ML20093K830
| ML20093K830 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 08/31/1984 |
| From: | BECHTEL GROUP, INC. |
| To: | |
| Shared Package | |
| ML20093K809 | List: |
| References | |
| NUDOCS 8410180188 | |
| Download: ML20093K830 (50) | |
Text
. ..
l
- l
- . g GEOLOGIC EVALUATION OF TRENCH EXPOSURE
~l l VOGTLE ELECTRIC GENERATING PLANT lI .
i L
l August,1984
.I I
Ll l .
- ig -
GEOLOGY GROUP I
.l :
88A!!8a*o!8a8%
l A PDR
I
'g GEOLOGIC EVALUATION OF TRENCH EXPC)SURE I
'I VOGTLE ELECTRIC' GENERATING PLANT .
I I
1I l August,1984
'I l
I l -
e-GEOLOGY GROUP g .
^
l-I l .
[ TABLE OF CONTENTS LI -
L 1.0 EXECUTIVE
SUMMARY
l
2.0 INTRODUCTION
3 3.0 GEOLOGIC SETTING I
S 3.1 Local Stratigraphy S 3.2 Trench Stratigraphy 7 3.3 Unconformities and Weathering Intervals 7 4.0 SMALL-SCALE STRUCTURES 10 4.1 contorted Bedding 30 4.2 Fractures, Joints, and Minor Offsets 12 l
lEW 4.4 Sand Dikes 23 S.0
SUMMARY
25 i
6.0 REFERENCES
28 l
I LI LI
.I 1
I I
I I
I
T~ .
LI I i LIST OF TABLES
,gW TABLE 1: Informal stratigraphic units exposed in trench wall.
LIST OF FIGURES l ?IGURE 1: Index Map.
l FIGURE 2: Longitudinal view of west trench wall showing magnitude of
'g contorted bedding.
L* FIGURE 3: Photo-morsic and geologic interpretation of trench, west wall.
FIGURE 4: Photo-mosaic and geologic interpretation of trench, east wall.
FIGURE 5: Surface geometry of Unit F.
FIGURE 6: Photo of small offsets with displacements ranging from 1 to 24 inches; West wall - Station 360 to 410. Offsets typically have normal displacements toward depressions.
1 FIGURE 7: Photo of arcuate faults, fractures, and clastic dikes over center of depression; West wall - Station 430 to 490.
(
i FIGURE 8: Photo of clastic dikes in upper part of Unit H; East wall -
Station 570 to 610. Dikes generally decrease in density i
! downward. Where dikes extend into undaelying strata, they are coincident with minor offsets or fractures.
FIGURE 9: Photo of clastic dikes in upper part of Unit H; East wall -
Station 220. Better developed dikes have an inner core of white-gray clay. Dikes thin and generally pinch-out downward; upward they merge with brown soil B-horizon or are truncated by I white eolian sand.
I I
I 11
,I
- I
I .
1.0 EXECUTIVE
SUMMARY
I A construction trench has been recently excavated at the Vogtle Electric Generating Plant (VEGP) site. The trench exposes Tertiary Coastal Plain sedirnents containing a variety of small-scale deformation structures, including warped bedding, fractures, joints, minor offsets, clastic dikes, and injected sand dikes. The great size of the trench coupled with knowledge of underlying stratigraphy gained from prior geologic investigations at VEGS offers a unique opportunity to evaluate the origin of these Coastal Plain small-scale structural features.
I The structural features are interpreted to be local phenomena related to dissolution of an underlying carbonate bed, the Utley Limestone, followad by one or more phases of plastic and brittle collapse of overlying Tertiary sediments. The collapse created depressions and folded bedding in the overlying strata. Fractures and joints are spatially associated with the depressions and resulted from brittle, tensional failure of consolidated and semi-consolidated sediment during collapse.
1.
Displacement along many fractures resulted from irregular differential settlement of blocks. Most displa:ements are normal into the subsiding i
l depression and many fractures and offsets are continuously over the centers of depressions. The offsets are laterally and vertically I
The sand dikes appear to result from plastic or liquid injection of loosely consolidated fine sand into the overlying, fractured, relatively E 1 0119g B
I 3 consolidated sedimentary rock. The sand probably mobilized in response to sudden increased ovorburden pressure during sediment collapse.
Clastic dikes resulted primarily from weathering and soil-forming processes preferentia!.ly enhanced along the pre-existing fractures and i offsets for1ned during the collapse. Their present geographic distribution is controlled by the depth of weathering and paleosol development in the Coastal Plain sediments and by subsequent erosion of l
the land surface, i
l The Coastal Plain structural features exposed in the trench are not tectonic features nor are they indicative of regionally significant
, E seismic activity. Orientations of the structures are localli consistent
!g but vary widely from location to location both within the trench and l l within the surrounding area. Similarly, three-dimensional reconstruction of the fold structures indicates that they are local depressions j
superimposed on a nearly horizontal bedding surface and do not have laterally persistent axial trends characteristic of tectonic deformation.
t I
" Age of the structures is poorly constrained. They are younger than the Eocene and Miocene host sediment and older than overlying late Pleistocene or Holocene eolian sand. With the exception of clastic dikes, the structures are also older than a major erosional event that lowered the Miocene land surface up to 20 feet and a major weathering LI I 2
- 0119s l
I I event which produced a well-developed relict soil on the eroded Miocene surface. These two events occurred over an interval of at least 100,000 years suggesting that the pre-dating structures are middle Pliestocene or older image. Clastic dikes probably developed during the major weathering / soil-forming event and thus may be as young as 10,000 to 100,000 years old.
I
2.0 INTRODUCTION
I Small-scale deformation structures are common in the Tertiary sediments of the upper Coastal Plain Province of southwestern South Carolina and northeastern Georgia. Clastic dikes, contorted bedding, fractures, i
joints, and small offsets have been observed by numerous investigators in varying degrees of development and preservation. Their general distribution in the upper Coastal Plain of this area is illustrated on the outcrop map of selected exposures prepared by McDowell and Houser (1983), who note that many additional exposures are also present.
Despite their widespread occurrence, the origin of these small-scale structures is poorly known. They have been variously attributed to l
l seismic or tectonic activity (Siple, 1967: Howell and Zupan, 1974; Zupan 1
and Abbott, 1975; Inden and Zupan, 1975, Seeber and Armbruster, 1981), to solution of underlying carbonate horizons and sediment collapse (Siple.
l 1967; Socor, 1980), and to weathering and soil-forming processes (Johnson and Heron, 1965 Heron, 1965; Heron and others, 1971). These varying lI E ,
0119s
I I hypotheses reflect the possiblity that each structure may have a different origin, or that the origin of each structure may differ from region to region. In addition, the interpretation of origin has commonly been hindered by limited outcrop dimensions and by insufficient inforination on underlying stratigraphy. These limitations have restricted observation of the lateral and vertical continuity of the structures and the relationships of the structures to one another, to the host sediment, and to the underlying stratigraphy.
This paper describes a recently exesvated, large trench-exposure of deformed Coastal Plain Tertiary sediments near the Vogtle Electric Generating Plant (VEGP), in Burke County, Georgia (Fig. 1). The trench f
W trends N25'W and is over 900 feet long, 30 to 45 feet deep, and 25 to 40 feet.across. Contorted bedding, fractures, joints, minor offsets, and
' two varieties of clastic dikes are well exposed in the trench walls (Fig.
2). The two variett.es of dikes include both those previously described in the literature but which, as this study indicates, are not true clastic dikes (e.g. extraneous material emplaced into the containing host sediment either from above or from below), as well as a form of injected clastic dike not previourly described in the literature of this area. In this paper, we retain the ;ommon usage of "clustic dikes" as a descriptive term for features similar to those described in the literature, while the injected clastic dikes are herein called " sand dikes" to simplify description and avoid confusion. The lateral and vertical dimensions of the trench permitted accurate determination of the I .
