Relative Lake Level Changes Research Articles

Identification of the subaerial unconformity, genesis, and distribution in Lower Triassic Baikouquan Formation, Mahu Sag, Junggar Basin, Western China

The genesis of unconformities involves multiple influences on basin formation and evolution, which affects the favorable reservoir and hydrocarbon distribution. Within the Early Triassic Baikouquan Formation in the Mahu Sag of the Junggar Basin, we identified subaerial unconformities (SU), namely SU1 and SU2. SU1 is characterized by regional, irregular valleys, whereas SU2 displays extensive lateral extent with comparatively lower relief. These distinctions stem from detailed analyses involving cores, well data, seismic profiles, and spatial distributions, enriching our understanding of SUs in the Junggar Basin. Key findings from our study include: (1) SU occurrences within the Baikouquan Formation span the falling-stage systems tract (FSST) and expanding system tract (EST), corresponding to relative lake level changes. SU1 emerges during descending lake levels, whereas SU2 develops during rising levels. (2) The extensive uplift of the Junggar Basin's perimeter, driven by the late Hercynian movement, heightened topographic gradient shapes a steeper lake shoreline profile, fostering SU development. Arid paleoclimatic conditions during the Permian-Triassic interval accelerate SU formation in the FSST. (3) SU typically comprises regional compound scour surfaces (RCS) and river intermittent exposure surfaces (IES). Continuous winnowing at RCS led to relatively high primary porosities, IES can develop better secondary porosity with superposed freshwater leaching. The investigation into the subaerial unconformity in the study area holds broader implications for comprehending depositional processes, reservoir distribution, and petroleum prospects, both locally and within a global lake basin context.

Lacustrine deposition in response to the middle eocene climate evolution and tectonic activities, Bohai Bay Basin, China

The lower unit of the third member of the Eocene Shahejie Formation (Es3L, 42.5 to ∼40Ma) is one of the most important petroleum exploration targets in the Bohai Bay Basin. Lacustrine deposits are widely distributed in the Es3Lunit of the Shulu Sag and display strong vertical and horizontal variations in lithofacies and geochemical characteristics. Based on core data, thin-section petrography, stable δ13C isotope analyses, and organic geochemistry data, eight lithofacies and six evolutionary lake stages are identified. Combining the results of the astronomical time scale (ATS) and the radiometric age, the correlation between the evolutionary lake stages of Es3Land the Eocene global climate curve was illustrated. Tectonic movement caused the basin to subside and resulted in shallow lake formation (Stage 1) during the cooling phase prior to the Middle Eocene Climatic Optimum (MECO); then, the lake level began to rise (Stage 2) with an increasingly warm and humid climate. Stage 3 corresponds to the peak of the MECO and was influenced by the warm and humid climate during the thermal maximum period, forming a deep, freshwater lake. This stage was followed by highly turbulent lake conditions (Stage 4), which were influenced by both the cooling climate and intensive tectonic activity. Subsequently, a stable lake (Stage 5) was formed, which was mainly controlled by the slightly warming climate since the tectonic movement was relatively stable, followed by another stage of turbulent lake conditions (Stage 6). The results show that the global mid-Eocene climate played an important role on the relative lake level changes and TOC enrichment. The MECO led to a rise in the relative sea-level and the obviously rise in relative lake-level in the Bohai Bay Basin. The evolution of the depositional settings was controlled by both global climate and tectonic activities and accounted for the deposition and distribution of lithofacies with distinctly different characteristics and origins.

Architecture and depositional processes of sublacustrine fan systems in structurally active settings: An example from Weixinan Depression, northern South China Sea

