Idades de soterramento de grãos de quartzo pelos isótopos cosmogênicos \'ANTPOT.26 Al\' e \'ANTPOT.10 Be\' foram obtidas em depósitos sedimentares que assorearam os sistemas de cavernas associados aos vales cegos dos riachos das Almas e Água de Rega, região de Iraquara (BA). Os resultados também incluem a caracterização faciológica e uma abordagem preliminar sobre a arquitetura dos depósitos, além do mapeamento em campo do contexto geomórfico dos sistemas de condutos e seu preenchimento sedimentar. Coberturas terciárias assentadas sobre todas as unidades pré-cambrianas testemunham que a superfície cárstica e os sistemas de condutosfazem parte de uma longa história de evolução, envolvendo episódios de exposição, soterramento e exumação. Durante os dois últimos milhões de anos, a drenagem superficial e os sistemas de cavernas estavam plenamente articulados na condução de água e sedimentos, com rotas de fluxo subterrâneas que incluíam ainda trechos labirínticos pré-existentes, que serviam de repositório de sedimentos durante os eventos de inundação, proporcionando também, rotas alternativas ao canal,na medida em que o sistema agradava. A sucessiva migração do canal por estas redes labirínticas originou o padrão distributário observado na Lapa Doce e na Gruta da Torrinha. Os depósitos sedimentares estudados nas cavernas dividem-se em dois grupos: fluviais e de água estagnada. Osdepósitos fluviais ocorrem na base e são constituídos por fácies de canal e fácies de inundação. As idades de soterramento de grãos de quartzo destes sedimentos apontam para um período de assoreamento fluvial compreendido entre 1,91±0,12 e 0,36±0,08 milhões de anos para o sistema Lapa Doce-Torrinha (riacho Água de Rega) e 1,37±0,15 e 0,87±0,17 milhões de anos para o sistema Cão-Talhão (riacho das Almas). No sistema Lapa Doce-Torrinha as idades de soterramento concentram-se no intervalo compreendido por dois períodos úmidos (350-450 Ka e 900-1000 Ka), registrados em estudos anteriores através do crescimento de tufas calcárias no semiárido baiano.Tal fato sugere que a agradação fluvial verificada, tanto nos rios quanto nas cavernas, esteja associada a fatores climáticos, particularmente o aumento da carga dos rios derivado da diminuição na estabilidade dos grãos nas vertentes exercida por uma vegetação arbustiva esparsa ou ausente. No topo, os depósitos de água estagnada, preferencialmente compostos por lamas, não possuem estruturas trativas ou de corrente e são associados a uma sedimentação em ambiente freático,para o qual é necessário considerar a subida do nível de base. Gretas de contração, além de relações estratigráficas e erosivas destes depósitos com crostas calcíticas evidenciam que eles não foram depositados em um evento único. Idades U/Th obtidas nas crostas calcíticas apontam para uma deposição durante o Pleistoceno Tardio. Interpreta-se que as lamas foram depositadas durante períodos de elevação do nível de base devido aos eventos úmidos abruptos de escala milenar que ocorreram no nordeste brasileiro ao longo dos últimos 210 ka. / \'ANTPOT.26 Al\' and \'ANTPOT.10 Be\' burial ages have been obtained from quartz grains sampled in extensive sedimentary deposits that fill cave systems associated with Das Almas and Agua de Rega creeks blind valleys, Iraquara region, Bahia (Brazil). The geomorphic context of the caves and their sedimentary record is presented, as well a facies analyses and a preliminary architecture approach for subterranean deposits. Tertiary covers deposited over all Precambrian geological units give evidence that karstic surface and conduit systems are features of a long term evolving landscape, sculpted during episodes of exposure, burial and exhumation. In the last two million years, surface drainage and cave systems were full connected in terms of water and sediment transport.Conduit systems still connected with preexisting passage networks, working as sediment repositories during floods and offering alternative routes to the channels as the systems aggraded. Sucessive channel migration led to the distributary pattern observed in the caves Lapa Doce and Gruta da Torrinha. The cave sedimentary record can be divided into two major categories: alluvial and slackwater deposits. At the bottom of the sediments, channel and flood facies were recognized in alluvial deposits. Quartz simple burial ages point to fluvial aggradation between 1,91±0,12 and 0,36±0,08 My in Lapa Doce-Torrinha cave system (Água de Rega creek) and between 1,37±0,15 and 0,87±0,17 million years in Cão-Talhão cave system (Das Almas creek). Burial ages from Lapa Doce-Torrinha samples group in between two past humid periods (350-450 Ky and 900-1000 Ky) recorded in previous studies from travertines growth in arid regions of Bahia State. This fact suggests that valley and cave aggradation is associated with climate factors, particularly an increase in river load derived from decreased stabilization of hillslopes due to a sparse or absent forest vegetation. At the top of sedimentary pile slackwater deposits are ordinarily muddy without tractive or current sedimentary structures. They are assigned to be deposited in a phreatic environment which, in turn, necessarily requires the base level to rise longer than seasonal floods. Mud cracks, erosive surfaces and stratigraphic relations to calcite crusts and flowstones prove that they were not deposited in a single event. U/Th ages from interstratal calcite crusts point to mud deposition during the Late Pleistocene. Slackwater deposits are interpreted to be a result of sedimentation during successive abrupt wet events defined on millennial time scale for the Brazilian northeast during the last 210ky.