E 4 0119s
I I relationships of all the structures to one another and to the host sediment, while detailed mapping of both walls provided data for three-dimensional reconstruction and analysis of the structures. In addition, previous VEGP geologic investigations have accurately defined the subsurface stratigraphy at the site (Georgia Power Co., 1984).
I The trench thus offers a unique opportunity to study the origin of Coastal Plain small-scale deformation. Our conclusion is that, at this locality, the contorted bedding, injected sand dikes, fractures, joints and small offsets are local phenomena that resulted from the dissolution of an underlying carbonate unit and subsequent collapse of overlying sediment. Clastic dikes formed by surficial weathering and soil-forming processes preferentially enhanced along these pre-existing fractures, joints, and offsets related to the collapse.
3.0 GEOLOGIC SETTING l
'The trench exposure is situated on the Atlantic Coastal Plain approximately 25 miles southeast of Augusta, Georgia (Fig. 1). It is approximately 4000 feet north of the VEGP site at latitude N33*9',
longitude W81'41', and has been excavated for disposal of construction waste.
I 3.1 Local Stratitraphy
, I The Atlantic Coastal Plain sediments consist of poorly to moderately consolidated sand, silt, marl and limestons of Cretaceous to Quaternary s
I m 93
I age which dip slightly to the southeast. The stratigraphy of these sediments at the site has been defined by previous drilling
.I investigations at VEGP and includes in descending stratigraphic sequence Quaternary eolian sand, the Miocene Hawthorn Formation, the upper Eocene Barnwell Group, and the middle Eocene Lisbon Formation (Georgia Power Company, 1984. Figure 2.5.1-3). The solian sand consists of brown, gray and white, very well sorted, subangular to subrounded, fine quartz sand.
The Hawthorn Formation is typically a poorly sorted, red, yellow and tan clayey sand. The Barnwell Group contains a variety of laterally .
discontinuous marine facies but is predominantly a red, brown, yellow and buff, well to poorly sorted, fine to coarse sand and sandy clay. The Lisbon Formation is typically a yellow-brown to green, fine to coarse, glauconitic quartz sand with lenses of clay and limestone.
I Approximately 75 feet beneath the surface at the trench site, the lower Barnwell contains the Utley Limestone. The limestone is 50 to 70 feet thick and consists of locally highly pervious, glauconitic, sandy coquina. Immediately underlying the limestone, an 80-foot-thick sandy marl aquiclude called the Blue Bluff mael is present in the upper Lisbon Formation.
l lI Site exploration at VEGP has defined shallow depressions or sinks in the sediments overlying the Utley Limestone (Georgia Power Company, 1984).
Isopach maps of the Utley Limestone drawn during these investigations indicate that the depressions result from dissolution and removal of lI E 8 0119g
,I
l iI
~
s .
material from the Utley Limestone and are not the expression of deeper structures in the Blue Bluff marl or lower units. Overlying sediments have collapsed into the depleted areas creating depressions in both the overlying strata as well as occasionally on the existing surface topography. The underlying Blue Bluff marl m intains a laterally I
consistent elevation and is not deflected across the depressions.
I 3.2 Trench Stratiaraphy E
coastal Plain sediments exposed in the trench include the Hawthorn Formation and the upper Barnwell Group, above the Utley Limestone. The limestone is not exposed. Late Pleistocene or Holocene eolian sar.d from 5- to 20-feet-thick overlies the Hawthorn and forms the upper part of the trench walls.
I For the purposes of mapping and evaluating deformation structures, these deposits are divided into nine 11thologically distinct informal units designated A through I in stratigraphically ascending order. These units are described in Table 1 and shown on the geologic maps of the trench walls in Figures 3 and 4. Tentative correlation of these units with the formally accepted stratigraphy described above suggests that Units A through G are part of the Barnwell Group, Unit H comprises the Hawthorn Formation, and Unit I is the Pleistocene or Holocene eolian sand.
I 3.3 Unconformities and Weatherina Intervals Two erosional unconformities and two, possibly three, intervals of weathering and soil-development are present in the stratigraphic sequence 0119g B
I I exposed in the trench. These unconformities and weathering intervals provide useful relative age information for constraining the age of the deformation structures.
E The oldest erosional event recognized in the trench occurred some time following deposition and local solution subsidence of the Miocene Hawthorn Formation (Unit H). The warped surface of Unit H was eroded to a planar surface of little or no relief. Based on the maximum magnitude of warping described below, this major erosional event must have lowered the land surface in some areas by 15 to 20 feet.
Following erosion, the surface of Unit H was exposed to a long period of
. weatherLng and soil development under stable surface conditions. Locally preserved at this surface is a strongly developed relict soil B-horizon I up to 3-feet-thick (Fig. 3 and 4). The base of the B-horizon is l
typically in sharp contact with a deeply weathered, mottled soil
- C-horizon. The C-horizon extends into Unit H from 5 to 10 or more feet.
Even under rapid soil-forming conditions, such a strongly developed soll l
j profile probably required more than 10,000 years to form and may have l
required in excess of 100,000 years to forin, f A second interval of less extensive erosion followed development of the soil and preceeded deposition of the eolian sand of Unit I. The erosion has everywhere removed the soil A-horizon, connonly removed the B-horizon, and channeled into the underlying weathered part of Unit H.
I e
I 0119g
,I
I .
I Local preservation of the B-horizon, however, indicates that the erosion was not generally extensive. The most significant erosion occurred at the northwest end of the trench where five-foot-deep channels are cut into Unit H on both walls and most of Unit H has been removod (Fig. 3, Sta. 250 to 280; Fig. 4. Sta. 250 to 280).
I Following this erosion, the solian sand of Unit I was deposited. A second interval of weathering and soil development is evident in the upper part of Unit I at the present topographic surface. The present-day soil has little or no development of soil horizons and probably required less than 10,000 years to form.
Each of these~ erosional and weathering events occurred during the late Miocene, Pliocene, or Quaternary. Although the time required for each I event is not known, the cumulative time is probably on the order of 100.000 to several 100.000 years. This geomorphic and pedologic evidence thus provides reasonably strong relative age criteria for constraining the age of development of the Coastal Plain deformation structures.
I An earlier third interval of weathering is also suggested by the strons mottling and presence of clay nodules in Unit G (Table 1). This horizon is separated from the overlying soil developed in Unit H by up to 10 feet of yellow, relatively unweathered sediment (Figure 4, Sta. 650). Weak clay-skins and granular peds aru present and the abundant clay in the unit may be, in part, pedogenic. Alternatively, the clay and silt of the i
E m ,g
' ' - ~m n ia u
I unit may have resulted from primary deposition, and the increase in weathering may reflect perched ground water on Unit G which localized chemical alteration in the unit.
E 4.0 SMALL-SCALE STRUCTURgS I
Six types of small-scale structures are exposed in the trench walls.
These include contorted or warped bodding, fractures, joints, minor offsets, irdected sand dikes of a variety not previously described in the literature, and clastic dikes of the variety previously described by Heron (1965), Siple (1967), Zupan and Abbott (1975), Socor (1980) and many others.
4.1 Contorted Beddinz Coastal Plain sediments exposed in the trench are deformad into a series of broad depressions and arches (Fig. 2, 3 and 4). The folds have an amplitude ranging fron 5 feet (Fig. 4, Sta. 410) to more than 20 feet (Fig. 4, Sta. 755) and a wavelength of 50 feet to more than 150 feet I (Fig. 5). They influence bedding attitudes in Units A through H; beds of Unit I are not deformsd. Bedt of Units D and E appear to locally thin over the crests of some arches and thicken into depressions (Fig. 3 Sta.
