Magnetic properties of some tertiary basalts from West Greenland

Summary Measurements of bulk magnetic properties, including the natural remanent magnetization (NRM), susceptibility and the Königsberger ratio, on over 250 samples of Tertiary basalts from Disko and Nûgssuaq, West Greenland are reported.The NRM intensities in basalts (geometric mean value 3.3 A/m in SI units) were on average three to four times as large as the induced magnetization intensities. The susceptibilities (geometric mean value 2.1×10^–2 SI units) were much more uniform than the NRM intensities. In the majority of samples, the NRM was predominantly of reverse (R) polarity, but samples from a few sites showed a remanence of normal (N) polarity.The NRM of both polarity classes (N, R) was very stable against alternating field (AF) demagnetization with median destructive fields of the order of 20,000–30,000 A/m (250–350 Oe), comparable to those for many stable continental and oceanic basalts. The viscous remanence intensity, as studied by storage tests on some specimens, was found to be an insignificant fraction of the original NRM, except in few cases.The low field hysteresis loops (Rayleigh loops) were studied for some specimens. A qualitative association was noted between wide hysteresis loop and relatively low AF stability, but no correlation was apparent between the loop type and the Königsberger ratio (Q _n) of a specimen.Contribution no. 6 Institute of Geophysics, University of Copenhagen.     

Author index 1984 (volumes 67–71)

Magnetic properties of samples from Bell Island sedimentary rocks have been studied. X-ray analysis indicates that the main magnetic mineral is hematite in all samples. The other iron-bearing minerals identified are siderite and chamosite. Microscope observations of thin sections suggest that the rocks consist of oolitic hematite in a matrix of siderite or calcite. The intensity of natural remanent magnetization (NRM) varies in the range of (0.03–0.4 A m^?1), depending on the percentage of hematite. The thermal demagnetization curves of NRM show in some cases a sharp increase in magnetization at temperatures in the range 500–600°C. The peaks that occur in these demagnetization curves are due to a chemical change of siderite during repeated laboratory heating. X-ray analysis confirmed that the newly formed material is magnetite. Since the original NRM has been masked by the new intergrown material, this would result in a serious error in the determination of paleomagnetic pole positions. The samples showing this behaviour were not considered for paleomagnetic study. The samples containing oolitic hematite in a calcite matrix exhibit very high stability of NRM, including directional stability until almost 670°C. For these samples, a virtual pole position based on N = 6 samples (32 specimens) demagnetized to 665°C is 34°N, 114°E, not far from published Ordovician poles for the North American craton.     

Remanent magnetization of a Pliensbachian limestone sequence at Bakonycsernye (Hungary)

Remanent coercivity spectra derived from IRM acquisition curves and thermal demagnetization of the IRM indicate that magnetite, haematite and minor amounts of goethite determine the magnetic properties of the Pliensbachian limestones at Bakonycsernye. These limestones have been sampled at approximately 7-cm intervals along a 10-m stratigraphic section which covers the whole Pliensbachian stage (Lower Jurassic) without any recognizable break in sedimentation. The primary natural remanent magnetization (NRM) is carried by detrital particles of magnetite and haematite, but it is seriously overprinted by a normal magnetization which originates from secondary haematite with a wide range of blocking temperatures. This haematite is believed to have formed diagenetically during one of the Mesozoic periods of normal polarity. However, the reversal pattern obtained after NRM thermal demagnetization at temperatures ≥450°C is thought to be characteristic of the Pliensbachian stage.     

Rock magnetism and paleomagnetic stratigraphy of forearc sediments of the Japan Trench, ODP Sites 1150 and 1151

Abstract Magnetic measurements were carried out to investigate rock magnetic properties and paleomagnetic directions of late and middle Miocene sediments recovered from the land side of the Japan Trench during the Ocean Drilling Program Leg 186. Because the low coercive component in natural remanent magnetization (NRM) normalized by anhysteretic remanent magnetization shows that the drilling‐induced magnetization is severe in the sections obtained by the advanced hydraulic piston coring method, careful analyses of demagnetization of NRM using the ‘demagnetization plane’ were carried out to decompose the direction and intensity. Magnetostratigraphic correlation down to the upper Miocene, supplemented by biostratigraphic data, revealed that the sedimentation rates are characterized by drastic changes, with the early Pliocene having the highest rate. This high sedimentation rate is related to the subsidence of the southern deep‐sea terrace of the Japan Trench.     

