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Ground penetrating radar (GPR) is a new technique in field sciences and is now commonly applied to studies of coastal dunes and beaches. The technique has yet to be applied on hard rocky coasts, and its ability to discern subsurface stratigraphy has great potential for investigating landform evolution on tectonically active shorelines where erosional surfaces are often buried by sediments derived from marine and nonmarine sources. In this study, we test the resolution of a 100- and 250-MHz GPR system on a series of Holocene uplifted shore platforms and gravel beaches in Wellington, New Zealand. The sediment thickness at the sites investigated ranged from a thin veneer to many meters and is composed of a mix of sand and gravel-sized material. It was found that the 100-MHz antenna did not have the resolution of the 250-MHz antenna and could not distinguish the buried platform surface. Using the 250-MHz antenna, bedding features within the unconsolidated sediment and the bedrock-sediment interface could be discerned. The high relief of the bedrock (meter scale), which outcropped on the surface, and the presence of buried boulders caused significant interference to the radar profiles through the creation of multiple and hyperbolic reflections. Despite these reflections, the GPR was able to quantify the morphology of the buried shore platform, thus indicating the utility of this technique for rocky coast research. [ABSTRACT FROM AUTHOR]

Abstract: Late Pleistocene fluvial terrace deposits within the Waipaoa River system of North Island, New Zealand provide some insight into the fluvial history of the region that can be potentially translated to the marine sedimentary record. Pebble counts and sand detrital modes from terrace remnants suggest significant compositional differences between these terraces and the modern stream deposits. The terrace deposits are enriched in sandstone lithics (sand and gravel), as well as monomineralic quartz and feldspar (sand). In contrast, the modern Waipaoa River is dominated by mudstone fragments, mainly products of gullying in the Waipaoa River headwaters region. Both the terrace and modern river sand show a compositional dependency on grain size, with increasing lithic components in the coarse sand fractions. Carbonate lithic content and proportions of lithic types in the modern river and terrace sediments can be related to the distribution of calcareous geological units across the region. For example, the calcareous lithics (sand and gravel) in the Mangatu River, a major tributary of the Waipaoa, are derived from deep-water facies (allochthon) that dominate the catchment. These carbonate facies are petrographically distinct from the marl (calcareous mudstone) that dominates elsewhere in the Waipaoa River system, such as the Pliocene units in the Waimata River catchment. The combined petrologic data sets from the modern rivers and terraces in the Waipaoa River system provide a model to interpret the provenance of sandy deposits in the offshore marine realm. [Copyright &y& Elsevier]

Abstract: Late Quaternary to Holocene landscape evolution in southern New Zealand was dominated by glacial outwash processes. Evolution of the drainage network on a regional scale was punctuated by numerous river capture events associated with outwash transport and deposition. River capture events can be inferred from geological and topographic observations throughout the region. Independent evidence for river capture and drainage reorientation can be obtained from genetic studies of a freshwater-limited fish (Galaxias ‘southern’, informal name). Regionally extensive interlinking of principal rivers (Mataura, Oreti, Aparima) via coalescence of alluvial plains onshore, and offshore at sea level lowstands, has resulted in a widespread genetic homogenisation of fish populations (<0.9% mtDNA divergence). Genetically similar populations of G. ‘southern’ are present in an adjacent catchment (Von) that was captured episodically by the neighbouring major river system (Clutha). The low degree of genetic divergence between Oreti and Von catchments (<0.15% mtDNA divergence) demonstrates that genetic interaction between fish populations was severed recently, probably during the early Holocene. This is in accord with radiocarbon dating (11–13 ka) of the youngest gravel level within the intervening divide. In contrast, morphologically similar fish in another adjacent major river (Waiau) have a minimum mtDNA divergence of 2.4% from the fish in the Mataura, Oreti, and Aparima Rivers. This genetic separation occurred at ca. 145–240 ka, based on the late Quaternary outwash terrace dating, in agreement with “molecular clock” estimates. Geological and genetic data in combination provide powerful tools for the elucidation of local and regional geomorphic evolution where river capture is an important process. The potential is strong for genetic data alone to provide information on the relative and absolute timing of river capture events, but must be interpreted in the context of severance of water connections between catchments and subsequent isolation of freshwater-limited populations. [Copyright &y& Elsevier]