Search results for "stratigraphy"

Microbially-induced Fe and Mn oxides in condensed pelagic sediments (Middle -Upper Jurassic, Western Sicily)

2011

Abstract This article presents a petrographic comparison of the Rosso Ammonitico facies of Western Sicily and the original Rosso Ammonitico Veronese of Northern Italy based on a total of 27 sections. The Rosso Ammonitico has been the subject of numerous controversies that range from bathyal to shallow-water platform sedimentation. Therefore it seemed interesting to verify if the term Rosso Ammonitico has the same geologic connotation from region to region. The Middle-Upper Jurassic Rosso Ammonitico of Western Sicily is a condensed succession formed during a period of extensional synsedimentary tectonics related to the spreading of the Ionian Ocean. Slope-to-basin or pelagic carbonate deposi…

Coarse-grained cryogenic aragonite as end-member of mineral formation in dolomite caves

2018

Abstract Cryogenic carbonate particles (single crystals and aggregates) have recently been recognized as important witnesses of permafrost dynamics, as they can be used to estimate the thickness and timing of development of permafrost. In this study, the petrography and geochemistry of coarse-grained cryogenic aragonite (CGCAr) identified in Zoolithen Cave in NE Bavaria, Germany, are described in detail for the first time. We provide a sequence of carbonate precipitation during freezing, where CGCAr mark the final crystallization phase in freezing water on ice. Our results support the notion that host rock composition, solution chemistry, and cave ventilation play an important role for arag…

Deep-water stromatolites andFrutexites Maslov from the early and Middle Jurassic of S-Germany and Austria

1993

Despite extensive discussions during the last 20 years stromatolites are still used by many geologists as unequivocal indicators of very shallow-water conditions. We investigated four stratigraphic units from the Lower and Middle Jurassic of southern Germany (Posidonien-Schiefer, Amaltheen-Ton) and of the Northern Calcareous Alps (Adneter Kalk, Klauskalk), which were formerly interpreted as shallow marine sediments by some authors due to the occurrence of stromatolites. Our interpretations of the macro-, micro- and ultrafacies of these sediments are not compatible with shallow-water settings. We therefore propose a deep-marine, aphotic origin of these stromatolites. Former interpretations o…

The origin and timing of multiphase cementation in carbonates: Impact of regional scale geodynamic events on the Middle Jurassic Limestones diagenesi…

2009

The Middle Jurassic carbonates of the eastern part of the Paris Basin display surprisingly low values of porosity and permeability (Φ < 15‰ and K < 0.5 mD). The main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs; a fate that did not befall their equivalents in deeper, central parts of the Paris Basin. Using petrographic and geochemical analyses (stable O and C isotopes, Sr isotopes, major elements), we identify six calcitic spar stages, two dolomite stages, and several episodes of fracturing and stylolitization ordered in paragenetic sequence.…

Carbon-isotope record and palaeoenvironmental changes during the early Toarcian oceanic anoxic event in shallow-marine carbonates of the Adriatic Car…

2013

AbstractGeochemical (δ13C, δ18O and Mn) compositions of Lower Jurassic shallow-water carbonates cropping out in Croatia were analyzed to elucidate the impact of the early Toarcian oceanic anoxic event (T-OAE) on the Adriatic Carbonate Platform (AdCP). The bulk-rock carbon-isotope records through the studied sections (Velebit-A, Velebit-B and Gornje Jelenje) are characterized by two significant excursions: (i) an initial positive trend interrupted by a pronounced negative shift (c. 2.5‰) that is followed by (ii) an increasing trend of positive values (up to 4.5‰). A comparison with δ13C trends obtained from well-calibrated sections from other localities in Europe shows that the overall chara…

Microstructure-specific carbon isotopic signatures of organic matter from ∼3.5 Ga cherts of the Pilbara Craton support a biologic origin.

2016

21 pages; International audience; The ∼3.5 Ga Dresser Formation from the North Pole Dome of the Pilbara Craton (Western Australia) contains some of the oldest evidence for life on Earth. Here, we present a detailed study of microstructure-specific carbon isotopic composition of organic matter (OM) preserved in Dresser Formation bedded cherts and hydrothermal chert vein using in situ Secondary-Ion Mass Spectrometry (SIMS). The OM in these rocks occurs mainly as clots that, together with minor fine OM layers and laminae, are considered primary textures formed prior to host rock lithification. Other than rare OM-rich stylolites, no evidence was found for later OM migration beyond the micromete…

Fossil wood in Middle–Upper Jurassic marine sedimentary cycles of France: relations with climate, sea-level dynamics, and carbonate-platform environm…

1998

Abstract Vegetation, climate, and sea-level oscillations interact in complex ways. Intuition suggests that climatic variations are recorded in geological deposits by both fossil phytoclasts and sediments. Therefore investigation of palaeobotanical remains within a precise sedimentological framework may help to decipher this much-debated interaction. A database of 129 Jurassic (Bathonian–Oxfordian) fossil wood samples from France is used here as a case study. The palaeoenvironment (freshwater swamp, carbonate lagoon, shoreface, argillaceous offshore) and the second-order relative sea-level phases were determined for each datum. There is no correlation between the wood genera distribution and…

FACIES HETEROGENEITY AND SEDIMENTARY PROCESSES ALONG A TECTONICALLY-CONTROLLED CARBONATE SLOPE: A CASE STUDY FROM THE CRETACEOUS OF WESTERN SICILY (I…

2020

Characterization and origin of permeability-porosity heterogeneity in shallow-marine carbonates: from core scale to 3D reservoir dimension (Middle Ju…

2014

21 pages; International audience; Nuclear magnetic resonance (NMR), stable isotope geochemistry of micro-sampled cores, NMR well-logs and 3D modeling are used to investigate the carbonate permeability-porosity heterogeneity along 230 m-thick limestones of the Paris Basin. Despite the global low porosity and permeability of the limestones, two aquifers units with porosity greater than 15% were identified. These two aquifers are very different in terms of pore through radii and NMR signal. The first one (A1: Aquifer 1) is a 7 m-thick mudstone unit, dominated by extended microporosity with pore throat radii of 0.25 μm to 0.3 μm. The second one (A2: Aquifer 2) is a 15 m-thick oolitic grainstone…

Late Carnian-Early Norian ammonoids from the GSSP candidate section Pizzo Mondello (Sicani mountain, Sicily).

2012

A small collection of ammonoids from the Upper Triassic Scillato Formation at Pizzo Mondello (Agrigento, Sicily) is studied. The specimens were collected in a framework of a project aimed at providing an integrated high-resolution bio-chronostratigraphic support to the Upper Carnian-Norian magnetostratigraphic scale defined at this site, that is located in an historical area from which G.G. Gemmellaro collected the Upper Triassic of ammonoids monographed at the beginning of the XX century. The specimens from Pizzo Mondello were bed-by-bed sampled and represent the first collection of Upper Triassic ammonoids described from Sicily since Gemmellaro time. Quite several levels of the Pizzo Mond…