庫(kù)車盆地古-新近紀(jì)蒸發(fā)巖沉積對(duì)喜馬拉雅構(gòu)造運(yùn)動(dòng)期次的響應(yīng)①

曹養(yǎng)同 楊海軍 劉成林 顧喬元 焦鵬程 盧玉紅

(1.中國(guó)地質(zhì)科學(xué)院礦產(chǎn)資源研究所 北京 100037; 2.塔里木油田公司勘探開(kāi)發(fā)研究院 新疆庫(kù)爾勒 841000)

庫(kù)車盆地古-新近紀(jì)蒸發(fā)巖沉積對(duì)喜馬拉雅構(gòu)造運(yùn)動(dòng)期次的響應(yīng)①

曹養(yǎng)同1楊海軍2劉成林1顧喬元2焦鵬程1盧玉紅2

(1.中國(guó)地質(zhì)科學(xué)院礦產(chǎn)資源研究所 北京 100037; 2.塔里木油田公司勘探開(kāi)發(fā)研究院 新疆庫(kù)爾勒 841000)

庫(kù)車盆地在古-新近紀(jì)時(shí)期發(fā)育巨厚的蒸發(fā)巖沉積,自下而上蒸發(fā)巖沉積地層主要有:古近系的庫(kù)姆格列木組、蘇維依組;新近系下部的吉迪克組,依據(jù)部分鉆井剖面資料,可識(shí)別出5個(gè)蒸發(fā)巖沉積旋回。庫(kù)姆格列木時(shí)期巨厚的蒸發(fā)巖沉積(Ⅰ1、Ⅰ2沉積旋回期)是燕山后期相對(duì)寧?kù)o的大地構(gòu)造環(huán)境反映;蘇維依時(shí)期蒸發(fā)巖沉積(Ⅰ3沉積旋回期)在巖性、沉積范圍上發(fā)生明顯改變,反映了早喜馬拉雅構(gòu)造環(huán)境下的不穩(wěn)定沉積,吉迪克早期巨厚的鹽、膏沉積(Ⅰ4沉積旋回期)及沉積區(qū)域的繼續(xù)遷移則反映了早喜馬拉雅構(gòu)造影響仍然存在但已經(jīng)減弱;吉迪克中期(Ⅰ5沉積旋回期)蒸發(fā)巖沉積結(jié)束,鹽湖沉積轉(zhuǎn)變?yōu)殛懺此樾紟r夾薄層石膏沉積,以砂、礫為主的山麓相沉積指示了當(dāng)時(shí)山體抬升、遭受剝蝕、快速堆積的沉積環(huán)境,反映了相對(duì)活動(dòng)的大地構(gòu)造環(huán)境,是中喜馬拉雅構(gòu)造運(yùn)動(dòng)時(shí)期的開(kāi)始?？梢?jiàn),庫(kù)車盆地的蒸發(fā)巖沉積與喜馬拉雅構(gòu)造運(yùn)動(dòng)有較好的對(duì)應(yīng)關(guān)系,是大區(qū)域的構(gòu)造運(yùn)動(dòng)在小區(qū)域范圍內(nèi)的地質(zhì)事件反映。

庫(kù)車盆地 蒸發(fā)巖 喜馬拉雅構(gòu)造期次 響應(yīng)

0 引言

在整個(gè)地質(zhì)歷史時(shí)期中,蒸發(fā)巖的分布很廣,從寒武紀(jì)到近代,除奧陶紀(jì)尚未發(fā)現(xiàn)鉀鹽外,其余地質(zhì)時(shí)代均有鉀鹽分布。世界上最重要的成鉀時(shí)代是寒武紀(jì)、泥盆紀(jì)、二疊紀(jì)、古近紀(jì)和新近紀(jì),說(shuō)明在地質(zhì)歷史時(shí)期中,主要的鉀鹽礦床分布與地殼運(yùn)動(dòng)大旋回的末期有關(guān),這因?yàn)槿蛐缘臉?gòu)造運(yùn)動(dòng)末期一般伴隨著海退和干旱的氣候環(huán)境[1]。Wout Krijgsman等[2]認(rèn)為西班牙的穆?tīng)栁鱽?卡塔赫納(Murcia–Cartagena)盆地蒸發(fā)巖建造形成受構(gòu)造運(yùn)動(dòng)控制,是對(duì)晚托爾通期(late Tortonian)至早梅辛期(early Messinian)構(gòu)造運(yùn)動(dòng)的響應(yīng),袁見(jiàn)齊等[3]認(rèn)為全球范圍的蒸發(fā)巖沉積與大地構(gòu)造條件(主要是裂谷作用)有關(guān),陸內(nèi)裂谷、陸間裂谷、大陸邊緣裂谷、大洋中基裂谷均發(fā)育不同程度的蒸發(fā)巖沉積,其沉積作用與裂谷的4個(gè)演化階段(穹隆隆起、沉陷和接受沉積、裂谷回返、大陸離散)緊密相關(guān)。塔里木盆地自中生代以來(lái),盆內(nèi)的斷裂活動(dòng)越來(lái)越弱,至中生代末期趨于停止,而盆地邊緣的斷裂活動(dòng)自中生代以來(lái)越來(lái)越強(qiáng),至新近紀(jì)時(shí)期達(dá)到高峰,使盆地邊緣大幅度下降,形成庫(kù)車前陸盆地[4],相應(yīng)地盆地古-新近紀(jì)蒸發(fā)巖沉積作用受構(gòu)造活動(dòng)的控制,與其有緊密地對(duì)應(yīng)關(guān)系。

