scholarly journals Eventos Neocenozoicos de reorganização de rede de drenagem: um paleovale do Rio das Velhas (Minas Gerais, Brasil) em seu médio curso?

2020 ◽  
pp. 1-10
Author(s):  
Antônio Pereira Magalhães Jr. ◽  
Luiz Fernando De Paula Barros ◽  
Luis Felipe Soares Cherem ◽  
Robson Clayton Pinto
Keyword(s):  
Late Quaternary ◽  
Minas Gerais ◽  
Main Channel ◽  
Optically Stimulated Luminescence ◽  
Drainage Network ◽  
River Catchment ◽  
Fluvial Deposits ◽  
Main Valley ◽  
Hydrographic Network

Resumo: O presente trabalho teve como objetivo apresentar e discutir indícios de processos de reorganização da rede de drenagem na média bacia do Rio das Velhas resultantes da reconfiguração de seu vale principal. Nesse sentido, diversos depósitos fluviais foram identificados, descritos e, alguns, datados por Luminescência Opticamente Estimulada (LOE). Os resultados sugerem que a descontextualização de um conjunto de depósitos fluviais em cotas superiores e topos de colinas e a existência de anomalias na organização da rede de drenagem nesse trecho seriam resultantes da mudança do traçado do canal principal do Rio das Velhas no Quaternário Superior. Palavras-chave: Níveis deposicionais fluviais; Luminescência Opticamente Estimulada; Evolução de rede hidrográfica.   Abstract:  Neocenozic events of drainage network reorganization: a paleovalley of the Velhas River (Minas Gerais, Brazil) in its middle course?This paper aimed to present and discuss clues of reorganization processes of the drainage network in the middle Velhas River catchment resulting from the reconfiguration of its main valley. In this sense, several fluvial deposits were identified, described and, some, dated by Optically Stimulated Luminescence (OSL). The results suggest that the decontextualization of a set of fluvial deposits in higher elevations and tops of hills, as well as the existence of anomalies in the organization of the drainage network in this stretch would results of the change of the main channel of the Velhas River during the Late Quaternary. Keywords: Fluvial depositional levels; Optically Stimulated Luminescence; Evolution of hydrographic network      

scholarly journals Phytogeographical patterns of dry forests sensu stricto in northern Minas Gerais State, Brazil

2013 ◽  
Vol 85 (2) ◽  
pp. 623-634 ◽  
Author(s):  
DANIEL M. ARRUDA ◽  
WALNIR G. FERREIRA-JUNIOR ◽  
REINALDO DUQUE-BRASIL ◽  
CARLOS E.R. SCHAEFER
Keyword(s):  
Late Quaternary ◽  
Sensu Stricto ◽  
Minas Gerais ◽  
Dry Forest ◽  
Floristic Similarity ◽  
Humid Forest ◽  
Quaternary Climate ◽  
Dominant Soil ◽  
Minas Gerais State ◽  
Semi Arid

The Deciduous Complex that occurs in northern Minas Gerais State, Brazil, raises questions about the floristic affinities of these formations in relation to neighboring phytogeographical domains. Little is known about the identity of the seasonal forest formations that comprise this complex, or about its relationships to abiotic components, such as soils, topography and climate. This study aimed to recognize the patterns of floristic similarity of all studied fragments of dry forest of northern Minas Gerais with soil and climate attributes, based on the available database. Cluster analysis indicated the existence of two floristic groups that had clear associations with either the Koppen's BSh (semi-arid) or Aw (seasonal tropical) climates. Likewise, the subdivisions of these groups showed clear associations with the dominant soil classes in the region. The Red-Yellow Latosol is the dominant soil classes in the BSh climatic domain, seconded by alluvial areas associated with Fluvic Neosols. The Aw domain comprised a much varied set of soils: Nitosols, Argisols, Cambisols and Litholic Neosols, most derived from the Bambuí limestone/slate formation. The ecotonal nature of northern Minas Gerais State provides a complex interaction between the flora of neighboring phytogeographical domains. This, allied to pedogeomorphological factors, allowed a better understanding of the effects of late Quaternary climate changes for the Deciduous Complex evolution. We conclude that the Latosols under present-day semi-arid climates (BSh) are relicts of former wetter climates, during which humid forest (semideciduous) expansion took place. Later, these semideciduous forests were subjected to a much drier climate, when selection for deciduousness led to the present-days Deciduous Complex scenario.

scholarly journals Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland

2017 ◽  
Vol 11 (3) ◽  
pp. 1265-1282 ◽  
Author(s):  
Graham L. Gilbert ◽  
Stefanie Cable ◽  
Christine Thiel ◽  
Hanne H. Christiansen ◽  
Bo Elberling
Keyword(s):  
Late Quaternary ◽  
Sediment Cores ◽  
River Delta ◽  
Optically Stimulated Luminescence ◽  
Delta Plain ◽  
Valley Fill ◽  
Subaerial Exposure ◽  
Facies Associations ◽  
Delta Progradation ◽  
Ice Content

