Paleogene Sedimentary Rocks Research Articles

New understanding on the interplay of longitudinal and transverse sediment dispersal: Combination of 3D seismic profile and u-pb ages of detrital zircons of Paleogene sedimentary rocks in the northern South China Sea

The northern South China Sea (SCS) experienced a significant transition from a lacustrine to marine environment in the Paleogene, and its deep-water basin of Zhu-II Depression is in particular extensively studied due to its richness in oil and gas resources. However, limited number of boreholes in the deep-water area has long constrained a better understanding on the provenance of the Paleogene strata and the associated sediment transport processes. In this study, detrital zircon U-Pb ages and three-dimensional (3D) seismic-reflection data were systematically employed to investigate the “source-to-sink” pathways and interplay of longitudinal and transverse sediment dispersal. Our results indicate that the Zhu-II Depression sediments of the northern SCS were predominantly derived from the surrounding nearby paleo-uplifts in the early and middle Eocene. A significant provenance shift took place in the late Eocene, when the local paleo-uplift source was replaced by a distant source from the western SCS. Sediments were transported from west to east by the “Kontum-Ying-Qiong River” as a longitudinal dispersal. In the Oligocene, the “Kontum-Ying-Qiong River” delivered large amounts of sediments from Central Vietnam to the eastern part of the northern SCS. Meanwhile, the Pearl River gradually evolved through regional tectonic processes and influenced the deep-water area of Zhu-II Depression as a transverse dispersal. Sediments from both “Kontum-Ying-Qiong” and Pearl Rivers converged and deposited as deep-water deltas in the Zhu-II Depression. This dual provenance system in the northern SCS deep-water area was featured by the interplay between longitudinal and transverse sediment dispersal. It was largely controlled by the tectonic-palaeogeographic pattern inherited from the Mesozoic arc system.

GEOLOGICAL INTERPRETATION OF NORTH MADURA OFFSHORE SEDIMENTARY BASIN BASED ON GRAVITY DATA ANALYSIS

The area of north Madura offshore is one of the sedimentary basins within the North East Java Basin which has interesting paleogeographical developments. These developments are the result of various sedimentation processes and changes in the depositional environments. The purpose of this study is to identify subsurface geological structures, delineate sedimentary sub-basins, and estimate sediment thickness. For that, we do spectrum analysis, optimum upward continuation filtering, spectral decomposition analysis, 2D forward modeling and 3D inversion of gravity data. The results of the spectral analysis show that the average thickness of sedimentary rocks in the study area is around 3.788 km. From the gravity data analysis, 10 sedimentary sub-basins were delineated, indicating structural patterns of basement high, grabens, and faults. 2D and 3D modeling revealed four layers of stratigraphy, in order from youngest to oldest are Tertiary-Neogene sedimentary rocks with a density value of 2.1 gr/cc, the Tertiary-Neogene sedimentary rocks with a density of 2.3 gr/cc, the Tertiary - Paleogene sedimentary rocks with a density of 2.45 gr/cc, and the basement layer identified as volcanic igneous rock with a density of 2.67 gr/cc.

New stratigraphic and paleoenvironmental constraints on the Paleogene paleogeography of Western Amazonia

The rise of the Andes and the associated propagation of the retroarc foreland basin during the Mesozoic Cenozoic in western South America shaped the paleogeography and paleoenvironmental settings of Western Amazonia. Much attention has been paid to the Neogene evolution of the Amazonian Basin, but few studies have investigated in detail the paleoenvironments of Western Amazonia during the Paleogene. We present a multi-proxy study that includes new biostratigraphic and paleontologic data, the interpretation of depositional environments and zircon U–Pb data from the Upper Cretaceous-Paleogene sedimentary sequence exposed in the Huallaga Basin (northern Peru). The biostratigraphic dating suggests that the lower part of the sequence is Maastrichtian in age. The maximum depositional age and maximum likelihood age according to the U–Pb zircon dating of Paleogene sedimentary rocks indicate Lutetian to Bartonian ages (from 43.5 ± 0.64 Ma to 37.6 ± 0.85 Ma). These results reveal a hiatus in the depositional record during Paleocene time. Two depositional systems can be distinguished: a lacustrine system composed of red mudrocks interbedded with thick sandstone layers and carbonate beds, and a siliciclastic tide-dominated system composed of fine-to medium-grained sandstones associated with tidal bundles, reactivation surfaces and heterolithic stratifications. However, the carbon and oxygen stable isotope values in carbonates tend to characterize a freshwater system, with a transition to brackish conditions toward the upper part of the section (Bartonian), thereby suggesting the presence of an estuary system. Finally, we suggest that the Bartonian shallow marine incursion recorded in the Huallaga Basin occurred from the north through the Caribbean Sea, and that it might have played a role in regional biodiversity patterns in the Paleogene.