1 地質(zhì)背景

新疆庫(kù)車盆地位于塔里木盆地的東北緣,北鄰南天山構(gòu)造帶。盆地內(nèi)構(gòu)造單元的劃分,一般自南向北依次可劃分為:前緣隆起帶,秋里塔格背斜(構(gòu)造)帶,拜城坳陷和陽(yáng)霞坳陷,克拉蘇-依奇克里克構(gòu)造帶,北部單斜帶(圖1),是一個(gè)再生前陸盆地[5～9]。盆地的演化始于晚二疊世[5],其全盛期發(fā)生在三疊紀(jì)[10],至侏羅紀(jì)初庫(kù)車前陸盆地的發(fā)育已經(jīng)完成[11],燕山期盆地繼續(xù)發(fā)育。至始新世末,由于印度板塊和歐亞板塊碰撞產(chǎn)生的遠(yuǎn)距離效應(yīng)[12],使得塔里木板塊向天山構(gòu)造帶俯沖,庫(kù)車前陸盆地復(fù)活再次接受沉積,形成庫(kù)車再生前陸盆地。盆地在古-新近紀(jì)時(shí)期主要為一套河湖相、山麓相沉積。整個(gè)盆地發(fā)育扇三角洲相、湖泊相、正常三角洲相沉積[13,14],自下而上一般劃分為:古近系的庫(kù)姆格列木組(E1-2k)和蘇維依組(E2-3s),新近系的吉迪克組(N1j)、康村組(N1k)、庫(kù)車組(N2k)。古近系主要為河湖相沉積[15],其下部庫(kù)姆格列木組發(fā)育巨厚的蒸發(fā)巖沉積[16],上部為少量鹽巖、膏巖、細(xì)砂巖、粉砂巖和泥巖沉積,新近系下部為河湖相沉積,上部為山麓相洪積,洪積物為礫巖、含礫砂巖、粉砂巖夾泥巖[17],整個(gè)盆地自庫(kù)姆格列木時(shí)期至吉迪克時(shí)期發(fā)育大量的鹽、膏沉積。研究表明,蒸發(fā)巖沉積不但與古代地層鹵水,與“成巖作用相”緊密相關(guān)[18,19],而且與構(gòu)造條件密不可分,特別是成鉀與否更是受構(gòu)造作用控制[20,21]。在構(gòu)造作用下,古-新近紀(jì)每個(gè)地層組沉積時(shí)期,蒸發(fā)巖沉積在巖性、沉積范圍、沉積中心上有明顯的變化,這種變化特征反映當(dāng)時(shí)構(gòu)造運(yùn)動(dòng)變化所形成的特定沉積環(huán)境,是對(duì)中國(guó)西部的喜馬拉雅運(yùn)動(dòng)構(gòu)造期次變化的響應(yīng)。

“喜馬拉雅運(yùn)動(dòng)”指新生代以來(lái)的構(gòu)造運(yùn)動(dòng)[22,23],對(duì)于構(gòu)造期次(構(gòu)造幕)的劃分,不同學(xué)者有不同的意見(jiàn)[24～26]。但大多數(shù)學(xué)者把喜馬拉雅運(yùn)動(dòng)分為三期,任紀(jì)舜[27]根據(jù)構(gòu)造旋回把喜馬拉雅運(yùn)動(dòng)分為三期,發(fā)生時(shí)間為:早喜馬拉雅運(yùn)動(dòng)(40～50 Ma);中喜馬拉雅運(yùn)動(dòng)(15 Ma);晚喜馬拉雅運(yùn)動(dòng)(2.4 Ma)。賈承造等[28]結(jié)合構(gòu)造、地貌、巖漿活動(dòng)把喜馬拉雅運(yùn)動(dòng)分為早、中、晚三期,其發(fā)生時(shí)間分別為(40 ～52 Ma)、(25 Ma)、(2.48 Ma)。李廷棟等[29]認(rèn)為喜馬拉雅運(yùn)動(dòng)在青藏地區(qū)可劃分3個(gè)幕:其時(shí)間分別為始新世末、中新世中后期、上新世-早更新世。塔里木東北緣的庫(kù)車盆地,正好處于塔里木盆地和南天山構(gòu)造帶兩大構(gòu)造單元的交界處,在強(qiáng)烈的構(gòu)造作用下,盆地的沉積特征(沉積物特征、沉積厚度變化、沉積中心遷移)必然受控于構(gòu)造作用。根據(jù)上述學(xué)者的觀點(diǎn),古-新近紀(jì)時(shí)期正是喜馬拉雅運(yùn)動(dòng)強(qiáng)烈的活動(dòng)期,其構(gòu)造活動(dòng)期次的變化必然引起沉積物沉積特征的變化,本文主要通過(guò)分析盆地古-新近系庫(kù)姆格列木組(E1-2k)、蘇維依組(E2-3s)、吉迪克組(N1j)蒸發(fā)巖沉積特征的變化,來(lái)研究蒸發(fā)巖沉積與喜馬拉雅構(gòu)造運(yùn)動(dòng)期次之間的響應(yīng)關(guān)系,分析喜馬拉雅運(yùn)動(dòng)構(gòu)造期次的發(fā)生時(shí)間。

