Meteor Zone Research Articles

Diagenetic effects on strontium isotopes in shallow-water carbonate sediments from Middle Miocene to Recent

Seawater 87Sr/86Sr ratios have been used as a proxy for continental weathering flux and the partial pressure of atmospheric CO2 (pCO2) in Earth's past, but the fidelity of 87Sr/86Sr records in marine carbonates under diagenesis remains controversial. To investigate this issue, we undertook an integrated chemostratigraphic study of 87Sr/86Sr, δ13C, and δ18O in bulk carbonate from three cores of the South China Sea region: lithified bulk carbonate of Late Miocene to Holocene age in the 607-m-long Xike-1 core (0–11,942 kyr B.P.) from the Paracel (Chinese: Xisha) Islands, and unlithified carbonate sediment in two shallow (<5-m deep) pushcores from the Spratly (Chinese: Nansha) Islands, Jiuzhang A (0–680 yr B.P.) and Jiuzhang B (0–350 yr B.P.). The carbonate sediment of the Jiuzhang cores yielded 87Sr/86Sr signatures matching those of modern seawater, confirming that carbonate sediments can be faithful archives of contemporaneous oceanic Sr-isotopic compositions. Four diagenetic zones were identified in the Xike-1 core based on δ13C and δ18O patterns: meteoric (Unit I, 0–161 m), mixed-diagenetic (Unit II, 161–215 m), and marine diagenetic zones (Unit III, 215–577 m), along with a second meteoric zone (Unit IV, 577–607 m). The bulk‑carbonate 87Sr/86Sr profile was not strongly altered by dolomitization or other processes in any of the diagenetic zones (although minor effects were observed in the marine zone). This study concludes that marine carbonates are likely to retain primary seawater Sr isotopic signatures even after undergoing multiple stages of diagenesis. This study provides detailed 87Sr/86Sr secular variations and continental weathering history since 12 Ma.

Radio meteor physics – a comparison between techniques from 1945 to the mid-1970's

A description of the physics of radar meteors from 1945 to the mid-1970s is presented. Concrete designs of various radars in different countries are presented. Harvard project is the best documented of these early radars, and we will focus on that radar. Application of multi-receiver stations for orbit determination became relatively common, especially with the advent of the IGY in 1957. Canada also built the Springhill Observatory around the time of the IGY, but of special note was the construction of several meteor radars in the USSR. The contribution of Kashcheyev and his scientific group to the development of radar meteor technologies was emphasized. A discussion of some equipment options of Balakleya geophysical complex in different years was held. Problems of meteor radar technologies in solving problems of astronomy and geophysics are noted. Meteor became a mainstay of upper atmospheric research into dynamical processes after 1960's. Such research was undertaken at multiple sites all over the Western global arena as well as in the USSR. In attention is paid to the history of changes in the methods of obtaining, processing and storage of meteor information. Some aspects of the application of innovative technologies in meteor radar systems were discussed, primarily in the study of winds and atmospheric circulation in the meteor zone. The advent of personal computers, plus the somewhat simultaneous development of digitizers in the early 1970's, was a major breakthrough for many areas of scientific research and studies. This work is the first part of a planned review of radar meteor physics and related technologies from 1945 to 2020.

Some features of the day-to-day MLT wind variability in winter 2017–2018 as seen with a European/Siberian meteor radar network

We present results of wind measurements near the mesopause carried out with meteor radars (MRs) at Collm (51°N, 13°E), Obninsk (55°N, 37°E), Kazan (56°N, 49°E), Angarsk (52°N, 104°E) and Anadyr (65°N, 178°E) from October 1, 2017 till March 31, 2018. The Collm and Kazan MRs are SKiYMET radars with vertical transmission and radio echo height finding, while the other radars operate with horizontal transmission and without height finding. We paid particular attention to the meridional wind variability with periods of 4–6 days and 9–11 days. The waves with these periods are seen as spots of the wave activity in the wavelet spectra and include oscillations with different periods and different discrete zonal wavenumbers. These wave packets successively propagate as a group of waves from one site to another one in such a way that they are observed at one site and almost disappear at the previous one. The 4–6 wave group includes planetary-scale oscillations (individual spectral components) which have eastward phase velocities and mostly zonal wavenumbers 2 and 3, and the vertical wavelength exceeds 70 km at middle latitudes. The source of the oscillations is the polar jet instability. The wave group itself propagates westward, and the amplitudes of wind oscillations are approximately 5–6 m/s as obtained from the wind data averaged over the meteor zone. The 9–11 day wave set propagates westward as a group and mainly consists of spectral components which have westward phase velocity and zonal wavenumber 1. Amplitudes of these wind perturbations strongly vary from station to station and can reach, approximately, 8 m/s. The vertical wavenumber is 0.014 km−1 as taken from the Kazan and 0.05 km−1 according to the Collm data. We obtained a global view on the waves by using the AURA MLS geopotential data. We found a good correspondence between wave features obtained from the MR wind measurements and the MLS data. To our knowledge, such a wave propagation of planetary wave in the mesosphere/lower thermosphere (MLT) region has so far not obtained much attention.