Tectonic transition from thrusting to polyphase non-confining deformation within the Semail Ophiolite along the sinistral, transtensional Issmaiya Fault Zone (Sultanate of Oman)

• The Oman Mountains record the transition between shortening during the obduction of the Semail ophiolite . • At least three extensional events: affected the autochthonous and allochthonous units after obduction: two between the latest Cretaceous and early Eocene and one after the mid-Eocene. • Allochthonous units underwent major extensional shearing immediately after the emplacement of the ophiolite. • The allochthonous units underwent two further extensional events: One between the latest Cretaceous and early Eocene, and the other one after mid-Eocene. Obduction of the Semail Ophiolite and deep-sea basin-derived rocks represent a major tectonic event during Late Cretaceous evolution of the Oman Mountains. These allochthonous units were thrust SW-ward onto the passive Arabian margin and platform, followed by the main uplift of the Saih Hatat Dome and minor uplift of the Jabal Akhdar Dome. We present new structural data that indicate major extensional and transtensional deformation affecting the ophiolite unit after its emplacement. The studied area is in the southeastern Oman Mountains and hosts the brittle “Issmaiya Fault Zone” (IFZ; ∼3 km in wide and ∼ 30 km long). Field work and satellite image analysis show that most faults affected the Semail Ophiolite and only a few faults cut through latest Cretaceous to Paleogene sedimentary rocks of the Ibra Basin. These constraints allow us to date most faulting to immediately after the Late Cretaceous emplacement of the Semail Ophiolite, lasting to the post-Paleogene. The IFZ strikes ∼NW-SE at an acute angle of ∼30° to the WNW-ESE oriented southern margin of the Saih Hatat Dome. Northwestward, the IFZ terminates at the southern boundary fault of the Saih Hatat Dome. Fault kinematics based on shear-fracture slip-indicators reveal vertical to steep NW/SE-striking fault planes with occurrence of mainly sinistral strike-slip and some extensional dip-slip faults. This highlights a latest phase in a constrictional strain field with N/S-extension, perpendicular to E/W-oriented and vertical shortening axes of a sinistral transtensional fault zone. We suggest that SW-ward thrusting of the Semail Ophiolite was followed by mainly sinistral transtension.

Paleogene Sedimentary Records of the Paleo‐Jinshajiang (Upper Yangtze) in the Jianchuan Basin, Yunnan, SW China

AbstractCenozoic surface uplift of Tibetan Plateau has driven the birth and reorganization of large river systems in Asia. The development of the Yangtze River, closely linked to plateau uplift, has important implications for the regional tectonic‐geomorphology processes, but is still under debate. The key scientific question is whether the Upper Yangtze (upper Jinshajiang) once flowed southeast to the South China Sea. In this study, we carried out provenance analysis on Paleogene sedimentary rocks in the Jianchuan Basin, composed of the Baoxiangsi, Jinsichang, and Shuanghe formations. We compared them with similar deposits in other regional basins, as well as with potential sources. Heavy‐mineral and geochemical data show that sediments from the Jinsichang formation are more mature compared with those from the Shuanghe and Baoxiangsi formations. The Jinsichang formation represents the products of a large fluvial system, whereas the Baoxiangsi formation is mainly dominated by local sources. The Shuanghe formation contains material from both distant sources and locally eroded materials. Detrital zircon U‐Pb age patterns from the Jianchuan Basin are similar to those in sediments in the Gonjo, Simao, and Chuxiong basins, and show great similarity with the modern Jinshajiang River. Statistical analysis of the zircon ages suggests that the Songpan‐Ganzi terrane was the primary source for all sediments, while the Yangtze Craton and northern Qiangtang terrane constitute secondary sources. Taken together these data confirm that a paleo‐Jinshajiang flowed south toward to the South China Sea from the SE Tibetan Plateau in the late Eocene, constraining the age of formation of the First Bend.