Sublacustrine fans developed in structurally active settings are commonly characterized by complicated depositional characteristics, which create great challenges to hydrocarbon exploration. To advance understanding their sedimentary architecture and depositional processes, a large-scale sublacustrine fan system in the Eocene Weixinan Depression, northern South China Sea has been identified and investigated through the comprehensive analysis of 3-D seismic, well-logging, and core data. This fan was deposited during a lake-level falling stage, covering an area of 55 Km2. It can be divided into two sections in the vertical direction by the sedimentary characteristics. The lower section mainly consists of thin layers of well-sorted fine sandstones with parallel bedding, which are interpreted as deposits of turbidity currents. By contrast, the upper section comprises thick layers of gravelly coarse sandstones with various deformation structures and widespread floating clasts, which should be the deposits of cohesive debris flows. Provenance analysis suggests that the development of complicated sedimentary characteristics has a close relationship with the occurrence of multiple sediment supply directions. The lower section was sourced by the western delta with long-distance transported well-sorted sediments, while the northern fan delta sourced the upper section with short-distance transported coarse-grained sediments. Its depositional process was mainly controlled by paleo-geomorphology, sediment supply, and relative lake level changes. The lower section, controlled by the flexure slope belt, is a typical sand-rich sublacustrine fan characterized by the low gradient (<1°–1.5°), while the upper section, controlled by the steep slope fault belt, is a gravel-rich sublacustrine fan dominated by intense faulting and high gradient (3.2°–4.5°). In addition, during the depositional period of the upper section, the relay ramps between en-echelon faults provided major entry points for coarse-grained sedimentary flows into the depression. Therefore, a deep-lacustrine model is proposed for the sublacustrine fan system, showing the detailed “triggering-transportation-deposition” process. This study outlines the complexity of the sedimentary architecture of sublacustrine fans in structurally active settings, and the proposed model may be applicable in other lacustrine basins.

The late Holocene record of Lake Mareotis, Nile Delta, Egypt

Abstract. Lake Maryut (northwestern Nile Delta, Egypt) was a key feature of Alexandria's hinterland and economy during Greco-Roman times. Its shores accommodated major economic centers, and the lake acted as a gateway between the Nile valley and the Mediterranean. It is suggested that lake-level changes, connections with the Nile and the sea, and possible high-energy events considerably shaped the human occupation history of the Maryut. To reconstruct Lake Maryut hydrology in historical times, we used faunal remains, geochemistry (Sr isotopic signature of ostracods) and geoarcheological indicators of relative lake-level changes. The data show both a rise in Nile inputs to the basin during the first millennia BCE and CE and a lake-level rise of ca. 1.5 m during the Roman period. A high-energy deposit, inferred from reworked radiocarbon dates, may explain an enigmatic sedimentary hiatus previously attested to in Maryut's chronostratigraphy.

Hydroclimatic changes in the British Isles through the Last-Glacial-Interglacial Transition: Multiproxy reconstructions from the Vale of Pickering, NE England

European paleoenvironmental records through the Last Glacial-Interglacial Transition (LGIT; ca 16-8 cal ka BP) record a series of climatic events occurring over decadal to multi-centennial timescales. Changes in components of the climatic system other than temperature (e.g. hydrology) through the LGIT are relatively poorly understood however, and further records of hydroclimatic changes are required in order to develop a more complete understanding on the phasing of environmental and anthropogenic responses in Europe to abrupt climate change. Here, we present a multiproxy palaeoenvironmental record (macroscale and microscale sedimentology, macrofossils, and carbonate stable isotopes) from a palaeolake sequence in the Vale of Pickering (VoP), NE England, which enables the reconstruction of hydroclimatic changes constrained by a radiocarbon-based chronology. Relative lake-level changes in the VoP occurred in close association (although not necessarily in phase) to threshold shifts across abrupt climate change transitions, most notably lowering during cooling intervals of the LGIT (∼GI-1d, ∼GI-1b, and ∼GS-1). This reflects more arid hydroclimates associated with these cooling episodes in the British Isles. Comparisons to hydrological records elsewhere in Europe show a latitudinal bifurcation, with Northern Europe (50–60°N) becoming more arid (humid), and Southern Europe (40–50°N) becoming more humid (arid) in response to these cooling (warming) intervals. We attribute these bifurcating signals to the relative positions of the Atlantic storm tracks, sea-ice margin, and North Atlantic Polar Front (NAPF) during the climatic events of the LGIT.

Alternating of aggradation and progradation dominated clinothems and its implications for sediment delivery to deep lake: The Eocene Dongying Depression, Bohai Bay Basin, east China

