Orientation of CRP-3 Core, Victoria Land Basin, Antarctica
R.D. JARRARD~,, T.S. PALJLSI~N*,
&T.J. W I L S O N ~
'Dept. of Geology & Geophysics. 717 WBB. Univ. of Ulah 135 S . 1460 East. Salt Lake City U T 841 12-01 1 1 - U.S.A.
^Dept. of Geology. University of Wisconsin. 800 Algonia Blvd.. Oshkosh. W1 54901 - U.S.A.
'Pept. of Geological Sciences. Ohio State University 275 Mcnclciihall. 125 S. Oval Mall, Colurnbus OH 43210 - U.S.A.
Received 28 October 2000: accepted in revisedfin-in 22 February 2001
Abstract
-
CRP-3 cores were not orientated with respect to North during coring operations. However, borehole televiewer (BHTV) logging did obtain azin~uthally o r i e n t a t e d images of the borehole wall, and c o r e processing included digital imaging of the outer surface of 85% of the cores. Images of many individual core segments can be digitally joined, or stitched, by rotating them to match the shapes of their adjoining surfaces and then closing the gap. By aligning features (fractures, bciiding, and clasts) on stitched-core images with correlative features on orientated BHTV images, we reorientated 231 m of core. or 25% of the cored interval. We estimate that the orientation uncertainty is  ± l o for entire stitched-core intervals,and  ± I S for individual features such as a single fracture or palaeomagnetic sample. Reliability of core orientations was confirmed by comparing azimuths of bedding and fractures measured directly within these reorientated cores to those measured within orientated borehole televiewer images.
INTRODUCTION
The C a p e Roberts P r o j e c t (CRP) is an i n t e r n a t i o n a l drilling p r o j e c t w h o s e a i m is t o reconstruct Neogene to Palaeogene palaeoclimate and the tectonic history of the Transantarctic Mountains a n d West Antarctic rift s y s t e m by o b t a i n i n g continuous cores and well logs from a site near Cape Roberts, Antarctica. Offshore Cape Roberts, tilting and erosion of strata have brought Miocene to Lower Oligocene sediments near the seafloor, under a thin v e n e e r of Quaternary s e d i m e n t s . T h e t h r e e C R P boreholes penetrate successively older portions of a
1600 m composite stratigraphic sequence.
The third CRP drillhole, CRP-3, cored 821 m of L o w e r O l i g o c e n e and p o s s i b l y U p p e r E o c e n e sedimentary rocks and 116 m of underlying Devonian s a n d s t o n e ( C a p e R o b e r t s S c i e n c e T e a m , 2 0 0 0 ) . Drilling and coring occurred in two phases: HQ-size drill rod (6.1-cm core diameter) was employed for coring of the interval 3-346 mbsf, followed by NQ- s i z e coring (4.5-cm core diameter) of the interval 346-939 n ~ b s f . Average core recovery was 97%. The section consists prin~arily of sandstones and muddy sandstones; other lithologies include common thin conglomerate beds and less common sandy mudstones and diamictites (Cape Roberts Science Team, 2000).
Cores from the three C R P drillholes w e r e not orientated with respect to North during drilling. Many C R P - 1 c o r e s c o u l d b e r e o r i e n t a t e d u s i n g palaeomagnetic techniques (Paulsen & Wilson, 1998), and many CRP-2/2A cores were reorientated (Paulsen
et al., 2000) based on borehole televiewer (BHTV) measurement of azimuths of petal center-line fractures (Moos et al., 2000). Our study applies an alternative technique to reorientate CRP-3 cores: alignment of features (fractures, bedding, or clasts) on core-scan images with correlative, orientated features on BHTV images.
