--> Tide-Dominated Facies Complex at Southern Terminus of Sunburst Sea, Cretaceous Kootenai Formation, Great Falls, Montana, by Robert K. Schwartz and Susan M. Vuke, #50045 (2007).

Datapages, Inc.Print this page

Click to view posters in PDF format.

Poster 1 (5.1 mb)               Poster 2 (1.6 mb)               Poster 3 (4.1 mb)   

Right click on poster to save.

 

PSTide-Dominated Facies Complex at Southern Terminus of Sunburst Sea, Cretaceous Kootenai Formation, Great Falls, Montana*

By

Robert K. Schwartz1 and Susan M. Vuke2

 

Search and Discovery Article #50045 (2007)

Posted June 12, 2007

 

*Adapted from poster presentation at AAPG Rocky Mountain Section Meeting, Billings, Montana, June 11-13, 2006. Because of the large file sizes represented by the posters, this adaptation does not include the layout of the original posters. The first digit of each figure numbers refers to the poster number. Text and figure captions are essentially the same as those on the posters.

 

1Department of Geology, Allegheny College, Meadville, PA, 16335 ([email protected])

2Montana Bureau of Mines and Geology, Butte, MT, 59701 ([email protected])

 

Abstract 

The Sunburst Member of the Lower Cretaceous Kootenai Formation in the Great Falls area represents the southern terminus of the earliest marine transgression into the Cretaceous foreland of western Montana. Ripple bundles, mud drapes, reactivation surfaces, rhythmically stacked two-part and neap-spring bundles of mud-sand laminations, flaser bedding, and flat-crested wave ripples document tidal dominance. Brackish to marine conditions are indicated by low ichnofossil diversity and extremely rare ammonoid fossils. A 7-14-m-thick, upward-fining sandstone lithofacies that contains channel- shaped erosion surfaces and stacked subhorizontal to low-angle inclined beds of large-scale trough and tabular cross-stratification represents sand-wave shoal development atop a tidal ravinement surface. The sand-wave lithofacies is overlain by less than 34 m of stacked, NE-SW trending, sandstone- and heterolithic-filled channels. Sedimentary structures within the sinuous channels indicate bank accretion, slumping, rhythmic tractive-slack sedimentation, bipolar flow, and minor wave influence. Toward the eastern and southern basin margin, stacked, tabular, upward-coarsening tidal bar successions and mudstone-dominated lithofacies merge laterally into thin tidal-flat and tidal-creek deposits. Tidal-flat and nonmarine coastal-plain facies regionally cap the entire assemblage. Although the Sunburst overlies the NW-SE-striking Sweetgrass Arch, fluvial paleocurrent and isopach data for the total Kootenai indicate a northward paleoslope and possible paleovalley control of Sunburst deposition along a local, elongate, NE-SW zone that transects the South Arch. Overall, the Sunburst represents southward transgressive-to-highstand systems development in a N-S-striking basin-scale embayment. The irregular coast included tide-dominated shorezone regions and estuaries along paleovalley tracts.

 

Background 

The Kootenai Formation in western Montana has traditionally been considered to be fully non-marine (e.g., Walker, 1974; Mudge and Rice, 1982; Berkhouse 1985). In particular, the quartz-rich Third Kootenai member (Sunburst Sandstone) was originally interpreted to be of fluvial and lacustrine origin (Walker, 1974). However, more recent work by Burden (1984), Hopkins (1985), Vuke (1987) and Farshori and Hopkins (1989) indicate a marine to brackish setting.

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uBackground

  uLong-term

  uPoster

uStratigraphy

uSand wave facies

  uProperties

uTidal Channel facies

  uProperties

uSubtidal sand bar/flat

  uProperties

uTidal flat / subtidal

  uProperties

uTrace fossils

uReferences

 

Purpose of the Long-term Study           

1. Provide detailed facies information for the Sunburst Sandstone and correlative strata in the Great Falls area.

2. Establish sequence stratigraphy relationships.

3. Provide a link between surface and subsurface physical properties.

 

Purpose of the Poster 

To demonstrate that:

1. At least 4 major tide-dominated facies make up the Sunburst Sandstone and equivalent strata.

-         Sand Wave (estuary shoal-and-channel complex)

-         Estuary Tidal Channel

-         Subtidal Sand Bar and Flat

-         Tidal Flat

2. The southern terminus of earliest marine transgression (Barremian) into the Cretaceous foreland was located just south of the Great Falls area and, the Sunburst represents southward transgressive-to-highstand systems development in a N-S-striking basin-scale "embayment."

