The sedimentology of Miocene shallow marine clastics of the Sandakan Formation of eastern Sabah

Transcription

1 :::?~~!b~ AnnuaL Ce!.r;icaL Cn/emice '96 June 8-9, 1996, K.ta K.tizabaLl, Sabah The sedimentlgy f Micene shallw marine clastics f the Sandakan Frmatin f eastern Sabah JON NOAD AND NEL HARBURY SE Asia Research Grup Research Schl f Gelgical and Gephysical Sciences Birkbeck Cllege and University Cllege Lndn United Kingdm Abstract: The Sandakan Basin lies n the east cast f Sabah and cntains sme excellent expsures, resulting in part frm the steep tpgraphy f the regin and frm the recent develpment f husing estates and rad cnstructin. These ften spectacular utcrps allw examinatin f the Micene successin, which has nt previusly been feasible. A ttal f 4 mnths has been spent cllecting sedimentlgical data thrughut the c. 25 km by 15 km basin. Over 70 measured sectins have been lgged acrss the basin and this, in cnjunctin with numerus macrfssil, micrfssil and ichnfacies studies, has allwed the differentiatin f the interbedded sands and clays, previusly described as a marginal marine successin, int facies assciatins ranging frm cntinental t shallw shelfal in rigin. Seven main facies grups are identified which range frm mangrve depsits cut thrugh by fluvial channels, thrugh delta tp with channels int facies depsited in a lagnallinterdistributary bay envirnment. These pass int shreface trugh r planar crssbedded sands with cmmn Ophimrpha r Skliths trace fssils and finally int ffshre marine muddy facies. Palaeseismicity is suggested by synsedimentary defrmatin, ften cnfined in discrete hrizns which can be traced ver several kilmetres. Detailed palaentlgical studies fthese rcks will allw develpment fthis facies scheme and further divisin f these systems int sub-envirnments. These well expsed marginal marine facies present an exceptinal pprtunity t develp a sequence stratigraphic framewrk f the Sandakan Basin thrugh the Micene. Examinatin f the eustatic/ tectnic cntrl f the system will then be applied t hydrcarbn-bearing strata in adjacent basins. Furthermre this study will cnstrain palaegegraphic recnstructins f the regin. NTRODUCTON A study f the Tertiary sedimentary rcks f eastern Sabah is imprtant t cnstrain tectnic mdels fr the evlutin f Nrthern Brne and the Sulu Sea. Several wrkers have presented sedimentlgical data frm the Ecene t Plicene strata expsed in the regin, but few detailed studies have been undertaken. Furthermre, such studies are ften f a recnnaissance nature and have nt addressed the reginal significance f individual frmatins. n this paper we present new and detailed sedimentlgical data frm the Sandakan Frmatin, which has frmerly been described as cnsisting ffluvi-deltaic t estuarine (Hutchisn, 1992) r shallw marine and deltaic sediments (Lee, 1970; Stauffer and Lee, 1972). The cnsiderable urban develpment in prgress in the regin arund Sandakan Twn makes this prject particularly timely and has allwed the measurement f numerus stratigraphic sectins, previusly unexpsed, thrughut the area. Sme f the sectins examined reach dimensins rarely encuntered in SE Asia (e.g. Taman nda Estate where cliff expsures are 300 x 100 metres) and allw detailed recnstructins f bedfrm gemetry and lateral facies variatins. Recnnaissance wrk might suggest there is a paucity f fssiliferus material in the Sandakan Frmatin. The preservatin ffaunalflra is very variable thrugh the frmatin, althugh Lee (1970) has dcumented numerus lcalities with fssils in the regin; we als have been able t cllect a gd deal f fauna frm certain intervals within these rcks. Disslutin f carbnate may be respnsible fr barren hrizns in sme cases, whilst ther intervals cntain little fauna fr envirnmental reasns. Many f the faunal assemblages have nt been previusly recrded frm NE Brne and include new species which cnstrain the sedimentlgical interpretatin fr the depsits. New faunal and sedimentlgical infrmatin frm the excellent expsures in the Sandakan regin will allw the cnstructin f a sequence Ce!. Sc. MaLaYdia, BuLLetin 40, JuLy 1997; pp