The Main Types of Paleogene Sedimentary Rocks and Conditions of their Formation on the Guyots of the Magellan Seamounts (Pacific Ocean)

he Paleocene–Eocene sedimentary complex is most widely developed among the sedimentary cover deposits of the Magellan Seamounts. It is composed of pelagic (nanoforaminiferal) and reef limestones, edaphogenic breccias and volcanoclastic rocks. The most widespread pelagic limestones form narrow (0.5–1.5 km) and extensive (up to 20 km) ribbon-like bodies that cover the upper parts of the slopes and the rim of the summit plateau. The maximum area of their distribution, which covers 315 km2, is noted on the Fedorov Guyot. Pelagic limestones and edaphogenic breccias outcrop over large areas and have reciprocal facies transitions. The Oligocene hiatus in sedimentation has been established in the sections of the Cenozoic sedimentary cover deposits of the studied guyots.

A Late Eocene‐Oligocene Through‐Flowing River Between the Upper Yangtze and South China Sea

AbstractWe test the hypothesis of a major Paleogene river draining the SE Tibetan Plateau and the central modern Yangtze Basin that then flowed south to the South China Sea. We test this model using U‐Pb dated detrital zircon grains preserved in Paleogene sedimentary rocks in northern Vietnam and SW China. We applied a series of statistical tests to compare the U‐Pb age spectra of the rocks in order to highlight differences and similarities between them and with potential source bedrocks. Monte Carlo mixing models imply that erosion was dominantly derived from the Indochina and Songpan‐Garzê Blocks and to a lesser extent the Yangtze Craton. Some of the zircon populations indicate local erosion and sedimentation, but others show close similarity both within northern Vietnam, as well as more widely in the Eocene Jianchuan, Paleocene‐Oligocene Simao, and Oligocene‐Miocene Yuanjiang basins of China. The presence of younger (<200 Ma) zircons from the Qamdo Block of Tibet is less easily explicable in terms of recycling by erosion of older sedimentary rocks and implies a regional drainage linking SE Tibet and the South China Sea in the Late Eocene‐Oligocene. Detrital zircons from offshore in the South China Sea showed initial local erosion, but with a connection to a river stretching to SE Tibet in the Late Oligocene. A change from regional to local sources in the Early Miocene in the Yuanjiang Basin indicates the timing of disruption of the old drainage driven by regional plateau uplift.

Geochemistry and petrogenesis of sandstones and their basaltic interlayers of Shexing Formation from Linzhou basin, South Tibet

