Geology Reference
In-Depth Information
Figure 1.1.6. Location of Pennsylvanian and Cretaceous/Tertiary coalfields in the United States. Based on Kim
and Chaiken (1993, p.3)
Possible Mechanisms for Increasing Coal Rank
The increased temperature necessary to increase rank is assumed to be related to depth of burial (Francis, 1961).
The increased pressure and deformation during tectonic activity are presumed to have little effect on coal rank
(Teichmuller and Teichmuller, 1982). The hydrothermal brines expelled from tectonic belts are currently postulated
as a mechanism of anomalous heat transfer (Copard et al., 2000).
A number of authors have described increases in the maturation of coal-bearing rocks as related to a particular
mechanism, i.e., depth of burial, magmatic intrusion, tectonic activity, and more recently, hydrothermal fluids. The
following examples demonstrate the variety of plausible mechanisms and are not intended to be a comprehensive
catalog of such studies.
Depth of Burial Paleo heat flow values and the thickness of eroded sediments in the Saar basin were evaluated
with one-dimensional thermal models based on vitrinite reflectance and temperature data (Hertle and Littke,
2000). The thermal maturity of the sediments is explained by deep burial and moderate heat flow. The calculated
heat flows imply a maximum burial of 30
-
40 km. The effect of volcanism on heat distribution was considered to be
much less than the effect of deep burial.
In the southern part of the Lower Saxony Basin, areas of high thermal maturation had previously been attributed to
magmatic intrusions (Petmecky et al., 1999). Based on numerical modeling, only deep burial and relatively low
heat flow produced a satisfactory fit between measured and calculated data. The low gradient in vitrinite reflectance
with depth and sedimentation rates of 170 m/m.y. support depth of burial rather than magmatic intrusion as the
coalification mechanism.
Although coalification patterns in the Upper Silesian Coal Basin generally followed Hilt
s Rule, deviations from it
were also observed (Sivek et al., 2002). Most of the localized variations can be explained by igneous intrusions and
tectonic deformation. Heat flow effects related to hydrothermal fluid migration are rare.
'
Search WWH ::




Custom Search