Soil development, relative dating, and correlation of late Quaternary marine terraces in southwestern Oregon

QUATERNARY RESEARCH 37, 667-t (IYY?l

Soil Development, Relative Dating, and Correlation of Late Quaternary Marine Terraces in Southwestern Oregon

JAMES G. BOCKHEIM

Department of Soil Sc,irncr. Uniwrsity of Wisc~on.sin. Madison. Wiscwnsirt 53706

HARVEY M. KELSEY

Depurtment of Geology, Wesiern Warhington UniwrAity, Bellin~ham. Washington 9X23

AND

JAMES G. MARSHALL III

Department of‘Soil Science. Uniwrsity of‘ Wisumsin. Madison, Wisconsin 53706

Received June 27, 1990

Flights of tectonically uplifted, late Quaternary marine terraces are preserved at several localities along the Oregon coast. Intervening coastal areas without marine terraces reflect net subsidence.

These gaps in the coastal terrace record make it difftcult to correlate terraces along the Pacific coast. To test the utility of soils in relative dating and correlation. two flights of marine lerraces

near Cape Blanc0 and Cape Arago were investigated. The terraces could be distinguished in each area from soil morphological properties and a quantitative index of soil development derived from

field descriptions. The soils in the two areas show a progression in development from spodosol\ to spodosols underlain by clayey material to ultisols. The lowest two terraces at Cape Blanco, which have reported age estimates of 80,000 and 105.000 yr. are correlative with the lowest two terrace\

at Cape Arago. The fifth and oldest terrace at Cape Blanc0 has no equivalent at Cape Arago. Soil development indices for the third and fourth terraces at each area allow two alternative \et5 of correlations. ,C’ 1992 Unwers~ty of Waahmpron

INTRODUCTION

Marine terraces in coastal Oregon are useful in evaluating crustal deformation along the Cascadia subduction zone (Kelsey, 1990; McInelly and Kelsey, 1990). These landforms occur discontinuously along the entire Oregon coast, but the most extensive and best-preserved marine terraces are along the southern Oregon coast between Coos Bay and Port Orford (Fig. 1).

The purposes of this paper are to de- scribe soil development on marine terraces in two areas, Cape Blanc0 and Cape Arago, and to assess the utility of soils in relative dating and correlating marine terraces sequences in coastal Oregon.

PREVIOUS WORK

Wave-cut platforms in the vicinity of

Cape Blanc0 are cut into Mesozoic sandstone and siltstone (Wells and Peck. 1961). The Cape Arago platforms are mostly cut into early Cenozoic sandstone and siltstone (Baldwin, 1974). The wave-cut platforms are overlain by late Quaternary marine terrace sediments that are 2 to 35 m thick and range from poorly consolidated pebble- cobble conglomerates to unconsolidated sands and silts (Kelsey, 1990). The predominant sediment at the surface of the marine terrace cover, on which the soils have developed, is unconsolidated, medium to fine sand. Although some of the soils have received eolian silt and sand, they have not been buried by alluvium and other terres- trial sediments. Therefore, we assume that soil development generally began soon af- ter terrace emergence.

In the Cape Aragc+Bandon area. south of

0033-5894/92 $3.00 CopyrIght 10 1992 by Ihe Univcrs~ry of Wa>hmgwn. All rights of reproduction m any form rexrved.

43O3(

43011

43-01

4204'

4203

(

5’ -

0’ -

t

5' -

0’ -

OREGON MARINE TERRACE SOILS

124-30' 124% 124”

\

L

I I I I 124'30' 124015' ,240

61

4P30'

FIG. I. Map showing location of the study areas and prominent fold axes developed in the late Pleistocene sediments. The inset depicts the tectonic setting.

Coos Bay (Fig. l), Griggs (1945) mapped four marine terraces at progressively higher elevations and named the lowest three the Whiskey Run, Pioneer, and Seven Devils terraces in ascending order. Adams (1984) subsequently named the fourth and highest terrace surface the Metcalf terrace. In the Cape Blanc0 area, Janda (1969) differentiated four marine terraces based on eleva- tion, cover stratigraphy, and soil development. From youngest to oldest, these terraces were named the Pioneer, Silver

Butte, Indian Creek, and Poverty Ridge terraces (Janda, 1970, unpublished results). Kelsey (1990) recognized a terrace younger than the Pioneer at Cape Blanc0 and named it the Cape Blanc0 terrace.

Age estimates for marine terrace deposits in southern Oregon are restricted to one numerical- and several correlation-age estimates. A coral (Balanophyllia elegans) col- lected from cover sediments on the Whis- key Run terrace at Coquille Point (Fig. 1) has a 230Th/234U age of 83,000 + 5000 yr

62 BOCKHtIM, KEL.SE\. AND MARSHAL.1

(Muhs et al., 1990). Stable-isotope data and amino acid ratios (D-alloisoleucinei t-isoleucine) were determined for mollusks at Coquille Point and compared to stable- isotope and amino acid data for the same species of mollusks on the lowest two wave-cut platforms at Cape Blanc0 (Muhs et al., 1990). These comparisons yielded correlation-age estimates of 80,000 yr for the Cape Blanc0 terrace and 105,000 yr for the Pioneer terrace.

