Pore Volumes Of Water Research Articles

Slope stability considering multi-fissure seepage under rainfall conditions

Fissures form the channel for rainwater infiltration, which accelerate the infiltration of rainwater into slope bodies, hence its important impact on the seepage field and stability of the slope. In this paper, taking one landslide of Liang-Wan freeway as the research object, firstly, the equivalent permeability coefficient method is used to homogenize the fissured soil. Then considering the boundary conditions of rainfall infiltration and groundwater level, a fluid–structure coupling model is established based on saturated–unsaturated seepage theory, and evolution characteristics of seepage, displacement and stress of the slope are studied. Based on these, the slope stability coefficient is determined. The results show that the rising rate of pore water pressure and volume water content of topsoil increases when multi-fissure seepage is considered, and the pore water velocity is larger in the local seepage range of fissures. With the increase of buried depth, the closer to groundwater level, the influence of multi-fissure seepage gradually weakens. The theoretical calculation results of slope displacement are more consistent with the field monitoring results. With the increase of rainfall time, the stability coefficient of slope decreases gradually, and the rate and range of decrease are greater.

Evolution of water content and suction of Opalinus Clay from recovery at the drilling site to handling in the laboratory

Advanced geotechnical engineering applications, such as shale gas extraction, CO2 geological sequestration, and geological radioactive waste storage, often involve various types of shales located at significant depths. Shales exhibit mechanical properties that are highly influenced by their hydration state and are exposed to substantial stress relief during extraction from considerable depths. This results in the development of elevated total suction (free energy per unit volume of pore water). While water content measurements are conventionally employed for characterizing these materials, ongoing discussions and uncertainties persist regarding the relevance and representativeness of laboratory suction measurements, particularly in light of potential influences stemming from core extraction and conditioning processes. A recent extensive borehole drilling campaign has provided a unique opportunity to offer scientific insights into specimens of Opalinus Clay shale, extracted from various locations and depths. These specimens were examined in their freshly extracted on-site condition and their freshly opened condition in the laboratory. Notably, it has been observed that suction and water content measurements acquired on-site immediately after core extraction differ from those obtained in the laboratory. The evolution of suction and water content from the field to the laboratory is closely linked to the main drying water retention behavior of the geomaterial.

A Temperature-Controlled Apparatus for Gas Permeability under Low Gas Pressure

The measurement of soil gas permeability is influenced by the temperature and pressure fluctuation in the low gas pressure region. In order to investigate these influences, a soil temperature-controlled apparatus connected to a low-gas-pressure supply equipment is proposed in this study. The low constant gas pressure is supplied by two Mariotte bottles, by which the airflow rate is measured. Meanwhile, the soil specimen is controlled by a temperature-controlled apparatus. During the test, the negative pore water pressure and volume change of the soil specimen are measured. Through the temperature-controlled apparatus, it is observed that as the temperature increases from 25 °C to 60 °C, there is a corresponding increase in soil sample porosity by 5.4%, while the negative pressure of pore water decreases by 11.1%. This can be attributed to the reduction in the surface tension of contractile skin caused by elevated temperatures. Furthermore, due to variations in gas viscosity with temperature, there was a significant decrease in the gas flow rate by 50.5%. And, the relationship between permeability and volumetric gas content at different temperatures in low-pressure regions well confirms the existing power-law model. In addition, the existence of a temperature-independent critical negative pore water pressure is observed, beyond which the intrinsic permeability remains constant. At 36 kPa of negative pore water pressure, the intrinsic permeability at 60 °C exhibits an 81.8% reduction compared to that at 25 °C. This decline in intrinsic permeability can be attributed to a diminished pore connectivity, resulting from elevated temperatures.

Seismic Performance of Drained Piles in Layered Soils.

