Papers by Judith McKenzie
Basaltic breccias cored at Hole 373A contain four generations of internally resedimented intercla... more Basaltic breccias cored at Hole 373A contain four generations of internally resedimented interclast limestone and four generations of void-filling calcite cement. Two of the limestone generations are pelagic carbonate oozes that infiltrated from the sea floor into voids. The other two generations of limestone apparently originated as diagenetic sediment which was precipitated and deposited within breccia interstices. Superimposed upon this complex pattern of resedimentation and cementation were repeated episodes of brecciation and fracturing. Oxygen and carbon isotopic compositions indicate that cementation of the breccias and lithification of the carbonate sediments occurred at low temperatures characteristic of deep bottom waters. Much if not all of this sea-floor carbonate diagenesis may be related to low temperature, submarine alteration of basalt. Ferruginous dolomites which lie stratigraphically above the basalts likewise formed at low temperatures, probably also as a conseque...
A “Strangelove” ocean in the earliest Tertiary
Geophysical Monograph Series, 2013
A" STRANGELOVE" OCEAN IN THE EARLIEST TERTIARY Kenneth J. Hsu and. ... A&qu... more A" STRANGELOVE" OCEAN IN THE EARLIEST TERTIARY Kenneth J. Hsu and. ... A" Strangelove" Ocean Considerable evidence has been presented that a meteor impact was responsible for mass extinc-tion at the end of the Cretaceous [Alvarez et al., 1980; Hsu, 1980]. ...
Sedimentology, 2010
Modern Ca:Mg carbonate stromatolites form in association with the microbial mat in the hypersalin... more Modern Ca:Mg carbonate stromatolites form in association with the microbial mat in the hypersaline coastal lagoon, Lagoa Vermelha (Brazil). The stromatolites, although showing diversified fabrics characterized by thin or crude lamination and/or thrombolitic clotting, exhibit a pervasive peloidal microfabric. The peloidal texture consists of dark, micritic aggregates of very high-Mg calcite and/or Ca dolomite formed by an iso-oriented assemblage of sub-micron trigonal polyhedrons and organic matter. Limpid acicular crystals of aragonite arranged in spherulites surround these aggregates. Unlike the aragonite crystals, organic matter is present consistently in the dark, micritic carbonate comprising the peloids. This organic matter is observed as submicron flat and filamentous mucus-like structures inside the interspaces of the high-Mg calcite and Ca dolomite crystals and is interpreted as the remains of degraded extracellular polymeric substances. Moreover, many fossilized bacterial cells are associated strictly with both carbonate phases. These cells consist mainly of 0AE2 to 4 lm in diameter, sub-spherical, rod-like and filamentous forms, isolated or in colony-like clusters. The co-existence of fossil extracellular polymeric substances and bacterial bodies, associated with the polyhedrons of Ca:Mg carbonate, implies that the organic matter and microbial metabolism played a fundamental role in the precipitation of the minerals that form the peloids. By contrast, the lack of extracellular polymeric substances in the aragonitic phase indicates an additional precipitation mechanism. The complex processes that induce mineral precipitation in the modern Lagoa Vermelha microbial mat appear to be recorded in the studied lithified stromatolites. Sub-micron polyhedral crystal formation of high-Mg calcite and/or Ca dolomite results from the coalescence of carbonate nanoglobules around degraded organic matter nuclei. Sub-micron polyhedral crystals aggregate to form larger ovoidal crystals that constitute peloids. Subsequent precipitation of aragonitic spherulites around peloids occurs as micro-environmental water conditions around the peloids change.
FEMS Microbiology Ecology, 2007
We investigated the precipitation of carbonate and phosphate minerals by 19 species of moderately... more We investigated the precipitation of carbonate and phosphate minerals by 19 species of moderately halophilic bacteria using media with variable Mg 21 /Ca 21 ratios. The precipitated minerals were calcite, magnesium (Mg) calcite, and struvite (MgNH 4 PO 4 Á 6H 2 O) in variable proportions depending on the Mg 21 / Ca 21 ratio of the medium. The Mg content of the Mg-calcite decreased with increasing Ca 21 concentration in the medium. According to the saturation indices, other minerals could also have precipitated. We observed important differences between the morphology of carbonate and phosphate, which may help us to recognize these minerals in natural systems. We studied the growth and pH curves of four bacteria in media specific for carbonate and struvite precipitation. We consider the biomineralization processes that produce carbonate and phosphate minerals, and propose a hypothesis for the lack of struvite in natural environments and ancient rocks.
