Implications For Depositional Environment Research Articles

Geochemistry of Middle Triassic radiolarian cherts from northern Thailand: Implication for depositional environment

Geochemical analysis reveals that Middle Triassic radiolarian cherts from northern Thailand, including Chiang Dao, Lamphun and Den Chai, are of biogenic origin. These cherts present slightly high SiO2 content which was possibly modified by diagenetic alteration and migration processes as indicated by negative correlation between SiO2 and most of the other major elements. The relatively high content of Cr, Zr, Hf, Rb and Th and high positive correlation of these elements with Al and Ti from the majority of cherts suggest a close relation to terrigenous component. The Ce anomaly (Ce/Ce*) with geometric means ranging from 0.85 to 0.93 is compatible with that of continental margin composition (0.67–1.52) from Murray et al. (1990) which is also consistent with low Eu anomalies (Eu/Eu*, 0.91–0.94). Moreover, the slightly low ratios of La and Ce NASC normalized (Lan/Cen, 0.91–0.94) and the low LREE and HREE ratios in most of our samples (Lan/Ybn, 0.62–0.85) are in agreement with the continental margin. The result from Lan/Cen vs. Al2O3/(Al2O3+Fe2O3) discrimination diagrams also supports the continental margin (residual basin, s. str.) interpretation. These geochemical results are compatible with geological evidence, which suggest that during the Middle Triassic, radiolarian cherts were deposited within a deeper part of a residual basin in which an accommodation space was possibly controlled by faults under extensional regime subsequent to Late Variscan (Permian) orogeny. Paleogeographically, the main Paleotethys which closed during Late Triassic should be located further to the west of these study localities. This scenario is in agreement with the current view of the Tethys in this part of the world.

Geochronology and Geochemistry of the Radiolarian Cherts of the Mada'er Area, Southwestern Tianshan: Implications for Depositional Environment

Abstract:In the southwestern Tianshan, the geologic ages of many strata and their depositional environments are still poorly constrained because of complex structures. The Mada'er area is located in the Kuokesaleling belt, Southwestern Tianshan. The cherts from the former Wupata'erkan Group contain abundant radiolarian fossils, including 10 species which are identified as late Devonian to early Carboniferous in age. Eleven chert samples have SiO2 contents ranging from 88.80 wt% to 93.28 wt%, and 2.02 wt% to 3.72 wt% for Al2O3. The SiO2/Al2O3 ratios of all samples vary from 23.84 to 46.11, much lower than those of the pure cherts (80–1400). These values suggest that the cherts contain high ratios of terrigenous materials. The Al2O3/(Al2O3+Fe2O3) ratios vary between 0.64 and 0.77, whereas V and Cu concentrations range from 10.92 ppm to 26.7 ppm and from 2.15 ppm to 34.1 ppm respectively. The Ti/V ratios vary from 25.53 to 44.93. The total REE concentrations of the cherts are between 30.78 ppm and 59.26 ppm, averaging 45.46 ppm. The (La/Ce)N ratios range from 0.81 to 1.12, and 0.88–1.33 for (La/Yb)N, averaging 1.09, which suggests a continental margin environment. Consequently, it is inferred that the cherts formed in a residual sea environment during the late Devonian to early Carboniferous time, which suggests that the collision between the Karakum‐Tarim and Kazakhstan‐Junggar plates did not occur at the time. In addition, the regional geological information indicates that the study area experienced a post‐collision stage during the early Permian, and thus it is likely that the collision between the two plates took place in the late Carboniferous.

Mineralogical and geochemical studies of Ypresian marly clays and silica rocks of phosphatic series, Gafsa-Metlaoui basin, southwestern Tunisia: implication for depositional environment