The provision of drains to geotechnical elements subjected to strong ground motion can reduce the magnitude of shaking-induced excess pore pressure and the corresponding loss of soil stiffness and strength. A series of shaking table tests were conducted within layered soil models to investigate the effectiveness of drained piles to reduce the liquefaction hazard in and near pile-improved ground. The effect of the number of drains per pile and the orientation of the drains relative to the direction of shaking were evaluated in consideration of the volume of porewater discharged, the magnitude of excess pore pressure generated, and the amount of de-amplification in the ground's motion. The following main conclusions can be drawn from this study. Single, isolated piles and a group of drained piles were tested in three series of shake table tests. Relative to conventional piles, the drained piles exhibited improved performance with regard to the generation and dissipation of excess pore pressure and stiffness of the surrounding soil, with increases in performance correlated with increases in the discharge capacity of the drained pile. The acceleration time histories observed within the pile-improved soil indicated a coupling of the rate and magnitude of porewater discharge, excess pore pressure generated, and de-amplification of strong ground motion. The amount of de-amplification reduced with increases in the number of drains per pile and corresponding reductions in excess pore pressure. The improved performance should prove helpful in the presence of sloping ground characterized with low-permeability soil layers that inhibit the dissipation of pore pressure and have demonstrated the significant potential for post-shaking slope deformation.

Influence of the fracture on the seepage stability of loess slopes

The development of fractures in loess slopes often has a great influence on the stability of slopes. In this paper, taking the homogeneous slope model as an example, fractures with different distances and depths from the slope top angle are provided at the top of the slope. Firstly, the influence of single fracture location and depth on slope stability is analyzed, and after the most unfavorable location and depth of the fractures are determined, the influence of the slope top fractures on the slope seepage field and slope stability under the conditions with and without rainfall is studied secondly. The results show that with the increase of the distance from the fracture to the top angle of the slope, the safety coefficient of the slope shows the change law of decreasing first and then increasing. The critical fracture depth corresponding to the fractures at different locations is different, and when the critical fracture depth is exceeded, the slope safety factor tends to be stable. At the end of the rainfall moment through 1-1 section to analyze, it is found that at this time the pore water pressure and volume water content of the soil at the bottom of the fracture at different depths are greater than those of the upper soil, and the shallow fracture has less influence on the seepage field of the slope, and through 2-2 section it is found that the pore water pressure and volume water content in the soil far from the fracture are greater than those of the soil near the location of the fracture. When 288 h after the end of rainfall, the pore water pressure and volumetric water content of the soil around the fracture in section 2-2 were greater than those far from the fracture location. With the passage of time, the pore water pressure at the location of the fracture gradually dissipated and the corresponding volumetric water content gradually decreased, indicating that the fracture had an obvious influence on the characteristics of the seepage field in the soil at different times of rainfall. Under the condition of no rainfall, there exists a critical depth of fractures affecting slope safety stability, while under the condition of rainfall, the slope safety coefficient continuously decreases with the increase of fracture depth, and there is no critical fracture depth. The research results promote the understanding of the safety and stability of loess fracture slopes and provide a reference for slope management.

Simulation of cemented paste backfill (CPB) deposition through column experiments: comparisons of field measurements, laboratory measurements, and analytical solutions

Estimating the as-placed properties of mine backfill is fundamental to optimizing the safety and productivity of underground mines. For cemented paste backfill (CPB), an important consideration is the extent to which self-weight consolidation during deposition may reduce the void ratio and enhance the binder’s effectiveness. Field monitoring and sampling campaigns can help investigate this phenomenon but they are expensive and logistically difficult. Therefore, mesoscale column experiments are performed in the controlled laboratory environment to better understand the coupling between self-weight consolidation and cement hydration. In this paper, columns are backfilled with uncemented paste tailings and with CPB and the pore water pressure, electrical conductivity, and volume changes are monitored during and after backfilling. The pore water pressure profiles at the end of backfilling are compared with an available analytical solution and restrictions on the solution’s validity are identified. Void ratios of samples taken from columns are compared with the ones obtained from field samples and the similarity indicates the filling conditions simulated in the laboratory are representative of field conditions. The changes in void ratio after curing were small compared to the initial void ratio of fresh CPB. The tests’ results help explain why self-weight consolidation during backfilling is not significant at the studied mine, which may be the case for many other mining operations as well.

Accurate determination of rare earth elements in small volumes of porewater from marine sediments by laser ablation solution sampling ICP-MS

An accurate method for ultratrace rare earth elements quantification in highly saline water with small volume sample consumption by laser ablation solution sampling ICP-MS.