 

Stratigraphy and Facies Distribution

(Figures 1-1 – 1-6) 

Figure 1-1. Correlation of nomenclature for Upper Jurassic and Lower Cretaceous rocks of west-central Montana and surrounding region. Correlation between Alberta subsurface and Great Falls, Montana, outcrops by Farshori and Hopkins (1989).

Figure 1-2. Isopach map of the Kootenai Formation and distribution of the Sunburst Sandstone (blue - subsurface, yellow - surface exposure). Isopach data from Walker, 1974. Green marks the region in which, according to Walker, occurrences of freshwater limestone are laterally equivalent to the Sunburst Member.

Figure 1-3. Study area and preliminary map of facies distribution.

Figure 1-4. Schematic cross-section of lower Kootenai facies distribution across the Sweetgrass Arch (modified from Walker, 1974).

Figure 1-5. Extent of "Sunburst Sea" into Montana.

Figure 1-6. Measured sections of facies types (profiles simulating geophysical well log)

 

Sand Wave Facies

(Figures 1-7 – 1-20) 

Figure 1-7. Upward-fining facies sequence at Fields, MT. Here the tidal body erosionally overlies estuary mudstone.

Figure 1-8. Sand wave body in disconformable contact with Kootenai fluvial sandstone, opposite Ryan Island.

Figure 1-9. Sand wave body in erosional contact with organic-rich mudstone, Ryan Island. Trough cross-stratification in the flow-transverse view appear as stacked tabular (two-dimensional) cross-stratified sets in the longitudinal view.

Figure 1-10. Diagram of outcrop (Figure 1-9), illustrating the composite nature of the lithofacies and the three-dimensional aspects of individual facies units and internal structures. The front panel of the diagram represents the back-left side of the outcrop (not shown in photo [Figure 1-9]); corresponding views are indicated by pink line.

Figure 1-11. Sand wave body in erosional contact with estuarine mudstone and flaser (tidal creek?) bedding, Ryan Island.

Figure 1-12. Sand wave facies in erosional contact with nonmarine mudstone and fluvial channel sandstone of the 2nd Kootenai member, Belt RR cut.

Figure 1-13. Channel-shaped base of sand wave body in erosional contact with estuary mudstone, south of Great Falls.

Figure 1-14. "Rusty Bed" appearance of Sunburst sandstone.

Figure 1-15. Stacked tabular sets of large-scale trough cross-stratification.

Figure 1-16. Longitudinal view of cross-stratification sets. Foreset units resting upon sloping surfaces reflect bedform migration along slopes mantling the extant composite sand wave.

Figure 1-17. Large-scale two-dimensional cross-stratification in the lower part of the facies, south side of Cochran Dam.

Figure 1-18. Reactivation surface.

Figure 1-19. Orthogonal views of inversely graded sand-avalanche tongues within two-dimensional and overlying smaller scale ripple bedding. Left: tranverse view. Right: longitudinal view.

Figure 1-20. Bipolar paleoflow evidenced by small-scale ripple bundle cross-stratification set.

 

Properties of Sand Wave Facies (Tidal Shoal Bar and Channel)  

     Overall

-         A relatively extensive, 5 to 14 m-thick, NE-SW elongate (?), upward-fining quartz sandstone body.

-         Pinches out to east and south toward basin margin; extends N and W into subsurface.

-         Disconformable lower contact above:

(1) Sunburst estuary mudstone and tidal bedding,

(2) non-marine Kk2 coastal plain facies, and

(3) fluvial lower Kootenai sandstone.

-         Overlain by tidal flat, subtidal/estuary mud, and tidal channel facies depending upon location.

 

     Internal Properties

-         A composite of southwestward-elongate bodies having a channel-shaped base and horizontal to slightly convex upper surface.