2 研究方法

蒸發(fā)巖沉積總是和碎屑巖沉積相互交替,形成沉積韻律,由于鹽湖水體淡-咸-鹽-咸-淡的韻律變化,相應(yīng)地沉積物發(fā)生由碎屑巖-膏巖-鹽巖-膏巖-碎屑巖的變化,這種變化可以形成多種微小的沉積韻律類型,如:泥巖-含膏泥巖-泥巖,粉砂巖-泥巖-含膏泥巖-石膏-含膏泥巖-泥巖-粉砂巖,泥巖-鹽巖-泥巖,泥巖-鹽質(zhì)泥巖-泥巖。根據(jù)石油鉆孔資料,分析鉆孔巖性剖面柱碎屑巖-膏巖-鹽巖-膏巖-碎屑巖沉積韻律的變化,對(duì)每口鉆井剖面逐步劃出四級(jí)、三級(jí)、二級(jí)、一級(jí)沉積韻律,其方法為先劃出小的沉積韻律,比如碎屑巖-膏巖的變化,定為四級(jí)韻律,然后相同的四級(jí)韻律合并成三級(jí)韻律,逐級(jí)向上合并,最后劃出一級(jí)韻律(沉積旋回)(表1),通過(guò)劃分,識(shí)別沉積旋回期次。對(duì)于每一期蒸發(fā)巖沉積旋回,其巨厚的蒸發(fā)巖沉積不但代表了當(dāng)時(shí)干旱炎熱的氣候環(huán)境,而且反應(yīng)了地質(zhì)歷史時(shí)期中相對(duì)寧?kù)o的沉積環(huán)境。當(dāng)巨厚的蒸發(fā)巖沉積旋回向以陸源碎屑巖為主的沉積旋回轉(zhuǎn)變時(shí),盆地相對(duì)寧?kù)o的沉積環(huán)境被打破,進(jìn)入到由構(gòu)造運(yùn)動(dòng)帶來(lái)的相對(duì)強(qiáng)烈的構(gòu)造環(huán)境。所以蒸發(fā)巖沉積旋回的識(shí)別及其沉積巖性的變化反映了沉積環(huán)境的變化,而這種大的沉積旋回正是對(duì)地質(zhì)歷史時(shí)期大的構(gòu)造運(yùn)動(dòng)在沉積環(huán)境上的響應(yīng)。

圖1 庫(kù)車盆地構(gòu)造簡(jiǎn)圖(據(jù)塔里木油田分公司資料,有修改)Fig.1 Schematicmap of structure in Kuqa Basin(quoted from data of Tarim Oilfield Corporation,amended)

圖2 鉆井位置圖Fig.2 Location of drilling holes

雖然盆地中發(fā)育眾多的近南北向逆沖斷層,可能使鉆井剖面所在的地層受斷裂影響而發(fā)生地層疊置現(xiàn)象,影響蒸發(fā)巖沉積旋回的識(shí)別,但結(jié)合鉆井具體地理位置和盆地?cái)嗔褬?gòu)造的分布及地層層位關(guān)系,考慮每口鉆井蒸發(fā)巖旋回所處的地層僅位于庫(kù)姆格列木組至吉迪克組之間,對(duì)于選取的13口鉆井來(lái)說(shuō),旋回劃分范圍均沒(méi)有受到斷裂構(gòu)造大的影響而發(fā)生地層疊置現(xiàn)象,另外,雖然微小的影響可能存在,以至于對(duì)于沉積韻律(特別是四級(jí)韻律的劃分)有可能產(chǎn)生影響,但不影響大的蒸發(fā)巖沉積旋回的識(shí)別。

表1 鉆井剖面柱沉積韻律劃分?jǐn)?shù)量統(tǒng)計(jì)Table1 Statistics of sedimentary rhythms on columns of drilling holes

通過(guò)對(duì)盆地13口鉆井蒸發(fā)巖沉積韻律劃分、沉積旋回識(shí)別和對(duì)比,在盆地古近系和新近系的吉迪克組中共識(shí)別出五個(gè)蒸發(fā)巖沉積旋回,其中庫(kù)姆格列木組兩個(gè)(自下而上為Ⅰ1、Ⅰ2沉積旋回),蘇維依組一個(gè)(Ⅰ3沉積旋回),吉迪克組兩個(gè)(下而上為Ⅰ4、Ⅰ5沉積旋回),其中盆地西部鉆井(TB1、DB2、QL1、QC1、KL4、XQ2、YT2)(圖2)共發(fā)育4個(gè)沉積旋回,分別為古近紀(jì)的Ⅰ1、Ⅰ2、Ⅰ3、和新近紀(jì)的Ⅰ4沉積旋回;盆地東部鉆井(KC2、DQ5、YH1、DN201、DN102)主要發(fā)育1個(gè)沉積旋回,為Ⅰ4沉積旋回,而DQ8井5個(gè)沉積旋回(Ⅰ1至Ⅰ5沉積旋回)均有發(fā)育,反映了古近紀(jì)至吉迪克組時(shí)期蒸發(fā)巖沉積由盆地西部向東部逐漸遷移。應(yīng)與這一時(shí)期的喜馬拉雅構(gòu)造運(yùn)動(dòng)有關(guān)。

3 庫(kù)車盆地蒸發(fā)巖沉積特征

3.1 蒸發(fā)巖類型及沉積序列特征

3.1.1 蒸發(fā)巖類型

盆地古-新近系蒸發(fā)巖主要為鹽巖和膏巖,少量白云巖和灰?guī)r。蒸發(fā)巖中含有鈣芒硝、硬石膏、光鹵石、鉀石鹽、雜鹵石、鉀石膏及氯化鈣等礦物。巖鹽分為紅鹽(巖)、青鹽(巖)、白鹽(巖)。巖鹽中發(fā)現(xiàn)鉀石鹽殘晶、雜鹵石、無(wú)水芒硝、氯化鈣等蒸發(fā)鹽類礦物,說(shuō)明此時(shí)屬炎熱干旱氣候,海水蒸發(fā)濃縮快速達(dá)到石鹽飽和結(jié)晶階段,后期干旱繼續(xù),局部地區(qū)出現(xiàn)雜鹵石、芒硝、甚至光鹵石。時(shí)代上,鉀鹽礦物及氯化鈣主要分布于始新統(tǒng)上部,鈣芒硝主要分布于中新統(tǒng),石鹽和石膏則廣泛分布于整個(gè)古近紀(jì)及新近紀(jì)的吉迪克時(shí)期。

