No description available.

The Baviaanskloof catchment is a semi-arid catchment located in the Cape Fold Mountains of South Africa. Little is known about the functioning of the complicated Baviaanskloof fluvial system and the role alluvial fans in the fluvial landscape. This thesis will contribute to field of geomorphology and, more specifically, to the field of fan morphometry by producing a standalone fan framework outlining methods to investigate the influence of external and internal control variables on alluvial fans. In this thesis, outcomes of the applied framework and case study are used to develop fan restoration guidelines for the Baviaanskloof Valley. The framework incorporates external and internal fan control variables at a valley-wide and local fan scale. External control variables include accommodation space, base-level change, and drainage basin inputs. Internal control variables include fan style, morphometry and fan channels. In order to apply the framework, fan morphometry data was required. This data was collected by creating a spatial plan of fans and basins in the valley. Outcomes of the applied framework include; an understanding of baselevel change on fans, relationships between fan basin characteristics and the fan surface and insight into fan channel processes. Results of the applied framework are investigated further using bivariate (correlation matrix) and multivariate (principle component analysis and regression analysis) analysis techniques. Significant relationships identified are: drainage basin area versus fan area, fan area and fan slope and drainage basin ruggedness and basin size. The primary outcomes of this thesis include an alluvial fan form-process framework, key considerations to be included in alluvial fan restoration projects and fan restoration guidelines. Contributions of this thesis to broader alluvial fan morphology science includes new insights into general fan literature by compiling a form-process alluvial fan classification framework to identify external and internal fan control variables and identify fan form. Additions have been made to Clarke’s (2010) evolutionary stages to describe stages 4 and 5 of fan evolution that has been adapted to describe fan evolution and differentiate between stages of mature fan evolution. This thesis has also contributed to the study of alluvial fans in South Africa, particularly in the Baviaanskloof Valley. The layout of the procedural guidelines and key considerations for an alluvial fan project provides a guide for rapid fan assessment for maximum cost and time benefits for stakeholders.

No description available.

A combination of geological and hydraulic techniques represents the most sensible approach to flood hazard analysis on alluvial fans. Hydraulic models efficiently yield predictions of flood depths and velocities, but the assumptions on which the models are based do not lead to accurate portrayals of natural fan processes. Geomorphological mapping, facies, mapping, and hydraulic reconstructions of past floods provide data on the location, types, and magnitude of flood hazards, respectively. Geological reconstructions of past floods should be compared with the results of hydraulic modeling before, potentially unsound, floodplain management decisions are implemented. The controversial Federal Emergency Management Agency procedure for delineating flood-hazard zones underestimated the extent, velocity, and depth of flow during recent floods on two alluvial fans by over 100, 25, and 70 percent, respectively. Flow on the alluvial fans occurs in one or more discontinuous ephemeral stream systems characterized by alternating sheetflood zones and channelized reaches. The importance of sheetflooding is greater on fans closer to the mountain front and with unstable channel banks. Channel diversions on five alluvial fans repeatedly occurred along low channel banks and bends where the greatest amount of overland flow is generated. Channel migration occurs through stream capture whereby overland flow from the main channel accelerates and directs erosion of adjacent secondary channels. The recurrence interval of major channel shifts is greater than 100 years, but minor changes occurred on all five fans during this century. Small aggrading flows are important, because they decrease bank heights and alter the location of greatest overland flow during subsequent floods. The results of this study demonstrate that (1) geological reconstructions of past floods can check the results of hydraulic models, (2) the character of flooding on alluvial fans can vary significantly in the same tectonic and climatic setting due to differences in drainage-basin characteristics, and (3) flood-hazard assessments on alluvial fans must be updated after each flood, because the location and timing of channel diversions can be affected by small floods.

Outcrops of late Quaternary deposits along the north–east coast of Mallorca were examined, and a high resolution chronological framework established using optically stimulated luminescence of quartz and feldspar grains. Coastal sections at Es Barrancar and Cala Mata record a complex succession of alluvial fan deposition with a minor aeolian component, mainly deposited during the last two glacial cycles. For the last ~200ka different orbital configurations appear to have produced a series of subtly different climatic scenarios that resulted in great variations in the regional availability of moisture. In turn, each of these climatic scenarios set in motion a distinct set of sedimentary processes, which imprinted themselves upon the character of fluvial system response recorded in the alluvial archives on Mallorca. Within the resulting complex of sediments were units of fluvially reworked aeolianite which, although truncated in places, were traceable laterally along wide sections of the sea front outcrops of both fan systems. These archives yielded 47 new OSL and pIRIR290 ages which suggest a number of previously unrecognised periods of enhanced fluvial activity. Luminescence ages identify significant ephemeral fluvial activity taking place during MIS 6, MIS 5 sub-stages d/c, b/a, and across the MIS 5/4 boundary. Another major phase of reworking corresponds with the middle part of MIS 3, and continued sporadically into the Last Glacial Maximum. These fluvial reworking events have been interpreted as having taken place during cold arid climatic intervals, when vegetation was at a minimum, precipitation was low and displayed a much higher degree of seasonality, enhancing the effects of runoff.

