eiA TRiNH VIET NAM

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Hoi nghj KHCN 2000 "Nganh Dau khi VietNam tnfdc them theky2r

eiA

TANG VA QUA

TRiNH

PHAT TRIEN TRAM TICH DE TAM THEM LUC DIA

VIET NAM

KS. Do Bat Vien Dau khi

TOM TAT

Trong nhifng nam gin day, cung vdi suphat then eua dia chat diu khi, nghien cim dia ting trim tieh De Tam a them luc dia Viet Nam da duge then khai deu khap. Ket qua phan chia dia ting eiia eac be da dugc ehinh ly bo sung bang to hgp cae phuang phap nghien cffv chuyen sau ve dia ting nhu thaeh dia ting, sinh dia ting, dia chan dia ting va thdi dia ting ma theo dd cae dan w dia ting tuang ffng cua cae be Sdng Hong, Cffu Long, Nam Cdn San va Ma Lai

• Tho Chu da dugc xac lap.

Cae tac gia da lien he dia ting giffa eae be va khu vffc phu can nhan thiy rang trudc khi hinh thanh cac be trim tieh De Tam la thdi ky san bang kien tao (Paleoxen), ddng thdi da khai quat lich sff phat then trim tieh De Tam them luc dia Viet Nam theo eac giai doan:

• Giai doan hinh thanh va phat then eae be trim tieh De Tam (Eoxen, Oligoxen).

• Giai doan phat then va md rdng eae trim tieh De Tam (Mioxen sdm, giffa).

• Giai doan xoa nhoa va thu hep cua bdn trung (Mioxen mudn).

• Giai doan hinh thanh them lue dia Bien Ddng (Plioxen).

Bao eao cung de cap den mdi quan he giua cae giai doan phat then va sff hinh thanh tieh tu diu khi.

M d O A U

Nghien cifu dja tang tram tich Oe Tam them lue dja Viet Nam gan lien vdi edng tac dieu tra tim kiem - tham dd - khai thae dau khf trong toan khu vue va da dat duge nhung ke't qua dang khfch le. Dac biet trong nhung nam gan day, cung vdi viec ap dung edng nghe tien tien trong tfnh vue dau khi, nghien curtJ dja tang da duge day manh, nhieu finh vue ehuyen sau ve dja tang da dugc chu y ap dung ddng bd d Viet Nam nhu:

thach dja tang, sinh dja tang, dja chan dja tang va thdi dja tang.

Sir dung td hgp cac phuang phap dd da eho phep dieu ehinh, loai bd mdt sd dan vj dja tang khdng cdn phii hgp, da chinh xac khdi lugng, ranh gidi, dac diem cua cac dan vj dja tang khac, ddng thdi cung lap nen mdt sd dan vj dja tang mdi, nhd dd cdt dja tang tram tfeh De Tam cua cac be Sdng Hdng, Phu Khanh, Ciru Long, Nam Cdn San, va Ma Lai -Thd Chu ngay cang dugc hoan ehinh, gdp phan lam sang td ljeh sir phat trien dia chat ciia cac be va trong toan khu vue, tU dd tim ra md'i quan he giua chiing vdi su hinh thanh va tich tu dau khi.

Oen nay ke't qua nghien eiru dja tang tram tieh De Tam them lue dja Viet Nam cd the dugc the hien theo cae bang tdng hgp dudi day:

Bang 1: Cae ddn vj thaeh dja tang - sinh dia tang - dja chan dja tang va thdi dja tang cua be Sdng Hdng Bang 2: Cae ddn vj thaeh dja tang - sinh dia tang - dja chan dja tang va thdi dja tang eua be' Curu Long Bang 3: Cae ddn vi thach dja tang - sinh dia tang - dja chan dja tang va thdi dja tang ciia be Nam Cdn San Bang 4: Cae dan vj thach dia tang - sinh dja tang - dia chan dja tang va thdi dja tang ciia be Ma Lai - Thd Chu.

Nhung bife tranh dia tang neu tren ciia cac be da tao nen su lien ke't tdng hgp giUa chiing vdi nhau

92

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Hoi nghj KHCN 2000 " Nganh Dau khi Viet Nam trffdc them theky21'

cung nhu giifa chiing vdi cae viing phu can. Chinh chiing da cho ta khai niem ve sir hinh thanh va phat trien cua tram tich De Tam, mdt qua trinh gan lien vdi su hinh thanh va phat trien ciia dja chat Bien Ddng. Qua trinh da dang va thu vj nay cd the dugc khai quat nhu sau:

1. Giai doan san bang kien tao trirdic khi hinh thanh cac be tram tich De Tam (Paleoxen)

Tram tfeh Paleoxen hau nhu khdng phat hien thay d them luc dja Viet Nam. Dieu dd phii hgp vgi nhan djnh rang: Paleoxen la thdi ky san bang kien tao mang tinh chat khu vue, do la ket qua ciia hoat ddng nang len va bj bdc mdn cua nhUng pha cudi eiing ehu ky tao nui Yen San. • - •. ' " ;

