Slate Martinsburg

Table II. Organic Analysis of Martinsburg Slate, Stoddard Quarry, Pen Argyh Pa ...

Response of Natural Coals to Metamorphism. The Martinsburg slate and its anthraxolite have clearly been subjected to low grade metamorphism. Presuming a low temperature origin such as suggested in the preceding section, at least part of the anthraxolite rank increase must be caused by this metamorphism. In order to evaluate this contribution to rank increase, it is useful to examine known cases of metamorphism of natural coals. MacFarlane (25) studied the thermal effects of intruded olivine basalt sills on Yampa coals (Colorado). He carried out parallel laboratory studies in which unaltered... 

Figure 2. Outline map of eastern Pennsylvania showing extent of Martinsburg formation (stippled), anthracite coal fields, and general trend of isocarbs. Principal cities shown are H, Harrisburg A, Allentown E, Easton and P, Philadelphia, Anthraxolite locality at Pen Argyl, slate belt...

The probable absence of any pre-Martinsburg carbon concentrations precludes a clastic origin for the nodules. In any case, they are found in the uniform gray slate (originally mud), which was precipitated in the deep, still basin very slowly and are not associated with the clastic debris of the turbidite sequences. Turbulent conditions would have been needed for transport of such pebbles into the environment. 

---