Organic carbon isotope gradient and ocean stratification across the late Ediacaran-Early Cambrian Yangtze Platform

Organic carbon isotope(δ13Corg) data from two well-preserved sections across a shallow-to-deep water transect of the late Ediacaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24‰. In the deep-water Longbizui section, δ13Corg values from time-equivalent strata of the Dengying Formation are mostly between –35‰ and -32‰. These new data, in combination with δ13Corg data reported from other sections in South China, reveal a 6‰–8‰ shallow-to-deep water δ13Corg gradient. High δ13Corg values(-30‰) occur mostly in shallow-water carbonate rocks, whereas low δ13Corg values(-32‰) dominate the deep-water black shale and chert. The large temporal and spatial δ13Corg variations imply limited buffering effect from a large dissolved organic carbon(DOC) reservoir that was inferred to have existed in Ediacaran-Early Cambrian oceans. Instead, δ13Corg variations between platform and basin sections are more likely caused by differential microbial biomass contribution to total organic matter. High δ13Corg values(-30‰) documented from shallow-water carbonates are within the range of typical Phanerozoic δ13Corg data and may record the isotope signature of organic matter from primary(photosynthetic) production. In contrast, low δ13Corg values(-32‰) from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.     

Thermal remagnetization and the paleointensity record of metamorphic rocks

We present a quantitative relationship between blocking temperature and time that, in principle, provides a calibration of thermal remagnetization in nature. For a given metamorphic temperature-time regime, one can decide whether a given laboratory blocking temperature (or for paleointensity work, a range of blocking temperatures) is consistent with primary natural remanence (NRM) or with a metamorphic overprint. Independent of the domain structure or the chemical composition of the magnetic minerals, two general types of behaviour are predicted. If the primary NRM possesses laboratory (or primary cooling) blocking temperatures within 100°C or so of the Curie temperature, thermal remagnetization at lower temperatures, even over times as long as 10⁶ years, is improbable. If the blocking temperatures are lower, viscous remagnetization is pronounced at temperatures well below those indicated by laboratory thermal demagnetization. An approximate scale of the “survival potential” of primary NRM in rocks of different metamorphic grades indicates that primary paleointensities are unlikely to be recovered from rocks metamorphosed above high-greenschist facies if the predominant magnetic mineral is nearly pure magnetite, or above middle-amphibolite facies if nearly pure hematite is predominant. Evidence from laboratory experiments and paleomagnetic field studies in metamorphic regions suggests, however, that these survival estimates are unduly optimistic. Chemical remagnetization through the destruction of primary magnetic minerals, and not thermal remagnetization, probably sets an effective upper temperature for the survival of primary NRM.     

Magnetostratigraphy of the Toarcian stratotype sections at Thouars and Airvault (Deux-Sèvres, France)

Magnetostratigraphic study of the Toarcian type sections of Thouars and Airvault (Deux-Sèvres, France) has yielded two reliable magnetic polarity sequences. Most samples were treated by mixed cleaning: thermal demagnetization (250°, 300° or 350°C) and subsequent alternating field demagnetization. Polarity intervals are easily identified and correlate well between the two sections using the biostratigraphic data provided by the detailed standard ammonite zonation of the Toarcian stage. The polarity sequence extends from ammonite horizon V (Pseudoserpentinum horizon,Serpentinus zone) to horizon XXV (Subcompta horizon,Aalensis zone); it shows 5 reversed and 5 normal polarity magnetozones.     

Paleomagnetism and ore mineralogy of some basalts of the Geirud Formation of Late Devonian - Early Carboniferous age from the southern Alborz,Iran