A method for a fast and economical in situ collection of pore water in sandy sediments

Marine sediment represents one of the most significant carbon reservoirs. Extraction of pore water from the uppermost 10 cm of the sediment column, just below the sediment-water interface, in coastal environments can be used to assess the rapid chemical changes caused by extensive subsurface biological and chemical reactions. However, owing to relatively large grain size of the sediment in some shallow coastal environments, sediment and pore water mixes quickly making collection of core samples for pore water extraction extremely difficult. Here, we present a simple method utilizing Rhizons to collect in situ pore water from coastal environments. We conducted both ex situ and in situ experiments, using fluorescein as a tracer, to understand the influence of overlying water during pore water collection through this method. These experiments also allowed us to assess the volume of pore water collected before fluorescein is observed in the samples at different vertical depths within the sediment column. We found that: 1. discarding the initial 2 mL of water minimizes the memory effect, 2. collection of 10 mL of water avoids interference from surrounding pore water and the overlying water column and 3. a vertical resolution of minimum 2 cm could be attained for sediments with grain size of 1 mm and less. We finally present data from two linear transects from different sites in the Gulf of Aqaba. Results from these case studies demonstrate expected patterns of high concentrations of iron and hydrogen sulfide in pore water from the sediment where surface coloration suggested iron and sulfate reduction was dominating, respectively. Both case studies, therefore, independently validated the Rhizon sampler method for collecting pore water in situ from marine sediments in coastal environments.

A giant sand injection complex: Processes and implications for basin evolution and subsurface fluid flow

Giant sand injection complexes form, intricate, basin-scale fluid plumbing systems and document the remobilisation and intrusion of several tens of cubic kilometres of sand within the shallow crust in stratigraphic units 1009s metres thick. This is the first detailed and extensive account of the Panoche Giant Injection Complex (PGIG), a regionally significant outcrop (>300 km²) and part of a larger subsurface development (>4000 km²) identified in boreholes and on seismic reflection data. Magnificent exposure of the PGIC occurs along the north western margin of the San Joaquin Valley and presents the opportunity to examine the regional geological significance of a giant sand injection complex and its origin in the context of a late Cretaceous – early Paleocene forearc basin. Between 25 and 49 km³ of sand were remobilised and injected, at least 0.35 km³ of which extruded onto the paleo-seafloor. Large sandstone intrusions often >10 m thick and laterally extensive on a kilometer scale formed saucer-shaped intrusions, wing-like intrusions and a variety of sill geometries along with volumetrically smaller randomly oriented dikes in a 200–300 m thick interval. Dikes prevail below and above this interval, some reaching the paleo seafloor and extruding sand. Networks of propagating hydrofractures form intensely brecciated host strata, some of which were intruded by sand. All intrusions formed in a single pulsed event in which the most intense hydrofracturing caused by supra-lithostatic fluid pressure occurred approximately 600 to 800 m below the paleo seafloor. A crudely orthogonal arrangement of dikes is preserved with most oriented normal, and less commonly oriented parallel to the oceanic trench associated with the late Mesozoic to early Tertiary North Pacific subduction. Dikes orthogonal to the trench opened against the minimum horizontal stress, which was parallel to the trench. Dikes parallel to the trench opened against the regional maximum horizontal stress along minor faults formed in extension caused by shallow crustal deformation. There is no evidence that compressional tectonics influenced the onset of elevated pore fluid pressure necessary to promote sand injection. However, tectonic compression was responsible for creating the basin physiography that locally increased subsidence and accelerated chemical diagenesis in the basin centre. PGIC outcrop, located along the basin margins, was unlikely to have experienced heating above 70 °C, equivalent about 2 km burial, so the effects of chemical diagenesis in the host strata of the injection complex had negligible potential to evolve significant pore water volume. In a deeper part of the basin approximately 150 km to the south, lateral equivalents of the host strata were subjected to heating >100 °C and would expel significant volumes of water displaced by quartz cementation and clay dehydration that caused lateral pressure transfer to the north and western margin of the basin where the PGIC formed. Estimates of the total volume of water expelled from the deep basin suggest that a fluid volume equivalent to a gross rock volume reduction <1% would have provided a fluid budget sufficient to fluidise and inject the sand that forms the PGIC. In terms of areal and vertical extent, volume and architecture the PGIC shares strong similarity with the regionally developed giant injectite systems of Tertiary age in the North Sea basin. In both cases regional sand injection is genetically linked to pressure transfer toward the basin margin from more rapidly subsiding basin centres. Aqueous fluid is derived from thermally driven chemical diagenesis of thick deep water clastic sandstone and smectitic mudstone or from deeper, stratigraphically older, aquifers.

