Journal of Sedimentary Research, 2008, v. 78, 335–356

Research Article

DOI: 10.2110/jsr.2008.039

SIGNIFICANT VOLCANIC CONTRIBUTION TO SOME QUARTZ-RICH SANDSTONES, EASTJAVA, INDONESIA

HELEN R. SMYTH,* ROBERT HALL, AND GARY J. NICHOLS.SE Asia Research Group, Department of Geology, Royal Holloway University of London, Egham, TW20 0EX, U.K.

e-mail: helen.smyth@casp.cam.ac.uk

ABSTRACT: Quartz-rich sedimentary rocks are commonly assumed to be the eroded products of cratons or recycled orogens.However, active or eroded acidic volcanic regions can also be an important, but commonly overlooked, source of quartz.Cenozoic sandstones from East Java, Indonesia, illustrate this point. They are rich in quartz, and it has long been assumed thatthey are the product of erosion of a continental source. However, new work using a variety of provenance indicators shows thatthe sandstones contain a significant, previously overlooked, volcanic component. A number of factors have contributed to theircharacter: quartz-rich source regions, eruptive volcanic processes, and tropical weathering. Ternary discriminant diagrams,such as QFL plots which use the ratios of quartz, feldspars, and lithic grains to interpret provenance from cratonic, volcanic,and recycled orogen hinterland, may mislead, particularly in tropical volcanic settings. The quartz from acidic volcanic sourcesis commonly overlooked because it is commonly assumed that quartz has a continental crustal source. Volcanic eruptiveprocesses can lead to crystal enrichment in rapidly eroded ash and sediments. Intense chemical weathering can haveconsiderable impact on the composition of sedimentary rocks by selectively removing labile minerals and lithic grains. Theresulting deposits may be texturally immature but compositionally mature, and rich in resistant minerals such as quartz andzircon. In tropical settings the widely held view that quartz-rich sandstones are mature sediments representing multiple phasesof recycling may in many cases be incorrect.

INTRODUCTION

This paper examines the provenance of tropical, Cenozoic quartz-richsediments from East Java, Indonesia. These sandstones have long been ofinterest (e.g., Rutten 1925; van Bemmelen 1949), and in particular to thepetroleum industry as several are proven hydrocarbon reservoirs (e.g.,Soetantri et al. 1973; Soeparyono and Lennox 1990; Ardhana 1993).Therefore their source, geographic distribution, depositional environ-ment, and characteristics are of importance in exploration. Theprovenance of these sandstones also provides important information onthe geological evolution of Java and the surrounding region.

If the East Java quartz-rich sandstones are plotted on traditionaldiscriminant diagrams such as QFL (Quartz, Feldspar, Lithic grains) andQmFLt (monocrystalline Quartz, Feldspar, total Lithic grains) ternaryplots (Dickinson and Suczek 1979), a ‘‘cratonic interior’’ provenance isindicated. However, detailed examination of the quartz grains in thesesandstones, by optical, SEM, and SEM-CL techniques indicates thatthere is a variety of types including igneous, volcanic, metamorphic,hydrothermal vein, chert, and recycled sedimentary quartz. In particular,the volcanic contribution, which has previously been overlooked, is ofgreat importance when considering the likely subsurface distributions ofsandstones, and in interpreting the geological development of Java. Thepaleoclimatic location of the sediment source regions is also ofimportance. The study area is presently located just to the south of theequator (between 6u and 9u S), and the potential source regions are within

the equatorial belt, as they were throughout the Cenozoic (Hall 2002).Therefore, the influence of tropical weathering must be consideredbecause of its well-documented effects on sandstone composition (e.g.,Dosseto et al. 2006; Suttner et al. 1981).This paper briefly summarizes the characteristics that allow different

types of quartz to be distinguished, drawing on published literature (e.g.,Ingersoll 1984; Basu et al. 1975; Bernet and Basset 2005; Gotte andRichter 2006) and studies of quartz from different rock types in the region(Table 1). The Cenozoic quartz-rich sandstones of East Java are thendescribed. This is followed by a discussion of potential continental,metamorphic, volcanic, and sedimentary source areas with considerationof transport mechanisms, transport distances, and paleogeographicalbarriers.

BACKGROUND TO THE STUDY AREA, EAST JAVA, INDONESIA

The island of Java is located in a central position within the Indonesianarchipelago (Fig. 1). It is situated on the southeast edge of the EurasianPlate, and to the south of the island there has been subduction of theIndian–Australian Plate along the Java Trench since the middle Eocene(Hall 2002). The southeastern part of the Eurasian Plate is known asSundaland (e.g., van Bemmelen 1949; Hamilton 1979) and is theMesozoic continental core of SE Asia. West Java is underlain bySundaland continental basement, but the rocks which constitute thebasement of East Java have been interpreted to be accreted slivers ofmetamorphosed arc and ophiolitic rocks (Hamilton 1979; Miyazaki et al.1998). These slivers were accreted to Sundaland during the Cretaceous.The southern part of East Java is now known to be underlain at depth by

* Present address: CASP, Department of Earth Science, University of

Cambridge, 181a Huntingdon Road, Cambridge, CB30DH, U.K.

Copyright E 2008, SEPM (Society for Sedimentary Geology) 1527-1404/08/078-335/$03.00

TABLE1.—

Description

oftheCenozoicqu

artz-richsand

ston

esof

EastJa

va,Indon

esia.T

ype1containmetam

orph

icqu

artz,T

ype2volcan

icqu

artz,and

Typ

e3ha

veamixed-provena

ncemetam

orph

ic,

volcan

ican

drecycled

sedimentary

quartz

(van

Bem

melen

1949

;Sartono

1964

;Sum

arso

1975

;Ardha

na19

93;Lun

tet

al.19

98;Lelon

o20

00;Smyth20

05).

Setting

Typ

e(s)

Id.Code

Mem

ber,Form

ation

Age

LocationInform

ation

Description

Typ

eSection

Latitude,

Longitude

Outcrop

Thin

sectionofthe

quartz-richsandstones

Environmentof

Deposition

EoceneSou

thern

Mou

ntains

1+

3i

Lukulo,

Karan

gsam

bung

Middle

Eocene

(P10

-11)

KaliLukulo

river

section,nearto

Karan

gsam

bung

Village,

Kebumen,

Central

Java

7.54

771S

,10

9.66

94E

Aseries

of

quartz-rich

sandstones

and

muddyinterbeds,

whichoverlie

basal

polymict

conglomerates.Up

sectionthe

sandstones

become

increasinglyarkosic.

Thesandstones

are

sublitharenites,

composedofmetam

orphic

andvein

quartz

and

lithic

frag

ments

ofchert,

basalt,an

dschist.Up

sectionthey

becomerich

inplagioclasean

dvo

lcan

iclithic

frag

ments.

Clastic

shoreline

inaterrestrialto

shallow

marine

(intertidal)setting.

Sedim

entsupply

from

avo

lcan

icsourceincreasesup

section.

1ii

Sermo,?N

angg

ulan?

Probab

lyMiddle

Eocene

(,56

.1Mazircon

U-PbSHRIM

P)

SermoReservo

ir,

Yogy

akarta

7.82

6S,

110.10

8EQuartz-rich,yellow,

laminated,

occasionally

chan

nelized

sandstones.

Interbedded

with

organ

ic-richmuds,

containingab

undan

tplantfrag

ments.

Dominated

by

metam

orphic

andvein

quartz.Theseare

texturallyan

dcompositionally

mature

quartz

arenites.

Tidal

flatsorestuary.

Freefrom

inputof

freshvo

lcan

icmaterial.

3iii

KaliSongo

,Nan

ggulan

Middle

Eocene

(NP16

)KaliSongo

river

section,

Nan

ggulan,

Yogy

akarta

7.72

558S

,11

0.20

059E

Quartz-rich

sandstones

and

conglomerates

with

abundan

tplant

frag

ments

andcoal

interbeds.

Quartz

arenites

tosublitharenites

rich

inmetam

orphic

andvo

lcan

icquartz.Abundan

tfresh

lathsofplagioclase,

and

volcan

iclithic

frag

ments.

Terrestrial

todeltaic.

Gradual

increase

inmaterialof

volcan

icsourceup

section.

1iv

Cak

aran

,Wungk

al-G

amping

?Middle

Eocene?

Hillsideexposure

onGunung

Cak

aran

,Klaten,

Central

Java

7.81

14S,

110.63

121E

Granular,yellow,

quartz-rich

sandstones

interbedded

with

chan

nelized

polymictic

conglomerates.

Sublitharenites,composed

ofmetam

orphic

andvein

quartz

andlithic

frag

ments

ofchert,basalt,an

dschist.

Terrestrial

setting.

No

contemporaneous

volcan

icactivity.

2v

Kresek

?Middle

Eocene?

South

ofGunung

Pendul,Klaten,

Central

Java

7.76

705S

,11

0.67

146E

Crystal-richquartz

sandstones

with

tuffaceousinterbeds.

Thinly

laminated

ban

dsofeuhedralan

dbipyram

idal

volcan

icquartz

crystalsan

dshards.

Airfalldepositionor

epiclastic

reworkingof

volcan

icdeposits

onashallow

marineshelf.

Miocene

Sou

thern

Mou

ntains

2vi

Jaten

Early

Miocene

196

1Ma(zircon

U-PbSHRIM

P)

Road

cutnearto

thevillag

eof

Tulukan

,Pacitan

District,East

Java

Province

8.13

847S

,11

1.26

913E

Yellow/white,

well-

sorted

and

crystal-rich

quartz

sandstones.