鹽巖和膏巖分布于整個(gè)盆地。野外地表隨處可見(jiàn)鹽霜、砂巖縫隙中滲出的鹽泉、鹽泉蒸發(fā)形成的鹽花等,鹽丘中可見(jiàn)大的食鹽晶體,部分鹽丘已作為鹽礦進(jìn)行開(kāi)采。膏巖一般和褐紅色、灰綠色砂巖、粉砂巖、泥巖互層,或呈夾層產(chǎn)出,地表和山坡上隨處可見(jiàn)風(fēng)化的片狀石膏、柱狀、板狀硬石膏?；?guī)r和白云巖在盆地分布相對(duì)較少,一般層厚幾米至十幾米(表2)。

3.1.2 沉積序列特征

整個(gè)盆地西部的蒸發(fā)巖沉積序列自下而上一般為:庫(kù)姆格列木早期的白云巖或灰?guī)r沉積序列,但厚度不大,主要發(fā)生在蒸發(fā)巖沉積旋回的底部,含有較多的生物碎屑;庫(kù)姆格列木早中期的膏巖組合序列,主要表現(xiàn)為先是膏質(zhì)泥巖(或泥質(zhì)膏巖)與泥巖交互沉積,后為膏巖與泥巖交互沉積;庫(kù)姆格列木中期,隨著鹽湖的進(jìn)一步咸化,出現(xiàn)鹽巖沉積序列,先是表現(xiàn)為膏質(zhì)鹽巖(或泥質(zhì)鹽巖)與泥巖交互沉積,后變?yōu)楦鄮r和鹽巖交互沉積,最后至巨厚的鹽巖沉積;庫(kù)姆格列木中晚期和蘇維依早期,又變?yōu)楹蛶?kù)姆格列木早中期一致的膏巖沉積序列,至蘇維依中晚期,則出現(xiàn)泥巖、粉砂巖沉積序列,反映了鹽湖水體的淡-咸-鹽-咸-淡的變化。

盆地東部蒸發(fā)巖沉積序列主要發(fā)生在吉迪克時(shí)期,其沉積特征同盆地西部基本一致,但膏巖沉積厚度比西部大,鹽巖沉積厚度比西部小,反映了盆地東、西部鹽湖在咸化期和鹽化期時(shí)間段長(zhǎng)短上的差異,這種差異應(yīng)與其對(duì)應(yīng)的氣候條件及構(gòu)造運(yùn)動(dòng)有關(guān)。

上述蒸發(fā)巖沉積序列中,蒸發(fā)巖沉積總是和碎屑巖(主要是泥巖、粉砂巖)交互沉積,反映了鹽湖在咸化(鹽化)過(guò)程中有淡水間斷注入,使鹽湖淡化,這種現(xiàn)象可能是天山山前淡水定期補(bǔ)給的結(jié)果,可能反映了庫(kù)車盆地在古近紀(jì)至新近紀(jì)早期長(zhǎng)期干燥炎熱的氣候背景下曾經(jīng)有短暫的濕潤(rùn)氣候條件發(fā)生。

3.2 盆地西部蒸發(fā)巖沉積特征

根據(jù)所搜集的資料,對(duì)13口鉆井巖性剖面進(jìn)行蒸發(fā)巖沉積特征分析,由于鉆孔剖面很長(zhǎng)(一般2 000 ～5 000 m),不可能詳盡地列出其沉積物巖性變化,所以只粗略地列出其碎屑巖和蒸發(fā)巖沉積變化,但不影響對(duì)蒸發(fā)巖沉積特征的分析和大的沉積旋回的識(shí)別。

盆地西部分布TB1、DB2、QL1、QC1、KL4、XQ2、YT2共7口鉆井,對(duì)于每個(gè)鉆井剖面,其蒸發(fā)巖沉積旋回見(jiàn)圖3。由圖上可見(jiàn),盆地西部共發(fā)育4個(gè)蒸發(fā)巖沉積旋回,分別為:庫(kù)姆格列木(E1-2k)時(shí)期2個(gè)(Ⅰ1、Ⅰ2沉積旋回期),蘇維依時(shí)期(E2-3s)一個(gè),吉迪克(N1j)時(shí)期一個(gè),每個(gè)旋回的沉積特征見(jiàn)表3。

由表3可以看出盆地西部蒸發(fā)巖沉積特征:庫(kù)姆格列木早期(Ⅰ1),蒸發(fā)巖沉積以TB1、DB2、XQ2井為中心,發(fā)育少量薄層的鹽、膏沉積,北部KL4井以巨厚膏巖為主、南部YT2井發(fā)生少量膏巖、白云巖沉積,代表了當(dāng)時(shí)盆地西部蒸發(fā)巖沉積的邊界,在盆地西部呈近北西-南東向展布;庫(kù)姆格列木晚期,沉積范圍在早期的基礎(chǔ)上繼續(xù)向南北方向擴(kuò)展,覆蓋了盆地西部大部分地區(qū);蘇維依時(shí)期,蒸發(fā)巖沉積由北部經(jīng)中部向南部遷移,沉積物由巨厚鹽、膏轉(zhuǎn)變?yōu)樯倭康谋邮?吉迪克時(shí)期,蒸發(fā)巖沉積發(fā)生在南部,沉積物由少量石膏又轉(zhuǎn)變?yōu)榫藓竦柠}、膏沉積。

表3 盆地西部蒸發(fā)巖沉積旋回特征Table3 Sedimentary characteristics of evaporate in the western Kuche Basin

圖3 盆地西部蒸發(fā)巖沉積特征Fig.3 Sedimentary characteristics of evaporate in the western Kuqa Basin

