Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ‐INTIMATE project)

It is widely recognised that the acquisition of high‐resolution palaeoclimate records from southern mid‐latitude sites is essential for establishing a coherent picture of inter‐hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ‐INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ‐INTIMATE has been the identification of a series of well‐dated, high‐resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High‐resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial–interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97‐2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice‐core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd.     

Archaean crustal growth through successive partial melting events in an oceanic plateau‐like setting in the Tanzania Craton

The detrital zircon population in quartzitic conglomerates from the northern Tanzania Craton yield ages between 2640 Ma and 2790 Ma which includes most of the igneous history from this part of the craton. The igneous evolution is characterised by mafic volcanism with an oceanic plateau‐like geochemical signature at ~2800 Ma followed by diorite and tonalite–trondhjemite–granodiorite dominated magmatism between 2790 and 2700 Ma, which transitioned into more evolved high‐K magmatism between 2700 and 2620 Ma. The ε_Hf values of the detrital zircons range from +2.4 to ?1.4 and change with time from radiogenic Hf pre‐2700 Ma (98% positive ε_Hf) to unradiogenic Hf post‐2700 Ma (41% positive ε_Hf). The petrological progression from mafic to felsic crust is reflected in the detrital age distribution and Hf isotopes and is consistent with juvenile mafic crust slowly maturing into more evolved felsic crust through a series of successive partial melting events in an oceanic‐plateau‐like environment.     

Geoarchaeological and Bioarchaeological Studies at Mira,an Early Upper Paleolithic Site in the Lower Dnepr Valley,Ukraine

New geoarchaeological and bioarcheological research was undertaken at the open‐air site of Mira, which is buried in deposits of the Second Terrace of the Dnepr River, roughly 15 km downstream from the city of Zaporozhye in Ukraine. Previous excavation of the site revealed two occupation layers dating to ∼32,000 cal BP. The lower layer (II/2) yielded bladelets similar to those of the early Gravettian, while the upper layer (I) contained traces of an artificial shelter and hundreds of bones and teeth of horse (Equus latipes). Mira represents the only firmly dated early Upper Paleolithic (EUP) site in the Dnepr Basin, and occupies a unique topographic setting for the EUP near the center of the broad floodplain of the Dnepr River. The site was visited during a period of floodplain stability, characterized by overbank deposition and weak soil formation under cool climate conditions. Mira was used as a long‐term camp, but also was the locus of large‐mammal carcass processing associated with a nearby kill of a group of horses (Layer I).     

Palaeostress analysis of the northern Nijar and southern Vera basins: constraints for the Neogene displacement history of major strike-slip faults in the Betic Cordilleras, SE Spain

This paper presents the results of a detailed structural analysis of the northern Nijar and southern Vera basins with special emphasis on the evolution of the regional stress field and the associated timing of movement of the Serrata, Gafarillos and Palomares strike-slip fault zones. These major fault zones control the Neogene deformation of the SE Internal Betic Cordilleras in Spain. Detailed stress analysis on Neogene sediments of the Vera and Nijar basins shows a strike-slip regime with NW–SE-oriented subhorizontal maximum principal stress (σ₁) during Tortonian and earliest Messinian times. Under the influence of this stress field, dextral displacement along the N090E-trending Gafarillos fault zone resulted in deformation of the sediments of the southern Sorbas and northeastern Nijar basins. During the early Messinian a clock-wise rotation of the stress field occurred. Stress analysis in rocks with late–early Messinian up to Quaternary ages in the Nijar and Vera basins indicates a strike-slip regime with N–S-oriented subhorizontal maximum principal stress (σ₁). Under the influence of this stress field the main activity along the N010E-striking Palomares strike-slip fault zone took place, resulting in deformation of the Neogene sediments of the southeastern Vera basin and culminating in a maximum sinistral displacement of more than 20 km. At the same time the stress field was not suitably oriented to exert a large shear component on the Gafarillos fault zone, which activity ended after the earliest Messinian. Fault and outcrop patterns of syntectonic Neogene sediments in the Vera basin show that displacement along the Palomares fault zone decreased at the end of the Middle Miocene although minor displacement phases may still have occurred during the Late Miocene and possibly even Pliocene. From the Middle Miocene onward, deformation in the Nijar basin was controlled by sinistral displacement along the N040E-trending Serrata strike-slip fault zone.     

Earthquake Stability Analysis of Rock Slopes: a Case Study

Stability analysis of Surabhi landslide in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India, has been simulated numerically using the distinct element method focusing on the weak zones (fracture). This is an active landslide on the main road toward the town centre, which was triggered after rainfall in July–August 1998. Understanding the behaviour of this landslide will be helpful for planning and implementing mitigation measures. The first stage of the study includes the total area of the landslide. The area identified as the zone of detachment is considered the most vulnerable part of the landslide. Ingress of water and increased pore pressures result in reduced mobilized effective frictional resistance, causing the top layer of the zone of detachment to start moving. The corresponding total volume of rock mass that is potentially unstable is estimated to 11.58 million m³. The second stage of this study includes a 2D model focussing only on the zone of detachment. The result of the analyses including both static and dynamic loading indicates that most of the total displacement observed in the slide model is due to the zone of detachment. The discontinuum modelling in the present study gives reasonable agreement with actual observations and has improved understanding of the stability of the slide slope.     

