25. heavy mineralogy of unconsolidated sands … · heavy mineralogy of unconsolidated sands in...

25. HEAVY MINERALOGY OF UNCONSOLIDATED SANDS IN NORTHEASTERN PACIFICSEDIMENTS: LEG 18, DEEP SEA DRILLING PROJECT

Kenneth F. Scheidegger and LaVerne D. Kulm, Oregon State University, Corvallis, Oregon;and David J. W. Piper, Department of Geology. Dalhousie University, Halifax, N. S., Canada

ABSTRACT

Immature, chemically unstable, pyroxene-amphibole heavymineral assemblages characterize the unconsolidated sands fromLeg 18. Sites 174A, 175, and 176 off the Oregon coast havereceived sediment from the upper portion of the Columbia Riverdrainage system during glacial times. The heavy mineral composi-tion of present-day Columbia River sands, dominated by sandsfrom lower Columbia River sources, is not typical of what it hasbeen in the past. Evidence for a change of sediment source wasfound in the lower part of Site 174A and suggests that this sitemay have received sediments from more northerly or southerlysources two million years ago. Sands found at Site 177A haveamphibole-rich assemblages except near basement where anepidote-rich assemblage is found. This drastic change inmineralogy at Site 177A, and the observed increased degree ofetching of pyroxenes with depth at Sites 174A and 175, indicatethat diagenesis is capable of modifying the character of heavymineral assemblages. Heavy mineral analysis of sediments fromthe Gulf of Alaska (Sites 178-182) suggest that there is noevidence of a sediment source beyond the coast ranges of Alaskafrom middle Miocene to the present.

INTRODUCTION

Deposits of unconsolidated sands are common in sedi-ments from all Leg 18 sites. Such coarse terrigenoussediments in the deep-sea environment are thought torepresent the coarse fraction of turbidity current depositsthat originated on, and were transported from, the unstablemargins of neighboring continental land masses. As aprerequisite to understanding the nature of the provenanceof the sediments at the various sites, a survey of the heavymineralogy of the coarse-grained sediments was conducted.Heavy minerals in such deposits are usually characteristic ofcertain source rock lithologies.

Particular emphasis is placed on the heavy mineralogy ofsands from Sites 174 A, 175, and 176 off Oregon (Figure 1)because considerable work has been done on the heavymineralogy of the potential sources of these sands (Kulm etal., 1968; Duncan and Kulm, 1970; Scheidegger et al.,1971). A primary objective is to determine if the sources ofsediments found at these sites have remained constantthrough the stratigraphic sections. Ascertaining the prove-nance of sediments found at Site 177A off VancouverIsland and Sites 178 through 182 in the Gulf of Alaska ismore speculative because relatively little work has beendone on the mineralogy of neighboring continental sedi-ment sources.

A secondary objective of this study is to describe andassess the importance of diagenetic changes of heavymineral assemblages in the stratigraphic section. Althoughmuch is known about the mineralogy of marine sediments,relatively little is known about how this mineralogy can

50°

4 0 '

KLAMATH RIVER

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120°

Figure 1. Submarine and continental features in the vicin-ity ofDSDP Sites 174A, 175, 176 and 177A.

877

R. F. SCHEIDEGGER, L. D. KULM, D. J. W. PIPER

change in response to processes acting within the sediment.At Sites 174A and 175, subtle changes in the character ofthe existing heavy mineral assemblages were noted,whereas, at Site 177A the changes involved the formationof a distinctly different assemblage.

METHODS OF ANALYSIS

Samples of sand-sized sediments were obtained from themore prominent, coarser-grained deposits. Material finerthan 62 microns was removed by wet sieving followingultrasonic disaggregation. The heavy mineral fractions ofthe sands were concentrated using tetrabromoethane (sp.gr. = 2.96) and were mounted in Aroclor (R.I. = 1.65).Most samples were composed of very fine sands.

Out of more than 220 samples a total of 37 wereselected for analysis. A quick preliminary investigation ofall samples has revealed that our 37 samples can beconsidered to be representative of the heavy mineralogy ofthe sands. Sediment, both above and below the intervalssampled, showed similar mineralogy. One hundred or morenonopaque, nonmicaceous heavy minerals per sample wereidentified with a polarizing microscope. The results of theanalyses are presented in Table 1.

