Geophysical signatures associated with fluid flow and gas hydrate occurrence in a tectonically quiescent sequence,Qiongdongnan Basin,South China Sea

Interpretation of high‐resolution two‐dimensional (2D) and three‐dimensional (3D) seismic data collected in the Qiongdongnan Basin, South China Sea reveals the presence of polygonal faults, pockmarks, gas chimneys and slope failure in strata of Pliocene and younger age. The gas chimneys are characterized by low‐amplitude reflections, acoustic turbidity and low P‐wave velocity indicating fluid expulsion pathways. Coherence time slices show that the polygonal faults are restricted to sediments with moderate‐amplitude, continuous reflections. Gas hydrates are identified in seismic data by the presence of bottom simulating reflectors (BSRs), which have high amplitude, reverse polarity and are subparallel to seafloor. Mud diapirism and mounded structures have variable geometry and a great diversity regarding the origin of the fluid and the parent beds. The gas chimneys, mud diapirism, polygonal faults and a seismic facies‐change facilitate the upward migration of thermogenic fluids from underlying sediments. Fluids can be temporarily trapped below the gas hydrate stability zone, but fluid advection may cause gas hydrate dissociation and affect the thickness of gas hydrate zone. The fluid accumulation leads to the generation of excess pore fluids that release along faults, forming pockmarks and mud volcanoes on the seafloor. These features are indicators of fluid flow in a tectonically‐quiescent sequence, Qiongdongnan Basin. Geofluids (2010) 10 , 351–368     

Geophysical and geochemical evidence of large scale fluid flow within shallow sediments in the eastern Gulf of Mexico,offshore Louisiana

We analyse the fluid flow regime within sediments on the Eastern levee of the modern Mississippi Canyon using 3D seismic data and downhole logging data acquired at Sites U1322 and U1324 during the 2005 Integrated Ocean Drilling Program (IODP) Expedition 308 in the Gulf of Mexico. Sulphate and methane concentrations in pore water show that sulphate–methane transition zone, at 74 and 94 m below seafloor, are amongst the deepest ever found in a sedimentary basin. This is in part due to a basinward fluid flow in a buried turbiditic channel (Blue Unit, 1000 mbsf), which separates sedimentary compartments located below and above this unit, preventing normal upward methane flux to the seafloor. Overpressure in the lower compartment leads to episodic and focused fluid migration through deep conduits that bypass the upper compartment, forming mud volcanoes at the seabed. This may also favour seawater circulation and we interpret the deep sulphate–methane transition zones as a result of high downward sulphate fluxes coming from seawater that are about 5–10 times above those measured in other basins. The results show that geochemical reactions within shallow sediments are dominated by seawater downwelling in the Mars‐Ursa basin, compared to other basins in which the upward fluid flux is controlling methane‐related reactions. This has implications for the occurrence of gas hydrates in the subsurface and is evidence of the active connection between buried sediments and the water column.     

Pliocene sand injectites from a submarine lobe fringe during hydrocarbon migration and salt diapirism: a seismic example from the Lower Congo Basin

Large‐scale conical and saucer‐shaped sand injectites have been identified in the Upper Miocene sediments of the Lower Congo Basin. These structures are evidenced on the 3D high‐resolution seismic data at about 600 ms TWT (two‐way traveltime) beneath the seabed. The conical and saucer‐shaped anomalies range from 20 to 80 m in height, 50 to 300 m in diameter, and 10 to 20 ms TWT in thickness. They are located within a sedimentary interval of about 100 m in thickness and are aligned over 20 km in dip direction (NE‐SW), above the NW margin of an underlying Upper Miocene submarine fan. We have interpreted the conical and saucer‐shaped anomalies as upward‐emplaced sand injectites sourced from the Upper Miocene fan because of their discordant character, the postsedimentary uplifting of the sediments overlying the cones and saucer‐shaped bodies, the alignment with the lateral fringe of the Upper Miocene submarine fan, and the geological context. Sand injection dates from the Miocene–Pliocene transition (approximately 5.3 Ma). The prerequisite overpressure to the sand injection process may be due to the buoyancy effect of hydrocarbons accumulated in the margins of the fan. Additionally, overpressure could have been enhanced by the lateral transfer of fluids operating in the inclined margins of the lobe. The short duration of sand injection and the presence of many sandstone intrusions suggested that the process of injection was triggered by an event, likely due to a nearby fault displacement related to diapiric movements. This is the first time that sand injectites of seismic scale have been described from the Lower Congo Basin. The localized nature of these injectites has led to a change in the migration path of fluids through the sedimentary cover. Consequently, the sand intrusions are both evidence and vectors of fluid migration within the basin fill.     