METHODS
CORE DATA ACQUISITION AND PROCESSING Essential first steps for core reorientation occurred during initial core processing at the drillsite. These steps included identification of core runs that could be fitted together by matching fractures across run breaks, refitting core across fracture breaks within core runs, and logging of all fractures where spinning of the core between drilling and entry into the core b a r r e l had d i s r u p t e d t h e continuity of t h e c o r e . Systematic examination and logging of all core breaks then allowed us to p a r t i t i o n t h e c o r e i n t o i n t a c t intervals which had undergone no internal rotations.
Each of these intact intervals must be reorientated independently, s i n c e rotations between adjacent intervals may have occurred. In CRP-3 core, -300 independent intact core intervals, ranging in length from 1 0 cm to 30.4 m , were logged. To date, our reorientation analysis has focussed on the longer intact core intervals and on intervals within heavily faulted zones.
Upon recovery and reconstruction of the core, red and blue scribe lines were drawn -180' apart along the length of the core. Dip and dip azimuth of ; i l l
core fractures were measured with reference io the
"ttrbitrary north" defined by the red scribe line. The c o r e was then cut into 1-111 s e g m e n t s . For all segments of core with enough integrity to pennit handling, we scanned the outer surface of the core u s i n g C o r e s c a n @ e q u i p m e n t leased from DM'l', Germany. The Corescan@ obtains digital images by rotating the whole core on rollers. After scanning. the c o r e was moved to the physical properties lab I'or analysis, split in half lengthwise at -90Â to the scribe lines. and finally the two resulting half-cores were placed into an archive-half box and a working-half b o x . As a c o n s e q u e n c e of this c o r e p r o c e s s i n g procedure, it is possible to retroactively reorientate any core features ( e . g . , bedding and fractures) or samples (e.g., palaeomagnetic plugs) with respect to North if two conditions are fulfilled: orientation with respect to the red scribe is measured, and the core interval has been reorientated with respect to North.
In post-field processing, we selected 17 intact core intervals for "stitching". Stitching is the process of digitally joining two or m o r e whole-core images, using DMT Corelog@ software. Using this software o n e c a n apply differential r o t a t i o n s to a d j a c e n t segments and merge the images into a single restored (pre-break) image. T h i s digital stitching is m o r e accurate than the manual refitting of core segments undertaken just before red scribing. Although the red scribe is positioned at the t o p left margin of each stitched-core image, downcore drift of the scribe away from the left margin occurs due to imprecise scribing.
S t i t c h e d c o r e i m a g e f i l e s w e r e i m p o r t e d i n t o WellCAD@ software at a vertical resolution of 1 mm.
After import, image files were converted from color to gray levels, then displayed using a false-color spectrum encompassing a short amplitude range, to enhance subtle variations in brightness. We assumed a uniform core diameter of 61 m m for H Q cores and 45 mm for NQ cores.
BHTV DATA ACQUISITION AND PROCESSING Borehole televiewer (BHTV) well logging was undertaken during three separate phases of CRP-3 drilling. T h e BHTV is an acoustic instrument that provides an image of surface reflectivity of the wall of a fluid-filled borehole (Zeinanek et al., 1970). An acoustic transducer in the tool fires a sound pulse that travels through the borehole fluid, bounces off the borehole wall, and returns to the transducer. As the tool is pulled up the borehole, the transducer rotates and o b t a i n s c o n t i n u o u s 360' i m a g e s of b o t h a m p l i t u d e and t r a v e l t i m e . R e f l e c t i o n a m p l i t u d e depends mainly on reflectivity and roughness of the borehole wall. Traveltime depends on diameter of the borehole. The spacing between data pixels is 3 m m vertically and 2.5O or 5 O horizontally, depending on acquisition parameters.