3.3 盆地東部蒸發(fā)巖沉積特征

盆地東部分布DQ8、KC2、DQ5、YH1、DN201、DN102共6口鉆井,對(duì)于每個(gè)鉆井剖面,其蒸發(fā)巖沉積旋回見(jiàn)圖4。由圖上可見(jiàn),盆地東部共發(fā)育5個(gè)蒸發(fā)巖沉積旋回,分別為:庫(kù)姆格列木(E1-2k)時(shí)期2個(gè)(Ⅰ1、Ⅰ2沉積旋回期),蘇維依時(shí)期(E2-3s)一個(gè),吉迪克(N1j)時(shí)期兩個(gè),每個(gè)旋回的沉積特征見(jiàn)表4。

表4 盆地東部蒸發(fā)巖沉積旋回特征Table4 Sedimentary characteristics of evaporate in the eastern Kuche Basin

圖4 盆地東部蒸發(fā)巖沉積特征Fig.4 Sedimentary characteristics of evaporate in the eastern Kuqa Basin

由表4可以看出盆地東部蒸發(fā)巖沉積特征:庫(kù)姆格列木早期(Ⅰ1)和晚期(Ⅰ2),蒸發(fā)巖沉積主要見(jiàn)于DQ8井,旋回Ⅰ1發(fā)育大量含泥灰?guī)r、少量石膏,旋回Ⅰ2是旋回Ⅰ1基礎(chǔ)上沉積范圍進(jìn)一步的擴(kuò)大,同盆地西部庫(kù)姆格列木時(shí)期蒸發(fā)巖沉積特征一致,這因?yàn)镈Q8井位于盆地中部所致。其旋回Ⅰ1大量的含泥灰?guī)r沉積,代表了旋回Ⅰ1時(shí)期盆地西部蒸發(fā)巖沉積范圍的東部邊界點(diǎn);蘇維依時(shí)期,蒸發(fā)巖沉積由巨厚鹽、膏轉(zhuǎn)變?yōu)樯倭康谋邮?由北部(KC2井:少量泥質(zhì)灰?guī)r)經(jīng)中部(DQ8、DQ5井:少量石膏)向南部(YH1井:少量石膏)遷移,DQ8、DQ5、YH1為蘇維依時(shí)期盆地東部蒸發(fā)巖沉積中心;吉迪克時(shí)期,蒸發(fā)巖沉積發(fā)生在整個(gè)盆地東部,范圍向南、北、西(KC2、YH1、DQ8)擴(kuò)大,并向東(DN201、DN102井)遷移,沉積了巨厚的鹽、膏;Ⅰ5旋回僅見(jiàn)于DQ8井,代表了蒸發(fā)巖沉積的衰退期。

圖5 庫(kù)車盆地古-新近紀(jì)蒸發(fā)巖沉積旋回范圍圖Fig.5 Scope of sedimentary circle of evaporation salt in Kuche Basin in Tertiary Period

通過(guò)對(duì)13口鉆井蒸發(fā)巖沉積旋回中蒸發(fā)巖厚度累加,利用Sufer軟件,可以初步圈出每個(gè)蒸發(fā)巖沉積旋回的沉積范圍(圖5)。從圖上可以看出,庫(kù)姆格列木時(shí)期,盆地西部的Ⅰ2旋回在Ⅰ1旋回基礎(chǔ)上向南北方向擴(kuò)展;蘇維依時(shí)期,沉積區(qū)一分為二,分別向盆地南部、東部遷移;吉迪克時(shí)期,盆地南部、東部的兩個(gè)沉積區(qū)繼續(xù)發(fā)育巨厚的蒸發(fā)巖沉積,這與上述盆地東、西部蒸發(fā)巖沉積特征相一致。

4 對(duì)喜馬拉雅構(gòu)造運(yùn)動(dòng)期次的響應(yīng)

鹽湖的蒸發(fā)巖沉積需要一個(gè)穩(wěn)定的沉積環(huán)境,在大地構(gòu)造環(huán)境穩(wěn)定的條件下,氣候持續(xù)的干燥炎熱,才能發(fā)育灰?guī)r、膏巖、鹽巖等蒸發(fā)巖沉積,間斷性的淡水注入湖盆可以使湖水淡化,發(fā)育部分碎屑巖沉積,構(gòu)成蒸發(fā)巖沉積旋回,但是蒸發(fā)巖沉積之前需要有一個(gè)長(zhǎng)時(shí)間的濃縮階段,此階段離不開(kāi)構(gòu)造作用[21],往往在構(gòu)造作用下鹵水才能反復(fù)振蕩濃縮,最終在構(gòu)造的穩(wěn)定區(qū)富集成鹽。

4.1 與早喜馬拉雅構(gòu)造期次的響應(yīng)

