Coral Ages Research Articles

Radiocarbon Calibration by Means of Mass Spectrometric 230Th/234U and 14C Ages of Corals: An Updated Database Including Samples from Barbados, Mururoa and Tahiti

As first shown by Bard et al. (1990a), high-precision 230Th-234U ages can be used successfully to calibrate the radiocarbon time scale beyond the high-precision tree-ring calibration that now reaches 11,900 cal bp (Kromer and Spurk 1998). Using mass spectrometric techniques, we measured 14C and 230Th ages on new samples collected from boreholes drilled off the islands of Tahiti and Mururoa (French Polynesia) in order to complement the database previously obtained on Barbados corals (Bard et al. 1990a, 1993).

The Rise and Fall of Last Interglacial Sea-Levels

The Rise and Fall of Last Interglacial Sea-Levels

Rates of uplift investigated through 230Th dating in the Gulf of Corinth (Greece)

The Sr, U and Th isotope compositions of fourteen coral samples from raised terraces on the south side of the Gulf of Corinth, Greece, have been analysed by high-precision mass spectrometry. 234U– 230Th ages of pure coral aragonite together with 87Sr/ 86Sr determinations provide the basis for an investigation of tectonic uplift rates in the W. Aegean over the last 350 ka. The Corinth basin is a continental fault-bounded depression formed by crustal extension northeast of subduction along the Hellenic trench and in the vicinity of the Aegean volcanic arc. The Sr isotope composition of present-day seawater in the Gulf of Corinth is indistinguishable from that in the North Atlantic, but this was not the case during earlier high stands (120, 190 and 240 ka ago) when 87Sr/ 86Sr ratios, as estimated from the corals, were apparently significantly lower than the ratios of their open-ocean counterparts. Although the cause of the earlier discrepancy between the two reservoirs is unknown, it is likely to result from one of two processes. Either circulation between the Gulf of Corinth and the open ocean may have been restricted at certain earlier highstands, or the lower Sr isotope compositions could be the result of diagenetic effects. The latter hypothesis is favoured by large variations in the initial 234U/ 238U ratio of the corals, by their unusually high Th contents, and by the observation that the underlying massive Miocene carbonate is severely altered. The ages of the corals as determined by mass spectrometry ranges between 70.2 and 385.5 ka for samples from terraces at elevations of 7 to 65 m above present sea-level. A mean uplift rate for this area of 0.3 mm/yr over the last 350 ka has been estimated by combining the coral ages with terrace heights, allowing for changes in sea-level during this period. The uplift here is probably caused by footwall uplift adjacent to large normal faults, and put constraints on likely fault slip rates, extension rates, and the timescales of earthquake recurrence.

RAISED MARINE TERRACES ALONG THE GULF OF ADEN COAST OF SOMALIA

Mapping in the Galweda-Elayu area of northern Somalia has revealed depositional and erosional marine terraces at elevations of approximately 16 m, 8 m, and 2 m. These terraces vary from 0–2300 m, 200–2200 m, and 0–800 m in width, respectively. Sediments exposed in stream-valley walls demonstrate that the two higher terraces were formed by marine transgressions followed later by regressions to below present sea level. Beach ridges on the terraced alluvial fan at the mouth of togga Galweda imply that sea level and/or land elevation varied by at least 6 m during the formation of the 16-m terrace and by at least 3 m during the formation of the 8-m terrace. 230Th/234U ages of corals suggest that the 8-m terrace was formed during deep-sea isotope substage 5c (105 kyr B.P.) and the 2-m terrace during substage 5a (80 kyr B.P.). A 7-kyr-old coral from above the present storm beach on the outer flanks of the 2-m terrace suggests that sea level in the Gulf of Aden was close to its present level by the middle Holocen...

