Evolution of the North Horowhenua Coastal Depositional System in Response to Late Pleistocene Sea Level Changes

<p>The convergent tectonic setting of New Zealand has lead to the development of a series of anticlines and troughs resulting from folding and faulting of basement greywacke in southwest North Island. The most extensive of these is the Kairanga Trough spreading from the Horowhenua to the Manawatu, which lies between the uplifting Tararua Range and subsiding South Wanganui Basin. This trough was a major depocentre for fluvial and shallow marine strata during the Quaternary. By utilising a 280m deep borehole from the Kairanga Trough, this thesis investigates how climate and sea level variations affected sedimentation in the north Horowhenua District. This borehole has recorded a near continuous record of climate and sea level change for the last 340ka. The lower part of the core is a marine sequence representing progressive infilling of the Kairanga Trough during 5th order (c.100ka) glacioeustatic fluctuations, which consequently produced 4 marine cyclothems. Transgressions and subsequent highstand periods are represented by shallow marine sediment, which were followed by fluvial aggradation during lowstand periods, then marine planation during subsequent transgressions. Cycle 1 developed during OIS 9 (340-300ka). Cycles 2 and 3 both formed during OIS 7 as a result of two closely spaced highstands centred around 245ka (OIS 7c) and 200ka (OIS 7a), which were separated by a period of lower sea level around 225ka (OIS 7b) that produced a disconformity. Cycle 4 formed during the Last Interglacial transgression (OIS 5e) and represents an incised valley fill. Progradation of a coastal strandplain and alluvial plain representing the latter stages of infilling of the Kairanga Trough with coastal and terrigenous sediment during the mid to late Last Interglacial and Glacial Periods is recorded in the sediment composing the top part of the borehole.</p>

Evolution of the North Horowhenua Coastal Depositional System in Response to Late Pleistocene Sea Level Changes

<p>The convergent tectonic setting of New Zealand has lead to the development of a series of anticlines and troughs resulting from folding and faulting of basement greywacke in southwest North Island. The most extensive of these is the Kairanga Trough spreading from the Horowhenua to the Manawatu, which lies between the uplifting Tararua Range and subsiding South Wanganui Basin. This trough was a major depocentre for fluvial and shallow marine strata during the Quaternary. By utilising a 280m deep borehole from the Kairanga Trough, this thesis investigates how climate and sea level variations affected sedimentation in the north Horowhenua District. This borehole has recorded a near continuous record of climate and sea level change for the last 340ka. The lower part of the core is a marine sequence representing progressive infilling of the Kairanga Trough during 5th order (c.100ka) glacioeustatic fluctuations, which consequently produced 4 marine cyclothems. Transgressions and subsequent highstand periods are represented by shallow marine sediment, which were followed by fluvial aggradation during lowstand periods, then marine planation during subsequent transgressions. Cycle 1 developed during OIS 9 (340-300ka). Cycles 2 and 3 both formed during OIS 7 as a result of two closely spaced highstands centred around 245ka (OIS 7c) and 200ka (OIS 7a), which were separated by a period of lower sea level around 225ka (OIS 7b) that produced a disconformity. Cycle 4 formed during the Last Interglacial transgression (OIS 5e) and represents an incised valley fill. Progradation of a coastal strandplain and alluvial plain representing the latter stages of infilling of the Kairanga Trough with coastal and terrigenous sediment during the mid to late Last Interglacial and Glacial Periods is recorded in the sediment composing the top part of the borehole.</p>

Post-LGM glacial retreat and Early Holocene monsoon intensification drives aggradation in the interiors of the Kashmir Himalaya

Understanding the response of glaciated catchments to climate change is crucial for assessing sediment transport from the high-elevation, semi-arid sectors in the Himalaya. The fluvioglacial sediments stored in the semi-arid Padder valley in the Kashmir Himalaya record valley aggradation during ~20 -10 ka. We relate the initial stage of valley aggradation to increased sediment supply from the deglaciated catchment during the glacial-to-interglacial phase transition. Previously-published bedrock-exposure ages in the upper Chenab River valley suggest ~180 km retreat of the valley glacier during ~20 - 15 ka. Increasing roundness of sand-grains and reducing mean grain-size from the bottom to the top of the valley-fill sequence hint about increasing fluvial transport with time and corroborate with the glacial retreat history. The later stages of aggradation can be attributed to strong monsoon during the early Holocene. Especially, the hillslope debris that drapes the fluvioglacial sediment archive may have resulted from the early Holocene monsoon maximum. We observe a net degradation of the valley-fill in the Holocene reflecting the weakening of summer monsoon or reduced input from the glaciers. Our study highlights the coupled effect of deglaciation and monsoon intensification in sediment transfer from the high-elevation sectors of the Himalaya.