Research has long recognized and studied the dynamics of groundwater processes. More recently, groundwater dependent ecosystems (GDEs) are being recognized for their diversity and vulnerability to anthropogenic impact. Groundwater in karst landscapes presents a distinctive situation where flow through the subsurface often moves rapidly on the scale of days and weeks as opposed to years or millennia in other systems. This distinctive situation of karst systems and their vulnerability to human impacts necessitate an integrated and multifaceted approach for the management of these important resources. However, development of such an approach is complicated by the difficulty of obtaining detailed data about the ecosystem, especially in remote areas of developing countries. Additionally, management difficulties related to political boundaries, jurisdictions, and land ownership can result in ineffective and inconsistent policies and practices across a single catchment. In order to address these issues, this dissertation creates a new composite model for groundwater dependent ecosystem (GDE) management in areas of karst development. Within this new composite model, the combination of the Karst Disturbance Index (KDI) and groundwater vulnerability mapping recognizes both human disturbance and how the physical nature of the karst will enhance this impact. These studies bridge the gap between science and management by connecting the final model to management strategies for a sub-catchment of the Rio la Venta watershed, the majority of which is within the Reserva de la Biosfera Selva el Ocote in Chiapas, Mexico. This composite model serves as an adaptable spatial tool for management planning and protection for all components of the karst environment.

>Magister Scientiae - MSc / Radon is a naturally occurring radioactive element in the 238U decay series that is found in high concentrations in certain geological formations such as Caves. Exposure to high concentrations of radon has been positively linked to the incidence of lung cancer. This study used Electret ion chambers and the RAD7 continuous radon monitor to measure radon concentrations in the Cango Caves in the Western Cape Province, South Africa. Measurements were taken during summer i.e. February 2004 and March 2005. The results for the radon activity concentrations range from the minimum of about 800 Bq.m-3 to a maximum of 2600 Bq.m-3. The two techniques give very similar results, though the Electret ion chamber results appear to be consistently higher by a few percent where measurements were taken at the same locations. A mathematical model has been developed to investigate the radon concentrations in the Cave. Diffusion and ventilation have been considered as mechanisms for explaining the distribution of radon concentrations. The ventilation rate in the Cave has been estimated under certain assumptions, and it is found to be about 7 ×10−6 s−1 for the Van Zyl hall which is the first large chamber in the Cave. The radon concentration increases as one goes deeper into the Cave, but then becomes fairly constant for the deeper parts. The annual effective dose that the guides are exposed to in the Cave as a result of the radon concentrations, depends strongly on the time that they spend in the Cave and in which, halls they spend most of their time in the Cave. The initial results indicate an annual effective dose of 4-10 mSv, but this needs to be further investigated. / South Africa

