干旱气候条件下陆相高分辨层序地层特征研究——以江汉盆地西南缘晚白垩世渔洋组为例

Characteristics of Lacustrine High-resolution Sequence Stratigraphy under Arid Climate : a case study of Yuyang Formation (Late Cretaceous) in Southwest of Jianghan Basin

江汉盆地西南缘白垩系上统渔洋组地层旋回主要受气候因素的影响。研究区渔洋组是在干旱气候条件下沉积的洪水—漫湖沉积体系,其气候变化的特点是短暂洪水期与较长干旱的间洪水期交替变化,同时表现出不同级别的旋回,在气候越来越干旱的背景下,洪水期持续的时间就会越短,洪水的规模也越来越小。在短期的气候变化旋回下,地层沉积特征表现为洪水期沉积的水道、砂坪等微相与干旱的间洪水期泥坪微相互层。在中期气候变化旋回下,主洪水期持续时间长、规模大,沉积分布广泛,形成较厚的灰色水道砂岩沉积和灰色泥岩沉积夹薄层的红色泥坪沉积,间洪水期沉积为砂坪、混合坪与泥坪互层构成。长期旋回表现为每个中期主洪水期越来越小、水道沉积规模变小,间洪水期形成的红色泥坪厚度逐渐加厚,代表气候越来越干旱。研究区的这种地层旋回变化特征反映出气候是地层旋回的主控因素,不仅控制地层的短期旋回,同时控制地层的中长期旋回。这些特征具明显的等时性和可对比性,为油田开发过程中小层对比及油层划分提供了理论依据。

The sequence in Yuyang Formation of late-Cretaceous in southwest of Jianghan Basin is controlled by arid climate. Due to the evolution of climate, the flood period and inter-flood period alternately occur. In short-term cycle, the sandstone of channel microfacies and sandflat microfacies deposits in flood period and the mudstone of mudflat microfacies deposits in inter-flood period. In midterm cycle, there appear several assemblages of short - term sequence cycle. The main flood period usually lasts quite a long time with a large scale, so there deposits a set of thick grey sandstone of channel microfacies and mudstone of distal microfacies with interlayers of laminar red mudstone of mudflat microfacies . Moreover, there is a set of sandflat, mixed-flat and mudflat microfacies in the main inter-flood period. Different from the two cycles above, in long-term cycle, it has a trend that the scales of the channel decrease in main flood period while the thicknesses of red mudflat increase in inter - flood period. All these characters in mid- ＆ long-term sequence cycle suggest the climate has a tendency to become more and more arid. In terms of the characters of sequences and microfacies in arid climate evolution, the authors build up a set of high-resolution stratigraphic sequence and make the stratigraphic correlation.