-         Vertical structural sequence: upward thinning, tabular to broadly wedge-shaped, cross-stratified beds ranging from about 2.5 m to 5 cm in thickness. Large- to medium-scale two-dimensional ("tabular") and three-dimensional (trough) cross-stratification typical.

-         Multiple internal erosion surfaces.

-         Lithic content typically high along the erosional (ravinement) base of the unit with concentrations of mudstone rip-up clasts.

-         Plesiosaur bone fragments and ammonites extremely rare.

-         Trace fossils include Ophiomorpha and Diplocraterion.

-         Other sedimentary structures:

o       Lateral ripple-bundle sequences with rare and poorly developed reactivation surfaces.

o       Rare small-scale reversed ripple foresets with larger ripple bundles.

o       Mud drapes very rare.

o       Avalanche sand-tongue structures within tabular-planar foreset beds.

o       Bundled mud-sand tidal laminations rare in between channel bodies.

o       Cross-stratification unimodal to multimodal with bipolar components in the SW-NE and NW-SE directions.

o       Stacked sets of medium- and small-scale cross-stratification with intervening erosional surfaces reflecting composite dune development as in modern tidal systems.

 Return to top.

Tidal Channel Lithofacies

(Figures 2-1 – 2-8) 

Figure 2-1. Tidal channel facies in erosional contact with underlying sand wave facies, Ryan Dam spillway. Nonmarine coastal plain and fluvial facies conformably overlie the Sunburst Formation.

Figure 2-2. Tidal channel facies in erosional contact with the underlying sand wave facies, Ryan Dam spillway.

Figure 2-3. Close-up of Figure 2-2, showing giant-scale trough cross-stratification within a channel body.

Figure 2-4. Overview of the tidal channel complex overlain by widespread tabular tidal flat (Sunburst) and maroon coastal plain facies (Kk4 member), Ryan Dam. Yellow lines mark the erosional base of major channel bodies in the exposure. Profile of section.

Figure 2-5. Close up of laterally and vertically stacked channel bodies (lower right of Figure 2-4). Oversteepened beds and compressional fold (arrow; see Figure 2-7) occur within slumped channel-margin unit at lower left.

Figure 2-6. Bioturbated bundles of neap-spring tidal-laminations within channel body.

Figure 2-7. Soft-sediment fold due to compression at the base of a channel-margin slump block.

Figure 2-8. Bioturbated heterolithic channel fill consisting of fine sand and organic-rich very fine sand.

 

Properties of Tidal Channel Facies 

     Overall

-         Exposures occur along the Missouri River gorge between Cochran Dam and Ryan Dam.

-         A complex of laterally and vertically stacked, clayey to clean quartzarenite; channel bodies up to 40 m thick and >5 km wide.

-         Erosionally overlies sand-wave facies; overlain by tidal bar to tidal flat and nonmarine Kk4 facies.

 

     Channel Body Properties

-         Upward-fining sandstone and heterolithic fill.

-         Channel-body orientations approximately NE-SW.

-         Individual channel widths: several to > 20-m; channel thicknesses: meter to 10-m scale.

-         Bedding: subhorizontal to concave and ECS-like; over-steepened beds within slump blocks.

 

     Sedimentary structures

-         Medium- to large-scale trough cross-stratification & small-scale ripple bedding.

-         Bank accretion bedding.

-         Mud drapes.

-         Wave ripples.

-         Vertically accreted spring-neap bundles of parallel lamination.

-         Slump blocks.

-         Trace fossils locally abundant; bioturbation fabric common, ranging up to 100%.

-         Paleoflow usually unimodal between SSW-SSE; rarely bimodal-bipolar with 2nd mode to north.

 

Subtidal Sand Bar/Flat Lithofacies

(Figures 2-9 – 2-17) 

Figure 2-9. Overview of Sunburst subtidal bar/flat succession near Morony Dam. A splay and estuary(?) channel facies vertically and laterally truncate (unshown at right) the bar succession at this locale.

Figure 2-10. Representative stratigraphic section of stacked subtidal bar/flat units and overlying tidal flat facies at Morony Dam site.

