Ro Data Research Articles

Improved Analyses and Forecasts of Hurricane Ernesto’s Genesis Using Radio Occultation Data in an Ensemble Filter Assimilation System

Abstract Radio occultation (RO) refractivity observations provide information about tropospheric water vapor and temperature in all weather conditions. The impact of using RO refractivity observations on analyses and forecasts of Hurricane Ernesto’s genesis (2006) using an ensemble Kaman filter data assimilation system is investigated. Assimilating RO refractivity profiles in the vicinity of the storm locally moistens the analysis of the lower troposphere and also adjusts the wind analysis in both the lower and upper troposphere through forecast multivariate correlations of RO refractivity and wind. The model forecasts propagate and enhance the added water vapor and the wind adjustments leading to more accurate analyses of the later stages of the genesis of the storm. The root-mean-square errors of water vapor and wind forecasts compared to dropsonde and radiosonde observations are reduced consistently. As a result, assimilating RO refractivity data in addition to traditional observations leads to a stronger initial vortex of the storm and improved forecasts of the storm’s intensification. The benefits of the RO data are much reduced when the RO data in the lower troposphere (below 6 km) are ignored.

Sensitivity of NWP model skill to the obliquity of the GPS radio occultation soundings

AbstractThe impact of accounting for the drift of the tangent point of the global positioning system radio occultation (GPS RO) profiles within a data assimilation system has been investigated. The GPS RO processing centers provide geographic coordinates for each retrieved value within a profile, as well as profile‐representative coordinates. Instead of assimilating each retrieved value with its corresponding latitude and longitude, several numerical weather prediction (NWP) centers have alternatively been using the profile‐representative horizontal coordinates. This study shows that this simplification of the geometry of the GPS RO data should be avoided when possible in order to get optimal results in terms of NWP forecast skill. Copyright © 2011 Royal Meteorological Society

Multiple tropopauses in the tropics: A cold point approach

[1] New criteria for the identification of multiple tropopauses (MTs) in the tropics are proposed using COSMIC GPS RO data during 2006–2008 in the tropical belt (±30° latitude) and radiosonde data from 5 tropical stations during 1999 to 2008 in the ±15° latitude. In the present study, we emphasized that many times the WMO definition is not able to identify all the complex structures, such as MTs, and developed alternate criteria to delineate the MTs over the tropics effectively. The new criteria are based on the cold point tropopause (CPT) and its neighborhood points of inflection in the temperature profile rather than on lapse rate, which is used in the WMO definition. The method using the new criteria (called the cold point method) identifies MTs that occur below (referred to as Lower Tropopause, LT) and above (referred to as Second Tropopause, ST; and Third Tropopause, TT) the CPT. The percentage occurrences of MTs determined using the cold point method differ from those found using the WMO definition. The percentage occurrence of MTs within the tropics maximizes at the equator, reaching higher values in the northern hemisphere (NH) summer and lower values in the NH winter. Among the MTs, the percentage occurrence of the ST is the highest, followed by that of the LT. The percentage occurrence of MTs within the tropics also shows large longitudinal variability.

A scenario for late Neogene Andean shortening transfer in the Camisea Subandean zone (Peru, 12 S): Implications for growth of the northern Andean Plateau

Precise knowledge of the timing of deformation in the Subandean zone of the Andean Plateau is a prerequisite for deciphering the late Neogene growth of the Andean Plateau. In this paper, we report new apatite fission-track (AFT) and vitrinite reflectance (Ro) data for a regional balanced cross section of the Camisea Basin in the central Peruvian Subandean zone, adjacent to the northern Andean Plateau. The balanced cross section shows that the structure of this basin is characterized by a broad internal passive roof duplex and external thrust- related anticlines. The balanced cross-section restoration shows 53 km (39%) of total horizontal shortening. We sampled Paleozoic to Cenozoic sedimentary strata for AFT and Ro analyses along the ∼4-km-thick vertical profile of the Mainique back thrust (passive roof thrust), the innermost preserved Subandean structure. Young components of AFT ages are spread between ca. 6 Ma and ca. 24 Ma. A break in the slope in the AFT ages determines the geometry of the Miocene partial annealing zone and the exhumation of the Mainique back thrust at ca. 6 Ma. Sequential restoration calibrated by AFT and Ro data indicates that the last ∼23 km horizontal shortening were accommodated by the Camisea thrust system over the past ∼6 m.y., giving a mean shortening rate of 3.8 mm/yr. Using this shortening rate for the first ∼30 km horizontal shortening, we calculate that the Andean shortening transfer into the Peruvian Subandean zone initially started at ca. 14 Ma. This result suggests that the transfer of shortening from the northern Andean Plateau to the Subandean zone occurred prior to the removal of dense lithosphere previously reported to have occurred between ca. 10 Ma and ca. 7 Ma. We rather propose that the late Neogene growth of the northern Andean Plateau mostly resulted from a continuous crustal shortening combined with lower-crustal flow.

