Hoi nghj KHCN 2000 "Nganh Dau khi Viet Nam tnfdc them theky2r
-i CAC TIEU CHUAN CO SINH C O A M Q T SO RANH GICJI DIA T A N G
DE TAM 6 CAC BON T R O N G KAINOZOI VEN BI^N VA THEM LUC DIA VIET NAM
"••• PGS.TS. NguySn Ngge Phan vien Hal di/dng hoc tai Ha Ngi KS. Pham Quang Trung Vien Dau khi
TOM TAT
Thang sinh dia tang tram tich De Tam a cae bon trung Kainozoi ven bien va them luc dia Viet Nam dugc xay dung chii yeu dua tren ca sd cac nhdm hoa thach bao tir phan hoa (palynology) va vi co sinh (foraminifera). Do dd, cae tieu chuan eo sinh dexae dinh cae ranh gidi dia tang a day ehu yeu la eae su kien sinh vat nhu su xuat hien lan dau hay su xuat hien lan euoi (FAD hay LAD), su phat then cue thinh hay su tuyet chiing cua cae dan vi phan loai dac trung eija eae nhdm hoa da ndi tren. Tong hgp eae tai lieu nghien ciru eho thay doi vdi mdi ranh gidi dia tang ton tai eac tieu chuan khac nhau, eu the:
1. Ranh gidi Eoxen • Oligoxen
• Bao tir phan hoa
> LAD cQa cac dang Proxapertites cursus, Striatricolporites undulatus, Thorites termiexinus, Ephedripites ovalis, Classopotlis sp., Plicapollis sp., Trudopollis sp., Kludkiospotites sp. v.v...
> FAD cua cae dang Verrutieolpohtes paehydermus, Gothanipollis bassensis, Liquidambarpollenites minutus, Lyeopodiumspohtes neogenicus, Tritobapollis elipptieus, v.v...
2. Ranh gidl Oligoxen • Mioxen difdi
• Bao tir phan hoa
> LAD eua eae dang'Verrutrieolpohtes paehydermus, Gothanipollis bassensis, Liquidambarpollenites minutus, Lyeopodiumspohtes neogenicus, Thiobapotlis ellipticus, Cicatricosispohtes dorogensis, Corsinipollenites sp.
(Jusiena sp.), Radiapollissp. v.v...
> FAD eiia cae dang Florehuetzia levipoli, Austrobuxus nitidus, Eugeissonia minor, Eehipenporites estalae, Coupenpolis sp. (Arenga sp.), Florsehuetzia semilobata, Stenoehlaena areolaris v.v...
> Suphat then cue thinh eua phan hoa Casuarinidites cainozoieus (trung Nam Cdn San).
• Vi CO sinh
Dudi mUc dia tang xuat hien cua Globoquadhna dehiscens dehiseens (trung Nam Cdn San).
3. Ranh gidi Mioxen difdl - giifa
• Bao tir phan hoa
> FAD eua cac dang bao tir phan hoa Eugeissona insignis, Canthium sp., Camptostemon sp., Cephallomappa sp., Florsehuetzia mehdionalis.
> Su phat trien cue thinh cua bao tir Magnastriatites howardi (trung Ciru Long va Nam Cdn San).
• Vied sinh
FAD dai bieu eua giong Orbulina spp., dudi tang xuat hien eua Paragloborotalia mayeri;
508 «
Hoi nghj KHCN 2000 "Nganh Dau khf Viet Nam tnfdc them theky 21'
4. Ranh gidi Mioxen giifa • tren 'i ^ , ' *• :'r;mc
• Bao tir phan hoa ;:; ^'C n - ! ' : . ; >;.''
> FAD eua eac hoa thaeh Fenestriletes spinosus, Strobilanthidites kundavaensis, Stenoehlaena laurifolia.
Acanthus sp., Anthocensporites spp., Daerydium sp..