270 to 350) while beds of Unit F locally thin and pinch-out over the crests of some arches (Fig. 4, Sta. 430 to 520) suggesting that some deformation may be contemporaneous with deposition. The thickening and I
10 0119s I
I thinning of units exposed in the trench, however, is partially artificial, resulting from the changing attitudes of the beds in the trench wall. Facies changes and ground-water iron-oxide alteration also obscure and complicate these thickness relationships.
The warps exposed in the trench walls ace not laterally persistent across the trench (Figs. 3 and 4). The number, size, and position of the deformation troughs and crests cannot be correlated from wall to wall indicating that the structures have a complex three-dimensional I- configuration.
I To analyze this configuration, the I, Y, and Z coordinates of 49 surveyed
\
points and bedding attitudes from 40 points were used to contour the l deformed surface of Unit F. The trench walls slope from 35 to 45 degrees permitting good three-dimensional reconstruction of the warped surface.
Figure 4 is a computer-generated contour reconstruction and mesh reconstruction of the upper surface of Unit F (and Unit E where F is not present) showing the outline of the trench and locations of the data used. Bedding attitudes were used as vectors to extend the contours into l the trench walls.
'E 4.1.1 Orinin - The contour reconstruction indicates that the coautal Plain sediments are deformed into a series of broad domes and sharp, circular depressions. There is no lateral persistence of synclinal or anticlinal fold axes or consistency in the size and orientation of the I
I u meg
E warps which would be typical of tectonically generated structures.
Rather, the domes and depressions appear to be the result of local, irregular subsidence or compaction of the sediment. In the case of Unit F, these depressions appear to be superimposed on an original bedding surface ranging in elevation from 243 to 246 feet. The dome crests are generally conformable at this elevation indicating that they are the remnants of this former original surface and that no vertical uplif t has occurred. The Utley Limestone is approximately 40 to 50 feet beneath the depth of the trench and dissolution and removal of material from the Utley, documented during previous VEGP site investigations (Georgio Power i
Co., 1984), suggests that the deformation of Coastal Plain sediments probably reflects collapse and subsidence of sediment into depleted areas of the Utley Limestone.
I 4.1.2 age - The age of sediment collapse is moderately well constrained. Collapse followed and possibly occurred contenparaneously j with the late Eocene and Miocene deposition of Units D through H. The collapse does not involve beds of Unit I and is clearly older than the major erosional event which eroded the warped surface of Unit H at least 100,000 and prob.oly more t.han several 100,000 years ago.
E 4.2 Fractures. Joints. and Minor Offsets Associated with the domes and depressions are numerous fractures, joints
,: and small offsets. These structures are most prevalent in Units D, E, F, I .
12 m eg
,' G, and H on the limbs of.the more strongly werped depressions. They
~
generally die-out do r. card into the lee ely ecc+elidsted s eds of Unita A, B and C and are truncated upward by Unit I. In the upper portions of Unit H, the fractures and offsets typically merge with clastic dikes; in some instances clastic dikes also extend undisplaced across offsets (Fig.
3, Sta. 410).
lI Yeacture orientations indicate that they are intimately related to development of the collapse depressions. Attitudes of 107 fractures and joints were obtained at four independent localities (Fig. 3, Sta. 400 to 440 and Sta. 500 to 550, Fig. 4, 3ta. 300 to 350 and Sta. 380 to 440).
The fractures are primarily vertical with trends ranging from east-west to northeast-southwest. Trend groupings are locally consistent at each
' *****' *"' *** '"*" '*"' "5 ' '" " "*"' ' "*"' ""55*"5 *
.E l 3 local control for fracture development, probably related to collapse of l
the depressions.
Numerous small offsets with displacements ranging, frma 1 to 24 inches see also evident in the trench walls. The larger of these are shown on Figuras 3 and 4. Most of the offsets have normal displacement toward or into depressions (Fig. 6); minor reverse displacements also occur near
- .I the crest of some arches. None of these offsets extend across the trench. Offsets with orientations trending across the trench ca.ceot be traced laterally from wall to wall.
1E 13 0119g 1
- - . - - . , . . , - , , . , . . - , - , - . . . . . . ~ . . - , . , . - , , - . _ . , . . . - - . . . _ , . , , - . , - , - . , , - - - - . _ . - _ . . , - - . . , . _ , , , .
,,-.-,n-, ,
- r. -
Attitudes of 46 offsets were recorded at eight separate localities of the 7
se trench (Fie. 3, Sta. 300 to 400, 450 to 500, 500 to 600, 680 to 750, and 750 to 850; Fig. 4. Sta. 550 to 600, 700 to 750, and 750 to 830). Offset plane orientations range from steeply dipping to flat-lying with trends of east-west, northwest, north-south, and northeast. The orientations are locally consistent on the limbs of individual arches and depressions but very strongly from fold to fold. thaltiple attitudes taken on some offsets indicate that the offset orientations vary up-section and in some instances actually arc over the centers of some depressions (Fig. 7).
~
Many offsets splay both up-section and down-section. Up-sec'. ion these splays are coincident with large zones of " clastic dike" development in tha upper weathered part of Unit H (Figs. 7 and 8}. Down-section, the offsets show decreasing displacement into the loosely consolidated sands of Units A, B, and C.
l i
I 4.1.2 Oriain - These several observations indicate that the offsets are local phenomena. They are spatially related to depressions and have resulted from sediment collapse, differential subsidence and brittle block failure of overlying semi-consolidated sediment. The offsets are l
not laterally or vertically continuous or consistently oriented regionally; thus they are not tectonically capable structures.
4.2.2 Age - Age of the fractures and offsets is poorly constrained.
l They are younger than the Eocene and Miocene deposits of Units A through 14 01193
H but older than the late Pleistocene or Holocene sand of Unit I. In addition, they typically merge with or are cut by clastic dikes and they are truncated by the erosional events and soil development which proceeded deposition of Unit I. These relations suggest that the offsets are at least 100,000 and probably more than several 100,000 years old.
l 4.3 Clastic Dikes LI clastic dikes are well exposed along the length of the trench. They
! occur predominantl'y in the upper, near-surface, weathered part of Unit H and have the following characteristics:
l
- 1. The dikes generally merge upward into the deeply weathered soil B-horizon at the surface of Unit H (Fig. 4, Sta. 180 to 250; Fig. 9) or, where this weathered horizon has been removed by erosion, the dikes are abruptly truncated and overlain by younger sediment of Unit I.
- 2. The dikes range from I num to greater than 20 cm across.
averaging 2 to 3 cm across. The better developed dikes contain a central core of dark grayish green to white clay up to 5 cm thick (Fig. 9). The clay is concentrically bordered by a zone of bleached clayey sand which, in turn, is bordered by a zone of iron-oxide cementation or enrichment.
I 15 0119s e
- 3. The dikes are best developed o<er areas of maximum warping and fracturing; they are less developed in areas where warping and fracturing of lower beds is minimal. Many dikes are coincident
.with or clust.or around fractures and offsets where these structures enter the weathered portion of Unit H (Fig. 3. Sta.
340 to 390, Sta. 450 to 480; Fig. 4, Sta. 580, Figs. 7 and 8).
I 4. Laboratory analyses indicate that the dikes represent slight weathering of feldspar and clay accumulation relative to the host sediment. Grain size analyses indicate that the clayey sand zone is texturally slightly enriched in clay and silt over the host sediment. I-ray diffraction analyses indicate that the central clay core is predominantly kaolinite with minor amounts of chlorite and illite, and that the clayey sand is I .
predominantly quartz with minor kaolinite, and is depleted in feldspar compared to the host sediment.
