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Direct dating of vertebrate fossils is difficult due to complex postburial diagenetic processes and the often low and heterogeneous concentration of radioisotopes (e.g., U) in fossilized bone material. Here, we demonstrate a novel approach to dating vertebrate fossils via laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of early diagenetic calcite cements precipitated within bone cavities of a Jurassic sauropod from the Sichuan Basin, South China. Early diagenetic calcite yielded a U-Pb age of 165.3 ± 3.6/5.6 Ma, in agreement with a maximum depositional age of 165.8 ± 1.0 Ma from detrital zircon ages of the surrounding rocks, suggesting that diagenesis occurred shortly after the death of the sauropod. This new age demonstrates that the best-known Jurassic large sauropod faunas in South China are much older than those in North America and Africa, suggesting the geographical isolation of South China. Authigenic apatite U-Pb dating on the fibrolamellar bones from the same sauropod gave a distinctly younger age, indicating more complex U-Pb system behavior, possibly due to U uptake by residual organic matter and recrystallization of apatite after early diagenesis. Our findings demonstrate that U-Pb dating of calcite cements within bone cavities has significant potential for constraining the burial age of vertebrate fossils, which could aid in constructing a more robust temporal framework for the radiation and evolution of vertebrates. [ABSTRACT FROM AUTHOR]

Giant gravel bars are important archives of megafloods; however, determining their depositional ages requires reliable geochronometric methods. Five gravel bars, reaching heights of 150-170 m, formed in the bedrock-lined Alberton Gorge along the Clark Fork River, Montana (USA), during draining of Glacial Lake Missoula (GLM). We report the first numerical ages for megaflood deposits in the GLM basin by successfully applying the novel optically stimulated luminescence (OSL) rock surface dating technique to date cobbles collected from three locations along one bar's transport direction. Depth-dependent infrared stimulated luminescence and post-infrared pulsed OSL signals showed that exteriors of only 3 out of the 38 collected cobble samples were well bleached by exposure to daylight before burial, and hence suitable for dating. The cobbles provided ages of 16.5 ± 0.9, 18.5 ± 1.4, and 21.7 ± 1.1 ka, all of which are indistinguishable from the average cosmogenic nuclide age of 18.2 ± 1.5 ka (n = 4) for a large megaflood in the Channeled Scabland, eastern Washington State. The average of the two younger ages, 17.5 ± 1.0 ka, is our best estimate of the deposit age. We interpret the older age to be from a cobble that was reworked by the flood. Our results show that these techniques have great potential for providing reliable chronologies for paleofloods and other high-energy depositional events. [ABSTRACT FROM AUTHOR]

Previous U-Pb dating of fossils has had only limited success because of low uranium content and abundance of common Pb as well as element mobility during late diagenesis. We report the first accurate U-Pb dating of fossilized soft tissue from a Pliocene phosphatized bivalve mold using laser ablation-inductively coupled mass spectrometry (LA-ICPMS). The fossilized soft tissue yields a diagenetic U-Pb age of 3.16 ± 0.08 Ma, which is consistent with its late Pliocene stratigraphy and similar to the oldest U-Pb age measured on accompanying shark teeth. Phosphate extraclasts give a distinctly older age of 5.1 ± 1.7 Ma, indicating that they are likely detrital and may have furnished P, promoting phosphatization of the mold. The U-Pb ages reported here along with stratigraphic constraints suggest that diagenesis occurred shortly after the death of the bivalve and that the U-Pb system in the bivalve mold remained closed until the present. Shark teeth collected from the same horizon show variable resetting due to late diagenesis. Data were acquired as line scans in order to exploit the maximum Pb/U variation and were regressed as counts, rather than ratios, in three-dimensional space using a Bayesian statistical method. [ABSTRACT FROM AUTHOR]