Fundamental study on the thermodynamic non-equilibrium freezing probability prediction model taking into account the super cooling phenomena in porous material

It is commonly considered that frost damage is caused by sudden freezing of supercooled water, which is a random phenomenon. Therefore, the aims of this study are to establish a prediction model for the probability of freezing until any lowest reached temperature, and to obtain the probability distribution function of the freezing point for the proposed analytical prediction model. First, theoretical prediction model for the probability of the instantaneous increment of ice content when lowest achieving temperature was known was derived based on these assumptions that building structure is an aggregation of small elements. Next, the freezing point measurement was carried out by using saturated mortar samples as the small element. As the results, it could be found that the first freezing due to supercooling occurred from -4 to -11 deg. C and the maximum probability was appeared at -7.5 deg. C. The average increment of ice content at every temperature closed to the 40 % volume of pore water until the thermodynamically-based freezing point. Moreover, the proposed method that can calculate the probability distributions of the instantaneous increment of ice content for any lowest achieving temperature from pore size distribution had good agreements with the measurement results.

A new integral model for predicting the hydraulic conductivity of saturated frozen soil

Hydraulic conductivity of frozen soil is indispensable for describing water flow process in freezing soils. However, this conductivity is difficult to measure in the laboratory. So, the objective of this study is to propose a simple and smooth hydraulic conductivity model for saturated frozen soil based on the soil freezing characteristic curve (SFCC). Considering that the volume of pore water approximately represents the pore volume, the distribution of effective pore radii changed as a function of temperature was determined by combining the SFCC and the Gibbs–Thomson equation. Based on the distribution of effective pore radii, Hagen-Poiseuille equation, Darcy’s law, relative hydraulic conductivity and tortuosity, a simple and smooth hydraulic conductivity model for saturated frozen soil based on the SFCC was proposed. To illustrate the model performance, eight existing experimental cases were analyzed. The results showed that predictions considering the three different tortuosity formulations were in good agreement with the tested data; the results were worse when not considering the tortuosity and the results were best when considering the tortuosity τF=B/rb2. Moreover, the predictive modeling power was related to the tortuosity function. Furthermore, the model was further compared with the previous models, the results of which showed the better performance of the proposed model. The model is quite simple and timesaving to use when the SFCC and the saturated hydraulic conductivity are available. This result provides a new idea for developing the hydraulic conductivity model of saturated frozen soil.

Dynamics of Hyporheic Exchange Flux and Fine Particle Deposition Under Moving Bedforms

AbstractDeposition of fine suspended particles can reduce hyporheic exchange flux (HEF), which may result in impairment of various ecological processes. However, the dynamics of fine particle deposition and streambed clogging are still not well understood, especially when the bed is in motion. We conducted flume experiments to study the effects of coupled sand‐clay dynamics on HEF with episodic (pulse) inputs of suspended kaolinite. Three experiments with a mobile sand bed and constant discharge were conducted with repeated injection of suspended kaolinite pulses at fixed concentration increments of 0.16, 0.41, and 0.66 g/L, respectively. HEF and participating porewater volume were assessed using tracer tests. Kaolinite deposition rates were inferred from turbidity measurements while deposition patterns were measured using core samples. We found that fine sediment primarily accumulated within a layer below the bedform scour zone, and that this layer was thicker when kaolinite was added in larger pulses. HEF declined linearly over time as kaolinite accumulated in the bed sediment; an increase of 0.1% kaolinite in the bed led to a decrease in HEF of 26.6 cm/day, regardless of the pulse concentration. However, the same kaolinite increase led to a reduction of 50% in participating pore volume for larger kaolinite pulses, versus only 30% for the smallest pulse. These results indicate that clogging occurs not just during and after high‐flow events, but also under constant flow conditions in which episodic deposition of suspended clay by HEF leads to the formation of a low‐conductivity layer in the bed.