Coral ages and island subsidence, Hilo drill hole

A 25.8‐m‐thick sedimentary section containing coral fragments occurs directly below a surface lava flow (the ∼1340 year old Panaewa lava flow) at the Hilo drill hole. Ten coral samples from this section dated by accelerator mass spectrometry (AMS) radiocarbon and five by thermal infrared multispectral scanner (TIMS) 230Th/U methods show good agreement. The calcareous unit is 9790 years old at the bottom and 1690 years old at the top and was deposited in a shallow lagoon behind an actively growing reef. This sedimentary unit is underlain by a 34‐m‐thick lava flow which in turn overlies a thin volcaniclastic silt with coral fragments that yield a single 14C date of 10,340 years. The age‐depth relations of the dated samples can be compared with proposed eustatic sea level curves after allowance for island subsidence is taken. Island subsidence averages 2.2 mm/yr for the last 47 years based on measurements from a tide gage near the drill hole or 2.5–2.6 mm/yr for the last 500,000 years based on the ages and depths of a series of drowned coral reefs offshore from west Hawaii. The age‐depth measurements of coral fragments are more consistent with eustatic sea levels as determined by coral dating at Barbados and Albrolhos Islands than those based on oxygen isotopic data from deep sea cores. The Panaewa lava flow entered a lagoon underlain by coral debris and covered the drill site with 30.9 m of lava of which 11 m was above sea level. This surface has now subsided to 4.2 m above sea level, but it demonstrates how a modern lava flow entering Hilo Bay would not only change the coastline but could extensively modify the offshore shelf.

The quaternary coral reef tracts of hateruma, Ryukyu Islands, Japan

The island of Hateruma is located at the southwestern end of the Ryukyu Island chain and covers an area of about 15 km2 with its highest point at 59.5 m.a.s.l. The morphology of Hateruma is characterized by an eight-step staircase (I to VIII after Ota et al., 1982) most of which eroded into the previously formed coral reefs (II and IV to VIII). This study presents 100 age estimations on 43 coral samples using electron spin resonance (ESR), alpha- and mass spectrometric U-series methods. The dating results imply that the Ryukyu Limestone was predominantly formed during oxygen isotope stages 7 and 5e. Two age estimates of around 300 ka suggest an earlier reef-building period. The main problem for establishing the Quaternary history of Hateruma lies in the fact that the coral ages and the staircase morphology do not correlate. Additionally, it is difficult to distinguish autochthonous from allochthonous samples, the latter having possibly been relocated by tsunamis. Corals relating to substages 5a and 5c (around 75 and 105 ka, respectively) are found in the immediate vicinity of much older samples. The results of this study prove the disappointing fact that Hateruma cannot yet be used as a tool for reconstructing palaeo sea levels.

Sea-level records at ∼ 80 ka from tectonically stable platforms: Florida and Bermuda

Studies from tectonically active coasts on New Guinea and Barbados have suggested that sea level at ∼ 80 ka was significantly lower than present, whereas data from the Atlantic and Pacific coasts of North America indicate an ∼ 80 ka sea level close to that of the present. We determined ages of corals from a shallow submerged reef off the Florida Keys and an emergent marine deposit on Bermuda. Both localities are on tectonically stable platforms distant from plate boundaries. Uranium-series ages show that corals at both localities grew during the ∼80 ka sea-level highstand, and geologic data show that sea level at that time was no lower than 7–9 m below present (Florida) and may have been 1–2 m above present (Bermuda). The ice-volume discrepancy of the 80 ka sea-level estimates is greater than the volume of the Greenland or West Antarctic ice sheets. Comparison of our ages with high-latitude insolation values indicates that the sea-level stand near the present at ∼80 ka could have been orbitally forced.

Thorium-230 Ages of Corals and Duration of the Last Interglacial Sea-Level High Stand on Oahu, Hawaii

Thorium-230 ages of emergent marine deposits on Oahu, Hawaii, have a uniform distribution of ages from approximately 114,000 to approximately 131,000 years, indicating a duration for the last interglacial sea-level high stand of approximately 17,000 years, in contrast to a duration of approximately 8000 years inferred from the orbitally tuned marine oxygen isotope record. Sea level on Oahu rose to >/=1 to 2 meters higher than present by 131,000 years ago or approximately 6000 years earlier than inferred from the marine record. Although the latter record suggests a shift back to glacial conditions beginning at approximately 119,000 years ago, the Oahu coral ages indicate a near present sea level until approximately 114,000 years ago.