Abstract Sediment routing in deep-water settings can be significantly different in lacustrine basins from their well-studied marine counterparts, which has been largely overlooked during the past decades. The seismically well-imaged lacustrine clinothems in the Eocene Dongying Depression provide a good opportunity to bridge the deep-water sediment partitioning with clinothem architecture and shelf-edge trajectories, which have been studied through the integration of 3D seismic data and well-logging data. In the study area, the Eocene delta-complexes are architecturally manifested as alternating aggradation dominated (AC) and progradation dominated clinothems (PC). The Eocene Dongying clinothem architecture has been documented in terms of shelf–edge trajectory angle (θsht), edge-to-toe distance (ETT), aggradation height (Ah), progradation distance (Pd) and maximum foreset angle (γmfa). Aggradation dominated clinothems are characterized by ascending shelf-edge trajectories with thick and widespread sand-prone bottomsets, suggesting higher efficiency of sediment delivery into the outlying lake floor. Progradation dominated clinothems, in contrast, are characterized by flat to slightly descending trajectories and generally by a lack of bottomsets. Alternations of rising and flat to slightly descending trajectories accompanied with different clinothem types probably indicate frequent relative lake level changes (on time-scales of 100s of kyr). Further analysis of seismic images and extensive well-logs suggest the distal aggradational bottomsets are generally consist of sub-lacustrine channel-lobe systems, whereas sediment slide, slump blocks occur in slope to slope toe areas of progradation dominated clinothems, which indicate varied processes of deep-water sediment transport associated with different clinothem types and shelf-edge trajectories. Lake-level, sediment supply, water salinity and density change induced by humid-arid climate cycle are suggested to be main factors controlling clinothems stacking pattern and sediment dispersal into deep-lacustrine. Humid climate are considered to be related with strongly aggradational clinothems, during which sediment can be directly transported to the distant bottomset areas due to increased sediment concentration and energy in river discharge. Whereas during dry periods, progradation dominated clinothems start to build under stillstand or falling lake level conditions, sediment generally accumulates at river mouth and collapses due to sediment overload or fault activity. Therefore, a relationship between deep-lacustrine depositional process and climatic signature was established which may provide new thoughts in both the study of deep-water sequences and deep-water exploration in lacustrine basins.

Late Quaternary lacustrine deposits of the Dead Sea basin: high resolution sequence stratigraphy from downhole logging data

Sequence architecture and depositional sequences of the Quaternary lacustrine succession deposited in the northern Dead Sea sub-basin were examined using logging data collected during the 2010-2011 ICDP campaign. Methods borrowed from sequence stratigraphy techniques were used to investigate the characteristics of sediments deposited in the central part of the northern lake. High resolution wire logging data combined with a detailed lithological description of the ICDP 5017-1-A deep borehole were used to examine depositional systems and related processes controlling their formation. Analysis of sedimentary stacking patterns and stratal surfaces within the late Pleistocene-Holocene lacustrine succession revealed 10 depositional sequences. It was possible to identify key stratal boundaries and to discern between three sedimentary stacking patterns interpreted here as representing lowstand systems tracts (LST), transgressive systems tracts (TST) and highstand systems tracts (HST). Examined together, they may be interpreted in terms of relative lake level changes. On the basis of the stratigraphic analysis complemented with new age dating, this article presents a record of the sediment accumulation pattern and a relative lake level curve reconstructed for the last ca 225 ka. Results show that stratigraphic units and depositional and erosional surfaces examined in the deep 5017-1-A borehole can be correlated to the proximal area of the basin. This means that changes in relative lake levels were generally synchronous and uniform across the Dead Sea basin. The creation of accommodation space in the northern Dead Sea was found to generally be in phase with paleoclimatic modulating lake levels, and not due to tectonics.

An application of sedimentation simulation in Tahe oilfield

The braided river delta develops in Triassic low oil formation in the block 9 of Tahe oilfield, but its sedimentation evolution process is unclear. By using sedimentation simulation technology, sedimentation process and distribution of braided river delta are studied based on the geological parameters including sequence stratigraphic division, initial sedimentation environment, relative lake level change and accommodation change, source supply and sedimentary transport pattern. The simulation result shows that the error rate between strata thickness of simulation and actual strata thickness is small, and the single well analysis result of simulation is highly consistent with the actual analysis, which can prove that the model is reliable. The study area belongs to braided river delta retrogradation evolution process, which provides favorable basis for fine reservoir description and prediction.

