Geochemistry of tetrapyrrole, tetraterpenoid, and perylene pigments in sediments from the Gulf of California

Results and discussion cover pigment analyses of 36 sediment samples recovered by Deep Sea Drilling Project Leg 64, and six samples from the Leg 64 site-survey cruise in the Guaymas Basin (Scripps Institution of Oceanography, Leg 3). Pigments investigated were tetrapyrroles, tetraterpenoids, and the PAH compound perylene. Traces of mixed nickel and copper ETIO-porphyrins were ubiquitous in all sediment samples, except for the very surface (i.e., <2 m sub-bottom), and their presence is taken as an indication of minor influxes of previously oxidized allochthonous (terrestrial) organic matter. Phorbides and chlorins isolated from Site 479 sediment samples (i.e., the oxygen-minimum locale, northeast of the Guaymas Basin) well represent the reductive diagenesis ("Treibs Scheme"; see Baker and Palmer, 1978; Treibs, 1936) of chlorophyll derivatives. Three forms of pheophytin-a, plus a variety of phorbides, were found to give rise to freebase porphyrins, nickel phylloerythrin, and nickel porphyrins, with increasing depth of burial (increasing temperature). Sediments from Sites 481, 10G, and 18G yielded chlorophyll derivatives characteristic of early oxidative alterations. Included among these pigments are allomerized pheophytin-a, purpurin-18, and chlorin-p6. The high thermal gradient imposed upon the late Quaternary sediments of Site 477 greatly accelerated chlorophyll diagenesis in the adjacent overlying sediments, that is, the production of large quantities of free-base desoxophylloerythroetioporphyrin (DPEP) occurred in a section (477-7-5) presently only 49.8 meters sub-bottom. Present depth and age of these sediments are such that only chlorins and phorbides would be expected. Carotenoid (i.e., tetraterpenoids) concentrations were found to decrease rapidly with increasing sub-bottom depth. Less deeply buried sediments (e.g., 0-30 m) yielded mixtures of carotenes and oxygen-substituted carotenoids. Oxygencontaining (oxy-, oxo-, epoxy-) carotenoids were found to be lost preferentially with increased depth of burial. Early carotenoid diagenesis is suggested as involving interacting reductions and dehydrations whereby dehydro-, didehydro-, and retro-carotenes are generated. Destruction of carotenoids as pigments may involve oxidative cleavage of the isoprenoid chain through epoxy intermediates, akin to changes in the senescent cells of plants. Perylene was found to be a common component of the extractable organic matter from all sediments investigated. The generation of alkyl perylenes was found to parallel increases in the existing thermal regime at all sites. Igneous sills and sill complexes within the sediment profile of Site 481 altered (i.e., scrambled) the otherwise straightforward thermally induced alkylation of perylene. The degree of perylene alkylation is proposed as an indicator of geothermal stress for non-contemporaneous marine sediments.

Radiocarbon ages of bottom sediments and sedimentation rates in depressions of the Red Sea rift zone

Sedimentation rates (SR) for metalliferous and ore sediments containing ore material in 15 depressions of the Red Sea rift zone are discussed. SR for normal sediments was ca. 3.2 cm/ka in the second half of Holocene, 14.3 cm/ka yrs in the first half of Holocene, and 21.3 cm/ka in Late Würmian. Accumulation of metalliferous and ore sediments requires considerable accumulation of hydrothermal matter. Ore sediments have been found primarily in the Atlantis II and Chain Deeps; average sedimentation rate in these depressions is 90.0 cm/ka. In other depressions geothermal activity during considered time intervals was lower, and ore material occurs as admixture or in layers.

Mineralogy and geochemistry at DSDP Leg 64 Holes

At DSDP Site 477, late Quaternary diatomaceous muds and delta-derived silty-sand turbidites at 2000 meters water depth have been extensively and progressively altered by a deep-seated heat source beneath a sill. Bulk petrologic and microprobe analyses have identified a crudely zoned paragenesis within 260 meters sub-bottom which ranges from unaltered to slightly altered oozes (0-50 m), anhydrite-dolomite claystones (105-125 m), illite-chlorite-pyrite claystones (125-140 m), chlorite-pyrite-calcite-carbonaceous claystones with traces of K-feldspar, albite, epidote (140-190 m), and chlorite-epidote-quartz-albite-pyrrhotite-sphene sandstone (190-260 m). Several petrologic features suggest rapid processes of ocean floor metamorphism: (1) friable and porous textures, (2) abundant relict grains with overgrowths, (3) idiomorphic habits on epidotes, feldspars, and quartz, and (4) a steep gradient in levels of alteration. Many aspects of this hydrothermal assemblage are similar to hydrothermally metamorphosed sandstones of the Cerro Prieto, Mexico, geothermal area.

