Cenozoic Cool-water Carbonates of the Great Australian Bight : Reading the Record of Southern Ocean Evolution, Sealevel, Paleoclimate, and Biogenic Production : Revised ODP Proposal - December 1994

This proposal advocates the drilling of a transect of holes across the southern continental margin of Australia; the largest cool-water carbonate shelf on Earth today. This latitude-parallel shelf along the northern margin of the Southern Ocean contains fundamental geological and paleoceanographic information of global geodynamic, sedimentological, paleobiological, and paleoclimatological
importance. The major objectives of this proposal are: 1) to ascertain the way in which a large, high- to mid-latitude shelf carbonate platform evolved throughout the past 65 m.y. in response to oceanographic and biotic change; and 2) to extract information contained in the carbonate sediments detailing global sealevel fluctuations, physical and chemical paleo-ocean dynamics, biotic evolution,
hydrology, and diagenesis. Furthermore, because of architectural and compositional similarities with many older Phanerozoic carbonate platforms, the results from the proposed drilling would be of tremendous importance for the actualistic modelling of ancient open platforms and ramps.

Offshore seismic data and limited drillhole information indicate that the margin has been the site of dominantly cool-water carbonate shelf deposition since the Eocene, and show a detailed accretionary history of progradation, erosion, and biogenic mound growth. The subsidence history is relatively simple, resulting in a 1 km-thick Cenozoic section. Onshore exposures provide a basis for predictive
analysis of the offshore sequences identified in seismic sections, and confirm that the sediments are predominantly soft, friable, and abundantly fossiliferous.

A shallow shelf to deep continental rise transect of 12 holes is proposed, located to penetrate inner shelf, outer shelf, upper slope, upper slope terrace, and continental rise settings. The primary drilling objective is a more detailed understanding of global environmental change in high- to mid-latitude settings. Cores from different facies at various depths during a range of geologic periods will yield a detailed anatomy of a Cenozoic cool-water carbonate shelf. The response of this depositional system to inferred sealevel fluctuations will be compared to records from warm-water, rimmed and un-rimmed carbonate platforms in order to test and refine the global sealevel curve, and most importantly to describe the reaction of cool-water carbonate depositional systems to different phases of the sealevel cycle. Biological and chemical paleoenvironmental proxies will be used to decipher a detailed
paleoceanographic record, in order to more precisely describe the timing and paleoceanographic effects of the opening of the Tasman Gateway, and the influence of the Leeuwin Current on paleoproductivity over time. The shelf-to-basin transect will also provide high resolution data on the tempo and pattern of biotic evolution in oceanic and neritic environments.

Secondary objectives are directed towards understanding the hydrology of a carbonate platform adjacent to a vast inland karst with sluggish water circulation; and the nature of early burial diagenesis (lithification and dolomitization) in a cold, seawater-dominated system.

本提案倡议在澳大利亚南部大陆边缘布设钻孔剖面——该区域分布有现今全球规模最大的冷水碳酸盐岩陆架（cool-water carbonate shelf）。这条沿南大洋北缘展布的纬向陆架，蕴含着具有全球地球动力学、沉积学、古生物学与古气候学重要意义的基础地质与古海洋学信息。

本提案的核心目标有二：其一，阐明大型中高纬度冷水碳酸盐岩台地在过去6500万年中如何响应海洋环境与生物群落变化而演化；其二，提取碳酸盐沉积物中记录的全球海平面波动、古海洋物理化学动力学、生物演化、水文地质与成岩作用相关信息。此外，由于该陆架与诸多显生宙古碳酸盐岩台地在结构与组成上高度相似，本次钻探成果对于古代开阔型台地与缓坡的现实主义模拟具有极高价值。

近海地震数据与有限的钻孔资料显示，自始新世以来，该大陆边缘一直以冷水碳酸盐岩陆架沉积为主，且保留了进积、侵蚀与生物丘生长的详细加积演化历史。其沉降史相对简单，形成了厚度达1千米的新生代沉积序列。陆上露头为地震剖面识别的近海沉积序列的预测分析提供了依据，并证实沉积物普遍质地松软、易碎且富含化石。

本次计划布设12个钻孔，组成从浅陆架延伸至深海大陆隆的剖面，以穿透陆架内区、陆架外区、上陆坡、上陆坡阶地与大陆隆等不同沉积环境。本次钻探的首要目标是更深入地解析中高纬度区域的全球环境变化。通过获取不同地质时期、不同深度不同岩相的岩芯，可全面解析新生代冷水碳酸盐岩陆架的沉积学特征。将该沉积系统对推测海平面波动的响应与暖水镶边及非镶边碳酸盐岩台地的记录进行对比，可验证并修正全球海平面变化曲线，尤为重要的是阐明冷水碳酸盐岩沉积系统对海平面旋回不同阶段的响应模式。本次研究将利用生物与地球化学古环境代用指标，重建高精度古海洋记录，以精准解析塔斯曼门户（Tasman Gateway）开启的时间及其古海洋学效应，以及勒文海流（Leeuwin Current）随时间变化对古生产力的影响。该陆架-盆地剖面还将为海洋与浅海环境中生物演化的速率与模式提供高分辨率数据。

次要钻探目标旨在解析两大科学问题：一是毗邻水循环滞缓的大型内陆喀斯特地貌的碳酸盐岩台地的水文特征；二是冷海水主导体系中的早期埋藏成岩作用（岩化作用与白云岩化作用）的性质。