Advances in Forensic Sedimentology

Forensic sedimentology is a relatively recently realized field. Sedimentological methods used to solve cases have evolved as the field has developed, beginning with simple identification of minerals and progressing to the examination of individual grains using highly advanced scanning electron microscopes. More simple methods, such as color analysis, are still used today, but in addition, forensic sedimentologists look at surface textures and grain size distribution. For instance, quartz grains were used in a forensic technique as sediment fingerprint. The particle size distribution is one of the important tests when analysing sediments and soils in geological studies. For forensic work, the particle size distribution of sometimes very small samples requires precise determination using a rapid and reliable method with a high resolution. FRITSCH laser granulometer offers rapid and accurate sizing of particles in the range 0.04–2000 μm for a variety of sample types, including soils, unconsolidated sediments, dusts, powders, and other particulate materials.

Grain size variation in sand column along Chhatrapur coast, Ganjam district, Odisha – A clue to the depositional environment

The concentration of heavy mineral placer deposits along the coastal tracts are function of various favourable factors i.e. hinterland geological formations, prevalence of favourable climatic condition, their transportation through intricate drainage systems and various coastal processes, which operated during the geological past. Textural analysis of the available unconsolidated sediments from the present deposits is of vital importance to decode the prevailing depositional environment while grain size analysis is the major parameter used. Present study highlights the grain size analysis of the identified sand column from Chhatrapur Mineral Sand Deposit along the coastal tract of Odisha to infer the environment of deposition of heavy mineral bearing sand and their heavy mineral content variation. Standard procedure of sampling, data analysis and interpretation techniques were adopted. Result shows that, sands from frontal and rear dune are characterized by distinct bi-modal distribution, medium to fine, moderately to well sorted with good positive skewness, whereas, sand from Inter-dunal region shows dominant unimodal, medium to coarse grain, moderately poorly sorted nature and slightly positive skewness. The better heavy mineral concentration (10 to 25 % grade) in frontal and rear dunes is attributed to prevalence of aeolian dune deposition accompanied by good sorting. In contrast, the low concentration of heavy mineral (3 to 6 %) in inter dune region is due to occasional fluvial regime and poor sorting of sediments. Thus, grain size analysis can be an effective tool to decipher local prevailing depositional environment, which has a bearing on heavy mineral concentration as well.

Interaction of magma and wet, unconsolidated sediments: a case study from Ilindenski Kamak, Chelopech Formation, Central Srednogorie

The Ilindenski Kamak is situated along the Ilindenska river valley, northwest of Chelopech village, and is composed of different types of volcanic and volcaniclastic rocks, which are interbedded by sandstones and mudstones, all of Late Cretaceous age. The architecture of the pile of extrusive andesitic rocks is interpreted as a subaqueous cryptodome or sill. The presented research deals with a variety of volcanic facies: 1, coherent andesitic domain; 2, quench fragmented domain (closely packed peperites); 3, globular peperites developed at the contact of wet, unconsolidated sediments.

Beach-face slope dataset for Australia

Sandy beaches are unique environments composed of unconsolidated sediments that are constantly reshaped by the action of waves, tides, currents, and winds. The most seaward region of the dry beach, referred to as the beach face, is the primary interface between land and ocean and is of fundamental importance to coastal processes, including the dissipation and reflection of wave energy at the coast, and the exchange of sediment between the land and sea. The slope of the beach-face is a critical parameter in coastal geomorphology and coastal engineering, necessary to calculate the total elevation and excursion of wave run-up at the shoreline. However, datasets of the beach-face slope remain unavailable along most of the world’s coastlines. This study presents a new dataset of beach-face slopes for the Australian coastline derived from a novel remote sensing technique. The dataset covers 13,200 km of sandy coast and provides an estimate of the beach-face slope at every 100 m alongshore, accompanied by an easy to apply measure of the confidence of each slope estimate. The dataset offers a unique view of large-scale spatial variability in beach-face slope and addresses the growing need for this information to predict coastal hazards around Australia. The beach-face slope dataset and relevant metadata are available at https://doi.org/10.5281/zenodo.5606217 (Vos et al., 2021)

