6. SITE 187. The Shipboard Scientific Party 1 SITE DATA

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1 6. SITE 187 The Shipbard Scientific Party 1 SITE DATA Date Occupied: Aug71. Psitin: 'N 'W Water Depth: 4577 meters. Penetratin: 370 meters. Number f Hles: One. Number f Cres: Fur. Ttal Cre Recvered: 6.8 meters. Acustic Basement: Depth: 160 meters Nature: Defrmed sediments Velcity: Apprximately same as Site 186, 2.0 km/sec. Age f Oldest Sediment: Early late Micene. Basement: Micene defrmed sediments. SUMMARY The sediment sequence at Site 187, lcated 2.3 miles sutheast f Site 186 (Figure 1), cnsists f diatmaceus silty clay that is lder but therwise virtually identical t that recvered at Site 186. Only fur cres were attempted t a ttal depth f 370 meters; they cntained sediment f Pleistcene, lwer Plicene, and late Micene age. Limestne fragments (ne f which cntains fecal pellets), silty mud, and an ice-rafted (?), runded graywacke pebble were recvered frm the cre catcher f Cre 1 at 164 meters. The tw limestne fragments cntain a lwer Pleistcene flra and prbably caved frm higher in the hle, as the assciated silt is f early Plicene age. Upper Micene disturbed (prbably by cring peratins) and indurated silty clay (claystne) with assciated diatmaceus sediment was recvered between 175 and 370 meters. Site 187 is lcated abve the "acustic basement" underlying the uter ridge f Atka Basin, Aleutian Terrace. This ridge is als the summit f the steeply slping inner wall f the Aleutian Trench. Drilling at this site shws that at least part f the acustic basement is defrmed sedimentary rck as ld as late Micene. These depsits presumably accumulated in Atka Basin. Near Site 186, beneath this basin, stratigraphically equivalent beds lie deeper than 926 meters. The structural displacement f late Micene beds between Sites 186 and 187 must be at least 750 meters. The surce area fr the allchthnus blck f middle Micene silty clay cred at Site 186 in beds f early Plicene age is presumably the ridge drilled at Site 187 (see Grw, this vlume). Descriptin BACKGROUND AND OBJECTIVES Site 187 is lcated ver the inner part f the uter "bedrck" ridge f Atka Basin, Aleutian Terrace (4577 m, crrected). The site is just 2.3 miles sutheast (132 T) f previus Site 186. The reference prfile (Figure 2) revealed abut 100 t 150 meters f pelagic debris verlying an acustically unreslvable "basement," which culd either be defrmed sedimentary debris r pssibly vesicular vlcanic rcks. Gravity data imply that the uter ridge is nt underlain by exceptinally dense material, hence defrmed sedimentary depsits were expected. 1 David W. Schll, U.S. Gelgical Survey, Menl Park, Califrnia; Je S. Creager, University f Washingtn, Seattle, Washingtn; Rbert E. Byce, Scripps Institutin f Oceangraphy, La Jlla, Califrnia; Rnald J. Echls, University f Washingtn, Seattle, Washingtn; Timthy J. Fullam, Standard Oil Cmpany f Califrnia, La Habra, Califrnia; Jhn A. Grw, Massachusetts Institute f Technlgy, Cambridge, Massachusetts; Itaru Kizumi, Osaka University, Osaka, Japan; Hma J. Lee, Naval Civil Engineering Labratry, Prt Hueneme, Califrnia; Hsin Yi Ling, University f Washingtn, Seattle, Washingtn; Richard J. Stewart, University f Washingtn, Seattle, Washingtn; Peter R. Supk, Scripps Institutin f Oceangraphy, La Jlla, Califrnia; Thmas R. Wrsley, University f Washingtn, Seattle, Washingtn Figure 1. Base map shwing the lcatin f Site c 279

