lembangan sedimen Kuaterneri di kawasan Olak Lempit - Banting Selangor, Malaysia ... Gula dan Simpang yang menindih batuan sedimen Formasi Kenny Hill.
Sains Malaysiana 36(2)(2007): 159- I 63
An Integrated Geophysical Study of the Quaternary Basin at Olak Lempit - Banting Area, Selangor, Maiaysia (Kajian Geofizik Bersepadu Lembangan Kuaterneri di Kawasan OIak Lempit
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Banting, Selangor, Malaysia)
Asour- RnHriur SeH,tsuotN, Ut,tnR HauzrH
a ZuRetoAH RAMLI
ABSTRACT
Atr integrated geophysical study was conducted to itwestigate tlrc subsurfoce regional structure and tlte presence of a Quatenmry setlintentary basin in tlrc Olak Lentpit - Banting area of Selartgor, MaLaysia. A regiotnl grattity sur-vey and the high resoltiiort reflectiort seistttic were etrtployed to deternitrc the tlichtess and areal distribution of the alluvial sedintentary basin as yveLL as to inttestigate tlrc depth and topograplry of the bedrock in the study area. Tlte sedinrcntary basit hosts one of tlte rttost intportari coastal alluvial aquiftr wliclt was used lo caler llte slrcrtage of dotnestic water supply during :lte worst water crisis tlnt ltit Ilte state of Selartgor irr 1998. Tlte surface geological. trtap slrov,s tltat itt general 707a of the sttrdy area is coverecl by Quntentatl deposits of Beruas, Gttla and Sirnpang Fornntiorts wliclt overlie the sedintentary bedrock of Ketuty H ill Fornntion. The Bertns Forrnatiort corisis/s of nminly clay, sattcly clay and peat of Holoceneflut,iatile-estuarine deposits, wlrcreas the Gula Fontnliorr represettts Holocette nrcrine to estuarine sedintents which ntostly consists of clay and ninor sand. Tlrc Sitttpang Fonnation (Pleistocene) is a cotrtittetttal deposit conrprising of gravel, sand, clay and silt. Tlte tnderlying Kenny Hill Fornntiort cottsists of a nlottotot'tous sequence of interbedded slnles, ntudstones and sandstotrcs. Tlrc rock is Carbonaceous irt age artd it fornts an tutdulatittg surface topography in tlrc eastent part of tlte study area. A total of t2l grat,ity stations were established usittg a La Coste & Rontberg gravity nrcte r and the elevatiotts of ntost of the statiotts were deterntined barontetrically using Tienrun-Wallace altimeters. The high resolutiort seisnic reflectiott using the contnon ntid poittt (CMP) or roll alottg teclutiqLre was carried out Ltsing a24 chanrtel signal ertlnncentenl seisnrcgraph and ltighfrequency geopltones. A total lertgtlt of abotLt 1.7 littt stacked seistttic section ltas beert accltLirecl itt tlis survey atrd a nearby borelrcle dara was used for itierpretatiott. A relatiye Bougr,ter anotrnly nnp slrcws an elortgated zotte of low grat,ilry anonraLy trettdirtg approxitrrutely NW-SE wlich is interpretetl to be tlrc depositiort center of tlte Quatennry basin. Tlte itterpreted gravity profiles rututing across the central area of tlte study area slnw tltat tlte basin lms tlickttess t,aries frorn lentll to several lruttdred ttrcters witlr tnaxintuttr depth to bedrock of about 27 5 nt. A grat,ity profile which passes tlrough tlrc eastent edge of tlrc basin was ntodeled witlt clepth to bedrock of about I78 nt beLow growtd wli.clr agrees t,ery welL witlt tltose obtaitted frotn Ilrc itierpreted seicnic sectiort and borelnle data. Tlrc stacked seistrtic sectiotl slrcv,s several high antplitude parallel to sub-paralleL reJlectiort overlying discorttitruos and low reflectiott pattent. Reflectiotts on tlrc eastern part of the sectiotl is nruch shallower thart the one observed on the westeilt part wlich clearly irtdicates tlrc presertce of basitnl slrltctlLre witlt a total itierpreted depth to bedrock of about 200 nteters.
Keywords: Quatentary basirt; seistnic sectiort; gravity ntodelirtg; subswface structure ABSTRAK
Penyiasatan geofizik bersepadu telalt dijalankan Luiuk ntengkaji struktur rantau bawah perntukaan dan kewuiudan lenrbantgan sedinten Kuatenteri di kawasan Olak Lentpit - Bantittg Selattgor, Malaysia. Sun,ei graviti rantau dan seisnns pantulan beresolusi titlggi telalt digutnkan utiLtk nrcnetltukatt ketebalan dan keluasart letrtbangan sedintett aLuviunt serta ntengkaji kedalarttatt dan topografi batuan dasar di kawasatt kajian. Lentbangan sedinrcrt ini nterupakan akuifer aluviuttt pantai pentin7 yang digutnkatt utttLtk nrcnantputg bekalan air sennsa berlakaqta krisis air terburuk di negeri Selangor pada tahwt 1998. Peta geologi tttertuttjLLkkatt kawasan kajiatr terdiri daripada 7)Vo etrclcrpau alut,itLrrt kLrcLtertrcri daripada Fornmsi Beruas, GLLIa datt Sitttparrg ),atrg rrtertittclilt batuan sedinrctt Forrrrusi Kettuy HiLl. Fonnasi Beruas itti kebanyakanttya nterupakart letnpLutg, lempL.tttg berpasir dart ganrbut daripada seditnen fluviatil-estuaritt yartg berusia Holosen, nrutnkala Fortrrusi Gula pula nterupakatt seditnett ntarirt-estLtarinl,alrt kebatryakatutya tercliri daripada lentpurtg dan sedikit pasir Fornnsi Sintpang pttla (berusia Pleistosett) nteru.pakut ettdapatt beruta 1,attg terdiri claripada gravel, pasir, lentpurry dan lodak. Batuan dasar Fonnasi Ketuty Hill terbentuk daripada selang lopis batu syal, batu luntpur and batu pasir Batuan irti berusia Karbort dan ntentbenruk tupografi. batvalt perntLrkaart beralutt di balmgian tintur kawasan kajian. Sebanyak l2l stesett graviti telalt diukur nrcttggwnkan nrcter graviti La Coste & Rotr$erg datt kethrygiatt kebanyakan stesert diletiLLkatt dengan trrcnggrunkan baronteter Tiennn-Wallace. Suryei seisruos pantulan beresolusi