Sampling pore water at a centimeter resolution in sandy permeable sediments of lakes, streams, and coastal zones

AbstractConcentration gradients in the solid fraction and pore water of modern sediments allow to identify benthic biogeochemical processes and the associated fluxes. Gradients are often obtained from layers sampled below the sediment–water interface from sediment cores. Numerous examples in the literature show results from cores collected in impermeable porous sediments, but very few from permeable sediment cores. Indeed, the acquisition of vertical profiles in sandy permeable sediments with a spatiotemporal resolution equivalent to that of muddy sediments is a challenge. We present here a simple protocol that allows sampling of sandy sediments and their interstitial waters with a vertical resolution of 1 cm. This method is suitable for shallow environments, such as intertidal zones, lakes, lagoons, and stream beds. The method is based on rapid conditioning of hand‐collected cores. The cores are pre‐cut lengthwise. Immediately after recovery, they are laid horizontally, opened, and sliced. Interstitial water is collected by centrifugation on site shortly after cutting the core with tubes equipped with a 0.2μm membrane. Optimally, 30 min is sufficient between core collection and conditioning of 12 sections of a 20‐cm long core. The examples shown indicate that the method is reproducible. Reduced dissolved compounds such as Fe(II), Mn(II), and NH4+show profiles without significant oxidation. At the time of core cutting, small volumes of pore water are seeping out of the core, but for sediments with a permeability of up to 10−10m2, this seepage does not disturb the shape of the pore‐water profiles.

Effects of Pore Water Volume on K0 for Sand Subject to Freezing and Thawing

AbstractIn this study, the coefficient of lateral earth pressure at rest (K0) for sand subject to freezing and thawing was investigated, focusing on the effect of pore water volume. Unfrozen (UF), ...

Discussed on a New Form of Resistivity Response Equation for Sandstone

The resistivity response equation of sandstone is the most important basis for well logging interpretation to determine the water saturation of reservoir, but the Archie formula and its derivations are all empirical formulas, and the test error by experimental data is more than 20%. Because the coincidence rate of the log interpretation of low resistivity oil layers and high resistivity water layers is low in the current, In order to further improve the calculation accuracy of reservoir water saturation, it is particularly necessary to deeply understand the essence of rock conductivity. Based on the main influencing factors of rock conductivity, It is considered that for rocks with given formation water resistivity and porosity, the influence of pore structure, size, argillaceous content and conductive minerals on rock conductivity is constant and is an inherent factor. rock resistivity only changes with the change of connected pore water volume, Therefore, the establishment of the relationship between rock resistivity and connected pore water volume conforms to the functional relationship form of dependent variable and independent variable, and can reflect the nature of the rock-electricity relationship. On this basis, the model of rock conductivity per unit volume is proposed, the response equation of sandstone resistivity is deduced, and the general form of the response equation of sandstone resistivity is obtained. The results show that the formula is in good agreement with the experimental data, with a correlation coefficient of more than 0.99, and the test error of the experimental data is no more than 5%, which can represent the theoretical form of the rock resistivity response equation. The new formula considers that rock resistivity and connected pore water volume or water saturation are power functions, which solves some obscure problems in rock resistivity response equation for many years. The parameters of the formula are the inherent property parameters of rocks, which have certain value in use. Based on the new formula, the formula of calculating the water saturation of a reservoir by using the ratio of radial resistivity has been obtained in practical application to some extent. it shows that the new formula is not only of theoretical significance, but also of practical application significance, and is worth further popularizing.

Distribution and formation of Mesozoic low permeability underpressured oil reservoirs in the Ordos Basin, China

The stratum pressure characteristics of Mesozoic reservoirs in the Ordos Basin were first studied. It was found that the Mesozoic reservoirs were mainly ultra-underpressured reservoirs with an average stratum pressure coefficient of 0.63–0.86 and the differences in the abnormal underpressure between the different regions and layers were distinct. The results showed that with increases in the eroded stratum thickness and temperature decrease in the reservoirs, the stratum pressure coefficients showed a decreasing trend. The pore water volume contraction in the Yanchang Formation was from 0.82% to 1.94% after tectonic uplift and stratum temperature reduction. It was proposed that because of the strong uplift of the basin for a long time at the end of the Cretaceous, the function of stratum erosion and paleotemperature reduction resulted in the formation of underpressured reservoirs. It is considered that this underpressured closed system of the Mesozoic in the Ordos Basin was advantageous for reservoir preservation and might have played an important role in adjustment, re-enrichment of hydrocarbons by migration, and oil and water distribution in reservoirs. The formation of underpressured anhydrous sand lens reservoirs in the Chang 7 subsection could be related to the distribution of such an underpressured closed system.