0 day, Paleoxen chinh la thdi ky ehuyen tiep giua hai giai doan van ddng tao niii Yen San (Jura - Creta - Paleoxen) va Hymalaya (Eoxen - Oligoxen - Neogen). Ket qua da dugc phan anh bang hai phire he kien true hoan toan khac nhau: phire he dudi (mdng ciia tram tich De Tam) lien quan den eae thanh tao Paleozoi - Mezozoi, bj udn nep, bien vj manh, va phUe he tren (tram tich De Tam) bao gdm cac tram tieh luc nguyen, luc nguyen vdi Kainozoi it bj bie'n vj va phat trien lien quan chat ehe vdi su hinh thanh phat trien cua cac bdn trung tren them. ; • • .|

2. Giai doan hinh thanh cac be tram tfeh De Tam (Eoxen-Oligoxen) i \ Vao dau Eoxen, do anh hudng eua cac pha dau van ddng tao nui Hymalaya, cac dirt gay sau cd

phuang Tay Bac - Odng Nam dugc hinh thanh tU trudc Oe Tam tiep tue hoat ddng trd lai, trong dd ed cac dirt gay Sdng Ld, Sdng Hdng, Sdng Hau, tao nen nhUng dja hao hep nhung rat sau dugc lap day bdi nhUng tram tfeh vun thd kieu molat (cudi, san ke't, eat ke't da khoang mau tfm dd he tang Phii Tien va Ca Cdi) cd be day ldn phan anh mure do phan dj dja hinh cao va nang lugng tram tfeh manh. Ke't qua cua nhifng hoat ddng kien tao kieu nay lam cho luc tach gian ngay cang manh, va de'n Oligoxen, hoat ddng cua he thd'ng durt gay sau theo phuang Ddng Bac - Tay Nam (Vung Tau - Cdn Sdn) cung tang. Cac hoat ddng tach gian eua Bien Ddng da md ra eae bdn trung eiia them luc dja va duge ngan each bang eac ddi nang khu vue. Nhu vay, thirc te la eae tram tich Oligoxen da dUge thanh tao ddng thdi vdi qua trinh tach gian va sut liin.

6 mien vdng Ha Ndi, cac tram tich De Tam dugc thanh tao trong dieu kien lue dja va phat trien thanh cac dai hep ciia cac tram tfeh lue nguyen thd d phfa Bae va ria Ddng Bac, cdn cac tram tich mjn thudng la set giau vat chat hCfu cd sinh dau (tang da me DAM1) thanh dai hep chay tU Trung tam de'n Id 103 rdi theo hudng keo dai ra Trung tam ciia be. Chung duge thay the dan bdi tudng eat, bdt ke't ven bd.

6 phan them luc dja mien Trung, eae thanh tao Oligoxen thudng lien quan de'n cae tudng tram tich dam lay va ven bien, nam ben canh cac khdi nhd cao. Cac tram tich set mang nhieu tinh bien, ed kha nang la cac tang sinh, chay thanh hai dai khdng lien tue tU Id 112- 114vatU115- 118keoxud'ng119-120.

Trong khi do d bdn trung Ciru Long, hoat ddng sut lun manh dan tU Tay Nam len Ddng Bae, hinh thanh 3 ddi tram tfeh ke tiep nhau: tU tam giac chau ehju anh hudng nhieu eua sdng hd de'n ddi trung gian va cudi Cling la ddi tam giac chau ehju anh hudng nhieu eua bien ehura vat chat hUu ed sapropen, dd la ngudn gdc tao nen eae tap da sinh dau DAMOLISAP (phan bd d Trung tam va phan Ddng Bae cua be). Cdn phan than cat phat trien trong cac tram tiqh delta cd do rdng tdi 10-20% ehinh la cae da chifa quan trgng.

Khae vdi bdn trung Ciru Long, bdn trung Nam Cdn San, vao thdi ky Paleoxen ed nhUng sut sau han thdng vdi bien md, vi vay tram tfeh Oligoxen d day chang nhUng dae trung bdi tudng ldng sdng bai bdi va chau thd (d phia Tay) ma cdn dae trung bdi tudng ven bien chira vat chat hifu ca sinh dau (DAMOLI) d Trung tam va phfa Ddng cua be'. Cac da chira lien quan de'n eac than cat cira sdng va tien delta d ria phia Tay eua be. Tuy nhien day eung ehi la cae da chira ed do rdng tU trung binh de'n kem (do rdng 10-15%).