The Rancholabrean Land Mammal Age (RLB) occurred in the late Pleistocene, incorporating at least the Wisconsin Glaciation and possibly the preceding interglacial ('Sangamon'). The RLB is defined based on the occurrence of Bison. The first occurrence (arrival time) of Bison is not well established and is still debated. A conservative approach toward the RLB includes: (1) restricting the RLB to faunas south of 55°. N latitude in North America, (2) defining the RLB by the earliest arrival of Bison south of this latitude, (3) placing the best-corroborated arrival time of Bison (therefore the beginning of the RLB) between approximately 210 and 160. ka, and (4) the end of the RLB is marked by the extinction of mainly large mammals as an event or process culminating at approximately 11 radiocarbon ka BP. RLB faunas contain a wealth of information including amphibians, reptiles, birds, and mammals, but clearly the most is known about the latter. Glacial climate regimes forced species into communities that do not occur today (nonanalog or disharmonious scenarios). The debate about the terminal RLB extinctions continues with the cause either being (1) overkill due to the arrival of the First Americans, or (2) the climatic and environmental defragmentation of biotic communities.

The Rancholabrean Land Mammal Age (RLB) occurred in the late Pleistocene, incorporating at least the Wisconsin Glaciation and possibly the preceding interglacial ('Sangamon'). The RLB is defined based on the occurrence of Bison. The first occurrence (arrival time) of Bison is not well established and is still debated. A conservative approach toward the RLB includes: (1) restricting the RLB to faunas south of 55°. N latitude in North America, (2) defining the RLB by the earliest arrival of Bison south of this latitude, (3) placing the best-corroborated arrival time of Bison (therefore the beginning of the RLB) between approximately 210 and 160. ka, and (4) the end of the RLB is marked by the extinction of mainly large mammals as an event or process culminating at approximately 11 radiocarbon ka BP. RLB faunas contain a wealth of information including amphibians, reptiles, birds, and mammals, but clearly the most is known about the latter. Glacial climate regimes forced species into communities that do not occur today (nonanalog or disharmonious scenarios). The debate about the terminal RLB extinctions continues with the cause either being (1) overkill due to the arrival of the First Americans, or (2) the climatic and environmental defragmentation of biotic communities.

No description available.

No description available.

The means in which fossil accumulations in the caves of southern Africa have formed is of great importance. One method of accumulation is via the collecting behaviours of a variety of mammalian species. The core of said behaviour is in the use of caves by these species. This project was designed to give insight to the way that animals in the Cradle of Humankind, South Africa are using caves today. The objective of this research is to give a new understanding to the amount that caves are used by various taxa in South African cave systems, with particular regard to taphonomic agents and potential taphonomic agents. This study was accomplished over a 20-month period by setting up motion sensor cameras outside of cave entrances at the Malapa Nature Reserve. Results have shown that animals use caves at high frequencies, crucial to recognize when examining fossil accumulations.

Sinkhole collapse is a common karst land-use risk around the world. In the Bahamas cover-collapse sinkholes do not exist because soil cover is thin; almost all collapse is due to cave ceiling failure. The most common cave types in the Bahamas are flank margin caves and banana holes. Flank margin caves have three entrance types: dissolution pit, side breach, or ceiling collapse. Both side breach and ceiling collapse are the result of mass erosional forces; pits by focused dissolution. It was previously proposed that slope was a controlling factor in Bahamian cave collapse. This study demonstrated that 7.5 minute topographic maps cannot resolve slopes accurately enough to predict potential collapse locations. Field surveys with 1 m contours allowed for a more concise slope range in which each entrance type preferentially occurred; collapse breaches and pits were common on gentle slopes and side breaches on steep slopes.

Banana holes are a common karst feature of The Bahamas and several theories have been presented to explain their origin. The current model for banana hole formation places their dissolution at the mixing zone at the top of the fresh water lens. This theory is based on the observation that banana holes are often found in the interior of islands, far from the dissolutionally aggressive fresh water lens margin. This study proposes that banana holes form at the lens margin as it follows a prograding strandplain. Spatial observations show that banana holes appear to be associated with low inland ridges and their orientation appears to correlate with features found on modern shorelines. Bedding features such as herringbone cross beds and back-beach rubble found in banana hole wall rock point to a progradational environment of deposition for banana hole host rock.