2 120 JON NOAD AND NEL HARBURY stratigraphic mdel fr the successin. This mdel will prvide valuable analgues fr ptential hydrcarbn prvinces in adjacent regins such as the Baram Delta, and will cnstrain tectnic mdels fr the regin. REGONAL SETTNG Oceanic spreading f the Suth China Sea began in the Palaegene and ceased arund 17 Ma, when the Dangerus Grunds blck cllided with Nrthern Brne (Clennell, 1996). n Western Sabah this led t the uplift f the Crcker Frmatin, cmprising turbidites flred by philitic basement (Tngkul, 1991). T the east the cllisin is thught t have initiated the develpment f the extensive melanges fund there (Clennell, 1996). Extensin fthe Sutheast Sulu Sea in the very early Micene, by rifting f the pre-existing philitic terrane, led t limited ceanic spreading (Tngkul, 1991). Eastern Sabah lay at the hinge f a spreading system (Hutchisn, 1992), thugh stretching was nt sufficient t generate ceanic crust (Clennell, 1996). Extensinal frces, tgether with cmpressin caused by the cllisin f the Dangerus Grunds blck, was accmmdated by wrench faulting, pening a series f sedimentary basins (Maliau, Malibau, Bukit Garam) in eastern Sabah during Micene times (Fig. 1). These basins verlie large areas f melange r distal Crcker turbidites, and are filled with a mixture f siliciclastics and vlcaniclastics with limited carbnates. Whilst basin evlutin was cntrlled by reginal tectnic events, their internal architecture and fill was cntrlled by lcal, gravity-driven subsidence and basement uplift which ften resulted in circular basin develpment (Tngkul, 1993; Clennell, 1996). SANDAKAN FORMATON LTHOFACES Seven lithfaciesllithfacies assciatins are defined frm ver seventy measured sectins in the regin surrunding the twn f Sandakan. We present detailed sedimentlgical lgs frm three sectins, Leila Rad, Bird Quarry and Taman nda (Figs. 3, 4 and 5), the lcatins f which are shwn in Figure 2. These utcrps have been selected t illustrate the facies encuntered within the Sandakan Basin. A detailed descriptin f each f the lithfaciesllithfacies assciatins is given belw. Fr the purpses f this paper nly the end members f each facies are described, thugh in reality an almst cmplete spectrum f facies can be bserved in the field. 1. Dark grey muds with abundant lgs and carbnaceus detritus Sectins: Leila Rad, Bird Quarry Descriptin. Thick chesive dark grey muds, with an abundant fauna. Typically the muds cntain large lgs, which are either silicified, r mre cmmnly carbnaceus with a black charcal-like appearance thught t be due t diagenetic alteratin (Fig. 6). The lgs may are ften bred by bivalves r wrms. There are als ccasinal thin caly bands, scattered smaller pieces f wd and rare rted trunks. Well preserved impressins f leaves can be recvered frm the muds, and stems f smaller plants are als bserved. A small amunt f subrunded dark amber clasts up t 5 cm in size may be present in sme lcalities. Palaentlgy. Bth bivalves and gastrpds ccur in all utcrps f this type. These are smetimes well preserved, with riginal shell material, but mre cmmnly nly as a partially rtted internal cast in irnstne. Arund 15 species have been identified (Table 1), and the bita is dminated by a fauna typical f a brackish water envirnment. A gd example is Hiatula, which prefers a marine envirnment, but lives directly belw freshwater runff, as well as ther brackish frms such as Crbicula. This is supprted by the presence f rare fragments f the carapace f Trinyx, a freshwater turtle (pers. cmm., Feb. 1996, Clin Pattersn, Natural Histry Museum, Lndn). Other fauna includes keeled wrm tubes f an unknwn species, and insects preserved within the amber. Types f insects include ants, parasitic wasps, thrips and spiders, all frms typical f trpical cnditins. nterpretatin. See Facies N.2 2. Channelised sands with trugh-crss bedding Sectins: Bird Quarry/Leila Rad Descriptin. Generally fine grained sands, with very channelised bases. These channels tend t pinch ut laterally, and they vary frm a few metres t at least 100 m in width (Fig. 7). The sands are trugh crssbedded, with the trughs usually in fairly thin sets i.e. 30 cm t 50 cm. Mud drapes are bserved in trugh-crss bedded sands frming channel fills. These pass up int finer silty sands cmmnly exhibiting climbing ripples, the ripples having the typically asymmetric frm f current ripples, and an average wavelength f Gel. Sc. MalaYJia, Bulletin 40

