Statza, Takatch, Schwartz_2014_Architecture Tide-Dom Shoreface (1)
1
ARCHITECTURE OF A TIDE-DOMINATED SHOREFACE SYSTEM IN THE LOWER CRETACEOUS KOOTENAI FORMATION, WEST-CENTRAL MONTANA STATZA, Mary, TAKACH, Marie, and SCHWARTZ, Robert K., Department of Geology, Allegheny College,Meadville, PA 16335 ABSTRACT Integrated long-distance, high-resolution photography and detailed outcrop analysis were used to document the architecture of a tide-dominated, low wave-energy, shoreface lithosome along the Missouri River Gorge near Great Falls, Montana. The lithosome (~18 m thick) consists of five vertically stacked, widespread, tabular units and scattered channel bodies. Internally, the tabular units (~2-4 m thick) coarsen upwards and the architecture of a representative unit includes a thin basal mudstone or heterolithic interval changing upward to a thicker bedded, amalgamated, fine- to rarely medium-grained sand- stone. However, the full vertical succession of five units are stacked in a net upward-coarsening succession in which the basal unit is mudstone dominated and successive units contain less mud. Sand fractions are quartzose, very well rounded, and very well sorted. Rhythmic bedding is characteristic and ranges from horizontal to convex on the tidal bar scale (dm wavelength). Scattered medium-scale trough cross-stratification and thin channel-shaped lenses (~1-15 m wide) indicate episodic current activity. Widespread erosional surfaces separate the units, as well as occur internally, causing localized discordances between units or the amalgamation of sandstone-dominated units. The channel bodies are relatively large (50-100's m wide, 5-10 m thick), contain heterolithic fill similar in composition to the tabular units, and transect one or more of the tabular units, documenting the coexistence of cross-shore channels. Diagnostic structures of tidal origin include mud couplets, neap-spring lamination sets, flaser- to-lenticular bedding, amalgamated ripple beds separated by reactivation surfaces, rhythmi- cally alternating ripple beds and parallel-laminations, mm-scale clay drapes, and lateral sets of small-scale ripple bundles. Small-scale wave-ripples (~ 4 cm spacing) are present on some sur- faces and hummocky cross-stratification is exceptionally rare. Trace fossils include Arenicolites, Ophiomorpha (very rare), Macaronichnus, Planolites, Piscichnus, horseshoe crab-like resting traces, and bivalve crawling traces indicating marine to slightly brackish conditions. Bioturba- tion index typically ranges between 3 and 6. A Glossifungites ichnofacies caps the succession. BACKGROUND 0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5 md st vfg fg mg cg vcg MASSIVE SANDSTONE BEDDED SANDSTONE CROSS-BEDDED SANDSTONE RIPPLE-BEDDED SANDSTONE MAROON MUDSTONE GRAY MUDSTONE BIPOLAR FORESETS TROUGH CROSS-BEDDING FLASER BEDDING LEGEND (1) (2-3) (4-5) (6) LOW BIOTURBATION SOME BIOTURBATION MODERATE BIOTURBATION HIGH BIOTURBATION (4-5) (1) (2-3) 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 (2-3) (1) (2-3) (4-5) (6) (2-3) (6) ACKNOWLEDGEMENTS This project would not have been possible without financial assistance from the Christine Scott Nelson Faculty Support Fund. Special thanks must be given to Susan Vuke for her selfless support, endless supply of encouragements and camping supplies (especially bear-spray), and for sheltering us Cowgirls and (old) Indians from the volatile Montana weather. An even special-er thanks to Bob Schwartz for his infinite support, encouragement, and supply of stories and falsehoods that kept us infinitely entertained/disgruntled. Sugar and FooFoo love ya, Old Man. CONCLUSIONS REFERENCES UNIT1UNIT2UNIT3UNIT4UNIT5Thickness (m) Three weeks of field research included outcrop