14. neogene tephrochronology from site …14. neogene tephrochronology from site 758 on northern...

Weissel, J., Peirce, J., Taylor, E., Alt, J., et al., 1991Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 121

14. NEOGENE TEPHROCHRONOLOGY FROM SITE 758 ON NORTHERN NINETYEAST RIDGE:INDONESIAN ARC VOLCANISM OF THE PAST 5 MA

J. Dehn,2 J. W. Farrell,3 and H.-U. Schmincke2

ABSTRACT

A tephrochronology of the past 5 Ma is constructed with ash layers recovered from Neogene sediments during drilling at ODPLeg 121 Site 758 on northern Ninetyeast Ridge. The several hundred tephra layers observed in the first 80 m of cores range inthickness from a few millimeters to 34 cm. Seventeen tephra layers, at least 1 cm thick, were sampled and analyzed for majorelements. Relative ages for the ash layers are estimated from the paleomagnetic and δ 1 8 θ chronostratigraphy.

The ash layers comprise about 1.7% by volume of the sediments recovered in the first 72 m. The median grain size of the ashesis about 75 µm, with a maximum of 150 µm. The ash consists of rhyolitic bubble junction and pumice glass shards. Blocky and platyshards are in even proportion (10%-30%) and are dominated by bubble wall shards (70%-90%). The crystal content of the layersis always less than 2%, with Plagioclase and alkali feldspar present in nearly every layer. Biotite was observed only in the thickestlayers.

The major element compositions of glass and feldspar reflect fractionation trends. Three groupings of ash layers suggest differentprovenances with distinct magmatic systems. Dating by δ 1 8 θ and paleomagnetic reversals suggests major marine ash-layer-produc-ing eruptions (marine tephra layers > 1 cm in thickness) occur roughly every approximately 414,000 yr. This value correlates wellwith landbased studies and dates of Pleistocene Sumatran tuffs (average 375,000-yr eruptive interval). Residence times of themagmatic systems defined by geochemical trends are 1.583, 2.524, and 1.399 Ma. The longest time interval starts with the leastdifferentiated magma.

The Sunda Arc, specifically Sumatra, is inferred to be the source region for the ashes. Four of the youngest five ash layersrecovered correlate in time and in major element chemistry to ashes observed on land at the Toba caldera.

INTRODUCTION

Purpose of this Study

The tephra layers recovered in the Pliocene to Holocene sedi-ments of Ocean Drilling Program (ODP) Leg 121 Site 758 (Fig.1) provide a unique record of explosive volcanism in the north-eastern Indian Ocean. Several hundred discrete ash layers, rang-ing from a few millimeters to 34 cm in thickness, were observedin Holes 758A, 758B, and 758C drilled on northern NinetyeastRidge (Peirce, Weissel, et al., 1989). The excellent core recoverythrough the Pliocene (102%), large volume of ash (1.7% bulksediment), and freshness of the glass are ideal for a tephrochro-nological study. This study focuses on the youngest of thesetephra layers (0.075 to 5.1 Ma).

Case studies in tephrochronology are especially useful fordetermining the (1) source region of the ashes; (2) volcanic,magmatic, and temporal evolution of the source regions; (3)eruptive cycles; and (4) lithostratigraphic and chronostratigraphiccorrelations in marine sedimentary sequences when numericallydated (Bitschene and Schmincke, 1990). The aim of this casestudy is to develop a tephrochronology for Site 758 using thestratigraphy, ages, and chemical compositions of the major ashlayers. Analyses were performed on 29 samples taken from 17major ash layers, labeled A through M, which had a thickness of1 cm or more (Fig. 2).

1 Weissel, J., Peirce, J., Taylor, E., Alt, J., et al., 1991. Proc. ODP, Sci. Results,121: College Station, TX (Ocean Drilling Program).

2 GEOMAR, Forschungszentrum für Marine Geowissenschaften der Christian-Albrechts-Universitat zu Kiel, Wischhofstraße Gebaude 3, D-2300 Kiel 14, FederalRepublic of Germany.

3 Department of Geology, Brown University, Providence, Rl 02912-1846, U.S.A.

Regional Setting of Site 758

Site 758 is at 5°23.05'N, 90°21.67'E, on the crest of NinetyeastRidge between Deep Sea Drilling Project (DSDP) Sites 216 and217 (Fig. 1). The water depth at Site 758 is 2924 m. At thislocality, Ninetyeast Ridge comprises several en echelon blocks.Site 758, which is on the southeast side of one such block, lies atleast 1000 m above the Bengal Fan.

Site 758 is approximately 1000 km from the nearest volcani-cally active region, Sumatra. Sumatra is the northernmost part ofthe Sunda Arc and has at least one restive caldera. The most recenteruption in this region was from the Toba caldera at approxi-mately 75,000 yr (Ninkovich et al., 1979; Rose and Chesner,1987, 1988). This caldera, one of the largest Quaternary calderason Earth (Smith and Bailey, 1968), is probably the source forseveral of the tephra layers.

Previous Studies of Northeastern Indian Ocean TephrasMost previous work has been performed on the youngest

eruption of the Toba Caldera (Ninkovich et al., 1979; Ninkovich,1979; Rose and Chesner, 1987; Chesner, 1988). These studies areprimarily land based, though some authors have studied pistoncores containing marine tephra layers correlated to the eruptions(Ninkovich et al., 1979; Ninkovich, 1979; Kennett, 1981). TheToba ash, as it is called in the literature, has been discovered atmany localities in the northeastern Indian Ocean (Ninkovich etal., 1979; Fig. 1). At least 800 km3 of ash was erupted from Toba(Rose and Chesner, 1987) and fell over a minimum area of 5 xI06 km2, mostly over the Bay of Bengal (Ninkovich et al., 1979;Fig. 1). The distribution of the ash may have reached as far as3000 km (Williams and Royce, 1982). Because Site 758 lieswithin this area, the recovery of the Toba ash and other tephralayers was expected.

Older eruptions of the Toba caldera complex occurred at 0.84(Diehletal., 1987) and 1.20 Ma(Nishimuraetal., 1977). Chesner

273

J. DEHN, J. W. FARRELL, H.-U. SCHMINCKE

500 1000

kilometers

Cores with Toba

Cores without Toba

Figure 1. Site 758 and other locations in the northeastern Indian Ocean where the youngest tephra layer from the Toba caldera

(75,000 yr) was recovered. The thickness of the layers in centimeters accompanies each point (after Ninkovich et al., 1979;

Ninkovich, 1979).

(1988) studied the last four eruptions of the Toba caldera at 0.075,0.450,0.840, and 1.2 Ma. He described these layers as the young-est Toba tuff (YTT), the middle Toba tuff (MTT), the oldest Tobatuff (OTT), and the Haranggoal dacite tuff (HDT). These tuffs aretentatively correlated to the Site 758 tephra layers as follows: YTTto layer A, MTT to layer C, OTT to layer E, and HDT to layer F.(A detailed description of the nomenclature follows.)

The drill cores previously recovered in the northeastern IndianOcean have not been suitable for the reconstruction of a continu-ous tephrochronology. The sedimentary records of Sites 216 and217 are marred by poor recovery and disturbance from rotarydrilling (von der Borch, Sclater, et al., 1974). Piston cores fromthe Bay of Bengal, such as those recovered aboard the Vema andthe Conrad, provide continuous and undisturbed records, butsample only the near-surface Pleistocene sediments (Ninkovich,1979).

METHODS

Based upon shipboard observation, 29 samples representing17 discrete ash layers were taken (Table 1). The grain size,morphology, and crystal components of the ashes were studied insmear slides and thin sections. Between 15 and 20 shards weremeasured in each slide by calibrated ocular scales.

The major element compositions of the glass shards and min-eral grains were determined using an ARL electron microprobewith natural glass and mineral standards at the Department ofMineral Sciences, Smithsonian Institution. Operating conditionswere 15-kV accelerating voltage, 10-µm beam spot, and 14-nAbeam current. Measured Na2θ and K2O concentrations may be

slightly lower (up to 1%) as a result of selective sodium andpotassium loss during the microprobe analysis.

DESCRIPTION OF THE TEPHRA LAYERS

Stratigraphy and Lithology

The ash layers were recovered in the nannofossil ooze of UnitI at Site 758 (Peirce, Weissel, et al., 1989). This unit consists oftwo subunits: IA is a nannofossil ooze with foraminifers and clayand clayey nannofossil ooze with foraminifers from 0 to 25.2 mbelow seafloor (mbsf), and IB is a nannofossil ooze with clay,foraminifers, and micrite from 25.2 to 121.7 mbsf. The ash layersare present in Pliocene (5.1 Ma) and younger sediments.

Many of the tephra layers are present in one hole, but not inthe neighboring one. All but one of the layers fall into the intervalsbetween cores, where as much as 2.7 m of sediments is notrecovered. This "under recovery" (Ruddiman et al., 1987) is aproduct of the coring method and is surmounted by constructinga composite stratigraphy. A detailed composite stratigraphy forthis section is presented by Farrell and Janecek (this volume). Theremaining tephra layer does not appear to correlate among theholes. The unique layer B in Hole 758A could be the result ofreworking of the sediments by slumping, bottom currents, orbioturbation (Bramlette and Bradley, 1942; Ruddimann andGlover, 1982).

Macroscopic Description of the Ashes

Tephra layers with thicknesses of 1 cm or more are defined as"major." Seventeen such layers were identified in the first 5.1 Ma(0-72 mbsf) of Site 758 and labeled A through M, with A the

274

NEOGENE TEPHROCHRONOLOGY, SITE 758: THE PAST 5 MA

Sample

APAT

AMP OH T

PS LA A ThicknessN G of layer

Hole 758

BDepth(mbsf)

AU-A AU-C

A-B

AL-A AL-C

B-A

C-A

D-A

E-A

F-A

C-B

d-B

E-B

G-B

C-C

H-A

I-A

H B

h-B

I-B

K-B

L-B

M B

oo o o o o

o o

o o

o oo o

o

o o o

o oo o o

(cm)

34

O

o

o oo

23

13

2

5

5

13

5

2

8

1

4

4

o

- 0

10

20

30

- 40

- 50

- 60

70

80

Figure 2. Tephrostratigraphic diagram of the upper Neogene tephras at Site 758. The samples are coded by layer (A-M), stratigraphic indicator (U = upper, L =

lower), and hole (A, B, or C). The minerals phases measured in each sample are represented by the circles. Quartz was present in every layer sampled; the other

mineral phases measured in the samples are AP AT = apatite, AMPH = amphibolite, BIOT = biotite, SAN = sanidine, and PLAG = Plagioclase. The thickness of

the layers is shown by the relative scale of the boxes; shading indicates layers dated by δ 1 8 θ . Note that layer B is not present in Holes 758B and 758C.

Table 1. Major ash layers and their maximum age range defined by paleomagnetic andδ 1 8 θ dating, thickness, depth, and sample locations at Site 758.

Layer

A (upper)A (mixed)A (lower)B(A?)CDdEFGHhIJKLM

Maximumage range

(Ma)

0.071-0.1100.071-0.1100.071-0.1100.071-0.1210.512-0.5380.731-0.7500.756-0.7600.774-0.7801.273-1.2941.596-1.6532.238-2.2653.664-3.6664.124-4.1314.552-4.5604.666-4.6674.759-4.7655.062-5.063

Thickness(cm)

343434

72313255

135281442

Depth(mbsf)

1.50-1.841.50-1.841.50-1.841.94-2.017.12-7.35

10.80-10.9311.25-11.2711.62-11.6719.82-19.8724.00-24.1331.20-31.2549.67-49.7056.67-56.7563.12-63.1365.09-65.1366.66-67.0071.61-71.63

Core,

758A

1H-2, 5

1H-2, 251H-2, 472H-1, 1142H-4, 38

2H-4, 1153H-3, 125DNE4H-5, 3

7H-2, 120DNE

1H-11H12X-46X47R-73R

section, interval (cm)a

758B

1H-1, 114

1H-5, 119

2H-2, 252H-2, 61DNE3H-4, 694H-3, 86H-2, 476H-7, 17

7H-6, 297H-CC, 148H-4, 1111H-10H

758C

1H-2, 14

1H-2, 27

1H-7, 1

1H

Tephra layers lost between cores are marked "do not exist" (DNE).

275


youngest layer and M the oldest. Layers identified by peaks in themagnetic susceptibility of the sediments (up to 113 × I0"6 cgs)are denoted by capital letters. The lowercase letters (d and h)identify those ash layers visible in the cores, but not readilyidentified by large susceptibility peaks. Because these two layersare thin (2 cm) in comparison with the other layers, it is probablethat they fall between points of the susceptibility measurement.

The major tephra layers appear as gray to grayish brown layersof varying thickness (Fig. 2). All the ash layers have sharp basalcontacts to the host sediment. The upper contacts are gradationaland show normal grading in size and density as well as tephraconcentration in the host sediment. The ashes are primarily com-posed of glass shards, pumice fragments, and crystals. No lithicclasts were observed in any of the layers.

The tephra layers are marine fallout ash layers formed byexplosive eruptions that dispersed the tephra, allowing it to accu-mulate over a large area (to a distance of at least 2500 km). Thetephra was deposited on the ocean surface and then settled throughmore than 2000 m of water. After deposition, reworking bybottom currents and bioturbation of the ash layers diffused thetephra within the host sediment. The combination of these frag-mentation, transport, and reworking mechanisms leads to theobserved grading of the tephra. All of the layers exhibit weaknormal grading of particle density, grain size, and particle con-centration in the host sediment (Fig. 3). Crystals are rare, com-prising less than 1 % of the ash volume with the exception of layersB and d, each of which has approximately 2% crystals by volume.Crystals, where present, are concentrated at the base of a layer.