3 THE SEDMENTOLOGY OF MOCENE SHALLOW MARNE CLASTCS OF THE SANDAKAN FORMATON OF EASTERN SABAH 121 O SEDMENTS Lwer Micene t ' Plicene clastic.. sedimentatin l'lililll Late Cretaceus t '. Early Micene deep marine D sedimentatin BAlABAC?' STRAT Banggi. ~ GNEOUS ROCKS 8 _"' Granitids ~ V ' t Micene ~ ~ 0 canlcs Quatemary v G Late Oligcene t Middle Micene pyrclastics and lava "'- BALABAC BASN OTHER UNTS!ii Early t Middle liliiii Micene melange units D Ophilitic basement and ceanic cver sediments Negene ceanic lithsphere Lineament Fault C> BANCAUAN / BASN / N t / /..,/-.' SANDAKAN BASN C'ELEBES SEA v KALMANTAN '''-''.~;''''~~. : :.':': : 117.,.~ Figure 1. Simplified gelgical map f nrth-east Sabah and the adjacent marine regin. After Clennell1996. Based n Tngkul, (1991,1993,1994), Clennell, (1991, 1992). Offshre infrmatin frm Hinz et al. (1989), Lee and Tham (1989), Hinz and Blck (1990) and Wng (1993). JuLy 1997

4 122 JON NOAD AND NEL HARBURY apprximately 20 cm (Fig. 8). This upper prtin is cmmnly biturbated, generally by mainly hrizntal burrws. Palaentlgy. One f the channels examined had bird ftprints preserved at the base f the sand, frm a castal wading bird such as the Green Plver (Fig. 9; pers. cmm., Febuary 1996, Clin pattersn). Other fauna is thught t have been lst t carbnate disslutin, but frtunately the assciated Facies 1 has an abundant fauna. nterpretatin fr Facies.1 and 2. These tw lithfacies are cmmnly' assciated, and it is pstulated that they represent m~andering fluvial channels (Facies 2) n a variety f scales, cutting thrugh mangrves (Facies 1) This envirnmental interpretatin is strngly supprted by the abundant brackish t fresh water fauna. The mst laterally extensive sands prbably. culd be better described as estuarine depsits. The mangrve depsits were prbably mre sparsely vegetated than sme mdem nes, as cals are rare, althugh lgs are fairly cmmn. 3. Heterlithic sediments Sectins: Taman nda (Fig. 10) Descriptin. One f the mst striking lithfacies assciatins in the Sandakan Basin is a very heterlithic set f interbedded very fine grained sands, silts and mudstnes. The sands are generally less than 150 cm in thickness, thugh thicknesses between 10 and 50 cm are mre cmmn. Tw end members are defined n the basis f bedding gemetries and internal bedfrms (Fig. 10): i) Very laterally persistent sands with extremely flat bases. ii) Channelised sands, cmmnly between 2 m and 30 m in width. The channels cut dwn int the beds belw fairly indiscriminately and shw evidence f reactivatin. The cream t yellw sands usually shw swaley crss-laminae, ften picked ut by carbnaceus material up t 2 cm in thickness. Generally nly ne set f swales is present in each sand. n places li N TAMAN NDA@66 & MAP OF SANDAKAN URBAN AREA SHOWNG LOCATON OF LOGGED SECTONS TAMAN NDA 39@ KEY Sectin discussed in text 39@ Lgged Sectin SANDARlN HARBOUR 143@& Fasili'"",us Sectin BRD =63.e, Meltes 500 SCALE Figure 2. Detailed lcatin map f the Sandakan area. Get. Sc. MataY.1ia, Bulletin 40