Division and characteristics of shale parasequences in the upper fourth member of the Shahejie Formation, Dongying Depression, Bohai Bay Basin, China

Shale parasequence analysis is an important part of sequence stratigraphy sudies. This paper proposed a systematic research method for analyzing shale parasequences including their delineation, division, characteristics and origins. The division method is established on the basis of lithofacies. Multi-method analysis and mutual verification were implemented by using auxiliary indicators (such as mineral compositions, geochemical indicators and wavelet values). A typical shale parasequence comprises a lower interval of deepening water-depth and an upper interval of shallowing water-depth (e.g., a shale parasequence including a high-total organic carbon (TOC) shale-low-TOC limy shale). Abrupt increases in pyrite content, TOC value, relative hydrocarbon generation potential ((S1+S2)/TOC), and wavelet values are indicative of parasequence boundaries. The proposed research method was applied to study the upper fourth member of the Shahejie Formation in the Dongying depression, Bohai Bay Basin. Results show that there were seven types of parasequences developed. A singular and a dual structured parasequences were identified. Three factors controlling the development of the shale parasequences were identified including relative lake level change, terrestrial input and transgression. The development of high-TOC (>2%) shale parasequences was mainly controlled by biological and chemical sedimentation. The low-TOC (<2%) shale parasequences were mainly deposited by chemical sedimentation. The diversities of shale parasequences were caused by four major controlling factors including climate, relative lake level change, terrestrial input and emergency (e.g., transgression).

Hydroclimatic variability in the Levant during the early last glacial (∼ 117–75 ka) derived from micro-facies analyses of deep Dead Sea sediments

Abstract. The new sediment record from the deep Dead Sea basin (ICDP core 5017-1) provides a unique archive for hydroclimatic variability in the Levant. Here, we present high-resolution sediment facies analysis and elemental composition by micro-X-ray fluorescence (µXRF) scanning of core 5017-1 to trace lake levels and responses of the regional hydroclimatology during the time interval from ca. 117 to 75 ka, i.e. the transition between the last interglacial and the onset of the last glaciation. We distinguished six major micro-facies types and interpreted these and their alterations in the core in terms of relative lake level changes. The two end-member facies for highest and lowest lake levels are (a) up to several metres thick, greenish sediments of alternating aragonite and detrital marl laminae (aad) and (b) thick halite facies, respectively. Intermediate lake levels are characterised by detrital marls with varying amounts of aragonite, gypsum or halite, reflecting lower-amplitude, shorter-term variability. Two intervals of pronounced lake level drops occurred at ∼ 110–108 ± 5 and ∼ 93–87 ± 7 ka. They likely coincide with stadial conditions in the central Mediterranean (Melisey I and II pollen zones in Monticchio) and low global sea levels during Marine Isotope Stage (MIS) 5d and 5b. However, our data do not support the current hypothesis of an almost complete desiccation of the Dead Sea during the earlier of these lake level low stands based on a recovered gravel layer. Based on new petrographic analyses, we propose that, although it was a low stand, this well-sorted gravel layer may be a vestige of a thick turbidite that has been washed out during drilling rather than an in situ beach deposit. Two intervals of higher lake stands at ∼ 108–93 ± 6 and ∼ 87–75 ± 7 ka correspond to interstadial conditions in the central Mediterranean, i.e. pollen zones St. Germain I and II in Monticchio, and Greenland interstadials (GI) 24+23 and 21 in Greenland, as well as to sapropels S4 and S3 in the Mediterranean Sea. These apparent correlations suggest a close link of the climate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern Hemisphere ice shields in the early last glacial period.

Radiocarbon Dating of Basal Peats Supports Separation of Lake Superior from Lakes Michigan-Huron about 1250 years ago

Lake Superior represents an important component of the aquatic ecosystem in North America. Along its south shore, ongoing lake-level rise, accelerated erosion, and wetland loss are major environmental concerns to coastal communities. A better prediction of the future of this shore requires placing the instrumental lake-level records in a geological context. However, our knowledge of the late-Holocene history of the world's largest freshwater body remains fragmentary. Here we present a sedimentary record of late-Holocene relative lake-level changes by dating transgressive basal peats resting directly on a sandy substrate along a bathymetric gradient in Bark Bay Slough, Wisconsin. Our record shows a moderate lake-level rise at 1.4±0.2mm/yr from about 2200 to 1250calyrBP as a result of relatively slow differential uplift of Bark Bay relative to the controlling outlet at Port Huron. The rise accelerated to 2.3±0.2mm/yr at about 1250calyrBP when Sault Ste. Marie emerged as the controlling outlet, thereby separating Superior from Lakes Michigan–Huron and giving rise to the modern hydrographic regime of the upper Great Lakes. The timing of this event in our record is about 1000 yr later than that estimated in most previous studies, but our data complement and confirm the younger age of lake separation inferred using a different methodology. Our results not only provide pertinent information for hydrological regulation, navigation operation, and infrastructural design in the upper Great Lakes, but also provide insight into freshwater wetland succession on flooded coasts.

