during previous glacial–interglacial cycles with no obvious impact on population size. Using individual migratory track data to hindcast monthly bioclimatic habitat availability maps through the last 120,000 y, we show altered seasonal use of suitable areas through time. Independently derived effective population sizes indicate a growing population through the last 40,000 y. We conclude that the migratory lifestyle enabled adaptation to shifting climate conditions. This indicates that populations of resource-tracking, long-distance migratory species could expand successfully during warming periods in the past, which could also be the case under future climate scenarios.

scholarly journals Late Quaternary stratigraphy and morphogenesis in the Danish eastern North Sea and its relation to onshore geology

2005 ◽  
Vol 84 (2) ◽  
pp. 113-128 ◽  
Author(s):  
B. Larsen ◽  
L.T. Andersen
Keyword(s):  
North Sea ◽  
West Coast ◽  
Late Quaternary ◽  
Coastal Protection ◽  
The West ◽  
Plan View ◽  
Deformation Front ◽  
The North ◽  
Quaternary Stratigraphy ◽  
Sand Accumulation

AbstractGeological structures and Late Quaternary stratigraphy of the shallow subsurface along the southernmost Danish North Sea coast have been investigated using seismic data and shallow boreholes. A large-scale glaciotectonic thrust complex has been mapped in an area of 15 km by 40 km in the Fanø Bugt area. The affected succession consists of Neogene and Quaternary sediments deformed down to a depth of 200 – 360 m. A kineto-stratigraphic correlation to onshore glaciotectonic deformation suggests that the deformation took place during a westward advance stage of the Late Saalian (Warthe) glaciation. The western limit of the glaciotectonic structures constitutes an N-S striking deformation front situated 35 km off the west coast. Based on the glacial stratigraphy outside the deformation front, it is suggested that the same ice advance that caused the glaciotectonic deformation, eroded the top of the thrust sheets, and subsequently deposited a lower unit of meltwater sediments and an upper heterogenous glacigenic unit. The upper glacigenic unit forms a bank about 30 km offshore. Between the bank and the shore, the surface of the Saalian glacial landscape forms a wide depression ca. 50 m below sea level. This basin has controlled deposition in the area since the late Saalian and is filled with sediments of late Saalian, Eemian, Weichselian and Holocene age. The base of the Holocene marine deposits is thus a flat erosional surface extending eastward several kilometres below the onshore coastal areas and the northern Wadden Sea. This surface was transgressed 8800 years ago. An inverted, in plan view T-shaped, Holocene sand accumulation approximately 25 km long, 30 km wide and 15 – 25 m thick is situated on top of this surface at Blåvands Huk. According to recent estimates by the Danish Coastal Protection Board some 2.5 million m3 sediments are supplied annually to the system from the north. In the last 3000 years, 25 km of the west coast and the associated shoreface slope have prograded ca. 3 km towards the west forming a barrier spit complex. Large aeolian dunes and cover sands now conceal the spit complex. Extending twenty km west of Blåvands Huk is a highly dynamic bank, the Inner Horns Rev, with active sand-accumulation on the slopes. The Inner Horns Rev bank has grown ca. 3.5 km westward during the last 800 years. The deposits seem to be sourced by the coastal longshore sand transport from the north. The Outer Horns Rev was previously assumed to be a Saalian terminal moraine. However, this investigation reveals that it is also mainly a Holocene marine accumulation landform, but sourced from the west. Other sand accumulations, which are situated 20 – 30 km west of the coast, are probably sourced from both the south and the west.

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