HEAVY MINERALOGY OF SANDS

Compositionally immature heavy mineral assemblages,dominated by relatively unstable amphiboles and pyroxenesand, to a lesser extent, by minerals of the epidote andgarnet groups, characterize the heavy mineral compositionof sands from Leg 18. The immature nature of the heavymineral suites of these sands is similar to that of theconsolidated, immature, feldspathic arenites described byHayes (Chap. 29, this volume) for Sites 177A, 178 and 181.

Sites off Oregon (174A-176)

Subequal amounts of pyroxenes (principally augite andhypersthene) and amphiboles (principally blue green andgreen hornblende) with lesser amounts of garnet andepidote minerals characterize the heavy mineral assemblagesfound at these sites (see Table 1 and Figure 1). Otherminerals, such as glaucophane, kyanite, staurolite, olivine,and zircon were usually present in trace amounts.

Trends among assemblages from Sites 175 and 176 arenot evident. At Site 174A, there is a high degree ofsimilarity between the heavy mineral assemblages aboveCore 34 and those present at Sites 175 and 176. Clearly,there is no reason to consider that these samples are notpart of a single population. Below Core 34, at about 370meters, however, the heavy mineralogy of the sampleschanges significantly to an amphibole-rich assemblage withlittle clinopyroxene and hypersthene. Only in the sectionbelow Core 34 at Site 174A is there any indication of achange in sediment source.

Work by Duncan and Kulm (1970) and others indicatethat the source of sediments found at Sites 174A, 175, and176 should be the Columbia River. This is logical since Site176 is close to the mouth of the Columbia and Sites 174Aand 175 contain typical fan-like deposits which have heavymineral assemblages that are similar to those found inpiston cores taken from Astoria Fan (see Figures 1 and 2).

Duncan and Kulm (1970) have shown that the ColumbiaRiver is the source of sediments found on Astoria Fan.

Although the heavy mineral assemblages from Sites174A, 175, and 176 and Columbia River-derived sedimentson Astoria Fan are similar, it is rather paradoxical to notethat present day Columbia River sediments are notablymore pyroxene-rich and perhaps more epidote-garnet poorthan are those found on Astoria Fan and at Sites 174A,175, and 176 (see Figure 2). Work by Whetten et al. (1969)has shown that such pyroxene-rich assemblages from thelower Columbia and from the Dalles and Bonnevillereservoirs reflect the significant contribution of pyroxene-rich detritus from Oregon's and Washington's CascadeRange (see Figure 1). Evidently, the heavy mineral suites ofthe Columbia River sands that are being carried to theocean at the present time are not typical of what ittransported in the past. Whetten et al. (1969) have alsopresented heavy mineral data for sands from the upperColumbia River reservoirs. Heavy minerals found in sandsfrom McNary Reservoir, which lies just downstream fromthe confluence of the upper Columbia and Snake rivers andthus should contain sands that are most representative ofthe coarse detritus being eroded from the upper part of theColumbia River drainage system, are quite similar to thosefound in Astoria Fan sands (see Figure 2). Clearly, theupper Columbia River drainage system must have been amore important source of sediments during glacial timesthan the lower Columbia drainages. This conclusion is inagreement with the work of Duncan et al. (1970) who showa temporal change in clay mineralogy of Columbia Riversediments during glacial and interglacial times.

It is not possible, however, to attribute the transitionfrom an amphibole-pyroxene assemblage in the upperportions of Site 174A to an amphibole assemblage below tovariations in mineralogy of Columbia River sediments.Below Core 34 (370 m), very little clinopyroxene andhypersthene were observed. One would not expect theseminerals to be impoverished in Columbia River sedimentsbecause extensive outcrops of basic igneous rocks arepresent in its drainage system. It is conceivable that such amineralogy change could be the result of a slightly finergrain size of the sands below Core 34. However, theobservation that similar very fine sands from Core 33 havepyroxene-rich heavy mineral assemblages makes it veryunlikely that the mineralogical differences can be the resultof selective sorting effects. Diagenesis was considered as acause of the mineralogy differences but rejected becausechemically unstable minerals, such as amphiboles andclinopyroxenes, were abundant. Although the pyroxenes inthe sands from the lower part of Site 174A are quiteetched, they are still sand-sized grains. It is evident thatetching has not been responsible for their relative scarcity.The subtle effects of etching observed on pyroxenes foundat Site 174A and 175 are discussed in detail below.