Validation of Global VTEC Maps Constructed Using Data Derived From COSMIC Constellation

在日固坐标系(地磁纬度和地方时)下, 累积地方时过去24h的COSMIC(Constellation Observing System for Meteorology Ionosphere andClimate)观测资料, 通过对110$sim$750km高度范围内的电子密度进行数值积分得到各掩星点的垂直TEC值, 进而利用Kriging方法插值产生近实时的全球地方时MAGLat2.5°×2h的COSMIC TEC图. 利用2008年1月1日至2010年6月30日共30个月的COSMIC数据, 逐日构建COSMICTEC图, 将其与全球导航卫星系统服务组织(International GNSS Service,IGS)发布的全球电离层TEC图(Global Ionospheric Maps, GIMs)以及OSTM/JASON-2卫星高度计观测值分别进行比对,证明利用COSMIC掩星资料构建全球电离层垂直TEC图是可行的.

Can gravity waves significantly impact PSC occurrence in the Antarctic?

Abstract. A combination of POAM III aerosol extinction and CHAMP RO temperature measurements are used to examine the role of atmospheric gravity waves in the formation of Antarctic Polar Stratospheric Clouds (PSCs). POAM III aerosol extinction observations and quality flag information are used to identify Polar Stratospheric Clouds using an unsupervised clustering algorithm. A PSC proxy, derived by thresholding Met Office temperature analyses with the PSC Type Ia formation temperature (TNAT), shows general agreement with the results of the POAM III analysis. However, in June the POAM III observations of PSC are more abundant than expected from temperature threshold crossings in five out of the eight years examined. In addition, September and October PSC identified using temperature thresholding is often significantly higher than that derived from POAM III; this observation probably being due to dehydration and denitrification. Comparison of the Met Office temperature analyses with corresponding CHAMP observations also suggests a small warm bias in the Met Office data in June. However, this bias cannot fully explain the differences observed. Analysis of CHAMP data indicates that temperature perturbations associated with gravity waves may partially explain the enhanced PSC incidence observed in June (relative to the Met Office analyses). For this month, approximately 40% of the temperature threshold crossings observed using CHAMP RO data are associated with small-scale perturbations. Examination of the distribution of temperatures relative to TNAT shows a large proportion of June data to be close to this threshold, potentially enhancing the importance of gravity wave induced temperature perturbations. Inspection of the longitudinal structure of PSC occurrence in June 2005 also shows that regions of enhancement are geographically associated with the Antarctic Peninsula; a known mountain wave "hotspot". The latitudinal variation of POAM III observations means that we only observe this region in June–July, and thus the true pattern of enhanced PSC production may continue operating into later months. The analysis has shown that early in the Antarctic winter stratospheric background temperatures are close to the TNAT threshold (and PSC formation), and are thus sensitive to temperature perturbations associated with mountain wave activity near the Antarctic peninsula (40% of PSC formation). Later in the season, and at latitudes away from the peninsula, temperature perturbations associated with gravity waves contribute to about 15% of the observed PSC (a value which corresponds well to several previous studies). This lower value is likely to be due to colder background temperatures already achieving the TNAT threshold unaided. Additionally, there is a reduction in the magnitude of gravity waves perturbations observed as POAM III samples poleward of the peninsula.