' ' h e BI11V logging tool includes two t u ~ r c l i ~ r o meters and three perpendicular m t i g n e i o m c ~ ~ ~ i ~ s , ('or tool o r i e n t a t i o n . T h e C R P - 3 a c c e l c r o i n c i c r loi.'s indicated that borehole deviation was minor, less t l 1 i 1 1 1
2 . 5 " from vertical ( C a p e Roberts S c i e n c e T C : I I I I , 2000). The two horizontal magnetometers provide :I
continuous record of tool orientation with r e s p r r t to magnetic north. so that all images can be convcrkvl from tool c o o r d i n a t e s to magnetic nortli. We converted the images from magnetic north to innb North c o o r d i n a t e s , using measurements 01' loc:11 deviation based on an on-ice reference magnctoii~c-ti--r ( J a r r a r d , M o o s . Wilson. Biicker & Paiilscn. this volume). T h e reference magnetometer iiiciictiird :I local deviation of 147- 148'. consistent wit11 t l ~ c a
International Geomagnetic Reference Field value. The reference magnetometer also confirmed that in;ignetic storms did not significantly affect local deviation.
B H T V l o g s w e r e run at a l o g g i n g spec!J of l i i i l ~ i i i n ~ ~ t e f o r 9 2 % of the C R P - 3 b o r e h o l e ; l'or details, see Cape Roberts Science Team (2000). Two intervals were not logged because borehole conditions were too unstable to risk losing the tool: t h e npprr fault zone (255.1-271.4 mbsf), and the bottom part 01' the borehole (898.5-939 nibsf). which was blocked by swelling clays in an altered intrusion. L o g quality varied from poor to excellent, generally improving with increasing depth. Much of the top half o f the B H T V l o g p r o v i d e d only rare returns f r o m the borehole wall, possibly because of ~ n ~ ~ d c a k e , 11 was usually possible, however, to identify enough feaiiires (i.e., fractures, bedding, and clasts) in this upper log to reorientate cores. In the bottom half of the log, these f e a t u r e s w e r e much more c o m m o n a n d the accuracy of reorientations increased accordingly.
T h e a m p l i t u d e i m a g e s w e r e most u s e f u l for identification of geologic features such as fractures, bedding, and clasts. The CRP-3 traveltime logs did not p r o v i d e r e l i a b l e m e a s u r e m e n t s of boreliole diameter, because of a combination of cycle skipping a n d p o o r c a l i b r a t i o n by t h e tool m a n u f a c t u r e r . Antaresa. They occasionally provided useful images of borehole features, particularly open fractures and clasts, but these features generally were imaged as well o r b e t t e r by t h e a m p l i t u d e l o g . A c c u r a t e measurement of borehole diameter is required for determination of dip magnitudes, both for bedding and fractures. We assumed a uniform diameter of 102 mm for H Q borehole and 8 0 m m for NQ borehole, based on dipmeter measurements of borehole diameter (Cape Roberts Science Team, 2000; Bucker, Jarrard, Niessen, and Wonik, this volume).
T h e C R P - 3 B H T V logs, like other CRP-3 well logs, exhibited up to 2.5 m of depth shift compared to coring d e p t h s , caused mainly by stretch of t h e logging cable. T h i s shift varied both between and within logging runs. We corrected the BHTV data to minimize depth shifts, based on identification of 337 correlative features on the core logs (Cape Roberts
Scieiii~c Team, 2000) and HI1TV imayes. Optimum depth shif't was calculated for each of I I intervals of BU'l'V log. The final shifted logs hii\le residual depth shifts 111:it are everywhere less than 10 cm, which is satisfiictory for reliable correlation of features between core images and BHTV images.
Both stitched-core a n d BHTV imagcs were first displayed as unwrapped, 0-360' azimuth images. A n entire stitchecl-core image. 5-30 111 i n Icngth. can be converteil f r o m relative azimuth to t r u e North coordinates with a single rotation. The magnitude of this rotation was determined by subjective visual identification of correlative features o n the stitchecl- c o r e ;ind B H T V i m a g e s . We used three t y p e s o f features: fractures, bedding. and clasts. Before picking feature azimuths, however. we first identified a n d quantified depth shifts between stitched-core a n d BHTV images. These shifts were nearly always less than 10 cm, but even minor unrecognized depth shifts can lead to rare spurious correlation of features.