The most logical explanation for the change in heavymineralogy found at Site 174A is that the sources ofsediment were different at an earlier time. Previous studiesby Kulm et al. (1968) and Scheidegger et al. (1971) suggestthat the amphibole dominant assemblage in the lowerportion of Site 174A is similar to the heavy mineralogy ofthe Klamath and Rogue rivers (Figures 1 and 2), the two

878

HEAVY MINERALOGY OF UNCONSOLIDATED SANDS, NORTHEASTERN PACIFIC SEDIMENTS

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largest rivers draining the largely metamorphic terrane ofthe Klamath Mountains of southern Oregon and northernCalifornia. Although the Klamath and Rogue rivers haveless epidote and garnet minerals than those from the lowerpart of Site 174A, many of the smaller drainages within the

Klamath Mountain provenance are rich in these compo-nents (Kulm et al., 1968). Admixture of sediments fromthe various river drainages may have created a heavymineral assemblage that is like those from Cores 37, 38, and39 of Site 174A. Another potential source of these sands

879


AMPHIBOLES AMPHIBOLES

DSDP SITESOFF

( i )(2)(3)

(4)(5)

(6)

(7)(8)

(1)(2)(3)(4)(5)

(1)(2)

OREGON

• 174 A2-1-60/629-3-25/2716-2-81/8326-2-130/13234-1-128/13037-3-31/3338-1-114/11639-3-137/139

Θ 1753-4-126/1289-4-94/9513-4-61/6220-1-62/6422-CC

D 1765-4-28/30 /5-6-81/83 /

SANDS

fk DALLAS RESERVOIR

AVE. LQWER COLUMBIARIVER

BONNEVILLERESERVOIR

GARNETS AND EPIDOTES PYROXENES PYROXENES

Figure 2. Triangular diagrams of heavy mineral assemblages of sands from DSDP sites off Oregon and fromAstoria Fan. Data on heavy mineral assemblages from major rivers contributing sands to the deep-seaenvironment off Oregon and from reservoirs on the Columbia River are shown for comparison.

may be the hornblende-rich sediments that are derived fromcoastal drainages of Vancouver Island and British Columbia(Easterbrook, 1963; Wiese, 1969; Carter, 1970). Sandsfrom Site 177A, which have apparently been derived fromsuch a hornblende-rich source, are similar to those found inthe lower part of Site 174A (compare Figures 2 and 3). Inaddition, the clay mineralogy from the lower part of Site174A and the upper part of Site 177A are similar (seeZemmels, this volume). If the sources of sediments found inthe lower part of 174A were either the Klamath Mountainsto the south or the Vancouver Island area to the north, it ispossible that the Site 174A area occupied a differentgeographical position and was not sedimentary provincereceiving sediment from the Columbia River. According toAtwater (1970) and Silver (1971), the Juan de Fuca Platehas been moving in a counterclockwise sense relative toNorth America. Two million years ago, Site 174A wouldhave been about 100 km to the southwest and in closerproximity to the Klamath Mountain provenance. If, on theother hand, the Juan de Fuca Plate has been coupled toNorth America (see Tectonic Summary, von Huene andKulm, Chapter 33, this volume) one would expect Site174A, which is moving away from the Juan de Fuca Ridgeat a rate of about 2.9 cm/yr (Vine, 1966), to have occupieda position about 58 km to the northwest 2 my ago. Such adisplacement would have brought Site 174A close to asedimentary province that has received sediments frommore northerly Vancouver Island-British Columbia sources

(Duncan and Kulm, 1970). Although heavy mineral analysisalone does not eliminate either of these models, it doessuggest the possibility that Site 174A entered the ColumbiaRiver sedimentary province about 2 my ago from either asoutherly or westerly direction.