Uranium-Series Ages of Marine Terrace Corals from the Pacific Coast of North America and Implications for Last-Interglacial Sea Level History

Few of the marine terraces along the Pacific coast of North America have been dated using uranium-series techniques. Ten terrace sequences from southern Oregon to southern Baja California Sur have yielded fossil corals in quantities suitable for U-series dating by alpha spectrometry. U-series-dated terraces representing the ∼80,000 yr sea-level high stand are identified in five areas (Bandon, Oregon; Point Arena, San Nicolas Island, and Point Loma, California; and Punta Banda, Baja California); terraces representing the ∼125,000 yr sea-level high stand are identified in eight areas (Cayucos, San Luis Obispo Bay, San Nicolas Island, San Clemente Island, and Point Loma, California; Punta Bands and Isla Guadalupe, Baja California; and Cabo Pulmo, Baja California Sur). On San Nicolas Island, Point Loma, and Punta Bands, both the ∼80,000 and the ∼125,000 yr terraces are dated. Terraces that may represent the ∼105,000 sea-level high stand are rarely preserved and none has yielded corals for U-series dating. Similarity of coral ages from midlatitude, erosional marine terraces with coral ages from emergent, constructional reefs on tropical coastlines suggests a common forcing mechanism, namely glacioeustatically controlled fluctuations in sea level superimposed on steady tectonic uplift. The low marine terrace dated at ∼125,000 yr on Isla Guadalupe, Baja California, presumed to be tectonically stable, supports evidence from other localities for a +6-m sea level at that time. Data from the Pacific Coast and a compilation of data from other coasts indicate that sea levels at ∼80,000 and ∼105,000 yr may have been closer to present sea level (within a few meters) than previous studies have suggested.

Climatic, eustatic, and tectonic controls on Quaternary deposits and landforms, Red Sea Coast, Egypt

The degree to which local climatic variations, eustatic sea level fluctuations, and tectonic uplift have influenced the development of Quaternary marine and fluvial landforms and deposits along the Red Sea coast, Eastern Desert, Egypt was investigated using a combination of remote sensing and field data, age determinations of corals, and numerical simulations. False color composites generated from Landsat Thematic Mapper and SPOT image data, digital elevation models derived from steieophotogrammetric analysis of SPOT data, and field observations document that a ∼10‐km‐wide swath inland from the coast is covered in many places with coalescing alluvial fans of Quaternary age. Wadis cutting through the fans exhibit several pairs of fluvial terraces, and wadi walls expose alluvium interbedded with coralline limestone deposits. Further, three distinct coral terraces are evident along the coastline. Climatic, eustatic, and tectonic uplift controls on the overall system were simulated using a cellular automata algorithm with the following characteristics: (1) uplift as a function of position and time, as defined by the elevations and ages of corals; (2) climatic variations driven by insolation changes associated with Milankovitch cycles; (3) sea level fluctuations based on U/Tb ages of coral terraces and eustatic data; and (4) parameterized fluvial erosion and deposition. Results imply that the fans and coralline limestones were generated in a setting in which the tectonic uplift rate decreased over the Quaternary to negligible values at present. Coralline limestones formed during eustatic highstands when alluvium was trapped upstream and wadis filled with debris. During lowstands, wadis cut into sedimentary deposits; coupled with continuing uplift, fans were dissected, leaving remnant surfaces, and wadirelated terraces were generated by down cutting. Only landforms from the past three to four eustatic sea level cycles (i.e., ∼300 to 400 kyr) are likely to have survived erosion and deposition associated with fluvial processes.

New uranium-series ages of the Waimanalo Limestone, Oahu, Hawaii: Implications for sea level during the last interglacial period

The Waimanalo Formation (limestone) of Oahu has been correlated with the last interglacial period based on U-series dating of corals by T.-L. Ku and colleagues. The limestone consists of growth-position corals and overlying coral conglomerate. An apparent bimodal distribution of ages for the growth-position corals (mean age = 133 ka) and the overlying coral conglomerate (mean age = 119 ka) has been interpreted to represent two distinct high stands of sea that occurred within the last interglacial period. Both growth-position corals and overlying, conglomerate coral occur in an outcrop east of Kaena Point and consist mainly of Pocillopora and Porites. U-series ages of growth-position corals that show closed-system conditions are 120 ± 3 ka and 127 ± 4 ka; overlying conglomerate corals have U-series ages that range from 120 ± 3 ka to 138 ± 4 ka. At Kahe Point, conglomerate corals have ages of 120 ± 3 ka and 134 ± 4 ka. These data show that the growth position corals are not systematically older than the conglomerate corals; thus, there is no evidence for two distinct high stands of sea. Waimanalo deposits at Kahe Point and Mokapu Point (new U-series ages of 134 ± 4 ka and 127 ± 3 ka) have beach deposits as high as 12.5 m and, at Mokapu Point, growth-position corals as high as 8.5 m. A last-interglacial sea-level stand of +8.5 to +12.5 m conflicts with estimates of +6 m from a number of tectonically stable coastlines and islands in the western Atlantic Ocean. We infer, therefore, that Oahu may be undergoing uplift at a low rate. This uplift may be due to compensatory lithospheric flexure, because the island of Hawaii has been subsiding throughout much of the Quaternary from volcanic loading. Because of this possible uplift, Oahu and islands like it elsewhere in the Pacific cannot be used as reference points for sea level during the last interglacial period.