Seismic evidence for fluid migration pathways from an overpressured system in the South China Sea

Overpressured systems and intense, anomalously hot fluid expulsion in the Yinggehai Basin of the South China Sea offer an opportunity to understand the history of fluid flow and the process of hydrocarbon accumulation in overpressured environments. Fluid migration pathways from overpressured compartments in the basin are largely controlled by the distribution of faults and fractures. Episodic opening of these faults are related to the dynamics of an overpressured system and tectonic movements during basin evolution. At the crests of diapiric structures, fluid expulsion is seismically imaged as chimney‐ or plume‐like features, low to middle seismic amplitudes, and intermittently chaotic and blank reflecting seismic facies. These fluid pathways are controlled by vertical faults, which commonly penetrate overpressured and overlying normally pressured zones. Fluid expulsion is also observed near the main faults, such as the No. 1 Fault at the north‐eastern margin of the basin. Investigation by sidescan sonar on onshore and offshore Hainan Island indicates that there are more than 100 gas seepages adjacent to the No. 1 Fault. Migration pathways in the diapiric structures are controlled by three types of fault and fracture. Penetrative faults formed by dextral strike‐slip movement of the Red River faults commonly occur in the centre of the diapirs, and may have been a triggering factor for the diapirism, and controlled their distribution. Hydrofractures occur in certain mud‐rich layers and may have been generated by hydraulic fracturing. Radial normal faults occur at the top of diapirs and were formed by the intrusive process. These fluid migration pathways played an important role in regional hydrocarbon accumulation.     

Transfer of hydrocarbons from natural seeps to the water column and atmosphere

Results from surface geochemical prospecting, seismic exploration and satellite remote sensing have documented oil and gas seeps in marine basins around the world. Seeps are a dynamic component of the carbon cycle and can be important indicators for economically significant hydrocarbon deposits. The northern Gulf of Mexico contains hundreds of active seeps that can be studied experimentally with the use of submarines and Remotely Operated Vehicles (ROV). Hydrocarbon flux through surface sediments profoundly alters benthic ecology and seafloor geology at seeps. In water depths of 500–2000 m, rapid gas flux results in shallow, metastable deposits of gas hydrate, which reduce sediment porosity and affect seepage rates. This paper details the processes that occur during the final, brief transition — as oil and gas escape from the seafloor, rise through the water and dissolve, are consumed by microbial processes, or disperse into the atmosphere. The geology of the upper sediment column determines whether discharge is rapid and episodic, as occurs in mud volcanoes, or more gradual and steady, as occurs where the seep orifice is plugged with gas hydrate. In both cases, seep oil and gas appear to rise through the water in close proximity instead of separating. Chemical alteration of the oil is relatively minor during transit through the water column, but once at the sea surface its more volatile components rapidly evaporate. Gas bubbles rapidly dissolve as they rise, although observations suggest that oil coatings on the bubbles inhibit dissolution. At the sea surface, the floating oil forms slicks, detectable by remote sensing, whose origins are laterally within ～1000 m of the seafloor vent. This contradicts the much larger distance predicted if oil drops rise through a 500 m water column at an expected rate of ～0.01 m s^?1 while subjected to lateral currents of ～0.2 m s^?1 or greater. It indicates that oil rises with the gas bubbles at speeds of ～0.15 m s^?1 all the way to the surface.     

Salt tectonics and shallow subseafloor fluid convection: models of coupled fluid‐heat‐salt transport