Thick Ypresian marly clays and silica rich rocks constitute the so-called interbedded facies of phosphatic series, in the Gafsa-Metlaoui basin, southwestern Tunisia. Mineralogical and geochemical investigations are carried out on selected samples from Kef Eddour section. The data obtained by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Energy Dispersive X-ray microanalysis (EDX) and chemical analysis and IR of clay fractions indicate that the bulk rock samples are composed of cristobalite-tridymite and dolomite. Observation by SEM showed the occurrence of dolomite as a well-crystallized and a weathered shape. Whereas, cristobalite-tridymite observed in the cherty bed appears as a spheres, filling the pore spaces. However, samples which contain moderately a significant amount of feldspars, clinoptilolite and pyrite occur in the upper part of Kef Eddour section. Clay minerals consist mainly of smectite, palygorskite, and sepiolite. In this clay assemblages, the N-alkane (m/z = 57) distributions, revealed that organic matter has phytoplankton and bacterial origin. The Pristane/Phytane ratio indicated that the organic matter is deposited in a reduced environment. In this latter, sulfate-reducing bacteria generate hydrogen sulfur, which is incorporated on the organic biomolecules that occurred at the lower part of Kef Eddour section. However, the high Fe activity on the depositional environment favored the occurrence of pyrite in the upper part.

Magnetic mineral study of Holocene marine sediments from the Alfonso Basin, Gulf of California - implications for depositional environment and sediment sources

Se presentan los resultados del estudio de propiedades magnéticas en sedimentos marinos colectados en la Cuenca Alfonso en la Bahía de la Paz, los cuales se analizan en términos de las fuentes de aporte y el ambiente de depósito en el sur del Golfo de California durante el Holoceno. El control estratigráfico se basa en fechamientos de radiocarbono, que indican una edad para los sedimentos de fondo del núcleo de alrededor de 7597-7831 años cal. B.P. La señal magnética está dominada por minerales de grano fino de titanomagnetitas, los cuales provienen de las secuencias de tobas silícicas expuestas en la Bahía de la Paz. La mineralogía magnética es relativamente homogénea como lo indican las mediciones de propiedades de susceptibilidad magnética, magnetización remanente y coercitividad. Los ciclos de histéresis magnética indican la ocurrencia de componente paramagnéticas y los ciclos correspondientes después de la corrección paramagnética muestran ciclos que saturan en campos bajos y altos valores de magnetización de saturación. Las gráficas de discriminación de estado de dominio magnético empleando cocientes de los parámetros de histéresis muestran que las muestras se agrupan en el campo de dominio pseudos-sencillo, sugiriendo mezclas de dominios sencillo y múltiple. Los registros de susceptibilidad magnética revelan valores altos de factores de dependencia de frecuencia, en particular en el segmento del Holoceno Medio, lo que sugiere contribuciones de minerales superparamagnéticos de grano fino y posible transporte eólico. La presencia de laminaciones finas, características de la secuencia de Alfonso indica condiciones anóxicas en el fondo de la cuenca. El ambiente de depósito durante el Holoceno parece ser dominado por sedimentos detríticos pluviales y sedimentos de grano muy fino y transporte eólico, con menor contribución de sedimentos biogénicos.

Lithostratigraphy and petrography of marine Jurassic rocks in the Mae Sot area, Tak Province, western Thailand: Implications for depositional environment and tectonics

Geology, lithostratigraphy, petrography, sedimentary structures and depositional environment of marine Jurassic rocks of the Hua Fai Group (HFG) from the Mae Sot area of Tak Province, western Thailand have been studied in detail. Based mainly on five measured sections in the Mae Sot Basin, the group can be divided into three formations: Khun Huai; Doi Yot; and Pha De, in ascending order. Seventeen sedimentary rock units have been established with a total thickness varying from 200 to 832 m. According to the fossil assemblages, the HFG was deposited during Toarcian–Bajocian. Analysis of lithofacies associations in the sedimentary sequences of the group discerns shoreface, fan-delta, protected lagoon, intertidal, subtidal and inner to outer ramp environments with occasional carbonate platforms and reef flats. Toarcian rocks are represented by transgressive–regressive (T–R) cycles that in the Aalenian gradually changed to highest sea level and water depth. During late Aalenian to early Bajocian, sea level was still changing to a transgressive phase, then after early Bajocian, sea level retreated again. The eustatic curves for the Toarcian–early Bajocian in Thailand correspond to the global situation, but differ significantly in the Late Jurassic–Cretaceous, when T–R phases were out of step with the global pattern and instead probably responded to local tectonic movements.

