摘要
The Asri basin is a typical half-graben basin. The east side of the basin is a steep slope controlled by synrifting and the west side is a widespread gentle slope. In the early Tertiary, it was filled with terrigenous clastic sediments composed of the Banuwati and Talang Akar formations from bottom to top. The latter is further divided into the Zelda member （lower part） and the Gita member （upper part）. The previous studies suggested that the early tertiary sediments are alluvial, fluvial and swamp deposits. In this paper, based on the core lithology, well logs and seismic data, the sediments should be alluvial, fluvial and lacustrine systems. The lacustrine system includes subaqeous fan, fan delta and delta, shore-shallow lake, deep lake and turbidite fan deposition. Alluvial fan, subaqeous fan and fan delta sediments were deposited in the early stage and located on the steep slope adjacent. The deltaic sedimentary system was usually distributed on the gentle slope of the basin. In the early Tertiary, the basin evolution could be divided into four stages： initial subsidence （matching Banuwati formation）, rapid subsidence （matching low Zelda member）, steady subsidence or fluctuation （matching middle Zelda） and uplifting （matching upper Zelda）. At the first stage, the alluvial fan, flood plain, braided stream sediments were deposited first with thick brown conglomerate and pebble sandstones, and then subaqeous fan sediments were interbedded with the thick lacustrine mudstones. At the second stage, shore-shallow lake and deep lake and turbidite fan sediments were deposited, with thin fine sandstones and siltstones interbedded with thick mudstones. At the third stage, thick fan delta and delta sandstones were deposited. At last came fluvial meandering, anastomosed and swamp sediments. Sediment supply was mainly from the west and the east, partly from the north.
The Asri basin is a typical half-graben basin. The east side of the basin is a steep slope controlled by synrifting and the west side is a widespread gentle slope. In the early Tertiary, it was filled with terrigenous clastic sediments composed of the Banuwati and Talang Akar formations from bottom to top. The latter is further divided into the Zelda member （lower part） and the Gita member （upper part）. The previous studies suggested that the early tertiary sediments are alluvial, fluvial and swamp deposits. In this paper, based on the core lithology, well logs and seismic data, the sediments should be alluvial, fluvial and lacustrine systems. The lacustrine system includes subaqeous fan, fan delta and delta, shore-shallow lake, deep lake and turbidite fan deposition. Alluvial fan, subaqeous fan and fan delta sediments were deposited in the early stage and located on the steep slope adjacent. The deltaic sedimentary system was usually distributed on the gentle slope of the basin. In the early Tertiary, the basin evolution could be divided into four stages： initial subsidence （matching Banuwati formation）, rapid subsidence （matching low Zelda member）, steady subsidence or fluctuation （matching middle Zelda） and uplifting （matching upper Zelda）. At the first stage, the alluvial fan, flood plain, braided stream sediments were deposited first with thick brown conglomerate and pebble sandstones, and then subaqeous fan sediments were interbedded with the thick lacustrine mudstones. At the second stage, shore-shallow lake and deep lake and turbidite fan sediments were deposited, with thin fine sandstones and siltstones interbedded with thick mudstones. At the third stage, thick fan delta and delta sandstones were deposited. At last came fluvial meandering, anastomosed and swamp sediments. Sediment supply was mainly from the west and the east, partly from the north.