Thermohaline convection associated with salt domes has the potential to drive significant fluid flow and mass and heat transport in continental margins, but previous studies of fluid flow associated with salt structures have focused on continental settings or deep flow systems of importance to petroleum exploration. Motivated by recent geophysical and geochemical observations that suggest a convective pattern to near‐seafloor pore fluid flow in the northern Gulf of Mexico (GoMex), we devise numerical models that fully couple thermal and chemical processes to quantify the effects of salt geometry and seafloor relief on fluid flow beneath the seafloor. Steady‐state models that ignore halite dissolution demonstrate that seafloor relief plays an important role in the evolution of shallow geothermal convection cells and that salt at depth can contribute a thermal component to this convection. The inclusion of faults causes significant, but highly localized, increases in flow rates at seafloor discharge zones. Transient models that include halite dissolution show the evolution of flow during brine formation from early salt‐driven convection to later geothermal convection, characteristics of which are controlled by the interplay of seafloor relief and salt geometry. Predicted flow rates are on the order of a few millimeters per year or less for homogeneous sediments with a permeability of 10^?15 m², comparable to compaction‐driven flow rates. Sediment permeabilities likely fall below 10^?15 m² at depth in the GoMex basin, but such thermohaline convection can drive pervasive mass transport across the seafloor, affecting sediment diagenesis in shallow sediments. In more permeable settings, such flow could affect methane hydrate stability, seafloor chemosynthetic communities, and the longevity of fluid seeps.     

Indications of formation water flow and compartmentalization on the flank of a salt structure derived from salinity and seismic data

Vertical and lateral variations in lithology, salinity, temperature, and pressure determined from wireline LAS logs, produced water samples, and seismic data on the south flank of a salt structure on the continental shelf, offshore Louisiana indicate three hydrogeologic zones in the study area: a shallow region from 0 to 1.1 km depth with hydrostatically pressured, shale‐dominated Pleistocene age sediments containing pore waters with sea water (35 g l^?1) or slightly above sea water salinity; a middle region from 1.1 to 3.2 km depth with near hydrostatically pressured, sand‐dominated Pliocene age sediments that contain pore waters that range from seawater salinity to up to 5 times sea water salinity (180 g l^?1); and a deep section below 3.2 km depth with geopressured, shale‐dominated Miocene age sediments containing pore waters that range from sea water salinity to 125 g l^?1. Salt dissolution has generated dense, saline waters that appear to be migrating down dip preferentially through the thick Pliocene sandy section. Sand layers that come in contact with salt contain pore waters with high salinity. Isolated sands have near sea water salinity. Salinity information in conjunction with seismic data is used to infer fluid compartmentalization. Both vertical and lateral lithologic barriers to fluid flow at tens to hundreds of meters scale are observed. Fluid compartmentalization is also evident across a supradomal normal fault. Offset of salinity contours are consistent with the throw of the fault, which suggests that saline fluids migrated before fault formation.     

Identification of pastoral sites using stable nitrogen and carbon isotopes from bulk sediment samples: a case study in modern and archaeological pastoral settlements in Kenya

The identification of pastoral sites in the East African archaeological record is problematic. Recently, a method for the identification of degraded livestock enclosure sediments had been developed that takes into account the geoarchaeological indicators of micromorphology, phytolith concentrations and the mineral assemblages. This suite of indicators may not always be present in degraded livestock enclosure sediments. This study presents an additional indicator by which degraded livestock enclosure sediments may be identified, namely the isotopic composition of organic nitrogen measured on bulk sediment samples. We studied a highly controlled ethnoarchaeological sequence of abandoned Maasai livestock enclosure sediments sampled in Rombo area, southern Kenya. The results were compared to archaeological sediments from the Elmenteitan Pastoral Neolithic site of Sugenya, southwestern Kenya, radiocarbon dated to ca. 2000 BP (uncalibrated). The sediments from both sites were studied using all four types of analyses, i.e., micromorphology, mineralogy, phytolith concentrations, and stable carbon and nitrogen isotopic compositions on bulk sediment samples. The results show that in abandoned livestock enclosure sediments of known ages a significant enrichment in the heavy nitrogen isotope (¹⁵N) occurs, and that carbon isotopic compositions may be useful for differentiating cattle from caprine enclosures following their dietary preferences (i.e., grazers vs. browsers). A similar pattern of ¹⁵N enrichment is observed in sediments sampled within the site of Sugenya while sediments sampled outside the site's perimeter are generally depleted in ¹⁵N. The micromorphological, mineralogical and phytolith analyses support the conclusion that the sediments from within the site of Sugenya represent degraded livestock enclosure sediments. The carbon isotopic composition from the degraded dung deposits strongly suggests that livestock kept at Sugenya were cattle. Overall, this study presents new empirical data that can be used for the identification of livestock enclosures, and shows that the isotopic signatures and geoarchaeological indicators can preserve for at least two millennia.     

