Labyrinth patterns in Magadi (Kenya) cherts: Evidence for early formation from siliceous gels

Sedimentary cherts, with well-preserved microfossils, are known from the Archean to the present, yet their origins remain poorly understood. Lake Magadi, Kenya, has been used as a modern analog system for understanding the origins of nonbiogenic chert. We present evidence for synsedimentary formation of Magadi cherts directly from siliceous gels. Petrographic thin-section analysis and field-emission scanning electron microscopy of cherts from cores drilled in Lake Magadi during the Hominin Sites and Paleolakes Drilling Project in 2014 led to the discovery of two-dimensional branching "labyrinth patterns" in chert, which are a type of fractal "squeeze" pattern formed at air-liquid interfaces. Labyrinth patterns preserved in chert from Lake Magadi cores indicate invasion of air along planes in dewatering gels. These patterns support the precipitation of silica gels in the saline-alkaline Lake Magadi system and syndepositional drying of gels in contact with air as part of chert formation. Recognizing cherts as syndepositional has been critical for our use of them for U-Th dating. Identification of labyrinth patterns in ancient cherts can provide a better understanding of paleoenvironmental and geochemical conditions in the past.

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Facies And Diagenesis Of Tabalar And Tendehantu Carbonate Formation In Mangkalihat Peninsula Area: An Outcrop Preliminary Study To Oligocene – Miocene Reservoir Candidate Prospect

Buletin Sumber Daya Geologi ◽

10.47599/bsdg.v7i2.105 ◽

2012 ◽

Vol 7 (2) ◽

pp. 78-91

Author(s):

Risman Adhitiya ◽

Merza Media Adeyosfi ◽

Syahreza S. Angkasa ◽

Felix Sihombing

Keyword(s):

Thin Section ◽

Carbonate Rock ◽

Carbonate Formation ◽

Data Compilation ◽

Sample Data ◽

Preliminary Study ◽

Thin Section Analysis ◽

Fair Poor ◽

Petrographic Thin Section ◽

Section Analysis

Mangkalihat peninsula is located between Kutai and Tarakan basins, which known as two Hydro Carbon (HC) Prolific basins in Eastern Borneo. The petroleoum system in this area is poorly known because of the different system between Kutai and Tarakan Basin. The field study is focusing in the eastern part of Mangkalihat Peninsula, where The Tabalar and Tendehantu Formation are exposed. The data compilation is from outcrop, thin section and plug sample which permeability and porosity values were measured by Klickenberg method. Outcrop analysis showed that Tendehantu Formation can be divided into two lithofacies, whileTabalar Formation has only one lithofacies. The petrographic thin section analysis showed three microfacies from the two formations. Pore destruction caused by diagenesis can de indicated with the presence of bladed and equant cement in vuggy pores, while the diagenetical development of porosity is marked by the microfracturing that was assumed to be formed by compaction and deep burial and matrix dissolution in some of the samples. Petrography and plug sample data integration shows the quality value of those carbonate rock as a reservoir from the permeability and porosity parameter. Based on the microfacies grouping showed in three microfacies, the porosity value is 5.26 - 17.32 % (tight to good), and permeability value is 0.041 – 7.27mD (fair – poor). The carbonate rock quality is influenced by the whole diagenetic processes that happened in each lithofacies.

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Morphometric Analysis through 3D Modelling of Bronze Age Stone Moulds from Central Sardinia

Minerals ◽

10.3390/min11111192 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1192

Author(s):

Stefano Cara ◽

Paolo Valera ◽

Carlo Matzuzzi

Keyword(s):

3D Reconstruction ◽

Bronze Age ◽

Digital Camera ◽

Stone Materials ◽

Photogrammetric Method ◽

Thin Section Analysis ◽

Experimental Rig ◽

Petrographic Thin Section ◽

Section Analysis

Stone moulds were basic elements of metallurgy during the Bronze Age, and their analysis and characterization are very important to improve the knowledge on these artefacts useful for typological characterization. The stone moulds investigated in this study were found during an archaeological field survey in several Nuragic (Bronze Age) settlements in Central Sardinia. Recent studies have shown that photogrammetry can be effectively used for the 3D reconstruction of small and medium-sized archaeological finds, although there are still many challenges in producing high-quality digital replicas of ancient artefacts due to their surface complexity and consistency. In this paper, we propose a multidisciplinary approach using mineralogical (X-ray powder diffraction) and petrographic (thin section) analysis of stone materials, as well as an experimental photogrammetric method for 3D reconstruction from multi-view images performed with recent software based on the CMPMVS algorithm. The photogrammetric image dataset was carried out using an experimental rig equipped with a 26.2 Mpix full frame digital camera. We also assessed the accuracy of the reconstruction models in order to verify their precision and readability according to archaeological goals. This allowed us to provide an effective tool for more detailed study of the geometric-dimensional aspects of the moulds. Furthermore, this paper demonstrates the potentialities of an integrated minero-petrographic and photogrammetric approach for the characterization of small artefacts, providing an effective tool for more in-depth investigation of future typological comparisons and provenance studies.

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