Interbedded

with

volcan

icmuds,

lign

ites,an

dpumice-rich

horizons.

San

dstones

are

dominated

byvo

lcan

icquartz

withpumice,

volcan

iclithic

frag

ments,

andplagioclase.

Quartz

types

includefaceted

bipyram

idal

crystals,

skeletal

orem

bay

ed,

shards,an

dmicrocrystalline

aggregates.

Close

toan

active

and/oreroding

acidic

volcan

icsourcein

aterrestrialsetting

possibly

ona

floodplain

or

man

grove

swam

p.

Primaryairfallan

depiclastic

reworking.

336 H.R. SMYTH ET AL. J S R

a sliver of Gondwana continental crust (Smyth et al. 2007; Smyth et al.2008) but there is no evidence to suggest that this fragment was exposedat the surface or available for erosion during the Cenozoic. The Cenozoicvolcanic and sedimentary rocks exposed on land in East Java weredeposited on this accreted basement.

Java is a volcanic island and contains the products of modern and olderCenozoic igneous activity. The volcanoes of the modern Sunda Arc aredistributed along the length of the island (Fig. 1). A second older arc isexposed in the Southern Mountains of East Java and runs broadlyparallel to, and south of, the modern arc (Fig. 1). This volcanic arc, herenamed the Southern Mountains Arc, was active from the Eocene to theearly Miocene (Smyth 2005). During much of the Cenozoic there was adeep basin, the Kendeng Basin (Fig. 1), located to the north of, andbehind, the Southern Mountains Arc (de Genevraye and Samuel 1972;Smyth 2005). From gravity calculations the depocenter is believed tocontain more than 10 km of sedimentary rocks (Waltham et al. 2008; C.J.Ebinger, personal communication 2005), which are locally exposed at thesurface in a fold thrust belt. A shallow marine clastic and carbonate shelf,the Sunda Shelf, formed the northern limit to the Kendeng Basin (Fig. 1).

In the Cenozoic sequences of East Java there are several quartz-richsandstones (ranging from litharenites to quartz arenites) of middle to lateEocene and early to middle Miocene age (Fig. 2, Table 1). They appear tobe compositionally mature, in as much as they are rich in quartz, but theyare texturally immature, in that many of the grains are angular oreuhedral. The sandstones also contain abundant zircons, of which manyare euhedral elongate prisms, a grain form which is typical of volcaniczircons (Mange and Maurer 1992). The origin and provenance of thesequartz-rich sandstones was one aim of this study.

Rutten (1925) discussed early differences in views about the source ofmaterial in Neogene sedimentary rocks of Java. Despite long-livedvolcanic activity, the contribution of volcanic material to the olderCenozoic sedimentary rocks of East Java has previously been consideredto be relatively unimportant. However, during the course of this study itbecame clear that many rocks considered to be terrigenous siliciclasticrocks (e.g., de Genevraye and Samuel 1972; Lunt et al. 1998) have asignificant volcanic component (Smyth 2005). To assess the importance ofthe volcanic contribution and identify possible source regions it wasnecessary to evaluate the compositions and characters of the East Javaquartz-rich sandstones, and consider the processes which may haveformed them.

FORMATION OF QUARTZ-RICH SANDSTONES

Quartz-rich sandstones, and in particular quartz arenites (in whichquartz exceeds 95%), are the subject of considerable, in many casesconflicting, discussion in the literature (e.g., Chandler 1988; Dott 2003;Johnsson et al. 1991; Potter 1978; Suttner et al. 1981; and referencestherein). The discussion of Dott (2003) addresses many of the commonmyths and misconceptions surrounding the formation of quartz arenites.Dott (2003) recalls the conventional wisdom of the mid-twentieth centurywhich emphasized the importance of multiple sedimentary cycles in theproduction of quartz-rich sandstones. In compositionally and texturallymature sandstones, the polycyclic selective removal of less stable mineralsby processes of abrasion was commonly thought to be the ultimate causeof maturation. However, during the later part of the twentieth centurydetailed investigations illustrated that quartz arenites could be theproduct of single sedimentary cycles and/or postdepositional diagenesis.

Today, we know that there are numerous, potentially interlinked,factors which may contribute to the formation of quartz-rich sandstones,including source-area characteristics, chemical weathering, climate,topography and orogenesis, multicycling, sediment transport and storagepathways, and diagenesis and/or leaching (e.g., Akhtar and Ahmad 1991;Avigad et al. 2005; Dott 2003; Folk 1974; Johnsson 1990; Johnsson et al.

Setting

Typ

e(s)

Id.Code

Mem

ber,Form

ation

Age

LocationInform

ation

Description

Typ

eSection

Latitude,

Longitude

Outcrop

Thin

sectionofthe

quartz-richsandstones

Environmentof

Deposition

Miocene

Kendeng

Depocentre

3vii

Lutut

Early-M

iddle

MioceneN5-N7,

NN4,

19.5

61.5Ma

(zirconU-Pb

SHRIM

P)

KaliLututriver

section,

Sem

aran

g,Central

Java

7.12

241S

,11

0.15

894E

Yellow

quartz

and

bioclasticrich

sandstones

overlying

basal

chan

nelized

conglomerates.

San

dstones

are

overlainbylaminated

siltstones,mudstones,

andvo

lcan

iclastic

rocks.

Quartz

isdominated

by

metam

orphic

grainswith

sign

ifican

tproportionsof

volcan

ican

drecycled

sedim

entary

quartz.The

sandstones

contain

abundan

treworked

Eocenean

dOligo

cene

bioclasts.

Unstab

le(slumping

anddew

atering)

shallow

marine

slopenearto

afluvial

source.

Miocene

ShelfEdg

e3

viii

Ngray

ong

Middle

Miocene

(N8-9)

Lodan

Quarry,

Rem

ban

gHills,

EastJava

6.83

4272

S,

111.67

713E

Brilliantwhiteto

yellow,ap

parently

mature,cleanquartz-

rich

sandstones,

interbedded

with

quartz-richsiltstones,

clay

stones,coal,and

thin

shallow

marine

limestones.

Quartz

arenites

dominated

bymetam

orphic

quartz

withasign

ifican

tproportionofvo

lcan

icquartz:meltinclusions,

shardshap

e.Abundan

telonga

teeuhedralzircons.

Terrestrial

tomargin

marinepossibly

atarivermouth.

TABLE1.—

Con

tinu

ed.

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 337J S R

1988; Johnsson et al. 1991; Suttner et al. 1981). The following sectionprovides an overview of some of the most important processes; the readeris referred to the references cited for more detailed discussion.

Chemical Weathering

Sediment maturity is mainly acquired through chemical weathering, aschemically unstable minerals are eliminated (e.g., Salano-Acosta andDutta 2005). Therefore, in most cases the daughter product of recycledsandstone should be mineralogically more mature than its parent sourcerock. In a few rare cases the daughter sediment may be mineralogicallyless mature owing to the breakdown (physical or chemical) of lithicfragments or large unstable grains (Friis 1978; Solano-Acosta and Dutta2005). There are a number of important controls on rates of chemicalweathering, such as residence time, climate, and presence and thickness ofa soil profile. It is generally accepted that tropical climatic settings havehigher rates of chemical disaggregation of source rocks and the resultantdaughter sediment than high-latitude settings.

Topographic Relief and Single-Cycle Sediments

Johnsson et al. (1991) describe the impact that topographic relief canhave on the sediment produced by chemical weathering based on a casestudy from the Orinoco River drainage basin. In this example, sedimentsproduced within areas of high, often steep, relief, such as orogenicterranes or parts of the elevated shield, are not as compositionally matureas sediments produced in areas of low, flat-lying topography. Johnsson etal. (1991) explain this in terms of sediment residence time andtransportation efficiency. In the areas of high relief, sediment transpor-

tation processes can remove weathered material as rapidly as it isproduced. In these areas the soil profile is commonly very thin or absent.The sediments produced closely resemble the parent rock, because thechemical weathering process is incomplete and the unstable minerals andlithics remain. In contrast, in the low-relief areas and flat uplanderosional surfaces of the Guyana Shield the weathering process is moreprolonged. Here the weathering rate exceeds the rate at which sediment isremoved and a thick soil profile is common. As a consequence, there is along soil residence time, there is destruction of unstable grains, and theresulting sediments are rich in quartz and have little resemblance to theirparent rocks.

Diagenesis

Diagenesis and deep leaching can lead to development of secondaryporosity and contribute to quartz enrichment. Franca et al. (2003) suggesta number of factors are required to produce secondary porosity. Theseinclude uplift of at least one basin margin to produce a hydraulic head,down-dip fluid escape route to remove water, abundant rainfall torecharge meteoric waters, and long-term tectonic stability. Dissolution byacid formation waters is also known to lead to enrichment of quartzwithin sandstones by leaching. In the Middle Jurassic Brent Sandstones ofnorthwest Europe nearly all the feldspar was dissolved from thesandstone without leaving a trace (Harris 1989).

Volcanic Processes

Volcanic processes are often overlooked in discussion of quartz-richsandstones. In acid arc settings, crystal-rich deposits are common because

FIG. 1.—Simplified geological map of East Java, showing the main geological subdivisions and stratigraphic units (adapted from Smyth 2005). Inset shows currentplate-tectonic setting and location of Sundaland.