No correlation- or numerical-age estimates exist for older terraces at Cape Blanc0 and Cape Arago. On the basis of the times at which sea level was as high or higher than present in the late Quaternary (Mesolella et al., 1969; Ku et al., 1974; Har- mon et al., 1983), McInelly and Kelsey (1990) suggest minimum possible ages for the Seven Devils and Metcalf terraces in the Cape Arago area of 125,000 and 200,000 yr. respectively. Using the same reasoning, Kelsey (1990) suggests minimum possible ages for the Silver Butte and Indian Creek terraces in the Cape Blanc0 area of 125,000 and 200,000 yr, respectively. The age of the Poverty Ridge at Cape Blanc0 is unknown. although Janda (1970) noted a lower Pleis- tocene Clinocardium in Poverty Ridge deposits and tentatively assigned the terrace an early to late Pleistocene age.

Few studies have been made of soils on marine terraces along the southern Oregon coast. Janda (1970) identified podzolic soils (spodosols) on the Pioneer and Silver Butte terraces, bisequal (podzolic over latosolic) soils on the Indian Creek terrace, and latosolic (ultisols) soils on the Poverty Ridge terrace. He used depth of oxidation, thickness of the E horizon, and color of the Bs horizon to distinguish among soils in the Cape Blanc0 area.

Buzzard and Bowlsby (1970) mapped the soils of the Cape Blanc0 area, and Haagen (1989) mapped the soils of the Cape Arago area. Hoppe (1989) provided analytical data for 10 profiles, including those on the Pio- neer, Indian Creek, and Poverty Ridge terraces in the Cape Blanc0 region. Nettleton

(JI tri. ( 1982) characterized 3 profiles In the Cape Arago-Bandon area, including soils on the Whiskey Run, Pioneer. and Seven Devils terraces.

Janda (1969) tentatively correlated terraces in the Cape Blanc0 and Cape Arago areas on the basis of lateral continuity. stratigraphic sequence, soil profile development, and erosional modification. He correlated the Pioneer terrace at Cape Blanc0 with the Pioneer terrace at Bandon. the lndian Creek terrace with the Seven Devils terrace. and the Poverty Ridge terrace with what was later named the Metcalf terrace. According to Janda’s (1969) scheme, the Silver Butte terrace at Cape Blanc0 had no equivalent at Cape Arago.

STUDY AREAS This study was confined to soils on ma-

rine terraces mapped in detail at Cape Blanc0 (Fig. 2) by Kelsey ( 1990) and at Cape Arago (Fig. 3) by Mclnelly and Kelsey (1990). Both study areas have mild, moist winters and cool, dry summers with abundant fog. Mean annual precipitation is 1800 mm, more than 70% of which falls from November through March (Buzzard and Bowlsby, 1970). The mean annual air temperature is 11.7”C. Summer (June. July, and August) and winter (December, Janu- ary, and February) temperatures show little variability and average 14.6” and 8.8”C, respectively.

Predominant tree species on the Cape Blanc0 and Pioneer terraces are Sitka spruce (Picea sitchensis) and shore pine (Pinus contorta var. contorta). The older terraces have a mixture of conifers. including Sitka spruce, Douglas fir (Pseudotsuga menziesii), Port Orford cedar (Chamaecy- paris lawsoniana), western hemlock (Z’suga heterophylla), and western red cedar (Thuja plicata). Much of the vegetation on the Pioneer and older terraces has been disturbed by clearing for pastures and timber harvesting.

METHODS Replicate soils (five) were excavated and

OREGON MARINE TERRACE SOILS 63

I* 124”30’ 124’=25’

:RRACE SEDIMENTS I I 1

;b = Cape Blanc0 FLORA CREEK

pi = Pioneer ib = Silver Butte FLORAS LK. kc = Indian Creek

K

pr = Poverty Ridge / 8

: BL$l&CK I.

31 oct#

39 ,‘.9 32 1’

CREEk I ZONE

420 5< 42050’

\y BATTLE-RO’CK 4 FAULT ZONE

42=‘4 I 12 l24o3O1 124O 25’

42’40’

FIG. 2. Map of the Cape Blanc0 area showing distribution of marine terrace deposits (Kelsey, 1990) and locations of soil pits. Soil pits are numbered as in Table 1 except that the year of sampling, 1989, has been removed.

described on leach terrace in the two study Soils were dug by hand to a minimum areas (Figs. 2 and 3). Soil pits generally depth of 1 m. A bucket auger was used to were located in areas distal to the back edge investigate horizons to a depth of 5 m. Pro- of the wave-c:ut platforms and where road file descriptions were recorded using crite- access was possible. We avoided areas se- ria of the Soil Survey Staff (1951, 1975, verely disturbed by logging and other hu- 1990) and modified by Birkeland (1984). man activities. We assume that the five soil We applied Harden’s (1982) quantitative profiles sampled represent the variation in index of soil development to soils of the two development on each of the terraces. regions. These indices were used for rela-