ESR dating of coral reefs in the South China Sea

ESR dating of aragonitic and calcitic corals, eolianite, calcrete, and corallineae from coral reefs in the South China Sea was applied to study of Quaternary reef geology. The ESR ages of calcitic corals correlated with the biostratigraphy, lithostratigraphy and geochemistry of Well Xi-Chen-1 and the oxygen-isotope stratigraphy of deep sea sediments, were reliable and up to 1.26 Ma. The selection of signals for dating and other related problems are discussed.

LATE DEVONIAN (FRASNIAN) CORALS FROM CENTRAL DOLPO, NEPAL

Rugosa and Tabulata from the Late Devonian of central Dolpo (Nepal) belong to the genera Kuangxiastraea , Scruttonia, Sinodisphyllum , Tabulophyllum (?), Fruehwirthia gen. n., Thamnopora , Cladopora , Alveolites and Alveolitella . The calcarenitic beds yielding the fossils are overlain by a prominent oolitic ironstone with thick ferruginous nodules and crusts. The age of the corals is probably Early Frasnian, thus younger than the Givetian fauna previously reported from eastern Dolpo. Biogeographic relations of the new fauna are with Western Europe and South China.

Increased production of cosmogenic 10Be during the Last Glacial Maximum

BERYLLIUM-10 (half-life 1.5 Myr) is produced by spallation of nitrogen and oxygen atoms by cosmic rays in the upper atmosphere. Its production rate is proportional to the flux of cosmic rays, which is modulated by solar activity and the strength of the Earth's magnetic field1,2. Weakening of the magnetic field allows more cosmic rays to impinge on the Earth's atmosphere, thereby increasing 10Be production. Here we report that the ocean-wide average accumulation rate of 10Be in Pacific sediments, which reflects the global average production rate of 10Be (ref. 3), was at least 25% greater during the height of the most recent ice age (∼ 24,000–16,000 yr ago) than during the Holocene (the past 10,000 yr). The higher production rate of 10Be records the lower intensity of the geomagnetic field during that period and is consistent with the hypothesis developed to explain the younger 14C ages of fossil corals compared with ages obtained by U–Th dating4. These results also point to a more general need to consider variations in production rate in geochronological studies using other cosmogenic nuclides.

Geochronology and subsurface stratigraphy of Pukapuka and Rakahanga atolls, Cook Islands: Late Quaternary reef growth and sea level history

Eustatic sea-level cycles superposed on thermal subsidence of an atoll produce layers of high sea-level reefs separated by erosional unconformities. Coral samples from these reefs from cores drilled to 50 m beneath the lagoons of Pukapuka and Rakahanga atolls, northern Cook Islands give electron spin resonance (ESR) and U-series ages ranging from the Holocene to 600,000 yr B.P. Subgroups of these ages and the stratigraphic position of their bounding unconformities define at least 5 periods of reef growth and high sea-level (0–9000 yr B.P., 125,000–180,000 yr B.P., 180,000–230,000 yr B.P., 300,000–460,000 yr B.P., 460,000–650,000 yr B.P.). Only two ages fall within error of the last interglacial high sea-level stand (∼125,000–135,000 yr B.P.). This paucity of ages may result from extensive erosion of the last intergracial reef. In addition, post-depositional isotope exchange may have altered the time ages of three coral samples to apparent ages that fall within glacial stage 6. For the record to be preserved, vertical accretion during rising sea-level must compensate for surface lowering from erosion during sea-level lowstands and subsidence of the atoll; erosion rates (6–63 cm/1000 yr) can therefore be calculated from reef accretion rates (100–400 cm/1000 yr), subsidence rates (2–6 cm/1000 yr), and the duration of island submergence (8–15% of the last 600,000 yr). The stratigraphy of coral ages indicates island subsidence rates of 4.5 ± 2.8 cm/1000 yr for both islands. A model of reef growth and erosion based on the stratigraphy of the Cook Islands atolls suggests average subsidence and erosion rates of between 3–6 and 15–20 cm/1000 yr, respectively.