Feature orientations can be picked in WellCAD@
in two ways: single-point and sinusoid. For example.
the azimuth of a bed or fracture top or bottom can be picked by just moving a cursor to a single point. The s a m e p r o c e d u r e c a n b e used to d e t e r m i n e t h e orientation of the top, bottom. edge, or center of a clast. Planar features such as most beds and fractures a n d some large clasts form a sinusoidal shape on t h e s e i m a g e s . T h e i r azimuths can be picked with greater accuracy by fitting a sinusoid to the feature outline; manual sinusoid picking is rapid and easily revised in WellCAD@. One can pick top or bottom or center azimuth of any feature, as long as exactly the same portion of the feature is picked on stitched-core and BHTV images. The difference between azimuths on core and BHTV images is used to reorientate core, by rotating the core to minimize such differences.
For c o r e reorientation, fractures, bedding, and clasts have different advantages and disadvantages.
F r a c t u r e s a r e g e n e r a l l y s t e e p e n o u g h a n d p l a n a r enough that their orientations can be picked with an accuracy of ±3 on both stitched-core and B H T V images, but many intervals of BHTV have few or no obvious fractures. Because bedding dips are usually shallower (-10-30° than fracture dips (-40-70°) down-dip azimuths of individual beds have lower accuracies: ±30 for -10' dips and  ± l o for 30 dips o n B H T V i m a g e s , a n d better on c o r e i m a g e s . Consequently, w e used shallow bedding dips for core reorientation only when several adjacent beds were identifiable. L a r g e clasts have virtually t h e s a m e shape on both stitched-core and BHTV images, but this generalization does not necessarily hold for small (<5 cm) clasts, because of the 2-cm drilled-out zone between the outer-core surface and borehole wall.
Consequently, individual clasts can have azimuths that
truly (lil'fer by 220" hctween core and borehole wall.
A strong tii.lvanfagc of cliists, particularly in the top half of the borehole, is that their reflectivity is s o l i f e r e n t f r o m surroinuli~ig scdimcnts that they are often the only type of geologic feature that can b e confidently identified in the B1 ITV images.
Correction o f the stitchccl-core images to t r u e North w;is undertaken i n two s t e p s . First, w h i l e d i s p l a y i n g side-hy-side core a n d B H T V i m a g e s , paircd stikched-core and BIHTV a z i m u t h s w e r e tabulated usiilg single-point (rather than sinusoid) a p p r o x i m a t e (  10") picks. Differences between stitched-core and 131 ITV azimuths were averaged to determine a single, first-order correction which was then applied to the stitcliecl-core i m a g e . T h i s correction, which gcecrally was accurate to ±15O permitted more confident matcliiiig of features during the s e c o n d - o r d e r , more a c c u r a t e p h a s e of r e o r i e n t a t i o n . T h i s second p h a s e involved determination and tabulation of both single-point and sinusoicl-picked azimuths, along with depths and types of features. Differences between stitched-core and B H T V a z i m u t h s were plotted vs. depth f o r e a c h stitched core, and this plot was examined to identify and exclude any strongly inconsistent picks, and t o l o o k f o r any s y s t e m a t i c d o w n - c o r e c h a n g e s that required further correction. If no systematic changes were detected, all measurements of stitched-core minus BHTV azimuth were used to calculate a single average second-order correction for the stitched-core interval. Figure 1 shows a 0.6 m interval of core and B H T V i m a g e s after s e c o n d - o r d e r c o r r e c t i o n ,
Fig. 1 - Example of a whole-core image (right) that has been reorientated to North by matching feature orientations to those seen on an orientated borehole televiewer image (left). These false-color images are for a 0.6 m interval at the top of a doleritic breccia unit. Most of the image is a single fractured clast: the top of the clast is evident at 789.93 mbsf on the BHTV image and 78995 cm bsf o n the core image. Planar features such a s the abundant fractures appear as sinusoids on each unwrapped (N-E-S-W-N) image. The sinusoids have higher peak-to-trough amplitudes on the BHTV image than on the whole-core image because the former is larger diameter.
i l l ~ ~ s t r a t i n g how a suite of correlative fractiires am1 clast tops provides an unambiguous orientation for this segment of core ( a s well a s for the ad.jacent 22.9 m. of stitched core).
