Geochemical interpretation of the Precambrian basement and overlying Cambrian sandstone on Bornholm, Denmark: Implications for the weathering history

Zhou, Lingli; Friis, Henrik; Tian, Yang; Nielsen, Arne Thorshøj

doi:10.1016/j.lithos.2017.06.019

Cited by 9 publications

(19 citation statements)

References 85 publications

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“…The letter A stands for Al2O3, CN for (CaO*+Na2O) and K is the content of K2O all in molecular proportions. The 290 ideal weathering trend for different types of parent rocks in the upper continental crust should be parallel to the A-CN axis, but due to diagenetic alteration the original data tend to deviate from the theoretical weathering trend (Babechuk et al, 2015;Fedo et al, 1995;Zhou et al, 2017). The trends for both basaltic andesite and gabbroic diorite samples uniformly deviate from the ideal weathering tendency and excurse to the K apex (Fig.…”

Section: Chemical Alterationmentioning

confidence: 93%

“…8A), which clearly indicates a relative K enrichment. The enrichment of K is always interpreted as K metasomatism due to conversion among clay minerals such as the transformation from kaolinite to illite, or from plagioclase to K-feldspar (Fedo et al, 1995;Nesbitt and Young, 1984;Zhou et al, 2017). K metasomatism results in a lower CIA value relative to the actual weathering intensity and can also explain the deviation from the PIA.…”

Section: Chemical Alterationmentioning

confidence: 99%

See 1 more Smart Citation

Rock alteration at the post-Variscan nonconformity: implications for Carboniferous-Permian surface weathering versus burial diagenesis and paleoclimate evaluation

Liang¹,

Ni²,

Linsel³

et al. 2021

Preprint

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Abstract. A nonconformity refers to a hiatal surface located between metamorphic or igneous rocks and overlying sedimentary or volcanic rocks. Those surfaces are key features to understand the relations among climate, lithosphere and tectonic movements during ancient time. In this study, the petrological, mineralogical, and geochemical characteristics of Variscan basement rock and its overlying Permian volcano-sedimentary succession from a drill core in the Sprendlinger Horst, Germany are analyzed by means of polarization microscopy, and environmental scanning electron microscope, X-Ray diffraction, X-ray fluorescence and Inductively Coupled Plasma Mass Spectrometry analyses. In the gabbroic diorite of the basement, the intensity of micro- and macro-fractures increases towards the top indicating an intense physical weathering. The overlying Permian volcanic rock is a basaltic andesite which shows less intense physical weathering compared to the gabbroic diorite. In both segments, secondary minerals are dominated by illite and a mix-layer phase of illite and smectite (I/S). The corrected chemical index of alteration (CIA) and the plagioclase index of alteration (PIA) indicate an intermediate to unweathered degree in the gabbroic diorite and an extreme to unweathered degree in the basaltic andesite. The τ value for both basaltic andesite and gabbroic diorite indicate an abnormal enrichment of K, Rb, and Cs that cannot be observed in the overlying Permian sedimentary rocks. Accompanying hydrothermal minerals such as adularia suggest subsequent overprint by (K-rich) hydrothermal fluids during burial diagenesis which promoted the conversion from smectite to illite. The overall order of element depletion in both basaltic andesite and gabbroic diorite during the weathering process is as follows: Large Ion Lithophile Elements (LILE) > Rear earth elements (REE) > High Field Strength Element (HFSE). Concerning the REE, heavy rare earth elements (HREE) are less depleted than light rare earth elements (LREE). Our study shows that features of supergene physical and chemical paleo-weathering are well conserved at the post-Variscan nonconformity despite hypogene alteration. Both can be distinguished by characteristic minerals and geochemical indices, with the results, a new workflow to eliminate distractions for paleoclimate evaluation and evolution is well developed.

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Section: Chemical Alterationmentioning

confidence: 93%

Section: Chemical Alterationmentioning

confidence: 99%

Rock alteration at the post-Variscan nonconformity: implications for Carboniferous-Permian surface weathering versus burial diagenesis and paleoclimate evaluation

Liang¹,

Ni²,

Linsel³

et al. 2021

Preprint

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“…Especially for continental nonconformities, the buried paleo-weathered surfaces provide an ideal opportunity to analyze the weathering and climate conditions during exposure (Jian et al, 2019;Zhou et al, 2017). This includes the alteration and deformation of minerals, such as changes in crystal morphology of primary and secondary minerals during the weathering process, which is also called supergene alteration (Borrelli et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Locally, however, the contact surface was overlain during the Triassic period. To date, the tectonic evolution in central Europe during post-Variscan times has been well studied (Matte, 1991;Ziegler et al, 2004). However, studies on weathering during the Permo-Carboniferous are fairly scarce.…”