印度与亚洲大陆的碰撞是青藏高原演化的重要构造事件，碰撞过程被记录在拉萨地块南部的晚白垩世到古新世的沉积-岩浆作用中。林周盆地的晚白垩世设兴组及其之后不整合覆盖的林子宗火山岩，是解析碰撞过程的重要记录。本文对设兴组最高层位的砂岩和玄武岩夹层进行了岩石学、地球化学和年代学研究，探讨了岩石成因和构造意义。设兴组砂岩属于杂砂岩，碎屑物质主要来自中酸性岩浆岩源区；锆石Hf同位素指示设兴组大部分碎屑物质来源于盆地北面的中部拉萨地块，少部分来自盆地南部的冈底斯岩基；砂岩中最年轻的碎屑锆石年龄指示林周盆地设兴组是在98Ma之后接受沉积的。以夹层产出在设兴组顶部的玄武岩和玄武安山岩，富集轻稀土元素、亏损重稀土元素、弱负Eu异常，强烈富集Ba、Th、U、Pb等大离子亲石元素，显著亏损Nb、Ta等高场强元素，属于高钾钙碱性玄武岩系列，与典型安第斯型玄武岩特征吻合。玄武岩和玄武安山岩的锆石均为捕获锆石，其最年轻碎屑锆石年龄限定了设兴组玄武岩的喷发晚于110Ma。综合分析表明，林周盆地晚白垩世时期为夹持在冈底斯岩浆弧与中部拉萨地块之间的弧后盆地，新特提斯洋壳晚白垩世俯冲到冈底斯弧和弧后盆地之下，大约在98~110Ma之后喷发到林周盆地的很少量中基性岩浆构成了设兴组顶部的玄武岩和玄武安山岩夹层，是新特提斯洋俯冲相关的幔源岩浆作用。林周盆地设兴组（晚于98Ma）与上覆的林子宗火山岩（底部约为65Ma）之间呈大约33Myr的构造间断，可能代表了冈底斯弧的碰撞之前的隆升剥蚀过程。;The collision between India and Asia was the most important tectonic event in the evolution of the Tibetan Plateau, which was recorded in the Late Cretaceous to Paleogene sedimentary and magmatic rocks in the southern Lhasa terrane. The Late Cretaceous Shexing Formation strata and later eruption of the Linzizong volcanic succession (ca. 65~45Ma) is the best candidate to show the collisional processes. This study provides new petrological, geochemical and zircon U-Pb geochronological data on the sandstones and basaltic interlayers collected from the highest level of Shexing Formation in the Linzhou basin in southern Tibet. The materials of the Shexing greywacke were from the felsic magmatic source region. Hf isotope implies that the majority of the sediments came from the central Lhasa terrane to the north of the basin, and others from the Gangdese arc batholiths to the south of the basin. The youngest age of the detrital zircons in Shexing sandstone constrains the deposition were later than 98Ma in Linzhou basin. The interlayers close to the top of the Shexing Formation are basalts and basaltic andesites, with enriched light rare earth elements (REE), depleted heavy REE, weak negative Eu anomaly, strongly enriched large ionic lithophile elements (LILEs, such as Ba, Th, U, Pb), and depleted high-field strength elements (HFSEs, such as Nb, Ta). These basalts and basaltic andesites are high potassium calc-alkaline basalt series, with the affinity of the typical Andes-type basalts from continental arc. The detrital zircons from these interlayers define their eruption to be later than 110Ma. Our results suggest that the Linzhou basin is the back-arc tectonic setting, which located between the Gangdese arc and the central Lhasa terrane during the Late Cretaceous. The Neo-Tethys Ocean subducted beneath the Gangdese arc and the back-arc system and triggered the mantle partial melting to produce the eruption of the basalts and basaltic andesites after 98~110Ma. The interval of 33Myr between the upper most Shexing Formation (98Ma) and the Linzizong volcanics (65Ma), may represent the uplift and erosion processes of the Gangdese arc before the collision of India and Asia.

Occurrence, composition, and origin of analcime in sedimentary rocks of non-marine petroliferous basins in China