We looked for and sonietiiiies detecte~l two types o f systematic down-core chances: drifts and breaks.
Sudden breaks, or offsets, of core-BHTV correction a n g l e w e r e identified i n aboiit one-fourth of t h e s t i t c h e d - c o r e intervals. T h e s e breaks indicate a previously undetected rotation between two portions o f stitched core, caused by a mismatch of adjacent core segments. Nearly all of the segment matches used within a stitched-core interval are unambiguous a n d a r e s o noted during initial scribing a n d later stitching, but a few are less reliable. Whenever our core-BHTV feature matching detected a core break, we checked original notes and core images to identify the precise depth of the break. We then reorientated the intervals above and below the break separately, based on core-BHTV azimuth picks for each interval.
Gradual drifts of core-BHTV correction azimuth a p p e a r to b e present within most s t i t c h e d - c o r e i n t e r v a l s . C l o c k w i s e ( l o o k i n g d o w n - c o r e ) d r i f t s predominate, but counterclockwise drifts also a r e observed. Most detected drifts total <20Â from top to bottom of a stitched-core interval, corresponding to azimuthal drifts of 1-5' per meter. The cause of these small drifts is uncertain. Slight misalignment within the Corescan@ equipment can impart gradual rotations of the image, so the instrument was aligned at t h e
et;.
2 - Azimuth tlilTerences between Seatitres o n c o r c ;nul Ixirehole televiewer iinages. after Sil-st-order cosrecl ion. Noir consistency of results for (liffcrent feature types. Also notr tin' previously undetected core break at 804 mbsf.start of the field season. Because these drifts arc too small and imprecisely known t o permit accnr:itc removal, we did not apply any within-interval dril't corrections.
Table 1 lists the stitched-core intervals t l i i i l we have r e o r i e n t a t e d , along w i t h s t a t i s t i c s for d e t e r m i n a t i o n s of c o r e - B H T V c o r r e c t i o n a n g l e : number of feature matches per core interval, mean reorientation angle (i.e., angle between top of the red
Tab. 1 - Core intervals that have been stitched and reorientated to North
top depth bottom depth #points reorient. angle std. dev. 95% conf.
(mbsf) (mbst] stitched image vs. N
204.47 234.47 26 98 17.6 12.8
404.20 413.53 16 308 16.1 8.6
45 1.08 -460.7 16 250 19.8 10.6
-460.7 463.07 4 86 7.7 12.3
538.72 562.60 3 1 115 15.3 5.6
574.95 579.48 12 129 22.4 14.2
579.48 588.26 16 303 14.1 7 .S
610.48 634.95 29 311 15.3 5.8
640.30 -664.2 19 178 13.2 6.4
-664.2 666.18 6 146 13.5 14.1
693 .S4 706.59 26 3 2 11.3 4.6
707.96 723.61 20 294 10.6 5 .0
787.03 804 .OO 72 185 1 1.6 2.7
804.00 810.48 23 347 15.0 6 .S
816.48 821.90 30 188 10.5 3.9
822.13 826.48 30 101 9 .S 3 .S
826.48 831.48 2 1 283 7.4 3.4
864.19 866.30 8 56 8.6 7.2
866.30 873.52 15 - 1 10.8 6 .0
873.60 876.20 11 127 7.6 5.1
876.65 880.44 14 19 11.4 6.6
894.48 904.25 16 262 8.6 4.6
s c r i b e a n d North). standard d e v i a t i o n , a n d 95%
conf'idi.'nce limits for this mean. Figure 2 provides i i n
e x a m p l e suite of core-BHTV azimuth picks ['or the interv;il 787.0-810.5 mbsf. Because this interval has more picks (95 total) than any of the other intervals, it bcst displays the relative accuracies of different types ol' picks (fractures, beds, and clasts). All three types ;ire clearly useful and yield concordant results.
