- Arsenic Contamination in Ground Water, Stable Isotopes, Ore Geology, Geochemistry, Sedimentary Geochemistry, Meteorite Impacts, and 16 morePaleoclimatology, Carbonate Diagenesis and Stratigraphy, Environmental Geochemistry, Analytical Geochemistry, Pyrite Formation, Paleooceanograhy, Sedimentology, Sulphur Stable Isotopes, Stable Carbon and Oxygen Isotopes, Paleofloods, Hydrogeochemistry, Trace element Geochemistry, Multivariate Data Analysis, Geostatistics, Mineral exploration, and Age of Chixculub impactedit
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excursion straddling the Harland Shale and Bridge Creek Limestone member (latest Cenomanian) at the Pueblo Stratotype, Colorado. Post-excursion,... more
Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excursion straddling the Harland Shale and Bridge Creek Limestone member (latest Cenomanian) at the Pueblo Stratotype, Colorado. Post-excursion, the delta13C values remain at approximately 2.0 ppm dipping only slightly in the early Turonian (H. helvetica zone). During the initial phases of the delta13C excursion, 5 planktic species consecutively become extinct (Rotalipora deekei, R. greenhornensis, R. cushmani, P. inornata, G. bentonensis). These are subsequently replaced in the latter stages of the excursions by 5 new species with high depth tolerances, resulting in no net diversity loss. The extinction is therefore likely to have been as a direct result from the increased water mass stratification. A temporary decrease in bottom water productivity is also suggested by oxygenated bottom waters (presence of Cibidicoides) and a minimum of low O_2 tolerant species (hetrohelicids). Elevated HI/OH...
Research Interests:
The distribution of As was explored in soils and crops in order to investigate the influence of irrigation with As rich groundwater on the soil–plant system, and to determine its impact on the environment and human health. The study was... more
The distribution of As was explored in soils and crops in order to investigate the influence of irrigation with As rich groundwater on the soil–plant system, and to determine its impact on the environment and human health. The study was carried out in an intensively cultivated ...
Research Interests:
The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the... more
The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ13Corg for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ13C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.
Research Interests:
Research Interests:
Stable isotopes of the surface dwelling planktic foraminifera Hedbergella planispira, its abundance variations, and mineralogical analysis of the Cenomanian–Turonian at Pueblo, CO, reveal cyclic variations in surface salinity due to... more
Stable isotopes of the surface dwelling planktic foraminifera Hedbergella planispira, its abundance variations, and
mineralogical analysis of the Cenomanian–Turonian at Pueblo, CO, reveal cyclic variations in surface salinity due to changes in
precipitation, freshwater influx, marine incursions and long-term sea-level fluctuations. Hedbergella planispira is a proxy for salinity variations, as indicated by 2–4x more negative d18O values in intervals of peak abundances as compared to intervals with reduced populations. Negative d18O values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods, accompanied by increased clastic transport. More positive d18O values reflect more normal marine salinities
as a result of arid periods and/or marine incursions and correlate with intervals of increased biogenic carbonate deposition. The magnitude of salinity variations during the low sea-level of the Hartland Shale is twice that during the sea-level transgression of the Bridge Creek Limestone. The rapid positive d13C shift that marks the onset of Oceanic Anoxic Event 2 (OAE 2) at Pueblo occurred over a period of about 100 ky (93.90–94.00 Ma), and coincided with the major sea level transgression that culminated in the deposition of the basal Bridge Creek Limestone. A positive d13C shift also occurred in the Rotalipora cushmani zone prior to OAE 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter. The likely cause for OAE 2 is depletion of 12C in the water column as a result of high primary productivity, whereas an earlier R. cushmani zone event was primarily caused by increased input of terrigenous organic matter. Both d13C events are associated with enhanced
organic matter preservation and anoxic or dysoxic bottom waters.