The thicknesses of the ash layers are based on visual inspec-tion, core photograph interpretation, and magnetic susceptibility.The thicknesses of the major tephra layers vary widely to amaximum of 34 cm for layer A and with an average thickness of9 cm (Table 1). Individually the layers appear to be a minorcomponent, yet together they comprise up to 1.7% of the sedi-ments recovered through the Pliocene. Thickness is the mostobvious difference between the tephra layers (Fig. 2). The thickestlayers, G, D, C, and A, represent two-thirds of the ash by volume.The remaining layers, B, d, E, F, H, h, I, J, K, L, and M, have anaverage thickness of only 4 cm.

Most of the layers correlate among the holes at Site 758, andthose that are not present in a hole usually fall into an interval lostbetween cores. Layer B in Hole 758A, however, does not correlateto any tephra layer in Holes 758B and 758C. Furthermore, thislayer falls into an interval fully recovered in all three holes at Site758. This tephra layer is atypical in other aspects as well. LayerB is crystal rich (2%) and has a large grain size (1-2 mm) relativeto the other ashes. It occurs only 12 cm below layer A and has anangular contact to the surrounding sediments (Fig. 3). Both theupper and lower contacts to the nannofossil ooze are sharp.Because it is so different from the other tephra layers and becauseit lies so close to layer A, this layer is thought to be a basal partof layer A, an ash pod, displaced downward in the core byslumping or reworking by bottom currents. The size and thicknessof the pod (7 cm) seem to rule out bioturbation. The grain size andhigh crystal concentration support the idea of a slump of densermaterial in the surrounding ooze. There is no sign of such distur-bance below layer A in Cores 121-758B-1H or 121-758C-1H,which are in holes 100 m away. The latter core was severelydisturbed by drilling and evidence of such a slump could beobscured.

Layer D was also not observed in Hole 758B, though thisinterval was recovered. Visual inspection of the cores shows anash layer, d, at the stratigraphic location where D would beexpected. Layer d is possibly a diffused or reworked tephra D.

cm

10

20

30

40

50

F I

Figure 3. Core photograph of the Toba ash (layers A and B). Layer A has anexpanded, yet typical, morphology of the tephra layers, with a sharp basalcontact to the host sediment and a gradational upper contact. Where present,crystals are concentrated at the base of each tephra layer, indicating a densitygradation. Layer B may be reworked from layer A.

276


Further evidence of the relationship between layers A and B andlayers D and d based on their chemical compositions is discussedin greater detail below.

Microscopic Description of the Ashes

The ash layers are a concentrated, yet loose, aggregation ofglass shards, pumice, and crystals within organic sediments. Theglass shards have a median grain size of 75 ± 25 µm, with amaximum size of 150 µm. Bubble wall shard forms dominate(70%-90%), followed by platy and blocky shards (10%-30%each) and crystals (typically <1%). The refractive index of theglass is low (less than 1.54) indicating a silica content of 70% orgreater (Schmincke, 1981). No brown volcanic glass of basalticcomposition was observed in any sample. The glass is alwaysisotropic and does not appear altered. Fractures, hydration cracks,or incrustation were not observed in smear slides or thin sections.The glass is probably slightly hydrated through interaction withseawater and/or interstitial water, but significant alteration has notyet taken place.

Quartz and feldspars comprise the bulk of the crystals in thetephra layers, followed by biotite, apatite, and amphibole. Quartzis present in every tephra layer sampled. Plagioclase is commonin 30-60-µm subhedral crystals displaying twinning but little orno zoning. Alkali feldspars occur in layers A, D, d, G, h, I, and Mas larger, 40-80 µm, euhedral to subhedral crystals. Only thecrystal-rich layers B, d, G, and I contain iron-bearing minerals,chiefly biotite and minor amphibole.

The grain sizes of the tephra (50-150 µm) suggest that thetransport distance was approximately 1000 km (Fisher, 1964;Walker, 1971). This supports the conclusion that the tephras camefrom nearest volcanically active region, Sumatra.

GEOCHEMISTRY OF THE TEPHRA LAYERS

Major element concentrations were determined for single glassshards and mineral grains using an electron microprobe. Volcanicglass of different morphology was analyzed in every sample, andPlagioclase and potassium feldspars were analyzed wherever pre-sent, as well as other crystal phases.

Geochemistry of the Glass Shards

The analyzed volcanic glasses are isotropic and appear freshwith major oxide sums ranging between 90% and 97%. Threegeneral morphological categories of shards were chosen for ana-lysis: platy, bubble wall, and blocky. These three forms weremeasured in each sample, but no significant change in major oxidecomposition was seen as a function of shard morphology. Anaverage of 10 shards was analyzed per thin section, with a mini-mum of one thin section per sampled layer (Table 2). Layer J wasnot sampled for chemical analysis because it was identified as a"major" layer only after onshore analysis of shipboard records.All the glasses are classified as high-silica rhyolites with Siθ2concentrations of 72% to nearly 79% and MgO concentrations ofless than 1%.

Plots of major oxide sums subtracted from 100 give roughestimates of the percentage of water in the glasses. The inferredwater contents are a result of hydration during subaqueous altera-tion and not of the original volatile content in the magma. Theinferred water contents show a slight drop from 6% to 5% at 35mbsf. The break in the water contents roughly corresponds withthe break between Subunits IA and IB (Pierce, Weissel, et al.,1989) and thus the clay and carbonate content in the surroundingsediments. This relation suggests that the preservation of theglasses, and thus the change in the water content, is partiallyinfluenced by the host sediment and interstitial water.

Variation diagrams of FeO, CaO, AI2O3, and K2O vs. Siθ2(Fig. 4) all show a distinct grouping by ash layer. Layer L standsout in every plot as the least evolved, with concentrations of2.43%-2.65% FeO and 72.25%-73.28% SiO2. Layer A, inferredto be the Toba ash from the 75,000-yr eruption of the Toba calderain Sumatra, is the most evolved layer, with concentrations of76.65%-78.89% Siθ2 and 0.72%-1.03% FeO. Layers A and Bhave similar compositions of major oxides, supporting the con-clusion that layer B is a displaced pod of layer A. Layers D and dare also chemically indistinguishable. Coupled with their stratig-raphic correlation, the chemistry of these two layers suggests thatthey could be the same layer in each hole.

Chemical trends are visible for CaO, FeO, and AI2O3 vs. Siθ2.Increasing silica concentrations correlate with lower CaO, FeO,and AI2O3 concentrations. These trends are expected, but do notcorrelate directly with depth, and thus the age, of the tephra layer.Layers L and E, although significantly different from the otherlayers in composition, lie along the trends formed by the othertephras. FeO content increases slightly with very high Siθ2 con-tents in analyses from layers H and A (increasing from 0.6% to0.8% FeO with Siθ2 of 78%-79%). The K2O vs. Siθ2 diagramshows groupings by tephra layer, but no clear trend. A trend inthis data could be obscured as a result of the large scatter in valuesof K2O. This scatter is probably caused by inaccuracies in meas-urement due to sodium and potassium evaporation during themicroprobe analysis or a gain in potassium through low-tempera-ture alteration.

Though no empirical correlation between age and chemicalcomposition is seen, several of the ashes are clearly related. Adiagram of CaO vs. FeO (Fig. 5) displays three trends, one whichlinks layers A, B, C, D, d, E, and F (Group 1), one relating H, K,and L (Group 2), and one relating I and M (Group 3). These samegroupings are less clear, though present, for AI2O3 vs. FeO. CaOvs. AI2O3 shows an inverted, yet similar, relationship betweenthese layers. These groupings of layers, though different in theirelement concentrations, all have similar element ratios. Since Zrand Nb cannot be measured by microprobe, Ca and Fe are used todetermine cogenetic trends in the ash layers. The correlation ofthese ash layer groupings could be supported by similar trends inMgO vs. FeO, but the MgO concentrations are too small to clearlydistinguish the relationships of the tephra layers.

In order to examine the change in the major oxides with age,plots were made of major oxides and major oxide ratios vs. depth(Fig. 6). Depth is plotted rather than age because different meth-ods were used to date the tephras and the measured ages vary byup to 0.04 Ma between methods. A more detailed discussion ofthe age of the tephra layers follows.

Certain oxides, such as AI2O3, show considerable scatterwithin a single tephra layer. Others, such as FeO, CaO, and Siθ2,are very well restrained within each layer. No general trend isvisible for the entire suite of layers; only smaller trends or group-ings among three or four consecutive or near consecutive layerscan be seen.

AI2O3 and CaO vs. depth display similar relationships with theexception of layer H, which is depleted in CaO relative to the otherlayers. The diagram of FeO vs. depth displays several groupings,from the less evolved magmas of layers L and E to the moreevolved magmas of layers K and H and layers D, C, and A,respectively. Silica has similar trends, suggesting that the ashesin each group become more silicic with time.

Ratios of the major oxides vs. depth also show groupings oftephra layers with similar element ratios. CaO/FeO vs. depth bestdisplays the three groupings. Within each group there is a de-crease in the mafic character of the magmas with respect to time.

277

Table 2. Percentage composition of major oxides from microprobe measurements of glass shards from Site 758.

Sample

LayerShard morphology

SiO2

A12O3

FeOMgOCaOK2ONa2OTiO2P2°5TotalH2O

758A-1H-2,25 cm

A7

75.0212.190.830.090.914.651.280.100.03

95.104.90

758A-1H-2,25 cm

APlaty

74.5312.070.730.030.694.803.100.080.00

96.033.97

758A-1H-2,25 cm

APlaty

72.9312.150.800.080.814.942.880.050.02

94.665.34

758A-1H-2,25 cm

ABubble wall

72.3011.870.760.050.784.842.900.070.01

93.586.42

758A-1H-2,25 cm

ABlocky

74.3912.090.790.080.825.052.870.070.02

96.183.82

758A-1H-2,25 cm

ABubble wall

73.6312.110.790.050.794.882.780.080.01

95.124.88

758A-1H-2,25 cm

ABlocky

74.8711.850.790.060.794.942.720.080.02

96.123.88

758A-1H-2,25 cm

ABlocky

73.6312.190.830.050.844.863.040.070.04

95.554.45

758A-1H-2,25 cm

APlaty

74.5911.800.740.050.674.883.140.060.02

95.954.05

758A-1H-2,25 cm

ABlocky

73.7312.060.850.060.764.812.830.050.03

95.184.82

758A-1H-2,25 cm

ABubble wall

74.6111.890.760.040.644.923.300.080.02

96.263.74

758A-1H-2,25 cm

ABubble wall

73.8112.040.740.030.665.053.060.060.01

95.464.54

758A-1H-2,25 cm

ABubble wall

74.2912.160.810.050.755.003.140.070.02

96.293.71

758A-1H-2,25 cm

ABubble wall

74.1211.910.800.040.784.872.970.090.02

95.604.40

Note: The inferred percent H2O is determined by the sum of the oxides subtracted from 100. ? = the shard form does not fall into the three categories.

Sample


SiO2

A12O3

FeOMgOCaOK2ONa2OTiO2

P2O5

TotalH2O

758A-1H-2,25 cm

ABlocky

74.3112.050.800.040.744.783.150.070.01

95.954.05

758A-1H-2,25 cm

ABubble wall

74.0112.100.790.050.834.893.100.090.02

95.884.12

758A-1H-2,25 cm

ABubble wall

74.7912.170.780.060.755.022.690.070.01

96.343.66

758A-1H-2,25 cm

APlaty

75.5011.960.770.030.765.073.030.070.02

97.212.79

758A-1H-2,25 cm

APlaty

74.4312.130.880.080.794.992.830.080.02

96.233.77

758A-1H-2,25 cm

ABlocky

75.1111.840.760.040.694.873.150.050.04

96.553.45

758A-1H-2,25 cm

APlaty

74.5311.900.780.030.704.912.920.070.02

95.864.14

758A-1H-2,25 cm

ABubble wall

74.1312.180.830.080.784.813.040.080.03

95.964.04

758A-1H-2,25 cm

ABlocky

74.7812.310.880.060.894.873.140.070.03

97.032.97

758A-1H-2,25 cm

ABlocky

74.3011.870.770.060.674.953.180.080.04

95.924.08

758A-1H-2,5 cm

ABlocky

71.9811.960.920.080.914.762.560.120.02

93.316.69

758A-1H-2,5 cm

A?