Site off Vancouver Island (177A)

The heavy mineral assemblages found at Site 177A arethe most unusual of any investigated from Leg 18. With theexception of the sands from below Core 21, these suites canbe characterized as amphibole assemblages with subordinateamounts of minerals of the epidote group (see Figure 3 andTable 1). Blue green hornblende is the dominant type ofamphibole. Between Core 21, Section 3 and Core 23,Section 5, a drastic change in the assemblages is evident.The heavy mineral suites of sands from Cores 23 and 26consist almost totally of minerals of the epidote group,namely epidote and clinozoisite. Other minerals identifiedfrom this lower section include garnet and zircon. It is clearthat the heavy mineral assemblages found in the lowersection of Site 177 A are chemically more stable and maturethan those found in the upper section.

Potential sources of sediments found at Site 177Ainclude the neighboring land masses of Vancouver Islandand western British Columbia. Wiese (1969) has reportedamphibole-rich assemblages from the northern end ofVancouver Island in Queen Charlotte Sound and Carter(1970) has found that relict sediments on the shelf off

880


AMPHI BOLES

DSDP SITEOFF VANCOUVER ISLAND

• 177 A(1) 3 - 3 - 1 5 / 1 6(2) 10-4-124/126(3) 13-1-135/137(4) 18-3-145/147(5) 20-3-97/99(6) 21-3-63/64(7) 23-5-89/89(8) 26-1-121/122

EPIDOTES AND GARNETS PYROXENES

Figure 3. Triangular diagram of heavy mineral assemblages found in sands from Site 111 A offVancouver Island.

Vancouver Island are rich in hornblende and epidote.Similarly, Easterbrook (1963) has suggested that heavyminerals derived from British Columbia are characterizedby a high content of hornblende. Since sands derived fromthe potential sediment sources are quite amphibole-rich, itis clear that these neighboring land masses supplied theamphibole-rich sands found in the upper portion of Site177 A.

Difficulties arise when one attempts to explain thechange in the lower Pliocene from an amphibole assemblage(above 272 m) to an epidote assemblage (below 352 m). Achange in provenance is a possible explanation for theobserved mineralogy differences although it is difficult toreconcile this with what is known about the presentgeology of neighboring land masses and the sediments thatare derived from them. The coast mountains of BritishColumbia consist largely of granodiorites, quartz dioritesand diorites with associated schists and gneisses (Easter-brook, 1963). Sediment studies by Easterbrook (1963),Wiese (1969), Carter (1970) and Carson (1971) indicatethat heavy mineral assemblages of sands found in thevicinity of Site 177A are characteristically rich in amphib-oles. Even if progressive denudation of a continentalsediment source can cause a stratigraphic succession ofheavy mineral assemblages in neighboring sediment deposits(Krynine, 1942), one would not expect amphiboles to betotally absent in any heavy mineral assemblage derived

from the progressive denudation of such a complex andvaried source rock terrane. The possibility exists that theonset of glaciation on the neighboring continental sedimentsources caused a greater influx of chemically unstable,amphibole-rich heavy minerals to the deep-sea environment.However, since the change in mineralogy occurred in thelower Pliocene, this appears to preclude this explanation.Weathering of unstable heavy minerals prior to depositioncould have significantly altered the heavy mineral assem-blages (van Andel, 1959) because epidote is slightly moreresistant to weathering than hornblende. This possibilitycannot be eliminated although it is strange that noweathered or unweathered grains of hornblende wereobserved from the lower part of Site 177A. Selectivesorting is also capable, in certain instances, of creating anepidote assemblage from an amphibole-pyroxene-epidoteassemblage (van Andel, 1959). However, van Andel alsoshowed that epidotes and hornblendes have nearly the samedensities and similar size distributions. Since their hydro-dynamic behavior is probably quite similar, it is difficult toenvision how a sedimentary process could so effectivelysort these heavy mineral species. On the basis of thisdiscussion, it seems that the observed changes in mineralogyhas not been caused by changes in sediment source or byprocesses acting on the sediments prior to deposition.Clearly, it is highly probable that diagenetic processesacting within the sediments have been responsible for the

881


formation of an epidote-rich assemblage in the lower partof Site 177A. This proposed explanation of the mineralogydifferences is examined below.

