RECONSTRUCTING PALEOCURRENT DIRECTION IN THE … · 2014-11-13 · ogy, strike, dip, and...
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● Asymmetric ripple marks exposed in Erie County, PA show a mean flow direction of N68°W. ● Flow direction fluctuates between S83°W – N42°W through time. ● Grain size for ripple marks range 0.2–0.4 mm with clays between particles. ● The majority of ripple marks are asymmetrical and range 0.2–4.5 cm tall (Table 1), indicating weak currents for their formation. ● No fossil fauna are found in deposits containing ripple marks but are found above and below these strata along with increased grain size. ● Wavelength between ripple crests range 6–31 cm (Table 1). ● Ripple flow direction’s match at the same elevations between seperate creeks, indicating flat lying bedrock of the Girard and Chadakoin formations. ● Due to a predominantly NW flow direction, it is postulated ripple marks trending northwest are likely formed during low-density basin edge turbidity currents. 140-8 RECONSTRUCTING PALEOCURRENT DIRECTION IN THE CHADAKOIN AND GIRARD FORMATIONS IN NORTHWESTERN PENNSYLVANIA MCCOY, Curtis*, Nicholas Kelly, and Lyman Persico Mercyhurst University, 501 East 38th St, Erie, PA 16546 *[email protected] Abstract Methods Ripple marks were located in shale deposits incised and exposed by Twenty Mile, Six Mile, Fourmile, Walnut, and Elk Creeks, in Erie County, PA (Figure 3). Locations were collected using a survey grade Trimble GPS and paper map. Average measurements of ripple spacing, height, symmetry, morphol- ogy, strike, dip, and orientation were recorded for each ripple set (Table 1) and recorded in strati- graphic order (Figure 1). Samples were taken from four locations for thin sections to determine aver- age grain size. Paleocurrent direction based on ripple mark orientation was plotted on a set of rose plots (Figure 4). All data was entered into an Excel database for analysis and compared to previous studies. Figure 2. Diagram of asymmetric ripples and defined ripple spacing and ripple height. Ripple Spacing (cm) Height ꜛ ꜛ ꜛ ꜛ Extensive exposures of late Devonian Chadakoin and Girard Formation (Conneaut Group) are exposed in Fourmile, Sixmile, Twentymile, Elk, and Walnut Creeks, Erie County, Pennsylvania. Both formations consist of medium-gray shale interbedded with 5–20 cm thick siltstone lenses. The relatively low energy marine envi- ronment of these formations allowed for the creation and preservation of ripple marks in the fine sand and silt lenses. Ripple crests are transverse sinuous in phase and out of phase. Average grain size of ripple mark sediment was 0.03 cm. Ripple heights rang from <0.5–3.25 cm (avg=0.95 cm) (std(h)=0.74 cm) and wave- lengths from 6–31 cm (avg=12.88 cm) (std(λ)=5) (n=103). Ripple marks were documented throughout Four- mile, Sixmile, Twentymile, Elk, and Walnut Creeks and mapped stratigraphically to reconstruct paleocurrent direction through time. Paleocurrent directions and changes in time were identified using rose diagrams and stratigraphy. During the transition from the Girard Formation to the Chadakoin Formation, asymetrical ripple crests record a shift in current direction from the northeast to the northwest with trend in flow direction at N10°E and S90°W. The shift in paleocurrent direction is hypothesized to be due to a change in dominant current forces of deep water bottom currents flowing par- allel to the continental margin of the Catskill Sea (N-NE) to basinal turbidite flows parallel to these currents (W-SW). Prograding continental slope during the transition from the Girard Shale to the Chadakoin Formation is one hypothesis explaining the observed changes in ripple current direction. Future work will consist of mapping ripple marks throughout all of North- western Pennsylvania along with using tech- niques developed by Diem (1985), Immen- hauser (2009), and Okoro etal (2010) to reconstruct paleo-water depth based on ripple height, ripple spacing, and grain size. Kilometers Miles VA TENN KY W. VA DELA MD NJ PENN NC 560 (Modified from Lundegard et al. 1985) 0 50 150 100 0 50 150 100 Figure 4. Paleocurrent map of Late Devonian turbidites in the Appalachian basin by Lun- degard et al. (1985). Data are from sole marks and have a mean trend of S87°W with a standard deviation of 32°. Location of observed asymmetric ripple mark flow direction in Erie County, PA (n=103) are shown in red and have a mean trend of N68°W. ꜛ ꜛ ꜛ ꜛ ꜛ Background The Late Devonian stratigraphic section in western Pennsylvania is characterized by a westward prograding delta system associated with the Acadian Orogeny, part of the overall Appalachian Orogeny (Harper 1999). The Catskill delta complex begins ap- proximately halfway across (east to west) Pennsylvania (Figure 6) forming a typical delta fed basin complex (Figure 7). The Girard Shale and Chadakoin Formation (Conneaut Group) (Figure 5) consist of medium-gray shales interbedded with thin tabular fine-grained sandstone lenses, ripple marks and are void of fossils. These features are consistent with Harper’s (1999) interpretations of the region as part of a delta-fed submarine ramp. Both the Girard and Chadakoin were deposited in the Late Devonian (Harper 1999) and are specifically associated with basinal deposits of the Catskill Sea (Woodrow 1985). Lundgard et al. (1985) used sole marks to map paleocurrents of Late Devonian turbidites in the Appalachian basin showing a mean slope direction of the basin as S87°W with a standard de- viation of 32° (Figure 4). Murphy (1973) and Woodrow and Isley (1983) interpret these deposits as part of a marine transgression, causing coarse clastic sediment to be trapped on the landward end of the coastal plain, only allowing fine-grained clastic sediment to reach the basin margin. The transgression of the basin margin also led to well-oxygenated water to be replace by denser, anaerobic water, leading to a great reduction in di- versity and abundance of marine fauna (Murphy 1973). This study hopes to further the understand what depositional processes and environmental conditions led to the formation of the Girard and Chadakoin for- mations during the Late Devonian of northwestern Pennsylvania. 0 5 15 10 Kilometers Ripple Elevation (ft amsl) 577 1050 Flow direction of ripple mark MAI Department of Geology Mercyhurst University Discussion References Cited Allen, P. A., 1981, Wave-generated structures in the Devonian lacustrine sediments of south-east Shetland and ancient wave conditions: Sedimentology, v. 28, p. 369– 379. Babcock, L. E. and Wegweiser, M. D., 1998, Upper Devonian (Chautauquan) Stratigraphy, Southern Lake Erie Shoreline Region, in Guidebook for the 63rd Annual Field Conference of Pennsylvania Geologists, Geotectonic Environment of the Lake Erie Crustal Block, p. 4–14. Diem, B., 1985, Analystical method for estimating palaeowave climate and water depth from wave ripple marks: Sedimentology, v. 32, p. 705–720. Harper, J. A., 1999, Chapter 7: Devonian, in Shultz, C. H., ed., The Geology of Pennsylvania. Pennsylvania Geological Survey, 4th ser., Special Publication 1, p. 108–127. Immenhauser, A., 2009, Estimating palaeo-water depth from the physical rock record: Earth-Science Reviews, v. 96, p. 107–139. Lundegard, P. D., Samuels, N. D., and Pryor, W. A., 1985, Upper Devonian turbidite sequence, central and southern Appalachian basin: Contrasts with submarine fan depos its, in Woodrow, D. L. and Sevon, W. D., eds., The Catskill Delta: Geological Society of America Special Paper 201, p. 107–121. Murphy, J. L, 1973, Protosalvinia (Foerstia) Zone in the Upper Devonian Sequence of Eastern Ohio, Northwestern Pennsylvania, and Western New York: Geological Soci ety of America Bulletin, v. 84, no. 10, p. 3405–3410. Okoro, A. U., Onuoha, K. M., and Okogbue, C. O., 2010, Oscillatory Ripples, evaluation of ancient wave climates and epierogeny in the Anambra basin and the Afikpo sub- basin, Southeastern Nigeria: Global Journal of Geological Sciences, v. 9, no. 1, p. 11–17. Sevon, W. D., 1985, Nonmarine facies of the Middle and Late Devonian Catskill coastal alluvial