73.4011.740.780.020.655.252.930.070.01

94.855.15

758A-1H-2,5 cm

ABlocky

74.8311.750.690.030.695.082.710.060.00

95.844.16

758A-1H-2,5 cm

ABlocky

74.7011.930.810.040.835.022.850.100.03

96.313.69

Sample


SiO2

A12O3


P2O5

TotalH 2O

758A-1H-2,5 cm

A7

74.6811.650.750.030.895.232.460.090.01

95.794.21

758A-1H-2,47 cm

BBubble wall

74.2211.770.890.020.794.932.780.050.00

95.454.55

758A-1H-2,47 cm

BBubble wall

70.2011.290.930.050.654.733.100.050.01

91.018.99

758A-1H-2,47 cm

BBubble wall

72.3112.010.860.010.794.792.920.080.00

93.776.23

758A-1H-2,47 cm

BBubble wall

72.4511.690.850.020.724.633.320.090.01

93.786.22

758A-1H-2,47 cm

BBlocky

74.8411.950.860.010.705.163.300.060.00

96.883.12

758A-1H-2,47 cm

BBlocky

73.1911.990.840.020.754.853.410.060.00

95.114.89

758A-1H-2,47 cm

BPlaty

73.0111.820.850.040.834.803.260.090.00

94.705.30

758A-1H-2,47 cm

BBubble wall

71.3611.580.790.040.644.683.210.070.02

92.397.61

758A-1H-2,47 cm

BBlocky

71.5012.050.920.040.964.692.880.090.02

93.156.85

758A-2H-1,114 cm

CBubble wall

72.4011.390.950.030.774.812.810.090.00

93.256.75

758A-2H-1,114 cm

CBlocky

73.4011.750.940.010.635.043.180.040.01

95.005.00

758A-2H-1,114 cm

CPlaty

72.0811.690.940.010.584.573.190.050.00

93.116.89

758A-2H-1,114 cm

CPlaty

72.2411.640.940.000.484.663.580.030.01

93.586.42

Sample


SiO2

A12O3

FeOMgOCaOK 2 ONa 2O

TiO 2

P 2 O 5

TotalH 2 O

758A-2H-1,114 cm

CBlocky

72.3911.53

0.960.000.555.043.03

0.04

0.00

93.546.46

758A-2H-1,114 cm

CBlocky

71.9311.550.920.010.654.893.12

0.07

0.00

93.146.86

758A-2H-1,114 cm

CPlaty

72.87

11.74

0.900.000.494.59

3.580.050.03

94.255.75

758A-2H-1,114 cm

CPlaty

72.3411.45

0.950.00

0.534.65

3.32

0.030.01

93.286.72

758A-2H-1,114 cm

CBubble wall

72.8311.580.930.000.54

4.493.35

0.060.00

93.786.22

758A-2H-1,114 cm

CBubble wall

71.3611.52

0.950.020.654.883.05

0.060.00

92.497.51

758A-2H-1,

114 cm

CBlocky

72.2611.41

0.930.020.82

4.653.03

0.090.00

93.216.79

758A-2H-1,114 cm

C

Bubble wall

72.7511.810.910.010.644.993.060.07

0.02

94.265.74

758A-2H-4,38 cm

D

Bubble wall

73.0611.72

0.800.030.74

5.102.87

0.060.01

94.395.61

758A-2H-4,

38 cmD

Bubble wall

73.21

11.780.870.02

0.795.01

2.760.070.00

94.515.49

758A-2H-4,38 cm

DBlocky

73.5211.900.820.02

0.80

4.933.06

0.08

0.00

95.134.87

758A-2H-4,

38 cmD

Blocky

73.39

11.760.810.010.74

4.882.950.060.01

94.615.39

758A-2H-4,

38 cmD

Platy

73.9711.94

0.880.030.77

5.05

2.670.07

0.00

95.384.62

758A-2H-4,

38 cmD

Blocky

74.4311.660.780.01

0.754.81

3.040.050.01

95.54

4.46

Sample


SiO2

A12O3

FeOMgOCaOK 2 ONa 2 O

TiO 2

P 2 O 5

TotalH 2 O

Sample


SiO2

A12O3

FeOMgOCaOK 2 ONa 2 O

TiO 2

P 2 O 5

TotalH 2 O

758A-2H-4,38 cm

D

Platy

73.8811.69

0.840.010.794.982.830.07

0.01

95.104.90

758A-2H-4,115 cm

E?

71.7512.37

1.170.110.87

4.093.77

0.130.04

94.305.70

758A-2H-4,38 cm

DPlaty

74.04

11.58

0.840.010.675.01

2.980.080.02

95.234.77

758A-2H-4,115 cm

EBlocky

72.2512.52

1.080.130.87

3.853.09

0.120.02

93.936.07

758A-2H-4,38 cm

D

Bubble wall

73.7611.82

0.790.010.675.29

2.800.080.00

95.224.78

758A-2H-4,115 cm

E

Bubble wall

71.8012.39

1.120.090.84

4.023.900.130.02

94.315.69

758A-2H-4,38 cm

D

Bubble wall

73.6211.84

0.80

0.030.785.023.10

0.050.00

95.244.76

758A-2H-4,115 cm

E

Bubble wall

70.6812.16

1.14

0.100.863.87

3.79

0.100.02

92.72

7.28

758A-2H-4,

38 cmD

Blocky

74.0911.57

0.860.000.694.743.21

0.050.01

95.224.78

758A-3H-3,125 cm

F

Platy

73.5611.72

1.030.000.834.732.93

0.030.01

94.84

5.16

758A-2H-4,

38 cmD

Bubble wall

73.3311.67

0.820.030.744.84

2.83

0.060.02

94.345.66

758A-3H-3,

125 cmF

Blocky

73.5611.42

1.06

0.010.844.79

2.80

0.050.03

94.565.44

758A-2H-4,

38 cmD

Blocky

76.05

11.92

0.870.060.784.50

0.92

0.110.00

95.214.79

758A-3H-3,

125 cmF

Bubble wall

72.77

11.92

1.08

0.010.724.60

3.16

0.070.02

94.35

5.65

758A-2H-4,

115 cmE

Bubble wall

72.26

12.27

1.150.110.823.90

3.88

0.120.03

94.54

5.46

758A-3H-3,125 cm

F

Platy

72.29

11.85

1.01

0.020.844.65

2.87

0.050.02

93.60

6.40

758A-2H-4,

115 cmE

Platy

71.85

12.38

1.100.090.843.96

3.69

0.140.01

94.06

5.94

758A-3H-3,125 cm

F

Blocky

74.0011.86

1.09

0.041.074.16

2.49

0.030.00

94.74

5.26

758A-2H-4,

115 cmE

Bubble wall

71.42

12.53

1.150.090.853.98

3.84

0.140.01

94.01

5.99

758A-3H-3,125 cm

F

Platy

72.9811.71

1.03

0.000.824.69

2.86

0.060.00

94.15

5.85

758A-2H-4,

115 cmE

Blocky

72.27

12.37

1.160.140.843.90

3.68

0.140.04

94.54

5.46

758A-3H-3,125 cm

F

Bubble wall

71.2512.14

1.30

0.030.995.04

2.90

0.080.02

93.756.25

758A-2H-4,

115 cmE

Bubble wall

70.33

12.85

1.220.150.973.83

3.94

0.180.03

93.50

6.50

758A-3H-3,125 cm

F

Blocky

72.8911.67

1.04

0.010.764.62

3.18

0.040.00

94.215.79

758A-2H-4,

115 cmE

Blocky

72.01

12.42

1.150.110.904.01

3.50

0.140.03

94.27

5.73

758A-3H-3,125 cm

F

Bubble wall

72.9511.57

1.07

0.000.734.74

3.010.050.03

94.155.85

758A-2H-4,

115 cmE

Platy

71.13

12.34

1.100.110.834.18

3.89

0.110.03

93.72

6.28

758A-4H-5,3 cm

H

Bubble wall

71.9111.47

0.760.020.484.38

3.530.040.02

92.617.39

m

TE

PH

RO

CH

1O

o«iCΛ

tn- j

pp

m

Table 2 (continued).

Sample

Layer

758A-4H-5,3 cm

HShard morphology Bubble wall

SiO 2

A12O3

FeOMgOCaOK2ON a 2 OT i O 2

P2°5TotalH 2 O

71.6611.300.670.030.444.372.830.040.02

91.368.64

758A-4H-5,3 cm

HBlocky

72.9011.680.710.020.474.003.560.030.03

93.406.60

758A-4H-5,3 cm

HBubble wall

72.7311.850.740.020.434.393.500.040.02

93.726.28

758A-4H-5,3 cm

HBubble wall

73.8911.75

0.740.010.423.853.510.050.02

94.245.76

758A-4H-5,3 cm

HBlocky

72.3311.550.740.030.424.102.940.040.01

92.167.84

758A-4H-5,3 cm

HBlocky

71.6911.600.730.020.494.353.170.050.03

92.137.87

758A-4H-5,3 cm

HBubble wall

72.7611.340.730.040.444.093.600.040.01

93.056.95

758A-7H-2,120 cm

1Blocky

74.2412.010.580.020.604.522.980.050.00

95.005.00

758A-7H-2,120 cm

1Bubble wall

74.9512.060.630.040.664.553.110.030.00

96.033.97

758A-7H-2,120 cm

IBubble wall

73.9011.840.590.020.644.673.060.030.01

94.765.24

758A-7H-2,120 cm

IBubble wall

72.4911.860.670.030.873.653.570.040.01

93.196.81

758A-7H-2,120 cm

IPlaty

72.5611.690.610.030.604.372.840.040.00

92.747.26

758A-7H-2,120 cm

IBubble wall

72.8812.320.900.131.183.443.320.100.03

94.305.70

758B-1H-1,114 cm

ABlocky

75.2211.920.740.040.634.853.190.050.04

96.683.32

DE

H

Z

_̂

2

C

θ

n

Sample


SiO 2

A1 2 O 3

FeOMgOCaOK2ON a 2 O

T i O 2

P 2 O 5

TotalH 2 O

758B-1H-1,114 cm

APlaty

75.7511.990.700.060.614.993.110.060.02

97.292.71

758B-1H-1,114 cm

A7

74.7911.790.780.040.805.073.100.080.03

96.483.52

758B-1H-1,114 cm

APlaty

76.1911.990.800.060.794.512.300.080.03

96.753.25

758B-1H-1,114 cm

ABlocky

75.9311.710.750.080.685.063.050.070.00

97.332.67

758B-1H-1,114 cm

ABubble wall

75.4911.940.770.070.794.943.460.080.01

97.552.45

758B-1H-1,114 cm

ABlocky

75.0411.810.800.200.765.033.07

0.100.03

96.843.16

758B-1H-1,114 cm

ABlocky

75.7412.180.790.050.765.143.140.080.02

97.902.10

758B-1H-1,114 cm

A7

74.8711.890.770.080.814.863.160.080.01

96.533.47

758B-1H-1,114 cm

ABlocky

75.3312.100.810.040.765.033.22

0.080.02

97.392.61

758B-1H-1,114 cm

ABlocky

75.0011.870.810.040.784.952.960.080.01

96.503.50

758B-1H-1,114 cm

ABlocky

74.7811.910.800.050.784.853.150.070.01

96.403.60

758B-1H-1,114 cm

ABubble wall

76.2512.210.780.050.665.173.180.080.02

98.401.60

758B-1H-1,114 cm

ABubble wall

75.0911.880.800.060.845.093.030.070.01

96.873.13

758B-1H-1,114 cm

ABlocky

75.1611.950.760.050.845.062.990.090.02

96.923.08

Sample


SiO2

A12O3

FeOMgOCaOK2ONa 2OTiO 2

P 2 O 5

TotalH 2 O

758B-1H-1,114 cm

APlaty

74.9011.740.760.040.67

5.113.230.070.04

96.563.44

758B-1H-1,114 cm

ABubble wall

75.1311.890.800.050.794.882.950.070.03

96.593.41

758B-1H-1,114 cm

APlaty

74.7211.990.760.060.765.113.040.070.06

96.573.43

758B-1H-1,114 cm

ABlocky

75.3911.920.800.070.724.903.180.070.03

97.082.92

758B-1H-1,114 cm

ABlocky

74.3212.020.860.040.784.973.290.090.02

96.393.61

758B-1H-1,114 cm

ABubble wall

73.6012.220.860.050.834.912.830.080.04

95.424.58

758B-1H-1,114 cm

ABlocky

74.4211.900.820.050.664.723.210.060.05

95.894.11

758B-1H-1,114 cm

ABubble wall

74.7411.880.810.040.694.663.240.050.05

96.163.84

758B-1H-1,114 cm

ABubble wall

74.4411.990.810.020.674.933.370.030.06

96.323.68

758B-1H-1,114 cm

ABlocky

74.5012.490.850.030.774.793.120.060.01

96.623.38

758B-1H-1,114 cm

ABlocky

75.2812.210.830.060.794.953.050.080.03

97.282.72

758B-1H-5,119 cm

CBubble wall

73.3211.610.910.030.794.722.960.070.04

94.455.55

758B-1H-5,119 cm

CPlaty

74.2412.020.980.010.624.953.190.030.01

96.053.95

758B-1H-5,119 cm

CBlocky

73.2411.680.920.040.724.93

3.110.040.01

94.695.31

Sample


SiO2

A12O3


P 2 O 5

TotalH 2 O

758B-1H-5,119 cm

CBlocky

73.0211.660.890.010.664.593.010.060.01

93.916.09

758B-1H-5,119 cm

CBlocky

72.4011.490.870.040.764.512.850.070.02

93.016.99

758B-1H-5,119 cm

CBlocky

73.0111.550.900.000.464.313.650.020.00

93.906.10

758B-1H-5,119 cm

CBlocky

73.0511.710.910.030.784.643.060.050.03

94.265.74

758B-1H-5,119 cm

CBubble wall

73.3911.910.890.020.654.593.300.050.01

94.815.19

758B-2H-2,25 cm

dBubble wall

73.0211.970.890.020.724.703.280.080.01

94.695.31

758B-2H-2,25 cm

dBubble wall

73.1211.640.840.020.764.593.230.060.01

94.275.73

758B-2H-2,25 cm

dBlocky

72.0711.500.810.020.754.553.140.030.03

92.907.10

758B-2H-2,25 cm

dBubble wall

72.1311.480.820.020.734.713.140.070.03

93.136.87

758B-2H-2,25 cm

dBubble wall

72.1411.750.860.010.724.473.240.040.01

93.246.76

758B-2H-2,25 cm

dBubble wall

72.3711.590.800.020.724.483.290.060.04

93.376,63

758B-2H-2,61 cm

E7

71.7212.271.160.090.853.993.840.120.02

94.065.94

758B-2H-2,61 cm

EBlocky

72.1412.211.220.090.933.973.820.160.05

94.595,41

758B-2H-2,61 cm

EBubble wall

70.0012.071.120.120.874.003.570.130.02

91.908.10

Sample


SiO2A12O3

FeOMgOCaOK2ONa2OTiO2P2O5

TotalH 2 O

758B-2H-2,61 cm

EPlaty

70.7412.251.270.110.864.193.600.150.06

93.236.77

758B-2H-2,61 cm

EBlocky

72.0912.371.140.090.834.063.680.120.05

94.435.57

758B-2H-2,61 cm

EPlaty

71.1312.161.150.120.884.103.460.110.02

93.136.87

758B-2H-2,61 cm

EBubble wall

71.4912.381.130.110.894.093.780.130.05

94.055.95

758B-2H-2,61 cm

EBubble wall

71.5612.081.130.100.843.993.760.160.05

93.676.33

758B-3H-4,69 cm

GPlaty

73.2311.350.710.050.595.192.880.130.05

94.185.82

758B-3H-4,69 cm

G?