The Valanginian Stage is marked by a period of global positive δ13C carbon cycle perturbation and biotic crises, which are collectively referred to as the Valanginian event (VE). Many attempts have been made to link the Paraná-Etendeka large igneous province volcanism with the VE. However, currently there is no conclusive proof to support this hypothesis, since the timing and duration of the volcanic activity are not known with sufficient precision. In this study, we significantly revise the time scales of magmatism and environmental impact of the Paraná magmatic province (PMP) in Brazil with new high-precision zircon U-Pb ages from the low-Ti Palmas and high-Ti Chapecó sequences. Our data demonstrate that signifi- cant volumes of low-Ti silicic rocks from the PMP erupted rapidly at ca. 133.6 Ma within 0.12 ± 0.11 k.y. The age of the high-Ti Chapecó sequence from central PMP is constrained at ca. 132.9 Ma and thus extends the duration of magmatic activity by ~700 k.y. Our new ages are systematically younger than previous ages and postdate the major positive carbon isotope excursion, indicating that PMP silicic magmatism did not trigger the VE but could have contributed to extending its duration. Within the framework of the stratigraphic column of the PMP, the earliest low-Ti basalts could have been responsible for the VE if they are at least 0.5 m.y. older than the low-Ti silicic rocks dated herein. [ABSTRACT FROM AUTHOR]

A co-investigation of mantle melting conditions and seismic structure revealed an evolutionary record of mantle dynamics accompanying the transition from subduction to collision along the Africa-Eurasia margin and the >1 km uplift of the Anatolian Plateau. New 40Ar/39Ar dates of volcanic rocks from the Eastern Taurides (southeast Turkey) considerably expand the known spatial extent of Miocene-aged mafic volcanism following a magmatic lull over much of Anatolia that ended at ca. 20 Ma. Mantle equilibration depths for these chemically diverse basalts are interpreted to indicate that early to middle Miocene lithospheric thickness in the region varied from ∼50 km or less near the Bitlis suture zone to ∼80 km near the Inner Tauride suture zone. This southward-tapering lithospheric base could be a vestige of the former interface between the subducted (and now detached) portion of the Arabian plate and the overriding Eurasian plate, and/or a reflection of mantle weakening associated with greater mantle hydration trenchward prior to collision. Asthenospheric upwelling driven by slab tearing and foundering along this former interface, possibly accompanied by convective removal of the lithosphere, could have led to renewed volcanic activity after 20 Ma. Melt equilibration depths for late Miocene and Pliocene basalts together with seismic imaging of the present lithosphere indicate that relatively invariant lithospheric thicknesses of 60–70 km have persisted since the middle Miocene. Thus, no evidence is found for large-scale (tens of kilometers) Miocene delamination of the lower lithosphere from the overriding plate, which has been proposed elsewhere to account for late Miocene and younger uplift of Anatolia. [ABSTRACT FROM AUTHOR]

Establishing temporal constraints on major volcanic eruptions is limited by the precision of existing geochronometers. Prior work on the La Garita caldera (Colorado, USA), created by the eruption of the Fish Canyon Tuff, failed to resolve temporal differences between pre-, syn-, and post-collapse eruptive units. Here, we report 40Ar/39Ar geochronologic data supporting a ~100 ka eruptive history of the La Garita caldera, and resolving the timing of the pre-caldera Pagosa Peak Dacite, syn-caldera Fish Canyon Tuff, and post-caldera dacite of Nutras Creek. Minimizing uncertainty in neutron fluence by rotating samples during irradiation and employing Bayesian statistical interpretation of analytical data enables resolution of the ~60 ka pre-caldera eruptive history and a hiatus of 0-20 ka prior to the eruption of post-caldera lavas. The improved precision demonstrated using these methods provides previously unresolvable temporal constraints on physical processes in the La Garita magmatic system and underscores the potential of unraveling other closely spaced events in geologic time. [ABSTRACT FROM AUTHOR]