338 H.R. SMYTH ET AL. J S R

FIG. 2.—Stratigraphy of East Java showing the distribution of quartz-rich sandstones (adapted from Smyth 2005); inset map shows the geographic locations. Codes (ito viii) are explained in Table 2.

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 339J S R

of the character of the erupted material and the sorting efficiency of theeruption mechanism. Quartz-rich ash deposits formed by Plinianeruptions may be abundant even at considerable distances from theerupting volcano (e.g., Rose and Chesner 1987; Carey and Sigurdsson2000). They are unstable and rapidly eroded (unwelded loose depositswhich commonly lack vegetation cover), and the non-quartzose materialis rapidly destroyed by weathering and transport. Thus, volcanism canlead to the formation of quartz-rich sandstones during a single cycle byproviding a volumetrically significant source in a very short time.

It is clear that a number of processes could have contributed to theformation of the tropical quartz-rich sandstones of East Java. However,characteristics of the grains, such as shape, internal structure, andalteration would be expected to be distinctive and aid discriminationbetween them. In order to assess the sources and processes that formedthe sandstones it is therefore important to identify the types of quartzthey contain. The following section summarizes the basis for distinguish-ing different quartz types.

VARITIES OF QUARTZ

There are numerous varieties of quartz. Those discussed here includeigneous (separated into plutonic, hypabyssal, and volcanic), metamor-phic, hydrothermal vein, chert, and recycled sedimentary (Fig. 3). Earlywork by Folk (1956, 1974), Basu et al. (1975), and Donaldson andHenderson (1988) showed that each of these quartz varieties hasdistinctive characteristics (Table 2) that allow them to be distinguishedoptically and using SEM-CL (scanning electron microscope cathodolu-minescence). In more recent years comprehensive discussions of quartzCL characteristics have been published which adds greatly to the datacollected by optical examination alone (e.g., Demars et al. 1996;Seyedolali et al. 1997; Hickel et al. 2000; Bernet and Bassett 2005; andreferences therein).

Grain Shapes, Types, Crystal Units, and Undulosity

The shape of detrital quartz grains ranges from euhedral forms withclear, well-defined crystal faces to anhedral grains without crystal faces.The grain shape may be changed during burial diagenesis and pressuresolution, producing concave, convex, and sutured contacts, and quartzovergrowths. The grains can be monocrystalline, polycrystalline orcomposite. The number of crystal units (Basu et al. 1975) that make upa polycrystalline grain depends on its origin. Grains from low-grademetamorphic rocks (Fig. 4) have the most numerous crystal units, high-grade metamorphic rocks have fewer, and plutonic rocks generally haveonly two or three crystal units per grain (Basu et al. 1975). Polycrystallinegrains from a metamorphic source are generally composed of small,similar sized crystal units which often show similar orientations.Composite grains, which can form in sedimentary, volcanic, plutonic,and metamorphic settings, usually have more random crystal orientationsand are variable in size. Suturing can result in composite grains, and insome examples other minerals such as feldspar are present. Distinctionbetween composite and polycrystalline grains can therefore be made onthe basis of composition, contacts, orientation of the crystal units withinthe grains, and extinction angles. Undulose extinction is caused byimperfections in the crystal lattice resulting from strain or impurities. Theangle of undulose extinction (Basu et al. 1975) is typically less than 5u inplutonic quartz but increases to over 5u in metamorphic rocks (Fig. 4).

Igneous Quartz

There are two polymorphs of quartz (Deer et al. 1998) but only one, aor low-temperature quartz, with trigonal symmetry, is stable at surfacetemperatures (, 573uC). At temperatures greater than 573uC, the stableform is the high-temperature b quartz polymorph, which has hexagonal

symmetry (Deer et al. 1998). When b quartz cools it inverts to a quartz,and when cooling occurs rapidly, as in volcanic settings, the quartz mayretain the hexagonal form of the high-temperature polymorph. Theresulting grain shape is often bipyramidal, but some additional trigonalfaces may be added during cooling. Conversely, when cooling occursslowly, as in plutonic settings, the grains have the trigonal form of aquartz.

Plutonic Quartz.—Plutonic quartz is milky white to translucent in handspecimen, and can have an anhedral (Fig. 3A) or euhedral shape withtrigonal form. Plutonic grains often have straighter grain boundaries thanthose of metamorphic quartz, and the crystals may, rarely, be zoned whenobserved using cathodoluminescence, recording the history of growth orcrystallization from the melt. Polycrystalline grains are uncommon, andthose that do exist generally have fewer than three crystal units per grain(Basu et al. 1975). Healed fractures filled with silica are common inplutonic quartz (Seyedolali et al. 1997; Bernet and Bassett 2005) and maylink along their length to open fractures. These fractures are uncommonin metamorphic quartz and are very rare in volcanic quartz (Seyedolali etal. 1997). In panchromatic images plutonic quartz appears light gray, andits microcracks and healed fractures are easily distinguished (Bernet andBassett 2005). In many granitic rocks quartz is a late-stage mineral whichinfills the gaps between other minerals, and therefore is irregular in shape.The grains eroded from such rocks have an anhedral shape and may becomposite. Fluid inclusions are especially common in quartz fromgranitic rocks (Shepherd et al. 1985) forming thin strings throughout thegrains (Fig. 3A). The simultaneous growth of two minerals such as quartzand alkali feldspar producing a granophyric texture is a feature ofplutonic origin. Such textures may be found in composite grains insedimentary rocks but often cannot be recognized unless the section isstained for feldspar.

Hypabyssal.—Quartz crystallized in high-level intrusions may havesome characteristics similar to both plutonic and volcanic quartz. If theintrusion is very close to the surface, the grains may form large euhedralphenocrysts (Fig. 3B), and the hexagonal shape of b quartz may bepreserved but is likely to be accompanied by additional trigonal faces.More commonly the grains have a trigonal form. The grains are typicallyclear and bright in thin section and are free from fluid inclusions, andcommonly show signs of melt reaction (see below).

Volcanic.—Volcanic quartz (Fig. 3C) can be very distinctive when freshbecause it is commonly monocrystalline, and clear and bright in thinsection (Leeder 1982). In some cases the hexagonal form of b quartz isretained after inversion to a quartz and the grains may have abipyramidal form. Composite grains may occur and owing to theirmicrocrystalline nature can easily be confused with authigenic chert (seebelow). The growth of microcrystalline or fibrous quartzo-feldspathicgrains from a crystalline core, known as ocelli or an ocellar texture, is alsoa common feature of volcanic quartz (Fig. 3C.7). Volcanic quartz grainshapes include euhedral, rounded, or embayed forms, and shardsmay also occur with a distinct cuspate shape, formed by breakup of apumice bubble wall or shattering of a fractured crystal (Fig. 3C.8).Rapid cooling usually results in clear, non-undulose quartz, butexplosive eruption may lead to strain, causing lattice imperfections andundulose extinction. Volcanic quartz may have a well-developedzonation, visible using cathodoluminescence (Fig. 3C.6), and curvedfracture patterns, which have the appearance of a cracked-tile, are also acommon feature.Melt reaction features, including rounding, and formation of embay-

ments (Fig. 3C.5) and skeletal grains, are common in both hypabyssaland volcanic quartz. Rounding of crystal edges is due to resorption(Donaldson and Henderson 1988), which is a consequence of a lack of

340 H.R. SMYTH ET AL. J S R

equilibrium between the crystal and the melt (McPhie et al. 1993). As aquartz phenocryst bearing magma rises, SiO2 solubility in the meltincreases as pressure decreases and quartz that was previously inequilibrium with the melt is partially resorbed (McPhie et al. 1993).Embayments are due to unstable growth, dissolution in the melt, or ‘‘gasbubble drilling,’’ which is a reaction with the melt as gas bubblesapproach the crystal (Donaldson and Henderson 1988). Embayments aredistinguished by their rounded shape from etching caused by corrosiveformation waters or pitting because of transportation. Volcanic quartzgrains may also develop a skeletal shape if the crystal edges form first,generating a framework or skeleton outline (Spry 1969); the faces betweenthe edges form more slowly and in some cases are infilled by otherminerals or can remain as voids.

Melt inclusions are diagnostic of a volcanic origin and can readily bedistinguished from fluid inclusions (Fig. 3C.9). Fluid inclusions arecommonly small, , 5 mm (Shepherd et al. 1985), and form stringsparallel to fractures within the grains. Melt inclusions, however, form atthe time of mineral growth, can be much larger, up to 200 mm (Shepherdet al. 1985), and may be arranged along growing faces so that they areparallel to zonation in the crystal.

Metamorphic Quartz

Quartz of metamorphic origin (Fig. 3D) has several diagnosticcharacteristics including undulose extinction angles, healed fractures,indistinct mottling under cathodoluminescence, strings of fluid inclusions(often needle-like), and anhedral, sutured or irregular grain shapes andcontacts (Basu et al. 1975; Donaldson and Henderson 1988; Demars et al.1996; Peppard et al. 2001; Boggs et al. 2002). Metamorphic quartz is morecommonly polycrystalline than plutonic quartz and the straining of thelattice during metamorphism and deformation results in higher angles ofundulose extinction (. 5u) compared to plutonic quartz (Fig. 3D).Impurities and abundant fluid inclusions may cause metamorphic quartzto be milky white. Mortar texture, in which large strained quartz grainsare surrounded by finely crystalline new quartz (Spry 1969), is commonlyobserved in quartz from metamorphic rocks. SEM-CL images ofmetamorphic grains are commonly mottled or patchy (Table 2). Shearingduring metamorphism results in the alignment of crystal units and thedevelopment of foliation in polycrystalline or composite quartz grains.Pressure fringes, commonly composed of fibrous quartz, calcite, chlorite,or muscovite, are abundant in low-grade metamorphic rocks, and theirshape is related to the original crystal around which they formed. Fringesmay resemble the ocellar texture common in volcanic rocks but are rarelypreserved after erosion and transportation (Spry 1969).