72.5011.280.670.060.574.933.030.140.00

93.186.82

758B-3H-4,69 cm

GBubble wall

73.9211.510.670.030.594.973.000.120.03

94.845.16

758B-3H-4,69 cm

GBubble wall

73.7011.540.660.040.655.023.080.120.01

94.825.18

758B-3H-4,69 cm

GBlocky

72.6411.490.690.050.604.913.240.110.03

93.766.24

758B-3H-4,69 cm

GPlaty

73.1711.110.710.050.564.713.090.130.00

93.536.47

758B-3H-4,69 cm

GPlaty

73.6011.470.720.030.584.653.200.110.04

94.405.60

758B-3H-4,69 cm

GBubble wall

73.3011.150.660.060.574.872.960.150.03

93.756.25

758B-3H-4,69 cm

GBubble wall

73.7111.480.710.030.584.943.150.150.03

94.785.22

2!

Otil1

Sample


SiO2

A12O3FeOMgOCaOK2ONa2OTiO2

P 2 O 5

TotalH 2 O

758B-4H-3,3 cm

HBubble wall

73.5011.670.810.000.494.333.370.030.04

94.245.76

758B-4H-3,3 cm

HPlaty

73.7311.820.840.000.444.373.310.060.02

94.595.41

758B-4H-3,3 cm

HBubble wall

73.0411.770.780.000.484.443.320.040.01

93.886.12

758B-4H-3,3 cm

H7

73.3911.800.740.010.474.903.380.060.06

94.815.19

758B-4H-3,3 cm

HBlocky

72.3111.750.760.010.434.313.590.050.02

93.236.77

758B-4H-3,3 cm

H7

73.0211.500.770.030.454.673.350.070.04

93.906.10

758B-6H-2,47 cm

hBlocky

72.3811.430.690.010.654.443.330.040.02

92.997.01

758B-6H-2,47 cm

hBubble wall

72.8411.710.660.020.634.783.250.050.02

93.966.04

758B-6H-2,47 cm

hBlocky

72.5111.350.640.010.644.843.120.060.00

93.176.83

758B-6H-2,47 cm

hBubble wall

73.3311.720.660.010.664.733.280.030.02

94.445.56

758B-6H-2,47 cm

hBubble wall

73,5011.660.650.000.614.662.870.040.02

94.015.99

758B-6H-2,47 cm

h7

73.7711.770.650.020.644.833.270.050.03

95.034.97

758B-6H-2,47 cm

hBubble wall

73.7211.790.710.020.654.863.320.040.01

95.124.88

758B-6H-2,47 cm

hBubble wall

72.9411.800.650.010.624.633.300.050.04

94.045.96


Sample


SiO2

A12O3


P 2O 5

TotalH2O

758B-6H-7,17 cm

IPlaty

73.4412.000.630.060.654.822.880.090.01

94.585.42

758B-6H-7,17 cm

IPlaty

73.1611.640.830.111.093.313.530.130.02

93.826.18

758B-6H-7,17 cm

IBubble wall

73.6711.850.590.070.674.803.170.080.04

94.945.06

758B-6H-7,17 cm

1

1

73.3612.140.600.090.694.993.200.060.06

95.194.81

758B-6H-7,17 cm

IBlocky

72.8111.950.860.131.143.403.540.110.03

93.976.03

758B-6H-7,17 cm

IBubble wall

72.2812.020.620.080.674.633.070.060.04

93.476.53

758B-6H-7,17 cm

IPlaty

73.3912.040.600.050.674.963.070.060.01

94.855.15

758B-6H-7,17 cm

1Platy

72.5511.790.710.070.954.043.450.070.04

93.676.33

758B-6H-7,17 cm

IBubble wall

72.0511.830.860.111.013.763.180.090.01

92.907.10

758B-6H-7,17 cm

IBlocky

73.4711.910.580.030.675.282.530.080.01

94.565.44

758B-7H-6,29 cm

KBubble wall

71.4911.510.970.050.574.423.480.090.03

92.617.39

758B-7H-6,29 cm

KPlaty

72.0111.580.890.030.524.443.420.050.02

92.967.04

758B-7H-6,29 cm

KPlaty

72.6111.670.910.020.524.673.240.060.01

93.716.29

758B-7H-6,29 cm

KBubble wall

71.8111.690.960.030.564.063.570.090.02

92.797.21

Sample


SiO2

A12O3


P2O5

TotalH2O

758B-7H-6,29 cm

KBlocky

72.0411.78

1.030.040.574.453.330.080.00

93.326.68

758B-7H-6,29 cm

KBubble wall

72.2811.790.980.020.614.643.430.080.01

93.846.16

758B-7H-6,29 cm

KBlocky

72.0911.380.880.030.484.463.360.040.01

92.737.27

758B-7H-6,29 cm

K7

71.8111.590.880.040.494.403.470.050.04

92.777.23

758B-7H-6,29 cm

KBlocky

71.1011.65

1.840.081.212.873.790.140.04

92.727.28

758B-7H-6,29 cm

KBubble wall

71.4711.540.890.030.535.043.160.070.03

92.767.24

758B-7H-CC,14 cm

LPlaty

67.2012.412.240.261.464.493.720.340.06

92.187.82

758B-7H-CC,14 cm

LBubble wall

68.5913.062.330.241.364.423.400.350.08

93.836.17

758B-7H-CC,14 cm

LBlocky

68.0512.472.360.231.364.323.660.360.05

92.867.14

758B-7H-CC,14 cm

LPlaty

68.3912.792.370.251.524.213.730.340.07

93.676.33

758B-7H-CC,14 cm

LBlocky

67.7912.502.360.281.424.603.570.360.05

92.937.07

758B-7H-CC,14 cm

LBubble wall

68.0512.752.450.281.344.423.950.320.02

93.586.42

758B-7H-CC,14 cm

LBubble wall

67.4012.832.470.301.374.384.130.330.08

93.296.71

Sample


SiO2

A12O3

FeOMgOCaOK2ONa 2 OTiO 2

P 2 O 5

TotalH2O

758B-7H-CC,14 cm

LPlaty

68.9712.782.420.261.374.483.970.360.05

94.665.34

758B-8H-4,111 cm

MBubble wall

71.1611.910.820.060.954.153.310.080.03

92.477.53

758B-8H-4,111 cm

MBubble wall

70.6511.840.910.100.993.783.350.080.04

91.748.26

758B-8H-4,111 cm

MPlaty

72.7511.660.780.090.884.173.280.050.05

93.716.29

758B-8H-4,111 cm

MBlocky

72.0711.670.740.080.934.193.220.060.06

93.026.98

758B-8H-4,111 cm

MBlocky

72.0311.800.730.060.814.013.360.060.04

92.907.10

758B-8H-4,111 cm

MBlocky

71.3411.770.770.080.964.003.170.070.02

92.187.82

758B-8H-4,111 cm

M7

71.2411.650.700.051.034.323.200.070.05

92.317.69

758B-8H-4,111 cm

MBubble wall

72.0411.870.740.080.794.113.040.070.03

92.777.23

758B-8H-4,111 cm

MBubble wall

71.0911.56

1.080.201.793.293.17

0.170.02

92.377.63

758C-1H-2,14 cm

ABlocky

71.5911.480.750.030.694.723.020.100.03

92.417.59

758C-1H-2,14 cm

ABubble wall

70.8011.440.780.030.694.823.000.040.05

91.658.35

758C-1H-2,14 cm

ABubble wall

73.2811.900.850.020.774.712.990.090.02

94.635.37

758C-1H-2,14 cm

ABlocky

72.5911.850.820.040.815.022.890.050.02

94.095.91

Sample


SiO2A12O3


P2O5

TotalH2O

758C-1H-2,14 cm

APlaty

73.3111.480.730.050.624.903.240.060.01

94.405.60

758C-1H-2,14 cm

ABubble wall

73.3911.950.800.060.785.092.840.070.03

95.014.99

758C-1H-2,14 cm

ABlocky

73.0712.310.840.050.814.763.010.060.00

94.915.09

758C-1H-2,14 cm

ABubble wall

72.5111.830.820.040.694.833.070.060.03

93.886.12

758C-1H-2,14 cm

ABubble wall

72.7311.980.830.060.794.832.970.080.04

94.315.69

758C-IH-2,14 cm

ABlocky

74.1911.960.790.020.674.873.190.040.01

95.744.26

758C-1H-2,14 cm

ABubble wall

73.1512.240.830.040.814.923.000.060.01

95.064.94

758C-1H-2,14 cm

ABubble wall

71.9612.200.810.051.054.382.910.060.02

93.446.56

758C-1H-2,14 cm

ABlocky

72.5611.780.790.030.694.933.040.060.02

93.906.10

758C-1H-2,14 cm

ABlocky

71.9911.820.820.050.654.712.980.070.05

93.146.86

758C-1H-2,14 cm

ABlocky

72.2812.130.840.020.804.862.990.070.04

94.035.97

758C-1H-2,14 cm

ABubble wall

72.1612.020.790.040.814.872.960.070.03

93.756.25

Sample


SiO2A12O3

FeOMgOCaOK2ONa2OTiO2P2O5

TotalH 2O

758C-1H-2,14 cm

ABubble wall

73.5811.950.740.160.765.002.870.090.04

95.194.81

758C-1H-2,14 cm

ABubble wall

71.1111.320.750.080.674.652.930.050.00

91.568.44

758C-1H-2,14 cm

ABubble wall

74.3511.640.770.050.684.893.160.080.02

95.644.36

758C-1H-2,14 cm

ABubble wall

73.2911.600.770.030.824.772.910.070.03

94.295.71

758C-1H-2,14 cm

ABubble wall

74.7411.690.760.030.644.753.220.080.02

95.934.07

758C-1H-2,14 cm

ABubble wall

73.8411.840.820.060.834.963.110.110.00

95.574.43

758C-1H-2,27 cm

ABlocky

72.8911.910.830.050.734.473.350.060.05

94.345.66

758C-1H-2,27 cm

APlaty

71.2912.140.790.050.804.602.750.050.04

92.517.49

758O1H-2,27 cm

ABlocky

72.5211.920.810.060.784.743.090.070.02

94.015.99

758C-1H-2,27 cm

APlaty

72.6412.070.790.040.784.633.180.060.04

94.235.77

758C-1H-2,27 cm

ABubble wall

71.7711.900.810.030.674.483.450.050.05

93.216.79

758C-1H-2,27 cm

APlaty

72.2011.820.790.050.694.883.090.060.02

93.606.40

Sample


SiO2


P 2 O 5

TotalH2O

758C-1H-2,27 cm

ABlocky

71.6311.930.860.050.804.673.140.080.02

93.186.82

758C-1H-2,27 cm

APlaty

73.2611.980.800.060.704.873.130.040.02

94.865.14

758C-1H-2,27 cm

ABlocky

71.9811.970.830.060.724.752.780.090.00

93.186.82

758C-1H-2,27 cm

ABubble wall

70.1611.810.940.190.834.393 . 1 0

0.080.03

91.538.47

758C-1H-2,27 cm

ABubble wall

71.9411.900.790.070.814.892.950.050.05

93.456.55


72 73 74 75 76 77 78 79 80 72 73 74 75 76 77 78 79 80

2.5

ofan

1.5

.5

i.e

1.6

1.4

oCO 1.2

u1

i—•—i—>—i—'—r

V

- LL

LL L L L L

13.8

13.4

13

CO

o

<

12.6

12.2

11.8

5.65.24.8

Ow 4.4

4

3.6

3.2

i • r

E

E n

+-h

J L_J i L i I I Ü J i I . I

72 73 74 75 76 77 78 79

SiO?80 72 73 74 75 76 77 78 79 80

SiO2

Figure 4. Variation diagrams of FeO, CaO, AI2O3, and K2O vs. Siθ2. All of the tephra layers are classified as high-silica rhyolites. Layer L is the leastevolved, and layer A the most evolved. FeO, CaO, and AI2O3 display trends resulting from fractionation in the magmas.

This is evident in the FeO, CaO, and AI2O3 concentrations in eachgroup.