Mineral composition and experimental results from XRD analyses of sediments from ODP Leg 190 sites

X-ray diffraction analyses of the clay-sized fraction of sediments from the Nankai Trough and Shikoku Basin (Sites 1173, 1174, and 1177 of the Ocean Drilling Program) reveal spatial and temporal trends in clay minerals and diagenesis. More detrital smectite was transported into the Shikoku Basin during the early-middle Miocene than what we observe today, and smectite input decreased progressively through the late Miocene and Pliocene. Volcanic ash has been altered to dioctahedral smectite in the upper Shikoku Basin facies at Site 1173; the ash alteration front shifts upsection to the outer trench-wedge facies at Site 1174. At greater depths (lower Shikoku Basin facies), smectite alters to illite/smectite mixed-layer clay, but reaction progress is incomplete. Using ambient geothermal conditions, a kinetic model overpredicts the amount of illite in illite/smectite clays by 15%-20% at Site 1174. Numerical simulations come closer to observations if the concentration of potassium in pore water is reduced or the time of burial is shortened. Model results match X-ray diffraction results fairly well at Site 1173. The geothermal gradient at Site 1177 is substantially lower than at Sites 1173 and 1174; consequently, volcanic ash alters to smectite in lower Shikoku Basin deposits but smectite-illite diagenesis has not started. The absolute abundance of smectite in mudstones from Site 1177 is sufficient (30-60 wt%) to influence the strata's shear strength and hydrogeology as they subduct along the Ashizuri Transect.

Geochemistry, lithology and maceral analysis at DSDP Hole 71-511

The quantity, type, and maturity of the organic matter in Recent through Upper Jurassic sediments from the Falkland Plateau, DSDP Site 511, have been determined. Sediments were investigated for their hydrocarbon potential by organic carbon and Rock-Eval pyrolysis. Kerogen concentrates were prepared and analyzed in reflected and transmitted light to determine vitrinite reflectance and maceral content. Total extractable organic compounds were analyzed for their elemental composition, and the fraction of the nonaromatic hydrocarbons was determined by capillary column gas chromatography and combined gas chromatography/mass spectrometry. Three main classes of organic matter can be determined at DSDP Site 511 by a qualitative and quantitative evaluation of microscopic and geochemical results. The Upper Jurassic to lower Albian black shales contain high amounts of organic matter of dominantly marine origin. The content of terrigenous organic matter increases at the base of the black shales, whereas the shallowest black shales near the Aptian/Albian boundary are transitional in composition, with increasing amounts of inert, partly oxidized organic matter which is the dominant component in all Albian through Tertiary sediments investigated. The organic matter in the black shales has a low level of maturity and has not yet reached the onset of thermal hydrocarbon generation. This is demonstrated by the low amounts of total extractable organic compounds, low percentages of hydrocarbons, and the pattern and composition of nonaromatic hydrocarbons. The observed reflectance of huminite and vitrinite particles (between 0.4% and 0.5% Ro at bottom-hole depth of 632 m) is consistent with this interpretation. Several geochemical parameters indicate, however, a rapid increase in the maturation of organic matter with depth of burial. This appears to result from the relatively high heat flow observed at Site 511. If we relate the level of maturation of the black shales at the bottom of Hole 511 to their present shallow depth of burial, they appear rather mature. On the basis of comparisons with other sedimentary basins of a known geothermal history, a somewhat higher paleotemperature gradient and/or additional overburden are required to give the observed maturity at shallow depth. A comparison with contemporaneous sediments of DSDP Site 361, Cape Basin, which was the basin adjacent and to the north of the Falkland Plateau during the early stages of the South Atlantic Ocean, demonstrates differences in sedimentological features and in the nature of sedimentary organic matter. We interpret these differences to be the result of the different geological settings for Sites 361 and 511.