Carbon and sulfur isotopic compositions of basal Datangpo Formation, northeastern Guizhou, South China: Implications for depositional environment

Isotopic compositions of Mn-carbonate and organic carbon from the same individual samples and sulfur isotopic compositions of pyrites in the basal Datangpo Formation were analyzed. Highly 34S-enriched pyrites ( δ 34S pyrite = 31.7–59.4‰) were precipitated in relatively occlusive pore water under anoxic condition in sediments, which is consistent with the observation of large and scattered pyrite framboids. The sulfidic deep ocean was not “oxidized” in the early Datangpo interglacial interval, thus the level of seawater sulfate remained low and marine δ 34S sulphate remained high. Low δ 13C car (average −7.4‰) and abnormal relationship between δ 13C car and fractionation ( Δ car–org) imply that the negative δ 13C car excursion may have resulted from oxidation of part of a large organic carbon reservoir. High Δ car–org (average 25.1‰) implicates high CO 2 level in the atmosphere. Small standard deviation (1.0‰) of δ 13C car values indicates the Mn-carbonate was precipitated near the water–sediment interface under dysoxic conditions rather than in occlusive pore water in sediments.

Petrographic and chemical traits of Cenomanian platform carbonates (central Lebanon): implications for depositional environments

This paper provides new data on the Cenomanian (Late Cretaceous) carbonates in Lebanon, which, due to their location and considerable thickness, represent an important segment of the broader Eastern Mediterranean platform. Detailed field and microfacies investigations have shown that the Late Albian–Cenomanian succession (i.e., the Sannine Formation in Lebanon) consists of a number of lithologically distinct strata. These are: micritic limestone, silicified micrite, bioclastic limestone, chalky limestone (foraminifera-wackestone), marl and marly limestone, dolostone and dolomitic limestone. The laminated micritic limestones are typically associated with chert nodules and bands, and are interpreted to have been deposited in deep marine environments. The bioclastic limestones have abundant skeletal fragments suggesting deposition in relatively shallow marine settings, an interpretation that is further supported by the presence of local palaeo-channels within the limestones. Geochemically, the formation includes five distinct chemical groups, each characterized by certain chemical traits reflecting the lithological nature of the various facies. The micritic limestones have relatively low concentrations of most major and trace elements (Mg, Sr, Si, Al, K, P, Ti and Rb). In sharp contrast, the marly limestone samples have the highest concentrations of most of these elements. The silicified micrites have a wide range of Si and Sr contents, but abundances of most elements are intermediate between those of the micritic limestones and the marly limestones. The chalky limestones have relatively low Si and Al, but relatively high P contents. The dolomitic limestones have the lowest Rb and Sr concentrations. The normalized REE patterns of representative samples of most of these rocks are parallel to subparallel and nearly flat. Based on facies analysis and chemical traits, we have constructed a carbonate platform ramp model for this succession, in which the dolostones and marly limestones were deposited in back ramp to subtidal environments, the bioclastic limestones accumulated in shallow, wave-dominated to deep ramp environment, and the micritic limestones and silicified micrites formed in a deep ramp environment. This ramp was influenced by sea-level fluctuations and tectonic activities. The proposed model has wider implications for the geodynamic evolution of the eastern Mediterranean region during the Cretaceous Period, and is consistent with interpretations of some other tectonically active margins worldwide.

Chemical Profiles across a Jurassic Stratiform Manganese Deposit at Katsuyama in the Mino Terrane of Central Japan: Implications for Depositional Environment, Diagenetic Metal Redistribution and Paleoceanography