Figure 2-11. Close-up of three to possibly four upward-coarsening subtidal bar/flat units. The upper parts of the 1st and 3rd units are truncated by a concordant to slightly discordant erosional surface (yellow lines); unclear for the 2nd unit. Laterally, coarser sandstone of different units can become amalgamated resulting in loss of unit identity.

Figure 2-12. Upward coarsening and sandstone-bed thickening within bar/flat unit 1.

Figure 2-13. Close-up of stacked tabular upward-coarsening bar/flat units.

Figure 2-14. Truncated convex bedding (yellow arrow) in unit 3 indicating a bar-form morphology prior to erosion. This view of the outcrop is lateral to Figure 2-11. Solid yellow lines designate well defined erosion surfaces, dashed line designates a speculative erosional surface.

Figure 2-15. Paired upper tubes of U-shaped burrows on a wave-rippled bed surface.

Figure 2-16. Ripple bedding within large-scale trough sets. Localized trough sets within the subhorizontally bedded tabular units indicate localized current scour-and-fill across bar deposits.

Figure 2-17. Unidirectional small-scale ripple cross-stratification with mud drapes indicating repetitive tractive tidal current flow in one direction alternating with slack-water conditions. Curviplanar scour surfaces in between or truncating the ripple sets may have resulted from erosion in front of superimposed ripple forms and/or stronger tidal current events.

 

Properties of Subtidal Bar/Flat Facies 

     Overall 

-         At Morony Dam: An 11-15 m-thick composite of up to five, vertically stacked, generally 2-4 m thick, upward-coarsening, mud (or heterolithic)-to-sand tabular units occurs directly above the basal Kootenai (Cutbank) fluvial sandstone. At Ryan Island: A relatively thin bar sequence (~5m) occurs above the sand wave facies.

-         The facies is directly overlain by tidal flat and coastal plain facies, or, locally truncated and overlain by estuary channel deposits.

-         Subhorizontal, low-angle, and convex-to-concave bedding indicates accretion upon wide, low relief, bar forms and adjacent subhorizontal surfaces.

-         Widespread, subhorizontal-to-slightly undulatory erosional surfaces truncate and occur within the Sunburst bar units. Sand-unit stacking and intervening erosion is consistent with episodic bar growth, abandonment (sand starvation), and tidal current breaching as occurs in modern estuary settings.

-         Other sedimentary structures

o       Localized low-relief, channel-shaped scours (m-scale width) with symmetrical fill.

o       Scattered wide (~5 m), low-amplitude (0.5-1.0 m) sets of trough cross-stratification.

o       Flaser bedding.

o       Rhythmic amagamated sets of small-scale ripple cross-stratification and parallel lamination.

o       Ripple cross-stratification usually unimodal to rarely bimodal-bipolar.

o       Bioturbation fabric common; trace fossils present but ichnospecies diversity low.

 Return to top.

Tidal Flat and Subtidal Facies

(Figures 3-1 – 3-ll) 

Figure 3-1. Upward fining and coarsening tidal-flat and subtidal successions above the sand wave facies at Fields, MT. "Mud" and "sd" above designate mudstone and sandstone-dominated zones at the end points of trends. Stratigraphic section shown in Figure 1-7.

Figure 3-2. Rhythmic mud and bioturbated sandstone tidal laminations.

Figure 3-3. Upward coarsening ("regressional") tidal flat-to-subtidal succession above the tidal channel facies at Ryan Dam. The maroon mudstone unit (M) represents a mud-flat setting whereas the overlying widespread tabular sandstone (see Figure 3-4) represents a higher energy subtidal setting.

Figure 3-4. Bioturbated trough cross-stratified subtidal sandstone. Wave ripple crosslamination and lateral sequences of small-scale ripple bundles occur locally.

Figure 3-5. Left-to-right: A. Upward coarsening succession of tidal bedding. B. Close-up of Figure 3-5A, illustrating bioturbated sandstone alternating with finer grained zones within which numerous alternating tractive flow and slack conditions are recorded (i.e., daily tidal flux). C. Close up of finer grained zone in Figure 3-5A, illustrating daily scale of tidal flux. Alternating tractive flow and slack conditions resulted in mm-scale mud drapes in between ripple foresets and subhorizontal sand laminations. The yellow line indicates a spring-to-neap sequence.