5 r~ :"e,.4' ~e. '.' BEDFORMS AND SEDMENTS KEY FAUNA 5m 4m 3m 2m 1m Om ----LL.,~~_ ESTUARNE SAND TUFF 29m 28m 27m 26m 25m 24m 23m 22m 21m 60 m f prly expsed shreface sands -=~ ~ ~ ~~ U;>U::~ VU - SST-? SHOREFACE SAND ESTUARNE SAND. MANGROVE. i ""n O" il:::> d'i-= rl""" MANGROVE "".-.;~ e MANGROVE "., 0< FLU VAL MANGROVE e t! e -= ~ ~ ~ ~~ Vi> U:::CU; - SST- 140m 139m 137m 136m 135m Trugll crssbeds Planar crssbeds Channehsed base Prly expsed nlerval Siumpecl hnzn Mud 5111 Sand :;<;;.ii Peat,:P -:;; 3:: ~ p -V ~ MANGROVE Carbnaceus matenal Fssil wd Amle, Gastrpds Bivalves Vertical burrws Hnzntal burrw 'Disc' burrw Wrm tube Turtle Birdltpnnts C1l1b ---1 m (fj m ~ m z b 5 G) -< " s:: 6 (") m z m (fj r 5 ::'E :;: ::D Z m (") s;: (fj -l (fj "-l m (J) z ~ z ;:jl ::D :;: ~ 6 z " m (fj -l m ::D Z (J) CD Figure 3. Leila rad measured sectin.

6 ' 01, ~!~~~~~~l,j::( (.~-- i:: :: ~ ',,{:> i-= n~ MANGROve S = ;--:--rr- "". >1 "" TRANSTONAL FACES SECTlON CONTNUES li=; nc:: c~~~~~s '.m 1.:-:- '''''''':':':''~. --,'-J :-:-:-J,,,:=:,~ ii;j~i~!: 11m :~:~:> 8tn ::: - 1m~ 6m~ n.,. MANGROvE - i 32m -:-:-J ".1::::::, 30m ~:.:-: :>9m l:_:_:_,.,.,r-:-:-_,, 1:::::, [::::: ~m :-~-_- ~: :: : : ~~: lie:: n=,j,'#--, "" "" "" r,- nr, nr SMALL S MANGROvE MANGROVe Sectin n ther side ~~~~~;; be/this -~ ~t][. :::::J! -:-: jl i ~t:::::jj ~~dm "".-.,p_&c.:"_ &e.,p_8tc.11 nil rll nil nil n " SHOREFACE bm~ 2.", MANGROVE.",":":":" 3m~ && :nm -.- ~: : : :; ;."- ~ f:::::= 2;>", ~: -:":- <a ' llj:~fl '. ::::::f J =-:-:f ~i:~:j ;; ~ ~ ~M {-:-:-: 2''''t=:=:=: [-:-:- ~t} i:::::: 1m~! ~ l~ M j.,. M ~~dm MANGROve,-~dn it"'" Figure 4. Bird quarry measured sectin. See Figure 3 fr key.

7 . ~. ' 6m.,., DelTA TOP S DELTA TOP 92m "m n~ n 90m " " " m " m ~ "'" "'" 'Om 87m U'm Om Om DELTA TOP S 86m DELTA DELTA TOP TOP w u CHANNElS S '70 " ~ a: 0 :z: " '" " m 811)1 80m 83m 82m LAGOON LAGOON W 79m 59m m DELTA.~ l W,", TOP sam On 57m 76m t 'l rl'l'r'l' " '" ~ ~- i ~~ '"'!' 1'1""1'1' -, '" " ~ ~ dfr ~ ~ ~; ~tl ~ ~ ~ ~cj 1l>!. l,.u ~ ~ ~~M ~~~t:j, SST, f- SST SST -' - ~ SST SST-t Figure 5. Taman nda measured sectin, See Figure 3 fr key,