2 10 km 2-way time, sec. Near " ^4'vH 0;i;.Wz 51 i. 7 Figure 2. Reference seismic reflectin prfile, btained by E. L. Hamiltn, 2 Aug 70. Objectives A cnsiderable bdy f circumstantial evidence exists that implies that the uter ridge, which is als the upper part f the inner wall f the adjacent Aleutian Trench, may be underlain by ceanic ffscrapings. The principal bjective f Site 187 was t (1) determine the nature f the rcks underlying the ridge, (2) establish their relatin t the sedimentary sectin drilled at Site 186, and (3) assess the pssibility that ceanic ffscrapings may be present. Pre- and Pst-drilling Survey OPERATIONS Site 187 is lcated 2.3 miles sutheast (132 T) f Site 186 alng the track f the reference prfile cllected by E. L. Hamiltn n 2 Aug 70. The ship was mved t this site with the drill string suspended belw the ship, therefre n seismic equipment was streamed. A new beacn was drpped at 1210 hrs n 12 Aug 71. The finally accepted psitin is: 'N; 'W. The reference seismic prfile is shwn in Figure 2. N air-gun prfile was made cming nt the site, but a pst-drilling survey was made which passed thrugh Sites 186 and 187 (Figure 3). A map shwing the surveys and track and site lcatins is shwn in Figure 4. Drilling Prgram Site 187 was ccupied frm 1215 hrs 12 Aug 71 (beacn away) until 1200 hrs 13 Aug 71 with alternate cring and washing frm the sea flr t a subbttm depth f 370 meters. At this depth a diatmaceus clayey silt, f early late Micene age, lithlgically similar t that encuntered at Site 186 was cred. Cring speed, which was slw, and the necessity t disembark persnnel at Adak n 14 Aug 71 required that the hle be abandned. Using Matthews Tables and infrmatin frm the U.S. Navy Undersea Research and Develpment Center, the snic depth f 2342 fms was crrected t 4538 meters giving a water depth f 4544 meters and a drill-flr depth f 4554 meters. Cnsidering the past errrs in this calculatin, the bttm belw drill flr was estimated at 4587 meters. This estimate then, gives an estimated depth belw sea level f 4577 meters. This is the accepted depth, inasmuch as, in rder t save time, the bttm was nt cred. N difficulties were encuntered in drilling this hle. A cring summary is given in Table 1. LITHOSTRATIGRAPHY The depsits recvered frm Site 187 are dark brwnish gray and live gray diatmaceus silty clay, identical t thse recvered at Site 186. An ice-rafted(?), runded 280

3 LO CO CO CO CO al HDG Q i i i Q. GO i Q. Lu Q I I Figure 3. Reflectin prfile btained by Glmar Challenger upn departure frm Site 187. pebble f graywacke was recvered frm the cre catcher in the Interval 164 t 173 meters alng with mud f early Plicene age and tw angular pieces f lwer Pleistcene limestne (ne f which included fecal pellets) prbably derived frm higher levels. In Cre 2 a light gray vitric ash was recvered (174 m) in beds f late Micene age. The final cre recvered frm 361 t 370 meters cntains highly disturbed layers f brittle claystne in an therwise sft sectin f diatmaceus silty clay. PHYSICAL PROPERTIES A limited number f GRAPE measurements and shre labratry density determinatins were made n the" sediment frm Site 187. These are presented n the site summary sheet. N trends are apparent ver the range tested. PALEONTOLOGY The fur cres taken at Site 187 cnsist f diatmaceus silty clay; the cre catcher f Cre 1 cntained tw limestne pieces, ne f which included fecal pellets. Only siliceus fssils have been fund. The limestne fragment f Cre 1 is Pleistcene in age and is thus nt indigenus t the silty clay, early Plicene, within which it is enclsed. This fragment presumably fell dwn the hle frm a higher stratigraphic level. Silty clay f the remaining cres are f late Micene age. 281

4 174 10'W 51 O 15'N Figure 4. Track f the Glmar Challenger in the vicinity f Sites 186 and 187. Calcareus Nannflra Althugh sme f the cres at this site cntain limestne bands, the site is apparently barren f nannfssils. Radilaria and Silicflagellates Occurrences f radilarians and silicflagellates frm Site 187 are shwn in Table 6, Chapters 27 and 28. In Cres 1 and 3 limestne and clay cntain different micrfssil assemblages and, in the case f Cre 1, the assemblages are even f different ages. A few radilarians were fund frm ther samples at this site, but withut any index taxa. As fr silicflagellates, the limestne f Cre 1 yields varieties f Distephanus speculum and Dictycha subarctis, apparently indicating Pleistcene age. Diatms The limestne f Cre 1 cntains many diatms f Pleistcene age. Diatm assemblages f assciated silty clay indicate an early Plicene age. The flra f Cre 4 is dminated by Cscindiscus marginatus frma and Denticula kamtschatica, and it seems t be lder than Cre 28 f Site 186. CORRELATION BETWEEN REFLECTION PROFILE AND STRATIGRAPHIC COMN See Crrelatin Between Reflectin Prfile and Stratigraphic Clumn reprt fr Site 186. Cre Wash 1 2 Wash 3 Wash 4 TABLE 1 Cring Summary - Site 187 Cred Interval Belw Bttm (m) Cred (m) Recvered (m) 3 pebbles in catcher (%)