Application of the (U‐Th)/He Thermochronometry to the Tectono‐Thermal Evolution of Sedimentary Basin—A Case History of Well KQ1 in the Tarim Basin

AbstractThe (U‐Th)/He thermochronometry of apatite and zircon has been used as a new technique to study the tectonic uplift and thermal history of sedimentary basins in recent years. Based on the tested apatite and zircon helium ages data from well samples, an evolution model of apatite He ages with depth and/or temperature is built, which illustrates that the apatite helium closure temperature is about 85°C in the Tarim basin. However, the zircon He ages reveal that these samples hadn't undergone its higher closure temperature. The thermal history since Ordovician in Well KQ1 has been modeled by using the He ages, AFT and Ro data. The modeling result shows that the thermal gradient was about 35.5°C/km in the end of Ordovician, and 33.3~34.5°C/km during the period of Silurian to Devonian, and it decreased to 27.6°C/km in the end of Cretaceous. Therefore, the (U‐Th)/He ages may provide a new tool to rebuilt the thermal history of sedimentary basins, especially for the Low Paleozoic carbonate stratum in Tarim basin which lacks normal thermal indicators.

Palaeogeothermal response and record of Late Mesozoic lithospheric thinning in the eastern North China Craton

Abstract The palaeotemperature recorded by vitrinite reflectance ( R o ) in the pre-Cenozoic uplifted stratigraphic strata, and in Palaeozoic–Mesozoic remnant basins outside the Cenozoic depocentres, has not been overprinted by later thermal events in the eastern North China Craton (NCC). Based on downhole R o data from the Palaeozoic and the Mesozoic subsections, we reconstruct the temperature gradients when the subsections reached their maximum palaeotemperatures in the Middle Triassic and the Cretaceous, and calculate the corresponding heat flow histories since the early Mesozoic. The temperature gradient and heat flow were much higher in the Cretaceous (35–43 °C km −1 and 73–83 mW m −2 , respectively) than in the Middle Triassic and at the present. The high palaeo-heat flow during the Late Mesozoic implies that the thickness of the ‘thermal’ lithosphere at that time was c . 65 km, about half the thickness of c . 135 km estimated for the Early Mesozoic. The change from a stable thermal regime to an active thermal regime took place during the Late Jurassic–Early Cretaceous ( c . 110 Ma). This tectonothermal event was accompanied by extensive surface erosion, and is also evidenced in the areas adjacent to the NCC, such as the South Yellow Sea and East China Sea basins. Our study provides not only geothermal evidence for the Late Mesozoic lithospheric thinning, but also additional constraints on the thinning mechanism, which is currently being debated.

Global monitoring of tropospheric water vapor with GPS radio occultation aboard CHAMP

The global positioning system radio occultation (GPS RO) technique provides a powerful tool for atmospheric sounding which requires no calibration, is not affected by clouds, aerosols or precipitation, and provides an almost uniform global coverage. The paper deals with application of GPS RO measurements from CHAllenging Minisatellite Payload (CHAMP) for the retrieval of tropospheric water vapor profiles. CHAMP RO data are available since 2001 with up to 200 high resolution atmospheric profiles per day. We introduce a new direct method for water vapor retrieval from GPS RO data. Additionally, a 1Dvar algorithm is used for this purpose. The so derived CHAMP water vapor profiles are validated with radiosonde data on a global scale. Here, both methods come to statistically comparable results revealing a negative bias of less than 0.1 g/kg and a standard deviation of less than 1 g/kg specific humidity in the mid troposphere. Potentials of CHAMP RO retrievals for monitoring the mean tropospheric water vapor distribution on a global scale are presented.

Striatal dopaminergic D2 receptor occupancy and clinical efficacy in psychosis exacerbation: a 123I-IBZM study with ziprasidone and haloperidol