依據(jù)前述學(xué)者對(duì)喜馬拉雅構(gòu)造期次劃分的觀點(diǎn):早喜馬拉雅構(gòu)造運(yùn)動(dòng)發(fā)生于40～50(52)Ma[27,28](始新世早期或者始新世末[29])。在此之前,庫(kù)車盆地處于燕山構(gòu)造期后的相對(duì)寧?kù)o期,海侵自古新世由古地中海沿天山南部深入到庫(kù)車盆地,海侵時(shí)斷時(shí)續(xù),在庫(kù)車盆地發(fā)育了高咸度瀉湖區(qū)和咸化瀉湖區(qū),氣候干旱①地質(zhì)礦產(chǎn)部礦床地質(zhì)研究所。新疆庫(kù)車盆地第三紀(jì)成鹽條件及找鉀遠(yuǎn)景研究報(bào)告,1980:36-70,發(fā)育了庫(kù)姆格列木(E1-2k)時(shí)期的巨厚蒸發(fā)巖沉積。而Ⅰ2沉積旋回在Ⅰ1旋回范圍基礎(chǔ)上的擴(kuò)大反映了二者之間有一個(gè)海侵范圍稍微擴(kuò)大的時(shí)期,應(yīng)該與“始新世早期塔里木盆地內(nèi)的海侵范圍在局部擴(kuò)展”①地質(zhì)礦產(chǎn)部礦床地質(zhì)研究所。新疆庫(kù)車盆地第三紀(jì)成鹽條件及找鉀遠(yuǎn)景研究報(bào)告,1980:36-70及古近紀(jì)中晚期,盆地處于伸展擴(kuò)張的構(gòu)造環(huán)境之中[26]有關(guān)。自蘇維依時(shí)期(E2-3s)開(kāi)始,蒸發(fā)巖沉積發(fā)生改變,主要表現(xiàn)為巖性上的變化(由巨厚鹽、膏向薄層石膏轉(zhuǎn)變)和沉積中心的變化遷移(沉積中心一分為二,自北西向東部、南部?jī)蓚€(gè)方向遷移),其變化正是早喜馬拉雅構(gòu)造期開(kāi)始的反映。由于早喜馬拉雅構(gòu)造運(yùn)動(dòng),塔里木盆地向南天山構(gòu)造帶俯沖,盆地的西北基地抬升[21],不但使得白堊紀(jì)至中新世盆地碎屑巖沉積中心向南遷移[34],而且導(dǎo)致鹽湖鹵水穩(wěn)定的沉積環(huán)境遭受破壞,被一分為二,分別向南、向東遷移,在遷移過(guò)程中,間斷受淡水的補(bǔ)給,發(fā)育少量的膏巖沉積。在整個(gè)蘇維依時(shí)期,蒸發(fā)巖沉積一直以少量膏巖為主,并不斷遷移,反映了早喜馬拉雅構(gòu)造運(yùn)動(dòng)的影響貫穿于整個(gè)蘇維依時(shí)期。

所以,早喜馬拉雅運(yùn)動(dòng)開(kāi)始于蘇維依(E2-3s)初期,并貫穿于整個(gè)蘇維依時(shí)期。對(duì)于蘇維依組上下年限的測(cè)定,李忠等通過(guò)對(duì)庫(kù)車盆地磁性地層學(xué)和生物地層學(xué)的研究,厘定為38～24.4 Ma[32～34],依據(jù)國(guó)際地層委員會(huì)2004年修訂的年代地層標(biāo)準(zhǔn)(始新世: 55.8±0.2～33.9±0.1 Ma),早喜馬拉雅運(yùn)動(dòng)應(yīng)開(kāi)始于始新世末期的“巴爾通階”末期和“普里亞本階”初期[35],即38 Ma左右(圖6),與中國(guó)地質(zhì)學(xué)擴(kuò)編版[26]及李廷棟等[29](青藏地區(qū)早喜馬拉雅運(yùn)動(dòng))認(rèn)識(shí)相一致。

4.2 與中喜馬拉雅構(gòu)造期次的響應(yīng)

庫(kù)車盆地蘇維依時(shí)期至吉迪克時(shí)期蒸發(fā)巖沉積發(fā)生改變,主要表現(xiàn)為巖性改變(由薄層膏巖、泥巖變?yōu)榫藓覃}、膏)和沉積范圍遷移(繼續(xù)向東、向南遷移,向東部分鹵水匯入羅布泊[21],向南表現(xiàn)為鹵水遷移和海水退卻),表明到蘇維依后期,早喜馬拉雅運(yùn)動(dòng)的影響逐漸減弱,構(gòu)造環(huán)境逐漸開(kāi)始趨于穩(wěn)定,鹵水在遷移過(guò)程中富集了大量鹽分,至吉迪克初期開(kāi)始在盆地東部、南部發(fā)育巨厚的蒸發(fā)巖沉積,這同庫(kù)姆格列木時(shí)期的構(gòu)造環(huán)境(燕山后期)相一致。自西向東,通過(guò)對(duì)YH1、DQ5、DN201、DN102四個(gè)鉆井巖性剖面分析,看出自蘇維依時(shí)期至吉迪克時(shí)期,蒸發(fā)巖沉積向東遷移,表明此時(shí)期內(nèi)蒸發(fā)巖一邊遷移一邊沉積,早喜馬拉雅構(gòu)造影響因素逐漸減小。對(duì)比庫(kù)姆格列木時(shí)期的蒸發(fā)巖沉積,其膏、鹽沉積厚度相對(duì)較小,這也與吉迪克時(shí)期早喜馬拉雅較為活動(dòng)的構(gòu)造環(huán)境有關(guān)。

吉迪克中后期(旋回Ⅰ5之后),盆地西部和南部的蒸發(fā)巖沉積結(jié)束,變?yōu)楹恿飨嗟年懺此樾紟r沉積,野外調(diào)查及鉆孔資料分析顯示:碎屑巖沉積由下向上粒度逐漸變粗,由泥巖逐漸變?yōu)楹[砂巖、礫巖沉積,并夾有部分薄層(厚0.5～3 cm)膏巖沉積,一方面反映了逐漸穩(wěn)定的蒸發(fā)巖沉積環(huán)境結(jié)束,另一方面,反映山麓相的粗碎屑巖沉積物說(shuō)明了山體快速隆升、剝蝕、搬運(yùn)、堆積的過(guò)程,應(yīng)與中喜馬拉雅構(gòu)造運(yùn)動(dòng)強(qiáng)烈的活動(dòng)期有關(guān),“新近紀(jì)初庫(kù)車盆地與南天山構(gòu)造帶的邊界呈滑動(dòng)上升模式[36]”和“自中新世庫(kù)車盆地與南天山構(gòu)造帶的邊界向南遷移[37]”均說(shuō)明了中喜馬拉雅構(gòu)造運(yùn)動(dòng)的開(kāi)始。另外,吉迪克中后期砂礫沉積物比蘇維依時(shí)期泥砂沉積物在粒度、分選、磨圓上明顯不同,顯示了中喜馬拉雅運(yùn)動(dòng)比早喜馬拉雅運(yùn)動(dòng)的活動(dòng)更加強(qiáng)烈。