Basaltic lavas from the southern Alborz, an area about 40 km northeast of Tehran, Iran, have been paleomagnetically investigated. The lavas are of Late Devonian-Early Carboniferous age, and belong to the basal member of the Geirud Formation. At 11 sites a total of 80 cores was drilled.Detailed analyses by means of progressive demagnetization of the natural remanent magnetization (NRM) were made both by the application of alternating magnetic fields and by heating. Also, on a number of specimens a study was done both with thin sections and with polished sections. There proved to be general agreement between the properties of the characteristic NRM and the kind of Fe-Ti oxides in the lavas. In the case of specimens containing magnetite only the characteristic NRM was entirely removed at temperatures just below 600°C, or in alternating fields up to 1500/2000 Oe peak value; on the other hand, in specimens containing both magnetite and a substantial part of hematite (martite) the final part of the characteristic remanence was removed at temperatures above 600°C, and this remanence resisted alternating fields above 2000 Oe peak value. From the characteristic site-mean directions of 5 sites an average paleomagnetic direction is computed withD = 210.8°,I = 66.9°, and α₉₅ = 3.9°.This result might be taken as an indication that at the Devono-Carboniferous transition the southern part of the Alborz was located in the present Indian Ocean off the Arabian coast.     

Chemocline instability and isotope variations of the Ediacaran Doushantuo basin in South China

Stable isotope analyses in sections across a shelf to basinal transect of the Ediacaran Doushantuo basin show substantial isotope variabilities. In Songlin section where sediments were deposited in an intrashelf basin, δ 13C values are persistently negative (_3‰ to _5‰, VPDB) through the entire Doushantuo Formation, similar to those obtained from the slope section in Wuhe (_5‰ to _10‰, VPDB). Shallow water sections in Weng'an and Duoding show two broad δ 13C anomalies overprinted with significant meter-scale variations, but none of the curves has similar absolute δ 13C values compared to the Yangtze Gorges areas in South China and other sections globally. Such isotope variations, if partially recording ancient seawater signature, imply spatial and temporal chemocline instability in the Doushantuo basin. In combination with available δ 13C records from other Ediacaran successions globally, the data from the Doushantuo basin are consistent, in first order, with the existence and oxidation of a large dissolved organic carbon (DOC) reservoir in Ediacaran oceans, but imply local environmental controls on Neoproterozoic isotope values and call attentions for using δ 13C anomalies as time lines in stratigraphic correlation.     

Upper Eocene travertine-lacustrine carbonate in the Jianchuan basin,southeastern Tibetan Plateau: Reappraisal of its origin and implication for the monsoon climate

The Asian monsoon is one of the largest climatic systems in the world, but age of its onset has been estimated differently ranging from the late Eocene to the Quaternary. We investigated the sedimentology and stable isotopic compositions of the upper Eocene Jiuziyan Formation, a terrestrial limestone unit in the Jianchuan basin, Yunnan Province in China. This limestone formation is restricted in several localities in the central part of the basin. Previously, this has been characterized as palustrine carbonate and the transition to the sublacustrine deposit of the overlying Shuanghe Formation was interpreted as the appearance of wetter climate during the late Eocene. Our observations of macro- and microfacies revealed sedimentary fabrics indicating rapid CaCO₃ precipitation, such as dendritic calcite and calcified reed stems, which are unlikely to develop in a simple lacustrine setting. High carbonate content (mostly >90 %) and restricted distribution of the Jiuziyan limestone indicate a depositional setting spatially limited and isolated from clastic influx. These findings, together with clearly higher δ¹³C values (−0.7 ‰ to +6.9 ‰) and lower δ¹⁸O values (−14.6 ‰ to −10.5 ‰) than those of the Shuanghe Formation, indicate that the limestone was mainly travertine, carbonate formed from endogenic spring water. The elevated δ¹³C resulted from a large amount of CO₂ degassing from spring water with high pCO₂. In addition, the occurrence of centimeter-scale lamination coupled with cyclic changes in δ¹³C and δ¹⁸O is almost identical with the modern annually-laminated travertine reported from Baishuitai in northern Yunnan Province, implying comparable amplitude of seasonal temperature and precipitation changes to the record of the modern travertine at Baishuitai. Our results do not contradict the previous interpretation of late Eocene wetting and additionally suggest the existence of the late Eocene monsoon climate in the Jianchuan basin.     