8 126 JON NOAD AND NEL HARBURY Table 1. Macrfssils in the Sandakan Frmatin. LOCALTY (and FOSSL NTERPRETED Lcality N.) TYPE SPECES ENVRONMENT FACES Bird Quarry (12) Bird Plver Castal Mangrve Gastrpda Naticidae nshre Cerithiacea nshre Thaidae? Nerite? ntertidal 1 unident. Bivalvia Hiatula Lw intertidal belw freshwater runff Smth venerid Crbiculidae? Ribbed venerid Brackish-freshwater Plantae Lgs Marginal-freshwater Whle leaves Marginal-freshwater Carb Material Amber Trace fssil Ophimrpha Shallw marine Shreface Leila Rad (40) Turtle Trinyx Fresh water Mangrve Gastrpda Vicarya ntertidal-brackish Bathilaria Cerithacea nshre Ribbed Cerithid nshre 6 unident. Bivalvia Oyster ntertidal Narrw smth? Pitar? Annelida Keeled Tube Plantae Lgs Marginal-freshwater Cals Marginal-freshwater Buli Sim Sim (9) Bivalvia Mytilid Shallw marine Shreface Pectinid Shallw marine Trace Fssils Ophimrpha Shallw marine Skliths Shreface Fk Kim Rd (143) Bivalvia Scallp Shallw marine Lagnal Oyster ntertidal Plicatula ntertidal Tellinidae Teredinadae Marginal-marine Mactrdae Shreface marine Nucula Marine Crustacea Annelida phiculus Typilbus? Calappa Prtunus 1 unident. Serpulid Shallw marine Gei. Sc. MaiaYdia, BuLLetin 40

9 THE SEDMENTOLOGY OF MOCENE SHALLOW MARNE CLASTCS OF THE SANDAKAN FORMATON OF EASTERN SABAH 127 Table 1. Macrfssils in the Sandakan Frmatin (cnt'd). LOCALTY (and FOSSL NTERPRETED Lcality N.) TYPE SPECES ENVRONMENT FACES St. Mnica's (138) Bivalvia Oyster Smth venerid ntertidal Lagnal Glycimeris? Marine Crustacea Prtunus W. Prtunus O. Calappa Prthenpe Ncia? Panpeus? 1 unident. Dg Quarry (69) Gastrpda Vicarya Brackish Mangrve Vicarya? Brackish Thaid Bivalvia 1 unident. Plantae Rted trees Mangrve Amber nsecta Parasitic wasp Trpical rainfrest Ants Gall Midge Thrips Spiders Batu Sapi (77) Gastrpda Nerita ntertidal Mangrve Muricid? Dsinia? 4 unident. Bivalvia Pisces Smth venerid Crbiculidae Telest Brackish-freshwater Plantae Lgs Marginal-freshwater Amber Carb material '.-:; " ~ July 1997

10 128 JON NOAD AND NEL HARBURY Figure 6. Dark grey muds with petrified lgs, Facies 1, Leila Rad. See Figure 2 fr lcatin and Figure 3 fr measured sectin at this lcality_ Figure 7. Channelised sands with trugh-crss bedding cutting thrugh grey carbnaceus mudstnes. These sands are interpreted as estuarine channels. Lcality N. 77 (see Fig. 2). Figure 8. The lwer sand interval is a channelised sand with trugh-crss bedding. This is verlain by thin, trugh-crss bedded estuarine sands, with mud drapes. These pass up int crss-bedded thick sands interpreted as shreface/shallw marine sedime ts cntaining abundant wave-ripples (Facies N.5), Bird Quarry. See Figure 2 fr lcatin and Figure 4 fr measured sectin at this lcality. Ge L. S c. MaLaYdia, BuLLetin 40