This interval also exhibits a 150' core break at 804 mbsi'. and a subtle clockwise drift of l O/m.
FRACTURE REORIENTATION PROCEDURE All fractures within intervals of orientated stitchcd c o r e w e r e reorientated to North by a d d i n g three rotation angles: (1) fracture orientation with respect to red scribe (measured in the field); (2) position of the red scribe on the raw stitched-core image (tabulated during stitching); and (3) rotation angle to rotate the raw stitched-core image to North (determined by matching corresponding features on stitched-core and BHTV images).
RESULTS
The overall core recovery r a t e f o r C R P - 3 was 97%. a n d 85% of the whole core was of sufficient integrity for whole-core s c a n n i n g ( C a p e Roberts Science Team, 2000). Confident fitting of adjacent c o r e segments is possible for continuous intervals ranging from <10 c m t o 3 0 m i n length. Of these p o t e n t i a l l y s t i t c h a b l e i n t e r v a l s , w e s e l e c t e d 17 i n t e r v a l s , 2 . 4 - 3 0 . 0 m l o n g , f o r s t i t c h i n g a n d reorientating via the c o r e - B H T V i m a g e matching procedure described above (Tab. 1). A total of 23 1.3 m , or 25% of the cored interval, was reorientated. We d i d not reorientate all cores, because the process is labor intensive (- 1-2 m per hour) and many intervals have few or no features that can be matched.
Reliability of core orientations can be gauged in t w o ways: by estimating errors associated with each step of the reorientation process, and by comparing azimuths of feature sets within reorientated cores to those within independent datasets.
The BHTV logs which are used as a ground-truth f o r c o r e reorientation p r o b a b l y h a v e an a z i m u t h a c c u r a c y of ±2 f o r t h e i n t e r n a l m a g n e t o m e t e r s (calibrated by Antaresm) and ±2 for local deviation (measured by our on-ice reference magnetometer).
J a r r a r d , Bucker, Wilson, & Paulsen (this volume) confirm the reliability of the BHTV orientations by comparing average structural dip azimuth for the shelf interval 100-789 m b s f based on B H T V (N66OE), dipmeter (N65OE), and regional seismic reflection profiles (N71°E) However, systematic azimuthal e r r o r s of <5O p r o b a b l y a r e not resolvable. Based solely on number and standard deviation of core- B H T V a z i m u t h m a t c h e s f o r e a c h s t i t c h e d - c o r e interval, 95% confidence limits for each correction c a n be calculated (Tab. 1). These confidence limits assume random errors and no undetected core breaks.
Third-order drifts of <20Â probably occur within some i n t e r v a l s , not biasing interval-average results but
hitising (liita from the top and hottom of the interval.
Within i ~ ~ l i v i ~ l t i a l sti[checl-corc intervals, the red- scribe line may drift o r jump by 100" or more. but such changes do not imply corresponding orientation e r r o r s h e c t ~ i i s e the c o r e stitching is much m o r e reliable and accurate than the red scribing. Fracture orientations and palaeomagnetic samples arc originally measured with respect to the red scribe with a n accuracy of  ± l O O and later picking of red-scribe orientation o n t h e stitched-core images has a n accuracy of ±2O C o i i i b i n i ~ i ~ ~ a r i a n c e s , we estimate that orientation uncertainty is ±1OC for entire stitched- core intervals, and  ± I S for individual features such as a single fracture or palaeo~iiagnetic sample.