analysis and Gigapan photo technology. The study area is located in western Montana, northeast of the city of Great Falls. The outcrop is exposed along the eastern bank of the Missouri River flowing north out of Morony Dam. Figure illustrating theorized southern extent of Cretaceous Barremian transgression into Montana. Arrows indicate tidal currents. Morony Dam outcrop represented by red circle. (Schwartz, 2007) Correlative stratigraphic column showing location of Sunburst Formation, primary constituent of tidal-shoreface outcrop along Missouri River. (Schwartz, 2007) Overview of basal, upward-coarsening unit 1 (~2.2m). Tabular, mud-dominant beds transition upward into sand-dominant, wavy bedding. Mudstone grades from maroon in color, due to reworking of underlying Kk2, to gray in upper part of the unit. An erosional scour surface separates unit 1 from overlying unit 2. 1.5m staff for scale. Beds transition from tabular to increasingly wavy-bedding up-unit. Scale is 15cm. Close up of maroon tidal bundles. Mudstone layers deposited during periods of reduced tidal current energy, while fine-grained sandstone beds deposited during periods of higher energy. Scale is 5cm. 3 cm Close up of sandstone beds displaying small-scale foresets, demonstrating kinematics of tidal current event (see arrow) Upper flow regime parallel laminations are followed by lower flow regime ripple bedding and muddy sand suspension fall out. Scale is 3cm. Overview of sandstone dominant unit 2 (~3.3m), consisting of several erosionally-based beds of ripple- to-crossbedded sandstone, capped by a muddy layer. Overall upward coarsening. 1.5m staff for scale. UNIT1UNIT2Mud-filled scour surface between units 1 and 2. Overall, bed set contacts within unit 2 are sharp, and are either amalgamated or separated by thin mudstone. A B A) Stacked small-scale ripple-bedding with bidirectional foresets, indicating reversing tidal currents. Relict bedding due to moderate bioturbation. Scale is 15cm. B) Close up of bedding with opposite foreset directions. A B C D Flaser bedding. Small-scale troughs are mantled by mm-scale mud-drapes. Scale is 15cm. Mottled sandstone fabric due to bioturbation. A) Biogenically deformed ripple-bedding. B) Relict stacked-ripple bedding. C) Relict small-scale troughs. D) Heavily ripple-bedded sandstone due to bioturbation. Horizontal and vertical trace fossils on sole of sandstone bed. UNIT 2 UNIT 3 2m Overview of sandstone dominant unit 3 (~3.5m), coarsening upward from interbedded mud and sandstone, into fine grained, amalgamated,wavy bedded sandstone beds. Well-defined, medium-scale foresets documenting reversing tidal currents. Scale is 15cm. A B A) Burrowed, ripple-bedded, fine-grained sandstone beds. B) Enlarged view of sandstone beds, showing small-scale foresets. A B C 15 cm UNIT 2 Schwartz, R. K., Vuke, S. M., 2007, Tide-Dominated Facies Complex at Southern Terminus of Sunburst Sea, Cretaceous Kootenai Formation, Great Falls, Montana: http://www.searchanddiscovery.com/documents/2007/07036schwartz (accessed July 2014). Overview of upward-coarsening unit 5 (~4.5m), composed of basal maroon mudstone containing fine-grained lenses of sandstone, transitioning up- unit into amalgamated sandstone. Some relict ripple-bedding, but sandstone beds are typically massive due to bioturbation. The unit is capped by highly- deformed, oxidized sandstone, most likely containing Glossifungites ichnofacies, indicating a firm ground setting. Black triangle indicates textural trend. 1.5m staff for scale. Overview of unit 4 (~4.3m). Unit coarsens upward from a base of alternating very-fine-grained sandstone and mudstone, into thicker, bioturbated sandstone beds. The unit contains a capping reddish-brown, oxidized bed of highly bioturbated sandstone, most likely containing a Glossifungites ichnofacies assemblage, indicating a firm ground setting. 