Marine Pennsylvanian

Donald R. Baker. It seems to me that your results on the distribution of boron and gallium have important implications for the work of others who have concluded that these elements are depositional environmental indications. I wonder if the enrichment of these elements in nonmarine rocks of Pennsylvanian age in the eastern U.S. may simply reflect their proximity to the source area and not have any real bearing on the depositional environment. And conversely, the lower content of these elements reported for marine shales may be caused by deposition of these facies in areas far removed from the source areas. What is your opinion ... 

Secondary, post-depositional chlorite is a common component in marine sands, where it commonly forms from the alteration of volcanic material or montmorillonite. X-ray analyses suggest that many of these chlorites are relatively iron-rich. A partial analysis (Weaver and Beck, 1972) of a clay chlorite from a Pennsylvanian sandstone from Oklahoma tended to confirm the idea that these clays are rich in iron 28% Si02,15.0% Al2 03, 23.9% Fe as Fe2 03, 5.3% MgO, 2.6% CaO, 1.2% K2O. 

Sources of Sulfur in Coal and Oil. The major coal beds of eastern North America are of Pennsylvanian age. During that time, there was a constantly fluctuating sea level across flat lowlands over the North American interior. Coal was formed just before the onset of marine conditions, so that coal swamp forests occurred on broad lands along or near the sea shore. Thicker sections accumulated on the more rapidly subsiding Illinois and Forest City basins and in the Appalachia fireland basin (14). 

At its simplest, an onlap trap may be a blanket sand that pinches out up-dip (Fig. 8D). It is sealed by impermeable rocks beneath and by an onlapping shale (generally the source rock, as well as the cap). Many unconformities are old land surfaces, however, and sands may be deposited in old topographic lows. Alternating hard and soft sediments may have been weathered and eroded to form scarps, dip slopes, and strike valleys. Fluvial or shallow marine sands may have been deposited along the old valleys and sealed by marine muds. Stratigraphic traps of this type are known as the Mississippian Pennsylvanian imconformity of Oklahoma. Alternatively, the unconformity may have been a planar land surface that was locally incised by alluvial valleys. These may have been sand filled and drowned by... 

---