Lower Cretaceous magnetic stratigraphy in Umbrian pelagic limestone sections

The magnetic stratigraphy of the Lower Cretaceous, pelagic Maiolica limestone has been investigated in three partially correlative sections at Gorgo a Cerbara, Presale and Frontale in the northern Umbrian Apennines of central Italy. The white, well-bedded limestone has a magnetic mineralogy dominated by magnetite. Stable magnetic directions isolated by thermal demagnetization define alternating polarity zones in each section. The magnetozone patterns are distinctive and can be correlated with the geomagnetic reversal history derived from the M-sequence marine magnetic anomalies. The three new sections confirm the polarity sequence for anomalies M0 to M10N. Although the Maiolica is inadequately dated, the correlated anomalies, together with the results of other investigations, allow tentative associations of anomalies M0–M19 with individual stages in the Lower Cretaceous and Upper Tithonian.The investigations also demonstrate the usefulness of magnetic stratigraphy in basin analysis. They yield mean sedimentation rates, confirm that there is a hiatus between the base of the Presale section and the underlying Jurassic formations, and show that a large part of the Frontale section has been cut out by faulting.     

Magnetostratigraphy across the Berriasian-Valanginian stage boundary (Early Cretaceous), at Cehegin (Murcia Province, southern Spain)

The Berriasian-Valanginian stage boundary near the town of Cehegin in the eastern Subbetic Cordillera of Spain is documented by a detailed ammonite zonation in pelagic limestones. Two magnetostratigraphic sections spanning the uppermost ammonite subzone of the Berriasian and the lower two zones of the Valanginian yielded identical magnetic polarity patterns. Remanent magnetization is predominantly carried by magnetite, and characteristic directions were obtained by thermal demagnetization. The mean characteristic directions from both sites have an inclination of 48°; however, the site declinations are divergent (030° and 074°) due to the tectonic disturbance of the region. The Cehegin polarity pattern can be correlated by means of ammonite and calpionellid zonation to the magnetostratigraphies of the Berriasian stratotype and several Italian sections, thereby enabling a unique correlation to the M-sequence magnetic polarity time scale. The Berriasian-Valanginian stage boundary is in the middle of normal-polarity chron M15n.     

Magnetic polarity stratigraphy of the Mio-Pliocene mammal-bearing Big Sandy Formation of western Arizona

The Big Sandy Formation in western Arizona consists of up to 65 m of clays, silts, sands and volcanic ashes that were deposited in a lacustrine paleoenvironment. Three paleomagnetic samples were collected from each of 54 sites spaced at stratigraphic intervals of no more than 5 m. After laboratory studies of pilot samples to determine their paleomagnetic characteristics, all other samples were measured for their NRM and then demagnetized in alternating fields of 150 Oe. After statistical filtering and a hierarchical site classification, 48 sites were used to interpret the magnetic polarity zonation.Vertebrate fossils from the Big Sandy Formation are collectively termed the Wikieup Local Fauna, and indicate a late Hemphillian Land Mammal “Age”. Three fission-track (zircon) dates from the Big Sandy Formation yielded a mean age of 5.5 ± 0.2 m.y. B.P. Using these radiometric data to calibrate the magnetic polarity zonation, it appears that the Big Sandy Formation spans late Epoch 6 to early Gilbert time (late Miocene to early Pliocene). The Wikieup Local Fauna is compared to two other roughly contemporaneous mammalian assemblages from New Mexico and Texas. Faunal differences previously thought to represent a very late Hemphillian age for the Wikieup Local Fauna are apparently related to ecogeographic variation and not time.     

Carbon isotope stratigraphy of Torinosu‐type limestone in the western Paleo‐Pacific and its implication to paleoceanography in the Late Jurassic and earliest Cretaceous

Carbon isotope stratigraphy of the Late Jurassic and earliest Cretaceous was revealed from Torinosu‐type limestone, which was deposited in a shallow‐marine setting in the western Paleo‐Pacific, in Japan. Two sections were examined; the Nakanosawa section of the late Kimmeridgian to early Tithonian age (Fukushima Prefecture, Northeast Japan), and the Furuichi section of the late Kimmeridgian to early Berriasian age (Ehime Prefecture, Southwest Japan). The age‐model was established using Sr isotope ratio and fossil occurrence. The limestone samples have a low Mn/Sr ratio (mostly <0.5) and lack a distinct correlation between δ¹³C and δ¹⁸O, indicating a low degree of diagenetic alteration. Our composite δ¹³C profile from the two limestone sections shows three stratigraphic correlation points that can be correlated with the profiles of relevant ages from the Alpine Tethyan region: a large‐amplitude fluctuation (the lower upper Kimmeridgian, ～152 Ma), a positive anomaly (above the Kimmeridgian/Tithonian boundary, ～150 Ma), and a negative anomaly (the upper lower Tithonian, ～148 Ma). In addition, we found that δ¹³C values of the Torinosu‐type limestone are ～1‰ lower than the Tethyan values in the late Kimmeridgian. This inter‐regional difference in δ¹³C values is likely to have resulted from a higher productivity and/or an organic burial in the Tethyan region. The difference gradually reduces and disappears in the late Tithonian, where the Tethyan and our δ¹³C records show similar stable values of 1.5–2.0‰. This isotopic homogenization is probably due to changes in the continental distribution and the global ocean circulation, which propagated the ¹³C‐depleted signature from the larger Paleo‐Pacific to the smaller Tethys Ocean during this time.     