plain, in Woodrow, D. L. and Sevon, W. D., eds., The Catskill Delta: Geologi cal Society of America Special Paper 201, p. 79–89. Woodrow, D. L. and Isley, A. M., 1983, Fades, topography, and sedimentary processes in the Catskill Sea (Devonian), New York and Pennsylvania: Geological Society of America Bulletin, v. 94, no. 4, p. 459–470. Woodrow, D. L., 1985, Paleogeography, paleoclimate, and sedimentary processes of the Late Devonian Catskill Delta, in Woodrow, D. L. and Sevon, W. D., eds., The Catskill Delta: Geological Society of America Special Paper 201, p. 51–63. Figure 1. Map of re- corded asym- metric ripples showing each location’s mea- sured flow direction in the Pennsylvania Lake Erie water- shed. Flow direction is shown along a gradational scale moving upsec- tion showing change in flow direc- tion through time. 20cm 14cm Figure 3. Examples of asym- metric ripples and ripple spacing from Fourmile Creek, Erie, PA. Conclusions The ripple marks are distributed with a mean current flow direction of N68°W (Figure 4). This is hypothesized to be due to basinal turbidite flows perpendicular to the Catskill Basin coastline (Figure 7). Stratigraphically, the observed ripple marks show a fluctuating mean flow direction ranging from S83°W – N42°W (Figure 1), indicating a relatively regular output of sediment along a distal slope (Figure 7). The lack of marine fauna, predominance of fine sand and clay shales, and small ripple marks in the lower portion of the Chadakoin and the Girard Formations indicate a marine transgression during this time (Figure 7). This data agrees with Woodrow and Isley (1983) who hy- pothesized a marine trangression during the late Devonian of the Catskill Sea, allow- ing for a reduction in sand-laden turbidity currents and a shift in oxygenated water zones. This would cause a shift in marine faunal populations to more oxygenated zones upslope. Southwestern New York Northwestern Pennsylvania Northeastern Ohio Knapp Formation Conewango Group Conneaut Group Northeast Shale Shumla Sandstone Westfield Shale Laona Sandstone Gowanda Shale Dunkirk Shale Canadaway Group Knapp Format- ion Bedford Shale Cussewago Sandstone Oswayo Riceville Shale Venango Format- ion Catskill Formation Chadakoin Formation Girard Shale Chagrin Shale Dunkirk Shale Bedford Shale Cussewago Sandstone Cleveland Member Three Lick Bed Chagrin Shale Huron Member Perrysburg Formation Ohio Shale Upper Devonian Series Mississippian ? (Modified from Babcock and Wegweiser 1998) Figure 5. Stratagraphic units of the Upper Devonian. Figure 7. Model of deposition in the Catskill Sea during a marine transgression. Depositional environment of the Girard and Chada- koin Formations high- lighted in red. Mud with few Distal Turbidites Silty Mud Pynocline junction with sea floor Distal Turbidites Shoreline ↑ Table 1. Ripple Spacing and Height Frequencies and Ripple Spacing vs. Height over time. Ripple Height (cm) (0.2 - 0.63) (1.92 - 2.35) (4.07 - 4.5) Count 0 20 10 30 40 50 Ripple Height Frequency Ripple Spacing (cm) Count Ripple Spacing Frequency (6 - 8.5) (11 - 13.5) (16 - 18.5) (21 - 23.5) (28.5 - 31) 0 4 8 12 16 20 24 Ripple Spacing Ripple Height Elevation (ft amsl) 580 620 660 700 740 780 820 860 900 940 980 1020 Ripple Spacing (cm) 6 10 14 18 22 26 30 Ripple Height (cm) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Girard and Chadakoin Formation Ripple Spacing vs. Ripple Height over Time (Modified from Woodrow and Isley, 1983, p. 465) Non Clastics Shale Sandstone Sand - Shale Ratio 8 1 1/2 1/8 1 8 Clastic Ratio Erosional Edge of Unit Isopach Contours Sand-Shale Ratio Lines Clastic Ratio Lines 0 80 160 240 Kilometers LATE DEVONIAN of Northeastern United States Isopach and Lithofacies Map (Modified from Sevon, 1985, p. 80) Figure 6. Overview lithofacies map of the Catskill Sea during the Late Devonian. VA KY IN OH NY PA DE NJ WV MD MI
Transcript of RECONSTRUCTING PALEOCURRENT DIRECTION IN THE … · 2014-11-13 · ogy, strike, dip, and...
● Asymmetric ripple marks exposed in Erie County, PA show a mean �ow direction of N68°W.