Sites in Gulf of Alaska (178-182)

About ninety heavy mineral separations of grains coarserthan 44 microns from sands and coarse silts from Sites 178through 182 have been examined. With the exception ofabout ten samples from ash beds and biotite-rich layers,most samples can be grouped into the following twoassemblages:1) An assemblage with abundant hornblende and hyper-

sthene that was found in the upper part of Site 178, allof 179 and 180, at least the upper fourteen cores of 181,and probably all of 182.

2) An assemblage with abundant hornblende and almost nohypersthene in the lower part of Site 178 down to atleast Core 49. The boundary between the two assem-blages in Site 178 is gradational, but probably fallsbetween Cores 12 and 26. Pinpointing the boundary ishampered by the lack of suitable material in thisinterval. Other than in hypersthene content, the twoassemblages are similar (see Figure 4 and Table 1). Theyappear to have been derived from a low or medium grademetamorphic source with some basic or intermediatecrystalline rocks. There is thus no evidence of a sourcebeyond the coast ranges of Alaska from middle Miocenetime to the present.

EVIDENCE OF INTRASTRATAL SOLUTION FROMHEAVY MINERAL ASSEMBLAGES

Heavy mineral assemblages, such as those from Leg 18that contain high percentages of chemically unstable augitesand hornblendes (Pettijohn, 1957), should be particularlysensitive to the effects of intrastratal solution. The highporosity of individual sand layers, which initially may havebeen about 35 to 40 percent (Hays, Chap. 9, thisvolume), probably allowed fluids to circulate freely throughrather than across individual layers. Each sand layer isgenerally bounded both above and below by relativelyimpermeable hemipelagic clays. During our preliminaryinvestigation of the heavy minerals found in these layers,we noted both subtle changes in the morphology ofindividual grains as well as drastic changes of the heavymineral suites. Our findings are in agreement with Petti-john's (1957) suggestion that intrastratal solution may becapable of modifying heavy mineral assemblages. In thefollowing discussion, the effects that were noted aredescribed. Failure to recognize the more drastic intrastratalsolution effects could make it impossible to determine theactual provenance of a deposit.

Site 175

Sands from Site 175 contain high percentages ofamphiboles, clinopyroxenes, and orthopyroxenes at allstratigraphic levels. While performing the heavy mineralcounts, it was noted that the degree of etching of bothclinopyroxenes and orthopyroxenes increased with increas-ing depth in the section (see Plate 1). This same effect wasnoted for Site 174A. To quantify the observations, sixteenheavy mineral slides of samples from different stratigraphic

levels at Site 175 were selected and thoroughly mixed. Aslide was then randomly selected and the first thirtyhypersthene grains observed were ascribed to unetched,slightly etched, moderately etched, and extremely etchedcategories. Hypersthene was selected for study because it iseasy to identify and because it is usually found as euhedralto subhedral prismatic crystals. In Figure 5, the results ofthis investigation are shown. Because of the subjectivity ofascribing an individual hypersthene to a particular categoryand of the inherent variability of small sample sizes, muchscatter exists. However, if one assigns each successivestratigraphic group of four samples to a class, it is clearlyevident that the degree of hypersthene etching increaseswith depth in the section.

The significance of hypersthene and clinopyroxene,etching is that if a sand layer remains open to thecirculation of intrastratal solutions, both of these compo-nents will ultimately disappear from its heavy mineralassemblage. Sediments deposited at Site 175 are youngerthan 1.85 my and those from Site 174A are younger than 5my. From our petrographic studies, it is evident that for thegeologic times reached in Sites 174A and 175, intrastratalsolution has not seriously modified the heavy mineralassemblages. However, if intrastratal solution were allowedto continue for perhaps 10 my at the rate it has for the last2 my, the character of the resulting heavy mineralassemblages would be significantly altered. One would notsee any evidence in the heavy mineral assemblages for thepresence of basic igneous rocks in the source rock terrane.

Site 177A

As discussed above, it appears unlikely that the transi-tion from a chemically unstable amphibole heavy mineralassemblage to a more stable epidote assemblage below Core21 has been caused by a change in provenance or by otherprocesses acting on the sands prior to deposition. Theformation of a nearly monomineralic epidote assemblage bythese means would require geologically unreasonablecircumstances for this area of British Columbia.