- 5. The dikes in virtually all cases are associated with mottling and clay nodules in the weathered portion of Unit H. The clay nodules are texturally similar to the clay in the dikes, although compositional similarity has not been determined.
l
- 6. The dikes and associated mottling decrease downward in density and size. In most cases, the dikes taper downward and pinch-out over a 5-to 15-foot interval (Fig. 4, Sta. 180 to 250, Eta. 580; 16 l
g 01195 E
w ..,. - - --g_., .,--3 ----. w,.- ..-..,--w ,.-9,.m.,.geg, a-,,. -wym,.,,_..y-- 9--,g y.y-.,-,.Wg_- .,,9.--.p--o,,.-m,,w-p.e-w-wm---- y-,9
-U' Fig. 9). Occassionally, however, a dike extends over 20 feet, .
through Unit H and into underlying units (Fig. 8). These dikes
-in all instan:es merge with fractures or offsets which continue at depth below the lower extent of the dike (Fig. 3 Sta. 340 to 390; Fig. 8).
.I
- 7. In the upper part of Unit H, many dikes also extend undisplaced across offsets (Fig. 3. Sta. 400 to 410) indicating that development of these dikes post-dates development of the offsets.
- 8. . The orientations of 104 dikes were recorded at three locations of the trench (Fig. 3, Sta. 200 to 240; Fig. 4 Sta. 180 to 250; Sta. 300 to 310). Similar to the orientations of fractures and offsets described earlier, the orientations of the dikes are I
locally consistent on the limbs of individual depressions or
.. arches but vary greatly from fold to fold. The dikes typically
! are vertical with principal average trends at the three
! localities of approximatey N45E, NSW, and N60E, respectively.
Dike orientatigny at Sta. 180 to 250 '(Fig. 4) are particularly significant for assessing the origin of the fractures in which the dikes lI. formed. These dikes are extremely well developed, spaced 1 to 2 feet apart (Fig. 9), and occur over a 70 foot distance across the center of a i major depression. Based on 56 attitudes, the dikes show a progressive variation or rotation in strike across the depression from N20E to N35W.
17 0119g
I '
At Sta.180 to 200, multiple att itudes on the same dikes indicate that the dikes are near vertical, arcuate structures. The progressive rotation in strike, arcuate shape, and spatial association with a depression strongly indicates a genetic relationship of fracturing and suissequent clastic-dike development with growth of the depression.
I 4.3.1 Orimin - As described by Heron and others (1971, p. 1801), the origin or development of clastic dikes involves three separate but interrelated problems: (1) origin of the fractures; (2) source of the clastic material; and (3) method of emplacement of the dike materials.
The field relations described above indicate strongly that the clastic dikes result from weathering and soil-forming processes preferentially
-. enhanced along local, pre-existing fractures, joints, and offsets. As described earlier, the fractures and offsets probably resulted from l
I tensional collapse during subsidence and development of depressions in f Coastal Plain sediments. There is no evidence in the trench to indicate concurrent fracturing with dike development due to stresses imposed by volume readjustments resulting from either soil weathering (as described by Johnson and Heron, 1971) or by soil dessication.
l 4.3.1 Remional Character - To further evaluate: (1) the source (s) of clastic material; (2) alternative methods of emplacement (e.g.
liquefaction or infilling from above); and (3) the role of ground water in their development, exposures of clastic dikes in an area within 25
' miles of the trench were examined to assess their ret,lonal occurrence and 18 0119g
-I I
character. These studies indicate that clastic dikes in the area have the following conson characteristics, in addition to those observed at the trench site:
I 1. The dikes are widely distributed through the region in deeply weathered clayey and silty sands of the Hawthorn and Barnwell Formations.
- 2. The dikes occur in nearly all exposures of the weathered profile but are race in exposures of stratigraphically lower, less weathered sediment.
- 3. The dikes are typically near vertical features with consistent local trends at three large exposures of N55E, N15W, and NSE, l
I respectively.
f
- 4. The dikes contain a central zone of bleached host rock bounded by a cemented zone of iron oxide. Sose dikes contain a clay l
Core.
- 5. Grain size analyses on samples from three localities indicate that the dike interval contains the same grain size distribution l
as the host sediment with slightly more silt and clay (excluding the clay core).
I g 0119g 19
i I 6. Pebble interbeds in the Hawthorn and Barnwell in several instances continue across and are contained within the clastic dike without evidence of vertical displacement or upward or
'.. downward movement of pebbles in the dike.
- 7. The dikes and associated mottling are clearly associated with changes in sedimentary facies. In some cases, the dikes and mottling abruptly die-out with depth at an impet mable and unruptured clay bed which apparently served as a barrier to ground-water migration. In other cases, the dikes become less frequent and die-out laterally as the host-rock matrix changed from a tight sandy clay to a less consolidated coarse sand and gravel. Permeability apparently changed from fracture permeability in the sandy clay to porous permeability in the coarse sand and gravel.
g 8. Ground-water migration along the dike is strongly indicated by common " pipe" structures within the dike. The pipes pinch and swell and are lined by cemented iron-oxide.
- 9. Geochemical reaction with ground water is indicated by concentric zonation in the host rock of iron-oxide accumulation around the dike. An interference pattern of this zonation commonly occurs where dikes cross one another.
I .
20 0119g
.,,, , . . , , ~ , . . - .
.m_
F I
_ 10. The clastic dikes appear to perpetuate fracture permeability g through a positive-feedback mechanism as the dike develops.
I. shrink and swell of the clay in the core of the dike rtintains an open fracture along the length of the dike. The open fracture enhances ground water migration, weathering, and
( accumulation of additional clay d ich, in turn, shrinks and swells. These open fractures are present today along many I. clastic dikes extending to several feet below the surface.
L
,.E
- 11. Infrequently, some dikes are laterally and vertically discontinuous and form an "en echelon" pattern suggestive of tensional stress fracturos.
=
- 12. At several locations, clastic dikes are developed along small offsets; at others, the clastic dikes are displaced by small
.E reverse faults.
- 13. Regardless of the origin of fractures, joints and offsets, clastic dikes appear to develop if the proper conditions of U weathering occur.
c b
5 4.3.3 Rezional Orimin - The field relations and laboratory data from the trench and surrounding area indicate that the source of clastic material is largely weathered in-situ host sediment supplemented by i_
i g do.o rd and m era 1 trans1oca uon o, es , prod _ ts e , ge _ d ter and um
=
e a g 21
- 0119g
I
.E pedogenic processes. There is no evidence of liquefaction and fluid injection or of clastic infilling from above: (1) There is no lower or upper primary source for the clay or clayey sand contained in the dike; (2) The "en echelon" pattern and continuation of primary sedimentary bedding across and within the dikes are difficult to reconcile with injection or infilling of material; and (3) the dikes do not exhibit the characteristics of liquefaction conduits described by Cox and Taiwani (1984) and Cox (1984) in the Pleistocene sediments near Charleston, S. C.
(The liquefaction dike conduits were highly variable in orientation and thickness and rapidly flared toward the surface into an inverted cone shape). In addition, many characteristics of the dikes (e.g., chemical zonstion, piping structures, clay weathering and accumulation) require an extended period of time to develop and are not the result of relatively instantaneous events such as faulting, liquefaction, or sediment infilling. In a sense, to define these features as " clastic dikes" is a misnomer in terms of their origin. The term, however, has attained common
! usage in current literature of Coastal Plain geology and is thus retained in this paper as a descriptive term for these features.
l 5 4.3.4 h - The age of the dikes exposed in the trench is poorly constrained. They are younger than the parent Eocene to Miocene deposits of Units A through H (Barnwell Group and Hawthorn Formation) and younger i
thau sediment collapse which produced the fractures and offsets along which ast.y dikes developed. They probably developed during the major weathering event which produced the relict paleosol on Unit H and are l
I 22 0119g I . . . -. _ - - . - - - - . _ . , . , . ~ , . _ _ - , _ . _ _ . _ . _ _ - - , , - - - . - . - , , _ . . - - - - - , _ _ . - _ _ _
thus older than the middle to late Pleistocene erosion of the Unit H paleosol and subsequent deposition of the late Pleistocene and Holocene solian sand of Unit I.