mineralogical analysis of the Cenomanian–Turonian at Pueblo, CO, reveal cyclic variations in surface salinity due to changes in
precipitation, freshwater influx, marine incursions and long-term sea-level fluctuations. Hedbergella planispira is a proxy for salinity variations, as indicated by 2–4x more negative d18O values in intervals of peak abundances as compared to intervals with reduced populations. Negative d18O values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods, accompanied by increased clastic transport. More positive d18O values reflect more normal marine salinities
as a result of arid periods and/or marine incursions and correlate with intervals of increased biogenic carbonate deposition. The magnitude of salinity variations during the low sea-level of the Hartland Shale is twice that during the sea-level transgression of the Bridge Creek Limestone. The rapid positive d13C shift that marks the onset of Oceanic Anoxic Event 2 (OAE 2) at Pueblo occurred over a period of about 100 ky (93.90–94.00 Ma), and coincided with the major sea level transgression that culminated in the deposition of the basal Bridge Creek Limestone. A positive d13C shift also occurred in the Rotalipora cushmani zone prior to OAE 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter. The likely cause for OAE 2 is depletion of 12C in the water column as a result of high primary productivity, whereas an earlier R. cushmani zone event was primarily caused by increased input of terrigenous organic matter. Both d13C events are associated with enhanced
organic matter preservation and anoxic or dysoxic bottom waters.
Research Interests:
Profound biotic changes accompanied the late Cenomanian d13C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover, though no mass extinction, beginning with the... more
Profound biotic changes accompanied the late Cenomanian d13C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover, though no mass extinction, beginning with the rapid d13C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding d13C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in
diversity to just two species, the dominant (80–90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here
demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.
diversity to just two species, the dominant (80–90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here
demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.
Research Interests:
Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of the new core Mullinax-1 and outcrops along the Brazos River and Cottonmouth Creek, Falls County, Texas, reveal the complex history of the... more
Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of the new core Mullinax-1 and outcrops along the Brazos River and Cottonmouth Creek, Falls County, Texas, reveal the complex history of the Chicxulub impact,
the event deposit and the K–T boundary event. The K–T boundary, as identified by the negative δ13C shift, first occurrence of Danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core Mullinax-1. The underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest Maastrichtian, as indicated by high stress microfossil
assemblages, small shells and burrows infilled with framboidal pyrite. The underlying event deposit, commonly interpreted as K–T impact tsunami, consists of a basal conglomerate with clasts containing Chicxulub impact spherules, repeated upward fining units of spherule-rich sands, followed by hummocky cross-bedded and laminated sands, which are burrowed by Thalassinoides, Planolites and Ophiomorpha and truncated by erosion. This suggests a series of temporally separated storm events with recolonization
of the ocean floor by invertebrates between storms, rather than a series of waning tsunami-generated waves. The lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the Chicxulub impact ejecta layer predates the event deposit, but was eroded and re-deposited during the latest Maastrichtian sea level lowstand. The original Chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late Maastrichtian clay- and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone CF1, which spans the last 300 kyr of the Maastrichtian. The yellow clay consists of cheto smectite derived from alteration of impact glass, as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and Chicxulub impact spherules from NE Mexico and Haiti. The Brazos sections thus provide strong evidence that the Chicxulub impact predates the K–T boundary by about 300 kyr, consistent with earlier observations in NE Mexico and the Chicxulub crater core Yaxcopoil-1.
