Pavle I. Premović

Vanadium in ancient sedimentary rocks of marine origin

Abstract The distribution of vanadium and vanadyl porphyrins in fractions (extractable organic, inorganic and kerogen) of the Serpiano marl and the La Luna shaly limestone has been determined by employing a variety of geochemical and spectroscopic techniques including atomic absorption, atomic emission, electronic absorption and electron spin resonance spectroscopies. High levels of vanadium and vanadyl porphyrins were found with the major part of the total vanadium located in the kerogen fractions of both rocks. In contrast, while the kerogen of the La Luna rock also contained the major fraction of total vanadyl porphyrins (70%), the corresponding value for the Serpiano marl is only 30%. No vanadyl species were present in the inorganic fraction of either rock. It is suggested that the source of vanadium in these rocks is volcaniclastic materials and that the vanadyl porphyrin entities were incorporated into the kerogen structure through abiotic, geochemical modifications of biosynthetic pigment-chlorophyll.

Physicochemical conditions of sedimentation of the Fish Clay from Stevns Klint, Denmark, and its detrital nature: Vanadium and other supportive evidence

Cretaceous-Tertiary (K/T) boundary samples of the Fish Clay in Denmark from three sites (Stevns Klint, Nye Klov and Dania) have been analyzed mineralogically and chemically. All samples contain major amounts of biogenic calcite and smectite. In some samples, minor amounts of authigenic pyrite and siderite (Stevns Klint), and lepidocrocite (Dania) are also present. To obtain an indication of the chemical nature of the V present in the Danish boundaries, the samples were analysed for V and vanadyl (VO2+) at various stages of selective leaching. The results obtained indicate that the bulk of V is associated with the smectite fractions (≥47% of total V); all VO2+ resides in the smectite portions. From the chemistry of VO2+, pyrite and carbonates, it is deduced that the oxidation potential and pH of the interstitial seawater of the Stevns Klint boundary was approximately 0.0 to −0.2 V and 6 to 7, respectively, during the accumulation of the lower black basal part, but rose during the accumulation of the upper grey part. The geochemical data do support the hypothesis that the Danish boundary smectite represents weathered clay (along with some asteroid and local material) that was redeposited to the Danish boundary sites after the K/T event. Substantial proportions of the VO2+ contents of the Nye Klov and Dania smectite were probably already contained in the detrital clay arriving at the site of boundary sedimentation, but at the Stevns Klint site they have been significantly augmented by uptake from the interfacial and interstitial seawaters through the humic substances involvement. Abundances and major mineralogical residences have been determined for trace metals: Cr, Ni, Co and Ga; and minor Fe. Much of these elements is located in the boundary smectite structure as the corresponding ionic forms (CrOH2+, Ni2+, Co2+, Ga3+ and Fe3+) and is strictly detrital in character, i.e., having been transported to the Danish boundary sites already contained in smectite. All these metals in the Danish boundary smectite are well above normal abundances in clays.

Copper and copper(II) porphyrins of the Cretaceous–Tertiary boundary at Stevns Klint (Denmark)

High levels of copper(II) (Cu 2a ) were found with the major part (s 90%) of the total Cu located in the smectite (Cu: 175 ppm) and kerogen (Cu: up to 1000 ppm) of the basal black marl of the Cretaceous^Tertiary (KT) boundary informal type sedimentary rock: the Fish Clay at Stevns Klint, Denmark. Anomalous abundance (4000 ppm) of the kerogen Cu 2a -porphyrins in this marl was detected by electron spin resonance. A model is proposed in which the enormous acid rains (caused by the KT asteroid impact) washed out the humics (already enriched with Cu 2a /Cu 2a porphyrins) of the top horizon of the nearby oxic soil into the Fish Clay Basin during the KT event. fl 2000 Elsevier Science B.V. All rights reserved.