Late quaternary uplift rates of marine terraces on the Pacific coast of North America, southern Oregon to Baja California sur

Marine terraces are common landforms along the Pacific coast of North America from southern Oregon to southern Baja California. We report 60 new uranium-series ages of marine terrace corals, hydrocorals, and other fossils. Terraces representing the ca. 80 ka and ca. 125 ka high stands of sea are the most common along the Pacific coast and we have used these ages, along with terrace shoreline angle elevations and paleo-sea-level estimates, to calculate Late Quaternary uplift rates. Uplift rates in the forearc region of the Cascadia subduction zone range from 0.45–1.08 m/kyr. Farther south, along most of the coast west of the San Andreas fault zone, uplift rates range from 0.15–0.35 m/kyr, but some areas have significantly higher rates of uplift and others have apparently experienced little or no uplift in the last 125 ka. In Baja California Sur, west of the East Pacific Rise, little or no uplift has occurred during the Late Quaternary. On average, the magnitude of rates of uplift for the tectonic regimes is as follows: Cascadia subduction zone > San Andreas fault zone region > East Pacific Rise region.

ESR dating of corals and pre-annealing effects on ESR signals

Corals commonly exhibit electron spin resonance (ESR) signals of A ( g = 2.0057), B ( g = 2.0031), and C ( g = 2.0007). Pre-annealing using a modern coral sample at 120–180°C has significantly changed gamma-ray sensitivities of the ESR signals. The sensitivities of all the three signals at first increased and then decreased with the pre-annealing. These results suggest that the amount of sources of the signals changes with geologic time. This effect can cause underestimation of ESR ages for Holocene and latest Pleistocene corals, and can cause overestimation for Early and Middle Pleistocene corals using signal C. Possible models associated with a monomer and a trimer of cation impurities for signals C and A, respectively, are discussed based on third order trap decay kinetics.

U-series ages of solitary corals from the California coast by mass spectrometry

The purpose of this study is to evaluate the feasibility of dating fossil solitary corals from Pleistocene marine strandlines outside tropical latitudes using the recently developed high sensitivity, high-precision U-series technique based on thermal-ionization mass-spectrometry (TIMS). The TIMS technique is much more efficient than conventional a spectrometry and, as a result, multiple samples of an individual coral skeleton, or different specimens from the same bed can be analyzed.Detached and well-rounded fossil specimens of the solitary coral Balanophyllia elegans were collected from relict littoral deposits on emergent marine terraces along the California coast at Cayucos terrace (elevation 8 m, previously dated at 124 and 117 Ky by α counting), Shell Beach terrace (elevation about 25 m, previously undated), Nestor terrace, San Diego (elevation 23 m, previously dated at 131 to 109 Ky ), Bird Rock terrace, San Diego ( elevation 8 m, previously dated at 81 Ky ). Attached living specimens were collected from the intertidal zone on the modern terrace at Moss Beach.Concentrations of 232Th in both living and fossil specimens are much higher than in reef-building corals (12 to 624 pmol/g vs. 0.1 to 1.6 pmol/g, respectively). However, because 230Th/232Th in Balanophyllia elegans are very low (2.22 × 10−3to 4.33 × 10−4), the high 232Th concentrations have negligible effect on the 230Th-234U dates. The high 232Th concentration in the living specimen (33.1 pmol/g) indicates that a significant amount of 232Th is incorporated in the aragonitic skeleton during growth, or attached to clay-sized silicates trapped in the skeletal material. The calculated initial 234U activities in the fossil specimens of Balanophyllia elegans are higher than the 234U activity in modern seawater or in the modern specimen. The higher initial activities could possibly reflect the influx of 234U-enriched continental water into Pleistocene coastal waters, or it could reflect minor diagenetic alteration, a persistent and fundamental problem in dating all corals.Samples from a compound specimen from the Cayucos terrace were subjected to different preparation procedures. Samples prepared by a standard acid washing procedure yielded 230Th-234U ages of 125, 123, and 122 Ky, whereas samples prepared by an abbreviated procedure without acid washing yield significantly lower ages of 113 and 112 Ky. Two other specimens from the same bed yielded 230Th-234U ages of 118 and 115 Ky. Also, two specimens from a stratigraphically higher bed yielded ages of 120 and 117 Ky, and three specimens from a lower bed yield ages of 115, 113, and 101 Ky. Nine of the twelve ages of the treated samples from the Cayucos terrace range from 125 to 113 Ky. However, the ages do not follow the stratigraphie order. Two possible interpretations are ( 1 ) the age of the terrace deposit is 125 Ky and all younger ages reflect variable diagenetic alteration or (2) the age of the terrace is 125 to 113 Ky and the ages reflect sediment reworking over a period of 12 Ky.Three specimens from a single bed on the Shell Beach terrace yield ages of 126, 122, and 121 Ky, similar to the older ages from Cayucos. The ages of solitary corals from the Cayucos and Shell Beach terraces are similar to ages of reef-building corals from terraces at numerous tropical localities. These are correlated with the last interglacial sea-level highstand, which probably stood 2 to 10 m above present sea level. The youngest ages and present elevations of the Cayucos and Shell Beach terraces yield tectonic uplift rates of 0.01 and 0.15 m/Ky, respectively, assuming the original elevation of each terrace was 7 m.Four specimens from the basal gravel on the Nestor terrace yielded ages of 145, 143, 137, and 133 Ky. The three oldest ages, however, are older than that associated with the last interglacial. The possible explanations for these older ages are ( 1 ) diagenic alteration or ( 2 ) the Nestor terrace deposits reflect in some way a poorly documented early phase of the last interglacial sea level high stand.