> LAD cua phan Florsehuetzia trilobata (trung De Tam Nam Viet Nam). , ; , , . , / - ' ••..---••• ^i^n
• Vicosinh isnoi ,=,, :^ - . i ,• MO^I
> FO cua Neogloboquadrina acostaensis.
. > Su tuyet chiing eiia Paragloborotalia mayeh. , ^^ , , , , , ,^
5. Ranh gidl Mioxen • Plioxen
• Bao tir phan hoa
> FAD eiia phan Impatiensidites previeolpus, Podocarpus imbrheatus.
> LAD eija Tsugapollenites sp. va ndc cua phan Florsehuetzia trilobata (trung Sdng Hong).
• Vicosinh
FO ciia Sphaeroidinella dehiscene dehiseene.
6. Ranh gidl Plioxen • Plelstoxen
• Bao tir phan hoa
> LAD cua Stenoehlaena laurifolia.
> FAD eiia phan Phylloeladus sp..
• Vicosinh
FADcOa Truncorotalia truneatulinoides, su tuyet chiing eua Globigenoides obliquus extremus.
M6OAU
Su phat trien tien hoa don tuyen (khdng lap lai) ciia gidi sinh vat the hien d su phat trie'n huyet thd'ng phat sinh tU dang nay sang dang khae. Mot sd dau hieu de nhan biet ciia qua trinh nay la su xuat hien lan dau va lan cudi eua mot sd don vj phan loai (tU cap phu loai, loai, gidng hay cae cap phan loai cao hon), su phat trien cue thjnh hay phat trien chiem uu the ve sd lupng ca the va su tuyet chiing (bie'n mat hoan toan tren Trai dat) eua mot sd ddn vj phan loai khae la nguyen tac ed ban ciia phudng phap sinh dja tang. Chfnh cae su kien sinh hpe nay la cd sd, tieu chuan de phan chia, lien he dja tang va xac djnh tudi tram tfeh.
Bai viet nay gidi thieu eac tieu chuan cd sinh chfnh eiia mot sd ranh gidi dja tang Oe Tam d cac bdn trung Kainozoi ven bien va them luc dja Viet Nam la bdn trung Sdng Hdng, bdn trung Ciru Long (ca phan ddng bang Nam Bd va them luc dja) va bdn trung Nam Cdn Sdn tren cd sd phan tfeh mau, tdng hdp cac ke't qua nghien cUu eiia hai nhdm hoa da la bao tir phan hoa (thuc vat) va vi cd sinh (nhdm ddng vat triing Id - foraminifera). Do tfnh dac thu eiia dieu kien thanh tao tram tieh d eac bdn trung ndi tren, phan dudi ciia cae mat cat dja chat phat trien ehu yeu la cac thanh tao tram tfeh tudng luc dja va chau thd ven bien, ehi gap cac di tfeh bao tir phan hoa cua thuc vat tren can va thuc vat ngap man ven bien, trong khi dd phan tren cua cae mat cat lai dac trung bang cae tram tfeh tudng bien chifa phong phii hoa thach ddng vat bien va bao tif phan. Do dd, hai nhdm hoa thach nay la nhUng ed sd ehfnh hd trd nhau va bd sung cho nhau trong viec xay
509
Hoi nghj KHCN 2000 "Nganh Dau khi Viet Nam tnfdc them theky 21'
dung thang sinh dja tang dja phuong va khu vue.
Nhd su tien bd eiia khoa hpe ky thuat, gan day nhieu su kien sinh hpe (dac biet la su xuat hien lan dau, lan cudi eiia cae cap phan loai thupc nhdm trung Id) d cae mat cat chuan eiia eac phan vj dja tang Kainozoi d mot sd ndi tren the gidi (dac biet la cac viing bien sau) da dupe xae djnh nien dai tuyet ddi bang phuang phap ddng vj phdng xa (K-Ar, ed tU, v.v...), NhUng sd lieu dja nien dai nay lam tang dp tin cay eua thang sinh dja tang va lam thuan tien cho viec lien he ehfnh xac dja tang khu vue.