The effect of periodic intermittency on the cyclic behavior of marine sedimentary clay

For subway systems built in coastal areas, the marine sediments are subjected to regular load sequences of waves and intermittencies, resulting in more complex reactions in their cyclic behaviors compared with those under the uniform cyclic loading applied in common studies. This research involved a series of experimental investigations into the undrained behavior of undisturbed saturated marine sedimentary clay subjected to cyclic loading with periodic intermittency considering the initial deviator stress and the conventional uniform cyclic triaxial tests for comparison. The results indicate that periodic intermittency significantly increases cyclic resistance, manifested by weakening of the long-term response and decreases in the number of vibration times required to achieve a steady state. The effect is greater with longer intermittency durations. Furthermore, changes in the pore water volume during cyclic loading were analyzed via nondestructive detection based on nuclear magnetic resonance. A conversion from bound water to free water was observed, referring to vibration magnitude and times. Lastly, the macroscopic results observed in triaxial tests and the microscopic results obtained in the nuclear magnetic resonance test appear to be closely related, indicating that the use of the variation in pore water is an applicable approach to delineate microchanges.

Early warning model for slope debris flow initiation

Early warning model of debris flow is important for providing local residents with reliable and accurate warning information to escape from debris flow hazards. This research studied the debris flow initiation in the Yindongzi gully in Dujiangyan City, Sichuan province, China with scaled-down model experiments. We set rainfall intensity and slope angle as dominating parameters and carried out 20 scaled-down model tests under artificial rainfall conditions. The experiments set four slope angles (32A degrees, 34A degrees, 37A degrees, 42A degrees) and five rainfall intensities (60 mm/h, 90 mm/h, 120 mm/h, 150 mm/h, and 180 mm/h) treatments. The characteristic variables in the experiments, such as, rainfall duration, pore water pressure, moisture content, surface inclination, and volume were monitored. The experimental results revealed the failure mode of loose slope material and the process of slope debris flow initiation, as well as the relationship between the surface deformation and the physical parameters of experimental model. A traditional rainfall intensity-duration early warning model (I-D model) was firstly established by using a mathematical regression analysis, and it was then improved into ISD model and ISM model (Here, I is rainfall Intensity, S is Slope angle, D is rainfall Duration, and M is Moisture content). The warning model can provide reliable early warning of slope debris flow initiation.

Delay Failure Mechanism of Rainfall-Caused Shallow Landslide

Shallow slope may be stable during rainfall but slide a period of time after rainfall stopped. This delay failure mechanism of rainfall-caused landslide is still unclear. This paper aims to reveal the mechanism of the delay failure of rainfall-caused landslides, and propose a monitoring and early warning scheme for such disasters. The characteristic of the seepage field after rainfall and its relations with the stability of slope are investigated numerically. The results show that, after the rainfall stopped, the pore water pressure and volume water content (VWC) of the deep slope will continue to change with the same trend as before the end of the rainfall for a period of time. For an observation point in slope, the VWC continues to increase, and matric suction continues to decrease, which continue to decrease the factor of safety after rainfall stopped. This is the direct cause of the delay failure. The detailed flow chart of the warning system is given as a solution.

Temperature and volume of global marine sediments

Abstract Marine sediments contribute significantly to global element cycles on multiple time scales. This is due in large part to microbial activity in the shallower layers and abiotic reactions resulting from increasing temperatures and pressures at greater depths. Quantifying the rates of these diagenetic changes requires a three-dimensional description of the physiochemical properties of marine sediments. In a step toward reaching this goal, we have combined global data sets describing bathymetry, heat conduction, bottom-water temperatures, and sediment thickness to quantify the three-dimensional distribution of temperature in marine sediments. This model has revealed that ∼35% of sediments are above 60 °C, conditions that are suitable for petroleum generation. Furthermore, significant microbial activity could be inhibited in ∼25% of marine sediments, if 80 °C is taken as a major thermal barrier for subsurface life. In addition to a temperature model, we have calculated new values for the total volume (3.01 × 108 km3) and average thickness (721 m) of marine sediments, and provide the only known determination of the volume of marine-sediment pore water (8.46 × 107 km3), equivalent to ∼6.3% of the volume of the ocean. The results presented here can be used to help quantify the rates of mineral transformations, lithification, catagenesis, and the extent of life in the subsurface on a global scale.