GEOQUÍMICA E PETROGRAFIA DE DEPÓSITOS QUATERNÁRIOS DA PORÇÃO SW DA PRAIA BRAVA, ARMAÇÃO DOS BÚZIOS, RJ, BRASIL: EDFRX E DIFRAÇÃO A LASER

Resumo: Este artigo apresenta os dados geoquímicos e petrográficos de sedimentos praiais da região SW da Praia Brava (PB) em Armação dos Búzios-RJ. Buscamos discutir os processos de intemperismo químico e proveniência, bem como, analisar o ambiente geoquímico e a sua relação com as fontes autóctones. Neste estudo foram utilizadas análises petrográficas, parâmetros texturais na distribuição de partículas, geoquímica e estatística com auxílio de Laser Difraction e Fluorescência de Raios-X com Energia Dispersiva. Os sedimentos estudados são compostos essencialmente de granadas, biotita, piroxênio (diopsídio e augita?), epidoto, monazita, hornblenda, ilmenita, zircão, rutilo, titanita, silimanita, cianita, além de quartzo. Os sedimentos investigados são reflexo dos litotipos encontrados regionalmente, indicando possivelmente uma forte correlação entre as rochas-fonte e os depósitos sedimentares. O ambiente de oxirredução é demarcado pela presença de óxidos de Fe, provavelmente hematita. O índice de alteração calculado suporta um grau moderado, onde micas são preservadas, totalmente ou em partes. Palavras-Chave: Sedimentos Inconsolidados; Depósitos Praiais; Intemperismo Químico. GEOCHEMISTRY AND PETROGRAPHY OF QUATERNARY DEPOSITS FROM SW OF PRAIA BRAVA BEACH, ARMAÇÃO DOS BÚZIOS, RJ, BRAZIL: EDFRX AND LASER DIFRACTION Abstract: This article presents the geochemical and petrographic data of beach sediments from the SW region of Praia Brava (PB) in Armação dos Búzios-RJ. We seek to discuss the processes of chemical weathering and provenance, as well as to analyze the geochemical environment and its relationship with autochthonous sources. In this study, petrographic analyzes, textural parameters in particle distribution (Laser Difraction), geochemistry (X-Ray Fluorescence with Dispersive Energy) and statistics were used. The studied sediments are essentially composed of garnets, biotite, pyroxene (diopside and augite?), epidote, monazite, hornblende, ilmenite, zircon, rutile, titanite, silimanite, kyanite, and quartz. The investigated sediments are similar to the lithotypes found regionally, thus possibly indicating a strong correlation between source rocks and sedimentary deposits. The redox environment is marked by the presence of Fe oxides, probably hematite. The alteration index supports a moderate degree, where micas are preserved, in whole or in part. Keywords: Unconsolidated Sediments, Beach Deposits; Chemical watering. GEOQUÍMICA Y PETROGRAFÍA DE DEPÓSITOS CUTERNARIOS DE LA PORCIÓN SW DE PRAIA BRAVA, ARMAÇÃO DOS BÚZIOS, RJ, BRASIL: EDFRX Y DIFFRACCIÓN LÁSER Resumen: Este artículo presenta los datos geoquímicos y petrográficos de sedimentos de playa de la región SO de Praia Brava (PB) en Armação dos Búzios-RJ. Buscamos discutir los procesos de meteorización química y procedencia, así como analizar el entorno geoquímico y su relación con fuentes autóctonas. En este estudio se utilizaron análisis petrográficos, parámetros texturales en distribución de partículas, geoquímica y estadística con la ayuda de Difracción Láser y Fluorescencia de Rayos X con Energía Dispersiva. Los sedimentos estudiados están compuestos fundamentalmente por granate, biotita, piroxeno (¿diópsido y augita?), Epidota, monacita, hornblenda, ilmenita, circón, rutilo, titanita, silimanita, cianita, además de cuarzo. Los sedimentos investigados son un reflejo de los litotipos encontrados regionalmente, lo que posiblemente indique una fuerte correlación entre las rocas generadoras y los depósitos sedimentarios. El entorno redox está delimitado por la presencia de óxidos de Fe, probablemente hematita. El índice de cambio calculado admite un grado moderado en el que se conservan las micas, ya sea total o parcialmente. Palabras clave: Sedimentos no consolidados; Depósitos en la playa; Meteorización química.

