Using Geochemical Analysis to Identify a Spatial Maturity Anomaly—an Example from the Upper Rhine Graben, Germany
Carolyn Lampe, Lorenz Schwark, 2012. "Using Geochemical Analysis to Identify a Spatial Maturity Anomaly—an Example from the Upper Rhine Graben, Germany", Analyzing the Thermal History of Sedimentary Basins: Methods and Case Studies, Nicholas B. Harris, Kenneth E. Peters
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Measurements of dispersed vitrinite in several exploration wells within the Tertiary and Quaternary rift sediments of the northern Upper Rhine Graben indicate a complex thermal history. While most wells show “normal” increasing maturity trends with depth, some lack any obvious trend. One of the investigated wells, Nordheim-1, even features a bell-shaped downhole anomaly having an inverse maturation trend. Abnormal maturation effects, such as oxidation, reworking, or deposition of previously coalified material from the hinterland, are ruled out as a result of the relative position of the well with respect to the graben shoulders or active fault systems. Thus, secondary maturation caused by focused, lateral hydrothermal fluid flow has been proposed.
To verify the measured maturity anomaly organic (Rock-Eval pyrolysis, methylphenanthrene distribution), geochemical analyses were used to obtain independent data for comparison. Tmax values from Rock-Eval pyrolysis and various ratios of methylphenanthrene isomers indicate abnormally high maturities at shallow depth. Like the vitrinite reflectance values, these techniques show maturities that are inconsistent with their present burial depth but support enhanced convective hydrothermal heat flow in these strata. The consistency of results obtained using independent techniques verifies a hydrothermal origin of the maturity anomaly and excludes other modes of alteration.
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Thermal histories of sedimentary basins are critical sources of scientific and practical information. They provide us with windows into past and present tectonic processes and the configuration of the crust and mantle. Using records of present and past temperature distributions, we can identify and constrain interpretations of tectonic events, distinguish different basin types and interpret pathways of fluid flow. These insights can be used calibrate basin and petroleum system models and to interpret and predict the distribution of minerals and petroleum, diagenesis and reservoir quality, and the geomechanical properties of rock units. This volume summarizes the current state of the art for many modern approaches used to estimate paleotemperature. Many techniques are now available based on both organic and inorganic components in the rock. Even techniques that are now many years old, such as apatite fission track analysis, have und