DR2010268
DATA REPOSITORY: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
The procedure for determining the paleocurrent direction indicated by cross-bedding in
the current study consisted of a two-step retro-deformation that initially “unfolds” megascopic
fold structures into a tabular plane that is tangent to the anticlinal and synclinal hinge lines
referred to as the sheet dip plane (Whitten, 1966). The dip of the sheet dip plane is subsequently
removed by a second rotation about its strike line until the original depositional horizontal
attitude of primary bedding is attained. In both rotation steps, foreset crossbeds that occur within
primary bedding are rotated in the same manner to retro-deform them into their original
depositional attitude. The paleocurrent direction is assumed to be in the azimuth direction of the
true dip of the foreset. It is important to note that in general the first-step rotation is unique for
each top/bottomset and foreset pair because this rotation occurs around the hinge line of the
dominant megascopic folding, therefore, each top/bottomset bed will have a different rotation
angular amount and sense depending on its position on the fold profile. The geometrical
relationships of the first-step rotation used to generate a tabular sheet from the folded strata is
depicted in Figure A-1. Note that the individually unique rotations (∀1 and ∀2) that are required
to rotate primary bedding around the hinge to become parallel to the unfolded sheet layer. The
second-step rotation affects all data equally, and is shown as the angle ∗.
Because of the many permutations of the first-step rotation large data sets are best
processed by programming a calculator or computer. A Windows®-compatible program with
supporting documentation useful for processing 2-step rotations may be downloaded at:
“http://www.usouthal.edu/geography/allison/w-netprg.htm”. The data files used with the
crossbed analysis program (“W-xbed.exe”) for this project are listed in tables A-1 through A-3.
The Kahatchee Mountain Group cross-bedding used for this study is distributed into
three separate subareas: 1) Columbiana Mountain on the northeast plunging portion of the
Columbiana Mountain syncline, 2) Talladega Springs along the east flank of the Kelly Mountain
window, and 3) northern Cleburne County (Figure 2). Bedding readings from Kahatchee
Mountain Group units (Waxahatchee, Brewer, Wash Creek formations) were selected and
plotted to define the geometry and attitude of megascopic folding that affects the subarea. The
least-squares statistical hinge or mean vector to poles to bedding were used to define the attitude
of the unfolded sheet layer (Figure A-1).
Columbiana Mountain Subarea
The Columbiana Mountain subarea is structurally controlled by a northeast plunging
syncline exposed along the northwest flank of the Kelly Mountain half-window (Figure 2). Poles
to bedding from Kahatchee Mountain Group metasediments (Figure A-2; Table A-1) define a
least-squares cylindrical fold hinge (25,N40E; R2=0.83), therefore, the unfolded sheet layer
attitude is N50W, 25SW for this subarea. A two-step retro-deformation of foreset crossbeds
from the subarea (Table A-1) results in a an average paleocurrent bearing of 137Ε and an
average paleoslope dip of 32Ε (Figure A-3).
Page 1 of 12
DR2010268
DATA REPOSITORY A: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Talladega Springs Subarea
The Talladega Springs subarea is located along the east flank of the Kelly Mountain
half-window (Figure 2) within the Kahatchee Mountain group metasediments. In this area the
structure of the stratigraphy is basically that on a southeast-dipping monocline affected some
minor cross-folding transverse to regional strike (Figure 2). This is reflected in the poles to
bedding stereonet plot in Figure A-4 that indicates a monoclinal structure with a least-squares
attitude of N16E,46SE. This attitude functions as the sheet layer for the two-step
retrodeformation rotations. The two paleocurrent directions are summarized in Figure A-5. The
paleoslope values were 7Ε and 15Ε (Table A-2).
Cleburne County Alabama Subarea
The northern Cleburne County subarea of exposed Kahatchee Mountain metasediments
are structurally controlled by a megascopic northwest-verging, isoclinal anticline containing the
basal Waxahatchee formation in the core of the structure (Figure 2). Because of the isoclinal
structure there is no well-developed cylindrical fold pattern to poles to bedding in Figure A-6,
therefore, the unfolded sheet layer attitude is simply the average mean attitude of bedding (i.e.
the plane normal to the least-squares vector fit to poles). Thus the isoclinal fold was unfolded to
an sheet layer attitude of N48E, 40SE in the first rotation step. The paleocurrent directions
derived from the retrodeformation kinematic analysis are displayed in Figure A-7. The average
azimuth direction for the 14 crossbeds is 136Ε (S44E), with a least-squares paleoslope value of
12Ε.
