Mesozoic sedimentary and volcaniclastic rocks dredged from the northern Exmouth Plateau and Rowley Terrace, offshore northwest Australia

An extensive program of dredging was undertaken by AGSO in 1990 on the northern Exmouth Plateau and Rowley Terrace margin, mainly to provide geological control for seismic interpretations. Forty-two major Mesozoic lithofacies types were recovered. The rocks indicate that: 1. During the Late Triassic (Norian-Rhaetian), the Rowley Terrace margin was, like the adjacent northern Exmouth Plateau, host to shelf carbonates, including reef and peri-reefal deposits. Volcanics were emplaced along the margin (particularly in the north) during the Late Triassic-Mid Jurassic, probably as a result of the commencement of rifting between Australia and Greater India. The volcanics were laid down partly or reworked into shallow water , producing hyaloclastites and tuffaceous mudstones with marine microfossils. By the Early Jurassic, carbonate deposition was restricted to relatively small areas with most of the outer Rowley Terrace being covered by thick, fluvial - paralic siliciclastics with marine interbeds. These deposits continued to be deposited until the early Late Jurassic. They were subjected in the ?Late Jurassic to subaerial exposure under arid conditions resulting in cementation by Fe-oxides. With the early Late Jurassic (Oxfordian- Callovian) breakup and formation of the Argo Abyssal Plain, the margin started to subside and thin, shallow-marine, Late Jurassic-Early Cretaceous sediments were deposited. These were followed, with continuing margin subsidence, by progressively deeper-water deposits, including Cretaceous and younger hemipclagic-eupelagic claystones, chalks, and marls. 2. Reefs grew in the area of the outer part of the Rowley Terrace during the Late Triassic. The potential therefore exists for Upper Triassic, reefal petroleum reservoirs to be present within the main part of the Rowley Sub-basin to the east, if reefs in that area were not prevented from growing by sand influx from rivers. Similarly, Lower Jurassic shallow-water platform carbonates, which are present on Triassic horst blocks beneath the central northern part of the Exmouth Plateau, could act as petroleum reservoirs if porosity is preserved. 3. During the Late Triassic and Early Jurassic there is a clear similarity between the facies and associated foraminiferal and ostracod microfaunas of the northern Exmouth Plateau/ Rowley Terrace area and thos e of other southern Tethyan margins, including the Northern Calcareous Alps. This indicates that broadly similar depositional conditions existed along much of Neo-Tethys at that time.

1990年，澳大利亚地质调查局（AGSO）在埃克斯茅斯高原北部与罗利台地陆缘实施了大规模疏浚工程，主要目的是为地震解释提供地质约束依据。本次工程共采获42种主要中生代岩相类型。相关岩石研究揭示以下认识：
1. 晚三叠世（诺利期-瑞替期），罗利台地陆缘与毗邻的埃克斯茅斯高原北部一致，均发育陆棚碳酸盐岩沉积，包括礁体及礁周相沉积物。晚三叠世-中侏罗世期间，沿该陆缘（尤其北部区域）侵位火山岩，其成因大概率与澳大利亚与大印度之间的裂谷作用启动有关。这些火山岩部分在浅水环境中沉积，或经改造后形成含海相微化石的玻屑凝灰岩（hyaloclastites）与凝灰质泥岩（tuffaceous mudstones）。至早侏罗世，碳酸盐岩沉积仅局限于相对狭小的区域，罗利台地外缘大部分区域被厚层河流-近海（fluvial-paralic）陆源碎屑岩覆盖，且夹有海相夹层。这套沉积持续至晚侏罗世早期。晚侏罗世时期，该区域在干旱条件下遭受大气暴露，进而发生氧化铁胶结作用。随着晚侏罗世早期（牛津期-卡洛维期）泛大陆裂解、阿尔戈深海平原（Argo Abyssal Plain）形成，该陆缘开始沉降，随后沉积了薄层浅海相晚侏罗世-早白垩世沉积物。伴随陆缘持续沉降，沉积环境逐步向深水环境过渡，形成白垩纪及更年轻的半远洋-远洋（hemipelagic-eupelagic）黏土岩、白垩及泥灰岩。
2. 晚三叠世时期，罗利台地外缘区域发育礁体。因此，若罗利次盆（Rowley Sub-basin）东部主体区域的礁体未受到河流输入砂体的阻隔，则该区域可能存在上三叠统礁型油气储层。同理，埃克斯茅斯高原中北部下方的三叠纪地垒块体上发育的早侏罗世浅水台地碳酸盐岩，若孔隙保存完好，亦可作为油气储层。
3. 晚三叠世至早侏罗世期间，埃克斯茅斯高原北部/罗利台地区域的岩相以及伴生的有孔虫与介形类微动物群，与包括北阿尔卑斯（Northern Calcareous Alps）在内的其他南特提斯陆缘具有显著相似性。这表明当时新特提斯洋（Neo-Tethys）多数陆缘区域的沉积环境大体相似。