11 THE SEDMENTOLOGY OF MOCENE SHALLOW MARNE CLASTCS OF THE SANDAKAN FORMATON OF EASTERN SA BAH 129 sme trugh crssbedding may develp, and here mre than ne set f crssbeds is cmmn. Even the thinnest f the sands (5 cm r less) usually cntains fresets. The sands within individual beds pass up int mre silty sediments, with climbing ripples ften extending t the tp sand cntact. Current ripples have been rewrked int symmetrical wave ripples in sme intervals. The silty sands are interbedded with grey mudstnes, which are ften highly biturbated, with cmmn vertical and hrizntal burrws. They cntain a spectrum f sandy starved ripples ranging frm scattered individual silty ripples t thin beds f sandy wave ripples (Fig. 11). Palaentlgy. Fssils in these sediments are very uncmmn, prbably due t disslutin, but a few casts f marine bivalves have been fund, including mdilids and scallps. n sme areas the siltier sediments d nt exhibit rippling, and n ccasins, these may yield exceptinally well preserved whle leaves. t is hped that identificatin f these frms will aid in palaeenvirnmental recnstructins. Mre Figure 9. Bird ftprints at the base f an estuarine channel, believed t be made by a plver, Bird Quarry. See Figure 2 fr lcatin and Figure 4 fr measured sectin at this lcality. cmmnly, hwever, the plant material has been cmminuted int very fine carbnaceus debris, which picks ut the crssbeds. nterpretatin. These lithfacies are interpreted as wave-dminated delta tp sediments. This is supprted by the cmmn wave ripples and very heterlithic beds and is supprted by the fauna which indicates a marine envirnment. The rewrked ripples shw that there is sme current activity, prbably near the estuary muth. The flat based sands are interpreted t have been depsited in parts f the delta tp with little tpgraphic variatin, while the mre channelised prtins are interpreted as either feeder channels crssing the delta tp r tidal channels. These channels can be distinguished frm the fluvial channels (Facies N. 2) by the presence f marine fauna. Where leaves are fund, these must have been depsited in a much mre prtected part f the cast, while the abundant carbnaceus laminae are cmminuted plant material prbably prduced in high energy cnditins. While nt a gd envirnmental indicatr, it is interesting t nte the presence f rare vertically cnfined cntrted r slumped beds within the sands f this lithfacies assciatin. n sme cases these may even develp int slump breccias, with remulded 'clasts' made up f small detached cntrted silty sand. These chatic hrizns prbably riginated by dewatering f individual beds, pssibly triggered by palaeearthquakes. n sme areas these cntrted beds can be traced ver several kilmetres at the same stratigraphic interval implying significant, albeit lcal, grund shaking. 4. Grey clays with rare silty sands Sectins: Taman nda Descriptin. These sediments cmprise thick grey clays, with ccasinal very thin but very laterally cnsistent silty sands. These have flat bases but may shw lw angle crssbeds and slightly rippled tps. nternal structures f many beds are bscured by develpment f irnstne during diagenesis. They cmmnly have thin carbnaceus laminae. There are als small winged channels, up t at least 50 cm in thickness, but generally less than 3 m in width. These shw trugh, r mre rarely swaley crssbedding. Palaentlgy. The fauna recvered frm this facies is very distinctive, and indeed helps t define this lithfacies. The mst cmmn cnstituent is small crabs, up t abut 3 cm in length, beautifully preserved as casts within the diagenically develped irnstne layers. At least 15 species have s far been identified, the cmmnest f which are July 1997

12 130 JON NOAD AND NEL HARBURY Figure 10. General view fthe sectin at Taman nda. A prgrading sequence f three lithfacies assciatins can be distinguished in this excellent expsure. The lwer interval cmprises structureless mudstnes cntaining abundant fssil crabs and rare winged channels, interpreted as having been depsited in a sheltered shallw marine envirnment (Facies 4). This unit is verlain by a heterlithic set f interbedded very fine grained sands, silts and mudstnes (Facies 3). The uppermst interval cnsists f thick shreface sands with abundant Ophimrpha (Facies 5). See Figure 2 fr lcatin and Figure 5 fr measured sectin at this lcality. Figure 11. Starved sand ripples in mudstne frm the heterlithic facies, Facies 3, Taman nda. See Figure 2 fr lcatin and Figure 5 fr measured sectin at this lcality. Ce!. S c. MaLaYJia, BuLLetin -10