Distribution of major and trace elements in La Luna Formation, Southwestern Venezuelan Basin

The La Luna Formation (Maraca section), Maracaibo Basin, was studied by means of V and Ni analysis of the bitumen, total organic carbon (TOC), total sulfur (St), major elements (Si, Al, Fe, Mg, Mn, Ca, Ti, Na, K, P), trace elements (V, Ni, Co, Cr, Cu, and Zn), and electron microprobe analysis (EPMA) of the whole rock, and St, major elements (Si, Al, Fe, Mg, Mn, Ca, Ti, Na, K, P), trace elements (V, Ni, Co, Cr, Cu, Zn, Mo, Ba, U, Th) and rare earth elements (La, Ce, Nd, Sn, Eu, Th, Yb, Lu) of the carbonate-free fraction. The results are discussed based on the organic and inorganic association of trace elements and their use as paleoenvironmental indicators of sedimentation. An association between V and organic matter is suggested by means of correlation between V and Ni vs. TOC, the use of EPMA (whole rock) and V and Ni concentrations (carbonate-free fraction), whereas Ni is found in the organic matter and the sulfide phase. Fe is present as massive and framboidal pyrite, whereas Zn precipitates into a separate phase (sphalerite), and Ni, Cu and, in some cases, Zn, can be found as sulfides associated with pyrite. Concentrations of V and Ni (bitumen), TOC, St, V, Ni, Cr, Cu and Zn (whole rock), U, Th, Mo (carbonate-free fraction) are indicative of changes in the dysoxic sedimentation conditions in the chert layers (TOC, St, V, Ni, Cu and low Zn and V/Cr 4). In the sequence corresponding to the argillaceous limestone, variations in the concentrations of TOC, St, V, Ni, Zn, Cu and Cr (whole rock) can be observed, also suggesting variable sedimentation conditions. The following is proposed: (i) sedimentation intervals under euxinic conditions associated with high contribution and/or preservation of organic matter, allowing a high concentration level of V and Ni in the organic phase and the accumulation of Cu, Zn and Ni (in a smaller proportion) in the sulfide phase; (ii) sedimentation intervals under anoxic conditions and in the presence of relatively lower H2S, which allowed lower concentrations of V and Ni in the organic phase and higher concentrations of Cu, Zn, and Ni in the sulfide phase. Rare earth elements (REE) concentrations exhibit a marked increase in Ce, Nd, Sm, Eu, Y and Lu for the QM-3 interval, relative to Post-Archean Average Shale (PAAS). REE enrichment in shales has been related to the presence of phosphate minerals such as monazite or apatite. However, these minerals were not detected through XRD or EPMA in the whole rock or in the carbonate-free fraction. The association of REE with organic matter is suggested due to the absence of phosphate minerals, although assessment of these elements require further analysis. # 2002 Elsevier Science Ltd. All rights reserved.

Thermal stability of the asphaltene/kerogen vanadyl porphyrins

Abstract Thermal stability of vanadyl porphyrins incorporated into the asphaltene/kerogen structures of the Dead Sea asphalt “float”, the La Luna Mara limestone and the Serpiano marl was studied by electron spin resonance (ESR). Comparative studies were also made on alkyl vanadyl porphyrins such as deoxophylloerythroetioporphyrins and (extracted and commercial) etioporphyrins and tetraphenylporphyrin. According to these studies, alkyl vanadyl porphyrins predominate in the asphaltene/kerogen framework. These porphyrins are stable up to 400°C during laboratory heating, but at and above this temperature their content sharply decreases. At 500°C and 600°C, the asphaltene/kerogen vanadyl porphyrins content follows a similar pattern to that at 400°C, except that at 600°C it was reduced to traces in less than 12 h. In addition, it is implied that a high proportion of the asphaltene/kerogen vanadyl porphyrins ( The asphaltene/kerogen vanadyl porphyrins kinetics during laboratory thermolysis are characterized by a step-wise pattern. This is attributed to thermolytic decomposition/demetallation of the asphaltene/kerogen alkyl vanadyl porphyrins with various energy barriers mediated by free radical intermediates. A rough extrapolation of pyrolytic data to longer times, based on both the Arrhenius equation and the often-quoted assumptions for the reaction rate decrease, infer that static laboratory pyrolysis of kerogen is irrelevant to natural geological processes characteristic of petroleum genesis.