Abstract Natural analcime, a highly brittle aluminosilicate mineral that dissolves easily during diagenesis, occurs in the sedimentary rocks of eight main non-marine petroliferous basins in China. This mineral has been well documented for the past 30 years and has proved to be significant for the formation of high-quality hydrocarbon reservoirs. The present study fully reviews analcime occurrences, chemical compositions, Si/Al ratios, origin and controlling factors, and influence on the hydrocarbon reservoir quality in Permian to Paleogene sedimentary rocks. Previous research has shown that analcime is commonly distributed within argillaceous laminae (l-type); occurs as intergranular cement (c-type), replacement (r-type), and crack filling (f-type) forms; or is closely intergrown with other authigenic/exhalative minerals (a-type). Analcime in lacustrine basins is slightly Al-rich and Na-poor, and its Si/Al ratios range from 1.95 to 2.80. The geochemical compositions of the analcime- and ankerite-bearing exhalites are characterised by enrichment in light rare earth elements and 13C and depletion in heavy rare earth elements and 18O, with negative Eu and positive Ce anomalies. Diagenetic analcime forms by the alteration of volcanic glass, clays, or zeolite precursors in saline-alkaline lakes or during buried diagenetic stages in sedimentary rocks. In addition, it coexists with other authigenic zeolite, carbonate, and clay minerals as well as albite. Hydrothermal analcime presumably precipitates from hydrothermal fluids and is not dependent on a local precursor mineral or volcanic glass; this type is commonly related to exhalative mineralisation of hydrothermal springs. The formation of natural analcime is controlled by various factors such as the composition of the parent material, temperature prevalent during crystallisation, chemistry of the fluid phase, and thermodynamic characteristics of the geological environment. As zeolites are formed in alkaline fluid phases, they become unstable in acidic pore water. Secondary pores created by analcime mineral dissolution, and intercrystalline micropores among analcime minerals, are highly significant in hydrocarbon reservoirs. Analcime-bearing mudstone, siltstone, dolostone, and exhalite are favourable lithofacies for unconventional hydrocarbon accumulation owing to its high brittleness and selective dissolution of analcime and other associated minerals.

Paleoenvironmental Reconstructions using Organic Source Indicators: A Summary of Examples from Sri Lanka

The qualitative and quantitative analysis of sedimentary organic matter (i.e., the residue of past biota) provides integrated histories of marine and continental past life and paleoenvironmental /paleoclimatic changes. Organic geochemical investigations are possible by combining (i) bulk properties such as elemental compositions, stable isotope ratios, and Rock-Eval pyrolysis data, and (ii) biomarker molecular compositions such as n-alkanes, sterol, and polycyclic aromatic hydrocarbons compositions. The analytical approaches described in this overview illustrate the published examples of lacustrine and marine organic geochemical studies in Sri Lanka. In summary, the Jurassic Andigama and Tabbowa Basins provide different sources of organic matter, followed by availability of nutrient for algal growth and the amount of land runoff to the basins. Rock-Eval analysis of the Cretaceous to Paleogene sedimentary rocks in the offshore Mannar Basin reveal the presence of gas-prone land-plant organic matter mainly and minor oil-prone algal organic matter. The amounts and types of organic matter variations in Bolgoda Lake sediments indicate changes in Holocene sea-level, coastal geomorphology, and continental climates during the last 7,000 years. In future directions, applications of novel organic geochemical proxies and understanding of original biologically synthesized materials in tropics would improve interpretations of paleoenvironmental changes. Besides, local and regional paleoclimatic proxy and model studies would refine future paleoenvironmental reconstructions in Sri Lanka.

A NE-Trending Oblique-Slip Fault Responsible for the 2016 Zaduo Earthquake (Qinghai, China) Revealed by InSAR Data

Twelve Sentinel-1 images are used to measure the surface displacements caused by the Zaduo earthquake on 17 October 2016 in Qinghai, China. Comprehensive analysis of the local geologic structure, focal mechanisms, relocated aftershocks, and fault geometrical parameters from nonlinear inversions of the InSAR data indicates that a NE-trending fault with a strike of ~ 61°, namely the Aduo fault, was responsible for this event. Further geodetic inversions for finite fault models show that the dip angle of this fault is 75° to the SE. The majority of the slip occurred at the depth from 5 km to 17 km, and the normal-slip component was comparable to the strike-slip component. The peak slip of ~ 31 cm occurred at a depth of ~ 10 km. The InSAR determined moment is 9.61 × 1017 N m with a rigidity of 30 GPa, equivalent to Mw 5.9. The geological map reveals that the Aduo fault was characterized by a left-lateral strike-slip component in the past, as evidenced by the offset of Paleogene sedimentary rocks. Our results for the Zaduo earthquake suggest that the Qiangtang block probably consists of two or more sub-blocks with different eastward extrusion velocities and that the deformation of the Qiangtang block is occurring not only along its boundaries but also in its interior.