Hydrogeologic Study of the Bryce Canyon City Area, Including Johns and Emery Valleys, Garfield County, Utah

Groundwater resources development and the threat of future drought in Garfield County, southwestern Utah, prompted a study of groundwater quality and quantity in the environs of Bryce Canyon National Park and Bryce Canyon City in Johns and Emery Valleys. Water quality, water quantity, and the potential for water-quality degradation are critical elements determining the extent and nature of future development in the valley. The community of Bryce Canyon City is an area of active tourism and, therefore, of potential increase in growth (likely from tourism-related development). Groundwater exists in Quaternary valley-fill and bedrock aquifers (the Tertiary Claron Formation and Cretaceous sandstone). Increased demand on drinking water warrants careful land-use planning and resource management to preserve surface and groundwater resources of Johns and Emery Valleys and surrounding areas that may be hydrologically connected to these valleys including Bryce Canyon National Park.

Providencia Island: A Miocene Stratovolcano on the Lower Nicaraguan Rise, Western Caribbean—A Geological Enigma Resolved

ABSTRACT The Providencia island group comprises an extinct Miocene stratovolcano located on a shallow submarine bank astride the Lower Nicaraguan Rise in the western Caribbean. We report here on the geology, geochemistry, petrology, and isotopic ages of the rocks within the Providencia island group, using newly collected as well as previously published results to unravel the complex history of Providencia. The volcano is made up of eight stratigraphic units, including three major units: (1) the Mafic unit, (2) the Breccia unit, (3) the Felsic unit, and five minor units: (4) the Trachyandesite unit, (5) the Conglomerate unit, (6) the Pumice unit, (7) the Intrusive unit, and (8) the Limestone unit. The Mafic unit is the oldest and forms the foundation of the island, consisting of both subaerial and subaqueous lava flows and pyroclastic deposits of alkali basalt and trachybasalt. Overlying the Mafic unit, there is a thin, minor unit of trachyandesite lava flows (Trachyandesite unit). The Breccia unit unconformably overlies the older rocks and consists of crudely stratified breccias block flows/block-and-ash flows) of vitrophyric dacite, which represent subaerial near-vent facies formed by gravitational and/or explosive dome collapse. The breccias commonly contain clasts of alkali basalt, indicating the nature of the underlying substrate. The Felsic unit comprises the central part of the island, composed of rhyolite lava flows and domes, separated from the rocks of the Breccia unit by a flat-lying unconformity. Following a quiescent period, limited felsic pyroclastic activity produced minor valley-fill ignimbrites (Pumice unit). The rocks of Providencia can be geochemically and stratigraphically subdivided into an older alkaline suite of alkali basalts, trachybasalts, and trachyandesites, and a younger subalkaline suite composed dominantly of dacites and rhyolites. Isotopically, the alkali basalts together with the proposed tholeiitic parent magmas for the dacites and rhyolites indicate an origin by varying degrees of partial melting of a metasomatized ocean-island basalt–type mantle that had been modified by interaction with the Galapagos plume. The dacites are the only phenocryst-rich rocks on the island and have a very small compositional range. We infer that they formed by the mixing of basalt and rhyolite magmas in a lower oceanic crustal “hot zone.” The rhyolites of the Felsic unit, as well as the rhyolitic magmas contributing to dacite formation, are interpreted as being the products of partial melting of the thickened lower oceanic crust beneath Providencia. U-Pb dating of zircons in the Providencia volcanic rocks has yielded Oligocene and Miocene ages, corresponding to the ages of the volcanism. In addition, some zircon crystals in the same rocks have yielded both Proterozoic and Paleozoic ages ranging between 1661 and 454 Ma. The lack of any evidence of continental crust beneath Providencia suggests that these old zircons are xenocrysts from the upper mantle beneath the Lower Nicaraguan Rise. A comparison of the volcanic rocks from Providencia with similar rocks that comprise the Western Caribbean alkaline province indicates that while the Providencia alkaline suite is similar to other alkaline suites previously defined within this province, the Providencia subalkaline suite is unique, having no equivalent rocks within the Western Caribbean alkaline province.

Post-LGM glacial retreat drives aggradation in the interiors of the Kashmir Himalaya

Understanding the response of glaciated catchments to climate change is fundamental for assessing sediment transport from the high-elevation, semi-arid to arid sectors in the Himalaya to the foreland basin. The fluvioglacial sediments stored in the semi-arid Padder valley in the Kashmir Himalaya record valley aggradation during ~19-11 ka. We relate the valley aggradation to increased sediment supply from the deglaciated catchment during the glacial-to-interglacial phase transition. Previously-published bedrock-exposure ages in the upper Chenab valley suggest ~180 km retreat of the valley glacier during ~20-15 ka. Increasing roundness of sand-grains and reducing mean grain-size from the bottom to the top of the valley-fill sequence hint about increasing fluvial transport with time and corroborate with the glacial retreat history. Our result also correlates well with late Pleistocene-early Holocene sediment aggradation observed across most Western Himalayan valleys. It highlights the spatiotemporal synchronicity of sediment transfer from the Himalayas triggered by climate change.