早中新世沟鞭藻植物地理区系

EARLY MIOCENE DINOFLAGELLATE PROVINCIALISM

对早中新世的沟鞭藻植物地理作了初步研究 ,提出北半球在当时可划分为 3个沟鞭藻地理区 ,即热带区、亚热带—温带区和北方区。热带区以典型的热带、亚热带种 Polysphaeridiumzoharyi丰富并存在偏爱热带、亚热带的种 Tuberculodiniumdinium vancampoae为特征 ,亚热带—温带区以同时存在 Tuberculodiniumdinium vancampoae和温带种 Bitectatodinium tepikiense,但缺失 Polysphaeridium zoharyi为特征 ,而北方区则以缺失 Polysphaeridium zoharyi和 Tuberculo-diniumdinium vancampoae二者且组合较贫乏为特征 ,亚热带—温带区的北界大致位于现今 68°N一线 ,此界线可随气温升高而北推 ,例如最温暖的早中新世晚期 ( 1 7～ 1 4 .5Ma)此界线可达 70°N。该带南界大致位于现今 4 5°N处 ,随着气候的转暖可能会变得模糊不清。北方区的海水此时凉而不结冰 ,即此时北极不存在冰盖。本文研究证实了前人根据大植物化石所得出的结论。

After suffering the Oligocene deterioration,the global climate showed a major warming trend during Early Miocene (21～15 Ma),which resulted in recovery and flourish of the biota including dinoflagellates.Thus the Early Miocene dinoflagellates are more diverse and thriving than the Oligocene ones.The present paper is intending to study Miocene dinoflagellate provincialism based on distribution pattern of Early Miocene dinoflagellate assemblages from north to south different localities.Three paleogeographic regions or zones may be recognized as tropical,subtropical temperate and the boreal regions on the basis of some temperature sensitive species.The tropical region is characterized by abundant Polysphaeridium zoharyi of typical tropic subtropical species and presence of Tuberculodinium vancampoae ,favor of tropic subtropic species; the subtropical temperate region is distinguished from the former in not having Polysphaeridium zoharyi but having Tuberculodinium vancampoae and temperate zone species Bitectatodinium tepikiense while the boreal region is characterized by poor assemblages with absence of both Polysphaeridium zoharyi and Tuberculodinium vancampoae .The boundary between subtropical temperate and boreal was about 68°N of the present latitude,further north than the present one and changed with temperature,for example,it reached to farthest north during the optimum (17～14.5 Ma).The boundary between tropical and subtropical was around 45°N of the present latitude or may be vague during the optimum.The present dinoflagellate study supports the same conclusion drawn by macrobotanic fossils as the follows: the sea water in the boreal region by that time was not too cold to freeze,i.e.there was no icecap in the Arctica.