3D lithostratigraphic model of the Paleogene of the onshore part of the Moesian Platform (Northeast Bulgaria)

The Paleogene sedimentary rocks in the north-easternmost part of the territory of Bulgaria have been penetrated by numerous boreholes. In terms of regional tectonic zonation, the study area is a part of the onshore sector of the Moesian Platform, which partly includes the South Dobrogea Unit and the easternmost part of the North Bulgarian Dome with its eastern slope. The lithostratigraphy of the Paleogene successions consists of six formal units (the Komarevo, Beloslav, Dikilitash, Aladan, Avren, and Ruslar formations) and one informal unit (glauconitic marker). For compiling an overall conception of the regional aspects (lithology, thickness, spatial distribution, and relationships) of the individual lithostratigraphic units and for illustration of their spatial distribution, a 3D lithostratigraphic model based on reinterpretation of individual borehole sections has been created. The model database was compiled by integration of the original lithological data from 338 borehole sections.

Three-dimensional (3-D) seismic imaging of conduits and radial faults associated with hydrothermal vent complexes (Vøring Basin, Offshore Norway)

Here, we document a suite of radial faults associated with hydrothermal vent complexes in the Vøring Basin, offshore Norway. These complexes have pyramid-shaped, cylindrical- and conical-shaped conduits, with a dome-, or eye-shaped morphology at their summit, intruding on Paleogene sedimentary rocks. Hydrothermal vents are intimate with the tips of magmatic sills that were emplaced at depths ranging between 1800 and 5800 ms Two Way Travel Time (TWTT). At shallower depths of 1800 to 3000 ms TWTT and intermediate depths of 3000 to 5000 ms TWWT, magmatic sills regularly intersect the lower parts of the vent conduits, which are characterized here as pipes. An important parameter that is used to characterize the morphology of a hydrothermal vent conduit is the width of the conduit, which is defined as the longest axis marking the extent of the vents' conduit within the surrounding host-rock strata. Our findings reveal that radial faults are commonly associated with the summits of hydrothermal vents, implying the existence of local stress fields around the vents, where the maximum compressive stress is radial and minimum stress is circumferential, which overrides the regional stress field and indicate variable stress regimes as opposed to tectonic faults. Importantly, circumferential stretching due to catastrophic plumbing of hydrothermal fluids, differential compaction and intensive fracturing enabled the polygonal faults to realign in a radial pattern resulting in the formation of radial faults at the vent summit. As a corollary of this work, we hypothesize that pyramid-shaped hydrothermal conduits are possibly markers of protracted sill emplacement in sedimentary basins.

A new dysagrionid damselfly (Odonata: Zygoptera: Palaeodysagrion) from mid-Cretaceous Burmese amber

AUTHOR, N. & AUTHOR, P. December 2017. Article title. Alcheringa 42, 301-305. ISSN 0311-5518. Dysagrionidae are common in Paleogene sedimentary rocks, but rarely recorded in the Mesozoic. This family, however, is diverse in Burmese amber. A new dysagrionid damselfly, Palaeodysagrion youlini Zheng, Chang & Chang sp. nov., is described here based on a well-preserved specimen (holotype) in Burmese amber. The new damselfly provides wing apex and body characters for Palaeodysagrion. It differs from Palaeodysagrion cretacia in having Arc slightly distal of Ax2, the midfork slightly basal of the nodus, Cr and Sn almost perpendicular to RA and RP and in having a simple wing system. This is the fourth dysagrionid damselfly described from the Burmese amber.Daran Zheng* [dranzheng@gmail.com], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210,008, PR China; Su-Chin Chang [suchin@hku.hk]*, Department of Earth Sciences, The University of Hong Kong, Hong Kong Special Administrative Region, PR China; Bo Wang† [bowang@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210,008, PR China. *Also affiliated with: Department of Earth Sciences, The University of Hong Kong, Hong Kong Special Administrative Region, PR China. †Also affiliated with: Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100,101, PR China.

