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.

植被与气候之间的关系为利用古植被变化推断古气候变化提供了依据。通过对来自尼日尔三角洲西部三个油井中恢复的孢粉进行植物生态学分组，实现了这一目标。在此次研究中，将标准沉积学、有孔虫生物地层学以及标记孢粉的整合应用于年龄限制。在最新的中新世（5.8-5.5百万年前），气候条件以湿润为主，直至5.5至5.0百万年前出现极端干旱条件。早更新世（5.0至3.4百万年前）总体湿润，而晚更新世（小于3.0至2.7百万年前）则极端干旱，在晚中新世/早更新世的边界处，湿润条件重现，但强度低于早更新世的湿润期。这一推断源于从2.4百万年前至2.0百万年前及更晚时期，开放植被如未分化的大戟科植物、Polygala属植物和葛藤以及山地Podocarpus milanjianus的繁盛。大戟科植物的繁盛记录了尼日尔三角洲在大约2.0百万年前晚中新世/早更新世时期A. gangetica的演化。早更新世晚期的区域湿润事件与河流森林、淡水沼泽和红树林花粉的明显峰值相关。本研究结果进一步支持了西非其他地区关于上新世晚期/早第四纪古气候变化的早期发现。在各个区域识别到了类似的定性孢粉地层学事件，这些事件对于年龄确定和区域生物地层学相关性具有重要意义。