Nhu vay vao thdi ky Eoxen - Oligoxen, cac thanh tao tram tich duge hinh thanh cung vdi qua trinh sut lun gay ra bdi cac hoat dgng tach gian d Bien Odng. Do dja hinh thay ddi va lun ehim khae nhau da tao nen

93

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Hoi nghj KHCN 2000 "Nganh Dau khi VietNam trffdc them theky 21'

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96

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97

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Hoi tighf'KttCN'aoBO' ''NganftD^ khliWit Nem trade tt^rrrtMl^zr

nhung sir thay ddi tirdng td sdng hd den tam giac chau ven bien. Day la nhOng phirc he tram tich ddng tao rifta. Qua trinh nay ket thuc bang ehuyen ddng dueng, tao nen be mat bao mon khu virc quan sat thay tren them luc djava khu virc phu can., ,

• / • • " ' ; I.'••:.' r , ^ ! T - - , r ' ; . / ^ p , j ! j / ; ^ ^ c H i ;

3. Giai doan phat trien va md rong cac be tram tich Oe Tam (Mioxen sdm - giu'a)

Nhir da ndi d tren, sau giai doan tao rifta ve ca ban cac bdn trung va cac dai nang tirang ddi va cac cae hd sut da dirac hinh thanh. Hoat ddng cd tinh chu ky trd lai ciia tao nui Hymalaya vao dau Mioxen sdm da tac ddng gay anh hudng den cae chuyen ddng nang len va ha xud'ng mang tinh khu virc. Qua trinh sut lun, oan vdng cua cac bdn trung da dirge hinh thanh trong Oligoxen nay lai tiep tue md rdng cung vdi cao trao bien tien khu virc. Tram tieh Mioxen sdm da phii chdng gdi tren eae tram tich Oligoxen va ehju anh hudng ke thira be mat dia hinh da dirac tao lap vao eud'i Oligoxen.

Dac diem eiia tirdng tram tieh Mioxen sdm - giifa ehii yeu la cac thanh tao luc nguyen va lue nguyen cacbonat trong dd cd ehda cac hoa da ddng vat bien (triing Id va Nannoplankton). Rd rang chung dirge thanh tao ti;png dieu kien delta, bien ven.bd va bien ndng. Tuy nhien, sir tien hoa tram tich trong tirng bdn trung cung dirge phan anh vdi mirc do khae nhau.

6 bdn trung Sdng Hdng va Ciru Long, qua trinh phat trien cac tram tich mang nhifng net tirang tu, cac pha bien tien tang dan tir Mioxen ha de'n Mioxen trung, xen vdi cac tram tich delta va bien tran vao ciing vdi sir md rdng ciia tam giac chau, va cao trao bien tien rdng rai hinh thanh Idp Rotalid (d trung Ciru Long) va Ammonia (d trung Sdng Hdng).

6 bdn trung Hue - Quang Da va Nam Cdn San, tram tieh bien ven bd, bien ndng lai chiem iru the.

Qua trinh phat trien cua cac tram tich tudng da vdi bien ndng da tao thanh eae ddi lien quan de'n nhifng khdi nang trong bien md, sach va khi hau ndng am, keo tir Id 115 de'n Id 118-119 (trung Hue-Quang Da) hayd khu virc tiep giap giifa Id 04 - 05 va phia Tay cua Id 12 (bdn trung Nam Cdn San).

Giai doan phat trien va md ron^ bae bdn trung De Tam da tao nen nhifng tang chira dau khi quan trpng, dd la nhifng doi eat, than cat lien quan den cac tram tfeh cira sdng, hoac tien chau thd trong cac tram tieh trudc delta. Mat khae, tan*g ehda cd y nghTa khdng kehi ptian quan trgng, trong dd la eae khdi da vdi nirt ne, lien quan den eac tram tich vdi am tieu bien ndng nhir da J<e tren.

4. Giai doan xoa nhoa - thu hep cac be tram tich Oe Tam (Mioxen muon)

Vao thdi ky Mixen mudn, mat cat tram tieh tirdng tam giac chau va bien ndng bj thu hep dan, thay vao dd la cac tram tieh luc dja (nhif Tien Hung), hoae tinh luc dja ngay cang tang (nhir he.tang Ddng Nai). Cac tram tich delta va bien ndng thu hep dan, ehi cdn thay d Trung tam bdn trung Sdng Hdng (ngoai khai), trung Hue - Quang Da, Trung tam bdn trung Ciru Long va bdn trung Nam Cdn San.

Uld

Cae da chira thude Mioxen tren chii yeu la tudng Idng sdng, bai bdi, dap eat cira sdng, doi cat thuy trieu Va tudng eat tien chau thd, bien ndng. Day la cac tang ehda tdt ddng thdi cung la cac ddi tugng quan trgng trong lirti kiem - tham dd dau kh'r, bdi vi ngay tren chiing la tang set chan khu virc (he tang Bien Ddng).

