Sublacustrine Springs Research Articles

Siliceous sublacustrine spring deposits around hydrothermal vents in Lake Taupo, New Zealand

Chimneys around hydrothermal vents at a depth of c . 140 m in the Horomatangi Reefs area in Lake Taupo, New Zealand, are composed of amorphous silica (opal-A) with lesser amounts of Mn-, Fe-, and Hg-rich precipitates. Detrital quartz and feldspar grains are found in the surrounding sediments. The associated biota includes fish, bacteria, sponges, crayfish, amphipods, copepods, ostracodes, annelids, and other unidentified organisms. Much of this biota, however, is not preserved in the opal-A deposits. Instead, the silicified biota includes filamentous microbes and diatoms, scattered coccoid microbes, fungal hyphae and spores, rare sponge spicules, and rare worm(?) tubes. The diatoms, coccoid microbes, and fungi were brought into the area with the detrital sediment. In ancient successions, distinction between sublacustrine, terrestrial, and some marine hot spring deposits may be difficult because the precipitates share many similarities. Distinction based on the biota is viable only if palaeoecological information can be inferred from accurately identified organisms. Unfortunately, silicification commonly disguises microbes and precludes their accurate identification. Diagenetic transformation of opal-A to its more stable polymorphs also destroys many original depositional fabrics and silicified microbes. Distinction between the different types of spring deposit may therefore depend on the interpretation of their overall sedimentological and stratigraphic setting.

The physical structure and dynamics of a deep, meromictic crater lake (Lac Pavin, France)

The characteristic feature of the physical structure of Lac Pavin is a distinct and permanent chemically induced density increase between about 60 and 70 m depth. This chemocline separates the seasonally mixed mixolimnion from the monimolimnion, which is characterized by elevated temperature and salinity as well as complete anoxia. Previously published box-models of the lake postulated substantial groundwater input at the lake bottom, and consequently a short water residence time in the monimolimnion and high fluxes of dissolved constituents across the chemocline. We present a new view of the physical structure and dynamics of Lac Pavin, which is based on the results of high-resolution CTD profiles, transient and geochemical tracers (tritium, CFCs, helium), and numerical modeling. The CTD profiles indicate the existence of a sublacustrine spring above rather than below the chemocline. A stability analysis of the water column suggests that vertical turbulent mixing in the chemocline is very weak. A numerical one-dimensional lake model is used to reconstruct the evolution of transient tracer distributions over the past 50 years. Model parameters such as vertical diffusivity and size of sublacustrine springs are constrained by comparison with observed tracer data. Whereas the presence of a significant water input to the monimolimnion can clearly be excluded, the input to the mixolimnion – both at the surface and from the indicated sublacustrine spring – cannot be accurately determined. The vertical turbulent diffusivity in the chemocline is well constrained to K ≈ 5×10-8 m2 s-1, about a factor of three below the molecular diffusivity for heat. Assuming thus purely molecular heat transport, the heat flow through the chemocline can be estimated to between 30 and 40 mW m-2. With respect to dissolved constituents, the very weak turbulent diffusive exchange is equivalent to a stagnant monimolimnion with a residence time of nearly 100 years. Based on these results and vertical concentration profiles of dissolved species, diffusive fluxes between monimolimnion and mixolimnion can be calculated. A large excess of helium with a 3He/4He ratio of (9.09 ± 0.01)×10-6 (6.57 Ra) is present in the monimolimnion, clearly indicating a flux of magmatic gases into the monimolimnion. We calculate a flux of 1.0×10-12 mol m-2 s-1 for mantle helium and infer a flux of 1.2×10-7 mol m-2 s-1 (72 t year-1) for magmatic CO2. The monimolimnion appears to be in steady state with respect to these fluxes.