Geologically constrained changes to landforms caused by human activities in the 20th century: A case study from Fukuoka Prefecture, Japan

Human activity has been recognized to be an important geomorphic agent, and the resulting changes to landforms and land cover are regarded as a global problem. Although there has been much research into the relationships between geomorphic processes and types of land use such as agriculture, mining, and urbanization, it is important to clarify spatiotemporal human impacts on topography on a regional scale when predicting future changes in land cover.This study examined changes in land use to clarify the distribution and impact of anthropogenic changes to landforms, as well as the influence of geology on the extent of these changes. In a case study from Fukuoka Prefecture, Japan, changes in land use over the last century were analyzed using a geographic information system (GIS). The study area, which covers approximately 4930 km2, has experienced urban development since 1950 and has a current population of over 5 million. Land use data were prepared using paper-based early editions of topographic maps. Subsequently, the distribution of anthropogenic landforms was evaluated by comparing landforms with regional geological data.GIS analysis using our prepared land use data, landform data, and regional geological data has clarified the following characteristics of the study area. (1) Land uses prior to 1950 were constrained by topographic relief. After 1950, land use was characterized by urban sprawl. Urban areas expanded and contained both higher elevations and steeper slopes at their margins. The relationships between land uses and landforms during this urbanization are unclear. (2) The area of urban land increased in the geological regions with Paleogene sedimentary rocks (PSD) and Mesozoic granitic rocks (GR) during the 20th century. The largest coal mining area in Japan was located in the PSD geological regions, and ancient iron working was common in the GR geological regions, particularly during the 7th century. This result indicates that the land use distribution, especially urban areas in sloping terrain, is related to the regional geology. (3) Deforestation related to land use resulted in steeper terrain in forest land in the PSD and GR geological regions. These changes to landforms in forest areas occurred as a result of rapid urban sprawl and have created many new boundaries between forest areas with steeper slopes and urban areas with gentler slopes. This phenomenon may have caused an increase in the frequency of sediment-related disasters.This case study indicates that predictions of anthropogenic changes to landform, which are important for the assessment of global climate change and natural hazards, must clarify the relationships between land uses, landforms, and regional geology.

有機・無機物質からみた天草古第三紀層の続成・変成作用

有機・無機物質からみた天草古第三紀層の続成・変成作用

Larger foraminiferal biostratigraphy of the upper Cretaceous (Campanian) to Paleogene (Lutetian) sedimentary rocks in the Haymana and Black Sea regions, Turkey

Larger foraminifera of the late Cretaceous (late Campanian) to middle Eocene (Lutetian) are recognized in the upper Cretaceous to Paleogene sedimentary rocks in the Haymana and Black Sea regions, Turkey. 114 diagnostic larger and benthonic foraminiferal species belonging to 66 genera including one new genus Chaldagia are identified, and 89 diagnostic species are documented as local ranges. Biostratigraphically useful 11 larger foraminiferal assemblage zones are described, and are correlated with two larger foraminiferal assemblage zones, NE India and Philippines in the Tethys region. Chaldagia haymanensis, n. gen., n. sp. and Scandonea samnitica De Castro are systematically described. Associated 52 planktonic foraminiferal species belonging to 23 genera are identified, and 90 larger and benthonic foraminifera and 40 planktonic foraminifera are illustrated. Some element concentrations of the Cretaceous-Tertiary (K-T) boundary layers (28-37 cm thick with goethite layers) were found in the MedetlÏ section, Görpazari, Black Sea region by the author’s research group. In there, Ir concentration was low and slightly elevated (0.24 ppb) in a sample of goethite layers, and foraminiferal taxa didn’t yield. The K-T Ir layers are well correlated with those in the Meghalaya, NE India. Sr isotope values (87 Sr/86 Sr, 0.707885 – 0.707819) in the K-T boundary layers in the Devrekani section, Kastamonu, Black Sea region agreed well with those in the K-T boundary regions of the world by the author’s research group.