Hydrothermal Vein Quartz

Vein quartz commonly has a milky white color due to fluid inclusions(e.g., Tucker 2001). The crystal faces may be clear but can bedistinguished from volcanic quartz by the abundance of fluid inclusions

and lack of concentric zoning. The crystals are in many cases elongateand columnar, in as much as they grow from a fixed point, often afracture wall, into an open space or vug, a texture known as combstructure (Spry 1969). Crystal terminations at either end of the columnare different, and if there is limited space within the fracture, the quartzmay form equant crystals.

Chert

Chert is cryptocrystalline or microcrystalline quartz formed either bysiliceous organisms such as radiolaria, diatoms, and sponges, or bysecondary replacement, usually of limestones (Adams et al. 1984). Inradiolarian and other biogenic cherts spherical and elongate skeletons cansometimes be distinguished, which allows easy identification (Fig. 3E).However, when the chert is fine grained or cryptocrystalline and does notcontain any visible biogenic structures, it may be difficult to determine theoriginal nature of the grain. When the chert forms as secondaryreplacement, it commonly has a radial fibrous growth texture,‘‘chalcedonic quartz’’ (Adams et al. 1984), which may be very similar tospherulites which form in devitrified siliceous volcanic glass (Fig. 3E, F).The spherulites are ‘‘radiating arrays of crystal fibers’’ (McPhie et al.1993), which consist of feldspar and quartz, and the staining of thinsections for feldspar and examination using SEM can assist with thedistinction of from other varieties of quartz.

Recycled Sedimentary Quartz

Detrital quartz that has been through multiple cycles of erosion iscommonly rounded and pitted, and may have brown corrosion rims(Fig. 3H). The grains usually lack the crystal faces common in hypabyssaland volcanic quartz. They may have quartz overgrowths, or a fringe ofother minerals such as calcite. Fractures which formed during transpor-tation are likely to be angular or irregular, and are open, in contrast to thecurved fractures which occur in volcanic quartz or the healed fractures inplutonic quartz. Diagenetic quartz formed as overgrowths on grains maycontain fluid inclusions which are very small, , 5 mm (Shepherd et al.1985), and are readily distinguishable from the much larger meltinclusions found within volcanic quartz.

CHARACTER OF THE QUARTZ-RICH SANDSTONES OF EAST JAVA

The Eocene and Miocene quartz-rich sandstones from East Java in thisstudy plot within the ‘‘recycled orogen’’ field on a standard Dickinsonplot. They have been reexamined and subdivided on the basis of the typesof quartz that they contain (Tables 1, 3). Fine to coarse sandstones wereselected for point counting using the Gazzi-Dickinson method (Gazzi1966; Dickinson 1970; Ingersoll et al. 1984), and the quartz types wereidentified using the criteria discussed above. A minimum of 300 grainswere counted from each sample. Where the quartz variety could not bedetermined the grains were assigned to an ‘‘unknown’’ category (up to 2%

R

FIG. 3.—Characteristics of quartz types commonly found in sedimentary rocks. Examples selected from Sumatra and Java, Indonesia, Tasmania, and Luzon. The scalebar is 1 mm unless stated otherwise. A) Plutonic: 1. Anhedral grain with melt inclusion, strings of fluid inclusions, and slightly undulose extinction. 2. Large late-stagefilling grain with healed fractures. 3. The individual crystals within this composite grain have variable size, orientation, and extinction. B) Hypabyssal: euhedral quartzphenocrysts from a high level intrusion. C) Volcanic: 1. Top left and right sketches of bipyramidal quartz. Lower sketch, bipyramidal grain with additional trigonal facesformed during cooling. 2. Photograph of a bipyramidal quartz. 3. SEM image of bipyramidal quartz. 4. Bipyramidal grains in a crystal-rich dacitic ash. 5. SEM image ofembayed quartz. 6. SEM-CL image showing concentric zoning within a large quartz phenocryst. 7. Ocelli texture and rounded fractures. 8. SEM image of a shard ofquartz. 9. Melt inclusions in quartz. D) Metamorphic and sheared: 1. Polycrystalline grains with numerous crystal units, and monocrystalline grains with unduloseextinction and strings of fluid inclusions. 2. Sheared quartz. E) Chert: 1. Radiolarian chert. 2. Authigenic chert with radial fibrous growth pattern. F) Volcanic sphericules(McPhie et al. 1993) formed in devitrified siliceous volcanic glass. G) Volcanic quartz aggregates easily confused with chert in thin section. The grains in thephotomicrograph of the left appear chert-like, but examination under SEM on the right shows the grains are aggregates of bipyramidal quartz grains. H) Recycledsedimentary: rounded grains, with etched surfaces and alteration halos. The grains contain numerous strings of fluid inclusions.

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 341J S R

342 H.R. SMYTH ET AL. J S R

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 343J S R

TABLE2.—

Typ

esof

quartz

foun

din

sedimentary

rocksan

dtheirdistinguishing

characteristics(S

pry19

69;Basuet

al.19

75;Leeder19

82;Ada

mset

al.19

84;Roedder

1984

;Sheph

erdet

al.19

85;

Donaldson

andHenderson

1988

;McP

hieet

al.19

93;Dem

arset

al.19

96;Seyedolaliet

al.19

97;Peppa

rdet

al.20

01;Boggs

etal.20

02;Bernetan

dBassett20

05).

Quartz

type

Grains

Colour

Polycrystalline

Undulosity

Inclusions

Zoning

Fracture

SEM-C

Lcolours

SEM-C

Ltextures

(andpan

chromatic

colors)

Sym

metry

Other

common

textures

Plutonic

Anhedral(space

filling)

+euhedral.

Can

bemono-,

polycrystalline,

or

composite.Grain

boundariesgenerally

straighterthan

inmetam

orphic

rocks

Milkywhiteto

tran

slucent

,3crystalunits

per

grain

Undulosity

isweak,

,5u

Fluid

inclusions

common

Well

developed

Healed

fractures

Blue-red,

may

overlap

with

volcan

ic

Ran

domly

oriented

microcracksor

healedcracks

areobserved

inalltypes

of

plutonic

quartz.

Lightgray

CL.

Rarezoning.

Trigo

nal

Mineral

inclusions,

meltreaction

textures,

gran

ophyric

growth

with

feldspar.

Plutonic

(Hyp

abyssal)

Euhedral,

monocrystallinegrainsClear

Not

common

weak,

,5u

tononundulose

May

be

free

from

inclusions

Common

Healed

fractures

Blue

Trigo

nal

(potential

preservation

ofhexag

onal

symmetry)

Meltreaction,will

dependupondepth

andcooling

history.

Volcanic

Euhedral,

monocrystalline,

composite

and

aggregategrainsalso

present,as

areshards

withadistinctive

cuspateshap

e.

Clear

Microcrystalline

aggregates

may

appearto

be

polycrystalline

Commonly

nonundulose

and

clear.Grains

may

hav

estrong

undulosity

incase

oflattice

imperfection.

Melt

inclusions

are

diagn

ostic

Present

Curved

lead

ingto

cracked-

tile

pattern

Blue

Concentric

zoningisvery

commonin

volcan

icquartz.

Homogeneous

CLisalso

commonly

obseverd

invo

lcan

icquartz.

CLligh

tgray

toblack.

Hexag

onal

withpossible

additionof

trigonal

facesduring

cooling

Skeletal

grains,melt

reactionslead

ingto

roundingofcrystal

faces,melt

embay

ments,

ocellulartexture

andbipyram

idal

grainshap

e.

Metam

orph

icAnhedral,suturedor

irregu

lar.

Milkywhiteto

tran

slucent

.3crystalunits

per

grain.Most

abundan

tin

low-

grad

emetam

orphic

rocks

Undulosity

is.

5uFluid

inclusions

common,

often

needle-

like.

Absent

Angu

lar

healedan

dopen

fractures

Blue-brown,

may

overlap

with

plutonic

Inhomogeneous

patchyor

mottledCL

____

Mortar

texture,

pressure

fringes,

foliationsin

polycrystallinean

dcomposite

grains.

Hyd

rothermal

Euhedral

Milkywhiteto

tran

slucent

___

Undulose

Fluid

inclusions

common

Not

concentric

May

be

present

Variable

insomecase

green

Trigo

nal

Grainsarecommonly

elonga

te,comb

texture.

Chert

Commonly

rounded

or

anhedralin

form

.The

quartz

canbe

cryp

tocrystalline,

microcrystalline,

or

fibrous

Variable

___

___

___

___

___

May

benon-

luminescentBlack

CLnot

easily

identified

usingSEM-C

L

___

Ifradiolarian

,spherical

and

elonga

teskeleton

may

bevisible.