Effect of relative lake-level changes in mire–lake system on the petrographic and floristic compositions of a coal seam, in the Most Basin (Miocene), Czech Republic

Exposures in the Bílina opencast mine provide a direct evidence that the 3.5m thick upper bench of the Main Seam in the Most Basin passes over a distance of about a kilometre into a hundred metres thick equivalent of clastic deltaic sediments with Gilbert-type mouth bars and thus clearly corroborates the co-existence of lacustrine delta–mire system. Deposition of the delta and the upper bench of the Main Seam were affected by five short-term lacustrine incursions, possibly related to tectonic subsidence before final lacustrine transgression took place. Between the temporary lacustrine incursions, delta mouth bars prograded into an extensive mire being separated only by a shallow compaction lake along mouth bars foreland. However, most clastics, introduced from delta were caught by dense vegetation in a narrow proximal zone of mire and did not affect more distal parts of relatively dry woodland mire with water table fluctuating around the surface. It is therefore characterised by low ash yield and increased resinite, fusinite and inertodetrinite contents. Palynological data indicate that the peat-forming vegetation of the upper bench of the Main Seam was dominated by Taxodiaceae (Glyptostrobus, Athrotaxis) and Calamus palm accompanied by paludal species of the family Pinaceae and rich undergrowth of ferns and Vaccinium-type Ericaceae. Progradation of delta mouth bars to the proximity of the study section is documented by increasing proportion of allochthonous elements produced by plants colonizing the flood plain and delta plain areas (Nyssa–Taxodium, Parrotia–Ulmus pyramidalis and Comptonia–Pinus oviformis associations). In contrast, during periods of temporary lacustrine transgressions the mire was replaced by open water environment, which favoured deposition of clay-rich coals or partings (>30% of ash yield) of the flooding horizons in spite of fact that delta body retreated to the basin margin and the clastics were introduced from a larger distance. Rare palynomorphs indicate only sparse vegetation cover of aquatic plants during this time. Clay content seems to be the best indicator of the water level fluctuations. Facies indices (e.g. TPI and GI) show only poor correlation to hydrological and floristic changes detected in the mire–lake system.

Minor Elements Utility in Paleo-lake Evolvement and Signification of Lower Tertiary Fning Formation，Gaoyou Sag, Subei Basin

According to the study vertical variations of trace elements: Boron(B) and Strontium(Sr) contents testing in clay rock of tertiary Funing Formation(from bottom to up :E1f1、 E1f2、 E1f3、 E1f4), Gaoyou sag, Subei Basin of China., the water of palaeolake in Gaoyou sag of Subei Basin changed from freshwater(E1f1、E1f3) gradually to salt water(E1f2、E1f4). The calcareous cement is formed in early diagenesis. It also means that Gaoyou palaeolake was twice opened to the sea from the first section of Fning Formation to the fourth (E1f1-E1f4). During the second and fourth of Funing Formation (E1f2、E1f4）, the Gaoyou palaeolake was the deepest and the area was largest. Comprehensive analysis of trace elements indicates that palaeo-salinity and depth fluctuated during different sedimentary periods. The sedimentary periods of Funing Formation can be divided into 9 intermediate cycles with relative lake level change. The paleolake level was relative rising quickly in the second and fourth of Funing Formation (E1f4) and relative descending quickly in the first Funing Formation (E1f1). Key words: palaeolake； trace elements； lower tertiary Fning Formation； Gaoyou sag

Sedimentologic and tectonic origin of an incised-valley-fill sequence along an extensional marginal-lacustrine system in the Basin and Range province, United States: Implications for predictive models of the location of incised valleys

