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Sediment Analysis of the Late Cretaceous Hell Creek Formation of Western North Dakota

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Sediment Analysis of the Late Cretaceous Hell Creek Formation of Western North Dakota OpenRiver Student Research and Creative Projects 2015-2016 Grants & Sponsored Projects 9-1-2015 Sediment Analysis of the Late Cretaceous Hell Creek Formation of Western North Dakota Henry Cole Winona State University Follow this and additional works at: https://openriver.winona.edu/studentgrants2016 Recommended Citation Cole, Henry, "Sediment Analysis of the Late Cretaceous Hell Creek Formation of Western North Dakota" (2015). Student Research and Creative Projects 2015-2016. 3. https://openriver.winona.edu/studentgrants2016/3 This Grant is brought to you for free and open access by the Grants & Sponsored Projects at OpenRiver. It has been accepted for inclusion in Student Research and Creative Projects 2015-2016 by an authorized administrator of OpenRiver. For more information, please contact [email protected]. Sediment Analysis of the Late Cretaceous Hell Creek formation of Western North Dakota Henry Cole Abstract Results This study focuses on the lithology of a Triceratops excavation site near Marmarth, North Dakota. Sediment sizes ranged from about 3.9 μm clays to 200 μm fine sands and vary in composition. Nine The excavation site, Hell Creek Formation, consists of sedimentary rocks, predominantly clays, separate lithologies were identified, and are presented in Figure 6. The Predominant lithologies are sandstones, and mudstones dating to the Late Cretaceous period approximately 66 million years mud, clay, and siltstones. Two distinct sandstone beds are present in the top section of the sample ago. Fossilized dinosaur skeletons and preserved concentrations of microfossils, or fossil micro- butte, both displaying cross bedding and evidence of root fossils. All sampled sediments were rich in sites, can be found in exposures of the Hell Creek Formation throughout Montana and North and organic material, identified as small dark spots in the rock. Siltstone SRP_C16-03 contained a 6cm lay- South Dakota. Sediment samples were collected directly from and near the Triceratops excavation er of lignite, with preserved plant fossils seen in figure 4. The Triceratops skeleton was found in clay- site. The majority of sediments present at the site are sand and silt-sized, representing floodplains stone SRP_C16-08 (figure 7) approximately 3 meters away from the sample column. and channel sands, with occasional plant fossils and thin coal layers. The types of sediment found at the site, along with evidence supporting the presence of terrestrial species, supports the inter- pretation that during the Cretaceous Period, the depositional environment of western North Da- kota was warm and wet, likely a paludal or transitional coastal environment similar to North America’s Gulf Coast today. Figure 4: (Right) Introduction The clays, sandstones and mudstones of the Hell Creek formation are considered to be terrestrial Lignite with pre- river channel and flood plain deposits. They were deposited at the edge of an inland sea that served plant fossils stretched across North America 66 million years ago, during the Cretaceous Period (Murphy, Figure 2: (Below) 2002). Many of these deposits contain fossilized skeletons, such as Triceratops, along with micro- fossil beds. Interpreting sediment data paired with fossil sites, geologists can ascertain the deposi- Marmarth North tional environment present during the cretaceous. Figure 7: Shepard Classification ternary plots for all nine separate units. Discussion The sediments collected from the study site coincide with the currently accepted interpretation of deposi- tional environments, samples collected and previous studies of the Hell Creek formation (Murphy et al.). The very fine clays (figure 7) with high organic matter suggests an environment of either low energy stand- ing water, or a floodplain. The latter theory is also supported by the cross-bedding present in the sand- stones just above and below the upper clays, interpreted as channel sands. These observations suggest dep- ositional environment to be interpreted as streams cutting across a floodplain. The silts, clays and muds would have been deposited during high water events when the stream channels overflow. During times when water exceeds channel capacity and overflows to the flood plain the sediment choked water rapidly spreads over the floodplain, loses energy and the suspended sediment drops out. This drastic loss of energy causes a build-up of sediment creating an embankment close to the channel, while also depositing finer ma- terial across the plain. As an additional line of evidence, the Triceratops excavation indicates a terrestrial depositional environment, as Triceratops were terrestrial animals. References Arens, N.C., and Allen, S.E., 2014, A florule from the base of the Hell Creek Formation in the type area of eastern Montana: Implications for vegetation and climate: Geological Society of America Special Papers Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas, p. 173–207. Johnson, K.R., Nichols, D.J., and Hartman, J.H., 2002, Hell Creek Formation: A 2001 synthesis: Special Paper Figure 1: Triceratops Excavation prior to study 361: The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An Integrat- ed continental record of the end of the Cretaceous, p.503 –510. Moore, W.L., 1976, Stratigraphy and environments of deposition of the Cretaceous Hell Creek Formation Methodology (reconnaissance) and the Paleocene Ludlow Formation (detailed), southwestern North Dakota. Report of in- Sediment and fossil samples were collected at Triceratops excavation site in the Hell Creek For- vestigations No. 56. mation near Marmarth, North Dakota (Figure 2). Sediment samples were collected from strata in Murphy, E.C., Hoganson, J.W., and Johnson, K.R., 2002, Lithostratigraphy of the Hell Creek Formation in the butte containing the Triceratops fossils. Samples were obtained by digging into the butte at North Dakota: Special Paper 361: The Hell Creek Formation and the Cretaceous-Tertiary boundary in the least 30 cm deep to ensure collection of originally horizontal sediments rather than slumped ma- northern Great Plains: An Integrated continental record of the end of the Cretaceous, p.9 –34. terial from above (Figure 3). Unique strata were identified using textural and color sediment analy- sis practices. Samples from each strata were collected using Ziploc® bags and individually coded Scannella, J.B., and Fowler, D.W., 2014, A stratigraphic survey of Triceratops localities in the Hell Creek For- according to their stratigraphic position, and stored for later examination in the fossil Preparation mation, northeastern Montana(2006 –2010): Geological Society of America Special Papers Through the End of lab at Winona State University in Winona, MN. Sediments were catalogued using the Shepard clas- the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas, p.313 –332 sification (Shepard, 1954). Additional sediment samples were set aside for possible future pollen Figure 3: (Left) Strat column for sampling strata adjacent to Triceratops excavation Shepard, F.P., 1954, Nomenclature Based on Sand-silt-clay Ratios: SEPM Journal of Sedimentary Research, analysis. v. Vol. 24, Figure 6: Stratigraphic column with labeled strata .
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