Oceanography, 2019
Permission is granted for individuals to read, download, copy, distribute, print, search, and lin... more Permission is granted for individuals to read, download, copy, distribute, print, search, and link to the full texts of Oceanography articles. Figures, tables, and short quotes from the magazine may be republished in scientific books and journals, on websites, and in PhD dissertations at no charge, but the materials must be cited appropriately (e.g., authors, Oceanography, volume number, issue number, page number[s], figure number[s], and DOI for the article). Oceanography is permitted only with the approval of The Oceanography Society.
We wish to thank the European Commission for its support of the Deep Sea & Sub-Seafloor Frontier ... more We wish to thank the European Commission for its support of the Deep Sea & Sub-Seafloor Frontier Coordination Action (Grant agreement 244099) and its main deliverable, this position paper. The DS 3 F Steering Committee gratefully acknowledges all scientists, policymakers and stakeholders contributing to workshops and conferences within the Coordination Action. The German Consortium for Marine Research, KDM, is thanked for hosting meetings in its Brussels representation and for its general support. Special thanks go to Susan Beddig for editing. Legal notice Neither the European Commission nor any person of the DS 3 F Steering Committee is responsible for the use which might be made of the following position paper. The views expressed in this publication are the sole responsibility of the authors and not necessarily of the European Commission. Reproduction is not authorised.
This proposal aims to address fundamental questions related to mechanisms responsible for the dra... more This proposal aims to address fundamental questions related to mechanisms responsible for the dramatic salinity fluctuations experienced by the Mediterranean Basin during the terminal stages of the Messinian Salinity Crisis (MSC) ~6 to 5 million years ago. The processes by which this large water mass underwent a rapid hypersaline-brackish-normal seawater evolution in ca. 600ky are still widely unknown: this refers in particular to the influence of monsoons via large African and Arabian river systems, and of the Paratethys, on the hydrological cycle and its evolution in the MSC. Just after the emplacement of up to 3-4 km of salt in the deepest part of the Mediterranean basin, short-lived and dramatic environmental perturbations led to the formation of brackish-water Lago-Mare deposits. These environmentally enigmatic accumulations may serve as a record to better understand diagenetic mechanisms responsible for dolomitization. Based on results of previous DSDP drilling (Leg 42, site 374), the Lago-Mare related dolomite deposit could hold the key for understanding the little known processes that lead to microbially-mediated, low-temperature formation of this geologically relevant carbonate mineral. The central and eastern Mediterranean MSC deposits are ideally located for understanding 1) the hydrological connectivity among all sub-basins and with the Paratethys, 2) the response of major circum-Mediterranean rivers to the demise of the Messinian salt giant and 3) the link between evaporite formation, microbial activity and dolomitization. Therefore, we propose to sample and analyse in these basins the record of the last stages of the MSC, including Lago Mare facies and the upper part of the evaporite/clastic series, which were not fully cored in previous scientific drilling campaigns (DSDP/ODP Legs 13, 42, 160). We propose to drill four sites, two in the Ionian Basin and two in the Levant Basin, which would penetrate (in descending order): open-marine Pliocene siliciclastic deposits hosting the hypothesized active dolomitization front; lacustrine Lago-Mare sulphate evaporites, carbonates, marls, and siliciclastic accumulations; and Upper Messinian salts. These sequences are accessible to riserless drilling; the depth below mudline ranges from ca. 600m to 1000m and TD is located within the top of the halite, without approaching the base of the main salt unit. The wider scientific objectives on the mechanisms of the MSC termination and probable biosphere modulated dolomitization processes are in line with the strategy of the 857-MDP2 Umbrella proposal 'Uncovering a Salt Giant', and complementary to the pre-proposal P857B 'Deep Sea Records of the Messinian Salinity Crisis (DREAM). The demise of a salt giant: climatic-environmental transition during the terminal Messinian Salinity Crisis
Natural Variations in the Carbon Cycle During the Early Cretaceous
The Carbon Cycle and Atmospheric CO2 : Natural Variations Archean to Present
Bottom water evolution in different bathymetric and paleogeographic environments are studied in l... more Bottom water evolution in different bathymetric and paleogeographic environments are studied in lower Cretaceous pelagic sediments deposited in the Central Tethys Ocean and along its southern continental margin and outcroppings in the Swiss and Italian Alps. A progressive shallowing of the low oxygen or anoxic water mass is seen in cycles of Barremian pelagic limestones and organic, carbon-rich shales from
The Sabkhas Of Qatar: An Ideal Place To Study The Origin Of Dolomitic Hydrocarbon Reservoir Rocks
Qatar Foundation Annual Research Conference Proceedings Volume 2014 Issue 1
