Sequence Stratigraphy, Third-Order Accommodation Events and Related Diagenetic History of the Middle Cambrian Bonanza King Formation, Southern Great Basin

本文拟对大盆地南部（加利福尼亚和内华达）中晚寒武世富矿王组旋回被动边缘碳酸盐岩进行层序地层学和成岩综合分析。地层高度在300 ~ 1350米之间，由克拉通边缘向陆架边缘和斜坡基底形成向西加厚的楔形岩相。富矿王由200米规模的碳酸盐岩旋回组成，提供了中晚寒武世三级相对海平面振荡的显著条带记录。初步结果表明，在Bonanza King平台上可以识别并绘制出4个半三级层序。厚的潮下旋回的间隔是海侵体系域的特征，薄的潮外旋回的间隔是高点体系域的特征，显示零星暴露证据的潮外旋回的薄带可能是层序边界带的特征。从克拉通边缘到外台地，早期白云岩环内丰度呈系统递减。层序边界带和上高地体系域旋回以白云岩为主，海侵体系域和下高地体系域旋回则保留大量灰岩。研究的目的有四个方面：1)以富矿王组良好的暴露程度、广阔的露头面积和非凡的旋回性为基础，解剖碳酸盐岩地层层序的内部解剖。循环叠加模式和跨平台趋势的可预测变化将用于识别组成系统域和边界不整合面。2)建立可靠的中晚寒武世调节曲线，并与已发表的曲线进行对比，以确定地层起伏对层序发育的控制程度。3)记录各频率海平面波动对富矿王碳酸盐岩早期成岩作用的影响。4)评价整个埋藏过程中流体-岩石相互作用过程中早期成岩相的结构、岩石物理和地球化学变化。本研究将层序地层学与富矿王组的海平面和成岩历史相结合，是破解科迪勒拉被动边缘早古生代碳酸盐岩成岩历史的首次重大尝试。

The proposed research involves a combined sequence stratigraphic and diagenetic analysis of cyclic passive margin carbonates of the Middle to Late Cambrian Bonanza King Formation of the southern Great Basin (California and Nevada). The formation ranges from 300 to 1350 meters and forms a westward-thickening wedge from craton margin to shelf-edge and base-of-slope facies. The Bonanza King is composed of 200 meter-scale carbonate cycles that provide a remarkable strip record of Middle to Late Cambrian third-order relative sea-level oscillations. Preliminary results suggest that four and a half third-order sequences can be recognized and mapped out across the Bonanza King platform. Intervals of thick subtidal cycles appear to characterize the transgressive systems tracts, intervals of thin peritidal cycles characterize the highstand systems tracts and thin zone of peritidal cycles exhibiting evidence of sporadic exposure probably manifest sequence boundary zones. Intracyclic abundance of early dolomite decreases systematically from craton margin to outer platform. Cycles in sequence boundary zones and upper highstand systems tracts are dominantly dolomite whereas cycles in transgressive systems tracts and lower highstand systems tracts retain abundant limestone. The objectives of the research are fourfold: 1) Dissect the internal anatomy of carbonate stratigraphic sequences using the excellent exposures, broad outcrop area and extraordinary cyclicity of the Bonanza King Formation as the data base. Predictable variations in cycle stacking patterns and cross-platform trends will be used to identify the component systems tracts and bounding unconformities. 2) Develop a reliable Middle to Late Cambrian accommodation curve of comparison to other published curves to determine the degree of eustatic control on sequence development. 3) Document the effects of sea-level fluctuations of all frequencies on early diagenesis of Bonanza King carbonates. 4) Evaluate the textural, petrophysical and geochemical changes that occur in early diagenetic facies during fluid-rock interaction throughout burial. This study integrates the sequence stratigraphy with the sea- level and diagenetic history recorded in the Bonanza King Formation and is the first major attempt to decipher the diagenetic history of early Paleozoic carbonates of the Cordilleran passive margin.