Feldspar Composition

Feldspar crystals were analyzed where present in each sample(Tables 3 and 4). A ternary plot of albite, anorthite, and orthoclaseshows four distinct groups (Fig. 7). Labradorites and bytownites(An6θ-9θ) occur in the least evolved tephras, in layers L, I, and F.The majority of the layers contain andesine with average compo-sitions of An25-55 as the main Plagioclase phase. Layer I, presentin three groups, displays bimodal Plagioclase compositions aswell as potassium feldspar. Layers G, D, and d contain sanidinecrystals that plot together around Or69-78 Andesine is also presentin these layers. Layer M, containing sodic sanidine crystals,stands alone along the trend, yet separate from the other tephras.

The feldspar compositions correspond to the glass composi-tions of the tephras (i.e., the least silicic ashes contain Plagioclasewith the highest anorthite content). The layers containing by-townite and labradorite crystals, L, I, and F, are the least evolvedlayers in each group defined by the CaO/FeO ratio of the glass.Layer L is the least differentiated of the tephra layers and theoldest in its cogenetic group (Fig. 8). Layer I displays the largestvariations in glass and Plagioclase compositions. Chesner (1988)described bytownite in the HDT, the least differentiated layer ofthe Pleistocene Toba tuffs. This layer is correlated through itsPlagioclase chemistry and eruption time (1.2 Ma) to layer F at Site

758. This indicates, however, that the dacitic whole rock onSumatra either had a rhyolitic glass matrix or that the uppermost,most differentiated portion of the zoned Toba magma chamberwas erupted and subsequently deposited as a marine fallout tephralayer. Chesner (1988) described the zoning in the Toba magmachamber, and the wide range in CaO, FeO, K2O, and AI2O3concentrations and Plagioclase compositions in layers I and Msuggests significant zoning within single eruptions.

Other Crystals in the Tephra Layers

Where present, other crystals in the samples were also ana-lyzed for major oxide composition (Table 5). These crystals werefound only in the lowermost part of each tephra layer, which wasnot always available for sampling. Therefore, the analyses do notrepresent a statistically valid sample of the entire suite of tephralayers.

Biotite, amphibole, and apatite crystals were measured inlayers A, C, d, G, H, I, and K (Fig. 2 and Table 5). The analysesof amphibole crystals in layers A and C closely match thosemeasured in the YTT and the MTT at the Toba caldera on Sumatra(Chesner, 1988).

DATING OF THE TEPHRA LAYERS

Relative ages were estimated for the ash layers based on theirposition within the chronostratigraphy provided by the paleomag-netic reversal record and the δ 1 8 θ record (Farrell and Janecek,

284


.5 1.5 2.5

13.8 -

13.4 -CO

oCM 1 3

<12.6

12.2

11.8

l.a

1.6

1.4

-i i i r—j i r

& EE F

I I I I | I I I I | I I I I | I I I I | I I

1.8

1.6

1.4

oCO 1-2

o1

L L L

-<§

• 1 • I • I i I i I i I

11.8 12.2 13.4 13.8

2.5

Figure 5. Variation diagrams of CaO and AI2O3 vs. FeO and CaO vs. AI2O3. Three groups of layers, best defined for CaO vs. FeO, represent magmas with

similar CaO/FeO ratios and thus similar provenance. Group 1 includes layers A (and B), C, D (and d), E, F, and G. Group 2 includes layers H, K, and L;

group 3,1 and M.

this volume). Paleomagnetic and δ 1 8 θ ages for the ashes wereestimated by linearly interpolating between the nearest magneticreversals and the nearest isotopic control points.

The δ 1 8 θ record from Site 758, which spans the past 2.5 Maat an average resolution of 6000 yr, provides an independentchronostratigraphy of much higher resolution than the paleomag-netic chronostratigraphy. A preliminary δ18O-based age modelfor the past 1.0 Ma was constructed by simple visual correlationof the Site 758 composite d 1 8 θ record to the global averageoxygen isotope record, the Spectral Mapping (SPECMAP) stack(Imbrie et al., 1984; Prell et al., 1986), and the Atlantic Site 607benthic δ 1 8 θ record (Ruddiman et al., 1989; Raymo et al., 1989).The correlations are discussed in detail in Farrell and Janecek (thisvolume). Initial correlation attempts appear successful, and sup-port for these correlations is provided by comparison to theplanktonic and benthic δ 1 8 θ stratigraphy from equatorial PacificSite 677 (Shackleton and Hall, 1989). Nevertheless, identificationof the d 1 8 θ chronostratigraphy in the planktonic foraminifer re-cord from Site 758 is subject to minor revision based on theaddition of new benthic foraminifer δ 1 8 θ data.

Table 6 contains a list of what are interpreted to be uniquetephra layers representing single eruptions and their age dates.Though the dates acquired by different methods do not exactlymatch, the correlation between the paleomagnetic dates and δ 1 8 θdates is good. The differences are primarily due to the lowerresolution of the paleomagnetic record.

Ash layer A falls near δ 1 8 θ stage 5.0 (Imbrie et al., 1984), thetransition between glacial stage 4 and interglacial stage 5. Theδ 1 8 θ age for layer A is 0.075 ± 0.004 Ma. This age matches thepreviously established value of 75,000 yr for the Toba ash (Nink-ovich et al., 1978, 1979; Rose and Chesner, 1987, 1988). The ageof layer B cannot be differentiated from layer A by paleomagneticor δ 1 8 θ means, further supporting the conclusion that it is amisplaced part of layer A.

Ash layer C lies between δ 1 8 θ stages 13.2 and 14.2, which areassigned ages of 0.513 and 0.538 Ma, respectively (Imbrie et al.,1984). These dates are close to the date of 0.49 Ma given byChesner (1988) for the MTT. The age of the layer coupled withthe similar chemical compositions strongly supports the correla-tion of these layers.

Layer D falls just below the paleomagnetic boundary separat-ing the Brunhes and Matuyama Chrons. In the δ 1 8 θ stratigraphy,the ash layer lies between stages 19.2(0.731 Ma) and 20.23 (0.750Ma). Ash layer D does not correlate to any previously describederuption from the Toba caldera.

Ash layer E occurs in the middle of δ 1 8 θ stage 21, dated at0.775 Ma. This layer is tentatively correlated with the OTT. TheOTT, however, is dated at 0.840 ± 0.30 Ma (Diehl et al., 1987),at least 37,000 yr older than layer E.

Ash layer F falls between δ 1 8 θ stages 45 and 46, which areapproximately equivalent to 1.273 and 1.294 Ma, respectively.This age correlates well with the HDT, dated at 1.20 ± 0.16 Ma.

285


0 10 20 30 40 50 60 70 80

13.8

h

13.4

oCD

2.5

1.5

Depth (mbsf)

D 10 20 30 40 50 60 70 80

O• i—i

in

080

79

78

77

76

75

74

73

78

1.6

1.4

.4

120

40

20

10 20 30 40I i

50 60•

70 80

i i I i i i I , I

F G

0 10 20 30 40 50 60 70 80

Depth (mbsf)Figure 6. Plots of major oxides and major oxide ratios vs. depth. No clear trend with depth is visible for the entire suite of layers. The three cogenetic groups are

visible for CaO/FeO vs. depth. Group 2 aligns with a CaO/FeO ratio of 0.6; group 1, approximately 0.8; and group 3, approximately 1.2.

Chemically, layer F is not a dacite; however, it does containbytownite crystals, as described on land in the HDT.

Layer G occurs between δ 1 8 θ stages 61 and 63, in the timeinterval from 1.596 to 1.636 Ma. Ash layer H lies between stages92 and 93, which are from 2.238 to 2.260 Ma.

A hiatus of 1.414 ± 0.016 Ma exists between layers H and h,the largest gap in the section without deposition of a major fallouttephra layer. The minimum time between major tephra layers is0.039 ±0.010 Ma. The average time interval between major tephralayers for the entire sequence is 0.414 Ma with a standard devia-tion of 0.363 Ma. The large standard deviation represents theirregularity of the time intervals between the entire suite of layers.

The ashes are divided into three groups based on theirCaO/FeO ratios, as defined in Figure 6 (Table 6). The duration ofactivity producing major tephra layers, or residence time, and theintervals between the eruptions is calculated for each group.

Group 1 (layers A through F) has a residence time of approxi-mately 1.206 Ma. The average time interval between major tephralayers is 0.279 Ma with a standard deviation of 0.208. Chesner(1988) reported eruption dates of 0.075 Ma for the YTT (layer A),0.450 Ma for the MTT (layer C), 0.840 Ma for the OTT (layer E),and 1.2 Ma for the HDT (layer F). These data give a mean intervalof 0.375 Ma with a standard deviation of 0.015.

286


Group 2 (layers H, J, K, and L) has a residence time ofapproximately 2.501 Ma. The mean interval between layers is0.840 Ma with a standard deviation of 1.276 Ma. This very highstandard deviation is the result of the long hiatus between layersH and J. Layer J, which was not sampled, is included in this groupsimply because of its stratigraphic position.

Group 3 (layers I and M) has a residence time of approximately0.935 Ma. If layer h is included in group 3, the residence timeincreases to 1.399 Ma with an average interval between majortephras of 0.698 Ma and a standard deviation of 0.334 Ma.

DISCUSSION

Evolution of the Tephras

The fractionation of quartz, Plagioclase, biotite, amphibole,and other mafic minerals, as well as alkali feldspars, is responsiblefor the chemical difference among the silicic tephra layers. Themafic minerals are generally absent from the tephra layers. Biotitewas observed in tephra layers A, C, G, h, and I, and amphibole inlayers A and K. Orthopyroxenes and clinopyroxenes, though notobserved in the marine tephra layers, are described by Chesner(1988) in the tuffs and ignimbrites of the Toba caldera. IncreasingFeO and CaO compositions and decreasing K2O concentrationsin the highly differentiated layers A and H indicate a final crys-tallization phase of alkali feldspars after the completion of plagio-clase and mafic mineral fractionation.

Dacitic crustal melts are inferred as the parent magmas, asrequired for the genesis of the Toba rhyolites (Chesner, 1988).Magma mixing with, or differentiation from, a basaltic magma isexcluded by the large volume of the silicic eruptions (>3000 km3

for Toba alone) and the complete lack of basaltic or andesitic glassshards or lithic clasts.

The bytownite crystals in layers L, I, and F, atypical forrhyolitic ashes, could have resulted as follows.

1. The bytownites are the remainder of a basaltic magmainjected into the rhyolite. In this case, sideromelane glass shardsand/or resorption or strong zoning of the Plagioclase crystals isexpected. None of these was observed.

2. The bytownites crystallized early in the then dacitic magma.This conclusion, however, is contradicted by the high MgO/FeOratio in the bytownites (>IO) relative to the magma (<0.15), andis still too high.

3. The magmas could have been contaminated by carbonate-rich wall rocks. This excess calcium would then crystallize in theform of the calcium-rich feldspars. The surrounding rocks arePaleozoic metasediments containing carbonate material (Aldissand Ghazali, 1984; Chesner, 1988) and thus could have been thesource for calcium.

4. High initial water pressure may contribute to the crystal-lization of anorthite-rich Plagioclase. Increasing water pressurelowers the crystallization temperature of Plagioclase (Deer et al.,1966).

MechanismsThe marine fallout tephra layers were formed as a result of

highly explosive eruptions, causing the observed high degree offragmentation and wide dispersal of the glass and crystals. Sucheruptions inject ash into the stratosphere, where it can travel forthousands of kilometers before being deposited. The ash is depos-ited upon the ocean surface, and then settles through the watercolumn. The thickness of the layer and average grain size of theglass shards are directly proportional to the volume and explosiv-ity of the eruption (Shaw et al., 1974).

Because the tectonic movement of Ninetyeast Ridge in thePliocene-Pleistocene is subparallel to the Indonesian Island Arc

(Peirce, Weissel, et al., 1989), the distance from Sumatra has notsignificantly changed in the period of marine tephra layer depo-sition (0-5.1 Ma). Site 758 has moved no more than 3° northwardduring this time. Similarly, the water depth of the site has deep-ened by no more than 150 m in the last 5 Ma (Shipboard ScientificParty, 1989). Because the thickness of the major ash layers variesfrom the defined limit of 1 to 34 cm and the distance from thesource has remained virtually constant, then the eruptions havehad differing mechanisms or characters. A plot of the CaO/FeOratio vs. the thickness of the ash layer yields trends for the threedefined cogenetic groups (Fig. 8). Layers with similar CaO/FeOratios vary in thickness with time. In the case of group 1, layersF and E, the thinnest layers, are the least evolved and earliesteruptions in the Toba series. As the silica content of the glassincreases the thickness of the layers increases and thus the explo-sivity of the eruptions. This trend is also seen in the two othercogenetic groups.

Time-Related TrendsFrom the three defined cogenetic groups, an average residence

time of approximately 1.7 Ma can be inferred for these silicicsystems. Variations in the residence time are related to the petro-genesis of the magmas. The three defined groups have varyingresidence times that can be correlated to the range of chemicalcompositions in the tephra layers. The longest residence timebelongs to group 2, which started with the least differentiatedmagma. The residence time of the Toba cycle (group 1) of ap-proximately 1.2 Ma is less than that of group 2 (approximately2.5 Ma). There is no indication, however, that this cycle is fin-ished. Another eruption in 300,000 yr would extend its residencetime, matching it more closely to group 2.