Mot phan eua bai viet nay (phan vi cd sinh) la ke't qua eiia Oe tai nghien cUu khoa hpe ma sd 7.2.7
"Dae diem sinh dia tang va co dia ly eae bon trung Kainozoi va cac vung phu can vdi ehung a Viet Nam" ciia Chuang trinh nghien curu ea ban thude ITnh vue eae Khoa hpc ve Trai dat giai doan 1998 - 2000 do Nguyen Ngpe ehii tri va phan bao tir phan hoa la cae ke't qua nghien cifu va tdng hpp eiia Pham Quang Trung. Ke't qua phan tfeh hai nhdm sinh vat ndi tren da dupe lien he va lien ket vdi nhau trong qua trinh nghien cifu sinh dja tang dja phuang va khu vue.
MOT SO NET V£ TiNH HlNH NGHIEN CCTU SINH OjA TANG T R A M TICH DE TAM d CAC BON TRUNG KAINOZOI VEN BIEN VA TH^M LLJC OIA VIET NAM
Ljch sif nghien eUu sinh dja tang eae thanh tao tram tfeh Oe Tam d eac bdn trung Kainozoi ven bien va them luc dja Viet Nam (luc dau chii yeu la viing trung Ha Ndi va bdn trOng Ciru Long) da dupe bat dau tU giUa nhUng nam 60 - 70 eua the ky nay va gan lien vdi ljch sir Oja chat dau khf d nude ta. Mac dii cae tram tfeh ndi tren chifa phong phii hoa thach eiia nhieu nhdm sinh vat khae nhau nhu bao tir phan hoa (Palynology) (1), triing Id (foraminifera) (2), phdng xa triing (radiolaria) (3), triing hat dau (Ostraeoda) (4), tao vdi (nannoplankton) (5), tao silic (Diatomeae) (6), reu ddng vat (Bryozoa) (7), ddng vat than mem (Mollusca) (8), ddng vat da gai (Echinodermata) (9), vet in la thuc vat (10), v.v... Nhung vi eac ly do khac nhau nen mdi ehi ed eae nhdm 1, 2 va 5 dupe nghien euru mot each tuong dd'i chi tiet d eae mife dp khac nhau [1-2, 7-9, 12-13,17-21,24-25], cac nhdm 4, 8 va 10 cung da cd mot sd tac gia ehu y tdi nhung van edn d dang rat sd lupe, eae nhdm edn lai ehi mdi dupe ghi nhan d dang cd mat va ehua dupe nghien eUu. Tuy vay, hien nay mdi ehi cd mot sd ket qua nghien cUu dupe edng bd, mot sd khae van cdn d dang tai lieu luu trU nen viec tham khao sir dung cd nhUng han che nhat djnh.
Dudi gdc dp sinh dja tang, cho de'n nay phan Idn eae nghien cUu ed sinh eiia eae nhdm sinh vat ndi tren d khu vue nghien cUu mdi ehi nham mue dfeh xae djnh tudi tram tfeh va minh hoa ndi dung cd sinh ciia eae phan vj dja tang ehUa chiing, cdn thang sinh dja tang thuc thu (thang sinh dja tang ddi) [13, 19-20] thi mdi ehi dupe bat dau va edn mang tfnh thir nghiem la chfnh do cdn thieu cac nghien cifu ehuyen sau. Oe gdp phan xay dung va hoan thien eac thang sinh dja tang dja phuong (dd'i vdi tUng bdn trung) va khu vue (tdng hop), dudi day xin gidi thieu eae tieu chuan sinh dja tang chfnh ciia mot sd ranh gidi dja tang Oe Tam ciia thang dja tang khu vue.