Constraining the rate and extent of mantle serpentinization from seismic and petrological data: implications for chemosynthesis and tectonic processes

We used seismic velocity as a proxy for serpentinization of the mantle, which occurred beneath thinned but laterally continuous continental crust during continental break up, prior to opening of the Atlantic Ocean. The serpentinized sub‐continental mantle is now exhumed, beneath the Iberia Abyssal Plain and was accessed by scientific drilling on Ocean Drilling Program legs 149 and 173. Chromatographic modelling of kinetically limited transport of the serpentinization front yields a front displacement of 2197 ± 89 m, a time‐integrated fluid flux of 1098 ± 45 m³ m^?2 and a Damköhler number of 6.0 ± 0.2. Whether either surface reaction or chemical transport limit the rate of reaction, we calculate timescales for serpentinization of approximately 10⁵–10⁶ years. This yields time‐average fluid flux rates for H₂O, entering and reacting with the mantle, of 60–600 mol m^?2 a^?1 and for CH₄, produced as a by‐product of oxidation of Fe⁺⁺ to magnetite and exiting the mantle, of 0.55–5.5 mol m^?2 a^?1. This equates to a CH₄‐flux of 0.18–1.8 Tg a^?1 for coeval serpentinization of the mantle that was exhumed west of Iberia. This represents 0.03–0.3% of the present‐day annual CH₄‐flux from all sources and a higher fraction of pre‐anthropogenic (lower) CH₄ levels. CH₄ released by serpentinization at or beneath the seafloor could provide substrate for biological chemosynthesis and/or promote gas‐hydrate formation. Finally, noting its volumetric extent and rapidity (<10⁶ years), we interpret serpentinization to be a reckonable component of tectonic processes, contributing both diapiric and expansional forces and helping to ‘lubricate’ extensional processes. Given its anisotropic permeability, actively deforming serpentinite might impede melt migration which may be of interest, given the apparent lack of melt in some rifted margins.     

Fluid mapping in deeply buried Ordovician paleokarst reservoirs in the Tarim Basin,western China

The storage spaces within deeply buried Ordovician paleokarst reservoirs in the Tarim Basin are mostly secondary and characterized by strong heterogeneity and some degree of anisotropy. The types of fluids that fill the spaces within these reservoirs are of great importance for hydrocarbon exploration and exploitation. However, fluid identification from seismic data is often controversial in this area because the seismic velocity for this particular reservoir could be significantly influenced by many factors, including pore shapes, porosity, fluid types, and mineral contents. In this study, we employ the differential effective medium‐Gassmann rock physics model to interpret and discuss the characteristics of conventional karstic carbonate reservoirs in the Tarim Basin that are filled with different fluids (oil, gas, and water) using logging data and thus objectively build corresponding fluid identification criteria. These criteria are subsequently evaluated by amplitude versus offset (AVO) forward analysis based on typical logging data and further applied to ascertain the reservoir fluid types in two different areas in the Tarim Basin based on prestack inversion results. For conventional carbonate reservoirs, gas can be distinguished from heavy oil and water, but heavy oil and water are broadly similar on seismic data. For condensate carbonate reservoirs, water can be differentiated from light oil (i.e., condensates) and gas, but light oil and gas demonstrate substantial similarities in terms of their seismic responses. The predicted fluid results are in good agreement with the results of drilling and oil testing. In particular, modeling the seismically resolvable reservoirs in the carbonate strata in the Tarim Basin, which have needle‐ and sphere‐shaped storage spaces (pore aspect ratio > 0.3) and clay content that is lower than 5%, indicates that fluid properties could be properly evaluated if the porosity is larger than 5% for conventional carbonate reservoirs and >7% for condensate carbonate reservoirs.     

A side-scan sonar and high-resolution Chirp sub-bottom profile study of the natural and anthropogenic sedimentary record of Lower Lough Erne,northwestern Ireland

A geophysical survey (side-scan sonar and high-resolution sub-bottom profiling) combined with established chrono- and bio-stratigraphic markers are used to reconstruct the evolutionary history of Lower Lough Erne, northwestern Ireland since the end of the last glacial. Discrete acoustic units define four prominent sedimentation cycles, one Late-glacial and three Holocene, within the seismic stratigraphy. Basin development is predominantly controlled by climate until the Mid Holocene when the effects of cultural activity are related to pronounced signatures in the seismic record. An enhanced reflector marking the termination of the Early Holocene sedimentation cycle is associated with the elm decline and forest clearance during the Neolithic (between approximately 5800 cal. BP and 5300 cal. BP). The associated increase in sediment input, by infilling minor topographic lows and basins, has a smoothing effect on the morphologic expression of the original basin. Onlapping and truncated reflectors in the penultimate acoustic unit define further modification of lake bed relief by removal of sediment from the system during engineered lowering of the lake levels that began in the 1880s. Acoustic anomalies identified on the side-scan sonar data are linked with cultural activity and are identified as having the potential to facilitate the recent establishment and migration of invasive zebra mussels through the Erne system.     