Are vanadyl porphyrins products of asphaltene/kerogen thermal breakdown?

The idea was examined that during early stages of thermal maturation of source rocks or petroleums, the release of bound vanadyl (VO2+) porphyrins (P) from the immature asphaltenes or kerogen could contribute to an increase in extractable VO2+-P. To simulate such a change in the laboratory, the Dead Sea ‘floating’ asphalt and total organic (bitumen + kerogen) fractions of the La Luna and Serpiano carbonaceous sedimentary rocks were heated at controlled temperatures (100, 200, 300 and 400°C) for different periods of time. Residual (and altered) asphaltenes or kerogens were then separated from the heated products and analysed for VO2+-P content by electron spin resonance. Three conclusions were reached: (1) thermal degradation of immature asphaltenes or kerogen generated no or very little (<1 wt%) extractable VO2+-P during simulated maturation of petroleums or source rocks and thus by inference during natural maturation; (2) petroleum VO2+-P by far are those that were saved from incorporation into asphaltenes or kerogen precursors (or young asphaltenes or kerogen) during diagenesis; and (3) a high VO2+-P content of a petroleum is not an indication of its immaturity.

Vanadyl ions in ancient marine carbonaceous sediments

Abstract Vanadyl ions in ancient shaly-type sedimentary rocks of marine origin from a variety of world sources and geological periods have been investigated using electron spin resonance. These and other results provide evidence that there are two types of vanadyl ions. The first is inorganically bound in the clay/ silicate fraction of these rocks and the second type is associated with vanadyl porphyrin compounds.

ESR study of OH radicals in irradiated lithium acetate dihydrate single crystals

Abstract The OH radicals originating from water of crystallization were identified in an irradiated single crystal of lithium acetate dihydrate. The OH radicals in two sites are related by the crystal symmetry. The principal values of the g tensor were determined to be (2.0038, 2.0071, 2.0457) and of the hyperfine tensor to be (−22.3, −45.8, +7.2) G. From the principal directions OH radicals appear to be formed from the water of crystallization located between the two planes of acetate ions in the crystal. The gmax value indicates that a strong interaction of the trapped radical with the surrounding molecules exists. The energy separation of the two OH oxygen pπ orbitals was estimated to be 1.3 ·10−10 erg.

The conspicuous red "impact" layer of the Fish Clay at Højerup (Stevns Klint, Denmark)

The marine Cretaceous-Paleogene boundary (KPB) section at Højerup-Fish Clay consists of a very thin red smectite-rich carbonate-poor (“impact”) layer overlain by a thick black marl. Similar red layers are found in the KPB sections at Agost in Spain and El Kef in Tunisia.Smectite of the red layer of the KPB section at Højerup is probably detrital and redeposited from adjacent coastal or marine areas. This clay mineral is likely mixed with a small amount of smectite derived from impact glasses. Most of the microspherules and nano-size glasses of the red layer at Højerup are probably detrital and simultaneously redeposited with smectite. The deposition of the red layer occurred for several decades to a century at most.

Spectrophotometric Study of Catechol Oxidation by Aerial O2 in Alkaline Aqueous Solutions Containing Mg(II) Ions.

Abstract Electronic absorption spectroscopy was employed to study the aerial oxidation of catechol (1,2-benzenediol) in alkaline aqueous solution containing an excess of Mg(II) ions. Graphical analysis by the matrix method of UV spectra recorded at regular time intervals gave a good fit for two absorbing species in solution. Based on this result and our earlier ESR spectroscopic investigations we concluded that two main absorbing species in this system are Mg(II)-spin stabilized o-benzosemiquinone anion radical and C-C dimer formed by the nucleophilic attack of catecholate anion on o-benzoquinone. Although the formation of 1,2,4-benzenetriol during the catechol oxidation has been detected in some ESR studies its presence was not indicated by this analysis probably because of the low and/or stable steady state concentration throughout the experiment.