Both mantle-derived clinopyroxene and orthopyroxene are generally homogeneous in water concentration, while water content in the coexisting olivine is affected by partial or complete loss during the ascent of the hosting magma. Here, we report the first record of water content profiles (higher water in the cores than in the rims) in natural orthopyroxene grains in peridotite xenoliths hosted by Cenozoic alkali basalts in Tianchang volcano, eastern China. The water contents of the coexisting clinopyroxene grains are homogeneous and are twice that measured in the cores of orthopyroxene grains, confirming previous chemical equilibrium between the two pyroxenes. The olivines (ol) are nearly dry (~0 ppm). These observations demonstrate that H diffusion in mantle orthopyroxene (opx) is faster than in clinopyroxene (cpx), and the relative mobility of H in each mineral phase could be quantified as:D̃ol > 10D̃opx > 1000D̃cpx (where is the chemical diffusion coefficient of hydrogen). Combining this with experimental diffusion coefficients from the literature, we infer that (1) the xenoliths remained in contact with the magma below 900 °C for several months, and (2) clinopyroxene remains the more reliable recorder of water from depth, and orthopyroxene should be used more cautiously but can be considered with olivine for tracing slow transport and cooling of magma. [ABSTRACT FROM AUTHOR]

A newly identified and dated segment of the South Tibetan detachment in the Karnali klippe, western Nepal Himalaya, constrains initiation of mid-crustal tectonically driven exhumation to the early Oligocene. The folded top-to-the-northeast high-temperature (~600 °C) shear zone separates amphibolite-facies rocks with a ca. 36-30 Ma prograde metamorphic history in the footwall from weakly to non-metamorphosed upper crustal rocks in the hanging wall. In situ dating of syn-kinematic--post-metamorphic peak monazite indicates that the base of the shear zone was active from ca. 30-29 to <24 Ma, and a post-deformation muscovite cooling age implies that ductile shearing had ceased by ca. 19 Ma. Deformation along the South Tibetan detachment in western Nepal was thus synchronous with thrustsense shearing along the lower boundary of a zone of migmatitic rocks, compatible with tectonic models involving mid-crustal channelized flow during the Oligocene. Along with other published data from the Himalayan range, this suggests that the South Tibetan detachment actively exhumed the middle crust for almost 20 m.y. [ABSTRACT FROM AUTHOR]

The snowball Earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale. Geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons. Here we present four new Re-Os geochronology age constraints on Sturtian (717-660 Ma) and Marinoan (635 Ma termination) glacial deposits from three different paleocontinents. A 752.7 ± 5.5 Ma age from the base of the Callison Lake Formation in Yukon, Canada, confirms nonglacial sedimentation on the western margin of Laurentia between ca. 753 and 717 Ma. Coupled with a new 727.3 ± 4.9 Ma age directly below the glacigenic deposits of the Grand Conglomerate on the Congo craton (Africa), these data refute the notion of a global ca. 740 Ma Kaigas glaciation. A 659.0 ± 4.5 Ma age directly above the Maikhan-Uul diamictite in Mongolia confirms previous constraints on a long duration for the 717-660 Ma Sturtian glacial epoch and a relatively short nonglacial interlude. In addition, we provide the first direct radiometric age constraint for the termination of the Marinoan glaciation in Laurentia with an age of 632.3 ± 5.9 Ma from the basal Sheepbed Formation of northwest Canada, which is identical, within uncertainty, to U-Pb zircon ages from China, Australia, and Namibia. Together, these data unite Re-Os and U-Pb geochronological constraints and provide a refined temporal framework for Cryogenian Earth history. [ABSTRACT FROM AUTHOR]

The high plateau of southern Africa is considered to be either uplifting due to mantledriven dynamic topography, or to have been stable since Mesozoic rifting. To address this debate, we determined rock uplift in South Africa from the long-term incision rate of the Sundays River, near Port Elizabeth, and from an uplifted marine terrace near Durban. We dated the terraces with cosmogenic 26Al and 10Be, using both isochron and simple burial dating methods. We fi nd that the Sundays River has incised at 16.1 ± 1.3 m/m.y. for the past ~4 m.y., and the marine terrace yields a rock uplift rate of 9.4 ± 2.2 m/m.y. These results are inconsistent with rapid Neogene uplift. [ABSTRACT FROM AUTHOR]