Page 2 of 12
DR2010268
DATA REPOSITORY: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Table A-1:
Sample
41
42
42
73
CO099
CO043
CO042
CO044
CO045
CO050
CO057
CO089
CO092
CO095
CO094
GE562
GE506
CO091
CO093
GE509
CO135
GE511
GE537
GE538
GE539
CO050
CO049
CO056
CO058
CO059
CO060
CO063
CO068
CO062
GE560
GE561
GE559
GE558
GE557
GE553
Columbiana Mt. Subarea Data
Top/Bottomset
Foreset
N 50 W 52 E
N 50 W 52 E
N 42 W 45 E
N 42 W 45 E
N 75 W 40 E
N 75 W 40 E
N 65 W 42 E OT N 65 W 42 E
N 00 E 45 E
N 19 E 30 E
N 13 E 30 E
N 00 E 30 E
N 27 W 30 E
N 07 E 50 E
N 00 E 30 E
N 32 E 45 W
N 50 E 25 W
N 69 E 30 E
N 43 E 20 W
N 00 E 23 E
N 50 W 67 E
N 76 E 70 W
N 09 E 30 E
N 67 E 17 W
N 17 E 70 E
N 60 E 62 W
N 48 W 22 E
N 49 E 36 E
N 58 E 37 W
N 07 E 50 E
N 00 E 25 E
N 32 W 40 E
N 66 W 35 E
N 56 W 40 E
N 69 W 35 E
N 57 E 80 W
N 40 E 30 E
N 48 W 35 E
N 17 W 56 E
N 43 W 13 E
N 42 W 23 E
N 39 E 50 W
N 06 E 51 E
N 29 E 90 E
Paleocurrent azimuth
159.0 (S21.0E)
135.2 (S44.8E)
143.0 (S37.0E)
061.7 (N61.7E)
Page 3 of 12
Paleoslope
25.6
23.2
34.0
36.9
DR2010268
DATA REPOSITORY A: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Table A-2: Talladega Springs Subarea Data
Sample
Top/Bottomset Foreset
Paleocurrent azimuth Paleoslope
NT668
N 12 W 48 E
NT669
N 42 E 64 E
NT675
N 56 E 22 E
N 70 E 26 E
201.7 (S21.7W)
6.9
NT676
N 15 E 43 E
N 10 E 57 E
088.3 (N88.3E)
14.5
NT418
N 15 E 56 E
NT665
N 40 E 25 E
NT662
N 02 E 60 E
NT663
N 20 E 82 E
AM0019 N 02 E 55 E
GE189
N 05 W 41 E
AM0017 N 02 E 55 E
GE179
N 54 W 82 W
NT671
N 18 E 70 E
GE185
N 42 E 25 E
NT705
N 40 E 12 E
NT707
N 49 E 51 E
NT706
N 00 E 75 E
GE124
N 06 W 14 W
Page 4 of 12
DR2010268
DATA REPOSITORY: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Table A-3: Cleburne County Subarea Data
Sample
Top/Bottomset
Foreset
RA1247
N 70 E 66 E
RA1204
N 20 E 60 E
RA1301
N 19 E 58 E
RA1300
N 15 E 60 E
RA1259
N 47 E 71 E
RA1085
N 55 E 36 E
N 47 E 42 E
RA1079
N 52 E 31 E
N 51 E 40 E
RA1079
N 55 E 26 E
RA1080
N 39 E 35 E
N 35 E 45 E
EB090
N 35 E 25 E
N 46 E 37 E
EB091
N 52 E 30 E
N 50 E 39 E
EB202
N 56 E 30 W
N 64 E 39 W
EB104
N 81 W 37 W
ER003
N 75 E 26 E
N 70 E 38 E
ER001
N 15 E 05 W
N 21 E 16 W
ER010
N 60 E 15 E
ER018
N 70 E 75 W
EO037
N 72 E 50 E
ER139
N 54 E 47 E
ER138
N 31 E 67 E
ER125
N 61 E 41 E
N 57 E 49 E
ER140
N 39 E 41 E
N 42 E 55 E
ER040
N 25 E 53 E
N 21 E 61 E
ER041
N 39 E 44 E
N 35 E 55 E
ER042
N 62 E 48 E
N 67 E 58 E
RA1086
N 52 E 31 E
N 58 E 39 E
Page 5 of 12
Paleocurrent azimuth
Paleoslope
100.3 (S79.7E)
133.4 (S46.6E)
7.8
14.2
104.9 (S75.1E)
157.1 (S22.9E)
134.3 (S45.7E)
182.2 (S02.2W)
10.3
13.2
9.1
10.1
156.3 (S23.7E)
247.4 (S67.4W)
12.3
11
127.0 (S53.0E)
151.2 (S28.8E)
098.1 (S81.9E)
114.5 (S65.5E)
171.4 (S08.6E)
167.0 (S13.0E)
8.5
14.2
8.7
11.4
10.8
8.7
DR2010268
DATA REPOSITORY A: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
δ
α2
α1
foreset bed
Figure A-1: Geometry of two-step retrodeformation to remove the deformation effects of
folding.
