Summary of Research Proposal

The following summary of my research proposal serves to explain the goals and nature of my work.

Sedimentology And Significance Of An Anomalous Quartzose Unit Within A Lithic-Rich Fluvial-Dominated Foreland Basin, Kootenai Formation, Western Montana

I. Project Statement

Overview:

In brief, the purpose of my project is to determine the origin of a poorly understood rock unit that occurs within in the Lower Cretaceous Kootenai Formation along the Missouri River near Great Falls, Montana. Immediately south of my proposed field area, the unit exhibits physical properties that indicate deposition in a shallow, tide-dominated, marine seaway that temporarily flooded the western Montana region about 120 million years ago (Fig.1) (Spinelli, 2001; Widrig, 2000). However, distinctly different properties are reported to characterize the unit a short distance to the north along my proposed study area.

Background and Purpose:

Foreland basins are large sedimentary basins that form upon continental crust alongside compressional plate mountain belts. Due to compression, the earth’s crust shortens and thickens at the plate margin producing an elongate mountain belt and an increase in crustal load upon the relatively thin and weaker crust of the adjacent continental interior. Because of this, thinner crust is simultaneously forced to subside forming a ~200-300 km wide sedimentary basin which extends along the length of the mountain belt (DeCelles and Giles, 1996; Schwartz and DeCelles, 1988). The foreland basin simultaneously receives lithic-rich sediment (that is sedimentary, metamorphic, and igneous debris) that is eroded from the adjacent mountain belt. Because of this dynamic relationship, sedimentary layers within the basin reflect mountain-belt growth by means of their particle composition and physical features that indicate transport by ancient rivers into the basin.

In westernmost Montana, the 120 million-year-old Lower Cretaceous Kootenai Formation was deposited in a foreland basin located east of such a mountain belt. Most data from the Kootenai is consistent with the above model and indicates lithic-rich sediment deposition in river systems and alluvial plains draining mountainous uplifts to west (Walker, 1974; DeCelles, 1986; Berkhouse, 1985). However, mineral composition, hydrodynamic indicators, and sediment transport direction data for the Third Kootenai Member (KK3), are inconsistent with all other Kootenai rock units. The occurrence of thick bodies of chemically stable and mechanically durable quartz sand and paleo-environmental evidence within the KK3 led Vuke-Foster (1987) to suggest a non-specific shallow marine origin with source areas located east of the foreland basin in the tectonically stable continental interior. Most recently, detailed studies of hydrodynamic indicators preserved within the KK3 document a high-energy tidal sea origin, similar to modern North Sea settings, associated with southward marine inundation of the foreland basin (Spinelli, 2001; Widrig, 2000). Compared to rocks in the Spinelli-Widrig study area (Fig. 1), the KK3 along the Missouri River are reported to be thinner and characterized by deep paleo-channel incision and sandy channel fill leading to past fluvial channel interpretations (Walker, 1974). However, the sandstone is also reported to be quartzose, similar to the tidal KK3 in the south.

The contradiction between fluvial channel (Walker, 1974) and open tidal sea (Spinelli, 2001; Widrig, 2000) interpretations for the same rock unit lead me to test for the alternate possibility of shoreline associated tidal channel origin in the Missouri River area. Specifically, the purpose of my study is several fold:

1) To collect data from physical structures within the KK3 that serve as evidence for hydrodynamic processes which are linked to specific types of environmental systems (such as fluvial channel vs. tidal channel)

2) To collect data from physical structures in order to document paleo-transport directions.

3) To compare my findings with those of Spinelli and Widrig and address the regional distribution of environmental systems in context of large-scale subsidence within the foreland.

My work would be the first detailed sedimentologic analysis of the KK3 along the Missouri River in which data would be linked to specific aspects of fluid motion as known from modern laboratory studies and modern systems. The findings should serve as unusual insight into the evolution and marine flooding of foreland basins including aspects of large-scale current circulation within the basin.

Methods:

The detailed sedimentology of outcrops will be used to identify KK3 environmental systems. Sedimentologic features such as bed geometry, texture, sedimentary structures, erosional surfaces, and faunal content serve as evidence for depositional environments. In addition, details of physical sedimentary structures, including vertical and lateral sedimentary structure sequences, will be analyzed to identify the kinematics of fluid motion and compared to those of particular modern depositional environments. For example, the properties of tidal flow, including reversing flow direction, repetition, time-velocity asymmetry, and spring-neap progression are recognizable in the rock record (Klein, 1970, 1985; Boersma and Terwindt, 1981; Allen, 1984; Kreisa and Moiola, 1986; Kvale and Archer, 1990; Meyers and Schwartz, 1994). Field techniques will include documentation of the geometry of features (description, photo, sketch, measurement) as well as the orientation of features (Brunton compass). Sediment transport patterns will be determined by means of standard cross-stratification measurement techniques using a dip direction indicator and Brunton compass (DeCelles, et al., 1983). Laboratory products will include computer plots of quantitative (paleocurrent) data, measured stratigraphic sequences, measured sedimentary structures, and all other graphics required for the resulting thesis.