Simulation of the parameters of the meteor radar system in order to optimize its operation

Since 1966 the Meteor Automated Radar System (MARS) has been operating at the Balakleya scientific testing ground of the Kharkov National University of Radio Electronics, which had provided with the unique scientific data on meteors and the earth's atmosphere.For a long time of operation the equipment has undergone considerable moral and physical obsolescence. The need to continue the meteoric research on the one hand, and the inability to do so on the available equipment on the other hand, requires the modernization of the complex with regard of the new objectives and new opportunities.Simple switch to the new element base without taking into account the changing of the working conditions and new research objectives is not reasonable. It is necessary to revise a number of parameters of the available equipment. A large number of factors can be found by means of modeling of the improved complex. However, the simulation can not be carried out without a major component - the model of the meteor-trail reflections. Therefore, the primary problem is to develop a model that would include the ground-based research equipment parameters and the model of the processes occurring in the meteor zone as well.The article proposes the structure of this model, presents the analytical concepts for some modeling stages and their graphic interpretation. The above model is implemented as a computer program. The above model is implemented as a computer program. It differs by the change of the signal amplitude in the meteor trail formation process; the ability to model meteor propagation to the "ultra-short" routs - between the main and offset points; as well as to determine the trail coordinates, which is necessary for further determination of the meteor radiant.

Fault-related fluid flow history in shallow marine sediments from carbonate concretions, Crotone basin, south Italy

We present the results of a multidisciplinary study on the relationships between the structural architecture of an extensional fault system in poorly lithified shallow marine sands and the associated pattern of diagenetic carbonate concretions. Based on their shape, spatial distribution, cement texture and chemistry, and isotopic signature, carbonate concretions are grouped into (1) tabular (encompassing also nodular and lens-shaped) concretions developed within the fault zones, and (2) elongate and coalescent strata-bound concretions formed adjacent and mostly parallel to fault zones. Cement chemistry and morphology, as well as stable carbon–oxygen isotopic signatures, indicate that tabular concretions formed during early diagenesis in the vadose mixing marine–meteoric zone, possibly during coseismic rupture propagation and, in the interseismic periods, as a result of slow capillary suction along the low-permeability fault zones. On the other hand, elongate concretions formed after regional uplift and during telodiagenesis by precipitation from meteoric, phreatic water flowing parallel to the fault zones, which acted as a hydraulic barrier. The concretion patterns record the evolution of fluid flow orientation and the changing chemistry of fault-zone fluids, which were fundamentally driven by fault system propagation and resulting fault architecture during two major diagenetic stages.

Authigenic dolomite cementation in the Upper Cretaceous Phosphate Formation, Western Desert, Egypt

The Upper Cretaceous Phosphate Formation in the Western Desert of Egypt displays a characteristic facies association that includes marine phosphorites interbedded with black shales and glauconitic sandstones. The upper part of the formation is characterized by the presence of thin phosphatic beds, which are filled-extensively-with disordered and non stoichiometric (mean MgCO 3 = 41.4 ± 0.34 mol%) authigenic dolomite cement. SEM and the back scattered images of these coarse crystalline dolomite cements reveal that they display planar euhedral crystal boundaries, polymodal crystal size distribution and variable inclusion pattern. The relatively low and wide ranged δ 18O (− 0.87 to − 4.15‰ VPDB) values of the dolomite cements coupled with their depleted Sr (mean = 187 ± 26 ppm) and high iron and manganese values (mean = 6851 ± 554 ppm and 11599 ± 229 ppm respectively) invoke that they were formed from mixed hypo-saline fluids within a mixing marine–meteoric zone probably during a low stand period at the vicinity of the Maastrichtian/Early Tertiary unconformity. Meanwhile, their negative δ 13C (− 1.31 to − 3.56‰ VPDB) values argue for a possible involvement of isotopically light carbon, derived from degradation of organic matter, during their precipitation.