Abstract. The Zackenberg River delta is located in northeast Greenland (74°30′ N, 20°30′ E) at the outlet of the Zackenberg fjord valley. The fjord-valley fill consists of a series of terraced deltaic deposits (ca. 2 km2) formed during relative sea-level (RSL) fall. We investigated the deposits using sedimentological and cryostratigraphic techniques together with optically stimulated luminescence (OSL) dating. We identify four facies associations in sections (4 to 22 m in height) exposed along the modern Zackenberg River and coast. Facies associations relate to (I) overriding glaciers, (II) retreating glaciers and quiescent glaciomarine conditions, (III) delta progradation in a fjord valley, and (IV) fluvial activity and niveo-aeolian processes. Pore, layered, and suspended cryofacies are identified in two 20 m deep ice-bonded sediment cores. The cryofacies distribution, together with low overall ground-ice content, indicates that permafrost is predominately epigenetic in these deposits. Fourteen OSL ages constrain the deposition of the cored deposits to between approximately 13 and 11 ka, immediately following deglaciation. The timing of permafrost aggradation was closely related to delta progradation and began following the subaerial exposure of the delta plain (ca. 11 ka). Our results reveal information concerning the interplay between deglaciation, RSL change, sedimentation, permafrost aggradation, and the timing of these events. These findings have implications for the timing and mode of permafrost aggradation in other fjord valleys in northeast Greenland.

A Preliminary Report of Changing Quaternary Mammal Faunas in Subalpine New Guinea

1993 ◽  
Vol 40 (1) ◽  
pp. 117-126 ◽  
Author(s):  
Geoffrey Hope ◽  
Tim Flannery ◽  
Boeardi
Keyword(s):  
Preliminary Report ◽  
Late Quaternary ◽  
Montane Forest ◽  
Mammal Species ◽  
Irian Jaya ◽  
Fluvial Deposits ◽  
Unknown Species ◽  
Holocene Record ◽  
Fossil Records ◽  
Mammal Faunas

AbstractThe faunas found in the mountains of central Irian Jaya have experienced dramatic changes through the late Quaternary. Remains of two previously unknown species of large marsupial, Maokopia ronaldi and Protemnodon hopei, have been recovered from unrelated cave and fluvial deposits which today occur in dense upper montane forest. Direct dating of the finds has not as yet been possible, but stratigraphic, sedimentologic, and palynologic evidence indicates that these species lived near a climatic treeline in subalpine grassland in the late Pleistocene. At higher altitudes a rockshelter provided the second known mid-Holocene record of Thylogale christenseni and Thylogale sp. cf. brunii, apparently extinct grassland wallabies. The two largest remaining subalpine mammal species are being locally exterminated by hunting, leaving only a large murid, Mallomys gunung, which weighs less than 2.0 kg. The area thus records the disappearance of a grassland-adapted fauna. The possum Pseudocheirops cupreus dominates in modem hunting returns, although this species is totally absent from the local fossil records. It may thus be in the process of invading a vacated and disturbed niche from the upper montane forest.

Optical dating of late Quaternary carbonate sequences of Saurashtra, western India

2017 ◽  
Vol 87 (1) ◽  
pp. 133-150 ◽  
Author(s):  
Komal Sharma ◽  
Nilesh Bhatt ◽  
Anil Dutt Shukla ◽  
Dae-Kyo Cheong ◽  
Ashok Kumar Singhvi
Keyword(s):  
Late Quaternary ◽  
Optically Stimulated Luminescence ◽  
Western India ◽  
Carbonate Sediments ◽  
Sampling Strategies ◽  
Aeolian Processes ◽  
Saurashtra Coast ◽  
Recent Deposition ◽  
Quartz Grains ◽  
Carbonate Deposits

AbstractBioclastic carbonate deposits that formed because of a combination of nearshore marine, fluvial, and aeolian processes, occur along the Saurashtra coast and in the adjacent interior regions of western India. Whether these carbonates formed by marine or aeolian processes has been debated for many decades. The presence of these deposits inland poses questions as to whether they are climate controlled or attributable to postdepositional tectonic uplift. In particular, the debate centres on chronologic issues including (1) appropriate sampling strategies and (2) the use of 230Th/234U and 14C ages on the bulk carbonates. Using traces (<1%) of quartz grains trapped in carbonate matrices, optically stimulated luminescence (OSL) dating of quartz grains, deposited along with the carbonate grains, provides ages for the most recent deposition events. The OSL ages range from >165 to 44 ka for the shell limestones, 75–17 ka for the fluvially reworked sheet deposits, and 80–11 ka for miliolites deposited by aeolian processes. These are younger than the 230Th/234U and 14C ages and suggest that the inland carbonate deposits were reworked from older carbonate sediments that were transported during more arid phases.

scholarly journals Interactions between channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

2019 ◽  
Author(s):  
Sara Savi ◽  
Stefanie Tofelde ◽  
Andrew D. Wickert ◽  
Aaron Bufe ◽  
Taylor F. Schildgen ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Signal Propagation ◽  
Main Channel ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Alluvial Fans ◽  
Fluvial System ◽  
Channel Network ◽  
Fluvial Deposits ◽  
The Impact

Abstract. Climate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel-network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may promote or prevent sediment to be moved within the fluvial system, creating different coupling conditions. A prograding alluvial fan, for example, has the potential to disrupt the sedimentary signal propagating downstream through the confluence zone. By analyzing different environmental scenarios, our results indicate the contribution of the two sub-systems to fluvial deposits, both upstream and downstream of the tributary junction, which may be diagnostic of a perturbation affecting the tributary or the main channel only. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which is essential for a correct reconstruction of the climatic or tectonic history of a basin.

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