A more plausible explanation for the change in miner-alogy is that the character of the heavy mineral assemblageshas been significantly altered by processes acting within thesediments subsequent to their deposition. The observedchange in mineralogy below Core 21 is analogous to thechange in heavy mineral assemblages between the calcare-ous concretions and the surrounding matrix of a sandstonefrom California (Bramlette, 1941). Bramlette showed thatthe calcareous concretions of this sandstone had 44 percenthornblende whereas the matrix had 5 percent and wasnotably enriched in epidote minerals. This difference inmineralogy was attributed to leaching of the amphibolesfrom the matrix by circulating intrastratal solutions. At Site177A, it is possible that the relative enrichment of epidote,garnet, and zircon has been caused by such preferentialdissolution of amphiboles since there is an indication thesethree components have similar relative abundances bothabove and below Core 21 (see Table 1). In addition, Hayes(this volume) has suggested the possibility diageneticchlorite has replaced amphiboles in the sandstones from thelower portion of Site 177A. Hayes has also suggested thatpermeating acidic fluids have subsequently dissolved some

882


AMPHIBOLES

IN

DSDP SITES

ULF OF ALASKA

( i )(2)(3)

(4)

(1)(2)(3)

(1)(2)

(1)(2)(3)(4)

\

\ (1)

• 1782-3-13/1516-4-116/11735-2-56/5848-1-49/51

• 1792-3-57/595-4-58-6010-3-79/81

4 iβo1-2-120/12225-CC

• I 8 I1-1-104/1069-3-4/614-1-6,5/6623-CC

• 1824-CC

EPIDOTES AND GARNETS PYROXENES

Figure 4. Triangular diagram of heavy mineral assemblages found in sands from DSDP sites in Gulf ofAlaska.

of this diagenetic chlorite and other constituents, therebycreating the patchy porosity observed in the sandstones.Conceivably, such chemically active intrastratal solutionscould have totally dissolved the diagenetic chlorite as wellas other constituents. The net effect of this may have beenthe creation of unconsolidated sands with epidote-richheavy mineral assemblages. Our limited data do not enableus to distinguish between preferential dissolution of amphi-boles or replacement of amphiboles by chlorite followed bydissolution of the chlorite. Nevertheless, it is logical thatdiagenetic processes have dramatically altered the heavymineral assemblages below Core 21.

CONCLUSIONS

1. Immature, pyroxene-amphibole assemblages charac-terize the heavy mineralogy of sands found at all Leg 18sites.

2. Except for sands found in the lower part of Site174A, where either a more northerly or southerly source isindicated, all sand deposits found at Sites 174A, 175, and176 have come from the Columbia River.

3. Present-day Columbia River sands have heavy mineralassemblages that are not typical of the sands it transportedduring the Pleistocene. During glacial times large quantitiesof amphibole-rich sediments were derived from upperColumbia River drainages and they dominated the

pyroxene-rich assemblages carried by rivers draining theCascade Range of Oregon and Washington.

4. Heavy mineral analysis of sands found at Site 177Aoff Vancouver Island and Sites 178 through 182 in the Gulfof Alaska suggest that the neighboring coast ranges ofBritish Columbia and Alaska, respectively, have been thesediment sources.

5. At Site 175, the degree of pyroxene etching increaseswith depth in the hole and points to the partial dissolutionof these unstable minerals by circulating intrastratal fluids.At Site 177A, the transition from an immature, amphiboleassemblage to a relatively mature, epidote heavy mineralassemblage has been attributed to the selective removal ofchemically unstable minerals by diagenetic processes.

ACKNOWLEDGMENTS

We wish to thank Drs. G. Ross Heath and John B. Hayesfor reviewing the manuscript and for making suggestions forits improvement. A special thank you is extended to MissSallie Hee and Mrs. Carol Lantz for preparing numerousheavy mineral slides.

REFERENCES

Atwater, T., 1970. Implications of plate tectonics for theCenozoic tectonic evolution of western North America.Bull. Geol. Soc. Am. 81, 35 13.

