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Earth-Science Reviews
Elsevier
Earth-Science Reviews

Elsevier

0012-8252

Earth-Science Reviews/Journal Earth-Science ReviewsSCIISTPAHCI
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    Seismic facies analysis: Past, present and future

    Xu G.Haq B.U.
    1页
    查看更多>>摘要：Seismic facies and lithofacies analysis, once considered a breakthrough in exploration applications, is currently a dynamic field because of the addition of several new concepts and interpretive procedures. In terms of basic theory, notable developments have taken place that encompass refinements in geological and geophysical concepts, including several enhancements to sequence-stratigraphic and facies distribution models, better knowledge of seismic response mechanism to small-scale stratigraphic structures and different rock types, as well as the emergence of new technologies, such as the one allows the restoration of original depositional architecture and spectral decomposition. A seismic facies analysis index system is proposed that includes nine independent parameters: position, external form, internal configuration, continuity, smoothness, amplitude, frequency, special waveforms, and appearance. The sedimentary systems established by traditional seismic facies analysis lack detailed lithofacies and hydrodynamic information. However, presently further subdivision of seismic lithofacies into more detailed categories is now possible, made available by the addition of new seismic parameters that are indicative of sedimentary structure and rock-type combinations. This enables interpreters to identify lithofacies details directly from the seismic data and reconstruct the sedimentary systems with greater precision (by superposition of the environment, lithofacies and flow paths). The seismic slice image analysis, including seismic geomorphology and seismic sedimentology, employs a stratal time slice, 90° phase shift, and spectral decomposition techniques to improve the resolution of the slice images, describe sedimentary micro-facies and understand sedimentary processes based on the geometric features of the time slice. The seismic facies auto-classification techniques are still at an early stage of development, but significant possibilities exist for future enhancements if the new seismic index system, where the accumulated knowledge of the skilled experts could be utilized advantageously. This paper will also serve as a summary of the state-of-the-art of seismic facies analysis.
      原文链接:
    • NSTL
    • Elsevier

    Tetrapod turnover during the Permo-Triassic transition explained by temperature change

    Angielczyk K.D.Sidor C.A.Liu J.Abdala F....
    1页
    查看更多>>摘要：Global temperatures significantly changed from the late Permian to the Early Triassic: the Earth transformed from a cool world to a hothouse climate. This transition undoubtedly had a strong impact on tetrapod physiology and distribution. During the global cooling, tetrapods generally increased their size; and the currently recognized late Permian tetrapod extinction, exemplified by the record preserved in the South African Karoo Basin, occurred in the late stage of cooling. Rapid warming in the Early Triassic is predicted to have resulted in extinctions and/or local extirpation of low latitude tetrapods, but the very limited fossil record from this region makes testing this hypothesis difficult. Warming is predicted to have had less negative impacts on the tetrapod diversity of mid-latitudes, and promoted the success of tetrapods in the high latitudes. Based on the known fossil record, a tetrapod gap could have existed in central Pangea between ~30°N and ~ 40°S, and lasting from the Induan to the early Spathian. However, the exact boundaries of this gap likely varied over time, and it could have encompassed a larger area during the hottest phases (Griesbachian and near the Smithian–Spathain boundary).
      原文链接:
    • NSTL
    • Elsevier

    Ultramafic-hosted volcanogenic massive sulfide deposits: an overlooked sub-class of VMS deposit forming in complex tectonic environments

    Patten C.G.C.Peillod A.Kolb J.Coltat R....
    1页
    查看更多>>摘要：Ongoing seafloor exploration highlights that ultramafic-hosted seafloor massive sulfide deposits (UM-SMS) are ubiquitous along slow to ultra-slow spreading ridges. These deposits are closely linked to low-angle detachment faults, are hosted in variably altered ultramafic rocks and are enriched in precious (Au-Ag), critical (Co) and base metals (Cu-Zn-Ni). Ultramafic-hosted volcanogenic massive sulfide (UM-VMS) deposits, however, are commonly thought to be scarce on land but an extensive deposit review from the geological record challenges this assumption. These deposits occur in complex tectonic settings often referred to as “tectonic mélange”, and their origin is often disputed (e.g. hydrothermally overprinted magmatic Ni-Cu massive sulfide) due to a late orogenic overprint that partly erase and/or overprint earlier seafloor-related features. Because of the uncommon host rocks, ore mineralogy and tectonic environment and the limited awareness of scientific and industrial communities, these deposits are difficult to interpret. Furthermore, although seafloor exploration greatly improved our understanding of these deposits, it has also induced a strong bias by focusing almost exclusively on mid-ocean ridge (MOR) environments. Ultramafic-hosted VMS deposits in the geological record, however, mostly occur in settings more recently interpreted as ocean-continent transitions (OCT) and/or supra-subduction zones (SSZ). Ophiolites formed in these environments are more likely to be tectonically emplaced during collision favouring the preservation of the UM-VMS deposits in the geological record. In this study we review more than sixty deposits present worldwide in the geological record and discuss the key features, which enable us to unambiguously classify them as ultramafic-hosted VMS deposits. Because of their unique nature and metal endowment, the ultramafic-hosted VMS deposits should be considered as a stand-alone sub-group of VMS deposits, which possibly represent untapped mineral resource with high future potential. Their discovery, however, requires specific, robust and tailored exploration and genetic models, which need to be further developed. Finally, studies of UM-VMS deposits in the geological record highlights that ultramafic-hosted hydrothermal systems on the seafloor can occur in very diverse plate tectonic environments and should drive further seafloor exploration in less well explored tectonic environments such as ocean-continent transition and supra-subduction zone.
      原文链接:
    • NSTL
    • Elsevier