Exploration into the Physical Factor of Meteor Detectibility

The comparative analysis of electron density models by Lebedinets and Kostylev was performed. The influence of the chosen model of the ionosphere meteor zone on the radio meteors noticeability was shown. Results of the MARS complex noticeability factor estimations were obtained. It was shown that the software developed can be used in future scientific investigations when obtaining real distributions of meteors' speed.

Morphology of nighttime ion, potassium and sodium layers in the meteor zone above Arecibo

We use over ten years’ incoherent scatter radar (ISR) data and several years of potassium and sodium resonance lidar data to study the morphologies of ion, potassium, and sodium layering activities in the mesopause region above Arecibo, Puerto Rico. A tidal effect is clearly seen in the layer trajectories of all three species. Semidiurnal ion layer tidal structure is observed in the spring, summer, and fall at above 105 km altitude. Below 100 km altitude, the most consistent ion layers occur at 95 km altitude at 1800 local time (LT) during most time of the year except in the summer. The strongest ion layers occur around sunset hours at 106 km altitude in the summer. Although both potassium and sodium are alkaline metals, their layers exhibit very different characteristics. Throughout the mesopause region, sodium layer trajectories are always downward throughout the year, in response to the diurnal tide in this region. The tidal effect on the potassium layers can be seen mostly in the 90–95 km altitude region. While the mesopause height does not appear to be related to the seasonal variations of the potassium layers centroid height, it does appear to have great influence on that of the sodium layers. The potassium layer abundance is highest in the summer and a secondary peak occurs in the winter. The semiannual variation of the potassium layer abundance may provide an important clue to a better understanding of the potassium chemistry.

CHEVRON-TYPE HALITE AND NODULAR ANHYDRITE IN THE TRIASSIC SUBSURFACE EVAPORITES OF THE IONIAN ZONE (WESTERN GREECE)

Samples of the Ionian zone (western Greece) subsurface evaporites, obtained from well cores in salt bodies and in depths ranging from 1000 to 3500m, are texturally studied. Layered halite rocks consisting of chevron-type halite crystals represent most of the specimens. Between the chevron -type halite crystals, which are fluid inclusions-rich, clear halite without inclusions has been diagenetically formed by dissolution and precipitation processes. Anhydrite always accompanies the halite rocks as crystals or nodules. No-occurrence of gypsum has been detected. Along halite grain boundaries dolomite crystals occur. Dolomite grew on halite crystal surfaces as an early diagenetic mineral. Some dolomite crystals are clearly derived by replacement of anhydrite crystals. Halite layers are rich in clay and carbonaceous material favoring reducing environment (presence of pyrite crystals). Chevron-type halite supports accumulation beneath a body of brine, possibly recording annual precipitation cycles. However, its close association with nodular anhydrite cannot exclude the possibility of halite development, in a shallow-water or emergent environment by displacement from capillary brines. Since the studied halite crystals show evidence of mineral replacements and displacement, we suggest an analogous mechanism including accumulation from a standing body of brine and subsequent textural modification in the groundwater zone. Although, Ionian subsurface evaporites have undergone the above-mentioned diagenetical processes, they still reU in their primary textural characteristics. Real brecciation has not been detected in subsurface, except of an in-situ pseudo-brecciation. This observation clearly shows that the outcropping evaporite solution-collapse breccias were formed in the realm of meteoric zone, after the Ionian zone orogenesis.

Ozone concentration at meteor heights determined from forward-scatter radar echoes

The ozone concentration has been measured in the meteor zone using a method of radar echo duration distribution suggested by Jones and Šimek (1995). Data obtained by the forward-scatter system during the Lyrid meteor shower period in five consecutive years 1992–1996 agree with the Solar Mesosphere Explorer results for the same heights of 95 km. The mean value of the ozone concentration [O 3]=(1.56±0.05)×10 14 m −3 has been derived from a total of 6596 radar meteor echoes with duration ≥1 s. The results for individual years indicating a possible decrease in [O 3] are discussed.

Long period wind oscillations in the meteor region over Trivandrum (8°N, 77°E)

The spectra of long period wind oscillations in the meteor zone over Trivandrum are presented. The spectral amplitudes were found to be much larger during June 1984 when the QBO in the stratospheric zonal wind was in a strong easterly phase compared with June 1987 when the zonal winds at the altitude of maximum QBO were weak westerlies. Zonal wind amplitudes for periods of 15 and 5 days were found to be most significant during these two June months. The amplitudes of these two oscillations in meridional wind were found to be as large as the amplitudes in the zonal wind. The vertical wavelength in both zonal wind and meridional winds of the 15-day oscillation is very large whereas for the 5-day oscillation the vertical wavelengths were 80 and 65 km during June 1984 and June 1987, respectively. The results are discussed.