Objective The aim of this study was to compare striatal dopaminergic D2 receptor occupancy (D2 RO) induced by ziprasidone and haloperidol and its relationship with clinical response and extrapyramidal side effects (EPS) in patients with acute psychosis exacerbation. Method Twenty patients hospitalized with an acute psychosis exacerbation were randomised in a single-blind study to receive either ziprasidone (80–120 mg/day) or haloperidol (5–20 mg/day) for more than 2 weeks. When stable doses were achieved, data on 123I-IBZM single-photon emission computed tomography (SPECT), as well as data on clinical efficacy (positive and negative symptoms scale [PANSS]) and EPS (Simpson Angus scale [SAS]), were compared between the two groups of patients. Clinical response was defined as a percentage of change of >30% in PANSS. Striatal D2 RO and clinical data were also compared between responders and nonresponders on each treatment group. Results All patients on haloperidol and four patients on ziprasidone showed EPS. Mean D2 RO was significantly higher in the haloperidol (74.7±3.5) than in the ziprasidone (60.2±14.4) group (Mann Whitney U-test [M-W U-test] 8.50; p=0.002). Five patients were responders, and five were nonresponders on each group of treatment. Haloperidol responders and nonresponders did not differ in D2 RO, duration of treatment, doses or EPS. Ziprasidone responders were on higher doses than nonresponders and showed higher D2 RO although below 74%. A positive correlation of ziprasidone D2 RO was found with dose (r Spearman 0.87; p=0.001) and with SAS scores (r Spearman 0.88; p=0.001). Conclusions Ziprasidone induces lower D2 RO and EPS than haloperidol, which is consistent with an atypical antipsychotic profile. A direct relationship of ziprasidone D2 RO with dose, clinical efficacy and EPS has been found in this study. These data suggest that high ziprasidone doses might be more beneficial in patients with psychosis exacerbation and claim for caution regarding EPS appearance with such high dosages.

The use of refractivity retrieved by radio occultation technique for the derivation of atmospheric water vapor content

The use of the GPS radio occultation technique (GPS RO) for retrieving physical and chemical parameters of the Earth's atmosphere has been deeply and widely investigated over the last decade. The technique has proved to be particularly precise in retrieving temperature profiles with high vertical resolution (<1 km). Temperature profiles are obtained for the dry part of atmosphere solving for the system of two equations (Smith and Weintraub equation for refractivity and the hydrostatic equilibrium relationship) with two unknowns (hydrostatic pressure P and temperature T). The system cannot be solved for the lower troposphere because water vapor pressure is not negligible. This makes it necessary to include some additional external information, such as humidity computed from meteorological analyses available from the European Center for Medium-Range Weather Forecasting (ECMWF) or the National Center for Environmental Prediction (NCEP), or zenith troposphere delays estimated from GPS ground station measurements [IAG2001 Scientific Assembly (2001); J. Geophys. Res. 102(D21) (2001) 27,221]. This investigates the possibility of retrieving humidity using the refractivity profiles derived from GPS RO data only. In particular with the proposed method, the dry pressure profiles are obtained fitting the refractivity of the outer troposphere layers (from h=h 250 K up to the stratopause) using the Hopfield dry atmosphere model [J. Geophys. Res. 74(18) (1969) 4487], in which ground pressure and temperature are the parameters to be estimated. In the second step humidity profiles are extracted by subtracting the dry refractivity given by the estimated Hopfield model from the values (wet + dry) retrieved by GPS RO. The refractivity profiles used in the work were retrieved from CHAMP GPS RO data [Geophys. Res. Lett. 28 (2001) 3263]. The humidity profiles obtained with the proposed technique have been compared and validated with profiles retrieved from radwinsonde observations (RAOB) over eight sites. The results are promising in that the new method seems to retrieve profiles comparable to those obtained using the method currently in use (TAO 11(1) (2000) 53).

P.2.059 Comparative efficacy of risperidone, clozapine and haloperidol in the treatment of schizoaffective disorders with manic symptoms