64 BOCKHElM. KE1.Sb.Y. /\luD MAKSHAI.1

IliKKACtSL:I~IMEN’I’; CHARLESTON FAU+&jC&$&,,&~ MINER CR. FAULT

SEVEN DEVILS FAULT ZONE

BAN&N

(7’30” 4305’

FIG. 3. Map of the Cape Arago-Bandon area showing distribution of marine terraces and location of soil pits (Mclnelly and Kelsey, 1990). Soil pits are numbered as in Table 2 except that the year of sampling, 1989, has been removed. Onshore structural data as mapped by McInelly and Kelsey ( 1990,

and references therein). Offshore data from Newton and co-workers (1980) and Clarke and co-workers

(1985).

tive dating and correlating terraces in the (moist color value), and pH. Soil pH was two study areas. Seven properties were measured potentiometrically in the labora- used in the analysis: clay films, texture plus tory on I:1 soil:water extracts. wet consistence (“total texture”), rubitica- Use of the comparative development in- tion (moist color hue and chroma), struc- dex requires that properties of the parent ture, moist consistence, melanization materials are similar. We were unable to


auger to the unoxidized beach sand (Cu horizon, see Birkeland, 1984) in all of the profiles. However, through an analysis of replicate profiles and road cuts, we were able to establish depths to Cu for soils used in the analysis. In the Cape Blanc0 region, the average depths were 125, 150, 225, and 325 cm for the Cape Blanco, Pioneer, Silver Butte, and Indian Creek soils, respectively (based on five profiles per terrace). We as- sumed a depth of 575 cm for the Poverty Ridge soil; this is a conservative estimate, because field ,investigations suggest that Poverty Ridge beach sediments may be weathered to depths of > 11 m. In the Cape Arago region, the average depths to the Cu horizon were 165, 140,250, and 275 cm for the Whiskey Run, Pioneer, Seven Devils, and Metcalf soils, respectively. Moist color of the Cu horizons was 2.5Y 612 (Cape Blanc0 region) or 2.5Y 5/4 (Cape Arago region); texture of the initial parent material was loamy sand or sand; all parent materials are structureless (single-grained), very friable, nonsticky and nonplastic, and de- void of clay films.

Following assessment of the parent material, we quantified each field property for a given horizon. These properties were nor- malized and summed for each horizon. The soil development index was calculated by dividing these sums by the number of quantified properties, multiplying by horizon thickness, and summing horizon products through the profile to the Cu horizon (Harden, 1982).

Soils on the terraces within a given locality were compared using analysis of variance (ANOVA) and nonparametric statis- tics. Morphological soil properties such as horizon thickness were tested for differences at the 0.05 probability level using ANOVA. The Mann-Whitney test, a nonparametric method for ranking unpaired measurements, was used to test differences in soil development indices between spa- tially adjacent marine terraces and between terraces of the two areas for correlation purposes.

RESULTS

Soil Morphology

Terrace sequence in the Cape Blanc0 area. Soils on the Cape Blanc0 terrace are poorly drained and have a thick (40 cm) A horizon over a weakly cemented ortstein layer (Bhsm horizon) with a sandy loam texture (Table 1 and Fig. 4B). Cracks in the ortstein layer contain illuvial humus and iron oxides. Some of the soils (89-S and 89- 31) have a thin (17-24 cm) clay-enriched (Bt) horizon, and others have old root chan- nels and other macropores filled with translocated clay.

Soils on the Pioneer terrace have two distinct morphologies that pertain to moisture regime. Well-drained soils on pastured up- lands (profiles 89-6 and 89-7) have a thick (3540 cm) A horizon over a Bt horizon av- eraging 42 cm thick and having a silty clay loam texture (Fig. 4A). A second type of Pioneer soil occurs under “pygmy” forest (wind-sculpted Sitka spruce and shore pine) in slight depressions on the landscape. Mapped as the Blacklock series (Buzzard and Bowlsby, 1970), these soils have been studied intensively in California by Jenny (1980). Blacklock soils on Pioneer surfaces are poorly drained and commonly have sandy loam textures (Table 1). These soils are differentiated from soils on the Cape Blanc0 terrace by having a thinner A horizon (25 cm), an E horizon, and a strongly and continuously cemented ortstein layer (Bhsm, Bsm horizons) (Fig. 4B).