● Flow direction �uctuates between S83°W – N42°W through time.
● Grain size for ripple marks range 0.2–0.4 mm with clays between particles.
● The majority of ripple marks are asymmetrical and range 0.2–4.5 cm tall (Table 1), indicating weak currents for their formation.
● No fossil fauna are found in deposits containing ripple marks but are found above and below these strata along with increased grain size.
● Wavelength between ripple crests range 6–31 cm (Table 1).
● Ripple �ow direction’s match at the same elevations between seperate creeks, indicating �at lying bedrock of the Girard and Chadakoin formations.
● Due to a predominantly NW �ow direction, it is postulated ripple marks trending northwest are likely formed during low-density basin edge turbidity currents.
140-8
RECONSTRUCTING PALEOCURRENT DIRECTION IN THE CHADAKOIN AND GIRARDFORMATIONS IN NORTHWESTERN PENNSYLVANIAMCCOY, Curtis*, Nicholas Kelly, and Lyman Persico Mercyhurst University, 501 East 38th St, Erie, PA 16546*[email protected]
Abstract Methods
Ripple marks were located in shale deposits incised and exposed by Twenty Mile, Six Mile, Fourmile, Walnut, and Elk Creeks, in Erie County, PA (Figure 3). Locations were collected using a survey grade Trimble GPS and paper map. Average measurements of ripple spacing, height, symmetry, morphol-ogy, strike, dip, and orientation were recorded for each ripple set (Table 1) and recorded in strati-graphic order (Figure 1). Samples were taken from four locations for thin sections to determine aver-age grain size. Paleocurrent direction based on ripple mark orientation was plotted on a set of rose plots (Figure 4). All data was entered into an Excel database for analysis and compared to previous studies.
Figure 2.Diagram of asymmetric ripples and defined ripple spacing and ripple height.
Ripple Spacing (cm)
Heightꜛ
ꜛꜛ ꜛ
Extensive exposures of late Devonian Chadakoin and Girard Formation (Conneaut Group) are exposed in Fourmile, Sixmile, Twentymile, Elk, and Walnut Creeks, Erie County, Pennsylvania. Both formations consist of medium-gray shale interbedded with 5–20 cm thick siltstone lenses. The relatively low energy marine envi-ronment of these formations allowed for the creation and preservation of ripple marks in the �ne sand and silt lenses. Ripple crests are transverse sinuous in phase and out of phase. Average grain size of ripple mark sediment was 0.03 cm. Ripple heights rang from <0.5–3.25 cm (avg=0.95 cm) (std(h)=0.74 cm) and wave-lengths from 6–31 cm (avg=12.88 cm) (std(λ)=5) (n=103). Ripple marks were documented throughout Four-mile, Sixmile, Twentymile, Elk, and Walnut Creeks and mapped stratigraphically to reconstruct paleocurrent direction through time. Paleocurrent directions and changes in time were identi�ed using rose diagrams and stratigraphy. During the transition from the Girard Formation to the Chadakoin Formation, asymetrical ripple crests record a shift in current direction from the northeast to the northwest with trend in �ow direction at N10°E and S90°W. The shift in paleocurrent direction is hypothesized to be due to a change in dominant current forces of deep water bottom currents �owing par-allel to the continental margin of the Catskill Sea (N-NE) to basinal turbidite �ows parallel to these currents (W-SW). Prograding continental slope during the transition from the Girard Shale to the Chadakoin Formation is one hypothesis explaining the observed changes in ripple current direction. Future work will consist of mapping ripple marks throughout all of North-western Pennsylvania along with using tech-niques developed by Diem (1985), Immen-hauser (2009), and Okoro etal (2010) to reconstruct paleo-water depth based on ripple height, ripple spacing, and grain size.
Kilometers
Miles
VA
TENN
KY
W. VADELA
MD NJ
PENN
NC
560
(Modified from Lundegard et al. 1985)
0 50 150100
0 50 150100
Figure 4.Paleocurrent map of Late Devonian turbidites in the Appalachian basin by Lun-degard et al. (1985). Data are from sole marks and have a mean trend of S87°W with a standard deviation of 32°. Location of observed asymmetric ripple mark flow direction in Erie County, PA (n=103) are shown in red and have a mean trend of N68°W.