Many hydrocarbon reservoirs - in Qatar and worldwide - are constituted of dolomite. For this reas... more Many hydrocarbon reservoirs - in Qatar and worldwide - are constituted of dolomite. For this reason, the origin of this Ca-Mg carbonate mineral has been extensively studied by generations of geologists, with the goal of exploiting gas and oil from rock reservoirs in the most efficient way. However, despite more than two centuries of research, several fundamental questions regarding the origin of sedimentary dolomite remain without a convincing answer. Recent research conducted in the field of geobiology suggests that dolomite formation may be the result of a microbial process, that is, organic molecules that in natural environments are produced by microorganisms seem to play a key role for dolomite nucleation at low temperatures in many geological settings. However, this innovative hypothesis is far from being unanimously accepted by the scientific community, and many details on the exact mechanism through which microorganisms mediate dolomite formation are still to be fully understood. The aim of this contribution is to summarize the most recent scientific studies that support the microbial model for dolomite formation, providing examples from culture experiments conducted in the laboratory using artificial growth solutions and from modern dolomite forming environments, such as the hypersaline lagoons located in the State of Rio de Janeiro (Brazil), the sabkhas of Abu Dhabi (UAE), and the sabkhas of Dohat Faishakh and Khor Al-Adaid (Qatar). Furthermore, we will elaborate on why we consider the coastal sabkhas of Qatar to be among the most ideal places on Earth where it is possible to study microbe-mineral interactions in evaporitic environments. In fact, thanks to the distinctive geology that characterizes this region, it is possible to obtain samples documenting the progressive transformation of the living microbial mats that mediate dolomite formation and other authigenic minerals into a fully lithified sediment, which is analogous to dolomite formations constituting economically important gas/oil reservoir rocks. This approach will provide key insights to test whether dolomite present in ancient evaporitic sequences can be interpreted as a fully biological product associated with early diagenesis or whether most of the dolomite forms during later stage metamorphic/replacement events that are controlled by purely abiotic processes. Finally, considering not only the scientific importance but also the aesthetic beauty of the Qatari evaporitic environments, we will discuss the idea and the challenges of transforming selected areas of the modern sabkhas into geoparks - protected natural reserves that would be of interest for the local Qatari population, as well as for tourists visiting Qatar.
Fossilized Extracellular Polymeric Substances And Microfossils Preserved In Ancient Dolomite
Qatar Foundation Annual Research Conference Proceedings Volume 2014 Issue 1
Dolomite is an important constituent of many economically important gas and oil reservoir rocks. ... more Dolomite is an important constituent of many economically important gas and oil reservoir rocks. Studies conducted in modern environments combined with microbiological laboratory experiments have shown that microbes and their extracellular polymeric substances (EPS) play an important role for the formation of primary dolomite at Earth's surface conditions. These studies showed that, at low temperature, Mg is incorporated into the carbonate mineral exclusively in the presence of specific organic molecules. However, because the organic molecules involved in the mineralization process rarely survive metamorphism and are usually not preserved in the carbonate mineral, identifying microbial dolomite in ancient rocks represents a challenging task. It remains, as yet, unclear what percentage of sedimentary dolomite is a primary microbially mediated precipitate vs. a secondary replacement product that formed during diagenesis or at high temperatures during metamorphism. A useful approach for evaluating the microbial origin of ancient dolomite is that of searching for microfossils and other microstructures of biological origin associated with the dolomite crystals. Here, we present the results of scanning electron microscopy (SEM) investigations of various ancient sedimentary dolomites. Several investigated samples include abundant filamentous microstructures that we interpret to be mineralized EPS. In some cases, these filaments form a well-structured alveolar pattern, whose architecture appears too complex to be the result of an abiotic process. In order to reinforce our interpretation, we also investigated modern biofilms, which include microstructures of EPS that are morphologically identical to the mineralized and preserved EPS in ancient dolomites. In some rare cases, we also found microfossils (i.e. mineralized cells) in close spatial association with the dolomite crystals. These occurrences are remarkable, considering that it is commonly thought that only chert has the potential of preserving the soft tissues constituting microbial cells. Although we cannot prove conclusively that the fossilized cells and EPS mediated the formation of the adjacent dolomite crystals, our results indicate that dolomite formation took place in environments where microorganisms and biofilms were an important component of the depositional setting. The "microbial factor", which has been proven to be essential for the precipitation of dolomite at low temperature in modern environments, may, therefore, have also been active during the formation of these ancient carbonates.