Rad

ialfibrous

growth.May

be

confusedwith

volcan

icsphericulesor

microcrystalline

aggregates

of

bipyram

idal

quartz.

344 H.R. SMYTH ET AL. J S R

of grains counted). In addition to thin-section analyses, SEM examina-tion was used was used to identify unknown minerals and grain surfacetextures. Additional analysis of polished thin sections by panchromaticSEM-CL and back-scatter imaging was also undertaken which aided theidentification of grains by optical techniques.

There are three types of sandstone:

N Type 1: Quartz and other fractions (minerals, lithics, and matrix clays)are almost entirely metamorphic.

N Type 2: Quartz and other fractions are entirely volcanic.

N Type 3: Quartz and other fractions have a mixed provenance. Thesesandstones are essentially a mix of Types 1 and 2, with the addition ofvarying volumes of recycled sedimentary and plutonic quartz. Aproportion of the plutonic quartz is considered to be hypabyssal.

The principal features of the Eocene andMiocene quartz-rich sandstonesare listed in Table 1. They are subdivided into four groups by area and age,and further subdivided into eight categories corresponding to specificlocations identified by roman numerals in the text (i to viii).

Type 1 Metamorphic Quartz-Rich Sedimentary Rocks

Pre-middle Eocene sandstones (i, ii, iv) are the oldest sedimentsexposed on land in East Java. They are restricted to the western part ofthe study area, where they rest directly on the basement (Table 1, Figs. 1,2, 5). They are terrestrial deposits (Smyth 2005), but they lackpalynomorphs or any other fossils and so cannot be directly dated.However, they are overlain by a succession of well-dated middle Eocenestrata (Lelono 2000). The pre-middle Eocene sandstones are dominatedby material of metamorphic origin, lack fresh intermediate to acidicvolcanic material, and are the only deposits identified in East Java thatcontain no evidence of contemporaneous volcanic activity.

In the Type 1 sandstones quartz constitutes 44 to 87% of the total QFLcount. These rocks are composed almost entirely of grains of vein quartz(Fig. 5) and polycrystalline quartz grains with numerous crystal units,suggesting a low-grade metamorphic origin. The remaining quartz isdominated by chert. Weathered laths of plagioclase feldspar and a fewgrains of very altered microcline feldspar form between 1 and 8% of thegrains counted. The sandstones and conglomerates also contain lithicclasts of chert, basalt, quartz–mica schist, and phyllite, and fragments ofquartzose vein material, all of which are lithologies that are typical ofrocks found in basement exposures in East and Central Java (Wakita andMunasri 1994; Miyazaki et al. 1998). In addition, the clay mineralogy(serpentinite, illite, and chlorite) of cements, and clay interbeds alsosuggests erosion of such basement rocks (Smyth 2005).

Type 2 Volcanic Quartz-Rich Sandstones

The Type 2 sandstones containing only volcanic material are restrictedto lower to middle Miocene strata of the Southern Mountains. Thesequartz-rich deposits are found in close proximity to the acid volcaniccenters of the Eocene to lower Miocene Southern Mountains Arc. Thebest-exposed example is the Jaten Formation (vi), located near Pacitan(Table 1, Figs. 1, 2, 6). The presence of lignite, channel structures, andabundant rootlets, and the lack of marine fauna, indicate a terrestrialdepositional setting, probably on the flanks of a volcanic center.

In the Type 2 sandstones quartz constitutes 82.5 to 95% of the total QFLcount (Table 3). The sandstones contain concentrations of coarse,bipyramidal quartz grains measuring up to 10 mm (Fig. 6). Other grainshave distinctive volcanic features including perfect crystal faces, large meltembayments, skeletal grains, negative crystals, rounded fractures, CLzonation, and melt inclusions. The sandstones contain volcanic lithicfragments and laths of plagioclase feldspar which have volcanic texturessuch as melt inclusions and embayments. The heavy-mineral fraction of theQ

uartz

type

Grains

Colour

Polycrystalline

Undulosity

Inclusions

Zoning

Fracture

SEM-C

Lcolours

SEM-C

Ltextures

(andpan

chromatic

colors)

Sym

metry

Other

common

textures

Recycled

sedimentary

Rounded,pitted

overgrowthsmay

be

observed.Lackof

preserved

crystalfaces.

Browncorrosion

rim

Dependson

original

source

Undulose

with

variab

lean

gles

dependingon

history

Strings

of

very

small

fluid

inclusions

,5

mmcommon

Lost

dueto

diagenetic

overprint

Commonly

seen

and

are

angu

laror

irregu

lar

open

fractures

Variable,can

benon-

luminescent

ifdiagenetic

Grain

shattering

___

Etching

+surface

alterationisa

commonfeature

of

recycled

grains.Pits

caneasily

be

distingu

ished

from

meltem

bay

ments.

TABLE2.—

Con

tinu

ed.

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 345J S R

Jaten Formation sandstones contains abundant fresh zircon grains whichare elongate and have length-to-breadth ratios greater than 5, a featurewhich is common in grains of pyroclastic origin (Mange andMaurer 1992).These sandstones are interpreted to have formed from the products of aPlinian eruption of crystal-rich magma that deposited ash, which wassorted during flow or fall, or subsequently reworked by epiclastic processes.

Several red siliceous beds crop out to the north of Pacitan in theWatupatok Formation. Previously these red beds were interpreted asdeep-water sediments because they resemble cherts. In thin section somegrains appear chert-like but do not contain radiolaria. SEM examinationshows that the grains are composed of microcrystals of bipyramidalvolcanic quartz held together with strings of silica (Fig. 3G.).

Type 3 Mixed-Provenance Quartz-Rich Sandstones

Middle Eocene and Miocene sandstones of mixed metamorphic,volcanic, recycled sedimentary, and plutonic provenance are distributedwidely in East Java.

Middle Eocene Quartz-Rich Sandstones of the Southern Mountains.—Directly above the oldest sedimentary rocks that include the Type 1sandstones, there is a thick unit, which may exceed 500 m in thickness, ofquartz-rich sandstones. These form the lower part of a well-datedsequence (Lelono 2000) of middle Eocene to lower Oligocene rocks (iii)known as the Nanggulan Formation (Table 1, Figs. 1, 2, 7). At the basethe quartz-rich sandstones are fluvial to shallow marine deposits, andthey pass upwards into a series of arkosic arenites which form the upperpart of the formation and are fully marine turbidites (Lelono 2000; Smyth2005).

The quartz-rich sandstones in the lower part of the NanggulanFormation are moderately sorted sublitharenites (Table 3) and have amixed provenance with components of metamorphic, volcanic, plutonic,and detrital quartz. In these Type 3 sandstones quartz constitutes 54 to81% of the total QFL count. A significant proportion (up to 47%) of thequartz is monocrystalline metamorphic grains, which are subrounded,with abundant strings of fluid inclusions, and undulose extinction. Quartz

grains with a clear volcanic origin are also present, and their abundanceincreases up section from 14 to 35%. There are also some volcanic lithicgrains that contain quartz. CL imaging confirms that many of the quartzgrains are fragments of much larger zoned volcanic grains (Fig. 7G). Inaddition to these quartz types plutonic and detrital grains with quartzovergrowths have been identified using SEM-CL images, but these arepresent only in the lowermost parts of the formation. The sandstones alsocontain feldspar, predominantly fresh plagioclase with a small number ofaltered microcline grains. Schists make up the majority of the lithicgrains; they are commonly small (, 0.5 mm) and well rounded.

Zircons are the most common heavy mineral. The zircon populationincludes fresh euhedral grains, elongated prisms, and broken prisms withsharp terminations. SHRIMP U-Pb dating of grains yielded ages of41.7 6 1 Ma and 42 6 0.9 Ma (P.J. Hamilton, personal communica-tion 2005), similar to the middle Eocene (49 to 37 Ma) biostratigraphicage for the formation. The remaining zircon grains are anhedral androunded with some evidence of zoning; these grains yielded much olderU-Pb SHRIMP ages. This indicates reworking of some older igneousmaterial but shows that at least some of the volcanic material was eruptedcontemporaneously.

The identification of quartz types and the other provenance techniquesindicate that the middle Eocene quartz-rich sandstones of the SouthernMountains contain predominantly two types of material: an oldermetamorphic component and a contemporaneous volcanic component.There is a clear increase up section in the percentage of volcanic quartz asmetamorphic quartz decreases (Table 3, Fig. 8), indicating a change inthe sediment supply. In addition there is igneous and recycledsedimentary material (average 31%).

Miocene Quartz-Rich Sandstones of the Kendeng Basin.—The Miocenequartz-rich sandstones of the Lutut Beds (vii), Semarang (Fig. 1), are notshown on the geological map for the area (Thaden et al. 1975) becausethey are exposed only in small outcrops. They are interpreted to havebeen deposited on the southern margin of the Kendeng Basin, and havesubsequently been deformed and moved northwards to their present-dayposition by thrusting (Smyth 2005).

FIG. 4.—Methods of distinguishing plutonic and metamorphic quartz. A) Classification of source by examining polycrystallinity and undulosity (redrawn from Basu etal. 1975). B) Distribution of true angles of undulosity in detrital quartz from plutonic and low-rank metamorphic sources (redrawn from Basu et al. 1975).

