江西龙虎山世界地质公园白垩系辫状河相沉积及其丹霞地貌发育特征

通过野外露头及相关室内研究,分析了龙虎山世界地质公园及邻区白垩系辫状河相沉积特征及其与丹霞地貌发育规律关系。研究认为:龙虎山世界地质公园丹霞地貌发育除了与冲积扇相沉积有关外,还与辫状河相沉积有关,表现为辫状河道巨厚砂体为丹霞丘陵地貌发育提供物质基础;发育于辫状河道中呈小型透镜体或扁平状、脉状体的河床滞留沉积和洪泛沉积,易风化剥蚀形成溶蚀风化崩塌型丹霞地貌。此外,多期河道的多旋回沉积交错叠置形成楔状交错层理,其层系上下界面平直,层系厚度在小范围内变化很快,层系内细层的倾向相反,为后期风化剥蚀提供了条件,易形成溶蚀风化崩塌型丹霞地貌。进一步研究发现丹霞丘陵地貌、溶蚀风化崩塌型丹霞地貌分布与辫状河相沉积平面展布具有较好的一致性,吻合度较高。本文首次研究了辫状河沉积体系与丹霞地貌发育特征的关系。     

石炭纪-早二叠世滇黔桂盆地北缘深水区的地层序列及沉积演化

通过分析石炭纪-早二叠世滇黔桂盆地北缘深水区的地层序列和沉积特征,探讨沉积演化过程及其控制因素。研究区深水地层序列包括下述的9个岩石地层单元:鹿寨组(C₁lz)、巴平组(C₁bp)、下如牙组(C₁xr)、上如牙组(C₁sr)、王佑组(C₁w)、睦化组(C₁m)、打屋坝组(C₁dw)、南丹组(C₁-P₁nd)和船埠头组(C₁c),并且可以识别出4种主要的深水沉积相:台间盆地相、斜坡相、深水陆棚相和台前斜坡相,以砂岩、碳质页岩、硅质泥岩、硅质岩、钙屑碎屑岩、泥晶灰岩和白云质灰岩为主要特征,与桂西南深水盆地的差别显著。依据地层序列和沉积组合的时空分布特征,可以将石炭纪-早二叠世滇黔桂盆地北缘深水区的沉积演化划分为3个阶段: 1)裂谷作用强烈期(早石炭亚纪汤耙沟期早期); 2)裂谷作用减弱期(早石炭亚纪汤耙沟期中期-德坞期); 3)裂谷作用稳定期(晚石炭亚纪-早二叠世)。     

太湖沉积对流域极端降水和洪水响应的研究

认识极端洪水特征和周期,急需建立长期洪水记录和序列。过去150 a来长江下游极端降水引发了多次太湖特大洪水,太湖湖泊沉积提供了长于观测资料的洪水记录。本文利用太湖中心开阔水域的近现代沉积,采用210Pb和137Cs测年法和粒度、磁学特征分析,与区域夏季降水和长江下游洪峰流量进行相关分析,恢复了太湖流域150 a来的历史洪水事件。根据长江下游极端夏季降水（Pjja≥90%百分位）和极端径流(Q≥90%百分位)以及历史文献记载,太湖流域自1840年以来约有24次特大洪水年,而湖泊沉积物砂级粒径与低频磁化率等特征能捕获与之对应的中洪水事件15次。这表明湖泊沉积记录能较好地反演过去洪水变化,为利用沉积记录认识百年极端洪水长周期变化和特征提供了沉积学、磁学等方面的科学依据。     

水城-紫云-南丹裂陷盆地晚古生代硅质沉积物地球化学特征及其地质意义

水城-紫云-南丹裂陷盆地位于右江盆地北缘,晚古生代该盆地内广泛分布包括硅质岩在内的碳酸盐岩台盆相沉积,其沉积组合及地球化学特征不同于大陆架型以及增生杂岩中硅质岩。对盆地内硅质沉积物的地球化学特征研究表明,南丹上泥盆统榴江组底部和河池中下二叠统四大寨组硅质沉积物多为基性火山喷发相关的火山热液成因,其具有较低的Al/(Al+Fe+Mn)值和Al2O3/TiO2值,紫云中下二叠统四大寨组硅质沉积物的Al/(Al+Fe+Mn)值和Al2O3/TiO2值分别为0.62±0.16和11.70±4.30,为含有火山碎屑的非热液成因,其他硅质沉积物多为正常海相沉积。晚泥盆世—早石炭世盆地内硅质沉积物多与泥岩和灰岩共生,硅质沉积物常具有中等Ce负异常(多在0.60～0.85之间)以及较高的Y/Ho值(多在30～45之间),除去SiO2稀释作用的影响后,其具有较低的稀土元素含量(∑REE+Y含量相当于PAAS组成的3倍以下)。而伴随着盆地的裂陷和扩张,到早中二叠世,盆地内硅质沉积物多与深灰色厚层灰岩共生,硅质沉积物常具有明显的Ce负异常(0.06～0.61)以及与开阔洋盆海水相似的Y/Ho值(40～92),除去SiO2稀释作用的影响后,其具有较高的稀土元素含量(∑REE+Y含量相当于PAAS组成的2倍以上)。     

Cross‐shelf colour zonation in northern Great Barrier Reef lagoon surficial sediments

A cross‐shelf colour zonation is observed in Great Barrier Reef lagoon surficial sediments from 12 to 18°S, with colours tending to lighten from inner to outer shelf. The phenomenon is particularly well defined south of Cairns where four zones occur. The colour zonation appears to reflect the abrupt facies changes that occur in the lagoon. Visual estimates of relative optical lightness for the zones are strongly related to carbonate content, and lightness class boundaries broadly follow carbonate contours, indicating that the mechanisms leading to the colour zones are related to those governing carbonate distribution.     