5 Q 100 σ - CSI 13 σ - CO ~ 1 (_> O i SILTY WJJH_ASH_ DIATOM OOZE WITH VOLC. SANDS SEMI- INDURATED CU < 1EISTOCE! DENSITY VELOCITY X.a ' ** 1 CSI 1 ' 0 ; NORTH [TERRACE) V.E. = 12 SOUTH (TRENCH) LO s - σ> > <C ^ VOLC. " SANDS S WITH L! CALCITE CEMENT Q WITH VOLC. SAND M. MIO. EXOTIC BLOCK RARE ASH VÖLC~! SAND (BURROWED) HOLE TERMINATED ' 1 i 1 z 1 a. M.MIC Z O _J Q_ - r - Figure 5. Crrelatin f the seismic reflectin prfile with physical prperties and the lithlgic clumn, Sites 186 and 187. i, ft V / - 283

6 NJ OO DEPTH (in) LITHOLOGIC DESCRIPTION DENSITY (gm/cc) Mean GRAPE Density, + Shre Labratry Density, x Water Displacement Density, COMPRESSIONAL WAVE VELOCITY (km/sec) limestne extic, graywacke pebble DIATOMACEOUS SILTY CLAY, dark gray and 1ive gray Z

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8 Site 187 Hle Cre 1 Cred Interval: FOSSIL CHARACTER LITHOLOGY m D A G PF Cre BF Catcher N R R M S R M AGE 1 PLEISTOCENE - LOWER PLIOCENE ZONE CD) Denticula seminae CS)- D. kamtschatica FOSSIL ABUND. PRES. SECTION METERS Explanatry ntes in Chapter 1 DEFORMATION LITHO.SAMPLE LITHOLOGIC DESCRIPTION cre catcher sample nly: 1) angular pieces f LIMESTONE (5-10 cm) dusky yellw (5Y 6/4) and med. light gray (N6) 2) runded GRAYWACKE pebble (5-10 cm) dark gray (N4) 3) small amunt f diatmaceus silty clay Site 187 Hle Cre 2 Cred Interval: FOSSIL CHARACTER AGE ZONE FOSSIL ABUND. PRES. SECTION METERS LITHOLOGY DEFORMATION LITHO.SAMPLE LITHOLOGIC DESCRIPTION UPPER MIOCENE CD) Denticula kamtschatica l l 1 I 1 I i I I VOID VITRIC ASH, light bluish gray Cre Catcher: Basic lithlgy: D A G DIATOM BEARING SILTY CLAY pp _ dark greenish gray (5GY 4/1) BF - N - - R R M with thin (1-2 cm) layers f SAND, S R M greenish black (5G 2/1) Cre Catcher and diatm rich znes, live gray (5Y 4/1) Explanatry ntes in Chapter 1 286

9 WET-BULK DENSITY, gm/cc i i i i i i i ' i i ' ' i «' " i POROSITY,% Grain Density 2 SECTION CM -0 /rr 1- h

10 Site 187 Hle Cre 3 Cred Interval: FOSSIL CHARACTER LITHOLOGY LITHOLOGIC DESCRIPTION VOID Cre Catcher (D) Denticula kamtschatica -80 Cre D PF r i BF N R S DIATOMACEOUS SILTY CLAY dark gray (5Y 4/1) Catcher: p Q _ R R _ M M Slide % diatms 25% silt 5% glass 40% clay XR % amrph 6% quartz 7% plag. 6% mica 2% chlr. 4% mnt. black streaks inclined 5-10 t hrizntal Site 187 Hle Cre 4 Cred Interval: LITHOLOGIC DESCRIPTION -140 DIATOMACEOUS SILTY CLAY live gray (5Y 3/1-3/2) Cre Catcher: Slide D C G 30% diatms PF _ 30% silt BF _ 40% clay N - - RS R M XR % amrph 5% quartz 7% plag. 6% mica 2% chlr. 2% mnt. TR clinp TR amphib R M sectin 2 cntains 1-2 cm thick disturbed layers f black (5Y 2/1) SAND Explanatry ntes in Chapter 1 288

11 WET-BULK DENSITY, gm/cc POROSITY,* r r irπ Grain Density -a 2 u M O-i SECTION CM r