346 H.R. SMYTH ET AL. J S R

In these Type 3 sandstones quartz constitutes 65% of the total QFLcount. The quartz types within the sandstones include metamorphic,volcanic, recycled sedimentary, and plutonic (Table 3). The metamorphicquartz (55%) has undulose extinction, and both polycrystalline andmonocrystalline types have been identified. The volcanic quartz (15%) iseuhedral, contains melt inclusions, and appears clear and bright. Thelithic fragments are diverse and include metamorphic, sedimentary,

bioclastic, and abundant volcanic rocks (Fig. 7). The bioclastic lithicclasts contain fragments of reworked Eocene and Oligocene fossils.

These sandstones contain three components: recycled Cenozoicsedimentary rocks, fresh contemporaneous acid volcanic rocks, andmetamorphic rocks. These are the only quartz-rich sandstones on land inEast Java which contain clear evidence of reworking of older Cenozoicsedimentary sequences (Smyth 2005).

TABLE 3.—Summary of the average percentages of each quartz type found within the quartz-rich sandstones of East Java.

ID I I I I II III III III IVSample Jhs2KK2 Jhs2KW1 Jhs2KW2 Jhs2KK38 Jhs2Sermo1 Jhs2NKS10 Jhs2NKS17 Jhs2NKS26 Jhs2JC5

QFL Q (% of QFL total) 71.0 77.5 44.1 68.9 87.4 81.1 56.5 54 78.5F (% of QFL total) 4.1 6.9 39.9 7.6 3.8 8.7 19.7 19 0.5L (% of QFL total) 24.9 15.6 16.0 23.5 8.8 10.9 23.8 23 21

Quartz counts QMNU nof 5 2 2 26 12 31 57 39 1QMU nof 0 0 0 0 1 0 2 0 0QM , 5% 6 1 0 13 15 11 39 56 1QM . 5% 101 93 110 7 114 46 111 42 37PC , 4 5 5 4 6 10 7 11 7 4PC . 4 57 59 92 1 54 96 22 13 122Chert 49 86 73 2 4 60 16 12 65Volcanic* 3 3 0 59 0 11 14 35 0Detrital 3 11 3 0 7 13 5 35 10VolLithic 0 0 1 34 0 2 1 31 0Metalithic 70 9 7 2 83 6 20 19 19SedLithic 1 31 8 1 0 17 2 11 41Unknown** 0 0 0 0 0 0 0 0 0Number 300 300 300 151 300 300 300 300 300

Quartz typesfrom optical,SEM, andSEM-CLimaging

Metamorphic 76.0 53.7 69.7 6.6 84.0 49.3 51.7 24.7 59.3Volcanic 2.7 1.7 1.0 78.8 4.0 14.7 24.0 35.0 0.3Recycled sedimentary 17.7 42.7 28.0 2.0 3.7 30.0 7.7 19.3 38.7Plutonic 3.7 2.0 1.3 12.6 8.3 6.0 16.7 21.0 1.7Unknown 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Quartzcategorieschosen (%)

Metamorphic 76.0 53.7 69.7 6.6 84.0 49.3 51.7 24.7 59.3Volcanic 2.7 1.7 1.0 78.8 4.0 14.7 24.0 35.0 0.3Recycled sedimentary andplutonic

21.3 44.7 29.3 14.6 12.0 36.0 24.3 40.3 40.3

ID IV V VI VI VII VIII VIII VIII VIIISample Jhs2Pendul1 Jhs2Kresek Jhs2Pac17A Jhs2Pac21 Jhs2Lutut11 Jhs1-012 Jhs1-006 Jhs1-008 Jhs2Ngr5

QFL Q (% of QFL total) 81.1 40.4 95 82.5 64.6 83.2 81.7 96 95.5F (% of QFL total) 0.5 53.4 0 10.5 0 13.1 10.1 1 2.2L (% of QFL total) 18.4 5.6 5 7 35.4 3.7 8.2 2 2.3

Quartz countsoptical (300were possible)

QMNU nof 16 32 0 2 22 64 19 53 29QMU nof 0 97 0 0 0 3 1 1 0QM , 5% 23 0 0 0 10 61 14 20 35QM . 5% 79 0 0 0 99 74 59 77 42PC , 4 19 2 0 0 16 12 34 20 14PC . 4 69 1 20 7 47 10 82 60 81Chert 10 0 0 0 26 2 9 9 9Volcanic* 1 162 214 219 13 16 22 9 12Detrital 6 0 0 0 9 17 37 33 32VolLithic 3 1 66 69 10 0 0 0 0Metalithic 72 0 0 0 20 4 16 15 30SedLithic 1 0 0 0 28 1 7 3 16Unknown** 1 5 0 0 0 0 0 0 0

Quartz typesfrom optical,SEM, andSEM-CLimaging

Metamorphic 73.3 32.7 6.7 2.4 55.3 34.5 52.7 51.0 51.0Volcanic 6.7 65.0 93.3 97.6 15.0 30.3 13.7 20.7 13.7Recycled sedimentary 5.7 0.0 0.0 0.0 21.0 7.6 17.7 15.0 19.0Plutonic 14.0 0.7 0.0 0.0 8.7 27.7 16.0 13.3 16.3Unknown 0.3 1.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Quartzcategorieschosen (%)

Metamorphic 73.6 33.2 6.7 2.4 55.3 34.5 52.7 51.0 51.0Volcanic 6.7 66.1 93.3 97.6 15.0 30.3 13.7 20.7 13.7Recycled sedimentary andplutonic

19.7 0.7 0.0 0.0 29.7 35.2 33.7 28.3 35.3

Q (Quartz), F (feldspar), L (lithics), QMNU (quartz, monocrystalline, non-undulose extinction, no other features), QMU (quartz monocrystalline, unduloseextinction, no other features and angle of extinction cannot be measured), QM , 5% (quartz monocrystalline , 5% undulose extinction), QM . 5% (quartzmonocrystalline . 5% undulose extinction), QPC , 4 (quartz, polycrystalline , 4 crystal units), QPC . 4 (quartz, polycrystalline , 4 crystal units).

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 347J S R

348 H.R. SMYTH ET AL. J S R

Miocene Quartz-Rich Sandstones of North East Java.—The Miocenequartz-rich sandstones of the Ngrayong Formation (viii), Rembang(Fig. 1), are well exposed in quarry sections along the flanks of the LodanAnticline. The sandstones were deposited on the southern edge of theSunda Shelf and pass onto the northern slopes of the Kendeng Basin (e.g.,Ardhana 1993). The sandstones have been described as compositionallymature, clean, and quartz-rich and have previously been interpreted to becratonic in origin and derived from Sundaland (e.g., Ardhana 1993;Sharaf et al. 2005).

In these Type 3 sandstones quartz constitutes 82 to 96% of the totalQFL count. Lithic grains are rare in these sandstones and range from 2 to8% of the total QFL count. These sandstones are unconsolidated and lackclays, cement, and/or matrix. The sandstones are composed nearlyentirely of well-sorted, often angular quartz grains. Because thesesandstones are so rich in quartz they are commonly referred to as ‘‘glasssands,’’ and they are used extensively by the local ceramic industry.

Thin-section and SEM-CL examination shows that between 13 and30% of the quartz grains are very angular, are euhedral, and have meltinclusions and weak concentric zoning indicating a volcanic origin. Thepredominant metamorphic quartz (up to 55%) includes anhedral,polycrystalline and monocrystalline types with undulose extinction andstrings of fluid inclusions. In addition, quartz grains of plutonic origin (upto 28%) and recycled sedimentary quartz (up to 19%) are also present.Feldspar is uncommon in the Ngrayong Formation; plagioclase is absentbut a few grains of extremely weathered microcline feldspar have beenidentified. Zircon grains (Fig. 7) are abundant, and there are significantproportions of elongate prisms (43%), typical of pyroclastic zircons, orequant euhedral grains (25%), with the remaining 32% being moderatelyto well-rounded grains. The preservation of crystal faces in 68% of thezircons indicates that they were not significantly reworked.

The presence of fresh volcanic quartz, angular but well-sorted grains,and pristine volcanic zircons raises questions about previous interpreta-tions that these sandstones were derived solely from continental Sunda-land (e.g., Ardhana 1993; Sharaf et al. 2005).

SOURCES OF QUARTZ FOR EAST JAVA SANDSTONES

This study indicates that there were three main sources of quartz for theCenozoic quartz-rich sandstones of East Java: metamorphic rocks, acidvolcanic material, and recycled sedimentary rocks. There were alsocontributions from plutonic sources.

Metamorphic Source Rocks

The most likely source areas of metamorphic material are the (1) UpperCretaceous and older basement of East Java and (2) basement rocks onthe edge of Sundaland such as those exposed in southeast Kalimantanand along the Karimunjawa Arch (van Bemmelen 1949).

In East Java the basement rocks are observed only in small exposuresin the western part of the study area at Karangsambung and Jiwo(Fig. 1). At these locations the lithologies exposed include mica andquartz-mica schists, basalts, cherts, serpentinites, metasediments, and arange of high pressure low temperature metamorphic rocks includingeclogites, garnet amphibolites, and jadeite–quartz–glaucophane rocks(Wakita and Munasri 1994; Miyazaki et al. 1998). The rocks are thoughtto be the metamorphosed equivalents of ophiolites and arc rocks (Wakitaand Munasri 1994; Miyazaki et al. 1998) accreted during Cretaceous

subduction along the Sunda margin. A subduction setting is supported bythe occurrence of high pressure low temperature jadeite–quartz–glaucophane-bearing rocks within the Karangsambung Basement Com-plex (Miyazaki et al. 1998). These rocks were subsequently uplifted in theLate Cretaceous.