CAC TIEU CHUAN CO SINH C O A UOT SO RANH GIOI OjA T A N G OE TAM 6 CAC BON T R O N G
KAINOZOI VEN BIEN VA TH^M LUC OIA VIET NAM
Thang dja tang Oe Tam khai quat ciia cac bdn trung Kainozoi ven bien va them luc dja Viet Nam hien dupe sir dung rdng rai gdm eae phan vj chfnh la: Eoxen, Oligoxen, Mioxen dudi, Mioxen giUa, Mioxen tren, Plioxen va phii tren chiing la Oe Tur (hang dau eua Bang 1). Odi vdi mdi bdn trung, thang dja tang gdm eae phan vj dja tang dja phuang khac nhau (thf du bdn trung Nam Cdn Son d Hinh 2). Oae diem tram tfeh va md ta dja tang eua tUng bdn trung ndi rieng va eua toan he thdng eae bdn trung Kainozoi ven bien va them luc dja nude nude ta ndi chung da dupe nhieu tac gia de cap tdi mot each tuong dd'i chi tiet va cd the tham khao dupe mot each d§ dang trong eac van lieu cdng bd va mot phan trong cac tai lieu luu trU, do dd trong bai viet nay khdng nhae lai ma chi de cap tdi cae tieu chuan cd sinh cua mot sd ranh gidi dja tang quan trpng.
Hoi nghj KHCN 2000 "Nganh Dau khi Viet Nam trudc them theky 21'
Cae tieu chuan sinh dja tang eiia eae ranh gidi dja tang d day dupe hieu la eac su kien sinh vat quan trpng danh dau mdc tien hoa ciia cac nhdm sinh vat ma dau an eiia ehung hien cdn ed the nhan biet dupe d eae mUe dja tang khac nhau trong eae mat cat dja chat. Qua nghien eUu, tdng hop cae ket qua phan tfeh bao tir phan hoa va vi cd sinh trong cae gieng khoan d cac bdn trung Sdng Hdng, Ciru Long, Nam Cdn Sdn va eac trung giua niii cho thay rang ddi vdi moi ranh gidi dja tang tdn tai eae tieu chuan cd sinh khae nhau, cu the:
1. Ranh gidi Eoxen - Oligoxen
Ve mat sinh dja tang, d khu vue nghien eUu, ranh gidi nay hien mdi ehi xae djnh dupe mot each tin tudng d pham vi phan phfa Bac bdn trung Sdng Hdng (trung Ha Ndi) va bdn trung Ciru Long tren co sd cac tieu chuan bao tir phan hoa. Cae tieu chuan dd la (Bang 1):
• Su xuat hien lan dau cua cae dang hoa thaeh: Verrutieolpohtes paehydermus (1), Gothanipollis bassensis (2), Liquidambarpollenites minutus (3), Lycopodiumsporites neogenicus (4), Trilobapollis elipptieus (5), Corsinipollenites sp. (Jussiena sp.) (6), Randiapollis sp. (7), v.v...
• Su xuat hien lan cudi eiia eiia cae dang bao tir phan hoa Proxapertites cursus (8), Striatricolporites undulatus (9), Triorites termiexinus (10), Ephedripites ovalis (11), Classopollis sp. (12). Plicapollis sp.
(13), Trudopollis sp. (14), Kludkiospotites sp. (15) v.v...
So sanh vdi eae tai lieu sinh dja tang khu vue thay rang cac dang 1 - 5 deu khdng gap trong Eoxen.
va ehi phan bd han che trong eae tram tfeh Oligoxen d viing bie'n Nam Trung Hoa, khu vue ban dao Ldi Chau thupc vjnh Bae Bd, vjnh Thai Lan [10, 11, Cdng ty dau khi BP, 1981]; eae dang 6 - 7 dTrung Qudc, Lien Xd cu cdn gap d Eoxen, nhung d Viet Nam mdi thay d mUe dja tang tudi Oligoxen; eae dang 8 - 1 5 la cac dang dae trung cho Eoxen, mac dau trong dd ed nhUng dang xuat hien tU Creta nhung cung ehi tdn tai den cudi giai doan nay [10-11,16].