Sunrise and range distribution of meteors

The influence of the sunrise effect on the ionization of the meteor zone has been found from the comparison of meteor echo range distributions obtained by the meteor radars at Springhill (120 000 echoes) and Budrio (7000 echoes) during the activity of the Geminids meteor shower. The position of the maximum of the echo range distribution corresponding to the motion of the shower radiant was found to be shifted to larger distances, as expected from the sunrise effect, independently of different antenna systems of the two equipments.

Carbonate Dissolution within the Meteoric and Mixing Zone Diagenetic Environments: Porosity Development within Late Pleistocene Reef and Reef-Associated Lithologies, Southeastern Barbados: ABSTRACT

Carbonate Dissolution within the Meteoric and Mixing Zone Diagenetic Environments: Porosity Development within Late Pleistocene Reef and Reef-Associated Lithologies, Southeastern Barbados: ABSTRACT

Tidal winds in the radio-meteor region over Trivandrum (8.5°N, 77°E)

Wind measurements using a meteor trail radar which performed during two June solstice and three December solstice months were analysed to study the tidal winds over Trivandrum (8.5°N). The ter-diurnal (8 h) component of wind was found to be as significant as the diurnal and semi-diurnal components. The modulations in the altitude profiles of amplitude and phase of the tidal wind components are interpreted to be due to higher order tidal modes. The amplitudes and vertical wavelengths of the tidal modes observed in the meteor zone are discussed.

Investigation of Aluminum Mass-Transfer in Sandstones, Southern San Joaquin Basin, California

Dissolved plagioclase is the main aluminum source and authigenic caolinite is the principal aluminum sink in quartzofeldspathic San Joaquin basin sandstones. Samples include Oligocene to late Miocene age marine sandstones, which presently contain modified-marine and meteoric pore fluids. Plagioclase porosity and kaolinite are found from 600-1,500 m (30-50C) in the meteoric zone and from 2,100-3,300 m (80-105C) in the modified-marine zone. Leached plagioclase is absent in some meteoric-zone reservoirs but appears in up to 60% of uncemented sandstones in other reservoirs. In contrast, skeletal plagioclase is pervasive in Stevens sandstones, appearing in greater than 80% of all uncemented samples. Point-count data imply that aluminum is conserved in Stevens sandstones with modified-marine pore waters, despite enrichment in organic acids and anions capable of mobilizing aluminum in soluble complex ions. Some Stevens sandstones have excess kaolinite but no samples have a pronounced aluminum deficiency. The average Stevens sandstone has gained 0.06 {plus minus} 0.1 g of aluminum per 100-cm{sup 3} sample. Aluminum is conserved in Stevens reservoirs with high-temperature, slow-moving pore fluids. In contrast, aluminum may be exported from sandstones subject to meteoric flushing, although the aluminum deficiency is not extreme and complementary zones of aluminum import are not found. Average aluminummore » loss from Vedder sandstones in meteoric reservoirs is 0.3 {plus minus} 0.1 g per 100-cm{sup 3} sample. Aluminum apparently is mobilized in low-temperature, fast-moving meteoric waters, which may be focused along shallow faults and fractures, resulting in local zones of intense diagenesis.« less

The Observations of Meteor Trail Made with Chung-Li VHF Radar

Chung-Li VHF radar is a low power(average transmitted power is only 3.6kw)and small aperture(physical antenna area is 4800 m^2)coherent ST radar. This radar can effectively observe the mesospheric meteor events if the appropriate radar parameters are set. In this paper, some results of meteor events observed over Taiwan area by Chung-Li VHF radar (operating frequency is 52 MHz) are obtained. We find that the height distribution of meteor trail is between 80km and 120km, and the peak value is occurred at about 93km. There is a remarkably diurnal variation in the appearance of meteor event, maximum at the morning hour and minimum around the dusk. The average life time of the meteor trail is about 0.35s. Furthermore, the diffusive coefficients in the meteor zone, calculated from the in form ationof life time of meteor tail, are also estimated and between 0.1m^2s^(-1)to 1m^2s^(-1). These results are quite consistent with the others' observations.