CONCLUSIONSDue to good core recovery and the large number of discrete

ash layers, Site 758 provides a unique opportunity to develop acomplete tephrochronology. The tephra originated from the Indo-nesian Island Arc, specifically its northernmost section, Sumatra.All of the tephras are high-silica rhyolites and share similareruption mechanisms. The ratio of CaO/FeO displays three groupsof ash layers that may belong to a single magma or magmaticsystem that has fractionated with time.

The four youngest layers are correlated to the last four erup-tions of the Toba caldera in Sumatra. The layers correlate in timeas well as chemical composition of the glass shards and feldspars.These layers all belong to the first cogenetic group defined by theCaO/FeO ratio. The other two groups have not been correlated toa known source on land.

The thickness of the tephra layers varies, though the distancefrom the volcanic source has not significantly changed. Thicknessof the tephra layers increases with time and silicic character ineach group, suggesting that the fractionation of the magmas leadsto more explosive eruptions.

The residence time of a given magmatic system is about 1.7Ma. A less evolved magma has a longer residence time than amore evolved one. This suggests that the composition of theparent magma affects the residence time of the magmatic system.

ACKNOWLEDGMENTSWe thank Bill Melson, Sorena Sorenson, Gene Jarosewich, Joe

Nelen, and Jim Collins of the Smithsonian Institution for usefuladvice and assistance with the microprobe analyses. This workgreatly benefited from the review of Dr. Peter Bitschene and theODP reviewers Jeffery C. Alt, Craig Chesner, and Bill Rose.Dehn's research was supported by the Deutsche Forschungs Ge-meinschaft grant no. Schm 250/37-1 to -3 and the Fulbright

287

Table 3. Microprobe analyses of Plagioclase crystals in the tephra layers at Site 758.

Sample 758A-1H-2, 758A-1H-2, 758A-1H-2, 758A-1H-2, 758A-1H-2, 758B-1H-1, 758B-1H-1, 758B-1H-1, 758B-1H-1, 758B-1H-1, 758B-1H-1, 758B-1H-1, 758C-1H-2, 758C-1H-2,25 cm 25 cm 25 cm 25 cm 25 cm 114 cm 114 cm 114 cm 114 cm 114 cm 114 cm 114 cm 14 cm 14 cm

Layer A A A A A A A A A A A A A A

SiO2 57.67 57.24 57.42 57.51 58.60 58.94 57.38 60.35 58.76 59.34 55.09 59.69 59.36 58.33TiO2 0.02 0.04 0.04 0.03 0.05 0.03 0.04 0.03 0.03 0.03 0.02 0.02 0.01 0.04A12O3 25.83 26.12 25.84 26.20 24.83 25.65 26.40 24.68 25.59 25.00 28.24 25.17 25.14 25.87Fe2O3 0.21 0.24 0.21 0.21 0.34 0.00 0.07 0.19 0.20 0.29 0.28 0.22 0.19 0.27FeO 0.00 0.00 0.00 0.00 0.00 0.19 0.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00MgO 0.01 0.01 0.02 0.01 0.08 0.02 0.00 0.01 0.02 0.09 0.03 0.00 0.00 0.00CaO 8.07 8.25 7.82 7.96 6.86 7.66 8.68 6.64 7.03 6.67 10.40 6.94 6.63 7.51Na2O 6.71 6.76 6.95 6.82 7.13 6.84 6.36 7.60 7.32 7.74 5.55 7.49 7.83 7.22K2O 0.55 0.54 0.57 0.52 0.87 0.60 0.49 0.75 0.76 0.81 0.37 0.68 0.66 0.65P2O5 0.04 0.05 0.05 0.04 0.04 0.03 0.05 0.02 0.03 0.09 0.05 0.01 0.03 0.02

Total 99.11 99.25 98.92 99.30 98.80 99.96 99.58 100.27 99.74 100.06 100.03 100.22 99.85 99.91

Si 10.42 10.32 10.37 10.36 10.60 10.56 10.34 10.73 10.51 10.55 9.92 10.62 10.57 10.42Ti 0.00 0.01 0.01 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01Al 5.50 5.55 5.50 5.56 5.29 5.42 5.61 5.17 5.39 5.24 5.99 5.28 5.28 5.45Fe3 + 0.03 0.03 0.03 0.03 0.05 0.00 0.01 0.03 0.03 0.04 0.04 0.03 0.03 0.04Fe2 + 0.00 0.00 0.00 0.00 0.00 0.03 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00Mg 0.00 0.00 0.01 0.00 0.02 0.01 0.00 0.00 0.01 0.02 0.01 0.00 0.00 0.00Ca 1.56 1.59 1.51 1.54 1.33 1.47 1.68 1.27 1.35 1.27 2.01 1.32 1.27 1.44Na 2.35 2.36 2.43 2.38 2.50 2.38 2.22 2.62 2.54 2.67 1.94 2.58 2.70 2.50K 0.13 0.12 0.13 0.12 0.20 0.14 0.11 0.17 0.17 0.18 0.08 0.15 0.15 0.15P 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.00 0.00 0.01 0.01 0.00 0.00 0.00

Sum Z 15.92 15.87 15.87 15.92 15.89 15.97 15.95 15.91 15.90 15.80 15.91 15.90 15.85 15.87SumX 4.04 4.08 4.08 4.04 4.03 3.98 4.01 4.06 4.06 4.12 4.03 4.06 4.12 4.09

Orthoclase 3.14 3.04 3.22 2.96 4.98 3.44 2.81 4.20 4.27 4.46 2.11 3.80 3.64 3.62Albite 58.19 57.91 59.68 58.99 62.04 59.65 55.41 64.61 62.54 64.72 48.09 63.62 65.64 61.20Anorthite 38.67 39.05 37.10 38.05 32.98 36.91 41.79 31.19 33.19 30.82 49.80 32.58 30.72 35.18

Sample 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2, 758C-1H-2,14 cm 14 cm 14 cm 14 cm 27 cm 27 cm 27 cm 27 cm 27 cm 27 cm 27 cm 27 cm 27 cm 27 cm

Layer A A A A A A A A A A A A A A

SiO2 60.05 58.98 60.97 61.49 57.80 57.75 59.80 58.80 58.01 57.02 58.01 58.36 57.33 57.39TiO2 0.04 0.03 0.02 0.02 0.02 0.02 0.01 0.04 0.03 0.01 0.01 0.01 0.02 0.02A12O3 24.90 25.25 24.76 24.65 26.52 26.83 24.67 24.94 25.82 26.65 25.73 25.50 25.76 25.62Fe2O3 0.20 0.20 0.19 0.00 0.21 0.18 0.19 0.19 0.19 0.19 0.21 0.20 0.14 0.18FeO 0.00 0.00 0.00 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.07 0.00MgO 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00CaO 6.66 7.17 6.39 6.35 8.23 8.51 6.42 6.53 7.69 8.15 7.34 7.33 7.64 7.84Na2O 7.79 7.44 7.63 7.60 6.79 6.53 7.52 7.46 6.87 6.61 6.96 6.85 6.61 6.66K2O 0.69 0.73 0.84 0.91 0.54 0.51 0.79 0.83 0.65 0.56 0.72 0.73 0.63 0.65P2O5 0.02 0.02 0.04 0.03 0.04 0.03 0.02 0.03 0.03 0.06 0.05 0.04 0.06 0.04

Total 100.35 99.82 100.84 101.21 100.15 100.37 99.42 98.82 99.30 99.25 99.03 99.04 98.27 98.40

Si 10.66 10.54 10.79 10.84 10.33 10.31 10.73 10.60 10.45 10.28 10.47 10.54 10.45 10.44Ti 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00Al 5.21 5.32 5.16 5.12 5.58 5.65 5.21 5.30 5.48 5.66 5.47 5.43 5.53 5.49Fe3 + 0.03 0.03 0.03 0.00 0.03 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02Fe2 + 0.00 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00Mg 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Ca 1.27 1.37 1.21 1.20 1.58 1.63 1.23 1.26 1.48 1.57 1.42 1.42 1.49 1.53Na 2.68 2.58 2.62 2.60 2.35 2.26 2.62 2.61 2.40 2.31 2.44 2.40 2.34 2.35K 0.16 0.17 0.19 0.20 0.12 0.12 0.18 0.19 0.15 0.13 0.17 0.17 0.15 0.15P 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01

SumZ 15.86 15.85 15.95 15.97 15.91 15.96 15.94 15.90 15.93 15.95 15.94 15.98 15.98 15.94SumX 4.10 4.12 4.02 4.00 4.05 4.01 4.03 4.06 4.03 4.02 4.02 3.99 3.97 4.03

Orthoclase 3.81 4.04 4.72 5.11 3.04 2.90 4.49 4.70 3.70 3.21 4.12 4.22 3.69 3.74Albite 65.33 62.61 65.14 64.91 58.07 56.45 64.90 64.23 59.50 57.57 60.58 60.19 58.77 58.32Anorthite 30.86 33.34 30.15 29.97 38.89 40.65 30.62 31.07 36.80 39.22 35.30 35.59 37.54 37.94