Palaeomagnetic determination of transgressive and regressive movements during the quaternary in the Black Sea

Summary The piston core with a length of 60·8 m from the Samotino-east structure of the Bulgarian Black Sea shelf (about 28·2 E, 42·8 N) is studied palaeomagnetically. 129 levels from the interval 2·5–60·2 m, generally represented by clays and aleurolitic muds, were sampled. The age of the sediments of this core was determined by correlation with another core, situated very close to the one concerned (3 km), whose fauna is known very well. Its age is Eopleistocene (Gurinian deposits), Upper Pleistocene (Neweuxinian deposits) and Holocene.Standard palaeomagnetic methods are used to determine the components of NRM and the main carriers of primary magnetization (AF and thermal demagnetization of NRM, thermodemagnetization of J_rs and J_s).It is assumed that the basic carrier of NRM is coarse-grained ferrimagnetic monoclinic pyrrhotite (T_B of 300 °C) or partly oxidized pyrite (T_B of 400 °C).It is shown that the pyrite concentration varies along the depth of the section. This palaeomagnetically established variation corresponds very well to the data on the transgressive and regressive phases in the Black Sea basin. For the Gurinian deposits these phases are connected with the Danube and Güns glacials, the D-G interglacial and G1-G2 interstadial. No such correlation has so far been mentioned in the literature to our knowledge.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990.     

Declination and inclination errors in experimentally deposited specularite-bearing sand

Naturally disaggregated specularite-bearing sandstone from the Triassic Moenkopi Formation, artificially deposited in controlled magnetic fields of ～5 × 10^?2 mT, acquires a stable remanent magnetization that has systematic errors in inclination and declination. Inclinations about 12° shallower than the applied fields are produced by deposition on a horizontal surface in still water. Deposition from flowing water on a surface inclined 6–10° results in inclination errors of as much as 20°. Water flowing obliquely to the applied field results in declination errors of about 10°, with declinations systematically rotated toward the upstream direction of current flow. These experimental results indicate that specularite-bearing sediment responds to the earth's field in a manner similar to magnetite-bearing sediment, and support observational evidence for a primary magnetization of depositional origin in specularite in red beds of the Moenkopi Formation.     

Jurassic magnetostratigraphy, 3. Bathonian-Bajocian of Carcabuey, Sierra Harana and Campillo de Arenas (Subbetic Cordillera, southern Spain)

Four sections in Majocian-Bathonian (Middle Jurassic) pelagic limestone with standard ammonite zonation have yielded magnetic polarity sequences. Magnetic directions in these red to white limestones were obtained by thermal demagnetization and were stable from about 300°C to in excess of 450°C. The polarity patterns indicate that the majority of the Bajocian and Bathonian is characterized by quite frequent reversals of the magnetic field. Lengthy periods of constant polarity, particularly constant normal polarity, were not observed. The average frequency of reversals is about 6 per ammonite zone, which roughly may be interpreted as a frequency of a reversal every 260,000 years, a rate comparable to that of the Miocene-Pliocene. Paleolatitudes of these sites (25–28°) are about 10° south of their present positions; variable clockwise block rotations within the Subbectic region have rotated these sites relative to stable Iberia.     

