Sabkha or Subaqueous Intrastratal Origin of Chickenwire Gypsum, DeQueen Formation (Cretaceous), Arkansas: ABSTRACT

Abstract

The DeQueen Formation comprises two members. The lower consists of thick, chickenwire gypsum with calcareous mudstones; the upper consists of thin-bedded limestones and shales with hopper halite molds, gypsum, and a celestite bed. Possible interpretations involving sabkha models are questioned. Stromatolites and dolomite are rarely present and correlation with the Ferry Lake Formation would imply a sabkha plain at least 250 km wide; extensive intra-formational erosion surfaces are absent. It has been suggested that the chickenwire beds were precipitated from standing water and that nodular structures resulted from secondary flowage of superjacent and subjacent muds into the gypsum as a result of compaction and shrinkage due to dehydration to anhydrite. A principal objection to this theory is the uniformity of texture of the mud screens even throughout thick gypsum beds and the lack of any structures directly attributable to flowage. Many features of the formation indicate a highly restricted, lagoonal environment of deposition. These include ostracod faunas and evaporite minerals indicative of salinities fluctuating between brackish and hypersaline, and sedimentary structures suggestive of extremely shallow water and even of emergence. Some limestone beds in the upper member contain unequivocal evidence of intrastratal gypsum crystal growth, and the possibility is here advanced that the chickenwire gypsum beds are also intrastratal in origin but that they formed on the floor of a lagoon rather than in a supratidal setting. The same mechanism, it is implied, may also account for the Ferry Lake chickenwire anhydrite throughout the east Texas-central Louisiana back-reef area of the Lower Cretaceous. End_of_Article - Last_Page 561------------