The Cretaceous basement and the Eocene sedimentary sequence areseparated by a regional angular unconformity. Based on the youngestages of the cherts in the Karangsambung Basement Complex (Wakita2000) and the ages of the oldest Eocene sedimentary rocks above theunconformity (Lelono 2000; Smyth 2005) the basement of East Java mayhave been uplifted and available for erosion for a period of around30 My. The almost complete absence of Paleocene sedimentary rocksfrom Java and Sumatra suggests that southern Sundaland was an elevatedregion following Late Cretaceous collision of a continental fragment withthe Sundaland margins (Smyth et al. 2008). This long period ofweathering and erosion could have resulted in enrichment of resistantminerals such as quartz and zircons.

The Karimunjawa Arch is an area within the shallow marine shelfnorth of Java (Fig. 8), which was elevated throughout most of theCenozoic and was therefore a potential source of sediment (e.g., Cater1981). The Karimunjawa Islands, which are found along the arch, arereported to contain exposures of pre-Cenozoic quartz sandstones andconglomerates, schist, and shale (van Bemmelen 1949) but the characterof the basement in this region is not well known. The location of theKarimunjawa Arch immediately to the northwest of East Java means thatmaterial could have been transported a relatively short distance across theshelf into the Kendeng Basin. To the east of this drainage divide lie theMeratus Mountains of southeast Kalimantan. The rocks exposed in theseareas are similar to those described from Java; they range in age from theMiddle Jurassic to the Late Cretaceous and comprise chert, siliceousshale, limestone, basalt, ultramafic rocks, schists, and sedimentaryvolcanic rocks (Wakita et al. 1998). However, it is not clear whetherthese rocks were available for erosion during the early Cenozoic.

Volcanic Source Rocks

The Southern Mountains Arc in East Java is the closest and most likelysource of acid volcanic material. The arc was active from the middleEocene until the early Miocene (42 to 18 Ma) and formed the southernmargin of the Kendeng Basin (Smyth 2005). Throughout the lateOligocene and early Miocene the volcanic activity in the SouthernMountains Arc was extensive, and produced by explosive Plinian-styleeruptions. The deposits range from andesite to rhyolite, with an averageSiO2 content of 67 wt% (Smyth 2005), and include thick mantling tuffs,crystal-rich tuffs, block and ash flows, pumice–lithic breccias, andesiticbreccias, and silicic lava domes and lava flows. In the SouthernMountains Arc, there is a record of a major eruption towards the endof the period of arc activity. Extensive deposits of this eruption arewidespread to the east of Yogyakarta; these were deposited in a shortperiod, possibly during one eruptive phase, between 21 and 19 Ma(Smyth 2005). Due to its position at the southern margin of the basin, thearc would have supplied volcanic debris, including volcanic quartz, to thebasin by pyroclastic flows, air fall from erupted ash columns and clouds,and epiclastic reworking. Ash-fall from large eruptions would have beendistributed over an extensive area including the shelf area to the north ofthe Kendeng Basin.

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FIG. 5.—Character of Type 1 quartz-rich sandstones. A) Photomicrograph of metamorphic grains from iv (Cakaran Member of the Wungkal–Gamping Formation)(scale: 1 mm). B) Photomicrograph showing metamorphic grains from basal i (Lukulo Member, Karangsambung Formation) (scale: 1 mm). C, D) BS (back scatter) andCL images of polycrystalline grains (Cakaran Member of the Wungkal–Gamping Formation) (scale: 200 mm). E) QFL plot showing the Type 1 sandstones. F) Triangularplot showing metamorphic, volcanic, and recycled sedimentary and plutonic quartz of the Type 1 sandstones.

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 349J S R

350 H.R. SMYTH ET AL. J S R

Volcanic processes are extremely efficient sorting mechanisms (e.g.,Walker 1972; Cas and Wright 1987). Crystal-rich, well-sorted depositscan be produced by single volcanic events, and by subsequent epiclasticprocesses. Concentration of crystals can occur in the magma chamber,during dome collapse, in the eruption column, or by reworking andweathering of tuffs, ash falls, and pyroclastic debris (Cas and Wright1987). Examples of quartz-rich and other crystal-rich volcanic depositsinclude sediments in the Lower Permian Collio Basin of the Italian Alps(Breitkreuz et al. 2001) and in the marine Paleozoic basins of the Sarrabusregion, SE Sardinia, Italy (Gimeno 1994).

Ash particles within an eruption cloud fall out at different distancesfrom the vent. This is dependent upon the terminal velocity of particles,which is determined by density and aerodynamic factors. Heavy lithicparticles reach their terminal velocity and fall out close to the vent, butcrystals and pumice are transported greater distances until they reachtheir terminal velocity and descend. This leads to ‘‘increased proportionsof crystals further from the vent’’ (Cas and Wright 1987). Thisphenomenon is noted in the air-fall deposits of the Fogo A, Azores,and the 1980 Mount St. Helens eruptions (Cas and Wright 1987; Fisherand Schmincke 1984; Fisher et al. 1998; Kaminski and Jaupart 1998;Veitch and Woods 2001).

Air-fall material is distributed over a wide area, it is commonly rapidlydeposited and rapidly reworked from land into sea, and it is very likely tobe mixed with sediment from other sources and redeposited. Aftereruptions in the tropics, lahars commonly carry large volumes of materialdownslope and mix ash and crystals with preexisting sediments. Due topost-eruptive reworking, mixing, and transportation, the paleocurrentindicators in sedimentary rocks in which this material is finally depositedmay not necessarily provide information on the ultimate source of thematerial. For example, the quartz-rich Ngrayong Formation wasdeposited in a terrestrial to shallow marine setting on the edge of theSunda Shelf and has numerous indicators of north-to-south sedimenttransport, including channels, cross-bedding, and the regional change infacies from terrestrial in the north to subsurface marine fans in the south(Ardhana 1993). The sediment is therefore interpreted to have beentransported southwards from the shelf onto the shelf edge, and the sourcefor this sediment has been assumed to be the continental rocks ofSundaland farther to the north (e.g., Ardhana 1993; M. Adams, personalcommunication 2001). The new provenance data suggest that the volcanicmaterial, including quartz, zircons, and clays, in these sandstones werethe result of ash-fall onto the Sunda Shelf. A significant component ofthis air-fall is now thought to be associated with the major eruption whichoccurred in the Southern Mountains Arc at around 20 Ma (Smyth et al.2005; Smyth et al. 2007; Smyth et al. 2008). The air-fall deposits on theshelf were subsequently reworked, mixed with metamorphic and recycledsedimentary material, and redeposited on the shelf edge. This illustratesthe importance of mixing and reworking of multiple sources of sediment,and indicates that the ultimate source for a significant proportion of thesediment was not only the Sundaland continent to the north but also theSouthern Mountains Arc to the south.

Recycled Sedimentary Source Rocks

The Cretaceous and older basement of East Java is the closest sourcefor recycled sedimentary material. In addition there are several otherpotential sources:

A. Karimunjawa Arch.—As discussed above, the Karimunjawa Archwas elevated throughout most of the Cenozoic and was therefore apotential source of sediment. Pre-Cenozoic quartz sandstones andconglomerates (van Bemmelen 1949) now exposed on KarimunjawaIsland north of Java could have provided a source for abundant recycledsedimentary quartz. It is also possible that quartz-rich sandstones weredeposited on the arch in the early Cenozoic and were subsequentlyremoved.

B. Eocene sedimentary rocks on land, East Java.—The Miocene LututBeds, described above, contain a reworked Eocene and Oligocene fauna,sedimentary lithic grains, and recycled sedimentary quartz. In addition,they contain fresh contemporaneous volcanic and metamorphic material.The abundance of volcanic material strongly suggests that thesesandstones are the product of Miocene uplift and erosion of lowerCenozoic volcanogenic rocks and older basement rocks in the SouthernMountains Arc.

Plutonic Source Rocks

Plutonic quartz does not occur in abundance in the sedimentary rocksof East Java, contributing only 9% of the total quartz in all of the quartz-rich sandstones analyzed in this study. The closest granitic rocks to EastJava exposed at the surface are the Cretaceous granites of the SchwanerMountains of SW Borneo. These granites are known (van Hattum 2005;van Hattum et al. 2006) to have been elevated between the late Eoceneand the early Miocene, providing material to the sedimentary rocks ofnorthern Borneo. The Schwaner Mountains granites have yielded a smalland distinctive range of isotopic ages including U-Pb ages from zircons(van Hattum 2005). Similar age populations of zircons are recognized innorthern Borneo sedimentary rocks (van Hattum et al. 2006), but are notseen in the zircons of East Java (Smyth 2005; Smyth et al. 2007; Smyth etal. 2008).

Other granites are located much farther away and include the Tin Beltof the Malay Peninsula and Sumatra, and the Tin Islands of the SundaShelf: Bangka, Billiton, and Belitung. Sediment produced by the erosionof these granites would require lengthy transportation by river systems,which in the case of Malay Peninsula or Sumatra would have exceeded1500 km. During the Cenozoic there were also paleogeographic barriersin the Java Sea, including two elongate elevated ridges, the Karimunjawaand Bawean Arches (Fig. 8), which were emergent throughout most ofthe Cenozoic (e.g., Bishop 1980; Cater 1981). The Karimunjawa Archseparates the East and West Java Seas: to the east of the arch lowerMiocene to Oligocene sedimentary rocks are marine but to the west mostof the lower Miocene and all of the Oligocene sedimentary rocks arenonmarine (Cater 1981). These arches, and the narrow basins whichflanked them, could have acted as sediment traps or barriers preventingdetritus from Sundaland entering the East Java system. In addition anumber of basins in the West Java Sea, such as the Billiton and ArjunaBasins, could have been sediment traps.