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UNETCHED

DSDPSITE 175(1) 3-1-125/128(2) 5-4-93/95(3) 5-5-61/63(4) 6-6-55/57(5) 9-2-35/36(6) 9-4-121/122(7) 10-5-128/130(8) 11-5-35/37(9) 14-1-112/114

(10) 14-6-126/128(11) 16-2-42/44(12) 19-2-146/148(13) 20-2-9/10(14) 20-2-133/134(15) 20-3-95/97(16) 22-CC

SLIGHTLY ETCHED MODERATELY TO EXTREMELY

ETCHED

Figure 5. Triangular diagram showing increasing degree of etching of hypersthenes with depth in thestratigraphic section at Site 175.

Bramlette, M. N., 1941. The stability of heavy minerals insandstone. J. Sediment. Petrol., 11, 32.

Carter, L., 1970. Surficial sediments in Barkley Sound andadjacent continental shelf. Ph.D. Dissert., University ofBritish Columbia, Vancouver, Canada.

Carson, B., 1971. Stratigraphy and depositional history ofQuaternary sediments in northern Cascadia Basin andJuan de Fuca Abyssal Plain, northeast Pacific Ocean.Ph.D. Dissert., University of Washington, Seattle,Washington.

Duncan, J. R. and Kulm, L. D., 1970. Mineralogy,provenance, and dispersal history of late Quaternarydeep-sea sands in Cascadia Basin and Blanco FractureZone off Oregon. J. Sediment. Petrol. 40(3), 874.

Duncan, J. R., Kulm, L. D. and Griggs, G. B., 1970. Claymineral composition of late Pleistocene and Holocenesediments of Cascadia Basin, northeastern Pacific Ocean.J. Geol. 78(2), 213.

Easterbrook, D. J., 1963. Late Pleistocene glacial eventsand relative sea level changes in the northern PugetLowland, Washington. Bull. Geol. Soc. Am. 74, 1465.

Krynine, P. D., 1942. Differential sedimentation and itsproducts during one complete geosynclinal cycle. 1stPanamerican Congress Mining Engr, and Geol. Proc. 2,537.

Kulm, L. D., Scheidegger, K. F., Byrne, J. V. and Spigai,J. J., 1968. A preliminary investigation of the heavymineral suites of the coastal rivers and beaches ofOregon and northern California. Ore Bin. 30, 165.

Pettijohn, F. J., 1957. Sedimentary rocks. 2nd Ed. NewYork. (Harper and Brothers) 718 p.

Scheidegger, K. F., Kulm, L. D. and Runge, E. J., 1971.Sediment sources and dispersal patterns of Oregoncontinental shelf sands. J. Sediment. Petrol. 41(4), 1112.

Silver, E. A., 1971. Small plate tectonics in the northeast-ern Pacific. Bull. Geol. Soc. Am. 82, 3491.

van Andel, Tj. H., 1959. Reflections on the interpretationof heavy mineral analyses. J. Sediment. Petrol. 29(2),153.

Vine F. J., 1966. Spreading of the ocean floor: Newevidence. Science. 154, 1405.

Whetten, J. T., 1966. Sediments from the lower ColumbiaRiver and origin of graywacke. Science. 152, 1057.

Whetten, J. T., Kelley, J. C. and Hanson, L., 1969.Characteristics of Columbia River sediment and sedi-ment transport. J. Sediment. Petrol. 39(3), 1149.

Wiese, W., 1969. Studies in properties, distribution, andheavy mineral contents of sediments in northern QueenCharlotte Sound. B. Se. Thesis, University of BritishColumbia, Vancouver, Canada.

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PLATE 1

Figures A, B, C Unetched hypersthenes. 175-5-5 (61-63 cm). Depthin section is 40.1 meters.

Figures D, E, F Unetched and slightly etched hypersthenes. 175-9-4(121-122 cm). Depth in section is 77.0 meters.

Figures G, H, I Slightly etched hypersthenes. 175-14-6 (126-128 cm).Depth in section is 127.6 meters.

Figures J, K, L Slightly and moderately etched hypersthenes.175-20-3 (95-97 cm). Depth in section is 179.9meters.

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100µ

• II

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