No description available.

No description available.

No description available.

The fault-bounded Cianzo basin represents a Cenozoic intermontane depocenter between the Puna plateau and Eastern Cordillera of the central Andean fold-thrust belt in northern Argentina. New characterizations of fold-thrust structure, nonmarine sedimentation, and sediment provenance for the shortening-induced Cianzo basin at 23°S help constrain the origin, interconnectedness, and subsequent uplift and exhumation of the basin, which may serve as an analogue for other intermontane hinterland basins in the Andes. Structural mapping of the Cianzo basin reveals SW and NE-plunging synclines within the >6000 m-thick, upsection coarsening Cenozoic clastic succession in the shared footwall of the N-striking, E-directed Cianzo thrust fault and transverse, NE-striking Hornocal fault. Growth stratal relationships within upper Miocene levels of the succession indicate syncontractional sedimentation directly adjacent to the Hornocal fault. Measured stratigraphic sections and clastic sedimentary lithofacies of Cenozoic basin-fill deposits show upsection changes from (1) a distal fluvial system recorded by vi fine-grained, paleosol-rich, heavily bioturbated sandstones and mudstones (Paleocene‒Eocene Santa Bárbara Subgroup, ~400 m), to (2) a braided fluvial system represented by cross-stratified sandstones and interbedded mudstones with 0.3 to 8 m upsection-fining sequences (Upper Eocene–Oligocene Casa Grande Formation, ~1400 m), to (3) a distributary fluvial system in the distal sectors of a distributary fluvial megafan represented by structureless sheetflood sandstones, stratified pebble conglomerates and sandstones, and interbedded overbank mudstones (Miocene Río Grande Formation, ~3300 m), to (4) a proximal alluvial fan system with thick conglomerates interbedded with thin discontinuous sandstone lenses (upper Miocene Pisungo Formation, ~1600 m). New 40Ar/39Ar geochronological results for five interbedded volcanic tuffs indicate distributary fluvial deposition of the uppermost Río Grande Formation from 16.31 ± 0.6 Ma to 9.69 ± 0.05 Ma. Sandstone petrographic results show distinct upsection trends in lithic and feldspar content in the Casa Grande, Río Grande, and Pisungo formations, potentially distinguishing western magmatic arc (Western Cordillera) sediment sources from evolving eastern thrust-belt sources (Puna‒Eastern Cordillera). In addition to growth stratal relationships and 40Ar/39Ar constraints, conglomerate clast compositions reflect distinct lithologic differences, constraining the activation of the Cianzo thrust and coeval movement on the reactivated Hornocal fault. Finally, U-Pb geochronological analyses of sandstone detrital zircon populations in conjunction with paleocurrent data and depositional facies patterns help distinguish localized sources from more distal sources west of the basin, revealing a systematic eastward advance of Eocene to Miocene fold-thrust deformation in the central Andes of northern Argentina. / text

The Pantano Formation comprises 1,250 m of alluvial, fluvial, lacustrine, and volcanic rocks deposited in a basin formed in response to regional extension during mid- Tertiary time in southeastern Arizona. During deposition, the locations and composition of sediment source areas varied as contemporaneous uplift occurred adjacent to the basin. The lower half of the formation was deposited as alluvial fans that prograded northward, westward, and southward; the upper half was deposited during southwestward retreat of alluvial fan deposition and the onset of lacustrine deposition. An andesite flow separates the two depositional regimes. Radiometric dates of 24.4 ± 2.6 m.y. B.P. for the andesite and 36.7 ± 1.1 m.y. B.P. for a rhyolitic tuff disconformably underlying the formation indicate that deposition occurred during Oligocene to early Miocene time. Proper stratigraphic sequencing and description, paleocurrent analysis, and gravel provenance study aided in understanding the depositional history of the formation.