Miocene to Quaternary paleoenvironments and uplift history on the mid Norwegian shelf

Based on benthic and planktic foraminifera, Bolboforma, oxygen isotope measurements and seismic data, major changes in Miocene, Pliocene and Pleistocene paleoenvironments on the mid Norwegian shelf are discussed and a possible scenario of the late Cenozoic uplift history is given. The dating of the Neogene sequence has been done using foraminifera and Bolboforma. Four main assemblage zones have been identified with nine distinct subzones.
Most of the Miocene sequence is preserved. The lower Miocene sediments contain only siliceous microfossils. A period of high fertility and upwelling in the study area prevailed. The early Miocene-early mid Miocene (15 Ma?) change from a siliceous to a calcareous rich microfauna, dominated by Nonion barleeanum, can be related to increased surface-water circulation due to overflow across the Iceland-Faeroe ridge. During the Miocene the temperature decreased in the study area. Evidence of increased amounts of coarser sediments may suggest that an uplift of the mainland areas occurred during the mid-late Miocene.
Lower Pliocene sediments contain a foraminiferal fauna that seems to occur in slightly colder conditions than the late Miocene fauna suggesting a further cooling. Possibly, Arctic waters entered the study area in the early Pliocene.
A very marked change in lithology (from compacted claystone to unconsolidated diamicton), fauna (from deep dwelling to shallow dwelling species) and seismic signature (from flat lying reflectors to prograding clinoforms) occurs during the mid?-late Pliocene. A two step cooling trend is indicated by the microfauna of these prograding wedges.
(1) The first wedge buildups might have been associated with an uplift of the mainland during the early late Pliocene (mid Pliocene, ca. 4 Ma). However, the age determination is somewhat uncertain and may very well be of late Pliocene age.
(2) The second step of wedge buildup is associated with a glacial phase where the dominating microfauna exists of arctic species. Large continental ice sheets might have occurred at this time reaching coastal areas and that possibly many of the geomorphological features such as the strandflat were made during this episode.
The Pleistocene epoch is represented by an increased percentage of boreal foraminifera intermingled with high arctic species which indicates that interglacial-glacial cycles prevailed and the dynamics of the glacier system changed.

本数据集基于底栖与浮游有孔虫（benthic and planktic foraminifera）、球旋虫（Bolboforma）、氧同位素测试及地震资料，探讨了挪威中部陆架中新世、上新世及更新世的古环境重大变化，并给出了晚新生代隆升历史的可能情景。新近系地层的定年工作借助有孔虫与球旋虫完成，共识别出4个主要组合带及9个明确亚带。
绝大多数中新世地层得以保存。下中新统沉积物仅含硅质微体化石，表明研究区曾经历高生产力与上升流发育阶段。早中新世至中中新世早期（约15 Ma），微体化石群从硅质组合转变为钙质富集组合，以巴利诺宁虫（Nonion barleeanum）为优势类群，这一转变可归因于冰岛-法罗海脊溢流作用导致的表层水环流增强。中新世期间，研究区水温持续降低。粗粒沉积物含量升高的证据，暗示中晚中新世时期陆地区域发生了隆升。
上新统下部沉积物中的有孔虫动物群，其生存环境较晚中新世动物群略冷，指示气候进一步变冷。上新世早期可能有北极海水侵入研究区。
中晚上新世（年代存疑）发生了极为显著的岩性、动物群及地震反射特征变化：岩性从压实泥岩转变为未固结混杂堆积，动物群从深水属种为主转变为浅水属种为主，地震反射特征从平伏反射层变为前积斜层。这些前积楔状体的微体化石群指示了两阶段降温趋势。
(1) 第一期楔状体的形成可能与上新世晚期早期（中上新世，约4 Ma）的陆地区域隆升有关。然而，该年代测定存在一定不确定性，其年代也完全可能属于上新世晚期。
(2) 第二期楔状体发育与冰期事件相伴，此时优势微体化石类群为北极种。当时可能已形成大型大陆冰盖并延伸至沿岸区域，诸多海岸地貌（如岸滩平原strandflat）均可能形成于这一时期。
更新世地层中，北方有孔虫的占比升高，并与高北极种混合产出，这表明研究区曾盛行冰期-间冰期旋回，且冰川系统的动力学特征发生了改变。