I 4.4 Sand Dikes I Sand dikes occur at three localities in the trench (Fig. 3, Sta. 570 to 590, Sta. 642 Sta. 830). The locality at Sta. 570 to 590 contains a large complex of sand dikes exceeding 20 feet in length. The latter two localities contain single, laterally discontinuous, thin dikes. The dikes consist of lavender, loosely consolidated, well sorted, very fine, clean quartz sand and are everywhere contained within Unit D.
orientation of the dikes varies greatly. At each locality, they dip t
steeply down the limbs of large depressions and flatten upward toward the crests of arches (Fig. 3, Sta. 570 to 590). Near their upward terminus, the dikes locally flare upward or sag downward (Fig. 3. Sta. 585 to 588). They locally intersect but do not penetrate Unit E; rather they migrate up-dip along the contact (Fig. 3, Sta. 575). Downward, toward the trough of the depression, the dikes thin, become irregular, and are difficult to distinguish as they enter Unit C.
lI l The sand dikes locally control the rate and direction of ground water flow. The dikes interupt ground water iron-oxide laminae and liesagang rings within Unit D and locally produce zones of iron oxidation which lI 23 0119s
_ __ - . . _ _ . , - . _ _ . . . . _ _ _ _ _ - _ . .__ _ . __ ___ _ _ _ . . , . - _ . _ _ _ . . . ~ . _ _ _ _ .
I ll
'W transect Unit D (Fig. 3. Sta. 570). In addition, thin bands of white
- kaolinite clay concentrated by ground water in the host sediment concentrically border portions of some dikes (Fig. 3, Sta. 575).
! 4.4.1 Orizin - The dikes probably originated by tiuid or plastic injection. The dikes have an apparent lower parent source in the fine i
sand beds of Unit C. Although a direct connection of the dikes with I Unit C was not observed, the fine sand of Unit C is nearly identical to the fine sand of the dikes: loosely consolidated, well sorted, clean, and predominantly composed of quartz. Close spatial association with limbs of major depressions suggests that the liquid injection resulted from development of the depression. Hypothetically, a sudden increase in overburden pressure during high water table conditions in response to subsidence and sediment collapse may have locally mobilized the loosely I consolidated sand of Unit C and possibly of Unit B. Plastic or fluid i
migration of the sand up-section probably occurred along previously dei,aloped or concurrently developing fractures in the overlying brittlely I deforming sediment.
i 4.4.2 Age - Age of the sand dikes is moderately constrained. They are l
younger than Units D and E and, if the dikes originated during sedituent l collapse as postulated above, they must also post-date Unit H because this unit is involved in the collapse. The dikes, however, are older than a subsequent period of sediment collapse which produced minor displacement of the dikes along offsets (Fig. 3, Sta. 580). The offsets, I
I 2.
I
I .
W in turn, localized clastic dike development during paleosol weathering of .
Unit H prior to erosion of Unit H in the Pleistocene and deposition of the solian sand of Unit I.
5.0 SUlstARY I
Coastal Plain small-scale structures evident in the VEGP trench are
. interpreted to be local phenomena related to dissolution at an underlying carbonate bed, the Utley Limestone, followed by one or more phased of plastic and brittle collapse of overlying sediments. They are not tectonic features nor are they indicative of regionally significant seismic activity.
Collapse of sediment over the disolving limestone created depressions in the Eocene and Miocene Coastal Plain strata. Fractures and joints are spatially associated with the depressions and _ resulted from brittle, tensional failure of consolidated and semi-consolidated sediment.
Displacement along many fractures resulted from irregular differential settlement of blocks. Most of these displacements are normal into the subsiding depression and many fractures and offsets are continuously over the center of depressions. The offsets are local in extent and small.
Wo offset extends across both walls of the trench.
I Sand dikes resulted from plastic or liquid injection of loosely consolidated fine sand into the overlying, fractured, relatively I
I =
0119s
I I consolidated sediment. The dikes dip steeply down the limbs of depressions and probably mobilized in response to increased overburden pressure during the early phase of sediment collapse. Fracturing and faulting during subsequent phases of collapse locally cut and displace the sand dikes. Clastic dikes resulted primarily from weathering and soil-forming processes preferentially enhanced along pre-existing fractures and faults. Their present geographic distribution is II controlled by the depth of weathering and paleosol development in the Hawthorn and Barnwell sediments and by subsequent erosion of the land 3 surface. Major dike trends at three localities in the trench, three localities in the surrounding area, and at localities reported by secor (1980), Heren (1971), and Zupan and Abbott (1975) vary widely supporting a local control for their development as opposed to a regional tectonic control.
The chronologic sequence of events leading to development of the small-scale deformation structures includes:
l 1. Deposition of the Cretaceous to Miocene Coastal Plain sediments.
LI l
- 2. Partial dissolution of the Utley Limestone.
iW l
- 3. Subsidence, collapse and irregular, differential settlement of the Barnwell and Hawthorn atrata probably in a sequence of
- phases. Local thickening of beds into depressions suggests thal dissolution and collapse may have begun during seditent deposition in the late Eocene or Miocene.
g ,
m 9g
I I
- 4. Plastic or liquid injection of sand dikes during an early phase of sediment collapse.
I 5. Fracturing, jointing, and offsetting of strata concurrent with sand-dike emplacement and during later phases of sediment
, collapse and differential subsidence.
- 6. Major episode et erosion which lowered the deformed surface of the Coastal Plain sediments to a relatively planar surface.
I
- 7. Development of clastic dikes during a major period of deep surface weathering and soil development.
'I 8. Local erosion and channeling into the weathered Coastal Plain surface.
- 9. Deposition of solian sand during the late Pleistocene or l Holocene.
- 10. Holocene surface weathering and weak soil development.
I I
lI I
I 2, 0119g
!I
I
6.0 REFERENCES
Cr". J . , aaM Ta l um i , P,, " Discovery of a Paleollouefaction Site Near Charleston, S.C.", Geolomical Society of America. Abstracts with I Protrams, v. 16, No. 3, pp 130, 1984.
Cox, J., "Palooseismology Studies in South Carolina". University of South I Carolina, Master Thesis, 1984.
Georgia Power Co., "Alvin W. Vogtle Units 1 and 2 Final Safety Analysis I Report", Appendix 2B, Section 2.5, 1984.
Heron S. D. , Jr. , Johnson, H.S. , Jr. , and Pooser, W. K. , " Clastic dikes I in the western Coastal Plain of South Carolina", Geological Society of America Special Paper 87, 1966.
Heron, S. D., Jr., Judd, J. B., and Johnson, H.S., Jr., Clastic Dikes
' I Associated with Soil Horizons in the North and South Carolina Coastal Plain" Geological Society of America Bulletin, v 82, pp 1801-1810, 1971.
I Howell, D. E., and Zupan, A. W., " Evidence for Post-Cretaceous Tectonic Activity in the Westfield Creek Area North of Cheraw, South E Carolina", South Carolina State Development Board, Division of lg Geology, Geological Notes, y 18, no. 4, pp 98-105, 1975.
l Inden, R. F., and Zupan, A.J.W., " Normal Faulting of Upper Coastal Plain l Sediments Ideal Kaolin Mine, Langley, South Carolina", Scuth Carolina State Development Board Division of Geology, Geological-Notes, y 19, pp 159-165, 1975.