Paleoredox conditions, hydrothermal history, and target vectoring in the Macmillan Pass base-metal district, Yukon, Canada: 2 – Pyrite paragenesis and mineral chemistry

ABSTRACT The MacMillan Pass district in Yukon, Canada, hosts the Tom and Jason clastic sediment-hosted Zn-Pb-Ag-(Ba) deposits. Pyrite-bearing drill core samples were collected from seven drill holes that intersected sulfide mineralization and time-stratigraphically equivalent rocks at varied spatial distances extending up to 3 km away from the deposits to assess the relative timing of pyrite mineralization and the chemistry of pyrite paragenesis. There are four pyrite morphologies: framboids and polyframboids (Py1), subhedral to euhedral inclusion-free crystals (Py2a), silicate inclusion-bearing nodules with serrated edges (Py2b), and euhedral idiomorphic overgrowths on preexisting pyrite morphologies (Py3). These morphological varieties correspond in time from syngenetic to earliest diagenetic growth (Py1), early to late diagenetic growth (Py2a, Py2b), and metamorphic crystallization and/or recrystallization of previous textural varieties (Py3). A representative subset of pyrite grains was analyzed for trace element contents and distributions by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Analyses by LA-ICP-MS reveal that each textural variety of pyrite has a distinct trace element composition that also varies depending on stratigraphic unit. A suite of clastic sediment-hosted sulfide mineralization-related elements was incorporated into Py2 within sulfide mineralized units at greater abundances than that in unmineralized units (e.g., Zn, As, Pb, Tl, Bi). Lead abundances and Pb/Se and As/Mo values in pyrite are the most robust vectoring tools documented. The timing for clastic sediment-hosted Zn-Pb mineralization was syn and/or post late diagenesis (Py2b). A Ba-enriched horizon was identified in rocks and this is interpreted to be the distal time-stratigraphic equivalent unit to Zn-Pb mineralization. The Ba-enriched horizon contains Py2 with anomalous metal (Tl, Co, Mn, Cd, Zn, Sb) contents and abundant macroscopic baryte, and it is interpreted to represent the distal expression of sulfide mineralization-forming hydrothermal activity. Four genetic models for mineralization are reviewed; however, the only model that is consistent with our whole rock and pyrite geochemistry involves venting of buoyant hydrothermal fluid, mixing with ambient seawater, and remaining or sinking into unconsolidated sediments, with lateral migration up to 2–3 km from the vent source.

Paleoredox conditions, hydrothermal history, and target vectoring in the MacMillan Pass base-metal district, Yukon, Canada: 1 – Lithogeochemistry of proximal and distal shales

ABSTRACT The MacMillan Pass District in Yukon, Canada, hosts the Tom and Jason clastic sediment-hosted Zn-Pb-Ag-(Ba) deposits. Bulk geochemical paleoredox proxies (Eu/Eu*, Ce/Ce*, Mo, Re/Mo, and Ni/Co) indicate anoxic–dysoxic water column and sulfidic porewater conditions persisted during the Late Devonian deposition of the Lower Earn Group host rocks. Positive Eu/Eu* anomalies (up to 3.31) in sulfide mineralization at the Tom deposit are consistent with relatively high temperature (probably >250 °C), reducing, acidic hydrothermal fluids that infiltrated laterally through unconsolidated sediments proximal to the hydrothermal upflow zone and/or exhaled at the seafloor as moderate- to high-density brines. Molybdenum and U enrichment factors (relative to upper continental crust) and Mo/organic C values are consistent with a moderately restricted basin; Mo/C values fall between those of the Black Sea (highly restricted) and the Framvaren Inlet (moderately restricted). A Ba-rich shale was identified in rocks that are distal and time-equivalent units to the Pb-Zn mineralization; based on the bulk chemical compositions and on previous S and Sr isotope studies, we interpret the baryte in this unit to be largely hydrothermal in origin and perhaps remobilized and reprecipitated during hydrothermal base-metal mineralization.