INFLUENCE OF TROPICAL WEATHERING AND USE OF

DISCRIMINANT DIAGRAMS

Today, and throughout the Cenozoic, the source regions that providedsediment to East Java were located close to the equator (Hall 2002) and as

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FIG. 6.—Character of Type 2 sandstones. A) Bipyramidal grain (scale: 1 mm). B) Photomicrograph showing poorly sorted sandstone of v (Kresek Member, WungkalGamping Formation). Note the two large clear, euhedral grains in the top right of the image (scale each box: 1 mm). C) Photomicrograph showing melt embayments fromvi (Jaten Formation) (scale: 500 mm). D) Quartz shard (scale: 1 mm). E, F) SEM-BS and SEM-CL images of a grain showing melt embayments and concentric zoning(Jaten Formation) (scale: 700 mm). G) QFL plot showing the Type 2 sandstones. H) Triangular plot showing metamorphic, volcanic, and recycled sedimentary andplutonic quartz of the Type 2 sandstones.

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352 H.R. SMYTH ET AL. J S R

a result had a tropical climate. Tropical weathering can have a significantimpact on the composition of sediment, and weathering processes canoccur during erosion of the source rock, during transportation ofsediment, after deposition, and/or when the resulting sedimentary rock isexposed at the surface.

Tropical Weathering

Tropical environments with high temperature and precipitation aresites of rapid weathering and erosion (e.g., White and Blum 1995; Dossetoet al. 2006). There are a number of well documented examples of theimpact of tropical weathering on rocks in both the ancient and themodern record. In the Narmada Basin in India (Akhtar and Ahmad 1991)the Lower Cretaceous Nimar Sandstone, a quartz arenite, was producedby single-cycle weathering of a cratonic source. The quartz was enrichedrelative to feldspar and other labile constituents by the ‘‘humid tropicalclimate and a long residence time in the soil horizon’’ (Akhtar andAhmad 1991). The resulting sediment is compositionally mature buttexturally immature. In a modern example from the Guaba Ridge in theLuquillo Mountains of Puerto Rico, Schulz and White (1999) recorded anincrease in quartz concentration in the soil profile developing abovegranitoid rocks. In the upper meter of the soil profile there is a 30%

increase in quartz (Schulz and White 1999). This enrichment is the resultof the selective removal of kaolinite. Unconsolidated volcanic depositsand sediments which are subject to tropical weathering are expected tobreak down much more rapidly than in lithified sediments or in graniticrocks.

Discriminant Diagrams

In tropical environments traditional assessments of maturity andprovenance from discriminant plots such as those of Dickinson andSuczek (1979) that focus on the proportions of quartz, feldspar, and lithicfragments may be misleading. In these settings rapid, intense, and deepweathering break down any labile minerals, mineral aggregates, andmany lithic fragments. The resulting sediment is rich in resistant mineralssuch as quartz and heavy minerals like zircon. As the unstable or weakfraction is removed the quartz content is enriched and the resulting sandscontain a higher proportion of quartz than the source rock. Datasets onthe composition of arc-related sediments (e.g., Dickinson and Suczek1979; Marsaglia and Ingersoll 1992) do not include modern tropicalenvironments, because there is a gap in samples collected around theequator between latitudes of 9.7u N and 16.5u S. Up to now fewprovenance studies have been published from tropical SE Asia and little

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FIG. 7.—Character of Type 3 sandstones. A) Photomicrograph showing a bipyramidal quartz grain in the center bottom left (scale: 1 mm). B) Photomicrograph of theangular, clear quartz grains and opaque mineral grains (scale: 500 mm). C) Elongate volcanic zircons from viii (Ngrayong Formation) (scale: 100 mm). D) Quartz lithicsfrom the vii (Lutut Formation) (scale: 1 mm). E) Weathered volcanic lithics from vii (Lutut Formation) (scale: 1 mm). F, G) SEM-BS and SEM-CL images of a quartzgrain exhibiting incomplete concentric zoning, indicating that it is a fragment of a much larger grain (200 mm) (Nanggulan Formation). H) QFL plot showing the Type 3sandstones. I) Triangular plot showing metamorphic, volcanic, and recycled sedimentary and plutonic quartz of the Type 3 sandstones.

FIG. 8.—Potential source areas for the quartz-rich sandstones.

ORIGIN OF SOME QUARTZ-RICH SANDSTONES, EAST JAVA, INDONESIA 353J S R

information from Indonesia, despite the size and the high sediment yieldsof this region at present (e.g., Milliman and Syvitski 1992; Milliman et al.1999), and its importance as a region of abundant volcanic and tectonicactivity throughout the Cenozoic (e.g., Hall and Smyth 2008). Theabundance of volcanic quartz in East Java suggests that more data areneeded from tectonically and volcanically active tropical regions such asIndonesia, and that discriminant plots should be considered in the light ofclimate at the time the sediment was eroded and deposited, as well as thepresent day.

CONCLUSIONS

Quartz can provide valuable provenance information. There arenumerous potential sources of quartz in sedimentary rocks, and themiddle Eocene to lower Miocene sandstones of East Java contain igneous(plutonic, hypabyssal, and volcanic), metamorphic, hydrothermal vein,chert, and recycled sedimentary quartz. However, each quartz type hasdistinctive characteristics which allow them to be distinguished, andcombined with other provenance information, can provide criticalinformation in interpreting sources, sediment pathways, and regionalgeological history.

In East Java, at the base of the Cenozoic succession, immediately abovethe basement, the oldest sandstones are dominated by quartz ofmetamorphic origin, but this gradually decreases up section, throughthe middle Eocene, as volcanic quartz becomes more abundant. Theincrease in volcanic material records the initiation of volcanism in theSouthern Mountains Arc and the early stages of arc growth from themiddle Eocene to the early Oligocene. This early Cenozoic period of arcactivity has previously been largely overlooked (e.g., Rutten 1925; vanBemmelen 1949; Hamilton 1988), partly because of the abundance ofyounger and more obvious volcanic products such as the ‘‘Old Andesites’’(van Bemmelen 1949) and because its acid character means that thevolcanic products produced by explosive eruptions are preserved mainlyin sedimentary rocks. First-cycle volcanic quartz arenites are preservedonly within or close to the arc. These quartz-rich sands were transportedaway from the arc and mixed with quartz derived from multi-stageerosion of local and more distant basement rocks. Farther away from arc,volcanic particles are interpreted to have fallen as ash onto the SundaShelf and into the Kendeng Basin. On the shelf the material wouldsubsequently have been reworked, enriched in quartz, and mixed withmaterial derived from uplifted basement blocks in the East Java Sea(Bishop 1980; van Bemmelen 1949) and redeposited on the edge of theSunda Shelf. The sedimentary rocks of East Java are dominated bymaterial eroded from (1) the basement, distributed by fluvial systems, and(2) from the Southern Mountains Arc, distributed by volcanic processesand subsequent epiclastic reworking.

Quartz-rich sandstones are not necessarily the result of erosion of acratonic or recycled continental crust in orogenic source regions. Activevolcanism or eroded acid volcanic rocks may be an important butoverlooked source of quartz. Volcanism can distribute quartz over a largearea during explosive eruptions. Quartz may be concentrated by a varietyof volcanic processes, and further enriched by reworking after eruption.In tropical settings weathering may further enrich sediments in quartz.The mixture of such quartz-rich material with the other sediment interrestrial settings, elevated highs, or shallow marine settings may meanthat the volcanic contribution is overlooked. The proportions of quartztypes in sandstones may change within a sedimentary succession and canprovide valuable information to aid interpretation of provenance and thegeological evolution of an area. In tropical environments it is possible torapidly enrich the quartz content of the sediment by the removal of labileminerals, lithic fragments, and clays. In such settings standard QFLdiscriminant diagrams may provide a misleading indication of prove-nance.

ACKNOWLEDGMENTS

The SE Asia Research Group at Royal Holloway University of Londonfunded this project. Financial assistance for SHRIMP U-Pb analyses wasprovided by a grant from the University of London Central Research Fundand by CSIRO, Australia. U-Pb SHRIMP dating was undertaken by JosephHamilton and Pete Kinny (Curtin University of Technology, Perth,Australia). The samples of granitic rocks were collected by Imtihanah in2000. We appreciate the field work support provided by LIPI (Lembaga IlmuPengetahuan Indonesia) and Eko Budi Lelono of LEMIGAS. We are gratefulto Terry Williams and Anton Kearsley of the Natural History Museum,London, for access to the SEM-CL and assistance with imaging. We alsothank Colin Macpherson, Heather Handley, Peter Lunt, Kevin D’Souza, BenClements, Cindy Ebinger, Marco van Hattum, Han van Gorsel, SimonSuggate, and Dave Waltham. We also are grateful to William Heins, KittyMilliken, M.J. Johnsson, and an anonymous reviewer for their comments,which greatly improved this manuscript.

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Received 8 May 2007; accepted 21 October 2007.

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