Freezing and melting behaviors of H2O‐NaCl‐CaCl2 solutions in fused silica capillaries and glass‐sandwiched films: implications for fluid inclusion studies

Fluid inclusions of the H₂O‐NaCl‐CaCl₂ system are notorious for their metastable behavior during cooling and heating processes, which can render microthermometric measurement impossible or difficult and interpretation of the results ambiguous. This study addresses these problems through detailed microscopic examination of synthetic solutions during cooling and warming runs, development of methods to enhance nucleation of hydrates, and comparison of microthermometric results with different degrees of metastability with values predicted for stable conditions. Synthetic H₂O‐NaCl‐CaCl₂ solutions with different NaCl/(NaCl + CaCl₂) ratios were prepared and loaded in fused silica capillaries and glass‐sandwiched films for microthermometric studies; pure solutions were used with the capillaries to simulate fluid inclusions, whereas alumina powder was added in the solutions to facilitate ice and hydrate crystallization in the sandwiched samples. The phase changes observed and the microthermometric data obtained in this study have led to the following conclusions that have important implications for fluid inclusion studies: (i) most H₂O‐NaCl‐CaCl₂ inclusions that appear to be completely frozen in the first cooling run to ?185°C actually contain large amounts of residual solution, as also reported in some previous studies; (ii) inability of H₂O‐NaCl‐CaCl₂ inclusions to freeze completely may be related to their composition (low NaCl/(NaCl + CaCl₂) ratios) and lack of solid particles; (iii) crystallization of hydrates, which is important for cryogenic Raman spectroscopic studies of fluid inclusion composition, can be greatly enhanced by finding an optimum combination of cooling and warming rates and temperatures; and (iv) even if an inclusion is not completely frozen, the melting temperatures of hydrohalite and ice are still valid for estimating the fluid composition.     

Lithology and fluid prediction from amplitude versus offset (AVO) seismic data

Seismic reflection data as used in the oil industry is acquired and processed as multitrace data with source‐receiver offsets from a few hundred metres (short offset) to several kilometres (long offset). This set of data is referred to as ‘pre‐stack’. The traces are processed by velocity analysis, migration and stacking to yield a data volume of traces with ‘zero‐offset’. The signal‐to‐noise enhancement resulting from this approach is very significant. However, reflection amplitude changes in the pre‐stack domain may also be analysed to yield enhanced rock physics parameter estimates. Pre‐stack seismic data is widely used to predict lithology, reservoir quality and fluid distribution in exploration and production studies. Amplitude versus offset (AVO) data, especially anomalous signals, have been used for decades as indicators of hydrocarbon saturation and favourable reservoir development. Recently, enhanced quantification of these types of measurement, using seismic inversion techniques in the pre‐stack domain, have significantly enhanced the utility of such measurements. Using these techniques, for example, probability of the occurrence of hydrocarbons throughout the seismic data can be estimated, and as a consequence the many pre‐stack volumes acquired in a three‐dimensional (3D) can be survey, reduced to a single, more interpretable volume. The possibilities of 4D time lapse observation extend the measurements to changes in fluid content (and pressure) with time, and with obvious benefits in establishing the accuracy of dynamic reservoir models and improvements in field development planning. As an illustration, recent results from the Nelson Field (UK North Sea), are presented where we show the method by which probability volumes for oil sands may be calculated. The oil–sand probability volumes for three 3D seismic datasets acquired in 1990, 1997 and 2000 are compared and production effects in these data are demonstrated.     