The pre-Permian record of bryophytes is restricted to a very limited number of liverwort occurrences in Middle and Late Devonian and in Pennsylvanian strata, and a putative liver-wort from the Middle Ordovician. The paucity of bryophytes, notably the apparent absence of mosses in the Carboniferous, is striking because this time interval is marked by the occurrence of extensive wetland environments that likely provided ideal habitats. We report three types of mosses from the Mississippian of eastern Germany that are the oldest unequivocal mosses known to date. Although the material is fragmentary, these finds show that mosses formed part of Carboniferous ecosystems. The moss remains were obtained by bulk maceration, a method that is not commonly used for studying Carboniferous floras. We anticipate that applying this method on material from other Carboniferous localities will show that mosses were more widespread in the late Paleozoic than previously thought. [ABSTRACT FROM AUTHOR]

Bowers Ridge is an ~700 km long arcuate ridge behind the Central Aleutian Arc in the Bering Sea. The lack of age and geochemical data for the ridge has hampered the development of geodynamic models for the evolution of the North Pacific and the Aleutian—Bering Sea region. Here we present the first geochemical and 40Ar/40Ar age data for the volcanic basement of Bowers Ridge and a seamount from the western end of the ridge sampled during R/V Sonne cruise SO201-1b. The northern Bowers Ridge basement (26-32 Ma) consists of mafic to intermediate calc-alkaline rocks with adakite-like (Sr/Y = 33-53, LaN/YbN = 3.3-7.8), high field strength element (HFSE)—depleted (e.g., NbN/LaN = 0.07-0.31) trace element patterns and Sr-Nd-Pb isotope compositions within the Western Aleutian Arc array, implying magma generation above an obliquely subducting slab. The seamount samples (22-24 Ma) are HFSE-rich alkaline olivine basalts (LaN/YbN = 3.3-3.9, NbN/LaN = 1.0-1.4) with minor arc-type trace element signatures (PbN/CeN = 1.4-1.6, KN/NbN = 1.7-1.9) but with Pacific mid-oceanic-ridge basalt (MORB)—like isotopic compositions, pointing to an origin by small-degree decompression melting from slightly subduction-modified mantle. The geochemistry of the recovered rocks can be explained by highly oblique subduction along the northern part of Bowers Ridge in its present-day configuration, consistent with an in-situ origin of Bowers Ridge as a Cenozoic island arc. [ABSTRACT FROM AUTHOR]

We develop an intercalibrated astrochronologic and radioisotopic time scale for the Cenomanian- Turonian boundary (CTB) interval near the Global Stratotype Section and Point in Colorado, USA, where orbitally infl uenced rhythmic strata host bentonites that contain sanidine and zircon suitable for 40Ar/39Ar and U-Pb dating. Paired 40Ar/39Ar and U-Pb ages are determined from four bentonites that span the Vascoceras diartianum to Pseudaspidoceras flexuosum ammonite biozones, utilizing both newly collected material and legacy sanidine samples of J. Obradovich. Comparison of the 40Ar/39Ar and U-Pb results underscores the strengths and limitations of each system, and supports an astronomically calibrated Fish Canyon sanidine standard age of 28.201 Ma. The radioisotopic data and published astrochronology are employed to develop a new CTB time scale, using two statistical approaches: (1) a simple integration that yields a CTB age of 93.89 ± 0.14 Ma (2σ; total radioisotopic uncertainty), and (2) a Bayesian intercalibration that explicitly accounts for orbital time scale uncertainty, and yields a CTB age of 93.90 ± 0.15 Ma (95% credible interval; total radioisotopic and orbital time scale uncertainty). Both approaches fi rmly anchor the fl oating orbital time scale, and the Bayesian technique yields astronomically recalibrated radioisotopic ages for individual bentonites, with analytical uncertainties at the permil level of resolution, and total uncertainties below 2‰. Using our new results, the duration between the Cenomanian-Turonian and the Cretaceous-Paleogene boundaries is 27.94 ± 0.16 Ma, with an uncertainty of less than one-half of a long eccentricity cycle. [ABSTRACT FROM AUTHOR]