Geochemical evidence for the formation of a large miocene “travertine” mound at a sublacustrine spring in a soda lake (Wallerstein castle rock, nördlinger ries, Germany)

“Travertines” (tufa pinnacles) of the Miocene Riescrater basin have been investigated to test whether carbon, oxygen and strontium isotopes can be used for the recognition of fossil subaquatic spring deposits in high-alkalinity settings. The Ries basin “travertines” have so far been interpreted as a product of subaerial to sublacustrine artesian springs discharging calcareous groundwater into a freshwater or slightly saline lake. However, recent studies on microfacies and fabric development propose a formation at Ca2+-supplying sublacustrine springs of a soda lake. Geochemical analysis of “travertines” of the castle rock Wallerstein, including “sickle-cell” limestones, thrombolites, non-skeletal stromatolites, and speleothems, now support the latter interpretation. High Sr contents surpassing that of the contemporaneously formed dolomitic algal biocherms of the lake shore point to an aragonitic composition of primary precipitates. the δ13C values of diagenetically moderately to weakly altered “travertine” facies types are in the same range of the impact-brecciated Upper Jurassic limestones, thus, are inconsistent with a mixture of soil-derived CO2 and CO3 2− from the Jurassic limestones. In addition, the δ18O values are too high to support a significant contribution of CO3 2− by meteoric waters seeping through marine Jurassic limestones. Instead the δ13C and δ18O values indicate an origin of the CO3 2− from a lake water body characterized by evaporation. This is consistent with a sodium-rich lake water as indicated by high sodium contents of aragonitic algal bioherms of the lake shore. The87Sr/86Sr isotope ratio of the “travertine” mound carbonates are consistent with calculated mixing of spring waters discharging from the crystalline basement and lake water high in dissolved inorganic carbon. This points to an origin of the divalent cations from sublacustrine spring waters. In turn,87Sr/86Sr isotope ratios of green algal reef carbonates of the lake shore are closer to that of the Upper Jurassic carbonates, due to surface run-off from surrounding limestone uplands.

Microbial fabric formation in spring mounds ("microbialites") of alkaline salt lakes in the Badain Jaran sand sea, PR China

The large sandy desert of Badain Jaran Shamo, Inner Mongolia, has several salt lakes located among megadunes with crests as high as 400 m. Most of the lakes are hypo- to hypersaline and alkaline, with pH values between 8.5 and 10. Because of their reef-like aragonitic pinnacles rising from the lake floor, Lake Nuoertu and Lake Huhejaran have been investigated in detail. The porous limestones of the tufa pinnacles ("spring mounds") result from a hydrochemically forced, exopolymer-mediated calcification of cyano-bacteria-dominated microbial mats at sublacustrine springs. The development of their enigmatic fabrics is documented for the first time. Sickle-cell-like and bubble-shaped fabrics reflect successive mineralization during degradation, shrinkage of the organic mucus, and gas formation by bacteria. Fossil analogues are known from the Pleistocene and Miocene (Riescrater lake), but older non-marine, Phanerozoic examples are expected. To the extent that these textures are associated exclusively with alkaline environments, they can be used to test the hypothesis of an alkaline ocean early in Earth history.

Microbial Fabric Formation in Spring Mounds ("Microbialites") of Alkaline Salt Lakes in the Badain Jaran Sand Sea, PR China

The large sandy desert of Badain Jaran Shamo, Inner Mongolia, has several salt lakes located among megadunes with crests as high as 400 m. Most of the lakes are hypo- to hypersaline and alkaline, with pH values between 8.5 and 10. Because of their reef-like aragonitic pinnacles rising from the lake floor, Lake Nuoertu and Lake Huhejaran have been investigated in detail. The porous limestones of the tufa pinnacles (spring mounds) result from a hydrochemically forced, exopolymer-mediated calcification of cyano-bacteria-dominated microbial mats at sublacustrine springs. The development of their enigmatic fabrics is documented for the first time. Sickle-cell-like and bubble-shaped fabrics reflect successive mineralization during degradation, shrinkage of the organic mucus, and gas formation by bacteria. Fossil analogues are known from the Pleistocene and Miocene (Riescrater lake), but older non-marine, Phanerozoic examples are expected. To the extent that these textures are associated exclusively with alkaline environments, they can be used to test the hypothesis of an alkaline ocean early in Earth history.