ꜛꜛ ꜛꜛ ꜛBackground
The Late Devonian stratigraphic section in western Pennsylvania is characterized by a westward prograding delta system associated with the Acadian Orogeny, part of the overall Appalachian Orogeny (Harper 1999). The Catskill delta complex begins ap-proximately halfway across (east to west) Pennsylvania (Figure 6) forming a typical delta fed basin complex (Figure 7). The Girard Shale and Chadakoin Formation (Conneaut Group) (Figure 5) consist of medium-gray shales interbedded with thin tabular �ne-grained sandstone lenses, ripple marks and are void of fossils. These features are consistent with Harper’s (1999) interpretations of the region as part of
a delta-fed submarine ramp. Both the Girard and Chadakoin were deposited in the Late Devonian (Harper 1999) and are speci�cally associated with basinal deposits of the
Catskill Sea (Woodrow 1985). Lundgard et al. (1985) used sole marks to map paleocurrents of Late Devonian turbidites in the Appalachian basin showing a mean slope direction of the basin as S87°W with a standard de-viation of 32° (Figure 4). Murphy (1973) and Woodrow and Isley (1983) interpret these deposits as part of a marine transgression, causing coarse clastic sediment to be trapped on the landward end of the coastal plain, only allowing �ne-grained clastic sediment to reach the basin margin. The transgression of the basin margin also led to well-oxygenated water to be replace by denser, anaerobic water, leading to a great reduction in di-versity and abundance of marine fauna (Murphy 1973). This study hopes to further the understand what depositional processes and environmental conditions led to the formation of the Girard and Chadakoin for-mations during the Late Devonian of northwestern Pennsylvania.
0 5 1510Kilometers
RippleElevation (ft amsl)
577
1050Flow directionof ripple mark
MAIDepartment of Geology
Mercyhurst University
Discussion
References Cited
Allen, P. A., 1981, Wave-generated structures in the Devonian lacustrine sediments of south-east Shetland and ancient wave conditions: Sedimentology, v. 28, p. 369– 379.Babcock, L. E. and Wegweiser, M. D., 1998, Upper Devonian (Chautauquan) Stratigraphy, Southern Lake Erie Shoreline Region, in Guidebook for the 63rd Annual Field Conference of Pennsylvania Geologists, Geotectonic Environment of the Lake Erie Crustal Block, p. 4–14.Diem, B., 1985, Analystical method for estimating palaeowave climate and water depth from wave ripple marks: Sedimentology, v. 32, p. 705–720.Harper, J. A., 1999, Chapter 7: Devonian, in Shultz, C. H., ed., The Geology of Pennsylvania. Pennsylvania Geological Survey, 4th ser., Special Publication 1, p. 108–127.Immenhauser, A., 2009, Estimating palaeo-water depth from the physical rock record: Earth-Science Reviews, v. 96, p. 107–139.Lundegard, P. D., Samuels, N. D., and Pryor, W. A., 1985, Upper Devonian turbidite sequence, central and southern Appalachian basin: Contrasts with submarine fan depos its, in Woodrow, D. L. and Sevon, W. D., eds., The Catskill Delta: Geological Society of America Special Paper 201, p. 107–121.Murphy, J. L, 1973, Protosalvinia (Foerstia) Zone in the Upper Devonian Sequence of Eastern Ohio, Northwestern Pennsylvania, and Western New York: Geological Soci ety of America Bulletin, v. 84, no. 10, p. 3405–3410.Okoro, A. U., Onuoha, K. M., and Okogbue, C. O., 2010, Oscillatory Ripples, evaluation of ancient wave climates and epierogeny in the Anambra basin and the A�kpo sub- basin, Southeastern Nigeria: Global Journal of Geological Sciences, v. 9, no. 1, p. 11–17.Sevon, W. D., 1985, Nonmarine facies of the Middle and Late Devonian Catskill coastal alluvial plain, in Woodrow, D. L. and Sevon, W. D., eds., The Catskill Delta: Geologi cal Society of America Special Paper 201, p. 79–89.Woodrow, D. L. and Isley, A. M., 1983, Fades, topography, and sedimentary processes in the Catskill Sea (Devonian), New York and Pennsylvania: Geological Society of America Bulletin, v. 94, no. 4, p. 459–470.Woodrow, D. L., 1985, Paleogeography, paleoclimate, and sedimentary processes of the Late Devonian Catskill Delta, in Woodrow, D. L. and Sevon, W. D., eds., The Catskill Delta: Geological Society of America Special Paper 201, p. 51–63.
