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FACIES ANALYSIS, ARCHITECTURE, AND DEPOSITIONAL
MODEL OF THE TIDALLY-INFLUENCED NATURITA
FORMATION (DAKOTA SANDSTONE)
Stephen Phillips, John Howell, Adrian Hartley –University of Aberdeen
▪Transgressive systems are less well-studied than their regressive
counterparts
▪Particularly tidal ones as a part of a basin-scale transgression
▪More focus is needed on these systems
▪The Naturita Formation has been interpreted as a fluvially dominated incised valley-
fill (Kirschbaum and Schenk, 2010)
▪We show that it is actually dominated by tidal deposits
▪What are the facies, facies associations, distribution, and architecture of
tidally-influenced deposits in the Naturita Formation of the San Rafael
Swell?
▪How is basin-scale transgression manifested in a foreland basin?
▪One piece of a larger puzzle:
▪Naturita Formation
▪Cedar Mountain Foredeep –GSA 2019
▪Cedar Mountain Backbulge –GSA 2019
Motivation
Western Interior Seaway –
Cenomanian Paleogeography
Modified From: Kirschbaum and Schenk, 2010
Field Area –San Rafael Swell, Utah, USA
▪Overlain by the Marine Tununk Shale Member of the
Mancos Shale
▪Underlain by the Fluvial Cedar Mountain Formation
▪Trough cross-stratification with multiple reactivation
surfaces, possibly some tidal bundling
▪Wavy to laminated heterolithics between and within
units
▪Ripples oriented up the slipface of some cross-stratified
beds up to 1.5m above channel base (i.e. Not just flow
separation)
▪Rare sigmoidal cross-stratification; always at the top of
the unit when present
▪Basal surface is scoured with common mud rip up clasts
that match Cedar Mountain mudstone in appearance
Reversing Current Indicators
Trough Cross-Stratification
Sigmoidal Cross-Stratification
Facies Associations –Tidally-Influenced Fluvial
▪Broadly sigmoidal in cross-sectional
view
▪Undulatory to wavy on 10’s of
meters scale
▪Trough cross-stratification
▪Sigmoidal cross-stratification
▪Ripple cross-stratification, all
orientations
▪Wavy to laminated heterolithics
▪Mud and carbonaceous drapes are
common
▪Ripples mantling the bar surface
and moving in the subordinate
direction are also common
Oblique View
Interbedded Heterolithics
Rippled Bars
Sigmoidal Cross-Stratification
~4m
HMB - Caineville Reef
SRS - Hadden Holes
Facies Associations –Tidal Channel: Sigmoidal Barform
▪Trough cross-stratification
▪Tabular cross-stratification
▪Mud and carbonaceous drapes are
common
▪Wavy to laminated heterolithics
Draped Foresets
Weathered Mud Drapes
Reversing Current
Facies Associations –Tidal Channel: Compound Barform
▪Inclined heterolithic stratification
▪Fining upward sequence
▪Teichichnus and planolites
▪Rippled and bioturbated sandstone
▪Foresets mantled by carbonaceous material and mud
▪Mire or peat swamp facies association overlies in some
locations, in others Mancos Shale directly overlies with
or without a transgressive ravinement unit
▪Generally overlies the tidal channel facies association
Facies Associations –Tidal Point Bar
▪Confined to two outcrop areas:
▪Henry Mountains Basin
▪Mussentuchit Wash
▪Upper shoreface trough cross-stratified sandstone
▪Lower shoreface hummocky cross-stratified sandstone
▪Fossiliferous sandstone
▪Shell material is always disarticulated and fragmented
▪Bioturbated sandstone
▪Sandstones are commonly both fossiliferous and bioturbated
▪Ophiomorpha and diplocraterion
Facies Associations –Marine Shoreface
Transgressive Ravinement
▪Very thin bedded sandstone and siltstone
▪Sedimentary structures commonly destroyed by bioturbation
▪Ripples sometimes preserved
▪Woody material present
▪Flat to slightly inclined or undulate bedding
Mantling Underlying Barform Sand Flat Mud Flat
Burrows
Facies Associations –Mud and Sand Flat –Coastal Plain
Rooting in Sandstone
Coal and Carbonaceous Mudstone
▪Bedded coal and carbonaceous mudstone
▪Rooting
▪Very thin to thin beds of bioturbated sandstone
▪Minor rippled and cross-stratified sandstone
▪Laterally adjacent to, or overlies, tidal channel facies association
Increasing
Marine
Influence
Architecture –Henry Mountains Basin
Viewed in LIME, Buckley et al., 2019
Depositional Model
Dalrymple et al., 1992; Dalrymple and Choi, 2007
Architecture –Western San Rafael Swell
1) Basal deposits are fluvial channels that have a tidal influence.
