Genetic Characteristics of Glauconite and Siderite: Implications for the Origin of Ambiguous Isolated Marine Sandbodies
Sharon A. Stonecipher, 1999. "Genetic Characteristics of Glauconite and Siderite: Implications for the Origin of Ambiguous Isolated Marine Sandbodies", Isolated Shallow Marine Sand Bodies: Sequence Stratigraphic Analysis and Sedimentologic Interpretation, Katherine M. Bergman, John W. Snedden
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Authigenic glauconite and siderite form under a limited range of well-documented geological and geochemical conditions. Because glauconite precursors need to remain at or near the sediment water surface for long periods of time in a setting where they can be repeatedly exhumed and shallowly buried, glauconite typically develops on the outer margins of continental shelves in areas of low sediment input. Based on these requirements, glauconite has traditionally been used as an indicator for transgressive sequences because transgressions tend to trap sediment on the continents. However, from a sequence stratigraphic standpoint, glaucony may be present in virtually any part of a depositional sequence due to remobilization. Glaucony can provide useful information for sequence stratigraphy only if variations in its abundance, physicochemical properties, and spatial/temporal characteristics are carefully documented.
Siderite typically forms in one of two distinct environments: one characterized by strongly reducing conditions (methanogenic zone), and one under slightly reducing conditions (post-oxic zone). Methanogenic siderite is more common in continental and fresh-water lacustrine than marine deposits. Post-oxic conditions are commonly associated with marine environments exhibiting moderately low concentrations of organic matter and low sedimentation rates. Siderite is also frequently found in association with sequence boundaries where it occurs as a secondary cement below the lowstand surface of erosion (LSE).
These restrictions on environment of origin provide information on the hydrologic regime and, by inference, the depositional and sequence stratigraphic setting of the host sediment in which these minerals are found. By examining the genetic significance of minerals such as glauconite and siderite, the origin of ambiguous, controversial, isolated marine sand bodies such as those discussed elsewhere in this volume may be clarified. This paper summarizes what is currently known about the chemical characteristics of these minerals and discusses generalized models of their distribution in a variety of sequence stratigraphic settings.
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Isolated Shallow Marine Sand Bodies: Sequence Stratigraphic Analysis and Sedimentologic Interpretation
Isolated Shallow Marine Sand Bodies: Sequence Stratigraphic Analysis and Sedimentologic Interpretation - Isolated shallow marine sand bodies are significant hydrocarbon reservoirs and understanding sand body genesis and geometry is critical to successful exploration and exploitation of these deposits. Recent advances in sequence stratigraphy have rekindled and refocused the discussions surrounding these important reservoirs. This volume stems from a 1995 SEPM sponsored targeted research conference that brought together the proponents of the differing interpretations to discuss facts and principles as they relate to isolated shallow marine sand bodies, using the controversial Lower Campian Shannon Sandstone as the focus for discussion.