Figure 1.Map of re-
corded asym-metric ripples
showing each location’s mea-
sured flow direction in the Pennsylvania Lake Erie water-
shed. Flow direction is shown along a gradational scale moving upsec-tion showing change in flow direc-tion through time.
20cm
14cm
Figure 3.Examples of asym-metric ripples and ripple spacing from Fourmile Creek, Erie, PA.
Conclusions
The ripple marks are distributed with a mean current �ow direction of N68°W (Figure 4). This is hypothesized to be due to basinal turbidite �ows perpendicular to the Catskill Basin coastline (Figure 7). Stratigraphically, the observed ripple marks show a �uctuating mean �ow direction ranging from S83°W – N42°W (Figure 1), indicating a relatively regular output of sediment along a distal slope (Figure 7). The lack of marine fauna, predominance of �ne sand and clay shales, and small ripple marks in the lower portion of the Chadakoin and the Girard Formations indicate a marine transgression during this time (Figure 7). This data agrees with Woodrow and Isley (1983) who hy-pothesized a marine trangression during the late Devonian of the Catskill Sea, allow-ing for a reduction in sand-laden turbidity currents and a shift in oxygenated water zones. This would cause a shift in marine faunal populations to more oxygenated zones upslope.
SouthwesternNew York
NorthwesternPennsylvania
NortheasternOhio
KnappFormation
ConewangoGroup
Conneaut Group
Northeast Shale
Shumla Sandstone
West�eld Shale
Laona Sandstone
Gowanda Shale
Dunkirk Shale
Can
adaw
ay G
rou
p
KnappFormat-
ion
Bedford Shale
Cussewago Sandstone
OswayoRiceville Shale
VenangoFormat-
ion Cat
skill
Form
atio
n
ChadakoinFormation
Girard Shale
ChagrinShale
Dunkirk Shale
BedfordShale Cussewago
SandstoneClevelandMember
ThreeLickBed
ChagrinShale
HuronMember
PerrysburgFormation
Oh
io S
hal
eU
pp
er D
evo
nia
nSe
ries
Mis
siss
ipp
ian
?
(Modi�ed from Babcock and Wegweiser 1998)
Figure 5.Stratagraphic units of the Upper Devonian.
Figure 7.Model of deposition in the Catskill Sea during a marine transgression. Depositional environment of the Girard and Chada-koin Formations high-lighted in red.
Mud with fewDistal Turbidites
Silty Mud
Pynocline junctionwith sea floor
Distal Turbidites
Shoreline
↑
Table 1. Ripple Spacing and Height Frequencies and Ripple Spacing vs. Height over time.
Ripple Height (cm)(0.2 - 0.63) (1.92 - 2.35) (4.07 - 4.5)
Cou
nt
0
20
10
30
40
50Ripple Height Frequency
Ripple Spacing (cm)
Cou
nt
Ripple Spacing Frequency
(6 - 8.5) (11 - 13.5) (16 - 18.5) (21 - 23.5) (28.5 - 31)048
12162024
Ripple Spacing
Ripple Height
Elevation (ft amsl)580 620 660 700 740 780 820 860 900 940 980 1020
Rip
ple
Spac
ing
(cm
)
6
10
14
18
22
26
30
Ripple H
eight (cm)
0.5
1
1.5
2
2.5
3
3.5
4
4.5Girard and Chadakoin Formation Ripple Spacing vs. Ripple Height
over Time
(Modified from Woodrow and Isley, 1983, p. 465)
Non Clastics
ShaleSandstoneSand - Shale Ratio
8 1 1/2 1/8
1
8
Clastic Ratio
Erosional Edge of UnitIsopach ContoursSand-Shale Ratio LinesClastic Ratio Lines
0 80 160 240Kilometers
LATE DEVONIANof Northeastern United StatesIsopach and Lithofacies Map
(Modified from Sevon, 1985, p. 80)
Figure 6.Overview lithofacies map of the Catskill Sea during the Late Devonian.
VA
KY
IN OH
NY
PA
DE
NJ
WVMD
MI