Well-drained soils on the Silver Butte terrace have a thin (10 cm) A horizon over a moderately thick (70-75 cm) Bt horizon with a silty clay texture (Fig. 4A). Soils with poor drainage are more common than those with good drainage on Silver Butte terraces. The poorly drained soils are bisequal; i.e., they contain two sequences of an eluvial horizon and its related illuvial horizon. The upper sequum is 70 cm thick, has a sandy loam texture, is podzolic, and has a slightly thicker E horizon than Pioneer soils (Fig. 4B). The lower sequum has an argillic

66 BOCKHEIM. KELSEY, AND MARSHALI.

TABLE I. DESCRIPTIONS OF KEPRESENTAUVL SOILS ON MARINE ~LRRACES NEAR CAN HI ,A>( o. OREGON”

Horizon

Al A2 Bhs 1

Bhs2 Bhsm BC cox

A E 2Bhsm 2Bsm 2BC 2cox

AE E E/B Bsl Bs2 Bhs Bhsm E’ Bt BC

Q

AEI AE2 AE3 E Bsm Btl Bt2 Bt3 Bt4 Bt5 Bt6 BC

A BhiA Btl Bt2 Bt3 Bt4 BC

Depth (cm)

FItAd texture structure

89-39 (Caoe Blanio)

o-22 SYR 2.512 4 jfcr-2vfgr vfr \otpo 0 4.6 22-40 SYR 2.512 SI Zcosbk-2mcr fr S/PO 0 52 4&52 SYR 312 \I ?msbk-2mcr fr SSlP\ 0 5.3 52-61 7.SYR 416 sl ?msbk-2mcr fr, eti Sb/P\ (I 5.4 61-69 7.SYR 516 s m-3copr et-i 5oipo 0 s.5 69-93 ?.SYR 517 s m-Osg vti so/p0 I1 s.4 93-100 IOYR 616 s nsg vfr so/p0 II s I

89-33 (Pioneer) Is12 SYR 311 I Zfcr vfr-fr dp5 0 4.0

12-20 SYR 611 I m-lcoor fi \lP 0 4.3

2&42 2.5Y hi? 1 m-3tk&-2fgr vfi so/p0 (I 4.9 42-61 2.5Y 612 IS m-2tkpl-2fgr ti so/p0 0 4.1 61-82 IOYR 514 Iv m-2fgr ti so/p0 VlhPO 4.h 82-100 IOYR 514 IS m-Oag ti so/p0 0 4.7

89-2 (Silver Butte) Cl7 IOYR 511 sl 1 mvfgr ti so/p0 0 4.3

17-31 IOYR 411 \I 1 mvfgr fi SS/PS 0 4.2 3 l-42 7.5 YR 412 & 7.5YR 518 SI 1 mvfgr ti ssips 0 4.4

42-50 IOYR 416 bl lmvfgr ti SSIPS 0 4.9 50-66 IOYR 516 4 m-2msbk ti sslps vlnpf 5.2

66-12 7.5YR 414 SI 2fsbk fr SbiPS 0 5.1

72-83 IOYR 716 & 5YR 418 al m eti saips 0 5.1 83-98 IOYR 4/h \ m-lvfgr fl so/p0 0 5.1

98-109 2.5Y 612 cl 2coabk ti sips I npo S.1 109-185 2.5Y 612 cl lmsbk 6 sip5 I-2npf 5.2 185-204 2.5Y 512 Cl 0s fr so/p0 2”PO 5.0

89-l (Indian Creek) 043 7.5YR 512 sil 1 mvfgr ti ssip5 0 4.4 8-29 7.5YR 512 bii lmvfgr ti SSlP5 0 4.4

29-45 7.5YR 312 sil I mvfgr ti SIPS 0 4.6 45-58 ?.SY 712 sil 3copr-Zvfabk ti S/P 3npf 4.8 58-63 7.5YR 518 sicl m et3 0 5.0 63-78 2.5Y 6/4 5icl 2mabk fr 5/P lnpf S.I

71100 IOYR 516 sic1 2tnp1 fr SIP 3npf 5.2 IO&l40 IOYR 416 sic 2mpl-Zfabk fr SIP 3npf 5.1 14&162 7.5YR 516 sic 2mpl-2fabk fr S/P 3npf s.1

162-263 SYR 516 sic 2mpl-Zfabk fr S/P 3npf 5.1 263-320 2.5Y 612 Gel fr ssips 0 32@AM SYR 416 cl 2fgr fr vslp 0 s.2

89-10 (Poverty Ridge) &I2 2.5YR 212 sil 2.3mcr vfr bolpo 0 4.6

12-30 5YR 313 cl 2.3mcr vfr SSIPS I npfpo 5.0 30-49 2.5YR 314 cl lcosbk-2cocr fr sslps 2npfpo 5.1 49-65 5YR 418 cl lcoabk-2mcr fr SIPS 3mkpfpo 5.1 65-78 5YR 418 cl lcosbk-2fcr fr sips 3npfpo 5.0 78-97 SYR 418 vkscl m eti VS/P ?npfpo 5.1 97-190 7.5YR S/8 vkscl m efi VSIP I npo 5.2

Moist wet ai) Lab consirtence consistence film\ Pi-i -~

” Symbols used are the same as given in Soil Survey Staff(l951, pp. 139-140): soil horizon nomenclature follows Sod Survey Staf’f (1990) except that Cox = oxidized (Birkeland, 1984).

horizon that averages 65 cm thick and has a clay loam or sandy clay loam texture (Table 1). Sandy, unoxidized beach deposits occur below the argillic horizon at depths ranging from 200 to 250 cm.