Water/Rock Interaction Efficiency and Seawater Dolomitization in the Eocene Avon Park Formation, Floridan Aquifer: ABSTRACT

The Floridan aquifer has often been proposed as a system of extensive meteoric carbonate diagenesis and mixing zone dolomitization. However, the dominance of marine isotope (C, O, {sup 87}Sr/{sup 86}Sr) and trace element (Sr, Fe, Mn) compositions in dolomites and limestones in the Eocene Avon Park Formation, Floridan aquifer, suggests that the very active low temperature meteoric groundwater system has, over the past 40 m.y., been an inefficient mechanism of diagenesis. {delta}{sup 18}O values of all but two replacement dolomites sampled range from +2.0 to +5.1 (PDB) with high Sr concentrations (90-325 ppm), indicating dolomitization by near-normal marine water involving no significant interaction with meteoric groundwater. The two {delta}{sup 18}O-depleted (0.0 {plus minus} 1) dolomites have low Sr concentrations ({approximately}100 ppm) suggesting limited recrystallization in meteoric water. Several dolomite samples have radiogenic {sup 87}Sr/{sup 86}Sr compositions (0.70810-0.70883 {plus minus} 2), but have heavy oxygen isotope compositions (> +2.0) and high Sr concentrations (<200 ppm) suggesting precipitation from cold Miocene age or younger seawater that circulated through the Florida platform. Most limestone stable isotope compositions cluster around marine values (({delta}{sup 18}O = {minus}1 to +1, PDB) {delta}{sup 13}C = +0.5 to +2.5) and have Eocene seawater {sup 87}Sr/{sup 86}Sr compositions (0.70775more » {plus minus} 2 to 0.70779 {plus minus} 2) with 400 to 500 ppm Sr. Isotopic compositions of limestones from the east coast of Florida are all within these ranges. Only some limestones from central Florida and the west coast contain depleted stable isotopic compositions and low Sr concentrations. The sample with the most depleted stable isotope values has a radiogenic {sup 87}Sr/{sup 86}Sr composition (0.70870 {plus minus} 2), suggesting that diagenetic meteoric water migrated through post-Miocene strata.« less

Some aspects of the diurnal and semidiurnal tidal wind field in meteor zone

The diurnal and semidiurnal tidal wind field variations in the altitudes between 80 and 100 km of the earth’s atmosphere over a mid-latitude station are studied by means of the phases of the zonal and meridional wind measurements made at Atlanta (34° N, 84° W). The rotation of diurnal tidal wind vector is seen to be clockwise at lower heights (80–86 km), swinging between clockwise and anti-clockwise at intermediate heights (88~96 km) and anti-clockwise at higher heights (96–100 km). The senses of rotation of diurnal and semidiurnal tidal wind vectors are compared between the stations located in the same and opposite hemispheres. The results are consistent with the tidal theory in the case of Atlanta and Adelaide (35°S, 139° E) whereas in the case of other stations considered in the present study, they showed marked variations.

Petrogenesis of Cenozoic, Temperate Water Calcarenites, South Australia: A Model for Meteoric/Shallow Burial Diagenesis of Shallow Water Calcite Sediments

ABSTRACT The Gambler Limestone is one of several extensive, shallow-water shelf carbonates of Eocene to Miocene age exposed along the southern margin of Australia. It is a muddy to grainy bryozoan calcarenite, with accessory benthonic foraminifers and echinoids. The sediments, originally composed almost entirely of calcite or Mg-calcite, have been in vadose and phreatic environments for over 10 Ma, yet are virtually unlithified. The only cements of any consequence are epitaxial on echinoids. Numerous karst features, dolines, caves, speleothems and surface karren attest to prolonged residence in the meteoric zone. The Gambler Limestone is presently one of the best fresh water aquuifers in Australia. Most flow occurs through intergranular pores in sediments with over 30% porosity. Cementation is by minor intergranular pressure solution which has developed under overburden of less than 100 m. The overlying Naracoorte Limestone (Miocene), a calcarenite of warmer water aspect, contains numerous aragonite molds and is well-cemented. We propose that such cool water limestones are a better model for the meteoric diagenesis of calcite sediments of all ages than are aragonite-rich tropical sediments. It is probable that many similar early and middle Paleozoic calcite limestones may have been in the meteoric zone for prolonged periods yet contain little or no petrographic or geochemical record of such exposure.

Tides in the middle atmosphere

Some recent progress in the study of tides in the middle atmosphere are reviewed, with special emphasis placed on radar observations at high latitudes, as well as data analysis methods used in the calculation of tidal structures. Observations carried out outside the meteor zone with MST radars and satellites are also presented. Theoretical and numerical advances on the diurnal tide are extensively discussed. Finally, some outstanding problems, which we hope will be solved in the near future are raised: the existence of hemispheric asymmetries in tidal structure; the role played by non-migrating modes at meteor heights and short time scales variations of tides.