13 THE SEDMENTOLOGY OF MOCENE SHAllOW MARNE CLASTCS OF THE SANDAKAN FORMATON OF EASTERN SABAH 131 swimming crabs (Table 1). There are als scallps, scattered ysters and ther marine bivalves; gastrpds, echinids and wrm tubes are cmmn. Occasinally large but infrequent well runded amber clasts ccur. nterpretatin. These sediments are interpreted as shallw marine lagnal r interdistributary bay facies, which lay in a relatively shaltered lcatin, prtected frm pen marine cnditins. The fauna is marine, but the fine grain size and cmmn swimming crabs shw that the current energy was medium bedded, with individual beds arund 10 cm t 20 cm in thickness. The sands are flat based, and bedding is swaley and undulating, but rarely cuts dwn int the beds belw. The mst distinctive feature f these beds -is the abundant vertical burrws, picked ut by ersin as' small sand pillars between beds. These burrws ~e thught t be the trace fssil Skliths. Palaentlgy. Mst f the fauna has been lst t disslutin, but ccasinal bivalve casts are f marine frms (see Lcality 9, Table 1). lw. The fragments f ysters may have been nterpretatin. The sediments are interpreted as washed in during strms, thugh it is pssible that ysters clnised harder areas f the seabed. 5. Crss-bedded thick sands having been laid'dwn as beach depsits, pssibly n bar frnts where persistent wave rewrking has remved th~ finer grained material. '7. Thin b~dded muds Sectins: Bird Quarryffaman nda Descriptin. Thj.ck sand dniinated sequences Sectins: West and Nrth f the 13a.n.dakan ccur in much f the Suthern and Eastern basin Sandakan Peninsula. These weather t frm large Descriptin. These sediment!;! are represented by scarps, which may reach mre than 100 m in height. featureless mudstnes, thugh sme thin silty beds The typical successin is a 2 m t 5 m: thick, flat ccur, which are generally less than 10 cm in based, fine ccasinally medium grained sand, with, thickness, with,slightly ersive bases. Mst f these trugh r mre rarely planar crssbedding n a are laterally impersistent, pinching ut ver a few metre-plus scale (Fig. 9). The sand grades up' metres. The silts shw crss-amiriatin and have slightly t a very fine grained sand, which may ccasinal hrizntal and vertical burrws, as well shw rippling, and is capped by a very distinctive as minr fine carbnaceus material n the bedding irnstne-cemented rippled hrizn. This cmmrily,planes. ' weathers ut t shw wave ripples ranging frm " Palaentlgy. Fauna rem-v'ed by disslutin. megaripples with a wavelength f arund 50 cm t' nterpretatin. These sedlld.ents are interpreted fields f smaller wave ripples shwing interference as pen marine shelf depsits, with the silts pssibly patterns typical f shallw marine seas washing representing strm-driven carser clastic incursins. ver an undulating seabed. Ladderback ripples are als develped in places. The rippled hrizqns are in tum verlain by thin but laterally persistent plastic grey clays, which give way vertically t the next sandbdy. Palaentlgy. N bdy fssils have been recvered frm the this facies. Ophimrpha burrws are generally abundant. nterpretatin. The bedfrms and Ophimrpha burrws in this facies suggest it was depsited m a shallw marine shreface setting, either lcated ffshre r adjacent t a beach. Smaller wave ripples are typical f shallw marine seas with an undulating seabed. 6. Thin t medium' bedded sands with Skliths Sectins: Sectin N. 9/142 Descriptin. These sediments are cmpsed almst entirely f sands, with interbedded mudstnes usually absent but ccasinally reaching a few centimetres in thickness. The sands are thin- CONCLUSONS 1. The Sandakan Frmatin cmprises apprximately 2 km f interbedded sandstnes and mudrcks frmerly interpreted as undifferentiated marginal marine facies cntaining little fauna. 2. The Sandakan Frmatin was depsited in a very large marginal marine system shwing a wide range f assciated depsitinal envirnments (Fig. 12). Sedimentary bedfrms and facies assciatins allw differentiatin f fluvial, estu,arine and shallw marine depsits. 3. The discvery f new macrfauna has been used t differentiate the varius envirnments. This fauna includes: bird ftprints and freshwater turtles, several crab species, gastrpds, bivalves and brers, trees, leaves, carbnaceus material and amber cntaining insects. 4. Further wrk will invlve synthesing the data cllected frm the Sandakan Frmatin bth spatially and stratigraphically, in the aim f JuLy 1997

14 (l N ESTUARY MOUTH MANGROVES PALAEOENVRONMENTAL RECONSTRUCTON FOR THE SANDAKAN FORMATON Key t nterpreted Lithfacies Assciatins ( ~ ) Mangrve facies ~) Fluvial Channels facies (3) Delta tp and channel facies (4) Lagnal r interdistibutary facies (5) Shreface facies (~ Skliths Shreface facies C?) Open marine facies Key t ymbls t. Mangrve ~~ Crab ":f.' f~. y TurUe Bird ftprints ~, Bivalves & Gastrpds nsects 1-" Skliths 0 Sand Mud Ophimrpha Water C z :z z :z m r= :r: :D CD C :D -< Figure 12. Palaeenvirnmental recnstructin f the Sandakan Frmatin.