Sample

Layer

SiO2TiO2

A12O3Fe2O3FeOMgOCaONa2OK2O

P2O5Total

SiTiAlFe3 +

Fe2 +

MgCaNaKP

Sum ZSumX

OrthoclaseAlbiteAnorthite

758A-1H-2,5 cm

A

57.920.02

26.700.000.170.008.376.270.610.05

100.11

10.390.005.640.000.030.001.612.180.140.01

16.043.93

3.5555.5040.94

758A-1H-2,47 cm

B

60.570.03

24.460.000.210.006.617.060.880.02

99.84

10.860.005.170.000.030.001.272.460.200.00

16.033.93

5.1362.5232.35

758A-1H-2,47 cm

B

59.900.02

24.190.000.180.016.746.940.870.02

98.87

10.850.005.170.000.030.001.312.440.200.00

16.023.95

5.0961.7633.15

758A-1H-2,47 cm

B

58.060.03

26,250.000.220.008.436.420.520.01

99.94

10.430.005.560.000.030.001.622.240.120.00

15.983.98

3.0056.2140.79

758A-1H-2,47 cm

B

56.950.00

26.190.220.00o.oo8.396.490.530.04

98.81

10.330.005.600.030.000.001.632.280.120.01

15.934.04

3.0456.5640.40

758A-1H-2,47 cm

B

58.480.04

25.640.230.000.007.846.970.530.01

99.74

10.490.015.420.030.000.001.512.420.120.00

15.914.05

2.9959.8237.18

758A-1H-2,47 cm

B

60.13' 0.0225.050.220.000.006.797.460.760.01

100.44

10.680.005.250.030.000.001.292.570.170.00

15.934.04

4.2763.6932.04

758A-1H-2,47 cm

B

60.730.02

23.860.230.000.006.197.710.930.03

99.70

10.860.005.030.030.000.001.192.670.210.00

15.894.07

5.2165.6629.13

758A-1H-2,47 cm

B

61.180.02

23.790.000.220.005.867.631.080.01

99.79

10.940.005.010.000.030.001.122.640.250.00

15.954.01

6.1465.9027.97

758A-2H-4,38 cm

D

61.300.01

24.120.000.170.006.087.410.980.00

100.07

10.950.005.080.000.030.001.162.570.220.00

16.023.95

5.6564.9229.43

758A-2H-4,38 cm

D

61.380.02

23.680.000.190.005.937.370.970.00

99.54

11.030.005.010.000.030.001.142.570.220.00

16.043.93

5.6665.3129.04

758A-2H-4,38 cm

D

59.360.04

25.240.000.190.007.006.750.770.01

99.36

10.710.015.370.000.030.001.352.360.180.00

16.073.89

4.5560.6834.77

758A-2H-4,38 cm

D

59.720.04

25.100.000.200.007.236.880.720.00

99.89

10.710.015.310.000.030.001.392.390.160.00

16.023.95

4.1760.6235.20

758A-2H-4,115 cm

E

58.840.01

25.680.240.000.007.287.290.480.03

99.85

10.520.005.410.030.000.001.392.530.110.00

15.934.03

2.7262.6934.59

Sample

Layer

SiO2

TiO2A12O3Fe2O3FeOMgOCaONa2OK2OP2O5Total

SiTiAlFe3 +

Fe2 +

MgCaNaKP

Sum ZSumX


758A-2H-4,115 cm

E

58.310.01

25.160.260.000.016.997.190.480.07

98.48

10.580.005.380.030.000.001.362.530.110.01

15.954.00

2.7863.2433.98

758A-3H-3,125 cm

F

49.500.01

31.480.420.000.01

14.673.050.180.07

99.39

9.090.006.820.060.000.002.891.090.040.01

15.914.02

1.0527.0571.90

758A-3H-3,125 cm

F

48.920.01

31.690.260.180.00

14.942.780.160.04

98.98

9.040.006.900.040.030.002.961.000.040.01

15.943.99

0.9424.9574.10

758A-3H-3,125 cm

F

50.250.03

31.250.440.040.02

14.193.250.260.08

99.80

9.190.006.730.060.010.012.781.150.060.01

15.923.99

1.5228.8669.62

758A-3H-3,125 cm

F

50.260.04

30.910.060.410.00

14.173.220.260.10

99.43

9.230.016.690.010.060.002.791.150.060.02

15.913.99

1.5228.7069.78

758A-3H-3,125 cm

F

51.260.04

29.960.470.000.00

12.883.930.340.07

98.95

9.420.016.490.060.000.002.541.400.080.01

15.904.01

1.9834.8763.15

758A-3H-3,125 cm

F

51.430.03

30.340.460.000.02

12.953.950.320.07

99.57

9.390.006.530.060.000.012.531.400.070.01

15.914.00

1.8634.9063.24

758A-7H-2,120 cm

I

48.630.03

32.360.270.000.00

15.232.910.110.05

99.59

8.910.006.990.040.000.002.991.030.030.01

15.904.05

0.6325.5373.84

758A-7H-2,120 cm

I

47.290.03

33.130.300.000.00

15.732.490.060.07

99.10

8.720.007.200.040.000.003.110.890.010.01

15.934.01

0.3522.1977.46

758A-7H-2,120 cm

I

61.190.01

24.260.000.130.005.707.690.750.02

99.75

10.940.005.110.000.020.001.092.670.170.00

16.053.93

4.3567.8527.79

758A-7H-2,120 cm

I

60.650.01

24.390.000.170.005.677.790.690.01

99.38

10.870.005.150.000.030.001.092.710.160.00

16.023.95

3.9968.4727.54

758A-7H-2,120 cm

I

60.950.02

23.880.000.150.005.387.860.880.03

99.15

10.940.005.050.000.020.001.032.740.200.00

16.003.97

5.0768.8726.05

758A-7H-2,120 cm

1

61.030.01

23.500.180.000.005.148.160.790.02

98.83

10.970.004.980.020.000.000.992.840.180.00

15.964.02

4.5170.8324.66

758A-7H-2,120 cm

I

61.220.02

24.270.000.130.005.347.880.830.06

99.75

10.930.005.110.000.020.001.022.730.190.01

16.033.94

4.8069.2625.94


Sample

Layer

SiO2

TiO2

A12O3

Fe2O3

FeOMgOCaONa2OK2OP2O5

Total

SiTiAlFe3 +

Fe 2 +

MgCaNaKP

Sum ZSum X


Sample

Layer

SiO2

TiO2

A12O3

Fe2O3

FeOMgOCaONa2OK2OP2O5

Total

SiTiAlFe3 +

Fe2 +

MgCaNaKP

Sum ZSum X


758A-7H-2,120 cm

I

61.850.01

23.470.000.110.004.928.130.820.02

99.33

11.070.004.950.000.020.000.942.820.190.00

16.033.95

4.7471.3923.87

758B-2H-2,61 cm

E

55.390.12

27.050.000.870.08

10.625.010.320.05

99.51

10.090.025.810.000.130.022.071.770.070.01

15.903.92

1.9045.1852.92

758B-1H-5,119 cm

C

58.030.01

26.200.000.190.017.966.510.590.03

99.53

10.450.005.560.000.030.001.542.270.140.00

16.023.95

3.4457.6338.94

758B-2H-2,61 cm

E

60.380.03

24.100.000.190.006.467.090.610.05

98.91

10.930.005.140.000.030.001.252.490.140.01

16.083.88

3.6364.1032.27

758B-1H-5,119 cm

C

57.820.02

26.110.230.000.008.086.610.600.01

99.48

10.420.005.540.030.000.001.562.310.140.00

15.964.01

3.4457.6338.93

758B-2H-2,61 cm

E

60.290.01

24.270.000.190.006.647.250.590.04

99.28

10.860.005.150.000.030.001.282.530.140.01

16.013.95

3.4364.1232.45

758B-1H-5,119 cm

C

57.880.01

25.950.000.210.007.846.500.660.03

99.08

10.470.005.530.000.030.001.522.280.150.00

16.013.95

3.8557.6938.45

758B-2H-2,61 cm

E

55.930.04

26.400.000.490.019.845.460.640.07

98.88

10.220.015.680.000.070.001.931.930.150.01

15.904.01

3.7248.2448.04

758B-1H-5,119 cm

C

57.100.02

26.570.220.000.008.386.450.570.04

99.35

10.300.005.650.030.000.001.622.260.130.01

15.954.01

3.2756.3040.42

758B-2H-2,61 cm

E

56.170.06

26.340.000.460.029.615.490.700.03

98.88

10.260.015.670.000.070.011.881.940.160.00

15.923.99

4.0948.7547.16

758B-1H-5,119 cm

C

56.540.01

27.210.110.090.008.946 .100.440.02

99.46

10.210.005.790.020.010.001.732.140.100.00

16.003.97

2.5653.8443.60

758B-3H-4,69 cm

G

60.270.01

23.800.000.230.006.127.030.890.01

98.36

10.970.005.110.000.040.001.192.480.210.00

16.083.88

5.3263.9230.75

758B-1H-5,119 cm

C

56.190.01

27.230.220.000.009.036.130.390.05

99.25

10.160.005.810.030.000.001.752.150.090.01

15.973.99

2.2653.8843.86

758B-3H-4,69 cm

G

60.330.03

24.010.000.210.006.097.060.860.02

98.61

10.950.005.140.000.030.001.182.490.200.00

16.093.87

5.1564.2330.62

758B-2H-2,25 cm

d

58.960.04

25.920.000.210.007.946.390.630.07

100.16

10.580.015.480.000.030.001.532.220.140.01

16.063.89

3.7057.0939.20

758B-3H-4,69 cm

G

61.630.02

22.950.000.270.005.936.681.140.05

98.67

11.230.004.930.000.040.001.162.360.270.01

16.163.78

7.0162.3930.61

758B-2H-2,25 cm

d

57.350.03

26.420.000.170.008.895.990.530.04

99.42

10.380.005.640.000.030.001.722.100.120.01

16.023.95

3.1053.2443.66

758B-3H-4,69 cm

G

60.990.03

23.850.000.230.006.107.070.880.06

99.21

11.020.005.080.000.030.001.182.480.200.01

16.093.86

5.2564.1630.59

758B-2H-2,25 cm

d

58.090.00

25.520.000.190.007.616.630.590.04

98.67

10.550.005.460.000.030.001.482.330.140.01

16.013.95

3.4659.0737.47

758B-6H-7,17 cm

1

59.840.04

24.810.120.000.006.317.710.620.06

99.51

10.710.015.230.020.000.001.212.680.140.01

15.944.03

3.5266.4430.05

758B-2H-2,25 cm

d

58.250.01

25.790.040.130.007.906.720.570.02

99.43

10.490.005.480.010.020.001.522.350.130.00

15.974.00

3.2758.6438.09

758B-6H-7,17 cm

I

60.030.01

24.740.140.000.016.337.740.660.05

99.71

10.720.005.210.020.000.001.212.680.150.01

15.934.04

3.7266.3129.97

758B-2H-2,25 cm

d

60.190.02

25.140.000.180.017.256.760.890.01

100.45

10.750.005.290.000.030.001.392.340.200.00

16.043.93

5.1659.5535.29

758B-6H-7,17 cm

1

58.780.01

25.060.160.000.017.227.600.410.02

99.27

10.550.005.300.020.000.001.392.640.090.00

15.854.13

2.2764.0833.64

758B-2H-2,25 cm

d

60.380.01

24.980.000.190.007.066.890.830.02

100.36

10.780.005.260.000.030.001.352.390.190.00

16.043.93

4.8260.7734.41

758B-6H-7,17 cm

I

59.510.02

24.780.160.000.026.697.620.510.05

99.36

10.670.005.240.020.000.011.292.650.120.01

15.914.05

2.8865.3931.73

758B-2H-2,61 cm

E

56.730.11

25.730.001.060.169.875.260.440.04

99.40

10.350.025.530.000.160.041.931.860.100.01

15.883.89

2.6347.8049.57

758B-7H-6,29 cm

K

55.170.08

25.990.880.000.119.415.950.370.06

98.02

10.140.015.630.120.000.031.852.120.090.01

15.774.06

2.1452.2245.64

n

Sample 758B-7H-6, 758B-7H-6, 758B-7H-6, 758B-7H-CC, 758B-7H-CC, 758B-7H-CC, 758B-7H-CC, 758B-7H-CC, 758B-7H-CC,29 cm 29 cm 29 cm 14 cm 14 cm 14 cm 14 cm 14 cm 14 cm

Layer K K K L L L L L L

SiO2 54.06 54.90 54.17 49.18 49.16 48.00 49.37 45.43 45.74TiO2 0.07 0.08 0.09 0.07 0.05 0.05 0.05 0.04 0.05A12O3 27.64 27.05 27.33 31.62 30.91 31.73 30.08 33.07 32.86Fe2O3 0.84 0.64 0.62 0.54 0.56 0.66 0.69 0.67 0.72FeO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00MgO 0.08 0.06 0.09 0.06 0.03 0.06 0.09 0.09 0.09CaO 10.79 9.74 10.12 14.47 14.50 15.62 14.22 17.15 16.92Na2O 5.38 5.90 5.61 3.10 3.26 2.83 3.73 1.65 1.83K2O 0.31 0.46 0.43 0.13 0.10 0.04 0.09 0.04 0.04P 2 O 5 0.06 0.06 0.09 0.10 0.10 0.08 0.08 0.10 0.12

Total 99.23 98.89 98.55 99.27 98.67 99.07 98.40 98.24 98.37

Si 9.84 9.99 9.90 9.04 9.09 8.86 9.13 8.51 8.55Ti 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01Al 5.93 5.80 5.89 6.85 6.74 6.90 6.56 7.30 7.24Fe 3 + 0.10 0.12 0.09 0.09 0.08 0.08 0.09 0.10 0.09Fe 2 + 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Mg 0.02 0.02 0.02 0.02 0.01 0.02 0.02 0.03 0.03Ca 2.10 1.90 1.98 2.85 2.87 3.09 2.82 3.44 3.39.Na 1.90 2.08 1.99 1.11 1.17 1.01 1.34 0.60 0.66K 0.07 0.11 0.10 0.03 0.02 0.01 0.02 0.01 0.01P 0.01 0.01 0.01 0.02 0.02 0.01 0.01 0.02 0.02

Sum Z 5.77 15.79 15.79 15.90 15.83 15.76 15.68 15.81 15.79Sum X 4.07 4.09 4.07 3.99 4.07 4.11 4.18 4.05 4.06

Orthoclase 1.77 2.61 2.46 0.76 0.58 0.23 0.51 0.24 0.23Albite 46.59 50.93 48.85 27.72 28.75 24.63 32.02 14.79 16.33Anorthite 51.64 46.46 48.69 71.51 70.67 75.14 67.47 84.97 83.44

J. DEHN, J. W. FARRELL, H.-U. SCHMESfCKE

Table 4. Microprobe analyses of alkali feldspar crystals in the tephra layers at Site 758.

Sample

Layer

SiO2

TiO2

A12O3

Fe2O3

MgOCaONa2OK2OP2O5

Total

SiTiAlFe3 +

MgCaNaKP

Sum ZSum X


758C-1H-2,14 cm

A

65.670.05

19.160.040.000.071.70

14.790.16

101.64

11.870.014.080.000.000.010.603.410.02

15.954.02

84.8414.820.34

758A-2H-4,38 cm

D

65.730.04

18.630.090.000.182.43

13.020.01

100.13

12.030.014.020.010.000.040.863.040.00

16.053.94

77.2021.900.90

758A-2H-4,38 cm

D

66.190.04

18.600.130.000.192.61

13.040.00

100.80

12.020.013.980.010.000.040.923.020.00

16.003.98

75.9623.110.93

758A-2H-4,38 cm

D

65.050.04

18.740.120.030.192.60

12.860.02

99.65

11.940.014.050.010.010.040.933.010.00

16.003.97

75.7723.290.94

758B-2H-2,25 cm

d

66.840.02

18.510.090.010.212.75

12.490.04

100.96

12.120.003.960.010.000.040.972.890.01

16.083.90

74.1424.81

1.05

758B-2H-2,25 cm

d

66.750.02

18.850.110.000.192.78

12.650.04

101.39

12.050.004.010.010.000.040.972.910.01

16.063.92

74.2624.800.94

758B-2H-2,25 cm

d

65.370.02

18.550.100.000.172.71

12.240.02

99.18

12.060.004.030.010.000.030.972.880.00

16.103.88

74.1724.960.87

758B-2H-2,25 cm

d

65.590.02

18.440.090.000.152.81

12.350.00

99.45

12.060.004.000.010.000.031.002.900.00

16.063.93

73.7425.500.75

758B-2H-2,25 cm

d

66.250.02

18.660.120.000.172.78

12.170.01

100.18

12.110.004.020.010.000.030.992.840.00

16.133.86

73.5925.550.86

758B-2H-2,25 cm

d

65.230.03

18.930.110.000.202.82

12.200.03

99.55

11.980.004.100.010.000.041.002.860.00

16.083.90

73.2625.74

1.01

Note: The sum of the cations for all analyses is 20.

Kommission and is part of a Ph.D. dissertation. Farrell's work wassupported by a grant from JOI/USSAC (TAMRF-20244).

REFERENCES

Aldiss, D. T., and Ghazali, S. A., 1984. The regional geology andevolution of the Toba volcano-tectonic depression, Indonesia. / . Geol.Soc. London, 141:487-500.

Bitschene, P. R., and Schmincke, H.-U., 1990. Fallout tephra layers:composition and significance. In Heling, D., Rothe, P., Förstner, U.,and Stoffers, P. (Eds.), Sediments and Environmental Geochemistry:Heidelberg (Springer), 48-82.

Bramlette, M. N., and Bradley, W. H., 1942. Geology and biology ofNorth Atlantic deep-sea cores between Newfoundland and Ireland. Pt.I: lithology and geologic interpretations. Geol. Surv. Prof. Pap. U.S.,196A:l-55.