the event deposit and the K–T boundary event. The K–T boundary, as identified by the negative δ13C shift, first occurrence of Danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core Mullinax-1. The underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest Maastrichtian, as indicated by high stress microfossil
assemblages, small shells and burrows infilled with framboidal pyrite. The underlying event deposit, commonly interpreted as K–T impact tsunami, consists of a basal conglomerate with clasts containing Chicxulub impact spherules, repeated upward fining units of spherule-rich sands, followed by hummocky cross-bedded and laminated sands, which are burrowed by Thalassinoides, Planolites and Ophiomorpha and truncated by erosion. This suggests a series of temporally separated storm events with recolonization
of the ocean floor by invertebrates between storms, rather than a series of waning tsunami-generated waves. The lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the Chicxulub impact ejecta layer predates the event deposit, but was eroded and re-deposited during the latest Maastrichtian sea level lowstand. The original Chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late Maastrichtian clay- and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone CF1, which spans the last 300 kyr of the Maastrichtian. The yellow clay consists of cheto smectite derived from alteration of impact glass, as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and Chicxulub impact spherules from NE Mexico and Haiti. The Brazos sections thus provide strong evidence that the Chicxulub impact predates the K–T boundary by about 300 kyr, consistent with earlier observations in NE Mexico and the Chicxulub crater core Yaxcopoil-1.
Research Interests:
The response of shallow-water sequences to oceanic anoxic event 2 and mid- Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the... more
The response of shallow-water sequences to oceanic anoxic event 2 and mid-
Cenomanian events 1a and 1b was investigated along the west African margin
of Morocco north of Agadir (Azazoul) and correlated with the deep-water
sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy,
mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach
section results show double peaks in d13Corg for mid-Cenomanian events 1a
and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic
oceanic anoxic event 2 d13C excursion (Rotalipora cushmani extinction, top of
CC10a biozone) and laminated (anoxic) black shale. In the shallow
environment north of Agadir, a fluctuating sea-level associated with dysoxic,
brackish and mesotrophic conditions prevailed during the middle to late
Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and
benthonic foraminiferal assemblages. Anoxic conditions characteristic of
oceanic anoxic event 2 (for example, laminated black shales) did not reach
into shallow-water environments until the maximum transgression of the early
Turonian. Climate conditions decoupled along the western margin of Morocco
between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary,
as also observed in eastern Tethys. North of Agadir alternating humid and dry
seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was
dry and seasonal. This climatic decoupling can be attributed to variations in
the Intertropical Convergence Zone and in the intensity of the north-east trade
winds in tropical areas.
Cenomanian events 1a and 1b was investigated along the west African margin
of Morocco north of Agadir (Azazoul) and correlated with the deep-water
sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy,
mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach
section results show double peaks in d13Corg for mid-Cenomanian events 1a
and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic
oceanic anoxic event 2 d13C excursion (Rotalipora cushmani extinction, top of
CC10a biozone) and laminated (anoxic) black shale. In the shallow
environment north of Agadir, a fluctuating sea-level associated with dysoxic,
brackish and mesotrophic conditions prevailed during the middle to late
Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and
benthonic foraminiferal assemblages. Anoxic conditions characteristic of
oceanic anoxic event 2 (for example, laminated black shales) did not reach
into shallow-water environments until the maximum transgression of the early
Turonian. Climate conditions decoupled along the western margin of Morocco
between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary,
as also observed in eastern Tethys. North of Agadir alternating humid and dry
seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was
dry and seasonal. This climatic decoupling can be attributed to variations in
the Intertropical Convergence Zone and in the intensity of the north-east trade
winds in tropical areas.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Engineering, Water, Arsenic, Water Purification, Filtration, and 16 moreAdsorption, Carbonates, Toxicity, Ground Water, Surface Water, Hazardous Materials, Cost effectiveness, Water Use, Hydrogen Peroxide, Waste Treatment, Conditioning, Industrial Waste, Reactor, Oxidation, Ferric Compounds, and Cacodylic Acid
Research Interests:
Research Interests:
Research Interests:
Research Interests: Evolutionary Biology, Palaeogeography, Geology, Geochemistry, Climate Change, and 13 moreStable Isotopes, Ecology, Sea Level, Clay Minerals, Stable Isotope, Mass Extinction, Trace Elements, Primary Production, Clay mineralogy, Environmental Conditions, Total Organic Carbon, Trace element, and Planktic Foraminifera
Yaxcopoil-1 (Yax-1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous-Tertiary (K/T) boundary. Instead, contrary... more
Yaxcopoil-1 (Yax-1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous-Tertiary (K/T) boundary. Instead, contrary evidence was discovered based on five independent proxies (sedimentologic, biostratigraphic, magnetostratigraphic, stable isotopic, and iridium) that revealed that the Chicxulub impact predates the K/T boundary by about 300,000 years and could not have caused the mass extinction. This is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest Maastrichtian zone CF1 and is corroborated by magnetostratigraphic chron 29r and characteristic late Maastrichtian stable isotope signals. These results were first presented in Keller et al. (2004). In this study, we present more detailed evidence of the presence of late Maastrichtian planktic foraminifera, sedimentologic, and mineralogic analyses that demonstrate that the Chicxulub impact breccia predates the K/T boundary and that the sediments between the breccia and the K/T boundary were deposited in a normal marine environment during the last 300,000 years of the Cretaceous.