Well-drained soils on the Indian Creek terrace have a thin (14 cm) A horizon over a moderately thick (90 cm) Bt horizon with

a clayey texture (Fig. 4A). Indian Creek soils with poor drainage are bisequal and have a similar horizon sequence as soils on the Silver Butte terrace (Table I and Fig. 4B). The main difference between the two soils is that the E and Bt horizons are thicker in Indian Creek soils. The upper sequum of Indian Creek soils is about 75 cm


Well-drained sequence Cape

Pioneer Silver

Blanco Butte 7

Indian CF32k

Po\~crl~ Rldce

BC

160 co

L i

B. Poorly drained sequence cape

BhCO Pioneer Silver Indian

Butte Creek Poverty

Ridge

200

FIG. 4. Diagrammatic epresentation of well-drained (A) and poorly drained (B) profiles on marine terraces near Cape Blanco, Oregon.

thick, has a silty clay loam or clay loam texture, and is, podzolic. The lower sequum has an argillic horizon that averages about 70 cm thick a.nd has a silty clay or sandy clay loam texture. Sandy, unoxidized beach deposits occur at depths in excess of 300 cm.

All of the F’overty Ridge soils we exam- ined are well drained. The argillic horizon commonly has a silty clay or clay texture and averages 1 m thick (Fig. 4A). Two of the profiles (89-10 and 89-28) have discontinuous ortstein that is impregnated with translocated clay. The C horizon of Poverty Ridge soils often has a sandy clay loam tex-

ture and colors ranging from yellowish red (5YR 5/8) to red (2.5YR 4/6, 5/8). The C horizon contains white patches of clayey material, manganese coatings on clasts, and highly weathered sandstone and siltstone clasts that upon removal leave clay impres- sions in the soil matrix. This material ex- tends to depths in excess of 11 m.

Morphological properties of all soils ex- amined on marine terraces in the Cape Blanco-Port Orford region, regardless of drainage class, were compared using analysis of variance. The thickness of the A horizon decreases from Cape Blanc0 through Silver Butte soils; the E-horizon thickness

68 BOCKHEIM, KELSEY. AND MARSHAI~I

increases from Cape Blanc0 through lndian Creek; and the Bsm (ortstein) horizon decreases in thickness from Cape Blanc0 through Poverty Ridge soils (Fig. 5). Soils on the Cape Blanc0 and Pioneer terraces are sandy throughout, i.e., in excess of 200 cm. Silver Butte and Indian Creek soils are bisequal with the upper, sandy sequum av- eraging 120 and 80 cm thick, respectively; and Poverty Ridge soils lack a sandy upper sequum. The Bt horizon increases in thickness from Cape Blanc0 through Poverty Ridge soils.

Bt Horizon

Cape Silver Indian Poverty Blanco Pioneer Butte Creek Ridge

FIG. 5. Thicknesses of the A, E, and Bsm horizons, sandy sequum, and Bt horizon for soils on marine terraces at Cape Blanco. Horizon thicknesses with similar lowercase letters are not different at P < 0.05 based on analysis of variance.

Other morphological soil properties useful in distinguishing among terraces at Cape Blanco-Port Orford that were not tested with analysis of variance include color and clay skins. Whereas the upper B horizon in Cape Blanc0 soils commonly is yellowish brown (IOYR 5/6), the corresponding horizon in Pioneer, Silver Butte, and Indian Creek soils is strong brown (7.5YR 516, Si 8); the upper B horizon of Poverty Ridge soils ranges from yellowish red (5YR 518) to red (2.5YR 4/6,4/S). Clay films on ped faces in Cape Blanc0 and Pioneer soils are common but generally are thin. In contrast, many clay films occur in argillic horizons of Silver Butte, Indian Creek, and Poverty Ridge soils. These films become progressively thicker with increasing age of the terraces. The depth to the Cu horizon increases from 125 cm in Cape Blanc0 soils to in excess of 575 cm in Poverty Ridge soils.

Terruw sequence in the Cmpe Arago- Bandon areu. Soils on the Whiskey Run terrace have sandy loam textures and are podzohc (Table 2). These soils have a moderately thick A and/or E horizon (37 cm) and under conditions of poor drainage a weakly cemented ortstein layer (Bhsm) that contains thin (4-10 mm) bands of illuvial organic matter or iron-enriched material (Fig. 6).

Soils on the Pioneer surface at Cape ArageBandon have sandy loam textures (Table 2). Unlike Whiskey Run soils, Pio- neer soils lack an A horizon; in poorly drained portions of the landscape the ortstein layer (Bhsm) is strongly and continuously cemented throughout (Fig. 6B).