10 cm 10 cm Interbedded sandstone and mudstone at base of unit 4. Scale is 20 cm. Localized, isolated lense of organic-rich mudstone, preserved by rapid deposition and deformed by compaction and/or dewatering. A A B B A) Massive sandstone beds. Scale is 15cm. B) Close up of sandstone bed showing biogenically caused absence of sedimentary structures. A) Tan, fine-grained sandstone with bioturbated, relict, subhorizontal laminations. Scale is 5cm. B) Close up of bioturbated laminations in A. 5 cm B A A) Possible load casts on underside of heavily bioturbated, oxidized, reddish sandstone bed. Scale is 50cm. B) Close up of load casts 50 cm sandstone mudstone A B C D A) Float block from highly oxidized, brown capping layer, showing heavy bioturbation and burrowing. B) Float block from red, oxidized sandstone bed. Moderate bioturbation and burrows. C) Float block. Bioturbation and burrowing. D) Float block. Bioturbation and burrowing. Fine to medium grained, oxidized, brown capping sandstone bed. Bed most likely contains Glossifungites ichnofacies, indicating firm ground settings during and after depositon. A) Large, ripple-bedded sandstone beds with amalgamated surfaces. Human scale is 1.57m. B) Side view of block in A, showing geometry of erosional surfaces. 1.5m staff for scale. C) Massive, highly bioturbated capping bed of unit 3. Location shown by yellow arrow in B. Wavy bedding, indicative of fluctuating tidal energy levels. Scale is 15cm. A B A) Flaser bedding. Small-scale troughs are mantled by mm-scale mud-drapes. Scale is 15cm. B) Close up of flaser bedding. 15 cm Paired- burrows. Arenicolites. Small, unlined, rarely branched Planolites. The five upward coarsening units represent shoreface tidal parasequences. The typical vertical succession of a shoreface parasequence consists of a mudstone dominant base, coarsening upwards into thicker, sometimes amalgamated ripple- bedded sandstone beds. The maroon mudstone within unit 1 is due to ravinement and reworking of the underlying maroon estuarine mudstone facies of Kk2 (Kootenai Formation). Similarly, reworking of the adjacent coastal plain mud, such as occurs in the overlying Kk4 unit (red mudstone coastal plain facies) could have contributed to the abundance of maroon mudstone within the capping Sunburst unit at Morony Dam (unit 5). Units 1 through 3 show an upwards net coarsening, where mudstone is replaced by sandstone as the dominant constituent. Following this net coarsening is a net fining trend from units 3 through 5, where mudstone becomes more prevalent with each successive unit, before overlapping of the mudstone-dominant Kk4 coastal plain system. The large quantity of tidal features, such as rhythmic bedding, tidal laminations, flaser-to-wavy bedding, amalgamated ripple-beds with erosional surfaces, and degree of bioturbation indicate the depositional environment was tidal dominated. An absence of features associated with wave-dominated shorefaces, such as wave-ripple cross-lamination, hummocky cross-stratificationand surf-zone related trough cross-stratification further supports this hypothesis. The limited diversity of the abundant trace fossils found within the units indicates a shallow water, brackish-marine setting. 5 cm Stratigraphic column detailing grain size, thickness (m), and sedimentary structures of five units studied at Morony Dam. UNIT1Close up of rhythmic mud-sand couplets, indicative of alternating suspension fallout-tractive flow conditions. UNIT2scour surface scour surface scour surface scour surface UNIT3UNIT4UNIT5Gigapan image of tidal shoreface succession in the Sunburst Member near Morony Dam.