2. Ranh gidi Oligoxen - IVIioxen dudi
Ranh gidi Oligoxen - Mioxen dudi deu gap trong tat ea cac bdn trung nghien curu va dae trung bdi eac tieu chuan sau:
• Bao tir phan hoa
> Xuat hien lan dau (FAD) ciia eac dang hoa thach Florehuetzia levipoli (1), Austrobuxus nitidus (2), Eugeissonia minor (3), Eehipenporites estalae (4), Couperipolis sp: (Arenga sp.) (5), Florsehuetzia semilobata (6), Stenoehlaena areolaris (7) v.v...
> Xuat hien lan eud'i (LAD) ciia cac hoa thaeh Verrutrieolporites paehydermus (8), Gothanipollis bassensis (9), Liquidambarpollenites minutus (10), Lyeopodium- sporites neogenicus (11), Trilobapollis ellipticus (12), Cicatricosisporites dorogensis (13), Corsinipollenites sp. (Jusiena sp.) (14), Radiapollis sp. (15), v.v...
> Su phat trien cue thjnh eiia phan hoa Casuarinidites cainozoieus (16) (trung Nam Cdn Sdn).
Trong cae van lieu bao tir phan hoa dja tang khu vue, su xuat hien lan dau eua eac dang 1 -7 cung dupe coi la eae tieu chuan eiia ranh gidi dja tang giUa Oligoxen va Mioxen d mot sd khu vue nhu Borneo (Indonesia), Natuna, Malaysia, v.v... [10, 15-16], edn eae dang 8 - 15 la nhifng hoa thaeh dac trung eiia Oligoxen va su tdn tai eua chiing deu khdng vudt qua ranh gidi nay.
• Vi cd sinh (Foraminifera)
Su xuat hien lan dau ciia Globoquadrina dehiseens dehiseens. Su kien nay gap han che chii yeu d
Hoi nghj KHCN 2000 "Nganh Dau khf Viet Nam tnfdc them the k^ 21'
phan Ddng Nam bdn trung Nam Cdn Sdn ndi tram tfeh bien Mioxen dudi phat trien rdng rai. Do dac diem mdi trudng thanh tao tram tfeh, d eac khu vue khae eiia bdn trung nay su kien sinh hpe tren thudng xuat hien d mure dja tang cao hon ranh gidi theo bao tur phan hoa.
Nghien eUu su phat trien eiia gidng Globoquadrina, mot sd tac gia da chifng minh dupe rang phu loai Globoquadrina dehiscens dehiseens (1) la ke't qua eiia su tien hoa tU phu loai Globoquadrina dehiscens praedehiseens (2) d phan co sd eiia Mioxen dudi [4 - 5] va su xuat hien ciia nd cung dupe coi nhu mot trong cac tieu chuan ciia ranh gidi Oligoxen - Mioxen d mot sd noi tren the gidi.
3. Ranh gidi Mioxen di/di - Mioxen giiira
Ranh gidi nay ed the nhan biet dupe mot each tuong ddi d l dang d tat ea eac bdn trung nghien cifu theo cae tieu chuan ed sinh nhu sau:
• Bao tif phan hoa
> Su xuat hien lan dau ciia cac dang bao tir phan hoa Eugeissona insignis (1), Canthium sp. (2), Camptostemon sp. (3), Cephallomappa sp. (4), Florsehuetzia meridionalis (5);
> Su phat trie'n cue thinh eiia bao tir Magnastriatites howardi (6) (trung Ciru Long va Nam Cdn Sdn).
NhCfng su kien phan hoa tren cung la nhOng tieu chuan cOa ranh gidi Mioxen dudi - giUa d vung bien Natuna, Borneo, Java (Indonesia) va Malaysia, v.v... [10,15].
• Vi ed sinh (Foraminifera)
Xuat hien lan dau ciia gidng Orbulina ma loai dien hinh cua nd la Orbulina universa. Tieu chuan nay the hien rd rang hdn ea d cac mat cat dja chat ndi cd eae tram tfeh bien phat trien uu the d eud'i Mioxen dudi va dau Mioxen giffa nhu d bdn trung Nam Cdn Son va mot phan d bdn trung Ciru Long. Su kien nay dupe cdng nhan rdng rai trong van lieu dja tang khu vue va the gidi la mdc ciia ranh gidi Mioxen dudi - giUa [3 - 5, 14,22 - 23,26,33] va ed nien dai tuyet dd'i la 15,5 -16 trieu nam each ngay nay [14,33].