Research Interests:
Spherule deposits, commonly interpreted as ejecta from the Chicxulub impact at Yucatán, Mexico, are present in many K-T (Cretaceous-Tertiary) sections. Geological mapping of the northern La Sierrita area, NE Mexico, revealed the presence... more
Spherule deposits, commonly interpreted as ejecta from the Chicxulub impact at Yucatán, Mexico, are present in many K-T (Cretaceous-Tertiary) sections. Geological mapping of the northern La Sierrita area, NE Mexico, revealed the presence of (1) multiple spherule deposits embedded in late Maastrichtian marls, which are folded or disaggregated (breccia-like). They are up to 6 m thick, locally present in two outcrop areas, and show limited lateral continuity. These deposits consist of mm–cm sized spherical to drop-shaped vesiculated spherules, angular to filamentous (ejecta-) fragments and abundant carbonate. They are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps-slides, liquefaction, and debris flows; welded components suggest an initial ground surge-like ejecta-dispersion mode. (2) A spherule deposit, 10–60 cm thick that constitutes the base of a channelized sand-siltstone deposit at, or close to, the K-T boundary and is characterized by wide lateral continuity. It is of similar petrologic composition to deposit (1), though slightly enriched in terrigeneous detritus, thus reflecting influx from proximal shelf areas. It is interpreted to result from debris flows and turbidite currents, though no size sorting and abrasion of ejecta has been observed. Petrological, mineralogical, and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the Chicxulub impact, with multiple deposits produced by subsequent remolding, reworking, and redeposition. Spherules and fragments have an Fe- (25–30 wt%), Al-, Mg-rich and Si-poor (SiO2) composition, and are altered to chlorite and iron-oxides, though rare K-rich mafic glass (~50 wt% SiO2; 5–8 wt% K) is also present. They contain Ti-, Fe-, K-rich schlieren, Fe-, Mg-rich globules, and rare µm-sized metallic and sulfidic Ni-, Co-rich inclusions. Carbonate as clasts and within spherules and fragments shows textures indicative of quenching and/or liquid immiscibility. Although potential ejecta fractionation and alteration make accurate evaluation difficult, this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments, in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination.