Johnson, H.S., Jr. and Heron, S.D., Jr., " Slump features in the McBean l Formation and younger beds, Riley Cut, Calhoun County, South
! carolina", South Carolina State Development Board, Division of l Geology, Geol. Notes, v. 9, no. 3, p. 37-44, 1965.
McDowell, R. C., and Houser B.B., Map Showing Distribution of Small-Scale Deformation Structurus in a part of the Upper Coastal Plain of South i
8 Carolina and Adjacent Georgia" U.S. Geological Survey Miscellaneous Field Studies Map MF-1538, 1983.
Secor, D.T., " Geological Investigation at the Chem-Nuclear Waste Storage site, Barnwell, South Carolina, February 24, 1980." Allied-ceneral Nuclear Services.
ll W Seeber, L., and Atinbruster, J.G., "The 1886 Charleston, South Carolina
[
Earthquake and the Appalachian Detachment," Journal of Geophysical Research, v 86, no. B9, pp 7874-7894, 1981.
I .
0119g
I .
Siple, G.E., " Geology and ground water of the Savannah River Plant and Vicinity, South Carolina" U.S.' Geological Survey Water Supply Paper 1841, p. 57-60, 1967. ,
I. Zupan, A.J.W., and Abbott, W.H., " Clastic Dikes" Evidence for Post-Eocene
(?) Tectonics in the Upper Coastal Plain of South Carolina", South Carolina State Development Board, Division of Geology, v 19, pp I 14-23, 1975.
.I I
l I
lI I
I I
I lI lI lI lI '
2'
'I 0119g
,I
' ~
LI s
(I 3
i g
.I
.I I
I I
I "fsbO@@
I
- I g
,E
.I I _ _
E Table 1: Infonnel stratigraphic Units Exposed in Trench Wall Unit Thickness (ft) Litholoar I 5 to 20 White, gray and tan, well sorted, loosely consolidated, fine quartz sand. Locally cross-bedded and unconformably overlies Unit H.
H 5 to 30 Yellow grading upward to red, moderately to poorly consolidated, sorted, sandy clay and I clayey sand. Gray and white clay mottles and clastic dikes locally conunon near upper contact decreasing in density down section. Strongly developed relict B-horizon locally preserved in I~ upper part of unit at contact with Unit I.
G 1 to 3 Red, consolidated clay, silty clay, and clayey silt. Many lane, prominent mottles of white I clay nodules.
F 1 to 2 Moderately consolidated, laminated, red and I yellow, moderately sorted silty fine sand.
E 1 to 2 Weakl'y, consolidated, moderately to well sorted, red, fine sand. Thin layers of consolidated I silt and clay locally present in lower part of unit.
D1 1 to 4 Locally overlies Unit D and is bright yellow, moderately sorted silt and fine sand.
D 4 to 7 Light to dark yellow, moderately consolidated, poorly sorted fine to coarse sand; generally bioturbated, locally mottled white with weathered shell or clay material.
C 4 to 6 Poorly consolidated, grayish-white, mottled red and purple, moderately to well sorted fine to medium quartz sand.
I B 2 to 4 Yellowish-tan, moderately consolidated, moderately to well sorted sorted, fine quartz I sand.
A 1 to 4 Loosely consolidated, gray to yellow, poorly sorted coarse sand with sparse pebbles.
I At 0.5 to 2 Lense of tight, grayish tan, clayey slit everywhere contained within Unit A.
I g 30 0119s I _.
g . .. - -. . - - . . _ . -
I ,
~
I I
.I
- I I
[I I ,
lE lI -
'I
'I FugilT@s
.E I
i l
I I ,
I-__ -- _ _ __ _ _ _ _ _
t I
,r - - -- - m
[ l- _ _ _ _ _ _ _ _ _ - - -
4 t_ _ _ - - -
G 1 8 4 \
,+0 \
g 4
O ** O G 5N e ATLANTA $ ,%
E O4N ,,7 i- 3 / <-
4 9 /
UGUSTA 9 /
\ S,,_ SOUTH C AROLIN A
! 9 A e* 1[
p\b j
TRENCH '
SITE VOGTL - 3, PLANT f
[g \
gV CHARLESTON 1
y r-I sEoRG1A sw 3
OD '
j/
' e ~
L ll h NG I l w*4 "
/
' @)
.g
\, b49 !
rx.j$y ~
I '___________________t ,
o
!I FLORIDA ' scA m ,N .,ms SEC5TEL LI VOGTLE ELECTRIC GENERATING PLANT TRENCH STUDY
,l
\
INDEX MAP
- I g ,,euee i
-.. ~~ -.. - - - - . . . -
I l.
1 L
l l
l l
l s
~~.:n r : 2 2. r=
- 6,. paan
, _ s
( ,
m .-.z v- ,.
- , m m- -
4 .
r ,. : 44, . -
a-a >.,. , x,p c.n
. ;g
- y' -s . ,ft ~,gi*-
m e-., l l . .- .. ,,
l I .- I K
Nhhh h- l
. x.
~ , ., , m y
- ' a e'
...% ,'- ( 5, gr,,,,a. x ,** , l p, g p" -
_ p 7
.. k, i 2). ;
3' Gl'~ ~-
, ? 6 k.,g- 'f,j'4 ,*,4
,.k & '
[. .
' j ff~ A p l h ! ' l
t u*t v .. : . .
,a,) , - .- w
- r.
'..s . . _ ._ y : ,l W - ~ - e' s~ .
'~; i .
./ 'r - ,
. s _, .
.,' J
,_,m- -
~ p, ' ,r., . ; Y r+ . .';, .'
. . :_-~ ;- '- . y- 'p.
M
(*,.. 'N ~
_ . ,.9, ',n - ! . . -
- se a ./
. ... . p ',a, ar j ,
( ~
.c - . ,
~ "p # f ~ . ' p - /,.j * . y '
j
_' .,- N_,- 4 ,
I Figure 2 - Longitudinal view of west trench wall showing magnitude of contorted bedding.
, l l
l I,
t l
i 4
I '
I
_ _ m
- NORTH I CHAfGELL M MS MLW IN LOOSE SAND sg
- f L(? .*f" u= Ji AtT21. P -
,n n,4 N 1 mt
- a. ., ,, ,
0 "Ma : arut..,. -
~
C OSSCURED NGOW M l0 W 1sTS w COE S NE g5 EE y : g s g , , ,
I a 3 I I 3 i i i 3do 350 I
300 se S T A T 1000 (F E E T )
telGRATION ALONS B
7 aSE OF 43047 E i
OVERTWII
/
I ,
\ Ste. 900 '
\
N N eEvas.E g va:= Or Sase omE c0 m.Ex N
N '
\ /
x .
\g /
'N. _ % , ~
/
- ~ g ~g +B-NDRIZONy -
te. . . .-
..... g g\ \ % g,ggj[gy[yj
.1 f**"
,/
- W
'" /
Sa.o r /
5 -
fC-r nx - -
M ggg, y hu. 900C45tED
.N
= S.0W E
gig
, , , .. ,, ,,E s I g I y i SSO s s 'i 400 se i s s
\i i 900 S T ATIO N (FEET) / \
\ ,
H@ E DIRE i 000$ PLEX D <
C s
M N 8 SYO
s'"
ARCUATE FRACTURES I FAULTS, AND CLASTIC DIMES
, r n.
7...y.. ,*,\ ,I=="
i .',.S. NORIM*
a '
- * * ',,,"' .Jft, ' ",',, ,'g .