Soils on Seven Devils terraces have two distinct morphologies relating to drainage class. Moderately well-drained soils have a thin (12-14 cm) A and/or E horizon, a 25- cm-thick Bhs horizon containing iron- enriched concretions, and a thick (90 cm) Bt horizon with a clay loam or clay texture (Table 2 and Fig. 6A). Poorly drained soils on the Seven Devils terrace have a podzolic morphology similar to that of soils on the Pioneer terrace and may be bisequal (Fig.

OREGON MARINE TERRACE SOILS

TABLE 2. DESCRIPTIONS OF REPRESENTATIVE SOILS ON MARINE TERRACES NEAR CAPE ARAGO-BANDON, OREGON~

69

HOliZOD Depth Munsell Field (cm) COtOr texture structure

Moist consistence

A s22 1OR 2/l E 22-33 7.5YR 512 2EIBhsm 3347 1OYR 512. 7SYR 518 20sm 47-56 1OYR 6/S 2BCm 5670 1OYR 618 2cox 7wKl 1OYR 616

A &6 1OYR 2/l E 6-20 IOYR 7/l Bhs 2&40 7.5YR 516 Bs 4ls61 IOYR 516 Bsm 6143 IOYR 516 B’hs 83-99 7SYR 414 BC 99-i 12 IOYR 6/8 cox 112-160 2.5Y 614 CU 160-180 2.5Y 5/4

A c4 E 414 Bhsl 1631 Bhs2 3149 Btl 4%74 Bt2 74126 Bt3 12&140’ Bt4 14C-165 Bt5 165-170 COX 170-200

5YR 211 5YR 6/l sil m- 1 fgr 5YR 4/6 Cl m-3fsbk

7.5YR 516 IOYR 516

7SYR 516 1OYR 518 1OYR 516 1OYR 518 5YR 5/6

A O-2.5 AE 2.5-10 Bhs I I O-26 Bhs2 26-36 Bhs3 36-47 Bt 47-78 Btgl 78-10.7 Btg2 107-122 Btg3 122-200 BCg 2Olk232

5YR 211 7SYR 4i2 sil m

5YR 314 sil Icosbk-3mcr 5YR 3/4 Sll lcosbk-3mcr

7.5YR 414 sil lcosbk-3mcr 1OYR 5/4 I lcosbk-2cocr 2.5Y 6/4 I m-2cosbk 2.5Y 616 I Icosbk-2fcr 2.5Y 612 sil m-lmsbk 2.5Y 514 sil m

89-48 (Whiskey Run) I 3CODr sl lmsbk-2mcr Sl ?tkpl-2cosbk IS 2vtkpLOsg S m-Osg S osg

89-14 (Pioneer. CA) Is Imsbk-lfgr’ IS m-lfgr SC 1 fgr SC1 lcosbk-lfgr 5 m-Osg 5 Icosbk-lfgr s m-Osg 5 m-Osg s osg

89-18 (Seven Devils) sil 2fcr

cl Zcosbk Cl Zmsbk C Zmsbk c Zmsbk C lmsbk cl lmsbk Is lfgr

89-16 (Metcalf) sil 2fcr

ti Ii Vfi vii ti ti

vfr fr vfr fr efi fr. vfi ti fr vfr

vfr fr fi Ii fi ti Ii ti fi vfr

vfr fi-vfi ti fr fr fr ti ti ii vfi

Wet consistence -~-

W/P s/p

so/p0 so/p0 so/p0 so/p0

so/p0 so/p0 so/p0 sslpo so/p0 sslpo so/p0 so/p0 so/p0

so/p0 soips ss/ps s/ps s/ps

vslps vslps vslp

S/P so/p0

ssJp0 sslps ssips ssips ssips s/ps

ss/ps sslps ss/ps sslps

Clay Lab films PH

0 4.0 0 4.6 0 4.5 0 4.4 0 4.5

vlkpo 4.5

0 4.2 0 4.5 0 4.9 0 5.0 0 5.0 0 5.2 0 5.2 0 5.2 0 5.3

0 4.2 0 5.1

lnpf 5.5 2npfpo 5.2 Zmkpfpo 5.1 3mkpfpo 5.1 3mkpfpo 5.1 Znpfpo 5.2 Zmkpfpo 5.2

0 5.2

0 0

lnpfpo I npfpo Znpfpo 3kpfpo 3kpfpo 3mkpfpo 2npfpo lnpf

4.3 4.8 4.9 5.1 5.4 5.1 5.2 5.2 5.2

u Symbols used are the same as given in Soil Survey Staff (1951, pp. 139-140); soil horizon nomenclature follows Soil Survey Staff (1990) except that Cu = no oxidation and Cox = oxidized (Birkeland. 1984).

6B). However, unlike Pioneer soils, thick clay skins occur within cracks of the ortstein layer in poorly drained soils on the Seven Devils terrace.

Soils on the Metcalf terrace have a thicker A horizon than soils on the Seven Devils terrace and lack an E horizon (Fig. 6). These soils have a moderately thick (82 cm) argillic hlorizon with a clay loam texture over gleyed subsoil (Fig. 6B). Profile 89-42 has discontinuous ortstein impregnated with translocated clay.