' t ' t d le'giai doan nay lien quan den cae chuyen ddng nang trong toan khu virc, tao nen be mat bao mdn giifa Mioxen giCfa va Mixen tren, ddng thdi tao nen phan Idn nhifng udn nep trong Neogen.

Giai doan Mixen mudn cd the xem la giai doan xoa nhoa hoat dgng md rdng cua cac bdn trOng tao nen be mat bao mdn phd bien d them luc dja Viet Nam.

5. Giai doan hinh thanh them luc dja (Plioxen)

Vao thdi ky Plioxen, hoat dgng bien tien bat dau anh hirdng va phat then rdng khap khu virc Bien Ddng.

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Hoi nghj KHCN 2000 "Nganh Dau khi Viet Nam trffdc them theky2r

Tram tich Plioxen, phii tren mat bao mdn nhir mdt bat ehinh hgp gde dac tri/ng, chiing bao gdm cat, bdt xen- ke, gan ke't y^'u den bd rdi ehda Glaueonit va vd ciing phong phu hoa da ddng vat bien (Foraminifera va Nannoplankton). Cac tap tram tieh the hien rd dae tinh phan Idp nghieng, thoai, song song hoac xien cheo vdi chieu day tang dan ve phia Trung tam va dirge md rdng virgt ra khdi khudn khd eac be.

Tirdng tram tich bien cung phan thanh nhifng ddi rd ret, chu yeu la them bien ndng, trong dd bdn trung Sdng Hdng va Cdu Long chii yeu la ddi trong va giifa ciia them edn d be Hue - Quang Da cd sif xen ke nhirng chu yeu la ddi giifa va ngoai.

Cd the ndi rang toan bd them luc dja Viet Nam ed sg thd'ng nhat va phat then trong thdi ky Plioxen:

dd la giai doan phat trien them luc dja, san bang, xoa nhoa cae anh hudng eiia hoat ddng dja chat trudc day, tao nen su thdng nha't ciia them luc dja Bien Ddng va khu vue Odng Nam A.

Tdm lai, ljch sir phat then tram tieh Oe Tam them luc dja Viet Nam gan lien vdi qua trinh hinh thanh va tach gian Bien Odng tao nen eac bdn trung bao gdm 4 giai doan lien quan de'n cac hoat ddng chinh: , ,^.,

• Cac hoat ddng tach gian bien Odng va tao cac bdn trung. ... _ ;, .

• Cac hoat ddng oan vdng md rdng va phat then cLia cac bdn trung. ' " • " '••:'^-'

• Cac chuyen ddng nang khu vue, phan cat va anh hudng thu hep eac bdn tram tich.

• Thanh tao them luc dja thd'ng nhat (Bien Odng), bien tie'n trong toan khu vue them luc dja Viet Nam.

TAI LIEU THAM KHAO

1. Od Bat, Phan Huy Quynh va n.n.k., 1983. D\a tang va lien he dia tang tram tich De Tam mien vdng Ha Ng/. LuutrdVOK.

2. Od Bat, 1987. Dia tang tram tieh Kainozoi be CCru Long them lue dia CHXHCN Viet Nam. Luu trd VDK.

3. Od Bat, 1993. Dia tang tram tich De Tam them lue dia Viet Nam. Luu trif VDK.

4. Le Van Cu, 1985. Cau triie dia chat va trien vgng dau khi viing bien Thuan Hai-Minh Hai. Luu trif VDK.

5. Phan Trung Dien, 1999. Phan tich va md hinh be Sdng Hdng. Luu trtf VDK.

6. Nguydn Quy Hiing, 1997. Minh giai tai lieu dia vat ty khu vffc nham nghien cffu eau triie dia chat va danh gia then vgng dau khi khu vffc quan dao Hoang Sa va phan mien Trung. Luu trO VDK.

7. Le Nhu Lai, 1995. Cau triic bien Ddng va luc dia trung Ddng Dffang. Cac cdng trinh nghien edu bien.

8. Phung Sy Tai, 2000. Dia chat va tiem nang dau khi tram tieh De Tam them lue dia Tay Nam Viet Nam.

Luu tru VDK.

9. Tdng Duy Thanh, Oang Vu Khiic, 1994. Quy pham dia tang Viet Nam. Luu tru cue Dja chat Viet Nam.

10. CCOP 1994. Souf/)Easf/As/ased;menfaryfaas/>i. CCOP. - i , . ,,..,,:., ,..,„^.

11 J. Lowe and A. Wonder, 1993. Application of biostratigraphy to sequence stratigraphic analyses in the offshore Cenozoic of Viet Nam, BP.

12 Tung - YI Lee, Lawrence A. Lower, 1995. Cenozoi plate reconstruction ofS.E. Asia. Tectonophysies - 251.

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