臺南科學園區臺南園區籌畫第三期擴建計畫,為了解預定區的文資內涵與全新世地理環境的變化,於八角寮遺址所在的看西農場進行100孔地質鑽探,深度皆為20公尺。本研究根據鑽探岩心分析,地層可見7種岩相,分別為礫石層、厚砂層、具波狀層理砂頁互層、泥質細砂層、碳質泥層、含生物碎屑泥層及具斑駁狀構造泥層等。依據岩相的組合特徵可以進一步劃分出氾濫平原、河洲、沼澤溼地及潮間帶等四種沉積環境。過去7,000年以來,研究區域大致以每年1.4±0.9~3.0±0.3mm速率向下沉陷(長期平均下陷速率為2.7mm/y),提供曾文溪河水氾濫時夾帶沉積物的堆積空間。因此在斷層活動導致的地層下陷與河流沉積等地質環境反覆變化的過程中,看西農場始終處於受潮汐影響的淺海至陸相河流的陸海交界環境,使得過去史前文化人的生活遺跡得以完整地保留下來。然而自1,267~1,066 yr BP之後,海平面既無變化,構造活動也維持穩定,氣候也無明顯變化,平原區的沉積速率卻增加,可能是因為鐵器時代(距今約1,800年)的開啟,史前人群開始利用鐵器的銳利與多樣性的工具模式,大舉進入山區開墾山林,導致河流上游山區植被與地形的變化致使河流夾帶泥沙量增加,擴大下游沖積扇的沉積作用,看西農場因此脫離沼澤濕地的沉積環境,改以沖積扇中上游的氾濫平原沉積模式為主。
In order to establish the third expansion plan in Southern Taiwan Science Park (STSP), the context of cultural assets and paleo-environmental change in projected area needs more detail information. Therefore, we have drilled 100 cores with 20-meter in depth around Pachiaoliao archaeological site to reveal the paleo-environmental change of Kanhsi Farm since 7,000 years ago. According to the coregraphs and stratigraphic correlation, seven sedimentary facies (such as conglomerate, thick-bedded sand, sand-clay interlayer with wavy structure, muddy fine sand, carbonaceous mud, bioclastic mud, and weathered soil bed) are recognized. Four paleoenvironment, including floodplain, sand bars, swamp/wetland and tidal flat, are reconstructed based on the sedimentary facies and association. In addition to the stratigraphic information, the Kanhsi Farm could situate at a junction between shallow marine and terrestrial fluvial zone where tide and river both are the dominant exogenic process over a long period. Combination of stratigraphic results from Kanhsi Farm and nearby area, the study area is subsided at a rate of 1.4 ± 0.9 ~ 3.0 ± 0.3mm /y in the past 7,000 years resulting from the activity of Hsinying active fault, that also provided a chance to completely conserve the living relics of ancient people. When the Iron Age (Niaosung Culture, ~1,800 yr BP) began, people used the imported sharp and durable iron tools into upstream area of Tsengwen River for land reclamation resulting in considerable vegetation and landform change. The incremental river sediment discharge would expand the development of river delta and tidal/wetland environment no longer existed around Kanhsi Farm and the weathered floodplain sediments from the top section of cores also provide deciphering records of terrestrial environment.