The main morphological features distinguishing soils on marine terraces in the

Cape Arag+Bandon area include thickness of the sandy sequum and the horizons that comprise it, presence or absence of an argillic horizon, and frequency and thickness of clay films. The thicknesses of the E and Bhsm horizons and the sandy sequum decrease from Whiskey Run through Met- calf (Fig. 7). Whereas Whiskey Run and Pi- oneer soils do not have an argillic horizon, the argillic horizon of Seven Devils and Metcalf soils averages 90 and 82 cm thick, respectively. Clay films are limited to a very few tubules in Whiskey Run soils. Many clay films are present in older soils,

70 BOCKHEIM, KELSEY. AND MARSHALL

FIG. 6. Diagrammatic representation of well- drained (A) and poorly drained (B) profiles on marine terraces near Bandon, Oregon.

and the films become progressively thicker with increasing age. Clay films are thin in Pioneer soils, moderately thick in Seven Devils soils, and thick in Metcalf soils.

Relative Dating

Soil development indices were used to rank the soils in order of relative age. The ranking for Cape Blanc0 soils is: Cape Blanc0 G Pioneer < Silver Butte < Indian Creek G Poverty Ridge (Fig. 8A). Soils on the Poverty Ridge terrace have significantly greater soil-development indices than those on the other terraces. Based on the Mann- Whitney test of the difference between indices, soils on the Indian Creek terrace are significantly different from those on Pio-

h h -__.

\+‘l~~\Ley Run Pmnccr Swen DC\ II\ LlC~ii~.ll t

FIG. 7. Thicknesses of the A, E. and Bsm horizons. sandy sequum. and Bt horizon for soils on marine terraces at Cape Arago. Horizon thicknesses with similar lowercase letters are not different at P 4 O.OS based on analysis of variance.

neer and Cape Blanc0 terraces but not from those on the Silver Butte terrace. Despite obvious differences in morphological properties, there are no significant differences in soil-development indices on the two younger terraces at Cape Blanco.

At Cape Arago the soils can be ranked: Whiskey Run d Pioneer 4 Seven Devils G Metcalf (Fig. 8B). Based on the Mann- Whitney test, soils on the Metcalf and Seven Devils terraces are significantly more developed than soils on the Pioneer


” ‘33 WR PI PI SB SD IC ME PR

CBWK PI PI SB IC SD ME PK

FIG. 8. Soil-development indices for marine terraces in southwestern Oregon. (A) Cape Blanc0 terrace sequence: CB, Cape Blanco; PI, Pioneer; SB, Silver Butte; IC, Indian Creek; and PR, Poverty Ridge. (B) Cape Arago terrace sequence: WR, Whis- key Run; PI, Pioneer; SD, Seven Devils; and ME, Metcalf. (C) Favored correlation of marine terraces based on indices <and terrace morphology (see text). (D) Alternative correlation of marine terraces. Values with similar lowercase letters are not different at P < 0.05 based on the Mann-Whitney test.

and Whiskey Run terraces. However, there are no significant differences between the Metcalf and Seven Devils soils and between the Pioneer and Whiskey Run soils.

DISCUSSION

Soil Evolution over Time

Soil evoluti’on at Cape Blanc0 and Cape Arago is determined by vegetation, subtle differences in relief that influence drainage, and time (Fig,. 9). Active dunes and fore-

dunes along the southern Oregon coast have poorly developed soils, primarily Typic Tropopsamments (Nettleton et al., 1982). Once these dunes become stabilized, spodic horizons may form under the influence of forest vegetation in 10,000 yr or less. For example, Nettleton et al. (1982) reported Entic Troporthods on stabilized dunes representing the Tenmile surface (530&10,800 yr).

Under well-drained, forested conditions, the spodic horizon may continue to develop, producing Typic Troporthods on Cape Blanco, Whiskey Run, and Pioneer terraces (Fig. 9). In slight depressions on these terraces, an ortstein layer may develop that retards moisture movement and yields Typic Tropaquods.

Andic Humitropepts occur within l-2 km of the Pacific Ocean on Cape Blanc0 and Whiskey Run terraces. Based on field data and unpublished analytical data, these soils have a thick (2 18 cm) A horizon with a bulk density of 1.0 g/cm3 or less and high levels of acid-oxalate-extractable aluminum and iron. Clays may increase in these soils over time, yielding Andic Haplohumults on the Pioneer terrace at Cape Blanco. To have andic soil properties, the parent materials do not need to contain volcanic ash (Soil Survey Staff, 1990).

Under conditions of free drainage, Typic Haplohumults are dominant on Silver Butte, Indian Creek, and Poverty Ridge terraces at Cape Blanc0 and on Seven Devils and Metcalf terraces at Cape Arago. In poorly drained depressions, Ultic Tropa- quods are found on Silver Butte, Indian Creek, and Seven Devils terraces and Aquic Haplohumults occur on the Metcalf terrace.