Abstract. Inorganic chemical compositions are determined for a series of rocks crossing an Early Jurassic stratiform manganese ore deposit in a chert-dominant sequence at Katsuyama, in the Mino Terrane of central Japan. The lithology in the vicinity of the manganese ore bed is classified into lower bedded chert, black shale, massive chert, manganese ore and upper bedded chert, in ascending order. The rocks surrounding the manganese deposit are anomalously high in certain elements: Pb (max. 29 ppm), Ni (1140) and Co (336) in the lower bedded chert, Mo (438), As (149), Tl (29) and U (12) in the black shales, V (210) and Cr (87) in the massive chert, and MnO and W (24) in the manganese ore. The aluminum-normalized profiles reveal a distinct zonation of redox-sensitive elements: Pb-Zn, Ni-Co-Cu(-Zn) and U-Cr in the lower bedded chert, Mo-As-Tl in the black shale, V(-Cr) in the massive chert, and Mn-Fe-Ba-W in the manganese ore, in ascending order. The lower and upper bedded cherts and manganese ore generally exhibit flat rare earth element patterns with positive Ce anomalies, whereas the uppermost part of the lower bedded chert, the black shale and massive chert have flat patterns with weak or nonexistent negative Ce anomalies and weak positive Eu anomalies. The strong enrichment in Ni, Co, W, Tl and As detected in the Katsuyama section is not recognized in other sediments, including those of anoxic deposition origin, but is identified in modern ferromanganese nodules, suggesting that metal enrichment in the Katsuyama section is essentially due to the formation of ferromanganese nodules rather than to deposition in an anoxic environment. The observed elemental zonation is well explained by equilibrium calculations, reflecting early diagenetic formation and associated gradual reduction with depth. The concentration profiles in combination with litho- and biostratigraphical features suggest that formation of these bedded manganese deposits was triggered by an influx of warm, saline and oxic water into a stagnant deep ocean floor basin in Panthalassa at the end of the middle Early Jurassic. Paleoceanographic environmental controls thus appear to be important factors in the formation and preservation of this type of stratiform manganese deposit.

CS relationships in shales hosting manganese ores from Mexico, China, and Newfoundland: Implications for depositional environment and mineralization

Organic carbon and sulfide sulfur contents of host rocks and ore bodies selected from three manganese deposits were tested and plots of carbon against sulfur of the type proposed by Berner were used to distinguish depositional environments. Molango, in east-central Mexico, is the largest of the three deposits examined. The ore bed of the Molango manganese deposit, east-central Mexico is the basal unit of the Chipoco Facies (Taman Fm., Kimmeridgian) and is underlain by laminated black shales of the “Santiago” Formation (Oxfordian). Black shales of the “Santigo” Formation are high in organic carbon (0.88–2.43%) and sulfide sulfur (2.45–9.27%). SC plots suggest an euxinic marine environment. The manganese ore bed consists of very finely laminated Mn-carbonate, shows a poor correlation between organic carbon and sulfide sulfur, and has a low content of sulfide sulfur. The upper part of the Chipoco Facies consists of organic-rich limestones and interbedded black shales. Both lithologies have a positive correlation between organic carbon and sulfide sulfur and may have been euxinic, although less so than the “Santiago”. Taojiang, a manganese deposit of south China, occurs in the Middle Ordovician Modaoxi Formation, and is smaller than the Molango deposit, but is still minable. The ore body consists of well crystallized rhodochrosite and Mn calcite and is hosted by interbedded black and gray shales below the ore body and gray mudstone above the ore body. The direct hanging wall and foot wall are Mn limestones. Black shales contain high organic carbon (0.58–4.3%) and sulfide sulfur (0.13–3.96%). Gray shale and gray mudstone contain low organic carbon and sulfide sulfur. Rhodochrosite ores and Mn limestone have low organic carbon and sulfide sulfur contents. The plots of carbon against sulfur show that the host rocks below the ore body are euxinic marine products, whereas the gray mudstone above the ore body is normal marine. The Manual's River prospect is a thin but widespread bed of manganese in eastern Newfoundland, Canada. A manganese carbonate bed is the basal unit of the Middle Cambrian Chamberlain's Brook Formation and consists of very fine-grained rhodochrosite. Host rocks consist of sideritic gray shale, gray shale, and black shale above the ore body and green shale and gray shale below the ore body. Both the ore body and host rocks contain very low organic carbon (0.21–2.19%) and sulfide sulfur (0.02–1.84%), which indicates nomal marine conditions. Comparison of the three manganese occurrences suggests that a thicker development of euxinic strata before the onset of manganese deposition leads to a thicker manganese ore body. If no euxinic conditions were present, only sub-economic manganese enrichments occur.

Surface Textures of Sand Grains from the Victoria Falls Region, Zambia: Implications for Depositional Environments and Local Archaeological Occurrences

Surface Textures of Sand Grains from the Victoria Falls Region, Zambia: Implications for Depositional Environments and Local Archaeological Occurrences