Chesner, C. A., 1988. The Toba tuffs and caldera complex, Sumatra,Indonesia: insights into magma bodies and eruptions [Ph.D. dissert.].Michigan Tech. Univ., Houghton.

Deer, W. A., Howie, R. A., and Zussman, J., 1966. An Introduction to theRock Forming Minerals. Essex, U.K. (Longman Group, Ltd.), 528 p.

Diehl, J. F., Onstott, T. C , Chesner, C. A., and Knight, M. D., 1987. Noshort reversals of Brunhes age recorded in the Toba Tuffs, NorthSumatra, Indonesia. Geophys. Res. Lett., 14:753-766.

Fisher, R. V., 1964. Maximum size, median diameter, and sorting oftephra. / . Geophys. Res., 69:341-355.

Imbrie, J., Hays, J. D., Martinson, D. G., Mclntyre, A., Mix, A. C ,Morley, J. J., Pisias, N. G., Prell, W. L., and Shackleton, N. J., 1984.The orbital theory of Pleistocene climate: support from a revisedchronology of the marine delta δ 1 8 θ record. In Berger, A., Imbrie, J.,Hays, J., Kukla, G., and Saltzman, B. (Eds.), Milankovitch and Cli-mate (pt. 1): Dordrecht (D. Reidel), 269-305.

Kennett, J. P., 1981. Marine tephrochronology. In Emiliani, C. (Ed.), TheSea (vol. 7): New York (Wiley), 1373-1436.

Ninkovich, D., 1979. Distribution, age and chemical composition oftephra layers in deep-sea sediments off western Indonesia. /. Vol-canol. Geotherm. Res., 5:67—86.

Ninkovich, D., Shackleton, N. J., Abdel-Monem, A. A., Obradovich, J.D., and Izett, G., 1978. K-Ar age of the late Pleistocene eruption ofToba, north Sumatra. Nature, 276:574-577.

Ninkovich, D., Sparks, R.S.J., and Ledbetter, M. T., 1979. The excep-tional magnitude and intensity of the Toba eruption, Sumatra: anexample of the use of deep-sea tephra layers as a geological tool. Bull.Volcanol., 41:286-297.

Nishimura, S., Abe, E., Yokoyama, T., Wirasantosa, S., and Dharma, A.,1977. Paleolimnol. Lake Biwa Japan Pleistocene, 5:313-332.

Peirce, J., Weissel, J., et al., 1989. Proc. ODP, Init. Repts., 121: CollegeStation, TX (Ocean Drilling Program).

Prell, W. L., Imbrie, J., Martinson, D. G., Morley, J. J., Pisias, N. G.,Shackleton, N. J., and Streeter, H. F., 1986. Graphic correlation ofoxygen isotope stratigraphy: application to the late Quaternary. Pa-leoceanography, 1:137-162.

Raymo, M. E., Ruddiman, W. F., Backman, J., Clement, B. M., andMartinson, D. G., 1989. Late Pliocene variation in Northern Hemi-sphere ice sheets and North Atlantic deep water circulation. Paleo-ceanography, 4:413-446.

Rose, W. I., and Chesner, C. A., 1987. Dispersal of ash in the great Tobaeruption, 75 ka. Geology, 15:913-917.

, 1988. World-wide dispersal of ash and gases from Earth'slargest known eruption, Toba, Sumatra, 78 ka. IGBP (Inter. AlfredWegner Conf, on the Contribution of Solid Earth Sciences). (Abstract)

Ruddiman, W. F., Cameron, D., and Clement, B. M., 1987. Sedimentdisturbance and correlation of offset holes drilled with the hydraulicpiston corer: Leg 94. In Ruddiman, W. F., Kidd, R. B., Thomas, E.,et al., Init. Repts. DSDP, 94, Pt. 2: Washington (U.S. Govt. PrintingOffice), 615-634.

Ruddiman, W. F., and Glover, L. K., 1982. Mixing of volcanic ash zonesin subpolar North Atlantic sediments. In Scrutton, R. A., and Talwani,M. (Eds.), The Ocean Floor: Chicago (Wiley), 37-67.

292



Sample

Layer

SiO2TiO2A12O3Fe 2 O 3MgOCaONa 2 OK 2 OP 2 O 5

Total

SiTiAlFe 3 +

MgCaNaKP

Sum ZSum X


758B-2H-2,25 cm

d

66.540.03

18.990.110.000.192.77

12.590.02

101.24

12.030.004.040.010.000.040.972.900.00

16.073.91

74.2324.82

0.94

758B-2H-2,25 cm

d

66.040.02

18.740.090.000.162.66

12.700.02

100.43

12.040.004.030.010.000.030.942.950.00

16.063.92

75.2523.96

0.80

758B-3H-4,69 cm

G

65.290.02

18.740.170.000.273.19

12.090.02

99.79

11.940.004.040.020.000.051.132.820.00

15.974.00

70.4328.25

1.32

758B-3H-4,69 cm

G

65.620.04

18.460.130.000.253.22

11.950.01

99.68

12.010.013.980.010.000.051.142.790.00

16.003.98

70.0728.70

1.23

758B-6H-2,47 cm

h

66.030.02

18.220.130.000.162.77

12.960.02

100.31

12.040.003.920.010.000.030.983.010.00

15.954.02

74.8924.33

0.78

758B-6H-2,47 cm

h

65.990.03

18.430.100.000.142.79

12.870.04

100.39

12.020.003.960.010.000.030.992.990.01

15.984.00

74.7024.61

0.68

758B-6H-2,47 cm

h

65.380.03

18.640.100.000.172.85

12.560.04

99.77

11.970.004.020.010.000.031.012.930.01

16.003.98

73.7325.43

0.84

758B-6H-2,47 cm

h

65.280.03

18.790.070.000.152.84

12.810.05

100.02

11.920.004.040.010.000.031.012.980.01

15.964.02

74.2525.02

0.73

758B-6H-7,17 cm

I

64.550.03

18.330.020.030.080.81

16.240.17

100.26

11.870.003.970.000.010.020.293.810.03

15.844.11

92.607.020.38

758B-8H-4,111 cm

M

64.510.09

18.780.440.001.086.357.060.04

98.35

11.780.014.040.050.000.212.251.650.01

15.834.11

40.0754.78

5.15

758B-8H-4,111 cm

M

63.770.12

18.790.510.011.246.825.960.04

97.26

11.750.024.080.060.000.242.441.400.01

15.834.08

34.3259.69

6.00

Ruddiman, W. F., Raymo, M. E., Martinson, D. G., Clement, B. M., andBackman, J., 1989. Pleistocene evolution: Northern Hemisphere icesheets and North Atlantic Ocean. Paleoceanography, 4:353^412.

Schmincke, H.-U., 1981. Ash from vitric muds in deep sea cores from theMariana Trough and fore-arc regions (south Philippine Sea) (Sites453, 454, 455, 458, 459). In Hussong, D. M., Uyeda, S., et al., Init.Repts. DSDP, 60: Washington (U.S. Govt. Printing Office), 473-481.

Shackleton, N. J., and Hall, M. A., 1989. Stable isotope history of thePleistocene at ODP Site 677. In Becker, K., Sakai, H., et al., Proc.ODP, Sci. Results, 111: College Station, TX (Ocean Drilling Pro-gram), 295-316.

Shaw, D. M., Watkins, N. D., and Huang, T. C, 1974. Atmosphericallytransported volcanic glass in deep sea sediments: theoretical consid-erations. /. Geophys. Res., 79:3087-3094.

Shipboard Scientific Party, 1989. Site 758. In Peirce, J., Weissel, J., etal., Proc. ODP, Init. Repts., 121: College Station, TX (Ocean DrillingProgram), 359-453.

Smith, R. L., and Bailey, R. A., 1968. Resurgent cauldrons. In Coats, R.R., Hay, R. L., and Anderson, C. A. (Eds.), Studies in Volcanology:Geol. Soc. Am. Mem., 116:613-662.

von der Borch, C. C, Sclater, J. G., et al., 1974. Init. Repts. DSDP, 22:Washington (U.S. Govt. Printing Office).

Walker, G.P.L., 1971. Grain-size characteristics of pyroclastic deposits./. Geol, 79:696-714.

Williams, M.A.J., and Royce, K., 1982. Quaternary geology of the middleSon Valley, north-central India: implications for prehistoric archae-ology. Paleogeogr., Paleoclimatol., Paleoecol., 38:139-162.

Date of initial receipt: 13 March 1990Date of acceptance: 31 October 1990Ms 121B-123

Figure 7. Ternary diagram of feldspars in the Site 758 tephras. The analysesfall into four distinct groups of An65-85, An25-55, Or40, and Oπo-76 Layers I,G, D, and d have sanidine, as well as andesine, crystals. Layers F, I, and Lcontain bytownite crystals, which is unusually rich in An for rhyolitic magmas.

293

Table 5. Microprobe analyses of major oxide concentrations in other crystals in the tephra layers at Site 758.

Sample

Layer

SiO2


P2O5

Total

Mineral

758B-1H-1,114 cm

A

45.348.61

21.578.35

10.341.041.521.700.17

98.64

Amphibole

758C-1H-2,14 cm

A

0.030.000.050.02

52.500.020.070.06

42.33

95.08

Apatite

758C-1H-2,27 cm

A

36.3914.1621.02

9.930.058.480.484.310.02

94.84

Biotite

758C-1H-2,27 cm

A

34.2315.2324.28

7.700.048.480.813.710.05

94.53

Biotite

758C-1H-2,27 cm

A

35.1114.3522.20

9.420.058.310.444.020.05

93.95

Biotite

758A-1H-2,47 cm

B

36.7213.8624.24

8.820.019.200.403.730.04

97.02

Biotite

758A-1H-2,47 cm

B

36.5814.2323.62

9.130.019.270.344.060.02

97.26

Biotite

758A-1H-2,47 cm

B

35.8014.0323.179.010.039.050.353.850.07

95.36

Biotite

758A-1H-2,47 cm

B

36.0914.4021.55

9.500.028.870.444.660.01

95.54

Biotite

758A-1H-2,47 cm

B

37.0714.2721.45

9.940.019.290.404.490.01

96.93

Biotite

758A-1H-2,47 cm

B

37.0213.9721.94

9.220.009.390.354.120.02

96.03

Biotite

758A-1H-2,47 cm

B

36.1514.2622.849.230.019.280.354.150.05

96.32

Biotite

758A-4H-4,3 cm

H

0.270.000.460.30

51.540.030.040.04

41.58

94.26

Apatite

758A-7H-2,120 cm

I

34.9915.1421.7910.000.048.660.383.190.04

94.23

Biotite

758A-7H-2,120 cm

1

36.3215.1119.9211.210.048.390.523.850.03

95.39

Biotite

758B-1H-5,119 cm

C

34.9714.3123.977.710.038.200.404.770.04

94.40

Biotite

758B-2H-2,25 cm

d

0.680.000.630.01

52.460.140.080.07

41.21

95.28

Apatite

758B-2H-2,25 cm

d

34.7813.9225.358.210.028.380.383.660.07

94.77

Biotite

758B-2H-2,25 cm

d

34.2114.4225.478.250.038.440.363.590.06

94.83

Biotite

758B-2H-2,25 cm

d

35.6613.7425.528.380.048.630.543.760.03

96.30

Biotite

758B-2H-2,25 cm

d

36.1813.7925.408.200.028.770.373.630.06

96.42

Biotite

758B-2H-2,25 cm

d

1.010.201.370.15

52.110.400.110.15

40.93

96.43

Apatite

758B-3H-4,69 cm

G

35.8014.3115.4313.360.048.810.454.650.04

92.89

Biotite

758B-4H-3,8 cm

H

0.180.001.320.15

53.220.000.100.06

41.21

96.24

Apatite

758B-6H-2,47 cm

h

35.1514.3424.677.920.058.740.333.710.05

94.96

Biotite

758B-6H-2,47 cm

h

31.525.240.620.01

32.561.790.760.05

26.65

99.20

Biotite

758B-6H-2,47 cm

h

36.1214.1724.457.850.078.730.443.620.03

95.48

Biotite

758B-6H-7,17 cm

1

35.8014.5321.899.810.068.990.353.120.06

94.61

Biotite

758B-7H-6,29 cm

K

50.661.499.52

13.8620.530.040.260.390.10

96.85

Amphibole


CaO/FeO

0.8 1.0

Figure 8. Plot of CaO/FeO ratio vs. thickness of the tephra layers. The threecogenetic groups display increasing tephra layer thickness with time andevolution of the magmas.

Table 6. Summary of the age of major tephra layers.

Layer

A

C

D

E

F

G

H

h

I

J

K

L

M

Age (Ma)

paleomagnetic

0.092-0.112

0.512-0.515

0.734-0.741

0.776-0.779

1.277-1.284

1.645-1.654

2.261-2.265

3.664-3.666

4.124-4.130

4.552-4.559

4.666-4.667

4.759-4.762

5.062-5.063

180

0.071-0.080

0.513-0.538

0.731-0.750

0.775

1.273-1.294

1.596-1.636

2.238-2.260

Intervalbetween

layers (Ma)

0.400-0.467

0.193-0.238

0.029-0.048

0.494-0.519

0.302-0.381

0.584-0.669

1.399-1.428

0.458-0.466

0.422-0.435

0.107-0.115

0.092-0.096

0.300-0.304

Groupa

1 2 3

*

*

*

*

*

*? *?

*

*?

*

*

*

*

*

Unclear group identification is noted with a question mark.

295

14. neogene tephrochronology from site …14. neogene tephrochronology from site 758 on northern...

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