Research Interests:
Research Interests:
Research Interests:
Examination of new expanded K/T boundary sections near Beloc, Haiti, reveals deposition of a glass spherule-rich deposit (SRD) and two (PGE) anomalies (one Ir-dominated and one Pd-dominated) during the early Danian Parvularugoglobigerina... more
Examination of new expanded K/T boundary sections near Beloc, Haiti, reveals deposition of a glass spherule-rich deposit (SRD) and two (PGE) anomalies (one Ir-dominated and one Pd-dominated) during the early Danian Parvularugoglobigerina eugubina Zone [Pla(l)]. The presence of the Haiti SRD within the early Danian is interpreted as being due to reworking. Ir is only slightly elevated within the SRD but forms an anomaly at the top of the SRD extending into the overlying pelagic limestones. It is unclear at present whether this Ir anomaly results from mechanical reworking of an impact at the K/T boundary, or an additional impact event in the early Danian. The second PGE anomaly upsection is dominated by Pd and Pt and is more compatible with a magmatic origin. This suggests a multi-event scenario consistent with one (and possibly two) impact(s), followed by a PGE-enriched volcanic event in the Caribbean.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT The unusually high grade hypogene zinc ore at Angouran in northwestern Iran (40.4% Zn, 1.9% Pb in the sulfide ore, 28.1% Zn, 4.4% Pb in the carbonate ore, and 110 g/t Ag) formed from an initially highly saline, reduced,... more
ABSTRACT The unusually high grade hypogene zinc ore at Angouran in northwestern Iran (40.4% Zn, 1.9% Pb in the sulfide ore, 28.1% Zn, 4.4% Pb in the carbonate ore, and 110 g/t Ag) formed from an initially highly saline, reduced, relatively acid hydrothermal brine at two successive sulfide and carbonate ore stages. The early ore stage consists of multiple phases of sphalerite dominated sulfide ore breccia with subordinate amounts of galena (± Pb sulfosalts), minor pyrite, and abundant barite. Sphalerite precipitated at moderate temperatures (≥ 155 °C) because of pH increase in the presence of hangingwall marble. Smithsonite precipitated at a higher pH value (≥ 7) and at lower temperatures (≤ 120 °C) from dilute solutions (salinities close to zero) by mixing of the Zn bearing brines with cool, HCO3− bearing waters. The first melting points of the primary (LV) fluid inclusions in sphalerite and in hydrothermal quartz are unusually low (≤ − 60 °C), close to the eutectic point of the ZnCl2–H2O system (− 62 °C). Total salinities taken from the ZnCl2–H2O system as a best approximation correspond to 26–41 eq mass % ZnCl2. The initial brine evolved to a CaCl2–NaCl rich solution with 27 eq mass % salinity. Gas densities (≤ 0.1 g cm− 3 for water vapor and ≤ 0.18 g cm− 3 for CO2) in the fluid inclusions indicate low pressure (≤ 5 bar for water vapor, and ≤ 100 bar for CO2) at the entrapment temperatures.At the first carbonate ore stage sulfides continued to precipitate characteristically as arsenopyrite with minor amounts of galena and pyrite. The abrupt change of the fluid composition at the sulfide–carbonate boundary was accompanied by a change of the fluid temperature and pressure that produced brecciation of the sulfide ore matrix and an almost total dissolution of barite and replacement by the hypogene smithsonite. Alteration is restricted to ore deposition and consists of weak sericitization and silicification with local dolomitization at the sulfide ore stage, and pervasive dissolution of the hangingwall marble, in particular at the carbonate ore stage.The breccia orebody at Angouran is sited at the crestal portion of a domed antiform at the lithological and thrust boundary of Neoproterozoic–Lower Cambrian footwall schists and the hangingwall marble in rapidly uplifted and exhumated Angouran Block east of the Geynardjeh Thrust Fault. The footwall schists occupy a detachment fault zone above imbricated nappe sheets of the basement metamorphic complex of the Sanandaj–Sirjan zone. During the Pliocene, the nappe sheets were thrust toward the southwest onto the Miocene felsic volcanic rocks of the Urumieh Dokhtar Volcanic Belt that are intruded by 10 Ma late Miocene basalts. The 11.9 Ma and 18.4 Ma zircon ages of the felsic volcanic rocks indicate the lower age limit of the ore body emplacement.The associations with large scale, mid-late Miocene, felsic volcanism along the active Tethyan belt, as well as the ubiquitous presence of the volcanic rock clasts in the sphalerite ore