Lacustrine bioherms, spring mounds, and marginal carbonates of the Ries-impact-crater (Miocene, Southern Germany)

The petrographic investigation of the Miocene Rieslake-carbonates gave rise to a modifiedDunham-scheme for classifying non-marine carbonates. If the fabric is not exclusively the result of hydromechanical or biogenic effects,Dunham-terms were extended by interpretative attributes describing processes responsible for the secondary fabric development (pedogenesis, early meteoric diagenesis). The lowermost investigated section reveals a distinct zonation of the lake shore during humid stages (carbonates of the infra-, eu-, and supralittoral), interrupted by playa-like interstages of arid conditions (desiccated mudflat). Dolomitic successions of sinter-veneered bioherms, built by green algae and cyanobacteria, form an incomplete ‘reef belt’ at the northern crater rim. Bioherm sequences were controlled by a seasonally oscillating lake level and fluctuations of higher order, which correspond to small-scale climatic fluctuations in the range of several hundreds to thousands of years. A superposed facies trend is recognized, which is the result of the decreasing eutrophy, alkalinity, and carbonate supersaturation. This reflects the climatic change to generally humid conditions at the end of Miocene. Originally thrombolitic sublacustrine spring mounds were caused by upwelling groundwater from permeable bedrock. Cement framestones of the mound core are considered to result from fabric alteration within the upwelling ground water and by emersions. Marginal carbonates of the Ries basin, inclusively bioherms, probably were originally Mg-calcitic. Aragonite was restricted to gastropod shells and sublacustrine spring mounds. Dolomitization is interpreted as essentially due to a fluctuating phreatic mixing-zone caused by meteoric groundwater, which underflowed saline water at the soda lake margin. The algal flora comprises cyanobacteria, possible cyanobacteria, green algae, few charophytes, endoliths, and problematic forms. A Recent contamination by endolithic fungi and lichens is evident. Occasionally preserved insect larval tubes, mass accumulations of pupal cases of flies, and arthropod eggs demonstrate that these groups were once a prominent part of the fossil soda lake ecosystem of the Nordlinger Ries.

Karstification without carbonic acid: Bedrock dissolution by gypsum-driven dedolomitization

Aggressive karstification can take place where dolomite and gypsum are in contact with the same aquifer. Gypsum dissolution drives the precipitation of calcite, thus consuming carbonate ions released by dolomite. Lake Banyoles, in northeastern Spain, is a karst lake supplied by sublacustrine springs, and karstic collapse is occurring in the immediate vicinity of the lake. Lake water is dominated by Mg-Ca and SO 4 -HCO 3 , and is supersaturated with calcite that is actively accumulating in lake sediments. Water chemistry, sulfur isotope composition, local stratigraphy, and mass-balance modelling suggest that the primary karst-forming process at at Lake Banyoles is dedolomitization of basement rocks driven by gypsum dissolution. Karstification takes place along the subsurface contact between the gypsiferous Beuda Formation and the dolomitic Perafita Formation. This process is here recognized for the first time to cause karstification on a large scale; this is significant because it proceeds without the addition of soil-generated carbonic acid. Gypsum-driven dedolomitization may be responsible for other karstic systems heretofore attributed to soil-generated carbonic acid.

Internal sources and sinks of water, P, N, Ca, and Cl in Lake Kinneret, Israel

Mass‐balance budgets linked among several materials are used to infer rates of processes affecting Lake Kinneret. Comparisons among budgets reveal the magnitudes of “internal” sources and sinks that cannot be directly inferred from individual budgets.A water budget indicates that ~180 × 106 m3 of sublacustrine spring water plus ungauged surface flow enters the lake annually‐about a fifth the total inflow and two‐thirds as much water as is lost to evaporation. This total ungauged inflow delivers about 90,000 t of Cl yr−1, nine times the stream input. Ca input from total ungauged flow is about a third the stream input, and the net internal Ca sink in the system is sufficient to precipitate 60,000 t of CaCO3 yr−1.Stream delivery of P, mainly as particulate material, is largely sequestered in the sediments (~100 t yr−1). At least 1,100 1 yr−1 of N, primarily as NO3− delivered by streams, are apparently lost to denitrification, while only 200 t yr−1 are sedimented. Cycling of N and P within the lake dominates over throughput in controlling standing stocks. Vertical mixing within the lake may play a dominating role in this cycling. Cycling of Pin the lake can be regarded as “closed”—a sediment‐water column turnover of materials with only minor hydrographic loss from the system. By contrast, N cycling is “open,” with an important net loss to the atmosphere.