The lithostratigraphy at the Pliocene-Pleistocene boundary exposed in Olduvai Gorge, East Africa, was used to determine the duration and cause of climate variations (wet-dry periods ). The area has rich paleontological and archaeological records, and the time interval is a critical period in human evolution. Five episodes of lake expansion and contraction can be interpreted from a stratigraphic interval (defined by tuffs) between ca. 1.85 and 1.74 Ma, suggesting precession-controlled cyclicity. The geochronometry of the sequence was determined using the paleomagnetic record (top of subchron CN2, 1.785 Ma), the ages of two tuffs (Tuff IB and Tuff IF), and sedimentation rates. Insolation (W/m2) variations calculated as a function of eccentricity and precession predict five cycles of varying insolation (±10%) between 2.0 and 1.5 Ma. Rainfall would have increased by one-third between dry and wet portions of each ~21,000 k.y. cycle. This study represents the first dated terrestrial record at the Pliocene-Pleistocene boundary with sufficient resolution to link lake cycles (a climate proxy) to astronomic forcing. The wet-dry climate pendulum may have been a factor in the natural selection processes of hominin evolution and the first wave of hominin migrations out of Africa (1.8 Ma). [ABSTRACT FROM AUTHOR]

New 40Ar/39Ar analyses from a transect across the major tectonic units of the southwest Amazon craton document the heterogeneous effects of the late Mesoproterozoic collision with the Grenville margin of North America. Basement rocks of the Amazon and adjacent Paragua cratons mostly preserve pre-Grenvillian ages (older than 1.3 Ga). Localized isotopic age resetting at 1.18–1.12 Ga is caused by Grenvillian activation of widespread, sinistral strike-slip shear zones in the Amazon basement. In the Nova Brasilândia belt between these two cratons, new 40Ar/39Ar data record cooling through 920 Ma after the granulite facies deformation of this suture zone. Regional cooling rates calculated from compiled U/Pb, 40Ar/39Ar, and Rb/Sr thermochronologic data are used to establish post-Grenvillian exhumation patterns for the southwest Amazon and the North American belt. Paleodepths calculated for 1.0 Ga along a transect of the restored 1300-km-wide belt vary from uniformly deep levels (15–30 km) exposed in North America to shallower levels (5–15 km) observed in the southwest Amazon. We interpret this difference as reflective of a change in tectonic architecture, i.e., thrust-dominated deformation in Laurentia versus strike-slip dominated deformation in the Amazon, with a commensurate variation in crustal thickness. This interpretation explains the widespread preservation of both pre-Grenvillian ages and collisional ages from the Amazon craton, in contrast with the more homogeneous array of cooling ages from the North American Grenville Province marking the postorogenic extensional collapse of an overthickened crust. The asymmetrical orogenic architecture from the reconstructed Grenville belt mirrors cross sections proposed for modern orogenic belts where deep-crustal rocks are not yet exposed. [ABSTRACT FROM AUTHOR]

Radioisotopic dating of subaerial and submarine volcanic and plutonic rocks from the Aleutian Island Arc provides insight into the timing of arc formation in the middle Eocene. Twenty-eight 40Ar/39Ar ages constrain the duration of arc magmatism to the last 46 m.y. Basaltic lavas from the Finger Bay volcanics, the oldest exposed rocks in the arc, gave an isochron age of 37.4 ± 0.6 Ma, which is 12–17 m.y. younger than a widely cited age of 55–50 Ma. Three main pulses of arc-wide magmatism occurred at 38–29, 16–11, and 6–0 Ma, which coincide with periods of intense magmatism in other western Pacific island arcs. Using the geochronology and volumetric estimates of crust generated and eroded over the last 46 m.y., we calculate a time-averaged magma production rate for the entire arc that exceeds previous estimates by almost an order of magnitude. [ABSTRACT FROM AUTHOR]