" "f .' .#*y(""*J
, , , ,y p,,[n s','"% ,' .**%9 l,~ . a H **
H %
D _
Y W h85W OBSCURED N35E W40E OBSCURED ISSW 2SSW IJ EW,28 SW 244sw geSE 3 3 3 1 3 8 3 I I I i a a i i u a i 3 .
SSO S00 450 400 3 T A T I ON (FEET)
L EGEND FLARE
/
... . Lithologic contoct, dotted @ = Eolian Sand where poorly exposed Offset @ = Howthorn(?) Fonnetion
- = Bornwell(7) Group
Mojer fracture or }oint.
8 5 5 % % A Clostic dike
\
l N 8
sN -
Base of soll B- horizon N80*W,25'NE Bedding attitude
\
- ,,,0TO VIEW A NOTES *-
% s uwew-I. Photographs teken free top e( esposite mail WEST EAST 2. Trench bearing N25'W 4.,
1 MN4/AsW//
SOUTH E IU OBSCURED
.. .. . _. L.- yy.7 ,: +.gg. =y = ~ ;- ~, . ;- . .;.g.._;.-
[ " .-
SAND DEE
~;. .,f .v N
% A- ;"" ,y,3 "~ . g... g.
C sa3
, SLUMP Af g 4 OBSCURED j ARCUATE FAULTS AND FRACTURES NIOW N I5W M40W M50W 8NE toSW 10NE N25W,10NE 28 NE
. . . . . . . . . . . . . . . . i SSO 800 750 TOO STAT 1ON (FEET)
FICURE 3 - PHOTO-MOSAIC AND GEOLOGIC INTERPRETATION OF TRENCH, WEST WALL.
. . .. ye ag . , - - - '
U
, n . ,.' . ,
. , m ..
n, - . - =...
, , . . . . . , , s..,
D ,
.c 7
- m. j g
., ,t.e w ..c-. .
-~ 4 i,,
M. ; - -
~
- a.c. . v g . w.,.
---:. m .
M..., . ,
- m. -
g
- . 4, 2.4. . 'w> . $ ~
'{, ,* ,, @ auny =~gg - ..,,,;-g . .
. - r - ~ , . .
3- , -, ., no ' ..s,; & . . ,,S
- '$ ,' . < - r-
.;.fy* f 5 5-? -
% O *'lf' ' ' *
?
l =
4 I
e- -g ry, "
-, f& =
t . .?
l - ~
l
, bY$
i c
,g
, , . . -w -@
'1.
+
4 h
- m. .t ass- w+* _
..e a* g V f9 -- - - * *
' ' ,, .miele
, -- , c
' ~ ,, ,m g .- ' ~ 4 .a6 * . -
.AYE g .-- '? ~ k : ' ' ' .
l sy .. -
. s. & n '
t
~ -
a ' ~ . --
xg
~
e.d * '"
-e ,
y, g y .- ' *[ f * ' ' " *
\,' /
, . v '
M Q ggye r- - _. a -sm . : .
,,.s r.
'A . :=s,. Q - .% .
[
,' .-g , . - ,
" . ' lt
'g -
I T te '~ -~71 r 3_p
, , ":" L
. w : e, a . _= -
.~
- - ,, c u _-
y
@'+-y. ,*
> .S.. , jim}~ .
_ a
)
p[
4 W ?d - d .-;c
.e gq,4. ' y.5 c
,_.._.?
,#y.7' D,' ll P. .. ? 7 ".Y. ,~ r...,---;
NO *en%]
%g,, . . . . w . w.; v.. _ _
' >., ; .. - . , ,' , me - 1.w ~
-)h . 8.W
' ose swsJ %L : R :, '2RT,g~y O'l'O %.-fu= +g~i%%. Q
,..u _
_ ~: ' - L . - - _ _.
.d
,.g 3 0 g t" m u u arts w " -
- ---:. x.~_.__._. _ . 2 -4
=.x 7 g
. A
, =
I ?
.... 's* ,r e s - r .. \'. s ',' ',=a' m l l I *) '* ";
W
- \.t i
- ( H t H ............ ....-
h-No e
- o
k C 'T A r =_ ' E c
' R OBSCURED 3
ass w u so w u sS E a no s m ao r. u lot 2SNE SSE - T eNw 353E SNE seSe _] ,
g i i i e i i e i i e i i i i ebo 650 700 sto STATION ( F E ET) ;
LEGEND
~ 'l 6
Bedding attitude UNIT 1 M80*W,25'NE Lithologic contact, dotted where H = Eohon Sand i d
- - - 4 poorly exposed 1 5-
@ = Howthorn(1) Forraation O'fset W = Sernwell ( t ) Group 3 j
_ _ tsojor frocture or joint I b x <s = *
- Clostic dike ~} ]
' "1 _.
_._.-- Base of soll B-Horizon y.
osSCURED -I 300RTH ' i CHANNEL -
.}
MARGIN _,,,,,.............-
., ! '}
~
g , , - _ .
D I
- r.. . . . . .. .
- . . .. = .a ,s $. 5,.h H 7g 7 W
I o8SCURED .g y 'I =
l N m es s .i
-]
1 g% 23Nw - s t N -a
! N ~'
l i e i 8 I ' 'N'g' 3b g.
, i , i e i i i I
200 IN N b I STATION ( F E ET ) N .I l '
}]
3 I
.i
{ }!
I l i I , _
q g
.i 1 I l T --
l gio too 200
\ CHANNEL
' 4J MARG -a 1 e 3
- _=
B HoRIZoM 1. y i
ARCUATE CLASTIC CLASTIC H olKES -
DIILES 7 i l
...~..t.._._- - - . . . - . . . - - . ..a. a
. . , s
.;(
L.
SOUTH r-I _
r-H *,..***... . D. . . . . . . . . . . * * . . * . .
l L.
. . -ll . . . . J , ..........
... _]
.... ~ .
A.
s, ~4*
t -* w &,.'. 2 ., - j D 'E N 29 W 4094 E N20E SSW 199E r - N 35E 20NW
' I 24SE ' ' '
L a s y a i s s I
. s y a i g 850 750 000 S T AT ION ( FEET)
[
I*
h -_ -
ffM \
pf4gg L Photogrephs tehen from top ef opposite well m
EAST </
& 3
- 2. Trench' hearing N 25'W 35 f t.
~
, 25 f t. **-
L*
Aie i q ,
j -.
- w.mwhWW t I i .m a==* "
3 l , u. *4; <, g ==, ' j w %= *
,M i..
p*~m s -H . . . . .. . ::. . 1.*.*:::::'.:::: * ' ' . . . . . . . . as i
- O E' -C ,
f -
pf '"g's F _
C -
w
E l
= -
.L _ ~ A p __
HS0W NI5 W N 40W N95E NIS W SSW i
. . . . i
, . . i 500 550 400 450 S T A T IO N ( F E ET )
N
' N FIGURE 4 - PHOTO- MOSAIC AND GECLOGIC INTERPRETATIO
- N .OF TRENCH EAST WALL -
N
~
N N
L2 %m I I 'g 240 230 - N N
'~
^
1 s _-
.. s e-nomrom M CLASTIC SAGES
-}
-v, -,,,. .,-e --w .- ..,a., ,,_.a._,..-.-g~w._.,__.__,..n,,_,-..-__.-,,,_n,., ___ - __. ,
1
,d'9hNM'?- -- f C t 9 'Y T d .
au a iTPA. ' 2.?* Yh ~. M F Q w m ~ M b. 4
~ =: Q .
h$$bEI.I $sEhMNNd
- .4
- ew~3**
, __ .4
.- i ,, ., n. ....z
. - k%-.
M %,r, Y =
l s 4 .. -%- __,
E' own, _,
L.