Minerals, geochemistry and x-ray power characteristics at DSDP Sites 54-424, 60-458 and 60-459

Secondary minerals filling veins and vesicles in volcanic basement at Deep Sea Drilling Project Sites 458 and 459 indicate that there were two stages of alteration at each site: an early oxidative, probably hydrothermal, stage and a later, low-temperature, less oxidative stage, probably contemporaneous with faulting in the tectonically active Mariana forearc region. The initial stage is most evident in Hole 459B, where low-Al, high Fe smectites and iron hydroxides formed in vesicles in pillow basalts and low-Al palygorskite formed in fractures. Iron hydroxides and celadonite formed in massive basalts next to quartz-oligoclase micrographic intergrowths. Palygorskite was found in only one sample near the top of basement in Hole 458, but it too is associated with iron hydroxides. Palygorskite has previously been reported only in marine sediments in DSDP and other occurrences. It evidently formed here as a precipitate from fluids in which Si, Mg, Fe, and even some Al were concentrated. Experimental data suggest that the solutions probably had high pH and somewhat elevated temperatures. The compositions of associated smectites resemble those in hydrothermal sediments and in basalts at the Galapagos mounds geothermal field. The second stage of alteration was large-scale replacement of basalt by dioctahedral, trioctahedral, or mixed-layer clays and phillipsite along zones of intense fracturing, especially near the bottom of Holes 458 and 459B. The basalts are commonly slickensided, and there are recemented microfault offsets in overlying sediments. Native copper occurs in one core of Hole 458, but associated smectites are dominantly dioctahedral, unlike Hole 459B, where they are mainly trioctahedral, indicating nonoxidative alteration. The alteration in both holes is more intense than at most DSDP ocean crust sites and may have been augmented by water derived from subducting ocean crust beneath the fore-arc region.

Oxygen-isotope composition, temperature and depth of formation of chert at DSDP Leg 62 Holes

We measured oxygen-isotope compositions of 16 siliceous rocks from Deep Sea Drilling Project Sites 463, 464, 465, and 466 (Leg 62). Samples are from deposits that range in age from about 40 to 103 m.y. and that occur at sub-bottom depths of 9 to 461 meters. Mean d18O values range from 28.4 to 36.8 per mil and 36.0 ± 0.3 per mil for quartz-rich and opal-CTrich rocks, respectively. d18O values in chert decrease with increasing sub-bottom depth; the slope of the d18O/depth curve is less steep for Site 464 than for the other sites which indicates that chert at Site 464 formed at higher temperatures than chert at Sites 463, 465, and 466. Temperatures of formation of cherts were 7 to 42°C, using the silica-water fractionation factor of Knauth and Epstein (1976), or 19 to 56°C, using the equation of Clayton et al. (1972). Temperatures in the sediment where the cherts now occur are lower than their isotopically determined temperatures of formation, which means that the cherts record an earlier history when temperatures in the sediment section were greater. Estimated sediment temperatures when the cherts formed are comparable to, but generally slightly lower than, those calculated from Knauth and Epstein's equation. The isotopic composition of cherts is more closely related to environment of formation (diagenetic environment) or paleogeothermal gradients, than to paleoclimates (bottom-water temperatures). Opal-CT-rich rocks may better record paleo-bottom-water temperature. In Leg 62 cherts, better crystallinity of quartz corresponds to lower d18O values; this implies progressively higher temperatures of equilibration between quartz and water during maturation of quartz. The interrelationship of d18O and crystallinity is noted also in continental-margin deposits such as the Monterey Formation - but for higher temperatures. The apparent temperature difference between open-ocean and continental-margin deposits can be explained by the dominant control of temperature on silica transformation in the rapidly deposited continental-margin deposits, whereas time, as well as temperature, has a strong influence on the transformations in open-ocean deposits. Comparisons between the chemistry and d18O values of cherts reveal two apparent trends: both boron and SiO2 increase as d18O increases. However, the correspondence between SiO2 and d18O is only apparent, because the two cherts lowest in SiO2 are also the most deeply buried, so the trend actually reflects depth of burial. The correspondence between boron and d18O supports the conclusion that boron is incorporated in the quartz crystal structure during precipitation

In-situ sediment temperature and pore water chloride concentration at pockmarks of the Nigerian continental margin

