NIGER DELTA PHYTOECOLOGICAL GROUPS DATA FOR THE NEOGENE-EARLIEST PLEISTOCENE

The relationship between vegetation and climate informed the use of paleovegetational changes to infer paleoclimatic changes. Palynomorphs recovered from three oil wells from the offshore western Niger Delta were categorized into phytoecological groups to achieve this. Standard sedimentology and foraminiferal biostratigraphy integrated with marker palynomorphs were also applied to constrain the age. In the latest Miocene (5.8-5.5 Ma), climatic conditions were mainly wet until between 5.5 and 5.0Ma when extreme dry conditions prevailed. The early Pliocene (5.0 - >3.4 Ma) was generally wet while the late Pliocene (<3.0 - 2.7 Ma) was extremely dry with wet condition re-occurring at the latest Pliocene/earliest Pleistocene boundary at a lower magnitude than the early Pliocene wetness. This is inferred from the bloom of open vegetation Acanthaceae undifferentiated, Polygala sp. and Asystacia gangetica along with montane Podocarpus milanjianus since 2.4 Ma through 2.0 Ma and younger. The Acanthaceae bloom recorded the evolution of A. gangetica in the latest Pliocene/earliest Pleistocene around 2.0 Ma in the Niger delta. The upper Early Pliocene regional wet event is associated with distinct peaks of riverine forest, freshwater swamp and mangrove pollen. Results here further support earlier findings from other parts of West Africa with respect to paleoclimatic changes of the late Neogene/earliest Quaternary. Equivalent qualitative palynostratigraphic events were recognized within the zones for age determination and the biostratigraphic correlation significance of the zones was stressed.

植被与气候的内在关联为利用古植被变化反演古气候变迁提供了理论依据。本研究通过对尼日尔三角洲西部近海三口油井中采获的孢粉型化石（Palynomorphs）按植物生态类群进行分类，以达成该研究目标。同时结合标准沉积学、有孔虫生物地层学以及标志性孢粉型化石，对地层年代进行限定。晚中新世晚期（5.8~5.5 Ma）气候整体以湿润为主，直至5.5~5.0 Ma期间极端干旱气候占据主导。上新世早期（5.0~>3.4 Ma）整体气候湿润，而上新世晚期（<3.0~2.7 Ma）则极端干旱；在更新世最早期/上新世最晚期边界处，湿润气候再度出现，但其湿润程度低于上新世早期。该结论基于2.4 Ma至2.0 Ma及更年轻地层中，开放植被类群的未分化爵床科（Acanthaceae undifferentiated）、远志属（Polygala sp.）、宽叶十万错（Asystacia gangetica）与山地生境的米兰达罗汉松（Podocarpus milanjianus）的繁盛事件推导而来。尼日尔三角洲地区2.0 Ma左右的上新世最晚期/更新世最早期地层中，爵床科的繁盛事件记录了宽叶十万错的演化历程。上新世早期上部的区域湿润事件，与河流森林、淡水沼泽及红树林花粉的显著峰值相对应。本研究结果进一步佐证了西非其他地区关于晚新近纪/早第四纪古气候变迁的既有研究结论。研究在用于年代界定的地层带中识别出了可对比的定性孢粉地层事件，并强调了这些地层带在生物地层对比中的重要意义。