Mineral precipitation and diagenesis in the sediments of the Lake Bogoria basin, Kenya Rift Valley

Summary Lake Bogoria is a perennial, saline, alkaline closed lake fed by hot springs and ephemeral runoff. Detailed studies of the sedimentology, mineralogy and chemistry of the late Quaternary sediments, both from exposures around the shoreline and from lake bottom cores, have provided abundant evidence for early diagenesis and mineral precipitation. Marginal fan-deltaic clastics exhibit carbonate (calcite, dolomite), iron oxide, opaline silica and zeolite (analcime, natrolite) cements, especially where groundwater is shallow and subject to evaporative concentration. Travertines associated with microbial activity around hydrothermal springs are predominantly calcite; high temperature, inorganically precipitated travertines are aragonitic. Most are relic deposits. In places, spring carbonates have been silicified (opal-A) or altered to fluorite in response to changing groundwater composition. Fan-delta conglomerates have been hydrothermally altered by alkaline spring waters yielding zeolites (analcime, thomsonite, clinoptiloite, mordenite), clay minerals, opaline silica and magadiite. The lacustrine sediments include prodeltaic clastics, organic oozes and sodium carbonate evaporites. Trona and nahcolite predominate in the central sub-basin. The local occurrence of thermonatrite may be associated with sub-lacustrine hydrothermal activity. In the north subbasin, evaporites are exclusively gaylussite. Sodium silicates (magadiite, kanemite) occur in black organic oozes and formed in an anoxic environment rich in sodium carbonate and dissolved SiO 2 . Other authigenic minerals in the lacustrine sediments include pyrite, siderite, fluorite, zeolites (analcime, mordenite, clinoptilolite), opaline silica (formed from a gel precursor around sub-lacustrine springs?) and vivianite.

Some aspects of the Ca and Sr weathering cycle in the Lake Kinneret (Lake Tiberias) drainage basin

Sr/Ca ratios in the clay (< 2 μ) weathering products of basalt rocks from the Lake Kinneret drainage basin were found to be very similar to the ratios in the rocks, indicating similar depletion intensities for the two elements. In the clays from the scoriae and some lapilli tuffs the ratios were found to be somewhat higher than in the corresponding rocks, indicating preferential retention of strontium in the clays. The ratio in drainage water from these areas was much lower than that obtained by mass balance calculations. The Sr/Ca ratio in Jordan river water draining primarily limestone areas is 2.3 · 10 −3. Very high Sr/Ca ratios in Lake Kinneret water were attributed to the influence of saline sublacustrine springs. The carbonate fraction from recent lake sediments was shown to have the Sr/Ca ratios characteristic for calcite precipitated biogenically in marine environments. The relative enrichment in strontium of the lake water was explained by the intensive precipitation of carbonates with low strontium distribution coefficients.

Pleistocene Algal Pinnacles at Searles Lake, California

ABSTRACT Searles Lake is a playa or dry lake which occupies the central floor of Searles Basin, a northwardtrending graben of the Basin and Range province in southeastern California. During pluvial periods of the Pleistocene epoch deep-water lakes filled Searles Basin, and in two of these lakes more than 500 pinnacled masses of calcareous tufa accumulated in an arm-like bay at the southwest end of the basin. Pinnacles are tower-, tombstone-, and cone-shaped masses and large limestone ridges. Most of the pinnacles are 10 to 40 ft high, but a few reach heights between 100 and 140 ft. Basal diameters or widths range from about 10 ft to as much as 500 ft and average 20 to 30 ft. Seven varieties of tufa compose the pinnacles; one of these varieties is also found in lenticular bodies buried in the lacustrine sediments underlying the pinnacles at the northern end of the bay. It is proposed that the pinnacles were precipitated by algae about the orifices of sublacustrine springs issuing along faults striking N. 65° W., N. 50° W., N. 30° E., N. 55° E., and N. 65° E. in the underlying basement rocks. Deposition of the pinnacles at the southwest end of the bay took place in a lake of Tahoe age which filled Searles Basin more than 32,000 years ago. Pinnacles midway along and at the northern end of the bay formed in a lake of Tioga age which initially flooded Searles Basin about 23,000 years ago and lasted until about 10,000 years ago. Tioga Searles Lake at its maximum stand was approximately 460 ft deep and at its highest stage the surface reached an elevation of about 2000 ft.