The Denali fault is the principal intracontinental strike-slip fault accommodating deformation of interior Alaska associated with the Yakutat plate convergence. We obtained the first quantitative late Pleistocene-Holocene slip rates on the Denali fault system from dating offset geomorphic features. Analysis of cosmogenic 10Be concentrations in boulders (n = 27) and sediment (n = 13) collected at seven sites, offset 25–170 m by the Denali and Totschunda faults, gives average ages that range from 2.4 ± 0.3 ka to 17.0 ± 1.8 ka. These offsets and ages yield late Pleistocene-Holocene average slip rates of 9.4 ± 1.6, 12.1 ± 1.7, and 8.4 ± 2.2 mm/yr-1 along the western, central, and eastern Denali fault, respectively, and 6.0 ± 1.2 mm/yr-1 along the Totschunda fault. Our results suggest a westward decrease in the mean Pleistocene-Holocene slip rate. This westward decrease likely results from partitioning of slip from the Denali fault system to thrust faults to the north and west. [ABSTRACT FROM AUTHOR]

The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially provides a unique tool for paleoclimatic reconstructions. In this paper we present the first successful application of this approach, based on combining laboratory-based experimental calibrations with archaeological samples from the Chalco site in the Basin of Mexico, dated using stratigraphically correlated 14C results and measuring hydration depths by secondary ion mass spectrometry. The resultant data suggest, first, that this approach is viable, even given the existing uncertainties, and that a cooling trend occurred in the Basin of Mexico over the past 1450 yr, a result corroborated by other paleoclimatic data. [ABSTRACT FROM AUTHOR]

We propose ending the distinction between the dual stratigraphic terminology of time-rock units (of chronostratigraphy) and geologic time units (of geochronology). The long-held, but widely misunderstood, distinction between these two essentially parallel time scales in stratigraphy has been rendered unnecessary by the widespread adoption of the global stratotype sections and points (GSSP—golden spike) principle in defining intervals of geologic time within rock strata. We consider that the most appropriate name for this stratigraphic discipline is "chronostratigraphy," which would allow "geochronology" to revert to its mainstream and original meaning of numerical age dating. This in turn makes the little-used formal term "geochronometry" redundant. The terms "eonothem," "erathem," "system," "series," and "stage" would become redundant, in favor of "eon," "era," "period," "epoch" and (disputably) "age." Our favored geologic time units may be qualified by "early" and "late," but not by "lower" and "upper." These suggested changes should simplify stratigraphic practice, encompass both stratified and nonstratified rocks, and help geologic understanding, while retaining precision of meaning. Keywords: stratigraphy; chronostratigraphy; geochronology. [ABSTRACT FROM AUTHOR]

We investigated, by means of optical dating, the chronostratigraphic nature of the sequence boundary associated with the last glacial in a sandy to gravelly compound paleovalley fill, just landward of the highstand shoreline in the Rhine-Meuse Delta (Netherlands). Laterally extensive fluvial strata deposited during oxygen isotope stage 4, coeval with a major sea-level fall, unconformably overlie estuarine deposits from stage 5 or fluvial deposits from the penultimate glacial (stage 6). These chronostratigraphic relationships differ substantially from widely used models and indicate (1) that sequence-boundary formation in this setting was associated with the onset of pronounced sea-level fall, shortly after 80 ka; (2) that the time gap represented by the sequence boundary may be extremely small (<10 k.y.); (3) that the age of the sequence boundary may decrease both updip and downdip of the highstand shoreline; and (4) that our study does not provide viable diagnostic criteria for a sea-level-controlled sequence boundary above the falling-stage systems tract. Despite the high-frequency, high-amplitude glacio-eustatic regime that might be considered ideal for the formation of an unambiguous unconformity, the last sequence boundary in this setting is commonly cryptic. [ABSTRACT FROM AUTHOR]

Investigates the hillslope soils in Bega Valley, New South Wales. Mechanisms of transport of soils; Determination of grain movements measured by single-grain optical dating; Calculation of downslope flux from soil production.