Section: Introductionmentioning

confidence: 99%

Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation

et al. 2021

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Abstract. A nonconformity refers to a hiatal surface located between metamorphic or igneous rocks and overlying sedimentary or volcanic rocks. These surfaces are key features with respect to understanding the relations among climate, lithosphere and tectonic movements during ancient times. In this study, the petrological, mineralogical and geochemical characteristics of Variscan basement rock as well as its overlying Permian volcano-sedimentary succession from a drill core in the Sprendlinger Horst, Germany, are analyzed by means of polarization microscopy, and environmental scanning electron microscope, X-Ray diffraction, X-ray fluorescence and inductively coupled plasma mass spectrometry analyses. In the gabbroic diorite of the basement, the intensity of micro- and macro-fractures increases towards the top, indicating an intense physical weathering. The overlying Permian volcanic rock is a basaltic andesite that shows less intense physical weathering compared with the gabbroic diorite. In both segments, secondary minerals are dominated by illite and a mixed-layer phase of illite and smectite (I–S). The corrected chemical index of alteration (CIA) and the plagioclase index of alteration (PIA) indicate an intermediate to unweathered degree in the gabbroic diorite and an extreme to unweathered degree in the basaltic andesite. The τ values for both basaltic andesite and gabbroic diorite indicate an abnormal enrichment of K, Rb and Cs that cannot be observed in the overlying Permian sedimentary rocks. Accompanying minerals such as adularia suggest subsequent overprint by (K-rich) fluids during burial diagenesis which promoted the conversion from smectite to illite. The overall order of element depletion in both basaltic andesite and gabbroic diorite during the weathering process is as follows: large-ion lithophile elements (LILEs) > rare earth elements (REEs) > high-field-strength elements (HFSEs). Concerning the REEs, heavy rare earth elements (HREEs) are less depleted than light rare earth elements (LREEs). Our study shows that features of supergene physical and chemical paleo-weathering are well conserved at the post-Variscan nonconformity despite hypogene alteration. Both can be distinguished by characteristic minerals and geochemical indices. Based on these results, a new workflow to eliminate distractions for paleoclimate evaluation and evolution is developed.

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“…The chemical composition of clastic sedimentary rocks, especially fine-grained terrigenous sediments, has been widely used to identify their provenance as well as to reconstruct tectonic setting, palaeoclimate and palaeogeography of their depositional basin (McLennan et al 1990;McLennan & Taylor, 1991;Armstrong-Altrin, 2015;Verma & Armstrong-Altrin, 2016;Armstrong-Altrin & Machain-Castillo, 2016;Armstrong-Altrin et al 2017;Hu, Wang & Wang, 2017;Zhou et al 2017;Amedjoe et al 2018;Zhai et al 2018). This approach is especially advantageous for well-preserved Precambrian-Cambrian (PC-C) sedimentary rocks, as they not only provide a window to the history of Earth evolution but also contain some pieces of evidence on the origin and distribution of life on the planet (Ugidos et al 2016;Tawfik et al 2017;Wang et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Provenance and geochemical variations across the Ediacaran–Cambrian transition in the Soltanieh Formation, Alborz Mountains, Iran

Etemad‐Saeed

Najafi

2018

Geol. Mag.

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The Soltanieh Formation in the Alborz Mountains of northern Iran is not only a key lithostratigraphic unit for reconstruction of the Iranian geological history, but also a globally outstanding succession to reveal variations in seawater composition across the Precambrian–Cambrian (PC–C) transition. Mineralogical and geochemical data from a continuous stratigraphic record of Lower and Upper Shale members of the Soltanieh Formation are used to define their provenance, tectonic setting as well as geochemical variations during the PC–C transition. The Soltanieh mudrocks are composed of quartz and plagioclase, with minor constituents of illite, chlorite and montmorillonite. The chemical index of alteration, A-CN-K (Al2O3 – CaO + Na2O – K2O) relations, index of compositional variability, and Th/Sc versus Zr/Sc ratios indicate low chemical weathering in source areas, compositionally immature and first-cycle sediments. Immobile trace-element ratios and discrimination diagrams, chondrite-normalized rare Earth element (REE) patterns and negative Eu anomaly, along with low total REE abundances and negligible Ce anomalies, demonstrate that the Soltanieh Formation was mainly derived from proximal felsic-intermediate Cadomian magmatic arc sources and deposited in a continental-arc-related basin on the proto-Tethyan active margin of Gondwana. The palaeoredox indicators exhibit a remarkable change in environmental condition from a suboxic to an oxic state across the PC–C transition from the Kahar Formation to the Upper Shale Member of the Soltanieh Formation. Moreover, a significant upwards increase of P, Ba, and Ca is likely associated with enhanced fluxes of nutrient elements during the PC–C transition, coeval with the building of collisional mountain belts during the amalgamation of Gondwana.

show abstract

Geochemical interpretation of the Precambrian basement and overlying Cambrian sandstone on Bornholm, Denmark: Implications for the weathering history

Cited by 9 publications

References 85 publications

Rock alteration at the post-Variscan nonconformity: implications for Carboniferous-Permian surface weathering versus burial diagenesis and paleoclimate evaluation

Rock alteration at the post-Variscan nonconformity: implications for Carboniferous-Permian surface weathering versus burial diagenesis and paleoclimate evaluation

Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation

Provenance and geochemical variations across the Ediacaran–Cambrian transition in the Soltanieh Formation, Alborz Mountains, Iran

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