matrix, provide strong evidence of the involvement of hydrothermal processes at Angouran. Ore fluids were successively and pulsatorily generated within the seismically active region. A following geothermal activity appears to have had a significant input in the formation of the carbonate ore of the hypogene, as well as the supergene stage. Stable isotope data suggest complex interaction of element sources and processes. Allowing a broad interpretation, the sulfur isotopic composition of the sulfides δ34S (3.9 to 7.4‰) suggests that the sulfur could be sourced from evolving, mixed magmatic–basinal brine. The isotopic composition of the hypogene smithsonites (δ13C: 2.72 to 5.51‰, δ18O: 18.4 to 22.8‰) broadly supports the local geology and field relationships, which comply with a marble wallrock source for the carbonate ores. They lend support to the assumption that smithsonite was deposited from solutions with isotopic composition similar to those involved in the hydrothermal dolomitization of the marbles. The excess of dissolved marble precipitated as large volumes of travertine and as late calcite veins (δ13C: 18.8 to 20.3‰, δ18O: 3.1 to 6.4‰) at the mineralization site. Isotope values of the travertine (δ13C: 4.5 to 6.6‰, δ18O: 20.1 to 21.1‰ V-SMOW) are consistent with the involvement of CO2 derived from thermogenic decarbonization of the host marble by waters of dominantly meteoric origin, most likely concomitantly with ore forming processes.The Angouran deposit is the only reported case of a two stage, hypogene zinc sulfide–zinc carbonate mineralization, and represents a new style of nonsulfide zinc mineralization.
Research Interests: Geology and Geochemistry
Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excursion straddling the Harland Shale and Bridge Creek Limestone member (latest Cenomanian) at the Pueblo Stratotype, Colorado. Post-excursion,... more
Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excursion straddling the Harland Shale and Bridge Creek Limestone member (latest Cenomanian) at the Pueblo Stratotype, Colorado. Post-excursion, the delta13C values remain at approximately 2.0 ppm dipping only slightly in the early Turonian (H. helvetica zone). During the initial phases of the delta13C excursion, 5 planktic species consecutively become extinct (Rotalipora deekei, R. greenhornensis, R. cushmani, P. inornata, G. bentonensis). These are subsequently replaced in the latter stages of the excursions by 5 new species with high depth tolerances, resulting in no net diversity loss. The extinction is therefore likely to have been as a direct result from the increased water mass stratification. A temporary decrease in bottom water productivity is also suggested by oxygenated bottom waters (presence of Cibidicoides) and a minimum of low O_2 tolerant species (hetrohelicids). Elevated HI/OH...
Research Interests:
Research Interests:
Zusammenfassung Reifen-, Ruß-, Motorenöl-, Asphalt-, Plastik- und Lackproben aus dem Straßenverkehr wurden auf ihre Kohlenstoff- und Schwefel-isotopenverhältnisse mit dem Ziel untersucht, die Frage zu beant-worten, ob diese... more
Zusammenfassung Reifen-, Ruß-, Motorenöl-, Asphalt-, Plastik- und Lackproben aus dem Straßenverkehr wurden auf ihre Kohlenstoff- und Schwefel-isotopenverhältnisse mit dem Ziel untersucht, die Frage zu beant-worten, ob diese Isotopenverhältnisse als Indikatoren für die Belastungssituation und die Schadstoffquellen bei der Untersuchung von straßennahen Böden eingesetzt werden können. Die δ11C-Werte der technischen Substrate lagen zwischen-30‰ und-18‰ relativ zum PDB-Standard, Dabei zeigte sich aufgrund der
Research Interests:
The TEX86 paleotemperature proxy, based on tetraether membrane lipids derived from aquatic Crenarchaeota has been applied in a variety of marine and lacustrine systems. A recent study analyzing a suite of 50 globally distributed lakes for... more
The TEX86 paleotemperature proxy, based on tetraether membrane lipids derived from aquatic Crenarchaeota has been applied in a variety of marine and lacustrine systems. A recent study analyzing a suite of 50 globally distributed lakes for TEX86 discovered that this proxy does not appear to work in all lake systems and that the TEX86 correlates well with both annual and
Research Interests: Climate Change, Sea Level, Clay Minerals, Stratification, Environmental Change, and 19 moreGlobal change, Seasonality, Sea level rise, Land Surface Temperature, Surface Water, Upper Cretaceous, Mass Extinction, Water Temperature, Sediment Traps, Lake superior, Deep water, Dinoflagellate cysts, Marine Environment, Annual Cycle, Particulate Matter, Nutrient Loading, Organic Matter, Suspended Particulate Matter, and Planktic Foraminifera