The last interglacial shoreline in Australia — A review

Marginal marine strata of last interglacial age occur in a range of morphostratigraphic settings around the Australian coastline. The lithofacies are similar to their Holocene equivalents but are partly lithified, elevated and laterally displaced inland. Uranium-series ages for corals and molluscs from widely separated localities around the Australian coastline are generally in accord with the accepted age for Oxygen Isotope Substage 5e (125,000 ± 10,000 BP), the value generally accepted for the last interglacial maximum. Amino acid racemisation has principally been applied to correlation of sequences with benchmark sites dated by the uranium-series method. Elevations of preserved last interglacial shorelines do not support the notion that Australia is a stable continent. Significant neotectonic anomalies include Cape Cuvier (+10.5 m), Fleurieu Peninsula (+6 m), the Coorong Coastal Plain (+10 m) and Tasmania (+32 m), each indicating contrasting degrees of local uplift. The Tasmanian sequences are the highest occurrence on the Australian continent and have been attributed to uplift as a result of mantle hotspot processes. With the exception of these tectonically uplifted sites, the height of the last interglacial sea surface around the Australian coastline is consistently below the 6 m level globally attributed to this high sea level stand. In Australia, the most consistent datum is from western Eyre Peninsula where a level 2 m above present mean sea level is ubiquitous. The more southerly limit of coral growth and wider distribution of subtropical molluscan fauna are in accordance with warmer ocean waters during Substage 5e (approximately 2°C). The extent of racemisation in molluscan fossils from southern Australia also excludes the possibility of a more equable latitudinal distribution of MAT during Substage 5e.

U/Th and 14C ages of corals from Barbados and their use for calibrating the 14C time scale beyond 9000 years B.P.

The mass spectrometry of 230Th and 234U has been developed on a thermal ionization mass spectrometer (VG Micromass 30). It is shown that the mass spectrometric determination is significantly more precise and reproducible than the classical radioactive method (α decay). The age errors obtained by this new technique of U-Th measurement are now comparable to that achieved by the 14C method which will allow us to pursue the 14C calibration on carbonates. The comparison between the U/Th and 14C ages obtained on the Holocene samples demonstrate that the U/Th ages are accurate because they are in agreement with the dendrochronological calibration. Beyond 9000 yr B.P. it is shown that the 14C ages are systematically younger than the U/Th ages with a maximum difference of about 3000 yr reached at about 20000 yr b.p. It is also shown that the two main problems are the thorium ionization efficiency and the mass separation of the magnet sector for the U/ 238U ratio measurement. Significant improvements can thus be expected from mass spectrometry through the use of sputtering ion sources for optimizing the ionization efficiency, additional magnetic and electrostatic sectors to improve the abundance sensitivity and ion counting detectors to increase the measurement statistics.