Incised valleys in extensional lacustrine systems should be common and significant petroleum targets, yet documentation and analysis of these systems are limited and, hence, so are predictive models for their location. Geologic mapping of the Miocene–Pliocene Humboldt Formation in Knoll basin, northeastern Nevada, has revealed a significant incised-valley system formed along the lacustrine margins of an extensional basin. The valley formed during a relative lake-level fall and incised into lacustrine shoreface and offshore sandstone and subsequently was filled with fluvial and eolian sediment as lake level rose. The valley's location was tectonically influenced; it is situated in the hinge zone of a syncline near the tip of the range-bounding fault system. Folding of the syncline was broadly synchronous with incision and filling, and it appears to have localized the valley along the topographically low hinge zone. Furthermore, the large relative lake-level change that produced the valley is only recorded in strata in the syncline area, suggesting that the location and cause of incision was greatly influenced by tectonics. Thus, the location of similar incised valleys in other extensional basins may be predictable if comparable tectonic features and processes are recognized. Our study suggests that the best locations to develop and preserve incised valleys are near the tips of normal faults during periods of overall high tectonic subsidence. Specific areas along basin-bounding faults where tectonically influenced incised valleys are more likely to form include fault-propagation folds, synthetic relay ramps near transfer faults, and areas that have large changes in fault slip. Although lake volume changes caused predominantly by climate change can be an important factor in producing incised valleys, tectonically influenced incised valleys are likely to be larger, better preserved, and more petroleum prone compared to climate-controlled incised valleys.

Seismic stratigraphy of the Upper Pliocene and Quaternary deposits in the South Caspian Basin

More than 10,000 km of seismic data were used for seismic stratigraphic analysis and differentiation of major depositional environments of Upper Pliocene and Quaternary strata in the central deepwater and eastern parts of the South Caspian Basin (SCB). The study shows that the conventional sequence stratigraphy concept works well in the South Caspian Basin. Clinoform complexes within Paleo-Amudarya shelf margin are bounded by regionally, seismically expressed sequence boundaries and flooding surfaces that can be traced to the deep basin. Sequence analysis and seismic facies interpretation showed that deposition of prograding clinoforms and deep-water turbidite systems were controlled by the relative lake-level change. Depositional interpretation of sediment infill indicates that in the South Caspian Basin, as in other closed basins with high terrigineous input, basinal deposition is from turbidity currents and slumps generated from large shelf-edge deltas. There are two distinct stratigraphic complexes interpreted from seismic data: lower, interpreted as homogeneous infill of mud-rich turbidites and deepwater lacustrine deposits (Upper Pliocene, i.e. Akchagyl and Aspheron), and upper, consisting of prograding clinoform packages and coeval deepwater fan systems and slumps (Quaternary). The source of the central basin turbidite infill was primarily the eastern “Paleo-Amudarya” shelf. Growing diapir folds structurally controlled deposition of large-scale fan systems in the central basin. The distribution of these fan systems is tied to location of the coeval thick shelf-margin complexes.

A 4,700-Year Record of Lake Level and Isostasy for Lake Michigan

Four relative lake-level curves (RLLCs), produced from five sites bordering Lake Michigan, show similar timings of high and low lake-levels during the late Holocene. However, glacial isostatic-adjustments and possibly tectonism experienced at each site are superimposed on these records of relative lake-level change. This effect causes the RLLCs to diverge from each other with time. The absolute magnitudes of lake-level fluctuations for the late Holocene can only be determined by quantifying and subtracting the component of vertical ground-movement from each RLLC. Both an exponential rate and a constant-rate equation for a shoreline undergoing isostatic adjustment were used to model vertical movement for each site. Results show that for at least the last 4,000 calendar years (cal BP) of record, vertical movement in Lake Michigan has obeyed both types of equations. The two models yield similar results because rates of vertical movement of the shorelines around Lake Michigan are small and the time frame for which lake-level data are available is so short that the exponential nature of isostatic change is not expressed. Except for the southern shore of Lake Michigan, all the study sites have experienced uniform isostatic uplift consistent with trends reported by the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data (1977) and Tushingham (1992). The southern shore of Lake Michigan, however, experienced a change in uplift rate relative to the Port Huron outlet about 1,400 cal BP. The residuals between the calculated rates of vertical movement at each site and its corresponding RLLC are a record of water-level change experienced at each site. Within the resolution of the technique used to construct the RLLCs, all the residual curves should be, and are, similar. A Fourier smoothing of the combined residual curves yields a “eustatic” lake-level curve for Lake Michigan over the past 4,700 cal BP. The results of the Fourier smoothing identify major lake-level fluctuations such as the Nipissing II and Algoma phases of ancestral Lake Michigan. The technique also resolves lower magnitude and shorter duration quasi-periodic lake-level fluctuations of about 160 years (120 to 200 years).