A joint research expedition between the French IFREMER and the German MARUM was conducted in 2011 using the R/V 'Pourquoi pas?' to study gas hydrate distributions in a pockmark field (1141-1199 m below sea surface) at the continental margin of Nigeria. The seafloor drill rig MeBo of MARUM was used to recover sediments as deep as 56.74 m below seafloor. The presence of gas hydrates in specific core sections was deduced from temperature anomalies recorded during continuous records of infrared thermal scanning and anomalies in pore water chloride concentrations. In situ sediment temperature measurements showed elevated geothermal gradients of up to 258 °C/km in the center of the so-called pockmark A which is up to 4.6 times higher than that in the background sediment (72 °C/km). The gas hydrate distribution and thermal regime in the pockmark are largely controlled by the intensity, periodicity and direction of fluid flow. The joint interaction between fluid flow, gas hydrate formation and dissolution, and the thermal regime governs pockmark formation and evolution on the Nigerian continental margin.

Chloroflexus spp. and Sulfurihydrogenibium spp. in microbial mats of the Nakabusa hot spring, Japan

Microbial mats develop in a wide range of aquatic habitats, such as geothermal hot springs, hypersaline ponds, marine cold seeps or hydrothermal vents. The Nakabusa hot spring is located in the Nagano Prefecture, Japan (36.3875N, 137.75E), dense olive-green microbial mats develop in regions where the slightly alkaline, sulfidic effluent has cooled to 65°C. The microbial community of such mats was analyzed by focusing on the diversity, as well as the in situ distribution and function of bacteria involved in sulfur cycling. Microbial mat samples were kept in sterile plastic tubes (for molecular analysis) or glass bottles completely filled with hot spring water to avoid oxidation. Samples were transferred to the laboratory on ice and used for physiological experiments within 8h. Quantification of cell biovolumes was carried out based on images of mat sections hybridized with Sulfurihydrogenibium- and Chloroflexi-specific probes, and stained with DAPI. In situ hybridizations (CARD-FISH) of thin matsections showed a heterogeneous vertical distribution of Sulfurihydrogenibium and Chloroflexus. Sulfurihydrogenibium dominated near the mat surface (50% of the total mat biovolume), while Chloroflexus dominated in deeper layers (up to 64% of the total mat biovolume).

(Table 2) Bottom-hole temperature measurements at DSDP Sites 68-501, 69-504, and 69-505

Drilling durin Deep Sea Drilling Project Legs 68, 69, and 70 on the southern limb of the Costa Rica Rift was used to study geothermal processes in the ocean crust. Two areas were drilled. One was a geothermally hot site on 6.2-m.y.-old crust, where topography is smooth, heat flow is close to that predicted by conductive cooling of the lithosphere (200 mWm**-2), and hydrothermal circulation may be sealed within the crust. The other was on 3.9-m.y.-old crust, where rough topography is associated with low heat flow (15 to 50 mWm**-2) and possible open convection of sea water. At both sites, about 250 m of siliceous-calcareous sediments overlies igneous basement. In the hot area, it blankets the topography, whereas in the cold area, basement outcrops still occur. Operations included numerous down-hole experiments in both areas and hydraulic piston coring of a 230-m sediment section in the hot area. Diagenesis of the sediments appears closely related to temperature. At the hot site, chert was found near basement, and the chemistry of pore fluids, sampled from both sediments and basement, is strongly influenced by reactions within the basement. Strong lateral gradients in the composition of pore fluids occur in the sediments. At the cold site, no chert was found, and bacterial processes within the sediment dominated the chemistry of the pore fluids. Basaltic basement in both areas consists mainly of pillow lavas and thin flows, with occasional more massive units. The basalt is relatively magnesian. The degree of alteration is very small in the cold area, but much more extensive in the hot area. Ease of drilling also shows a strong contrast. Basement penetration reached 562 m in the hot area and was halted because of lack of time; at the cold site, 43 m of basement was cored only with difficulty. The most intensive in-hole experiments were conducted in the hot area. Successful runs with the borehole televiewer allowed basement lithology to be determined and showed the presence of more and less fractured zones. Pulse tests using a single borehole packer gave values of basement permeability of about 2 to 40 millidarcies. Numerous temperature logs established a broadly conductive in situ temperature gradient, with temperatures reaching 120°C at 562 m into the basement. However, anomalously low temperatures in the upper part of the hole, which persisted after drilling disturbance had decayed away, showed that cold ocean water was flowing down the hole and into the basement at about 90 m below the base of the sediments, at rates of about 80 to 100 m/hr. The packer records indicate a pressure at this depth of 10 bars below hydrostatic.