對(duì)于中喜馬拉雅構(gòu)造運(yùn)動(dòng)開(kāi)始的時(shí)間,分歧較大,賈承造等[28]認(rèn)為中喜馬拉雅運(yùn)動(dòng)開(kāi)始于25 Ma、任紀(jì)舜等認(rèn)為始于15 Ma[27],李廷棟等[29]和任紀(jì)舜等認(rèn)為的時(shí)間相近,始于中新世中后期。本次研究通過(guò)分析吉迪克組蒸發(fā)巖沉積時(shí)限,結(jié)合李忠等對(duì)庫(kù)車盆地吉迪克組年代上下界限的厘定(24.4Ma～ 16.9Ma)[32～34]及國(guó)際地層委員會(huì)修訂的年代地層標(biāo)準(zhǔn)(中新世:23.03～5.322 Ma),認(rèn)為中喜馬拉雅運(yùn)動(dòng)應(yīng)開(kāi)始于吉迪克組Ⅰ5蒸發(fā)巖沉積旋回結(jié)束,大致開(kāi)始于吉迪克(24.4～16.9 Ma)后期(約18 Ma左右)(圖6),位于中新世初期的“布爾迪加爾階”中期,這一點(diǎn)與前人的研究(25 Ma、15 Ma、中新世中后期)不同。

4.3 與全球海平面變化的關(guān)系

根據(jù)Bilal U Haq等[38]對(duì)古-新近紀(jì)全球海平面變化曲線的研究,把海平面變化曲線與庫(kù)車盆地蒸發(fā)巖沉積旋回及喜馬拉雅構(gòu)造運(yùn)動(dòng)其次進(jìn)行對(duì)比(圖6)?？梢钥闯鋈呋緦?duì)應(yīng)。庫(kù)姆格列木早期,盆地發(fā)育Ⅰ1蒸發(fā)巖沉積旋回,此時(shí)全球海平面處于較高位置,基本無(wú)變化,反映穩(wěn)定的構(gòu)造環(huán)境,由于古新世時(shí)期,古地中海的海水侵入庫(kù)車盆地,斷斷續(xù)續(xù)的侵入使得盆地高咸度瀉湖發(fā)育,發(fā)育少量薄層灰?guī)r、膏巖、鹽巖沉積。庫(kù)姆格列木晚期,全球海平面總體上依然很高并伴隨間斷的升降,在52.5～53.5 Ma時(shí)海平面達(dá)到本時(shí)期最高值,這與“始新世早期塔里木盆地內(nèi)的海侵范圍在局部擴(kuò)展”相一致,導(dǎo)致蒸發(fā)巖沉積在旋回Ⅰ1基礎(chǔ)上其沉積范圍向盆地南北方向擴(kuò)展。蘇維依時(shí)期全球海平面大幅度下降,反映了全球范圍內(nèi)的構(gòu)造運(yùn)動(dòng)抬升,早喜馬拉雅構(gòu)造運(yùn)動(dòng)開(kāi)始,庫(kù)車盆地海水退卻,盆地受近南北向擠壓導(dǎo)致西北部基底抬升,鹵水向南、向東遷移,旋回Ⅰ3發(fā)育少量鹽、膏沉積。至吉迪克時(shí)期,全球海平面下降總體趨于穩(wěn)定,大地構(gòu)造環(huán)境穩(wěn)定,庫(kù)車盆地剩余的陸內(nèi)湖水在干旱氣候條件下,分別在盆地西南部、東部發(fā)育Ⅰ4旋回沉積,盆地東部可能受北部天山淡水的間斷補(bǔ)給,發(fā)育Ⅰ5沉積旋回。此后全球海平面開(kāi)始了2次急劇升降,時(shí)間在15～18 Ma,預(yù)示著中喜馬拉雅構(gòu)造運(yùn)動(dòng)的開(kāi)始,在15 Ma之后海平面大幅度下降,至10 Ma時(shí)降到-50 m以下,反映了比早喜馬拉雅運(yùn)動(dòng)更加強(qiáng)烈的中喜馬拉雅構(gòu)造運(yùn)動(dòng)的發(fā)生,庫(kù)車盆地徹底轉(zhuǎn)為陸源碎屑巖沉積。

5 結(jié)論

通過(guò)對(duì)庫(kù)車盆地古-新近紀(jì)蒸發(fā)巖沉積特征分析及與喜馬拉雅構(gòu)造運(yùn)動(dòng)期次的響應(yīng)分析,獲得以下認(rèn)識(shí):

圖6 蒸發(fā)巖沉積旋回與喜馬拉雅構(gòu)造期次關(guān)系Fig.6 Correlation on sedimentary cycle of evaporate and Himalayan tectonic phase

(1)穩(wěn)定的大地構(gòu)造環(huán)境是庫(kù)車盆地巨厚蒸發(fā)巖發(fā)育的必要條件,但干燥炎熱的氣候條件應(yīng)該是主要因素,而構(gòu)造變動(dòng)又可以使鹵水遷移,蒸發(fā)巖沉積移位。

(2)庫(kù)姆格列木時(shí)期是燕山構(gòu)造運(yùn)動(dòng)后期穩(wěn)定構(gòu)造環(huán)境的反映,沉積了巨厚的鹽、膏層。