The origin of the deposits of tufa in Mono Lake [California

Deposits of calcareous tufa have formed and are probably forming now ill numerous alkaline-carbonate lakes of the western United States. Many of these deposits in the Mono and Lake Lahontan basins are mushroom-shaped and lie at the orifices of what are or were sublacustrine springs. The mushroom-shaped masses are composed of concentrically arranged lithoid, dendritic, and thinolitic tufa with the core usually lithoid and the dendritic, and thinolitic layers alternating concentrically outward. The tufa is shown here to be formed as the result of mixing waters of varying calcium and carbonate content which react essentially in accordance with the solubility product of calcium carbonate in distilled water. The thinolitic and dendritic tufas are believed to be the result of either solution and redeposition within the masses or of varying rates of deposition on the outside of the tower. The possibility is presented that many of the deposits of lithoid tufa on the shores of alkaline lakes are formed by precipitation at the contact of rain-wash and lake water.

Water Temperature and Transparency of the Tugaru Zyûniko Lake Group. (2) Limnological Studies of the Tugaru Zyûniko Lake Group. Part 2

In connection with these lakes, the writer studied in the water temperatures together with the air temperatures on three occasions, namely, in the middle of Aug. 1933, in the begining of July 1934, and on the last of July 1934 being assisted by Messrs. K. KOBA, N. OBARA, I. NAGATU, N. ANDÔ, and K. SIBATA. Accurate observations of deep water temperature were attempted by means of a RICHTER & WIESE reversing thermometer attached to an EKMAN water bottle. The data obtained are given in Table. 5 (pp. 351-355). The effects of climate and lake morphology on the thermal conditions of these lakes appear to be alike in all of them. Since all these lakes, being situated in hollows are well protected from wind, the differences in thermal conditions in summer are due not to winds, but to another cause, namely the inflowing of cold spring and cold river water which, except in the case of Subalpine lakes, which are fed by turbid water of large rivers formed by melting snow, however do not as a rule play so great a rôle in Japanese lakes. We can easily classify them into three thermal types. _??_ The above figures are those for the last ten days of July, 1934. The Ôike Type corresponds to the thermal type of L. Hangetuko, the Otikutinoike type to the Oodairanuma subtype, and the Aoike type to the Tutanuma subtype of the writer, according to his published paper on thermal types of Japanese lakes in summer.(1) The Ôike type includes small and deep lakes with or without warm inflowing water that does not disturb the deep water temperature. The water of the bottom is very cold. A temperature as low as 3.88°C was observed at 25 meters in Ôike lake in July 1934. The Otikutinoike type includes on the other hand, those in which enter a large amount of cold water from the springs in the upper stream. The Aoike type corresponds to the thermal conditions of small spring ponds. Slight dichothermics were discovered in Lakes Aoike and Ôike in the Kosigutinoike Lake Group. That in the former is due to the inflowing of two kinds of springs with different temperatures and salinities at different levels. Although the latter is probably due to sublacustrine springs, it is probable that its warm bottom temperature is a sign of the autumnal warming of the previous year, a possibility recently proposed by FINDENEGG in the case of Austrian lakes. The water of spring ponds were blue and very transparent. A 25cm white disc was visible down to their bottoms (7 to 9 meters). Lakes withh poor phytoplankton production were green, and their transparency exceeded 5 meters. The maximum value in the summer was 8.3 meters. The transparency of lakes with abundant growth of Diatomn, chiefly Astrionella formos and Melosira granulata, were reduced to 2-3 meters. The most turbid water (transparency between 0.7 to 1.6 meters) was in Lakes Itobatakenoike and Gobônoike, due to thick water bloom of the blue algae Anabaena sp. Suspension of fine clay particles derived from the pearlitic tuff that composes the region also helped to reduce the transparency of all lakes of the Tugaru Zyûniko Lake Group.