The aim of this study was to compare striatal dopaminergic D2 receptor occupancy (D2 RO) induced by ziprasidone and haloperidol and its relationship with clinical response and extrapyramidal side effects (EPS) in patients with acute psychosis exacerbation.Twenty patients hospitalized with an acute psychosis exacerbation were randomised in a single-blind study to receive either ziprasidone (80–120 mg/day) or haloperidol (5–20 mg/day) for more than 2 weeks. When stable doses were achieved, data on 123I-IBZM single-photon emission computed tomography (SPECT), as well as data on clinical efficacy (positive and negative symptoms scale [PANSS]) and EPS (Simpson Angus scale [SAS]), were compared between the two groups of patients. Clinical response was defined as a percentage of change of >30% in PANSS. Striatal D2 RO and clinical data were also compared between responders and nonresponders on each treatment group.All patients on haloperidol and four patients on ziprasidone showed EPS. Mean D2 RO was significantly higher in the haloperidol (74.7±3.5) than in the ziprasidone (60.2±14.4) group (Mann Whitney U-test [M-W U-test] 8.50; p=0.002). Five patients were responders, and five were nonresponders on each group of treatment. Haloperidol responders and nonresponders did not differ in D2 RO, duration of treatment, doses or EPS. Ziprasidone responders were on higher doses than nonresponders and showed higher D2 RO although below 74%. A positive correlation of ziprasidone D2 RO was found with dose (r Spearman 0.87; p=0.001) and with SAS scores (r Spearman 0.88; p=0.001).Ziprasidone induces lower D2 RO and EPS than haloperidol, which is consistent with an atypical antipsychotic profile. A direct relationship of ziprasidone D2 RO with dose, clinical efficacy and EPS has been found in this study. These data suggest that high ziprasidone doses might be more beneficial in patients with psychosis exacerbation and claim for caution regarding EPS appearance with such high dosages.

Practical identifiability of model parameters by combined respirometric-titrimetric measurements

An earlier study on theoretical identifiability of parameters for a two-step nitrification model showed that a unique estimation of the yield YA1 is possible with combined respirometric-titrimetric data, contrary to the case where only one type of measurement is available. Here, the practical identifiability of model parameters was investigated via evaluation of the output sensitivity functions and the corresponding Fisher Information Matrix (FIM). It appeared that the FIM was not sufficiently powerful to predict the practical identifiability of this case with combined measurements as parameters could indeed be identified despite the fact that the FIM became singular. The accuracy of parameter estimates based on respirometric and titrimetric data and combination thereof was also investigated. Estimation on titrimetric data (Hp) was very accurate and a fast convergence of the objective function towards a minimum was obtained. The latter also holds for estimation on oxygen uptake rate data (rO), however with a lower accuracy. Parameter estimation based on oxygen concentration data (SO) was more complex but resulted in a higher accuracy. Thus, when the highest accuracy is needed it is recommended to estimate parameters initially on Hp and/or rO data, and to subsequently use these parameters as initial values for final, and more accurate estimation on SO data.

Implications of vitrinite-reflectance suppression for the tectonic and thermal history of the Malay Basin

Vitrinite-reflectance profiles for wells in the Malay Basin are generally consistent, and appear at first glance to accurately represent present-day thermal maturities. However, these measured Ro values are much lower than one would expect for wells with such high present-day geothermal gradients. Consequently, calculated Ro values can only be fitted to the measured Ro data by proposing a strong and recent heat pulse. In this scenario, the paleoheat flow was much lower than the present heat flow, and rose to the present levels within the last few million years or less. A plausible tectonic history for the Malay Basin can be constructed that justifies this scenario, because Quaternary volcanics and hot springs are known, and because the last 10 million years has seen renewed subsidence after a period of uplift during the Middle Miocene. However, FAMM (Fluorescence Alteration of Multiple Macerals) data obtained from seven wells indicate that the measured Ro values are much too low in most of the Malay Basin. Ro values have been suppressed by the presence of abundant liptinite and perhydrous vitrinite, probably as a result of marine influence, except along the western margin of the basin and in the far northwestern end. Calibration of the paleoheat flow with F AMM data permits use of a much more constant thermal history at each location. In this model, the main heat flow increased during Oligocene rifting in proportion to the amount of crustal extension, and then has subsequently decayed exponentially to modern levels. Using this paleoheat flow model, hydrocarbons are generated much earlier and maturities in the basin are much higher than if the paleoheat flow model is. calibrated using the measured Ro data. These conclusions in turn indicate that the recent tectonic history of the Malay Basin has probably been rather gentle, in keeping with evidence from sedimentation rates. Although we are not yet certain how common vitrinite suppression is globally or in the Malay Basin, these results indicate that (1) all data sets should be routinely checked for vitrinite suppression, especially in areas where the phenomenon has been recognized; (2) any thermal model requiring a significant recent heat pulse to match measured and calculated Ro values should be viewed with suspicion until validated independently; and (3) errors in reconstruction of thermal and tectonic history can often lead to significant errors in exploration decisions.

