Environmental Significance of Pisoliths, Mississippian Madison Formation of the Williston Basin, Bottineau, Renville, and McHenry Counties, North Dakota: ABSTRACT

Abstract

Pisoliths from the Mississippian Madison Formation of North Dakota originated in an agitated, shallow-water marine environment. Evidence for this interpretation includes: (1) association of pisoliths with ooliths and marine fossils; (2) well-rounded clastic pisolith morphology; (3) vertical facies succession in core from open-marine facies through the pisolith-oolith facies band into lagoonal and intertidal facies featuring fenestral fabrics and possible tepee structures; (4) upward-shallowing cycles with reverse grading, submarine hardgrounds, and desiccation features. Madison pisolites (pisolith-rich carbonate) differ markedly from those set forth by Dunham as indicators of vadose, soil conditions: (1) they lack fitted polygonal structure; (2) they have large amounts of primary pore space or cemented pore space; (3) they contain no peds (soil components); (4) no evidence of rooting is visible; (5) no classic caliche horizons are present; (6) only minor occurrence of vadose cements postdate pisolith initiation, development, and deposition; (7) no evidence for replacement of parent rock was observed. Similar evidence was used by Esteban, and Esteban and Pray, to show that the type Capitan Formation pisoliths were not formed by soil-forming processes. Pisoliths and pisolites should be viewed in relation to other carbonate allochems, sedimentary structures, and diagenetic fabrics to determine their origin and environmental significance. End_of_Article - Last_Page 507------------