4. Ranh gidi Mioxen giCira - Mioxen tren
Ranh gidi nay d eac bdn trung Kainozoi ven bien va them luc dja nude ta dupe xac djnh bang cae tieu chuan sinh dja tang sau :
• Bao tif phan hoa
> Su xuat hien lan dau cua cac hoa thach Fenestriletes spinosus (1), Strobilanthidites kundavaensis (2), Stenoehlaena laurifolia (3), Acanthus sp. (4), Anthoeerisporites spp. (5), Daerydium sp. (6).
> Su xuat hien lan eud'i ciia phan Florsehuetzia trilobata (7) (trung Oe Tam Nam Viet Nam).
Theo eac tai lieu sinh dja tang khu vue thf su xuat hien lan dau ciia cac dang 1, 4 deu dudc ghi nhan d phan co sd eua cae tram tfeh Mioxen tren d vung bie'n Natuna, Borneo (Indonesia); ciia cac dang 2 - 3 va 5 d phan thap nhat eua eac mat eat tram tfeh Mioxen tren d viing vjnh Thai Lan, Sabah (Malaysia), Mianmar, Bangladesh, v.v... Su xuat hien lan cudi ciia dang 7 thay d Java, Kalimantan, Natuna, Borneo, v.v...
• Vi ed sinh (Foraminifera)
> Sir xuat hien lan dau cua loai Neogloboquadrina acostaensis;
512
Hoi ngh j KHCN 2000 "Nganh Dau khi Viet Nam trifdc them theky 21'
Bang 1. Cac dang bao tir phan hoa chfnh trong tram tfeh Oe Tam d Viet Nam
H o a d a b a o tiSf ptUfn
PentapoUenites sp.
AraucariacUes australis Aquilapottenltes sp.
Spizonocolpiles baculatas Proxaperites cursus
Ephedripites avails.
Triorites termiexinus Plicapollis sp.
Classopollis sp.
Sporopottis sp.
Striatricolporites undulatus Trudopollis sp.
Klukiosporites sp.
Uquidambarpottenites minutus Gothanipollis bassensis
Trilobapollis ellipticus Verrutrieolporites paehydermus Lycopodiumsporites neogenicus Randiapollis sp.
Corsinipollenites sp. (Jussiena sp.) Cicatricosisporites dorogensis Margocolporites vanwijhei AInipollenites verus Florsehuetzia trilobata Tricolpollenites sp. (Retitricolpo.) Tsugapollenites sp.
Ephedripites sp.
Florsehuetzia levipoli F. meridionalis F.semilobata Pinuspollenltes sp.
Crassoretitriletes nanhaiensis C. vanraadshooveni Canthium sp.
Cephalomappa sp.
Camptostemon sp.
Eugeissona insignis Acanthus sp.
Penestrites spinosus Strobilanthidites kundavaensis
Anthoeerisporites spp.
Daerydium sp.
Stenoehlaena laurifolia Impatiensidites previeolpus Podocarpus tmbricatus Phylloeladus sp.
Eugeissona minor Austrobuxus nitidus Couperipollis sp.
