羌塘盆地查郎拉地区中生代岩相古地理初探

以实测剖面和路线地质填图剖面为基础,采用地层优势相 (亚相 )法和综合分析法首次系统地重建了羌塘盆地查郎拉地区中生代的岩相古地理。指出晚三叠世以海陆过渡相占主导地位,形成海退沉积旋回;由NE向SW依次出现三角洲相→滨岸相→滨浅海相带。中侏罗世浅海相沉积较发育,从NE向SW依次发育三角洲→台地相→浅海陆棚相带,呈NWW~SEE向展布,沉积中心应在中部偏西南侧,在J₂ q期和J₂ b期形成两次海侵高潮,总体组成两个由海侵→海退的沉积旋回。晚侏罗世海陆过渡相沉积较发育,从NE向SW依次发育三角洲相→潮坪相→台地相带,呈NW~SE向展布。白垩纪岩相古地理存在早晚差异 :早期为残留海背景下的台地边缘浅滩-局限台地相沉积,形成第三次海侵高潮;晚期全区迅速抬升,形成冲积扇~辫状河流相的磨拉石红色复陆屑沉积旋回及多物源供应格局。中生代沉积物源主要来自北部的中央隆起带,次为东部高地及西部隆起区;在沉积演化过程中,不同时代的沉积物源有所差别,且地形总体保持了北高南低、东高西低的格局。

Preliminary Research on the Mesozoic Lithofacies-Palaeogeography in the Chalangla Area, Qiangtang Basin, Northern Tibet

For the first time, the paper systematically rebuilds the Mesozoic lithofacies and palaeogeography in the Chalangla area of Qiangtang Basin in Northern Tibet by using methods of stratigraphically dominant facies/subfacies and integrated analyses. This is on the basis of the measured sections and route geologic survey profiles as well as sedimentary facies analyses. Marine-continental transition facies were dominant in Late Triassic, forming regression sedimentary cycles and consequently developing delta facies, coastal facies, and littoral-neritic facies belt from NE towards SW. In the Middle Jurassic epoch developed neritic facies deposits, consequently delta-platform-neritic continental shelf facies occurred from NE towards SW and displayed in NWW～SEE direction. Twice marine transgression peaks occurred at J₂ q Period and J₂ b Period,and constituted two sedimentary cycles from marine ingression to regression. In the Late Jurassic epoch developed sea-continental transitional facies,which were delta, tidal flat, platform facies belts and displayed in NW～SE direction.In the Cretaceous period discrepancy in lithofacies and palaeogeography was present from the early to late. In the early stage developed platform edge shallow facies to restricted platform facies on the background of remnant sea, which formed the third marine transgression peak. After rapid overall swelling, in the late stage occurred alluvial fan-braided river facies sedimentary cycles made of red polyterrigenous molasse deposits with multi-source supplying. The Mesozoic provenance was mainly the central uplift belt in the north, and secondly the highland in the east and uplift region in the west. In the process of sedimentary evolution, sedimentary source areas were different in different geologic ages, and the terrain in general,was characteristic of being higher in north and east but lower in south and west.