Late Neogene sedimentary facies and sequences in the Pannonian Basin, Hungary

Abstract Detailed sedimentological, facies and numerical cycle analysis, combined with magnetostratigraphy, have been made in a number of boreholes in the Pannonian Basin, in order to study the causes of relative water-level changes and the history of the basin subsidence. Subsidence and infilling of the Pannonian Basin, which was an isolated lake at that time occurred mainly during the Late Miocene and Pliocene. The subsidence history was remarkably different in the individual sub-basins: early thermal subsidence was interrupted in the southern part of the basin, while high sedimentation rate and continuous subsidence was detected in the northeastern sub-basin. Three regional unconformities were detected in the Late Neogene Pannonian Basin fill, which represent 0.5 and 7.5 Ma time spans corresponding to single and composite unconformities. Consequently two main sequences build up the Late Neogene Pannonian Basin fill: a Late Miocene and a Pliocene one. Within the Late Miocene sequence there are smaller sedimentary cycles most probably corresponding to climatically driven relative lake-level changes in the Milankovitch frequency band. Considering the periods, the estimated values for precession and eccentricity in this study (19 and 370 ka) are close to the usually cited ones. In the case of obliquity the calculated period (71 ka) slightly deviates from the generally accepted number. Based on the relative amplitudes of oscillations, precession (sixth order) and obliquity (fifth order) cycles had the most significant impact on the sedimentation. Eccentricity caused cycles (fourth order) are poorly detectable in the sediments. The longer term (third order) cycles had very slight influence on the sedimentation pattern. Progradation, recorded in the Late Miocene sequence, correlates poorly in time within the basin. The dominant controls of this process probably were changes of basin subsidence rate and the very high sedimentation rate. The slow, upward trend of silt and sand bed thickness as well as that of the grain size also reflects the local progradation.

Water-level changes in Lake Baikal, Siberia: Tectonism versus climate

Relative changes in the level of Lake Baikal, amounting to hundreds of meters in Quaternary time, are well documented. Data presented here show that tectonic displacements of the lake outlet or former shoreline features are entirely sufficient to explain these relative lake-level changes. In contrast, the morphology and hydrology of the lake make its level hydrologically insensitive to climate change. Available evidence indicates that, throughout the past several hundred thousand years, Lake Baikal was a dilute, through-flowing lake controlled by the level of its outlet. On the basis of geologic data alone, climatic effects on lake level, whatever their magnitude, are difficult to separate from those caused by active rift tectonism. However, consideration of (1) the hydrologic budget of the lake and (2) the configuration of the outlet suggests that potential lake-level fluctuations due solely to climate change were less than about 2 m.

Paleoclimatic implications of Holocene lake-level fluctuations, Owasco Lake, New York

Radiocarbon-controlled stratigraphic data from Owasco Lake valley, New York, document two cycles of relative lake-level change during the Holocene in response to regional variations in effective precipitation. Lake highstands occurred at 10.5 and 6.9 ka, with an intervening lowstand at 9 ka. The 10.5 ka highstand occurred during the well-known Killarney–Younger Dryas cold interval (11.2–10.0 ka) in response to decreased evaporation and increased precipitation. The driest interval of the early-middle Holocene occurred ∼ 9 ka, at the time of maximum summer solar insolation. A second highstand occurred during the Hypsithermal (∼ 8.5–5.5 ka) in response to increased precipitation at a time when the interior of North America underwent maximum aridity. This out-of-phase relationship between northeastern North America and the midcontinent during the Hypsithermal may have been a consequence of a northward shift of the jet stream and a change of precipitation patterns in response to increased global warmth. If the Hypsithermal can be used as an analog for potential global warming, the northeastern United States may experience future increases in regional precipitation.

The contribution of TOPEX/POSEIDON to the global monitoring of climatically sensitive lakes

Remote sensing and long‐term monitoring of closed and climatically sensitive open lakes can provide useful information for the study of climatic change. Satellite radar altimetry offers the advantages of day/night and all‐weather capability in the production of relative lake level changes on a global scale. A simple technique which derives relative lake level changes is described with specific relevance to the TOPEX/POSEIDON geophysical data record data set. An assessment of the coverage and global tracking performance of both the NASA radar altimeter and the solid state altimeter over these lakes is discussed, and results are presented for the first 1.75 years of the mission. Lake level time series were acquired for 12 closed lakes, six open lakes, and three reservoirs, providing information in many cases where ground gauge data are unobtainable or the lake is inaccessible. The results, accurate to ∼4 cm rms, mark the beginning of a very accurate lake level data set, showing that TOPEX/POSEIDON can successfully contribute to the long‐term global program.