15 THE SEDMENTOLOGY OF MOCENE SHALLOW MARNE CLASTCS OF THE SANDAKAN FORMATON OF EASTERN SABAH 133 develping a sequence stratigraphic mdel t explain the sedimentary evlutin f the frmatin. Faunal data will allw the develpment f a bistratigraphic znatin scheme and help in determining the palaebathymetry f the Sandakan sediments. 5. The data cllected will allw recnstructin f the Micene palaegegraphy f the Sandakan Basin, and crrelatin with adjacent ffshre data. REFERENCES CLENNELL, M.B., The rigin and tectnic significance f melanges in Eastern Sabah, Malaysia. Jurnal f Sutheast Asian Earth Sciences. Special ssue: Orgenesis in actin - Tectnics and prcesses at the West Equatrial Pacific margin, 6,3/4, CLENNELL, M.B., The melanges f Sabah, Malaysia. Unpublished Ph.D. thesis, University f Lndn. CLENNELL, M.B., Far-field and Gravity Tectnics in Micene Basins f Sabah, Malaysia, n: Hall, R. and Blundell, D.J. (Eds.), Tectnic Evlutin f SE Asia. Gelgical Sciety f Lndn Special Publicatin, 106, HNz, K, FRSCH, J., <EMPTER, E.H.K, MANAF MOHAMMAD, A., MEYER, J., MOHAMED, D., VOSBERG, H. AND WEBER, J., Thrust tectnics alng the cntinental margin f Sabah, Nrthwest Brne. Gelgische Rundschau, 78(3), HNz, K AND BLOCK, M., Summary f gephysical data frm the Sulu and Celebes Seas. n: Rangin, c., Silver, Manuscript received 9 June 1996 E.A. and vn Breymann, M.T. (Eds.), Prceeding f the ODP, nitial Reprt, Ocean Drilling Prgram, 124, HUTCHSON, C.S., The Sutheast Sulu Sea, a Negene marginal basin with utcrpping extensins in Sabah. Gelgical Sciety Malaysia Bulletin, 32, LEE, CHA PENG AND THAM, KC., Circular Basins f Sabah. Prceedings Gelgical Sciety f Malaysia Petrleum GelgySeminar,Kuala Lumpur, 1989 (abs.). Bull. Gel. Sc. Malaysia, 29, 54. LEE,D.T.C.,1970.SandakanPeninsula,EasternSabah,Eastern Malaysia. Gelgical Survey f Malaysia, Brne Regin, Bulletin,5,1-75. STAUFFER, P.H. AND LEE, D.T.C., Sedimentlgy f the Sandakan frmatin, East Sabah. Gelgical Survey f Malaysia, Gelgical Papers, 1, TONGKUL, F., Tectnic evlutin f Sabah, Malaysia. Jurnal f Sutheast Asian Earth Sciences. Special ssue: Orgenesis in actin - Tectnics and prcesses at the West Equatrial Pacific Margin, 6, 3/4, TONGKUL, F., Tectnic cntrl n the develpment f the Negene basins in Sabah, East Malaysia. n: Teh, G.H. (Ed)., Gelgical Sciety Malaysia Bulletin 33, Special Publicatin. Prceedings sympsium n the Tectnic framewrk and energy resurces f the western margin f the Pacific Basin, TONGKUL, F., The gelgy f nrthern Sabah, Malaysia: its relatinship t the pening f the Suth China Sea. n: M.F.J. Flwer, X. Kan-Yuan and D.E. Hayes (Eds.), Tectnphysics. Special ssue n "Gelgy and Gephysics f the Suth China Sea and Envirns", 235,1-2, WONG, R.H Sequence stratigraphy f the Middle Micene t Plicene suthern ffshre Sandakan Basin, E.Sabah,Malaysia. Bull. Gel. Sc. Malaysia,33, JuLy 1997