Figures 3 and 4 provide comparisons of bedding and fractures within reorientated cores to those within nearly i n d e p e n d e n t d a t a s e t s . T h e latter a r e n o t c o m p l e t e l y independent, because the o r i e n t a t i o n process uses a combination o l bedding, fracture, and clast azimuth matches, but we have invariably found that the three types of matches are consistent.
Figure 3 shows mean bedding dip directions f o r five intervals of Beacon sandstone (Jarrard, Biicker, Wilson, & Paulsen, this volume). Bedding orientations were separately picked and averaged from reorientated stitched-core images and orientated BHTV images.
F o r all five i n t e r v a l s , c o r e s and B H T V i n d i c a t e similar dip azimuths and similar clip magnitudes; 95%
confidence limits, not shown, detect no significant differences between core and BHTV dip azimuths f r o m t h e s a m e interval. S o m e intervals h a v e significantly different d i p directions than o t h e r s , p r o b a b l y b e c a u s e of brecciation and a s s o c i a t e d structural tilting, and these differences are reflected by
0 televiewer
Fig. 3 - Average directions (azimuth and dip) of bedding dip for five reorientated-core intervals of Beacon s a n d s t o n e (Jarrard, Bucker, Wilson, & Paulsen, this volume). shown as poles to bedding on a zoomed equal area projection (outer circle is 40' dip, not 90'). Note similarity of results from reorientated core images (solid circles) to those from borehole televiewer (open circles) from the same interval (line joining pair of circles).
sitnilar offsets of both core-based and BHTV-based clip directions.
The deepest fault zone in CRP-3 core is at 790- 802 mbsf> within a doleritic breccia. We have been able to stitch and reosientate this entire i ~ ~ t e r v a l . I - < ~ g ~ i r e -. 4 c o m p a r e s f r a c t u r e orientations within reorientated core, reorientated stitched-cose inlages, atld B H T V i m a g e s . T h e t h r e e datasets a r e q u i t e co~~sistent in indicating two fracture sets: steep dips to the west and shallow d i p s t o t h e ENE. T h i s agreement provides further confirmation of the overall accuracy of the core orientation process.
The reliability of the core reorientation method can be tested by conducting rotation cl~istes tests on n a t ~ ~ r a l fractures found within the core (e.g., Hailwood
& Ding: 1995). Fractures should show an improved
cl~lstering upon rotation back to iii sit14 orientations b e c a u s e they typically f o r m with systematic orientations with respect to a segional stress field (e.g., Kulander et al., 1990). Wilson & Paulsen (this volume) d e t e r m i n e f r a c t u r e o r i e n t a t i o n s f o r all measured fractures within intervals that have been reorientated to-date. Raw directions are, as expected, virtually random, whereas l-eorientated fractures exhibit a strong NNE clustering of strikes, thereby demonstrating that the core reorientation process is successful.
The core reorientations of this study provide a framework fol- several other types of CRP-3 core analysis. The palaeomagnetic r e s ~ ~ l t s of Florindo et al.
(this v o l ~ ~ i n e ) can provide pole positions rather than just p a l a e o l a t i t ~ i d e s . C o r e fi-acture patterns a r e determined by Wilson & Paulsen (this volume), and core bedding patterns are documented by Jarrard, Bucker et al. (this volume).
A C K N O W L E D G E M E N T S - T h i s r e s e z ~ r c l ~ \vas s u p p o ~ ? ( ~ l by t h e N a t i o n a l S c i e n c e F o ~ ~ n d a t i o n (OPP-95273 l 0 ;in(I OPP-95 17394). W e sincerely t l ~ a ~ i k C.J. Biicker f o r 151 I'I'V l o g g i n g aiid S . J u d g e f o r c o r e s c m n i n g ; t h e i r e f S o r ( s I i i i i l
the f o ~ ~ n d a t i o n f o r this project, W e t l i ; i ~ ~ k B . L ~ i y e ~ > ( i y k ;111(l
J. KLick f o r constructive reviews.
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