Page 6 of 12
DR2010268
DATA REPOSITORY: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Poles to Columbiana Mt. Subarea Bedding
N 10
350
Least-squares fit
N(data):40
Fit:25,N40E
S.D.:16.34
X
2
R :0.830
340
20
330
:25.53(27.7)
2
30
Sheet Dip=N50W,25NE
320
40
310
50
300
Cylindrical fold hinge
Cylindrical Fold Girdle
(Cylindrical fit)
290
60
70
280
80
W
E
260
100
250
110
240
120
230
130
220
140
210
150
200
190
S
170
160
40 DATA
Figure A-2: Poles to bedding with least-squares cylindrical fold hinge and sheet dip plane
attitude.
Page 7 of 12
DR2010268
DATA REPOSITORY A: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Columbiana Mt. Paleocurrent
N 10
350
Least-squares fit
N(data):4
Fit:32,S43E
S.D.:37.33
2
340
20
330
X :57.16(15.1)
30
320
40
310
50
300
60
290
1
70
280
80
W
E
260
100
250
110
240
120
1
230
130
1
1
220
210
140
150
200
190
S
170
160
4 DATA
Figure A-3: Rose diagram for paleocurrent direction trends in the Columbiana Mt. subarea.
Page 8 of 12
DR2010268
DATA REPOSITORY: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Poles to Talladega Springs Subarea Bedding
Least-squares fit
N(data):18
Fit:44,N74W
S.D.:33.79
2
X :23.12(15.1)
340
350
N
10
20
330
30
320
40
310
50
300
60
Sheet Dip=N16E,46SE
290
70
280
80
(Vector fit)
W
E
260
100
250
110
240
120
230
130
220
140
210
150
200
190
S
170
160
18 DATA
Figure A-4: Poles to bedding from Talladega Springs subarea with least-squares vector fit
defining a monoclinal attitude of N16E, 46SE.
Page 9 of 12
DR2010268
DATA REPOSITORY A: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Talladega Springs Subarea Paleocurrent
N 10
350
340
20
330
30
320
40
310
50
300
60
290
70
280
80
1
W
E
260
100
250
110
240
120
230
130
1
220
140
210
150
200
190
S
170
160
2 DATA
Figure A-5: Paleocurrent direction rose diagram derived from Talladega Springs subarea
(paleoslope = 7 & 15).
Page 10 of 12
DR2010268
DATA REPOSITORY: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Poles to Cleburne Co. Subarea Bedding
Least-squares fit
N(data):25
Fit:50,N42W
S.D.:29.52
2
X :10.81(15.1)
340
350
N
10
20
330
30
320
40
310
50
300
60
290
70
280
80
Isoclinal Sheet=N48E,40SE
W
E
260
100
250
110
(Vector Fit)
240
230
120
130
220
140
210
150
200
190
S
170
160
25 DATA
Figure A-6: Poles to bedding from Cleburne Co. subarea data yielding a least-squares
isoclinal sheet attitude of N48E, 40SE.
Page 11 of 12
DR2010268
DATA REPOSITORY A: RETRODEFORMATION OF
CROSSBED DATA TO DETERMINE PALEOCURRENT
DIRECTION
Cleburne Co. Subarea Paleocurrent
N 10
350
Least-squares fit
N(data):14
Fit:12,S44E
S.D.:33.49
X
2
340
20
330
:23.68(15.1)
30
320
40
310
50
300
60
290
70
280
80
W
E
260
100
250
110
1
2
240
120
230
130
220
140
210
200
190
S
170
160
3
150
14 DATA
Figure A-7: Rose histogram of paleocurrent azimuths from the retrodeformed Cleburne
County subarea (mean paleoslope = 12).
Page 12 of 12