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Transcript of Statza, Takatch, Schwartz_2014_Architecture Tide-Dom Shoreface (1)
ARCHITECTURE OF A TIDE-DOMINATED SHOREFACE SYSTEM IN THE LOWER CRETACEOUS KOOTENAI FORMATION, WEST-CENTRAL MONTANASTATZA, Mary, TAKACH, Marie, and SCHWARTZ, Robert K., Department of Geology, Allegheny College,Meadville, PA 16335
ABSTRACTIntegrated long-distance, high-resolution photography and detailed outcrop analysis were used to document the architecture of a tide-dominated, low wave-energy, shoreface lithosome along the Missouri River Gorge near Great Falls, Montana.
The lithosome (~18 m thick) consists of �ve vertically stacked, widespread, tabular units and scattered channel bodies. Internally, the tabular units (~2-4 m thick) coarsen upwards and the architecture of a representative unit includes a thin basal mudstone or heterolithic interval changing upward to a thicker bedded, amalgamated, �ne- to rarely medium-grained sand-stone. However, the full vertical succession of �ve units are stacked in a net upward-coarsening succession in which the basal unit is mudstone dominated and successive units contain less mud. Sand fractions are quartzose, very well rounded, and very well sorted. Rhythmic bedding is characteristic and ranges from horizontal to convex on the tidal bar scale (dm wavelength). Scattered medium-scale trough cross-strati�cation and thin channel-shaped lenses (~1-15 m wide) indicate episodic current activity. Widespread erosional surfaces separate the units, as well as occur internally, causing localized discordances between units or the amalgamation of sandstone-dominated units. The channel bodies are relatively large (50-100's m wide, 5-10 m thick), contain heterolithic �ll similar in composition to the tabular units, and transect one or more of the tabular units, documenting the coexistence of cross-shore channels.
Diagnostic structures of tidal origin include mud couplets, neap-spring lamination sets, �aser-to-lenticular bedding, amalgamated ripple beds separated by reactivation surfaces, rhythmi-cally alternating ripple beds and parallel-laminations, mm-scale clay drapes, and lateral sets of small-scale ripple bundles. Small-scale wave-ripples (~ 4 cm spacing) are present on some sur-faces and hummocky cross-strati�cation is exceptionally rare. Trace fossils include Arenicolites, Ophiomorpha (very rare), Macaronichnus, Planolites, Piscichnus, horseshoe crab-like resting traces, and bivalve crawling traces indicating marine to slightly brackish conditions. Bioturba-tion index typically ranges between 3 and 6. A Glossifungites ichnofacies caps the succession.
BACKGROUND
0
.5
1
1.5
2
2.5
3
3.5
4
4.5
5
md st vfg fg mg cg vcg
MASSIVE SANDSTONE
BEDDED SANDSTONE
CROSS-BEDDED SANDSTONE
RIPPLE-BEDDED SANDSTONE
MAROONMUDSTONE
GRAYMUDSTONE
BIPOLARFORESETS
TROUGHCROSS-BEDDING
FLASERBEDDING
LEGEND
(1)
(2-3)
(4-5)
(6)
LOW BIOTURBATION
SOME BIOTURBATION
MODERATE BIOTURBATION
HIGH BIOTURBATION
(4-5)
(1)
(2-3)
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
13
13.5
14
14.5
15
15.5
16
16.5
17
17.5
18
(2-3)
(1)
(2-3)
(4-5)
(6)
(2-3)
(6)
ACKNOWLEDGEMENTSThis project would not have been possible without �nancial assistance from the Christine Scott Nelson Faculty Support Fund.
Special thanks must be given to Susan Vuke for her sel�ess support, endless supply of encouragements and camping supplies (especially bear-spray), and for sheltering usCowgirls and (old) Indians from the volatile Montana weather.
An even special-er thanks to Bob Schwartz for his in�nite support, encouragement, and supply of stories and falsehoods that kept us in�nitely entertained/disgruntled. Sugar and FooFoo love ya, Old Man.
CONCLUSIONS
REFERENCES
UNIT
1
UNIT
2
UNIT
3
UNIT
4
UNIT
5
Thic
knes
s (m
)
Three weeks of �eld research included outcrop analysisand Gigapan photo technology.