Figure 3-6. Two temporal scales of tidal sedimentation: A - The spring-to-neap ("biweekly") tidal cycle is reflected by individual upward-fining bundles of sand and mud laminations. B - Longer term cycle (e.g., yearly) is reflected by overall upward fining and coarsening of tidal bundles.

Figure 3-7. Close-up of bundled tidal laminations and biogenic structures.

Figure 3-8. Wave-ripple bedforms and corresponding internal structures from within tidal flat facies.

Figure 3-9. Flaser bedding containing symmetric and asymmetric (current-modified) wave-ripple cross-lamination.

Figure 3-10. Flaser bedding containing undulatory sandstone laminations and asymmetric wave-ripple cross-lamination.

Figure 3-11. Flat-crested wave ripples caused by emergence in intertidal setting.

 

Properties of Tidal Flat / Subtidal Facies 

     Overall

-         The facies occurs at the top of the Sunburst interval with a thickness range of ~1- 12 m.

-         The upper contact is transitional into oxidized mudstone and lithic sandstone of the nonmarine Kk4.

-         Sandstone- and mudstone-dominated units occur; each type of unit consists of upward-fining and upward-coarsening successions.

-         The composite vertical succession ranges from being a single upward-fining unit to multiple, upward-fining and coarsening units that culminate with fining into the Kk4.

-         Widespread, generally tabular, rhythmic beds and the presence of tide- and wave-associated structures indicate deposition in tidal and subtidal flat settings.

-         Vertical increases in mudstone, degree of bioturbation, organic debris, and oxidation reflect landward shallowing and energy decrease from intertidal mixed to supratidal mud-flat settings.

-         Thicker, coarser, amalgamated sandstone beds with a relative abundance of current ripple forms, medium-scale trough cross-stratification, and undulating or channel-like scour surfaces are consistent with modern subtidal sand-flat settings where tidal-current and wave-energy increases.

 

     Other sedimentary structures

-         Flaser bedding and wavy bedding.

-         Bimodal cross-stratification.

-         Lingoid/lunate- and flat-crested wave-ripple bedforms.

-         Mud drapes.

-         Bundles of spring-neap parallel laminations.

-         Shallow erosional channels (gullies) and furrows (gutters) filled with sand and mud (produced on tidal flats during emergence and runoff).

-         Abundant bioturbation, commonly overprinting physical structures. Various ichnogenera including Planolites, Diplocraterion, and lingulid and horseshoe crab trace fossils (an estuarine tidal flat association).

 

Trace Fossils

(Figures 3-12 – 3-20) 

The following trace fossils, although mostly unidentified, serve to further establish a marine to brackish water setting.

 

Sand wave 

 

Tidal Channel (Figure 3-15)

 

Tidal Flat 

 

Tidal Channel Subtidal Bar/Flat 

 

References Cited 

Berkhouse, G.A., 1985. Sedimentology and diagenesis of the Lower Cretaceous Kootenai Formation in the Sun River Canyon area, northwest Montana: M.S. thesis, Indiana University, Bloomington, IN, p. 1-26.

Burden, E.T., 1984. Terrestrial palynomorph biostratigraphy of the lower part of the Mannville Group (Lower Cretaceous), Alberta and Montana, in Stott, D.F., and Glass, D.J., eds., The Mesozoic of Middle North America, Canadian Society of Petroleum Geologists Memoir 9, p. 249-270.

Farshori, M.Z., and Hopkins, J.C., 1989. Sedimentology and petroleum geology of fluvial and shoreline deposits of the Lower Cretaceous Sunburst Sandstone Member, Manville Group, southern Alberta: Bulletin of Canadian Petroleum Geology, v. 37, p. 371-388.

Hopkins, J.C., 1985. Channel-fill deposits formed by aggradation in deeply scoured, superimposed distributaries of the Lower Kootenai Formation (Cretaceous): Journal of Sedimentary Petrology, v. 55, p. 42-52.

Mudge, M.R., and Rice, D.D., 1982, Lower Cretaceous Mount Pablo Formation, northwest Montana: U.S. Geological Survey Bulletin, v. 1502 D, p. 1-19.

Vuke, 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: Tobacco 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.

 

Return to top.