Examines the global correlation using magnetic susceptibility data from Lower Devonian rocks. Identification of synchronous variation in global erosion; Identification of the lower devonian, pragian-emsian, and lower-upper emsian stage boundaries in the bolivian well samples.

Examines the discontinuity in metamorphic pressure-temperature-time paths in the Main Central thrust zone in Nepal. Transfer of material from the lower to upper plate; Presence of a single strong foliation due to isoclinal folding; Effect of footwall metamorphosis on thrust reactivation.

Investigates single crystals of dispersed trace pyrite using laser probe method. Comparison of age results to step heating ages of amphibole and phlogopite; Observation of internal isochrons in step-heated crystals; Application to the dating of ores,sediments,and hydrocarbon migration.

Investigates the exhumation of the northern part of the Coast Mountains, British Columbia using apatite helium thermochronometry. Geologic setting; Inverse correlation of helium sea-level age with local mean elevation along the traverse; Speculations on the origin of the increase in exhumation.

Determines the [sup40]Argon-[sup39]Argon geochronometry of pseudotachylytes from the North Cascade Mountains in Washington by vacuum encapsulation. [sup39]Argon loss; Textural and minerological features; Differences between total-gas age, argon-retention age and plateau age.

Presents an example of how the sensitive high-resolution ion microprobe (SHRIMP) zircon dating method can provide a terrane-specific geochronological fingerprint for a rock and thus help to reveal major tectonic boundaries within orogens. Geologic background of the European continent; SHRIMP dating of the inherited zircons from the moravo-silesian.

Reports the discovery of a Pliocene uplift of the northern Tibetan Plateau in China. Account on the geology of the Tibetan Plateau; Factors influencing the change in deposition and paleoslope of the region; Impact of a change in depositional facies on sedimentation rate of the uplift; Hypothesis on the geological dating of main uplift of the region.

Explores the timing of mineralization at the Navan zinc-lead deposit in Ireland. Examination of diagenetic fabrics within the main ore and the Boulder Conglomerate; Geology of the Navan deposit; Evidence of premineralization dolomite in the Boulder Conglomerate; Hypothesis on the origin of the navan mineralization.

Explores cyclical patterns of sonic logs and gamma-ray astrochronology of Pliocene sediments from the Gulf of Cadiz, Southern Spain. Implication for Mediterranean sapropels and astronomical oscillations; Analysis of precession-induced oscillations of annual rainfall; Application of the method to interregional correlation and astronomical dating.

Examines the astronomical calibration age for the Oligocene-Miocene boundary of the Deep Sea Drilling Project Site 522. Characterization of the stratotype section for the base of the Miocene; Relevance of Miocene stratotype section in magnetic chron representation; Relationship between nannofossil range and magnetostratigraphy.

Examines crystal residence times using in situ uranium-lead (U-Pb) dating of zircons from the Bishop Tuff in east-central California. Maximum mean crystal residence time for zircon; Analysis of zircons from fallout and intercalated ash-flow deposits and unpolished rims; Storage of Bishop Tuff rhyolite prior to eruption.

Examines the use of optical dating of dune sand for the study of sea-level change in Massachusetts. Agreement on sea level between optical ages of barrier dune sand and evidence from salt-marsh peat sampled behind the barrier; Relevance of accurate records of relative sea-level change in modelling isostically forced crust and mantle behavior.

Presents a study using two independent surface-exposure dating techniques to estimated minimum and maximum-limiting ages, of the precarious boulders in southern California and Nevada and the elapsed time since the site where shaken down. Ages of the precarious rocks in Yucca Mountain Nevada; Analysis of 24-rock varnish samples; Conclusion and implications for seismic hazard studies.