We hypothesize that well-drained and poorly drained spodosols on marine terraces in southern Oregon are ultimately converted to ultisols (Fig. 9). With good drainage, clays accumulate progressively over time, leading to a gradual thickening of the argillic horizon in Haplohumults. Sev- eral soils on Seven Devils and Poverty Ridge terraces have discontinuous ortstein

72 BOC‘KHkIM. KELSEY, .AND MARSHAL.1

Cape Rlanco. Whiskey Run marine terraces

(SO.000 yr)

Silver Butte, Indian Crceh. Swen Devils nl;li-inc‘ terraces (-1 7.5 OOO-

3O.itl yr)

Metc;~lt. Poverty R~d~:r marine

li’lI;lcc\ l>501).001J yr)

FIG. 9. Proposed soil succession in relation to vegetation, drainage. and time in south-coastal

Oregon.

that has become impregnated with clay. Continuous ortstein in poorly drained spodosols (i.e., Tropaquods) may be destroyed by cracking during summer desiccation and root elongation. Breakup of the ortstein would allow free drainage, yield an oxidiz- ing regime, and enable migration of clay into what was previously a spodic horizon. The clays may be produced from weather- ing of primary minerals and synthesis of secondary minerals as was reported by Chadwick et al. (1990) on marine terraces in northern California.

Correlation of Marine Terraces

We used soil development indices to correlate marine terrace sequences at Cape Blanc0 and Cape Arago (Fig. 8C and 8D).

Soil development is similar on the Cape Blanc0 and Whiskey Run terraces, suggest- ing that these terraces are correlative. The Whiskey Run terrace at Coquille Point has a numerical age of 83,000 2 5000 yr (Muhs et al., 1990). Soils on the Pioneer terraces at Cape Blanc0 and Cape Arago are comparable and slightly more developed than the Cape Blanc0 and Whiskey Run soils. The Pioneer terrace at Cape Blanc0 has been assigned a correlation-age from amino- stratigraphy of 105,000 yr (Muhs et al.. 1990).

Based on soil-development indices, soils on Silver Butte and Seven Devils terraces are comparable (Fig. 8C). Moreover, the Silver Butte terrace is backed by a paleo- sea cliff that has approximately the same


degree of degradation as the Seven Devils paleo-sea cliff. However, comparison of the suite of profile-development indices for both soils makes possible an alternative correlation in which the Silver Butte terrace has no equivalent at Cape Arago (Fig. 8D). If this is the case, then an unusual terrace preservation scenario could be present on the Oregon coast, namely the 125,000 yr sea-level highstand may be preserved as only a single 2.6km* terrace remnant (Sil- ver Butte) along a 70-km coastal reach of uplifted terraces from Coos Bay to south of Cape Blanc0 .

The Indian Creek terrace at Cape Blanc0 is most likely correlative with the Metcalf terrace at Cape Arago (Fig. 8C). However, soils on the Metcalf terrace are similar to soils on the Seven Devils terrace, so con- ceivably the Indian Creek terrace is correlative with the Seven Devils terrace (Fig. 8D). On the batsis of soil development, the Indian Creek could be older than both of these soils (Figs. 8A and 8B), but this pos- sibility is unlikely because the morphology of the Indian Creek terrace is at least as well preserved as that of the Metcalf terrace.

The Poverty Ridge soil at Cape Blanc0 is by far the most strongly developed soil (Figs. 5 and 7) and apparently has no equivalent in the Cape Arago sequence (Figs. 8C and 8D).

SUMMARY

Soils developed on elevated marine terraces near Cape Blanc0 and Cape Arago illustrate a progression in development from spodosol:s, to spodosols underlain by clay-enriched material, to ultisols. Soil- development indices were useful in distinguishing among terraces at each locality and in correlating terraces between the two study areas.

At Cape Blanc0 the relative ages of the soils are: Cape Blanc0 < Pioneer < Silver Butte < Indian Creek G Poverty Ridge; at Cape Arago tlhe relative ages of the soils

are: Whiskey Run G Pioneer < Seven Dev- ils < Metcalf.

From soils data, we correlate the Cape Blanc0 terrace with the Whiskey Run terrace and the Pioneer terrace at Cape Blanc0 with that at Cape Arago. Soil characteris- tics and soil-development indices on the older terraces allow for at least two sets of correlations. However, in both sets of correlations, the Poverty Ridge terrace at Cape Blanc0 is distinctly older and has no equivalent at Cape Arago.

ACKNOWLEDGMENTS

Funding for this project was supplied by the Surti- cial Processes Program, Division of Earth Sciences, National Science Foundation (EAR 8903470). We ap- preciate constructive criticism of this manuscript by Drs. P. W. Birkeland, J. W. Harden, K. McSweeney, D. R. Muhs, and F. C. Ugolini. The Oregon State Parks kindly allowed us to investigate soils in Cape Blanco, Floras Lake, and Cape Arago State Parks. Mr. M. R. Hewitt and Mr. A. LaTomme assisted us in locating sampling sites.

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Documents

Soil development, relative dating, and correlation of late Quaternary marine terraces in southwestern Oregon