The study area is located in western Montana, northeast of the city of Great Falls.The outcrop is exposed along the eastern bank of the Missouri River �owing northout of Morony Dam.
Figure illustrating theorized southern extent of Cretaceous Barremian transgression into Montana. Arrows indicate tidal currents. Morony Dam outcrop represented by red circle. (Schwartz, 2007)
Correlative stratigraphic column showing location of Sunburst Formation, primary constituent of tidal-shoreface outcrop along Missouri River. (Schwartz, 2007)
Overview of basal, upward-coarsening unit 1 (~2.2m). Tabular, mud-dominant beds transition upward into sand-dominant, wavy bedding. Mudstone grades from maroon in color, due to reworking of underlying Kk2, to gray in upper part of the unit. An erosional scour surface separates unit 1 from overlying unit 2. 1.5m sta� for scale.
Beds transition from tabular to increasingly wavy-bedding up-unit. Scale is 15cm.
Close up of maroon tidal bundles. Mudstone layers deposited during periods of reduced tidal current energy, while �ne-grained sandstone beds deposited during periods of higher energy. Scale is 5cm.
3 cmClose up of sandstone beds displaying small-scale foresets, demonstrating kinematics of tidal current event (see arrow) Upper �ow regime parallel laminations are followed by lower �ow regime ripple bedding and muddy sand suspension fall out. Scale is 3cm.
Overview of sandstone dominant unit 2 (~3.3m), consisting of several erosionally-based beds of ripple-to-crossbedded sandstone, capped by a muddy layer. Overall upward coarsening. 1.5m sta� for scale.
UNIT
1
UNIT
2
Mud-�lled scour surface between units 1 and 2. Overall, bed set contacts within unit 2 are sharp, and are either amalgamated or separated by thin mudstone.
A
B
A) Stacked small-scale ripple-bedding with bidirectional foresets, indicating reversing tidal currents. Relict bedding due to moderate bioturbation. Scale is 15cm. B) Close up of bedding with opposite foreset directions.
A B
C DFlaser bedding. Small-scale troughs are mantled by mm-scale mud-drapes.Scale is 15cm.
Mottled sandstone fabric due to bioturbation. A) Biogenically deformed ripple-bedding. B) Relict stacked-ripple bedding. C) Relict small-scale troughs. D) Heavily ripple-bedded sandstone due to bioturbation.
Horizontal and vertical trace fossils on sole of sandstone bed.
UNIT 2
UNIT 3
2m
Overview of sandstone dominant unit 3 (~3.5m), coarsening upward from interbedded mud and sandstone, into �ne grained, amalgamated,wavy bedded sandstone beds.
Well-de�ned, medium-scale foresets documenting reversing tidal currents.Scale is 15cm.
A
BA) Burrowed, ripple-bedded, �ne-grained sandstone beds. B) Enlarged view of sandstone beds, showing small-scale foresets.
A
B
C
15 cm
UNIT 2
Schwartz, R. K., Vuke, S. M., 2007, Tide-Dominated Facies Complex at Southern Terminus of Sunburst Sea, Cretaceous Kootenai Formation, Great Falls, Montana: http://www.searchanddiscovery.com/documents/2007/07036schwartz (accessed July 2014).
Overview of upward-coarsening unit 5 (~4.5m), composed of basal maroon mudstone containing �ne-grained lenses of sandstone, transitioning up-unit into amalgamated sandstone. Some relict ripple-bedding, but sandstone beds are typically massive due to bioturbation. The unit is capped by highly-deformed, oxidized sandstone, most likely containing Glossifungites ichnofacies, indicating a �rm ground setting. Black triangle indicates textural trend. 1.5m sta� for scale.
