台灣中部的桂竹林層沉積年代為晚中新世至早上新世，為台灣前陸盆地最老的地層，本層記錄了由被動大陸邊緣轉變為前陸盆地的過程。本研究結合露頭的沈積相研究與台灣中部的鑽井資料，提出桂竹林層沉積環境的時空演變以及岩層厚度之側向變化，藉上述資料來探討台灣前陸盆地形成初期的發育過程。 沉積相的研究結果顯示整體桂竹林層之沈積環境演變，由最下部河口相的的關刀山砂岩段，往上過渡至遠濱相的十六份頁岩段，再往上則變淺為三角洲環境的魚藤坪砂岩段。由露頭與井下資料所繪製之桂竹林層三岩段厚度分布圖，可以看出明顯的岩層厚度側向變化。關刀山砂岩呈由北向南減薄的趨勢，且在彰化地區缺失。顯示北港高區北側在前陸盆地形成初期可能出露於地表，之後因造山帶荷重而逐漸下沉，導致關刀山砂岩以進覆的方式，往南覆蓋在前陸盆地基盤(北港高區)之上。另外，魚藤坪砂岩的沈積物則往造山帶的方向(向東)增厚。顯示於上新世早期，由於造山帶荷重的影響漸增，盆地已轉變為西淺東深，南北帶狀之形貌。 配合層序地層學的觀念，以沈積相為基礎可得到6種次層序。利用次層序疊加形式，及重要地層面辨識，將桂竹林層劃分為4個層序。底部3個層序的發育與全球海水面變化約略一致，唯獨第4個層序無法與全球海水位變化相對應，推測最頂部的層序可能受到造山帶荷重下壓與沉積速率加快所影響，使得與全球海水面變化不一致。 The sediments of the Kueichulin Formation were accumulated during the late Miocene to early Pliocene. This formation is the lowest succession of the Taiwan foreland sequence, providing the stratigraphic records that reveal the transition from passive-margin to foreland basin sedimentataion in central Taiwan. By employing sedimentary facies analysis on 3 outcrop sections and well-log stratigraphic studies the depositional systems and early development of the central Taiwan foreland basin have been established. There are four major depositional systems, namely the tide-dominated estuary depositional system, the wave-and-storm influenced shallow-marine depositional system, the barrier-island complex and lagoon depositional system and the tide-dominated delta depositional system. A series of isopach maps, shows a change of the depocenter of the three members of the Kueichulin Formation. During the late Miocene and in the earliest phase of the foreland basin development, the depocenter of the Kuantaoshan sandstone was similar to that of the passive margin. Later on, in the early Pliocene, the depocenter of the Yutenping Sandstone migrated further southward, where the Peikang basement High became submerged and started receiving sediments owing to rapid subsidence. Sequence stratigraphic analysis reveals that the Kueichulin Formation consists of four sequence. The development of the first three sequences correlates well with the eustatic sea-level fluctuation. The development of the last sequence deviates from eustasy, indicating that rapid foreland basin subsidence and high rate of sedimentation may have modulated the sequence development.