High-frequency polarity swings during the Gauss-Matuyama reversal from Baoji loess sediment

Paleomagnetic records of the Gauss-Matuyama reversal were obtained from two loess sections at Baoji on the Chinese Loess Plateau. Stepwise thermal demagnetization shows two obvious magnetization components. A low-temperature component isolated between 100 and 200–250°C is close to the present geomagnetic field direction, and a high-temperature component isolated above 200–250°C reveals clearly normal, reversed, and transitional polarities. Magnetostratigraphic results of both sections indicated that the Gauss-Matuyama reversal consists of a high-frequency polarity fluctuation zone, but the characteristic remanent magnetization directions during the reversal are clearly inconsistent. Rock magnetic experiments demonstrated that for all the specimens with normal, reversed, and transitional polarities magnetite and hematite are the main magnetic carriers. Anisotropy of magnetic susceptibility indicates that the studied loess sediments have a primary sedimentary fabric. Based on virtual geomagnetic pole latitudes, the Gauss-Matuyama reversal records in the two sections are accompanied by 14 short-lived geomagnetic episodes (15 rapid polarity swings) and 12 short-lived geomagnetic episodes (13 rapid polarity swings), respectively. Our new records, together with previous ones from lacustrine, marine, and aeolian deposits, suggest that high-frequency polarity swings coexist with the Gauss-Matuyama reversal, and that the Gauss-Matuyama reversal may have taken more than 11 kyr to complete. However, we need more detailed analyses of sections across polarity swings during reversals as well as more high-resolution reversal records to understand geomagnetic behavior and inconsistent characteristic remanent magnetization directions during polarity reversals.     

Sediment budgeting: A case study in the Katiorin drainage basin,Kenya

The primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in Kenya. Results indicated that transfer of sediments (‘inputs’) from primary source areas was minor in comparison to changes in storage. The major sediment source area within the Katiorin drainage basin was the colluvial hillslope zone. The net change in storage within this zone was approximately 2100 Mg yr^?1. Surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments. Sediment storage within the in-channel reservoir increased by 60 Mg yr^?1, which was minor when compared to the total store of sediment in this reservoir. During 1986, the channel network stored only a small fraction ( < 3 per cent) of the sediment delivered from the hillslope subsystem. Therefore, the in-channel reservoir had limited influence on sediment conveyance to the basin outlet. These data indicate that a static equilibrium condition cannot be assumed within the Katiorin drainage basin. Such an assumption would result in erosion estimates of approximately 5.5 mm yr^?1 for the entire basin (based on a sediment output of 7430 Mg km^?2 yr^?1 and a measured bulk density of 1.35 Mg m^?3). However, this masked the actual rates of 1.2 to 7.1 mm yr^?1 in subbasin primary source areas, and rates of 0.6 to 17 mm yr^?1 for colluvial material in the various subbasins. The extreme accelerated erosion rates resulted from minimal ground vegetation, steep slopes, soil crust formation, an erodible substrate, and a well-integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet.     

Internal seiche pumping between sill-separated basins

Abstract

Despite their close proximity and similar dimensions (～ 200m deep × 10km long × 2km wide) the two eastern basins of Lake Lucerne, Gersauersee and Urnersee, exhibit considerable differences in their internal behaviour, particularly during late winter and spring. The two lakes are separated by a small intermediate basin (～ 120m deep × 4km long × 1km wide) with sills of approximately 90m depth at each end. We report results of a field program conducted over the period February—May, 1988, when observations were obtained from weekly CTD transects and from three thermistor string/current meter moorings deployed for two months, one near each sill and the third at the southern end of Urnersee near Fluelen. During the observation period the stratification, relative surface to bottom density difference, &Delta;ρ/ρ, was 12 × 10^?6 in Gersauersee and 4 × 10^?6 in Urnersee. Following wind events a large amplitude internal seiche in Gersauersee (vertical excursions of ～50m and period ～60 hours) effectively pumped the heavier Gersauersee bottom water onto the intermediate basin and eventually into the hypolimnion of Urnersee. Temperature spectra show a peak at this seiche frequency at all levels at the Gersauer sill but only near the bottom at the sill in Urnersee. Coherence estimates between the bottom temperatures at Gersauer sill and Fluelen showed a significant peak at period 60 hours suggesting transmission of energy from the Gersauersee seiching motion through the weaker stratification of Urnersee to Fluelen. The phase relationships indicate that the wave phase speed decreases as the wave propagates into the region of weaker stratification. Application of a simple two-layer Defant model which includes topographic variations confirms these observations. The estimated volume exchange due to seiche pumping is only a small fraction of the Urnersee hypolimnion. However, the dissipation of energy transferred from the Gersauersee seiche may be an important contribution to mixing in the deeper waters of Urnersee.