Focuses on the composition of mafic deep crustal and shallow mantle xenoliths hosted in the Chino Valley and Camp Creek latites of central Arizona, while highlighting the use of the Re-Os dating model. Details on the formation of xenoliths.

Outlines the role played by erosion in the thermotectonic evolution of organic belts of the Himalayan Region. When was it first recognized; What represents oldest exposed continental foredeep sediments; Information which suggests that 40Ar/39Ar dating of white micas has provided maximum depositional ages; Reference material available.

Studies the felsic granulites from the Bohemian masdif of Central Europe. Role of zircon in granulite evolution; Geochronometry of zircon; Behavior of crustal rocks under extreme pressure-temperature conditions.

Dates an episode of intense postimpact metamorphism in the core of the Vredefort impact structure of South Africa, using U-Pb geochronology of single grains of zircon and monazite. Geologic setting and sample descriptions; Indlandsee leucogranofels; Norite; Age of impact and core metamorphism; Causes of thermal imprint.

Presents a method for determining coral-based climatic histories using 13C enrichments driven by synchronized spawning. Analysis of coral from the Great Barrier Reef and eastern Indian Ocean; Period of coral spawning; Results of 13C/12C ratio measurements.

Describes a new strategy for dating depositional landscape surfaces using situ-produced cosmogenic radionuclides. Method of constraining inheritance; Applications of fluvial systems; Quantification of long-term exhumation rates and transport times.

Examines the reliability of 10Be produced in situ in dating moraines located in Wind River Mountains, Wyoming. Dryas; Cosmogenic-nuclide surface-exposure methods of dating boulder or bedrock surfaces.

Attempts to distinguish sudden from gradual extinctions by employing the 50 % confidence interval approach. Aim of the study; Methods; Results; Discussion; Implications.

Discusses the use of paleomagnetic dating of cave sediments to calculate the maximum incision rate of the East Fork Obey River. Paleohydraulic relation between the caves and the surface stream; Presence of normal-to-reverse polarity transition in sediments deposited within the caves; Vertical distribution of sediment polarity.

Estimates the age of the Rajamundry Traps in India around the late Cretaceous-early Paleocene with the use of K-Argon dating. Geochronological and geochemical analysis; Equivalence in the stratigraphy of the Rajamundy Traps and the Deccan Traps.

Examines the use of time-dependent strontium (Sr) isotope variations of seawater as a procedure for constructing a reference curve to date and correlate marine sedimentary rocks. Methods of constructing the time curve of marine rocks using Sr/Sr isotope variations; Identification of problems related to Sr isotope stratigraphy.

Deals with the time-temperature history of geologic samples based on Argon (Ar) dating. Evaluation of two competing hypotheses on technothermal evolution; Incremental heating results; Laser mapping results; Interpretation of incremental heating data for slowly cooled samples; Tectonic implications; Research directions in 40Ar/39Ar thermochronology.

Presents data on the dating of the hominid fossils named Lucy and the First Family and the Hadar Formation in Ethiopia. Sediment accumulation rate; Implications for the geomagnetic polarity time scale; Biostratigraphy and hominid evolution.

Determines the ages of the Gaborone and Kanye rapakivi granite sequences in the Witwatersrand basin hinterland in southern Africa by using the Uranium-Lead zircon dating methods of T.E. Krogh. Sampling and geologic relations; Geochemistry of dated samples; Isotope results.

Comments on the evidence presented by Anthony R. Prave (1999) regarding the age of the Proterozoic Kingston Peak Formation in Death Valley, California. Sordough Limestone Member as one of carbonate units within Kingston Peak Formation; Comparison of data from Death Valley rocks with chemostratigraphic record from other Neoproterozoic rocks; Reply of Prave.

Presents a debate regarding the paper `Mono-sample Pb-Pb dating of pyrrhotite and tourmaline: Proterozoic vs. Archean intracratonic gold mineralization,' in 1996. Justification for theories made in the paper; Comments from persons on the paper; Details on the interpretation of the paper.