In the wake of the idea that surface derived dissolved organic carbon (DOC) plays an important role in the mobilization of arsenic (As) from sediments to groundwater and may provide a vital tool in understanding the mechanism of As... more
In the wake of the idea that surface derived dissolved organic carbon (DOC) plays an important role in the mobilization of arsenic (As) from sediments to groundwater and may provide a vital tool in understanding the mechanism of As contamination (mobilization/fixation) in Bengal delta; a study has been carried out. Agricultural fields that mainly cultivate rice (paddy fields) leave significantly large quantities of organic matter/organic carbon on the surface of Bengal delta which during monsoon starts decomposing and produces DOC. The DOC thus produced percolates down with rain water and mobilizes As from the sediments. Investigations on sediment samples collected from a paddy field clearly indicate that As coming on to the surface along with the irrigation water accumulates itself in the top few meters of sediment profile. The column experiments carried out on a 9 m deep sediment profile demonstrates that DOC has a strong potential to mobilize As from the paddy fields and the water recharging the aquifer through such agricultural fields contain As well above the WHO limit thus contaminating the shallow groundwater. Experiment also demonstrates that decay of organic matter induces reducing condition in the sediments. Progressively increasing reducing conditions not only prevent the adsorption of As on mineral surfaces but also cause mobilization of previously sorbed arsenic. There seems to be a cyclic pattern where As from deeper levels comes to the surface with irrigational water, accumulates itself in the sediments, and ultimately moves down to the shallow groundwater. The extensive and continual exploitation of intermediate/deep groundwater accelerates this cyclic process and helps in the movement of shallow contaminated groundwater to the deeper levels.
Research Interests:
High concentrations of As in groundwater frequently occur throughout the world. The dissolved concentration, however, is not necessarily determined by the amount of As in the ambient sediment but rather by the partitioning of As between... more
High concentrations of As in groundwater frequently occur throughout the world. The dissolved concentration, however, is not necessarily determined by the amount of As in the ambient sediment but rather by the partitioning of As between different minerals and the type of fixation. Sequential extractions are commonly applied to determine associations and binding forms of As in sediments. Due to the operational nature of the extracted fractions, however, the results do not provide insight into how and where precisely As is bound within mineral grains and no information about elemental associations or involved mineral phases can be gained. Furthermore, little is known about possible geochemical alterations that actually occur within a single grain during sequential extraction. Therefore, micro-synchrotron X-ray fluorescence analysis was applied to study the micro-scale distribution of As and other elements in single sediment grains. Arsenic was found to be mainly enriched in Fe oxy-hydroxide coatings along with other heavy metals resulting in high correlations. Phosphate leached 34-66% of As from the studied grains. The release of As in this leaching step was accompanied by the disappearance of correlations between As and Fe as well as by a higher Fe/As ratio compared to untreated samples. During the Fe-leaching step the coatings were largely dissolved leading to much lower concentrations of As and Fe. The correlation between As and Fe was preserved only in association with K, indicating the presence of both elements in silicate structures. Several distinctive features were observed such as the release of Fe, Mn and Cr during phosphate leaching as well as the lowering of mean K concentrations due to the Fe-leaching which indicates that not only target mineral phases were dissolved in these extraction steps. The importance of re-precipitation processes during sequential extraction was indicated by a consistently observed increase of the Fe/As ratio from the untreated to the Fe-leached samples.