Illite/Smectite Diagenesis and Its Variable Correlation with Vitrinite Reflectance in the Pannonian Basin

AbstractThe correlation between illite/smectite (I/S) diagenesis and mean vitrinite reflectance (Ro) data is examined in mudrocks from a hydrocarbon exploration well (geothermal gradient 35°C km−1) from the Great Hungarian Plain of the Pannonian Basin System. The expandability of I/S decreases with depth and there is a change from random to ordered mixed-layering at about 2500 m depth. At this depth Ro is about 0.6%. Comparison of the correlation of expandability and Ro from this study to published data for the Vienna Basin and the Transcarpathian Basin, sub-basins of the Pannonian Basin System, shows that the correlation is systematically different for each sub-basin, according to their thermal histories. In the Vienna Basin (geothermal gradient 25°C km−1), for any given value of Ro, the expandability of I/S is less than in the Transcarpathian Basin (geothermal gradient 55°C km−1) and the sediments are older and more deeply buried. Data from the present study are intermediate. This variation is believed to be due to the effect of time on the smectite-to-illite reaction. Results of an optimization procedure to calculate the kinetics of the smectite-to-illite reaction, using as input the expandability depth profiles, and thermal histories constrained by comparison of observed and calculated Ro data, showed that I/S diagenesis in the Pannonian Basin System can be modelled by a single first order rate equation: −dS/dt=elog(A)−E/RT⋅S where S = fraction of smectite layers in I/S, t = time (Ma), e = exponential function, log(A) = frequency factor = 7.5 (Ma−1), E = activation energy = 31.0 kJ mol−1, R = universal gas constant, and T is temperature in Kelvin. This result also suggests an important role for time. By combining the kinetics of the smectite-to-illite reaction with a kinetic model of vitrinite maturation it is possible to define a domain within which all ‘normal’ (burial diagenesis) correlations between Ro and I/S diagenesis should lie. Such diagrams can be used to identify different thermal histories related to different geotectonic settings and ‘anomalous’ data such as that affected by igneous intrusions.

A Simpler Kinetic Model of Vitrinite Reflectance

We have developed SIMPLE-Ro as a simpler but conceptually compatible alternative to existing kinetic models for vitrinite reflectance, such as VITRIMAT and EASY%Ro. Where calculations are done using the isothermal-segment approach, SIMPLE-Ro is much faster. Where the constant-heating-rate-segment approach is used, SIMPLE-Ro and EASY%Ro are of similar speed. SIMPLE-Ro is based on a single activation energy in each time step, rather than on a range. This activation energy changes as a function of Ro, thus simulating the maturity-dependent change in activation-energy distribution observed in nature. SIMPLE-Ro can be calibrated to any desired distribution of activation energies, or can be calibrated against measured Ro data independent of any other kinetic model.

Thermal Maturity of Bowie Coals in Southern Portion of Piceance Basin, Colorado: ABSTRACT

Although the thermal maturity of coals is determined primarily by age and depth of burial, shallow Cretaceous coals in the Piceance basin of Colorado display anomalously high thermal maturities, indicating that age and present depth of burial are not adequate to explain their high thermal maturities. The objective of this study was to investigate the physical factors that may have contributed to the high thermal maturity of the Piceance basin coals. Vitrinite reflectance (Ro), which increases with coal rank and provides a quantitative index of thermal maturity, was used to measure the thermal maturity of the coals. An examination of published Ro data and Ro analyses of coal samples from mines, outcrops, and well cuttings indicated that most of the thermal maturity of these coals is due to the thickness of overburden that covered the coals in Pliocene time. A plot of vitrinite reflectance versus reconstructed depth of burial during Pliocene time shows a reasonably good fit, however, some Ro values are too high to be explained solely by depth of burial. A map of Ro was constructed using data obtained by subtracting predicted Ro values from actual values. When compared with a geothermal gradient map, most of the positive Ro residuals correlated with that were related to known igneous intrusives. Some anomalous hot spots may be related to unknown buried intrusives. A residual Ro map, modified on the basis of the geothermal gradient map, was combined with the preliminary Ro map (based on reconstructed Pliocene depth of burial) to show that the resultant Ro is due to depth of burial and geothermal hot spots. A final thermal maturity map was used to select areas in the Piceance basin that are most likely to contain thermally mature coals. The same procedure can be used to predict the thermal maturity of coals in other basins. End_of_Article - Last_Page 857------------