(3)早喜馬拉雅運(yùn)動(dòng)開(kāi)始于蘇維依初期,即始新世末期(38 Ma),構(gòu)造擠壓使得盆地西北部基底抬升,蒸發(fā)巖沉積環(huán)境改變,沉積區(qū)一分為二,沉積中心向南、向東遷移,構(gòu)造影響一直持續(xù)到蘇維依末期,在不穩(wěn)定的構(gòu)造環(huán)境下發(fā)育蘇維依組少量的石膏沉積,吉迪克早期,構(gòu)造環(huán)境趨于穩(wěn)定,構(gòu)造影響仍然存在但很微弱,東部、南部的兩個(gè)沉積區(qū)分別繼續(xù)向東、向南遷移,發(fā)育巨厚的鹽、膏沉積。

(4)中喜馬拉雅運(yùn)動(dòng)開(kāi)始于吉迪克后期(約18 Ma左右),即中新世初期,此時(shí)Ⅰ5蒸發(fā)巖沉積旋回結(jié)束,構(gòu)造運(yùn)動(dòng)使得山體快速抬升、遭受剝蝕,盆地轉(zhuǎn)為山麓相、河流相沉積,并夾有薄層石膏沉積。

總之,庫(kù)車盆地的蒸發(fā)巖沉積與喜馬拉雅構(gòu)造運(yùn)動(dòng)及全球海平面升降有較好的對(duì)應(yīng)關(guān)系,是大區(qū)域的地質(zhì)事件在小區(qū)域范圍內(nèi)的地質(zhì)事件反映。

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Response on Sediment of Evaporate in Kuqa Basin from Paleogene to Neogene Period and Himalayan Tectonic Phase

CAO Yang-tong1YANG Hai-jun2LIU Cheng-lin1GU Qiao-yuan2JIAO Peng-cheng1LU Yu-hong2
(1.Institute of M ineral Resources,Chinese Academy of Geological Sciences,Beijing 100037; 2.Research Institute of Petroleum Exp loration and Development of Tarim Oil Field,Korla,Xinjiang 841000)

Sediment of evaporite with gigantic thickness had been developed in Kuqa Basin from Paleogene to Neogene period,and the main stratum were composed of Kumugeliemu group,Suweiyi group(Paleogene),and Jidike group(Neogene)。Going with transformation of the water of saline lake changing from fresh water,saline water,to brine,and then to saline water,fresh water,accordingly,the sediment changes from clastic rock,gypsum,to saline rock,and then to gypsum,clastic rock,so the sediment of evaporate and clastic rock is alternated each other,and the sediment rhythm or gyration come into being.Based on some datum of drill holes,5 sedimentary cycles of evaporite are given。Ⅰ1andⅠ2sediment cycles have been developed in Kumugeliemu period。Ⅰ1sediment cycle,which mainly developed in early Kumugeliemu period,has been fulled of folium saline rock,gypsum,limestone or dolomite,clastic rock,notonly is the sediment scopemainly attached center to Tubei1,Dabei2 and Xiqiu2 drilling holes, but also attached borderline to Kela2 drilling hole in north of basin and Yangta 2 drilling hole in the south of basin, and extended from northwest to southeast。Ⅰ2sediment cycles have been developed in late Kumugeliemu period,has been fulled of gigantic and thick saline rock and gypsum,and the sediment scope han been extended based on early sediment scope。Ⅰ3sediment cycles has beenmainly developed in Suweiyi period,and influenced on the early Himalayan tectonicmovement,the floor in north-west of basin was uplifted,so the sediment area was split into two parts which moved not only from north to south but also from west to east.Themain sediment is clastic rock and gypsum contained clastic rock,and the evaporite sedimentmoved from north,middle,to south of Kuqa basin in the west,in the east of basin itmoved from west to east.The gigantic thickness sediment of evaporite in Kumugeliemu period (Ⅰ1、Ⅰ2sediment cycles)reflects comparatively quiet tectonic setting after Yanshanmovement;and the sediment of evaporate has been changed obviously on lithology and scope in(Ⅰ3sediment cycles)in Suweiyiperiod,so unsteadily tectonic setting has been reflected in early Himalayan tectonic phase.Sediment of evaporite with gigantic thickness (Ⅰ4sediment cycles)had beenmainly developed in east of basin in Jidike period,and a few in south of basin,comparing sediment of evaporate in west of basin in Kumugeliemu period,the thickness of saline rock is attenuation but the gypsum is opposite,which reflects the long time of salty lake and the short time of saline lake.Themovement from west to east of the sediment area reflects the early Himalayan tectonicmovementwas still continuing In spite of its decline.The sediment of evaporate(Ⅰ5sediment cycles)has been breaken down in Jidike period,and it han been changed into continental sedimentation,so the setting of themountain uplifted,denuded,cumulated fleetly,was indicated by piedmont deposits,and themiddle Himalayan tectonicmovement period were coming.So it is a good corresponding relation on sediment of evaporite in Kuqa Basin and Himalayan tectonic movement,and it is a reflection of geology eventmade by large-scale tectonic movement in small areas.

Kuqa Basin;evaporate;Himalayan tectonic phase;response

曹養(yǎng)同 男 1975年出生 博士研究生 礦物、巖石、礦床學(xué) E-mail:cyt1941@yahoo.com.cn

P512.2

A

1000-0550(2010)06-1054-12

①塔里木盆地重要蒸發(fā)巖坳陷成鹽及油氣生儲(chǔ)條件研究項(xiàng)目(批準(zhǔn)號(hào):41005050002),國(guó)家“十一五”科技支撐課題(編號(hào):2006BAB07B06);中國(guó)地質(zhì)科學(xué)院礦產(chǎn)資源研究所中央級(jí)公益性科研院所基本科研業(yè)務(wù)費(fèi)項(xiàng)目(編號(hào):K0807)共同資助成果。

2009-07-08;收修改稿日期:2009-10-29