Stratigraphy, mineralogy, and geochemistry of Upper Cretaceous deposits from the Minnesota and Cottonwood River valleys, southwestern Minnesota
Abstract
The dissertation consists of 3 chapters. Chapter 1, dealing with Upper Cretaceous, non-marine deposits along the Minnesota River valley, applies standard and sequence-stratigraphic concepts to correlate lithologies on the eastern side of the Western Interior Seaway with the better characterized deposits from Nebraska, Iowa, and South Dakota. Cretaceous deposits from southwestern Minnesota are correlative with the Nishnabotna and Woodbury Members of the Dakota Formation, the Graneros Shale, and the Greenhorn Formation. Two major unconformities, forming sequence boundaries, separate the underlying saprolite from the Nishnabotna deposits and Nishnabotna from Woodbury deposits. These unconformities resulted from eustatic sea-level drops during the late Albian (98 Ma) and early Cenomanian (95.5), respectively. Chapter 2 discusses the chemistry and genesis of the uncommon clay mineral, berthierine. It was found in a buried laterite from the Late Cretaceous (Cenomanian) in southwestern Minnesota. It formed beneath a lignitic horizon in which reducing solutions percolated through a laterite comprised of gibbsite, kaolinite, and goethite. Unusual in its lack of Mg, this mineral has a structural formula close to an idealized Fe-berthierine--$\rm Fe\sb2Al\sb2SiO\sb5(OH)\sb4.$ Apart from their chemistry, the unique feature of the Minnesota Fe-berthierine is their formation in an exclusive non-marine depositional environment. They formed in situ as part of a lateritic weathering profile developed on a broad, low relief peneplain. Evidence of formation under non-marine conditions include the presence of (1) scattered lignitic fragments; (2) concretions forming casts and molds of woody material; and (3) a non-marine Unio-like fossil. Chapter 3 compares and contrasts the Minnesota kaolin deposits with the truly "world-class" kaolin deposits in Georgia. Both deposits formed from similar bedrock under similar chemical-weathering conditions during the hot-and-humid climatic conditions of the mid-Cretaceous. Differences in quality and quantity of these deposits relate not only to the different lengths of time under which these separate areas underwent leaching, but also accommodation space which is linked to subsidence.
Degree
Ph.D.
Advisors
Fritz, Purdue University.
Subject Area
Geochemistry|Geology|Mineralogy
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