Modeling thermal convection in supradetachment basins: example from western Norway

The juxtaposition of fault‐bounded sedimentary basins, above crustal‐scale detachments, with warmer exhumed footwalls can lead to thermal convection of the fluids in the sediments. The Devonian basins of western Norway are examples of supradetachment basins that formed in the hanging wall of the Nordfjord‐Sogn Detachment Zone. In the central part of the Hornelen and Kvamshesten basins, the basin‐fill is chiefly represented by fluvial sandstones and minor lacustrine siltstones, whereas the fault margins are dominated by fanglomerates along the detachment contact. Prominent alteration and low‐greenschist facies metamorphic conditions are associated with the peak temperature estimates of the sediments close to the detachment shear zone. Fluid circulation may have been active during the burial of the sediments, and we quantify the potential role played by thermal convection in redistributing heat within the basins. Different models are tested with homogeneous and layered basin‐fill and with material transport properties corresponding to sandstones and siltstones. We found that thermally driven fluid flow is expected in supradetachment basins as a transient process during the exhumation of warmer footwalls. We demonstrate that the fluid flow may have significantly affected the temperature distribution in the upper five kilometers of the Devonian basins of western Norway. The temperature anomaly induced by the flow may locally reach about 80°C. The sedimentary layering formed by sand‐ and siltstones strata does not inhibit fluid circulation at the scale of the basin. The presence of fluid pathways along the detachment has an important impact on the flow and allows an efficient drainage of the basin by channelizing fluids upward along the detachment.     

Diverse origins and timing of formation of basinal brines in the Gulf of Mexico sedimentary basin

A review of five different field areas in the Gulf of Mexico sedimentary basin (GOM) illustrates some of the potentially diverse chemical and physical processes which have produced basinal brines. The elevated salinities of most of the formation waters in the GOM are ultimately related to the presence of the Middle Jurassic Louann Salt. Some of these brines likely inherited their salinity from evaporated Mesozoic seawater, while other saline fluids have been produced by subsequent dissolution of salt, some of which is occurring today. The timing of the generation of brines has thus not been restricted to the Middle Jurassic. The mechanisms of solute transport that have introduced brines throughout much of the sedimentary section of the GOM are not entirely understood. Free convection driven by spatial variations in formation water temperature and salinity is undoubtedly occurring around some salt structures. However, the driving mechanisms for the broad, diffusive upward solute transport in the northern Gulf rim of Arkansas and northern Louisiana are not known. In the Lower Cretaceous of Texas, fluid flow was much more highly focused, and perhaps episodic. It is clear that many areas of the Gulf basin are hydrologically connected and that large‐scale fluid flow, solute transport, and dispersion have occurred. The Na‐Mg‐Ca‐Cl compositions of brines in the areas of the Gulf Coast sedimentary basin reviewed in this article are products of diagenesis and do not reflect the composition of the evaporated marine waters present at the time of sediment deposition. Large differences in Na, Ca, and Mg trends for waters hosted by Mesozoic versus Cenozoic sediments may reflect differences in: (i) the sources of salinity (evaporated seawater for some of the Mesozoic sediments, dissolution of salt for some of the Cenozoic sediments); (ii) sediment lithology (dominantly carbonates for much of the Mesozoic sediments, and dominantly siliciclastics for the Cenozoic sediments); or (iii) residence times of brines associated with these sediments (tens of millions of years versus perhaps days).     

Migration of Mn-rich fluids through normal faults and fine-grained terrigenous sediments during early development of the Neogene Vallès-Penedès half-graben (NE Spain)

The Miocene siliciclastic sediments infilling the Vallès‐Penedès half‐graben are affected by two sets of structures developed during the extensional tectonics that created the basin. The first set, represented by extension fractures infilled with mud and sands, is attributed to seismically induced liquefaction. The second set, represented by normal faults, corresponds to a high‐permeability horsetail extensional fracture mesh developed near the surface in the hanging walls of normal faults. The incremental character of the vein‐fills indicates episodic changes in the tectonic stress state and fault zone permeability. Two episodes of fluid migration are recorded. The first episode occurred prior to consolidation and lithification when shallow burial conditions allowed oxidizing meteoric waters to flow horizontally through the more porous and permeable sandy layers. Development of clastic dikes allowed local upward flow and dewatering of the sandy beds. Liquefaction and expulsion of fluids were probably driven by seismic shaking. During the first episode of fluid migration there was no cementation of the sandstone or within the fractures, probably because little fluid was mobilized by the predominantly compaction‐driven flow regime. The second episode of fluid migration occurred synchronously with normal fault development, during which time the faults acted as fluid conduits. Fluids enriched in manganese, probably leached from local manganese oxyhydroxides soon after sedimentation, moved laterally and produced cementation in the sandstone layers, eventually arriving at the more porous and permeable fault pathways that connected compartments of different porosities and permeabilities. Carbonate probably precipitated in fractures saturated with meteoric water near the ground surface at a transitional redox potential. Once the faults became occluded by calcite cement, shortly after fault development, they became barriers to both vertical and horizontal fluid flow.     