References Cited

Allen, J.R.L., 1984, Sedimentary structures: their character and physical basis: Developments in Sedimentology, v. 30.
 
Berkhouse, G.A., 1985, Sedimentology and diagenesis of the Lower Cretaceous Kootenai Formation in the Sun River Canyon area, northwest Montana. [MS thesis]: Bloomington, Indiana University, p. 151.
 
Boersma, J.R., and Terwindt, J.H.J., 1981, Neap-spring tide sequences of intertidal shoal deposits in a mesotidal estuary: Sedimentology, v. 28, p. 151-170.
 
DeCelles, P.G., 1986, Sedimentation in tectonically partitioned, non-marine foreland basin: the Lower Cretaceous Kootenai Formation, southwestern Montana: Geological Society of America Bulletin, v. 97, n. 8, p. 911-931
 
DeCelles, P.G., and Giles, K.A., 1996, Foreland basin systems. Basin Research, v. 8, p. 105-123.
 
DeCelles, P.G., R.P. Langford, and Schwartz, R.K., 1983, “Two New Method s of Paleocurrent Determination from Trough Cross-Stratification.” Jour. Sedimentary Petrology, v. 53, no. 2, p. 629-642.
 
Klein, G. de V., 1970, Depositional and dispersal dynamics of intertidal sand bars: Journal of Sedimentary Petrology, v. 40, p. 1095-1127.
 
Klein, G. de V., 1985, Intertidal flats and intertidal sand bodies, in Springer-Verlag, Coastal Sedimentary Environments, p. 186-284.
 
Kreisa, R.D., and Moiola, R.J., 1986, Sigmoidal tidal bundles and other tide generated sedimentary structures of the Curtis Formation, Utah: Geological Society of America Bulletin, v. 97, p. 381-387.
 
Kvale, E.P. and Archer, A.W., 1990, Tidal deposits associated with low-sulfur coals, Brazil Fm. (Lower Pennsylvanian), Indiana: Journal of Sedimentary Petrology, v. 60, n.4, p. 563-574.
 
Meyers, J.H. and R.K. Schwartz, 1994, Summary of Depositional Environments, Paleogeography, and Structural Control on Sedimentation in the Late Jurassic (Oxfordian) Sundance Foreland Basin, Western Montana. In Caputo, M.V., Peterson, J.A. and Franczyk, K.J. eds., Mesozoic Systems of the Rocky Mountain Region, USA: Society of Economic Paleontologists and Mineralogists Society for Sedimentary Geology, p. 331-349.
 
Schwartz, R.K and P. DeCelles, 1988, Cordilleran Foreland Basin Evolution in Response to Interactive Cretaceous Thrusting and Foreland Partitioning, Southwestern Montana. Geological Society of America Memoir 171, p. 489-513, plus 34 page microfiche appendix on facies analysis.
 
Spinelli, M. B., 2001, Tidal Indicators within the Quartzose Third Member of the Lower-Cretaceous Kootenai Formation(Kk3, West-Central Montana, [Senior Research Thesis]: Meadville, PA, Allegheny College.
 
Vuke-Foster, S. M., 1987, Marine tongue in the Middle Kootenai Formation north of Helena, Montana, in Berg, R.B., and Breuninger, R.H., eds., Guidebook of the Helena Area, west-central Montana, Special Publication 95: Tabacco Root Geological Society. Twelfth Annual Field Conference, p. 63-64.
 
Walker, T.F., 1974, Stratigraphy and depositional environments of the Morrison and Kootenai Formations in the Great Falls area, central Montana. [PhD thesis]: University of Montana, p.195.
 
Widrig, A. K., 2000, Estuarine Tidal Delta Deposits within the Fluvial-Dominated Early Cretaceous Foreland of West-Central Montana, [Senior Research Thesis]: Meadville, PA, Allegheny College.
 
Widrig, A. K., and Schwartz, R. K., 2001, Estuarine Tidal Deposits within a Fluvial Dominated Cretaceous Foreland Basin, Western Montana. Northeastern Section of the Geological Society of America, v. 32, p. 60.