Burial Thermal Histories, Vitrinite Reflectance, and Laumontite Isograd: ABSTRACT

The optical reflectance of vitrinite has become the standard basis for quantitative judgments of integrated temperature-time (burial) histories. Inferences about the crystallization temperature of the calcium zeolite laumontite also have been used repeatedly for such purposes. In a few cases, these 2 approaches have been combined or their results compared. As generally employed, neither approach has quantitative validity. Factors other than temperature and time play roles in the way that burial history affects vitrinite reflectance (Ro). In particular, the organic geochemical environment exerts a strong and variable local-to-regional influence on the rate of increase of Ro versus temperature. Hydrocarbon-rich environments retard the rate of Ro increase; hydrocarbon-deficient environments accelerate it. Local (interbed) Ro divergencies up to 0.5% result, and regional (interbasin) divergencies are equal or possibly greater. Much of the scatter in compilation plots of Ro versus TTI may result from such divergencies. Laumontite, where it can crystallize at all, precipitates according to specific stringent requirements of fluid pressure and temperature. The crystallization temperature at the laumontite isograd ranges from 32°C (1 atm) to 193°C (Pf = 1,325 atm). The crystallization rate is geologically instantaneous, completely unlike the time-dependent organic reactions responsible for the progressive aromatization of coal macerals during kerogen maturation, providing an instantaneous pressure-sensitive maximum-recording thermometer. Paleotemperatures to constrain interpretations of Ro data may be one of the greatest values to be gained from studies of diagenetic laumontite. End_of_Article - Last_Page 285------------

GEOLOGIC TIME AS A PARAMETER IN ORGANIC METAMORPHISM AND VITRINITE REFLECTANCE AS AN ABSOLUTE PALEOGEOTHERMOMETER

Substantial published and unpublished data contradict accepted laws of organic metamorphism. Significant amounts of C15+ hydrocarbons and kerogen with significant generation potential exist in sediments which have been buried at high temperatures for long periods of geologic time. Graphite formation and greenschist metamorphism do not occur at model‐predicted burial times and temperatures. Maturation levels for sediments with long (up to 240 million years) burial times are much lower than expected, and conversely, higher than expected for sediments with short (2 million years) burial times. The threshold of intense petroleum generation is not detectable in Plio‐Miocene sediments at minimum temperatures of 160° C.Literature examination reveals that the only solid documentation of time as a controlling parameter in organic metamorphism is in the works of Karweil (1955), Lopatin (1971) and Connan (1974). Scrutiny of these authors' study areas reveals that all have had moderate to extreme paleogeothermal gradients from incipient and aborted rifting, extrusive and intrusive igneous activity, hydrothermal activity, orogenesis and/or uplift and erosion. Levels of organic metamorphism attributed to geologic time by the above authors are better explained by high paleogeothermal gradients resulting from major geologic activity.Mean vitrinite reflectance (RO) data have been compiled from different sedimentary basins currently at or near maximum geothermal gradients with sediment burial times ranging from 2–240 million years. The RO data from these basins show a strong correlation (r = 0.97) of increase in R, with increase in temperature. These same data show no correlation of increasing Ro with increasing burial times for any temperature interval. R, data from sedimentary basins affected by high‐temperature geothermal systems with heating times of only 1,000–10,000 years overlie R, data from these petroleum‐bearing sedimentary basins with burial (heating) times of 2–240 million years.Contrary to accepted thought, there is no evidence from the natural system that petroleum generation‐maturation reactions have first‐order reaction kinetics. By contrast, a substantial body of evidence from petroleum generation‐maturation laboratory studies carried out in closed water‐ wet systems show that these reactions are characterized by multiple‐order reaction kinetics.Geologically older sediments clearly tend to be more organically mature than younger sediments at the same burial temperatures. However, this correlation ismorea reflection that older sediments have had a greater chance of being affected by a major geologic event with an accompanying high heat flow. The major conclusions of this paper are that: (1) geologic time has no observable effect on organic metamorphism; (2) vitrinite reflectance can be used as an absolute paleogeothermorneter; and (3) the accepted models of organic metamorphism at the very least need substantial revision.