- 期刊
古植物孢粉沉積指標與氣候變遷－以花蓮平原為例
A Pollen-Spore Analysis of Hualien Plain Cores and Its Implication on Paleoenvironmental Changes (7~13 kyr BP)
摘要
運用花蓮平原（明義、北埔與慈濟）三處鑽井岩芯，富含植物微小化石（ca 20um）的生物地層研究，能鑑別13～7千年前（簡記為13～7 kyr BP）、穩定沉積環境中孢粉組成的氣候意義。生物層序觀點能提取以孢子、花粉的訊號意義，搭配北半球碳素資料庫IntCal20所提供的嶄新定年校正與貝葉斯機率模型解析。首先發現於明義井（MY 19～88m）的深度內，泥質地層完整保存古孢粉的連續分布。明義井亦可區辨出最顯著的地史事件，就是「全新世突涼暴雨事件（MY 50～55m, cal. 9722～10101 BP）」，沼澤中繁盛蕨類植被受激烈上游沖刷物破壞後再步入緩慢恢復。北埔井的古生態學研究，則能觀測到深厚湖泊沉積物（BP 23～74m）。暖期內的持續海面上升，可見到「海進擾動縞狀泥層事件（BP 60.5m, cal. 13245 BP）」。最緻密的縞狀泥層（BP 60～64m）內原存有高達67%的蕨類佔比，但持續的海進讓接續泥層（BP 50～55m）只剩7～14%蕨類，伴隨的平行現象是半鹹水生鹵蕨（Acrostichum aureum, BP 45.6～63.8m）持續入侵古北埔湖；甚至（BP 46.5, 50.2m）出現紅茄冬（Bruguiera sp.），顯示沼澤紅樹林植物約在cal. 13008, 13077 BP擴張至此。最終「海進最高點事件」出現於全新世初暖濕期，在北埔井（BP 30.6m, cal. 11598 BP）鹵蕨紀錄顯示海水持續湧入北埔河口，同時伴隨暴雨，成為未有人類遷移前的瀉湖環境。故以花蓮平原所得62個植物分類群，依其物候劃分為七大類氣候功能群；分別描述三處岩芯、採樣76層位的孢粉組成，依序描述五期的古氣候變遷。總結花蓮濱海環境的地理演育，蕨類孢子的波動訊號反映出強降雨時期，可搭配暴雨沖刷移置超微化石的事件比對。半封閉濱海盆地所出現的鹵蕨、紅茄冬指標，對海進反應敏銳。檢視沉積岩相與古孢粉歷時紀錄，可標記突發的特殊氣候變遷事件。當13～7千年前由冷期進入全新世暖期，暴雨與海進兩大作用力，在花蓮海岸刻畫出眾多地史訊號。
並列摘要
This study examines biological compositions, rich in small fossils (ca 20um) of plant pollen and fern spores, in the three drilled cores in the Hualien plain: Mingyi (MY), Beipu (BP) and Tzuching (TC). It explores a well-preserved paleo-environment from the glacial to the interglacial warm period (13~7 kyr BP). The spore-fern perspectives reveal the significant meaning of geological events, combined with the new dating correction according to the northern hemisphere carbon database IntCal20, and the Bayesian age-depth model of probability simulation. A total of 62 plant taxa were obtained from the Hualien drill wells, which were divided into seven climatic functional groups according to their phenology. The palynological examination of 76 horizons was carried out, and the climate description of five phases was obtained. MY (19~88m) strata can identify the Event 1: "Holocene sudden cool rainstorm event (MY 50~55m, cal. 9722~10101 BP)", after the flourishing fern spores in the swamp. The river mouth was destroyed by an intense upstream erosion following a slow recovery. BP (23~74m) had deep lake sediments after the Event 2, "Rising sea level disturbed the laminated sediments in the cold period (BP 60.5m, cal. 13245 BP)". The sea rising impacted the fern composition from 67% (BP 60~64m) to 7~14% (BP 50~55m). Mangrove indicators (Acrostichum aureum) invaded the brackish water with Bruguiera sp. into the BP Lake (BP 45.6~63.8m). Finally, Event 3, "The peaking sea rising" occurred in the warm humid period of the early Holocene (BP 30.6m, cal. 11598 BP). The seawater continued to pour into the lagoon environments before human migration. To summarize the geographical evolution of the Hualien coastal environment, the fluctuation signal of spore-fern spores reflects the period of heavy rainfall, which can be compared with the events of displaced nanofossils. Ancient palynological records can mark sudden climate changes, indicating heavy rain and sea rising with many geohistorical signals along the coast of Hualien.