Discussion and Reply: Shaping the Australian crust over the last 300 million years: Insights from fission track thermotectonic imaging and denudation studies of key terranes

Ellis Fjord is a small, fjord‐like marine embayment in the Vestfold Hills, eastern Antarctica. Modern sediment input is dominated by a biogenic diatom rain, although aeolian, fluvial, ice‐rafted, slumped and tidal sediments also make a minor contribution. In areas where bioturbation is significant relict glaciogenic sediments are reworked into the fine‐grained diatomaceous sediments to produce poorly sorted fine sands and silts. Where the bottom waters are anoxic, sediments remain unbioturbated and have a high biogenic silica component. Three depositional and non‐depositional facies can be recognised in the fjord: an area of non‐deposition around the shoreline; a relict morainal facies in areas of low sedimentation and high bioturbation; and a basinal facies in the deeper areas of the fjord.     

Stratigraphy and fluvial sedimentary facies of the Neocomian lower Strzelecki Group,Gippsland Basin,Victoria

The Strzelecki Group incorporates Berriasian to Albian, fluvial sediments deposited in the Gippsland Basin during initial rifting between Australia and Antarctica. Neocomian strata of the lowermost Strzelecki Group are assigned to the Tyers River Subgroup (exposed in the Tyers area) and the Rhyll Arkose (exposed on Phillip Island and the Mornington Peninsula). The Tyers River Subgroup incorporates two formations: Tyers Conglomerate and Rintoul Creek Formation. The latter is subdivided into the Locmany and Exalt Members. Ten fluvial sedimentary facies are identified in the lowermost Strzelecki Group: two gravelly facies; four sandy facies; and four mudrock facies. Associations of these facies indicate: (i) prevalence of gravelly braided‐river and alluvial‐fan settings during deposition of the Tyers Conglomerate; (ii) more sluggish, sandy braided to meandering fluvial systems during Locmany Member sedimentation; and (iii) a return to active, sandy, braided‐river settings for deposition of the Exalt Member. The Tyers Conglomerate and Rhyll Arkose rest on an irregular erosional surface incised into Palaeozoic rocks of the Lachlan Fold Belt. The overlying Rintoul Creek Formation incorporates more mature sediments where lithofacies associations varied according to base‐level change, variations in subsidence rates, and/or tectonic uplift of the principal sedimentsource terranes to the northwest.     

The Cainozoic geology of the Middle Shoalhaven Plain

The Middle Shoalhaven Plain is a large, tray‐like depression bounded in the west by the Mulwaree fault and in the east by cliffed Permian sediments. The plain is probably Mesozoic in origin and was partially alluviated during the Early to mid‐Eocene. Much of the plain and sediments were covered by basalts during the Late Eocene. This was followed by an episode of deep weathering, which culminated in the formation of widespread bauxitic and lateritic crusts and manganocrete and silcrete during the mid‐Tertiary. A second minor weathering event is recorded during the latest Tertiary to Early Pleistocene. Two new basalt dates are consistent with earlier ones at about 43 Ma. Palaeomagnetism shows bauxites and ferricretes to be mid‐Tertiary.     

Kenn Plateau off northeast Australia: a continental fragment in the southwest Pacific jigsaw

The submarine Kenn Plateau, with an area of about 140 000 km², lies some 400 km east of central Queensland beyond the Marion Plateau. It is one of several thinned continental fragments east of Australia that were once part of Australia, and it originally fitted south of the Marion Plateau and as far south as Brisbane. It is cut into smaller blocks by east- and northeast-trending faults, with thinly sedimented basement highs separated by basins containing several kilometres of sediment. In the Cretaceous precursor of the Kenn Plateau, Late Triassic to Late Cretaceous basins probably rested unconformably on Palaeozoic to Triassic rocks of the New England Fold Belt. Rift volcanism was common on the northern plateau and was probably of Early Cretaceous age. Late Cretaceous extension and breakup were followed by Paleocene drifting, and the Kenn Plateau moved to the northeast, rotated 30° anticlockwise and left space that was filled by Tasman Basin oceanic basalts. During these events, siliciclastic sediments poured into the basins from the continental mainland and from locally eroding highs. After a regional Late Paleocene to Early Eocene unconformity, siliciclastic sedimentation resumed in proximal areas. In deep water, radiolarian chalks were widely deposited until biosiliceous sediment accumulation ended at the regional Late Eocene to Early Oligocene unconformity, and warming surface waters led to accumulation of pure biogenic carbonates. Calcarenite formed in shallow water on the margins of the subsiding plateau from the Middle Eocene onward. Some seismic profiles show Middle to Late Eocene compression related to New Caledonian obduction to the east. Hotspots formed parts of two volcanic chains on or near the plateau as it moved northward: Late Eocene and younger volcanics of the Tasmantid chain in the west, and Late Oligocene and younger volcanics of the Lord Howe chain in the east. As the volcanoes subsided, they were fringed by reefs, some of which have persisted until the present day. Other reefs have not kept up with subsidence, so guyots formed. The plateau has subsided 2000 m or more since breakup and is now subject solely to pelagic carbonate sedimentation.