,,,.c y g,-,,,-
3 ,4: *.e- , .
s
-4 4 t v.
g +, .&, c., * .
- y. .
g
- s. % .-
,. '. .x
%.4 :. y,_ ;. ga.g
. , , 4 ,
/
South Trench Bearing N25 W >
_ ) ( k'd N'T
\\N m
) '/ ) 'E ' S
Y 5 '/ ' '
i r x \ Wb N l$b Y h )l cN hk k$h
-25 #f, ,ff, ,A, , , , , , ,NNNM, , , , , , , W\, \\,\," /, /, ///ID, , ,a,W 850 825 800 775 750 725 700 675 650 625 600 575 5:
Sta!
Structure Contour Map, Surface of Unit F - Trench Plan View 250g d 2455
[240j -
j $*0.! = " " ' -
g2253 ~
2205 <
j s i s s i,<
- k 620 800 3
Outh 750
'25 4
650 1 600 575 550
- 25 Mesh Perspective View Statio n 500 Vertical Exaggeration 2X ee t) 450 i
3
\
North n'_' ' 2hW4444Ja;4 'L'u'd ' ' ' ' ' ' ' ' ' ' 'y ' ' 'y ') '/ / / / / i1 \ ' 'C .
b lA ,
]ll] h { /
lElRAshW: '/RMQ W A T~o n NM\\qT iiir ieii iiie iiei
,+2" ~N \ / / / / / / /
i i e ig' i e agi i i i 4,5 ieij'i'iss ' so ' 2s ' '
\ -
2o 225 on (fe2t)
TI APERTUR8 CARD furface of Unit F Explanation
+ Surveyed Elevation k ' -m 0 Elevation Extrapolated From Bedding Attitude
/
(/ Contour !nterval 1 Foot l
,/
.- )
5/ Also Available 6
'1'
,2 Aperture Card
~
- 9, BECHTEL 523 SAN FRANCISCO 37s Vogtle Electric Generating Plant 3
323 . Trench Study 0
273 ,
Surface Geometry 2s0 I of Unit F Nor th ' " " *
- 9510 Figure 5 .
_ _ _ (4todolff -01 .
y., gg g g g, s . . .de ' -e. . a r & id D' 8 l'Af.4J' 1 . m W,-. app .a 4% ~....
.e
.i~ 4 .
.,4 w A 7,- . , e ,,?: > ;u,d
- A. , 'a ~ < ., v >
r v. .x - ..
.h h-k
( k# *f 'A ge',
,', L ', " r, w a. . :wa- -
-r u :
WQ2% l }y,, >r > '
. . \
" w f n *h. W .: #;'
. .c?,, .p + M - 4 '
- f . p ; g-.v- '1 4 : .
k
=
n,: . ., .
- a. 1
. .g; _ s _ ,i s . ..Ay, ^, "
... .. y.
t
.., ;' w g
_ . , . - ,. .' . . . . ;fs '
.qu!;
a
..,..e$.,,,, 'e .
L
,... t ,
. ;. , 'O :4
'**s-
.,....L'.
tY ' ',.a ..* Q $7 {.. - , * ' - ' *y *A.
4
%namu Figure 6 - Small offsets with displacements ranging from 1 to 24 inches; west wall -
Station 360 to 410. Offsets typically have normal displacement toward depressions.
I
-g f
- r,ag ,s W ._ . . , - .. . ,. . . g- ,, ,
l .. f. -
wesasy h W . , f 4 ~.T
^: - W g, i
=
W,' p , g h_. -
l 4 .76 N '1
?$ v/ k
- d ei ;e, f;W. U:. , ;. ' , -e - 24. 1,p n*v in * %.Y. . (N\..J
- w .
r#
f j- ? 'h { .
'.?J' l b :. y
- 4 %d
~~
', }.
.i h'- $
~
) s.' s ~ 7 f.
(( , ] .. ' .
..I t._ _, f _ ' ~ 1 - -
- .,p .
] .. ,
., ,? ._ . ,, _ ) ,
- '.x - '
s- -
1 J -
p &y *
-s, . -
V+
l-
^
b :
. . , o , ,'_
- a. . . > . . .. .-
. . .y . .
. .., I ,
.a m
n .. ; . -
.. , .<. 4,'. ,
- y. .
- Qu,,s'. . R . i .
s - *. . .o..,,..
, s tr. % ..3; ,
.f . . -
.s
, u.agy .
- n. .
. a ~~.
' _ h. f.w :. %At
%.~y . ; } A.. ' .s N' - &,dWJ)
-- n. .
.t.
.a_,. _, ,
j Figure 7 - Arcuate faults, fractures and clastic dikes over center of depression; west wall-Station 430 to 490. E ._-___._. _ ,-.____ _ __ .._ _ -._ . _ _ _ _ - - -- - --
_._...=.u;_==-----. -- - -m--- --_m., _ _ . _ _ I p .e .g e, 4.; .- . . h w- t,ar%.e %....s a-- b - -
,,fyj),;. ,
?A.
- ,* ,, .:r - w-2a > - - - * . , ,
W
. ,. ] , ; r ypi
. y = % 1 -- S'.'W. .iiti'.
.s M'W-W"g.,"*:,Y
...,4 ..
$ XW*
. t -
a4-6 Mm=4AAdvper.M4sg,
,d,w s.
- p. , ,, , p.
,, : q .,- .
W w*==4 ..t V... %..< w.g 3, .
; . . . .. ct,e . ,- s g .,y p, g . , . ..-
3..+ ., .1 : l _ _ , , .y m . .@= l 'I t4 _._ 4 t;3, . . . ,
.4 5 .',.;gq. , , - l
- n. .,
. . e,r. . , s. }.:)
pg. .- .w. g.. v c3r. . - , - j' ., at , . .-
,E
,. g .
j
<. s..
m ' h.,- ]
.? '
, .,a
-~;-
v a n .
$- . _ , . (p; s,. . . . . .
<-. ~- t y . . .. . . . . . _ -
~ #
- 4 g ;. , .
~ '
E . . ,
,,, , , * . . J=# ysi .:y w . = > - f . ,. ...j
. ,- t- , , . . -
lI ' - Figure 8 - Clastic dikes in upper part of Unit H; east wall-Station 570 to 610. Dikes generally I decrease in density downward. Where dikes extend into underlying strata, they are l coincident with minor offsets or fractures. I
X .
,f
[.. ~
*~
Q } .
.. ' /[ [-h "h d N, ..
k1 /,( ... -( 4 1g p' !,;QM>(h?Q:.? Q ;;.{.p%
)' ;. '!
*h' {g) S ~ Y... ,;4A'* e, ',f.l y. . ( . 4.g g.,.g e ..
i s
'c.s ;
-wN K. x .- : t =. y(.
S'~WV + , : R <. .>. s.,a v . 9 ' .t 2 ,,(.. g,g ;' g . \ ,
,'T>,, .
!' ' l g .-. . g>f y !, g,i ' .' . \ *. * ' .' , s , g l , .
x c. ,. A ,, , . l y) . . y(.,4
;1 wx.; ;
'-. 3 f }. l., , 'Q . '
s f i.(O s ' . \ O.h ) l
..N.s n.. ,7 I
-Q', . ..-
..y , ; . ' ,Si . ,.
(. .,
, A P v. ~
~
- e f.p '
1 L ' '- ,,
. ji ' . % C i -* .
4; y h R, , y ; ?- fiQ _ ~ ? := Figure 9 - Clastic dikes in upper part of Unit H; east wall - Station 220. Better developed dikes have an inner core of white clay. Dikes thin and generally pinch-out downward; upymrd they merge with brown soil B-horizon or are truncated by white eolian sand. _ \}}