Feeding the Crusades: Archaeobotany,Animal Husbandry and Livestock Alimentation on the Baltic Frontier

ABSTRACT

The integrated results of micromorphology, plant macrofossil, pollen, phytolith, and non-pollen palynomorph analyses represent an important study of two thirteenth-century Teutonic Order castles at Karksi (Livonia), and Elbl?g (Prussia). The research examines deposits that formed during the period of active crusading. At Karksi, the investigation of a midden and of the organic-rich sediment beneath allows the diachronic use of this area to be understood. Freshwater aquatic indicators are consistent with the occurrence of shallow stagnant water, as also suggested by a waterlaid pond sediment identified in thin-section. Coprophilous spore taxa suggest the use of the pond as a watering hole. Plant macrofossils from the midden represent a range of habitats, mostly from wet/damp areas, as well as pastures and meadows, and also woodlands. Fragments of millet are embedded within herbivore dung in thin-section showing the use of this grain as fodder. At Elbl?g, parasite ova may derive from animal feces as they also occur in the dung observed in thin-section, and a range of coprophilous fungal spore taxa were extracted. The results reveal information about the range of livestock that the Teutonic Knights kept, whereabouts within the castles the animals were stabled, and what fodder was used.     

Preliminary U-series and Thermoluminescence dating of excavated deposits in Liang Bua sub-chamber,Flores, Indonesia

We report the results of a test excavation of deposits in a limestone cave sub-chamber located beneath the main chamber of Liang Bua, Flores, Indonesia; the discovery site of the small hominin species, Homo floresiensis. Well-preserved remains of extinct Pleistocene fauna and stone artefacts have previously been identified on the surface of a sediment cone within the sub-chamber. Our excavation of the deposits, at the base of the sediment cone in the sub-chamber (to 130 cm depth) yielded only a few fragmentary bones of extant fauna. Uranium/Thorium (U-series or U/Th) dating of soda straw stalactites excavated from 20 to 130 cm in depth demonstrates that the excavated sediments were deposited during the Holocene. Red Thermoluminescence (TL) dating of the sediments at the base of the excavation (130 cm depth) indicates these sediments were last exposed to sunlight at 84 ± 15 ka (thousand years), similar to red TL ages of cave sediments from the main chamber. Together, these results indicate that the surface faunal remains, which are morphologically analogous to Pleistocene finds from the main chamber excavations, were transported to the sub-chamber relatively recently from the main chamber of Liang Bua and probably originated from conglomerate deposits at the rear of the cave and from deposits around the front entrance. There is no evidence for hominin occupation of the sub-chamber, instead it seems to have acted as a sink for cultural materials and fossil remains transported from the surface via sinkholes. Despite the small number of finds from the test excavation, it is possible that more extensive excavations may yield additional transported cultural and faunal evidence at greater depths.     

Hydrologic and geochemical controls on soluble benzene migration in sedimentary basins

The effects of groundwater flow and biodegradation on the long‐distance migration of petroleum‐derived benzene in oil‐bearing sedimentary basins are evaluated. Using an idealized basin representation, a coupled groundwater flow and heat transfer model computes the hydraulic head, stream function, and temperature in the basin. A coupled mass transport model simulates water washing of benzene from an oil reservoir and its miscible, advective/dispersive transport by groundwater. Benzene mass transfer at the oil–water contact is computed assuming equilibrium partitioning. A first‐order rate constant is used to represent aqueous benzene biodegradation. A sensitivity study is used to evaluate the effect of the variation in aquifer/geochemical parameters and oil reservoir location on benzene transport. Our results indicate that in a basin with active hydrodynamics, miscible benzene transport is dominated by advection. Diffusion may dominate within the cap rock when its permeability is less than 10^?19 m². Miscible benzene transport can form surface anomalies, sometimes adjacent to oil fields. Biodegradation controls the distance of transport down‐gradient from a reservoir. We conclude that benzene detected in exploration wells may indicate an oil reservoir that lies hydraulically up‐gradient. Geochemical sampling of hydrocarbons from springs and exploration wells can be useful only when the oil reservoir is located within about 20 km. Benzene soil gas anomalies may form due to regional hydrodynamics rather than separate phase migration. Diffusion alone cannot explain the elevated benzene concentration observed in carrier beds several km away from oil fields.