Inherited structural controls on fault geometry, architecture and hydrothermal activity: an example from Grimsel Pass, Switzerland

Exhumed faults hosting hydrothermal systems provide direct insight into relationships between faulting and fluid flow, which in turn are valuable for making hydrogeological predictions in blind settings. The Grimsel Breccia Fault (Aar massif, Central Swiss Alps) is a late Neogene, exhumed dextral strike-slip fault with a maximum displacement of 25–45 m, and is associated with both fossil and active hydrothermal circulation. We mapped the fault system and modelled it in three dimensions, using the distinctive hydrothermal mineralisation as well as active thermal fluid discharge (the highest elevation documented in the Alps) to reveal the structural controls on fluid pathway extent and morphology. With progressive uplift and cooling, brittle deformation inherited the mylonitic shear zone network at Grimsel Pass; preconditioning fault geometry into segmented brittle reactivations of ductile shear zones and brittle inter-shear zone linkages. We describe ‘pipe’-like, vertically oriented fluid pathways: (1) within brittle fault linkage zones and (2) through alongstrike- restricted segments of formerly ductile shear zones reactivated by brittle deformation. In both cases, low-permeability mylonitic shear zones that escaped brittle reactivation provide important hydraulic seals. These observations show that fluid flow along brittle fault planes is not planar, but rather highly channelised into sub-vertical flow domains, with important implications for the exploration and exploitation of geothermal energy.

Origin of the gases released from the Acqua Passante and Ermeta wells (Mt. Amiata, central Italy) and possible environmental implications for their closure

The Mt. Amiata volcano (Tuscany, central Italy) hosts the second largest geothermal field of Italy. Its SW and NE sectors are characterized by the presence of several CO2-rich (mayor que95% by vol.) gas discharges. An intense Hg mining activity had taken place from the 19th century up to the end of the ?70s, particularly close to Abbadia San Salvatore, during which two drillings (Acqua Passante and Ermeta) intercepted a CO2-rich gas fertile horizon. The related gases are emitted in the atmosphere since 1938 and 1959, respectively, causing severe concerns for the local air quality. In this work the results of a geochemical and isotopic survey carried out on these gas emissions from March 2009 to January 2014 are presented. CO2 fluxes from both the two wells and soil from an area of about 653,500 m2 located between them were measured. The two wells are emitting up to 15,000, 92 and 8 tons y-1 of CO2, CH4 and H2S, respectively, while the computed soil CO2 output was estimated at 4,311 ton y-1. The spatial distribution of the CO2 soil flux suggests the presence of preferential patterns, indicating sites of higher permeability. Since the local municipality is evaluating the possibility to plug the Ermeta vent, a temporarily closure should first be carried out to test the possible influence of this operation on the diffuse soil degassing of deep-originated CO2 in the surrounding area. This implies that diffuse soil gases should carefully be monitored before proceeding with its definitive closure.

Reason and Being of Engineering Geology

This paper demonstrates the importance of a holistic comprehension of the Earth like a planet that is alive, not only in its Biosphere, looking at the atmosphere-ocean-crust-mantle interactions as its different sectorial expressions (climate, fluid-dynamics, morpho-dynamics, tectonics…) following the solar radiation and nuclear geothermal sources of energy. It considers the environmental incidence of different engineering activities to realize their underfeeding as the raison, and leads to that holistic formation as the being of the engineering geology

Asymptotic analysis of vertical geothermal boreholes in the limit of slowly varyng heat injection rates

Theoretical models for the thermal response of vertical geothermal boreholes often assume that the characteristic time of variation of the heat injection rate is much larger than the characteristic diffusion time across the borehole. In this case, heat transfer inside the borehole and in its immediate surroundings is quasi-steady in the first approximation, while unsteady effects enter only in the far field. Previous studies have exploited this disparity of time scales, incorporating approximate matching conditions to couple the near-borehole region with the outer unsteady temperatura field. In the present work matched asymptotic expansion techniques are used to analyze the heat transfer problem, delivering a rigorous derivation of the true matching condition between the two regions and of the correct definition of the network of thermal resistances that represents the quasi-steady solution near the borehole. Additionally, an apparent temperature due to the unsteady far field is identified that needs to be taken into account by the near-borehole region for the correct computation of the heat injection rate. This temperature differs from the usual mean borehole temperature employed in the literatura.