Proceedings of the Ocean Drilling Program, 107 Scientific Results
Strontium isotopic ratios of gypsums recovered from upper Miocene (Messinian) evaporites at ODP L... more Strontium isotopic ratios of gypsums recovered from upper Miocene (Messinian) evaporites at ODP Leg 107 Holes 652A, 653B, and 654A (Tyrrhenian Sea) are lower than expected. The values for the Messinian balatino-like gypsum, single gypsum crystals, and anhydrites range from 0.70861 to 0.70886 and are approximately 25 x I0-5 less than would be expected for evaporites precipitated from Messinian seawater (0.70891-0.70902). Pre-evaporitic planktonic foraminifers from Hole 654A show variable degrees of dolomitization and 87 Sr/ 86 Sr values that irregularly decrease upward from normal marine values approximately 81m below the lowest evaporite occurrence. This suggests diagenetic alteration by advecting interstitial water with a low 87 Sr/ 86 Sr ratio or that the lower Sr isotopic ratios for the Messinian evaporites could have resulted from a greater influence of fresh water on the Sr isotopic composition of the desiccating Tyrrhenian Sea. Fluctuations of the 87 Sr/ 86 Sr-ratio for evaporites in the sedimentary cycles recognized for Holes 653B and 654A, the generally low Sr isotopic ratio of river water entering the Mediterranean Sea, and the presence of dwarf marine microfossils suggest that the 87 Sr/ 86 Sr ratio of the evaporites responded to hydrologic variations in a very restricted basin with variable rates of marine and fresh water input. The strontium isotopic ratios of the Messinian anhydrites from the proposed lacustrine sequence at Hole 652A fall in the same range as the marine evaporites from Holes 654A and 653B. This suggests a common or similar origin of the brines at the three locations. The complex depositional and hydrologic conditions in the Mediterranean during the Messinian salinity crisis preclude the use of Sr isotopic values from the evaporites for stratigraphic correlation and dating. They are, however, very useful in the interpretation of the depositional history of the basin. General calculations assuming a closed system suggest that the 87 Sr/ 86 Sr ratio of Messinian seawater (-0.7090) could be reduced to that of the evaporites (-0.7087) by mixing with fresh water (e.g., Nile River) in times of I0 4 to I0 5 yr.
Calibration of the d18O paleothermometer for dolomite precipitated in microbial cultures and natural environments
Geology, 2005
Role of microbial community in stalactite formation, Sahastradhara caves, Dehradun, India
Current Science, 2005
Speleothems found in three caves in Sahastradhara, Dehradun, India were studied to understand if ... more Speleothems found in three caves in Sahastradhara, Dehradun, India were studied to understand if geomicrobiological processes were involved in mineral formation. Mineralogical studies (XRD and SEM-EDAX) of the stalactite samples revealed that calcite is the dominant mineral. An abundant microbial community (9 × 10 5 cells, g sed - 1 ) was detected by direct microscopic observation after DAPI staining. Application of fluorescence in situ hybridization techniques (FISH), based on the presence of rRNA, demonstrates the presence of a large number of active microbial cells (around 55 % of the total cell number). The microbial community is dominated by Eubacteria, mainly sulphate-reducing bacteria (representing 10% of the total microbial community), but Archaea are also present. A significant fraction of these cells are active, indicating the high probability of their participation in biomineralization processes involved in the stalactite formation. This conclusion is at variance with the established classical model for stalactite formation based entirely on inorganic processes associated with carbonate solubility.
Precision bio- and isotope-stratigraphy and the
Sedimentology, Apr 1, 2003
Recent dolomitic sediment samples from Lagoa Vermelha, Brazil, were examined microscopically to s... more Recent dolomitic sediment samples from Lagoa Vermelha, Brazil, were examined microscopically to study the process of bacterial fossilization in carbonate sediments. Bacteria-like bodies were intimately associated with carbonate mineral surfaces, and coatings on the former demonstrate the calcification of single bacterial cells. The bacterial fossilization process in Lagoa Vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate-reducing bacteria, which were isolated from the Lagoa Vermelha sediments. These cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process. In mixed culture experiments, bacterial colonies became calcified, whereas in pure culture experiments, single bacterial cells were associated with dolomite surfaces. Dolomite nucleated exclusively in bacterial colonies, intimately associated with extracellular organic matter and bacterial cells. Electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of Ca 2+ and Mg 2+ onto the cell surfaces, indicating the role of the bacterial surface in carbonate nucleation and bacterial fossilization. The affinity of the cells for Mg 2+ was related to the capability of the strains to mediate dolomite formation. Combined with sulphate uptake, which dissociates the [MgSO 4 ] 0 ion pair and increases the Mg 2+ availability, the concentration of Mg 2+ ions in the microenvironment around the cells, where the conditions are favourable for dolomite precipitation, may be the key to overcome the kinetic barrier to dolomite formation. These results demonstrate that bacterial fossilization is a consequence of the cell surface involvement in carbonate precipitation, implying that fossilized bacterial bodies can be used as a tool to recognize microbially mediated carbonates.
Has the relationship between the oxygen isotopic composition of precipitation and air temperature remained constant over the last century? An example from central Europe
Nanoscale characterization of organic matter in modern stromatolites
Report of the Editor
Sedimentology, Feb 1, 1991
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Papers by Judith McKenzie