From Lower Albian to Santonian times the counterclockwise rotation of the Iberian Plate resulted in a number of periods of rifting and relative falls in sea level. During the Middle Albian, these events brought about an important influx of siliciclastic sediments within a deltaic-estuarine system that deposited the Escucha Formation. Significant coal deposits have been recorded in freshwater swamp plain (upper delta plain) and brackish water swamp (lower delta plain) environments. The distribution and thickness of the workable coal of the study area are controlled by the stratigraphy, paleogeography, sedimentology, and tectonic structure. These coals, which have been classified as mainly subbituminous, are characterized by their high sulfur content (6 to 7.3 percent dry basis average of worked coal). The study of the sulfur content of the coal seams of the Castellote and Calanda Sub-basins reveals three types of sulfur distribution: vertical variation within individual coal seams, stratigraphic variation, and lateral variation within the basin. These three types of sulfur distribution have two principal controlling factors; the sedimentologic setting and external factors, the latter probably due to the leaching of the sulfur of pre-Cretaceous evaporites.

The concentration of arsenic (As) in U.S. coal is significant in coal cleaning, coal utilization, and environmental considerations. Arsenic is significant because of its potential toxicity for plants and animals. This chapter examines concentrations and modes of occurrence of arsenic in U.S. coals. The data used in this study are from more than 5,000 determinations of As in coal samples, analyzed on an as-received basis using wet chemical and instrumental neutron activation analysis (INAA). Variation in As content was related to coal provinces and coal regions, coal rank, geologic age, sulfur and ash contents, heating values, and stratigraphic and lateral variation. The As content of foreign coal, roof- and floor-rock and coal partings, and coal wastes is discussed. The mode of occurrence of As is reviewed. It appears that the bulk of arsenic in coal is in sulfide minerals, primarily iron sulfides. Much of the arsenic-bearing sulfides may be epigenetic in origin, or the arsenic may have been emplaced by reaction of pyrite with arsenic-bearing mineralogic solutions. Low levels of arsenic (<5 ppm) may be organically associated. Analysis of the As data indicated the following. (1) Appalachian and Western Interior coals have the highest As content; Fort Union and Wind River regions have the least. (2) There is no systematic relation between As content and coal rank, coal deposit age, and total sulfur content; however, there is a sympathetic relation with pyritic sulfur content. (3) Arsenic concentration is highest in coal with heating values between 12,000 and 13,000 Btu/lb. (4) Stratigraphic profiles of As content for four areas show wide variations, with samples from western Kentucky displaying the least variation and samples from the southern Appalachians the most. Pyritic sulfur-content variations generally parallel those of As content. (5) Arsenic distribution maps of a small area in the Western Kentucky coal field generally show As content increasing from the basin toward the margin. (6) Roof and floor rocks contain similar amounts of As as in U.S. coal; arsenic content in U.S. coal is much less than that in coal wastes. (7) Arsenic enrichment factors reveal little difference on the basis of geologic age and coal rank regardless of whether average shale or the crustal averages are used for comparison. There are significant differences in enrichment factor values between some coal provinces or regions.