Overview of unit 4 (~4.3m). Unit coarsens upward from a base of alternating very-�ne-grained sandstone and mudstone, into thicker,bioturbated sandstone beds. The unit contains a capping reddish-brown, oxidized bed of highly bioturbated sandstone, most likely containing a Glossifungites ichnofacies assemblage, indicating a �rm ground setting.
10 cm
10 cm
Interbedded sandstone and mudstone at base of unit 4. Scale is 20 cm.
Localized, isolated lense of organic-rich mudstone, preserved by rapid deposition and deformed by compaction and/or dewatering.
A
A
B
BA) Massive sandstone beds. Scale is 15cm. B) Close up of sandstone bed showing biogenically caused absence of sedimentary structures.
A) Tan, �ne-grained sandstone with bioturbated, relict, subhorizontal laminations. Scale is 5cm. B) Close up of bioturbated laminations in A.
5 cm B
AA) Possible load casts on underside of heavily bioturbated, oxidized, reddishsandstone bed. Scale is 50cm. B) Close up of load casts
50 cm
sandstone
mudstone
A B
C DA) Float block from highly oxidized, brown capping layer, showing heavy bioturbation and burrowing. B) Float block from red, oxidized sandstone bed. Moderate bioturbation and burrows. C) Float block. Bioturbation and burrowing. D) Float block. Bioturbation and burrowing.
Fine to medium grained, oxidized, brown capping sandstone bed. Bed most likely contains Glossifungites ichnofacies, indicating �rm ground settings during and after depositon.
A) Large, ripple-bedded sandstone beds with amalgamated surfaces. Human scale is 1.57m. B) Side view of block in A, showing geometry of erosional surfaces. 1.5m sta� for scale. C) Massive, highly bioturbated capping bed of unit 3. Location shown by yellow arrow in B. Wavy bedding, indicative of �uctuating tidal energy levels. Scale is 15cm.
A
B
A) Flaser bedding. Small-scale troughs are mantled by mm-scale mud-drapes.Scale is 15cm. B) Close up of �aser bedding.
15 cm
Paired- burrows. Arenicolites.
Small, unlined, rarely branched Planolites.
The �ve upward coarsening units represent shoreface tidal parasequences.The typical vertical succession of a shoreface parasequence consists of a mudstone dominant base, coarsening upwards into thicker, sometimes amalgamated ripple-bedded sandstone beds. The maroon mudstone within unit 1 is due to ravinement and reworking of the underlying maroon estuarine mudstone facies of Kk2 (Kootenai Formation). Similarly, reworking of the adjacent coastal plain mud, such as occurs in the overlying Kk4 unit (red mudstone coastal plain facies) could have contributed to the abundance of maroonmudstone within the capping Sunburst unit at Morony Dam (unit 5).
Units 1 through 3 show an upwards net coarsening, where mudstone is replacedby sandstone as the dominant constituent. Following this net coarsening is a net �ningtrend from units 3 through 5, where mudstone becomes more prevalent with each successive unit, before overlapping of the mudstone-dominant Kk4 coastal plain system.
The large quantity of tidal features, such as rhythmic bedding, tidal laminations, �aser-to-wavy bedding, amalgamated ripple-beds with erosional surfaces, and degree of bioturbation indicate the depositional environment was tidal dominated. An absence of features associated with wave-dominated shorefaces, such as wave-ripple cross-lamination, hummocky cross-strati�cationand surf-zone related trough cross-strati�cation further supports this hypothesis.
The limited diversity of the abundant trace fossils found within the units indicates a shallow water, brackish-marine setting.
5 cm
Stratigraphic column detailing grain size, thickness (m), and sedimentary structures of �ve units studied at Morony Dam.
UNIT
1Close up of rhythmic mud-sand couplets, indicative of alternating suspension fallout-tractive �ow conditions.
UNIT
2
scour surface scour surface scour surface scour surface
UNIT
3
UNIT
4
UNIT
5
Gigapan image of tidal shoreface succession in the Sunburst Member near Morony Dam.
