推荐回答(1个)
现代全球气候条件降雨量分为四个带,赤道至南、北纬15°为赤道降雨带,南、北纬15°至45°为亚热带干旱带,南、北纬45°至70°为温带降雨带,南、北纬70°以上极区为干旱带。成煤植物的繁殖受古气候的控制,赤道降雨带和南、北纬温带降雨带是成煤有利气候带。
古地磁资料反映出石炭纪的聚煤带靠近赤道主要分布在小于30°的古纬度上,二叠纪及其以后时代的聚煤带靠近极地。全球各时代煤分布偏离现代降雨带的现象,与古构造、古地理演变有关。板块的位移,古地理的改观,致使聚煤带迁移。
通过恢复古大陆的位置编制全球各时代古地理图,推断古气候认为,泥盆纪成煤区集中在赤道附近,南、北半球气候非常干燥。石炭纪煤发育广泛,可以分布在各纬度带,但仍集中在赤道附近。二叠纪气候多变,煤聚积在南、北半球中、高纬度带,甚至扩展到南极地区,赤道附近出现蒸发岩。三叠纪时期,全球气候干旱,早、中三叠世全球聚煤作用停止,中三叠世蒸发岩从赤道扩展到古纬度40°地区,晚三叠世聚煤作用主要在北纬55°以北和南纬30°以南地区。晚三叠世、早侏罗世全球湿度不断增加,中侏罗世又重新出现干旱环境,赤道为宽阔的干旱带,向两极为潮湿带,聚煤作用集中在45°~70°纬度范围。白垩纪,聚煤作用主要在高纬度带,蒸发岩分布在低纬度带,其分界线较侏罗纪时期纬度偏高,为45°~55°。第三纪,全球温度逐渐降低,老第三纪北半球气候温暖潮湿,聚煤作用与白垩纪时期相同,集中在北纬70°附近,蒸发岩则由白垩纪时期的北纬45°退缩到30°以南。中新世早期,全球气候转暖、潮湿,冷暖交替直到上新世末期,新第三纪聚煤范围比老第三纪范围要大。
古气候是成煤的重要影响因素,在一定的条件下还可成为决定性的因素。自显生宙以来,地球表面大气圈层冷暖、干湿不断变化,但总是围绕赤道和两极形成温暖潮湿和寒冷干旱带周期性的交替变化。由古气候决定了全球性的晚古生代前为腐泥煤成煤期,晚古生代后为腐殖煤成煤期。晚古生代以来,石炭—二叠纪、晚三叠—早白垩世、第三纪为主要成煤期,早中泥盆世、早中三叠世、晚白垩世为聚煤间断期。由古气候决定全球性聚煤时代的分布规律在中国大陆亦不例外。
中国聚煤期古气候变化是全球古气候变化的一部分。古生代陆缘发展阶段,中国统一大陆尚未形成,各板块所处地理位置有所差别,古气候与古板块当时所处的古地理位置有关。新元古代至早古生代华南板块位于赤道附近,有形成腐泥煤的浅海低等生物繁殖,腐泥煤(石煤)主要发育在华南板块。晚古生代中晚期石炭至二叠纪,华南、华北板块均处于赤道潮湿气候带,有成煤的古植物大量繁衍。藏滇板块处于冈瓦纳大陆,准噶尔—兴安活动带处于安加拉大陆,均属南、北半球有利聚煤的潮湿古气候带。中生代始,统一的中国古大陆基本形成,古气候亦随之发生变化。受全球干旱气候影响,早、中三叠世除藏滇板块南部和海南为半潮湿气候外,整个大陆均为不利于植物生长的干旱、半干旱气候。晚三叠世时期,中国南方大陆处于炎热潮湿气候带,具有成煤古气候条件,为该期大陆成煤相对好的地区。中国北方大陆虽然处于温暖半潮湿气候带,也有成煤的古植物生长,但成煤较差。早侏罗世,北方大陆仍为温带潮湿气候,成煤植物生长繁茂,是最好的成煤时期。但大陆西南部(四川—滇中)由晚三叠世潮湿古气候转为干旱气候带。中、晚侏罗世,中国大陆古气候发生了很大变化,除大陆东北部和藏南仍为潮湿气候带和热带—亚热带潮湿气候有成煤植物生长,大陆大部地区变为干旱气候带。早白垩世基本保持了中、晚侏罗世气候状况。晚白垩世,仍为不利于成煤植物发育的干旱气候。老第三纪重现了中、晚侏罗—早白垩世气候带,一条北西向干旱带遍及整个大陆,仅有东北、华北及西南保持了温带、热带潮湿气候带有利成煤植物生长的条件。新第三纪,大陆干旱气候带范围缩小,东部沿海转为亚热带温暖气候,已被海水淹没的南黄海、东海和南海,曾有潮湿适宜成煤植物生长的古气候,形成新第三纪含煤盆地。在大陆西部由于青藏高原的隆升,仅有川西—云南为热带—亚热带气候适于成煤古植物的生长繁殖。从中国大陆温带聚煤带与亚热带干旱带的分布界线分析,自晚三叠世以来,总体上是由南向北推移,其间白垩纪至渐新世位移不大且有回返。
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