2) As transgression continues, these basal fluvial deposits are overlain by subtidal bars, point bars,
and mud/sand flats.
3) Continued transgression coupled with wave ravinement produces a regional transgressive lag.
▪Preservation of estuarine deposits in topographically low areas
▪Erosion dominates in topographically high areas.
4) After the entire field area has been transgressed.
Architecture –Western San Rafael Swell
▪Facies belts migrate south and west through time
▪San Rafael Swell outcrop is shown as crosshatched
area
▪The transition from foredeep to forebulge is roughly
equivalent to the eastern flank of the San Rafael Swell
▪May have contributed to the location of
preserved estuarine deposits
▪Complete removal of Naturita Formation
deposits on the eastern flank
▪Embayment in this part of the seaway was common
▪Utah Bight
▪Tidal deposits focused here
▪Van Cappelle et al., 2018
Cobban et al. (1994)
Conclusions
▪The Naturita Formation of the northern Henry Mountains Basin and San
Rafael Swell is primarily of tidal-estuarine and marine origin
▪It can be subdivided based on facies associations that are arranged in a
predictable fashion top to base:
▪Transgressive ravinement
▪Shoreface
▪Tidal point bar, mud/sand flats, and mire/peat swamp
▪Tidal channel
▪Tidally influenced fluvial
▪Topography played a role in the deposition and preservation of Naturita
Formation deposits
▪The Naturita Formation is an ideal case study for thin transgressive
deposits, especially when located in areas that have experienced large
scale flooding
References
▪Buckley, S.J., Ringdal, K., Naumann, N., Dolva, B., Kurz, T.H., Howell, J.A., Dewez, T.J.B., 2019,
LIME: Software for 3-D visualization, interpretation, and communication of virtual geoscience
models, Geosphere, 15(1).
▪Cobban, W.A., Merewether, E.A., Fouch, T.D., and Obradovich, J.D., 1994, Some Cretaceous
shorelines in the western interior of the United States, in Caputo, M.V., Peterson, J.A., and Franczyk,
K.J., Mesozoic systems of the Rocky Mountain region, USA, SEPM, p. 393-414.
▪Dalrymple, R.W., Zaitlin, B.A., and Boyd, R., 1992, Estuarine facies models: Conceptual basis
and stratigraphic implications: Journal of Sedimentary Petrology, v. 62, no. 6, p. 1130-1146.
▪Dalrymple, R.W., and Choi, K., 2007, Morphologic and facies trends through the fluvial-marine
transition in tide-dominated depositional systems: A schematic framework for environmental
and sequence-stratigraphic interpretation: Earth-Science Reviews, v. 81, no. 3-4, p. 135-174.
▪Kirschbaum, M.A., and Schenk, C.J., 2010, Sedimentology and reservoir heterogeneity of a valley-fill
deposit—a field guide to the Dakota Sandstone of the San Rafael Swell, Utah: U.S. Geological Survey
Scientific Investigations Report 2010–5222, 36 p., 1 plate.
▪Van Cappelle, M., Hampson, G.J., Johnson, H.D., 2018, Spatial and temporal evolution of
coastal depositional systems and regional depositional process regimes: Campanian Western
Interior Seaway, U.S.A., Journal of Sedimentary Research, v. 88, p. 873-897.
▪Virtual Outcrop viewed in LIME
▪Field work funded by SAFARI