Multiple Barrier-Island and Deltaic Progradational Sequences in Upper Cretaceous Coal-Bearing Strata, Northern Kaiparowits Plateau, Utah: ABSTRACT

Abstract

The Kaiparowits coalfield, Utah, contains reserves of 20 billion tons of coal which are confined to three major coal zones within the John Henry Member of the Straight Cliffs Formation (Upper Cretaceous). Mapping and subsurface work in the northern part of the coalfield End_Page 796------------------------------ indicates that the coal-bearing strata accumulated during seven minor progradations of the shoreline of the Cretaceous seaway. The lower and middle coal zones consist of eight and six seams, respectively, and were deposited in a swamp 20 km wide on the landward side of a barrier-island complex. The upper coal zone consists of a single seam that accumulated in interdistributary swamps in a deltaic setting. The three coal zones were deposited during the three of the seven progradations that are completely developed. The remainder are incompletely developed and do not contain significant coal seams. Complete vertical sequences of barrier-island and deltaic progradation are present in the Straight Cliffs Formation. Incomplete progradational sequences are usually composed of transition, shoreface, and foreshore deposits. The repetitious nature of the several progradations and transgressions of barrier-island deposits and the local incompleteness of their development suggest periodic fluctuations in the quantity of sediment supplied by longshore transport currents from deltas northwest of the study area. Delta-lobe abandonments probably resulted in the periodic interruption of sediment supplied to the barrier-island complex and allowed sufficient time for compactional subsidence in the barrier complex to cause minor transgressions. End_of_Article - Last_Page 797------------