Water Resources Implications of Global Warming: A U.S. Regional Perspective

The implications of global warming for the performance of six U.S. water resource systems are evaluated. The six case study sites represent a range of geographic and hydrologic, as well as institutional and social settings. Large, multi-reservoir systems (Columbia River, Missouri River, Apalachicola-Chatahoochee-Flint (ACF) Rivers), small, one or two reservoir systems (Tacoma and Boston) and medium size systems (Savannah River) are represented. The river basins range from mountainous to low relief and semi-humid to semi-arid, and the system operational purposes range from predominantly municipal to broadly multi-purpose. The studies inferred, using a chain of climate downscaling, hydrologic and water resources systems models, the sensitivity of six water resources systems to changes in precipitation, temperature and solar radiation. The climate change scenarios used in this study are based on results from transient climate change experiments performed with coupled ocean-atmosphere General Circulation Models (GCMs) for the 1995 Intergovernmental Panel on Climate Change (IPCC) assessment. An earlier doubled-CO₂ scenario from one of the GCMs was also used in the evaluation. The GCM scenarios were transferred to the local level using a simple downscaling approach that scales local weather variables by fixed monthly ratios (for precipitation) and fixed monthly shifts (for temperature). For those river basins where snow plays an important role in the current climate hydrology (Tacoma, Columbia, Missouri and, to a lesser extent, Boston) changes in temperature result in important changes in seasonal streamflow hydrographs. In these systems, spring snowmelt peaks are reduced and winter flows increase, on average. Changes in precipitation are generally reflected in the annual total runoff volumes more than in the seasonal shape of the hydrographs. In the Savannah and ACF systems, where snow plays a minor hydrological role, changes in hydrological response are linked more directly to temperature and precipitation changes. Effects on system performance varied from system to system, from GCM to GCM, and for each system operating objective (such as hydropower production, municipal and industrial supply, flood control, recreation, navigation and instream flow protection). Effects were generally smaller for the transient scenarios than for the doubled CO₂ scenario. In terms of streamflow, one of the transient scenarios tended to have increases at most sites, while another tended to have decreases at most sites. The third showed no general consistency over the six sites. Generally, the water resource system performance effects were determined by the hydrologic changes and the amount of buffering provided by the system's storage capacity. The effects of demand growth and other plausible future operational considerations were evaluated as well. For most sites, the effects of these non-climatic effects on future system performance would about equal or exceed the effects of climate change over system planning horizons.     

Macroseepage of methane and light alkanes at the La Brea tar pits in Los Angeles

Geologic seepage of methane and light (C₂-C₅) alkanes was measured at the La Brea Tar Pits in Los Angeles. Samples were collected using flux chambers with stainless steel canisters and analyzed using gas chromatography. Average seepage rates from individual seepage sites were 970 ± 330 mg/h of methane, 14.0 ± 5.5 mg/h of ethane, 9.1 ± 3.7 mg/h of propane, 3.7 ± 1.6 mg/h of i-butane, 0.33 ± 0.16 mg/h of n-butane, 260 ± 120 μg/h of i-pentane, and 5.3 ± 1.9 μg/h of n-pentane, while maximum seepage rates exceeded 17 g/h of methane, 270 mg/h of ethane, 190 mg/h of propane, 95 mg/h of i-butane, 10 mg/h of n-butane, 7 mg/h of i-pentane, and 0.1 mg/h of n-pentane. These absolute fluxes have an additional unknown amount of error associated with them due to sampling methodology, and should be taken as the lower limit of emissions. Samples collected revealed generally dry gas, with high methane emissions relative to the light alkanes. Overall emissions from the tar pits were found to come not only from the active geologic seepage, but also from the outgassing of the standing asphalt at the site. Using the gas ratios, which are negligibly affected by errors introduced by sampling methodology, observed in this study, daily emissions of C₂ – C₅ alkanes from the La Brea area were estimated to be 4.7 ± 1.6 Mg, which represents 2–3 % of total emissions in the entire Los Angeles region.     

The Middle Miocene to Recent Davis Strait Drift Complex: implications for Arctic�CAtlantic water exchange

A large-scale contourite drift complex has been recognised on multi-channel 2D reflection seismic data acquired in the south-eastern Davis Strait and adjacent Labrador Sea slope offshore West Greenland between 63°?C66°N. Based on well-tie data, the drift complex developed from the Middle Miocene to the Recent. It has been mapped in a wide variety of water depths ranging from about 700?m, at a NNW-ESE-elongated crest located above structural highs in the Davis Strait, to more than 2,000?m beyond the slope to the Labrador Sea. The overall drift geometry has been described by subdivision into two first-order seismic units, enabling the generation of time-isochore maps. The reflection patterns demonstrating current-related deposition are illustrated by seismic examples. The time-isochores of the two first-order seismic units show lateral changes in their depocentres: the lower unit is absent in a zone slightly displaced south-westwards of the present-day crest, indicating changes in the prevailing deepwater current system during the Early Pliocene. The observations can be explained by two alternative palaeoceanographic scenarios: (1) either the present-day oceanographic setting with Arctic?CAtlantic water exchange across the Davis Strait was largely established by the mid-Miocene, with only minor adjustments during the Early Pliocene caused by tectonic movements, or (2) it became established during the Early Pliocene as a consequence of enhanced northward flow across the Davis Strait due to lowering of the sill depth.