Echiperiporites estalae Stenoehlaena areolaris
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514
Hoi nghj KHCN 2000 "Nganh Dau khi Viet Nam trudc them theky 21'
> Sir bien mat hoan toan (tuyet chiing) ciia Paragloborotalia mayeri va Fohshella fohsi. •' '•' N. acostaensis la loai ehi'thj cua ddi N16 eiia thang sinh dja tang ddi eiia Blow [4]. Odi nay nam d day Mioxen tren va ed mat d hau het cac bdn trung Kainozoi thude dai nhiet ddi va can nhiet ddi eua Trai dat hien nay. Nien dai xuat hien lan dau eua gidng, loai nay theo eac tac gia l<hae nhau giao ddng trong l<hoang 9,1 -10,2 trieu nam trude day [14, 23, 33] (nien dai nay cung la nien dai ciia ranh gidi Mioxen dudi - giUa eiia thang dja tang thdng nhat), trong khi dd, thdi diem xuat hien lan eud'i ciia Par. Mayeri la 10,4 trieu nam
va hoan toan tuyet chiing d ranh gidi tren. . . , . ! . 5. Ranh gidi Mioxen tren - Plioxen
Ranh gidi nay d cac bdn trung nghien ciiru dudc xac dinh theo cae tieu chuan cd sinh sau :
• Bao tir phan hoa ' • ••'•' t,
> Xuat hien lan dau eua phan Impatiensidites previeolpus (1), Podocarpus imbrrieatus (2);
> Xuat hien lan eud'i eiia cae dang Tsugapollenites sp. (3) va ndc eiia phan Florsehuetzia trilobata (4) (trung Sdng Hdng).
Trong eae van lieu dja tang khu vue, loai 1 gap lan dau d phan co sd ciia cac mat cat tram tich Plioxen d viing bien Natuna va Borneo (Indonesia), loai thU 2 d khu vue vjnh Thai Lan, Sabah, Myanmar, Borneo va Bangladesh; cae dang 3 - 4 xuat hien lan eud'i d mire ranh gidi dja tang Mioxen - Plioxen ciia cac khu vue khac nhau d Odng Nam A (Borneo, cira sdng Chau Giang, v.v...).
• Vi cd sinh (Foraminifera)
Xuat hien lan dau ciia phu loai Sphaeroidinella dehiseens dehiseens, ehii yeu d bdn trung Nam Cdn Sdn. Oay la dang hoa thaeh chi dao dja tang eiia ddi N9 (ciia thang dja tang ddi eiia Blow, [4]) d phan co sd ciia Plioxen thude vung bien An Op - Thai Binh Duong. Nien dai tuyet ddi ciia su kien nay giao dpng trong khoang 4,8 - 5,1 trieu nam each ngay nay [14,23,33].
6. Ranh gidi tren cua Plioxen H Tieu chuan cd sinh ciia ranh gidi nay d eae bdn trung nghien curu la :
• Bao tir phan hoa
> Xuat hien lan cudi cua hoa thaeh phan hoa Stenoehlaena laurifolia (1).
> Xuat hien lan dau cua phan Phylloeladus sp. (2).
0 eac khu vue vjnh Thai Lan, viing bien Natuna/Sarawak, Java, Kalimantann, Borneo, Myanmar, Trung Qudc, An Op, v.v... dang 1 cung ehf gap d mUc dja tang eao nhat la dinh ciia eae mat cat tram tfeh Plioxen.
• Vi cd sinh (Foraminifera)
Xuat hien lan cudi va tuyet ehung ciia dang lobigerinoides obliquus extremus (1). Cung d khoang mire dia tang nay bat dau xuat hien mot loai rat dac trung ciia he Oe TU la Truncorotalia truneatulionoides (2). Cac su kien nay gap phd bie'n hon ca d bdn trung Nam Cdn Sdn.
Nien dai cua su kien 1 la 1,8 trieu nam va nien dai ciia su kien 2 la khoang 1,9 trieu nam trude day [23]. Nhu vay, ca hai su kien sinh hpc tren deu nam trong 1,8 - 2,0 trieu nam la nien dai eiia ranh gidi Neogen - Oe TU theo hoa thaeh Odng vat dupe eae nha nghien curu vi cd sinh sir dung khdng chi d khu vue
515
Hoi nghj KHCN 2000 "Nganh Dau khi Viet Nam trudc them theky 21'
An Op - Thai Binh Duong ma edn d nhieu noi tren the gidi.
TAX Ll£U THAM KHAO
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