Geologic history of the Neogene “Qena Lake” developed during the evolution of the Nile Valley: A sedimentological, mineralogical and geochemical approach

Siliciclastic and carbonate sediments were laid down in southern Wadi Qena and around the Qena Nile bend (Middle Egypt) in a lacustrine–alluvial environment which dominated a relatively wide lake, the “Qena Lake” that interrupted the Nile course during the Neogene time. These sediments are represented mainly by the oldest dominantly lacustrine chocolate brown mudstones of the Khuzam Formation that accumulated nearer to the center of that lake (now forming a 185m terrace above sea level), overlain by the dominantly lacustrine carbonates and marls of the Durri Formation which accumulated during semi-arid conditions, mainly nearer to the periphery of the lake (now forming 170, 180 and 185m terraces a.s.l. in the studied sections). The water level of the “Qena Lake” reached 240m. above sea level, as indicated by the maximum carbonate elevation reached in the region. Finally fanglomerates of the Higaza Formation with its chert and limestone conglomerates accumulated during torrential periods at higher elevations (forming 240, 300 and 400m terraces a.s.l.). These three formations accumulated in this particular area before and during the unroofing of the basement rocks of the Eastern Desert, west of the watershed. According to the known Early Miocene initial development of the Nile Valley, beside the occurrence of similar deposits of Oligocene age along the eastern side of the basement range, the earlier known Pliocene age given for these sediments in the Qena area is here questioned. It might belong to earlier Miocene?–Pliocene times.As the basement rocks of the Eastern Desert were still covered by Cretaceous–Paleogene sedimentary rocks while the Khuzam, Durri and Higaza Formations were accumulating in the Qena Lake region, it is believed, contrary to the belief of some authors, that the basement rocks of the Eastern Desert were not the source of these sediments. The carbonate petrographic study, beside the X-ray, and the11 major oxides and 22 trace elements analyses, all point to that the mudrock sediments of the oldest Neogene Khuzam and Durri Formations of the “Qena Lake” phase were carried out and entered the area of southern Wadi Qena and around the Qena Nile bend mainly from the south. The intermediate igneous rocks of southern Egypt and northern Sudan were the main source areas. Additional contributions had possibly come from the weathering of the non-marine to brackish Cretaceous (pre-Campanian) shales of southern Egypt.Accumulation of conglomerates with mixed igneous and sedimentary clasts followed (forming 7 terraces in Wadi Qena, ranging from 240m in the north to 140m a.s.l. in the south), constituting the newly introduced Late Pliocene formation; El Heita Formation. These conglomerates were mainly drained from the then exposed basement rocks of the middle parts of Wadi Qena, and cut through the older Neogene sediments. Later on, after the lake became connected to the northern parts of the Nile Valley, the lake water level was lowered to 180m a.s.l., and another lake with this lower level was formed (Isawiyya Lake). With the successive lowering of water level the younger well known Issawia, Qena, Abbassia and Dandara Formations accumulated successively; nearer to, and within, the present Nile Valley.

Paleoenvironment and paleoecology of a Late Paleocene high-latitude terrestrial succession, Arkose Ridge Formation at Box Canyon, southern Talkeetna Mountains, Alaska

Paleogene sedimentary rocks of the Arkose Ridge Formation (Talkeetna Mountains, Alaska) preserve a record of a fluvial–lacustrine depositional environment and its forested ecosystem in an active basin among the convergent margin tectonic processes that shaped southern Alaska. An ~800m measured succession at Box Canyon indicates braid-plain deposition with predominantly gravelly deposits low in the exposure to sandy and muddy facies associations below an overlying lava flow sequence. U–Pb geochronology on zircons from a tuff and a sandstone within the measured section, as well as an Ar/Ar date from the overlying lava constrain the age of the sedimentary succession to between ~59Ma and 48Ma. Fossil plant remains occur throughout the Arkose Ridge Formation as poorly-preserved coalified woody debris and fragmentary leaf impressions. At Box Canyon, however, a thin lacustrine depositional lens of rhythmically laminated mudrocks yielded fish fossils and a well-preserved floral assemblage including foliage and reproductive organs representing conifers, sphenopsids, monocots, and dicots. Leaf physiognomic methods to estimate paleoclimate were applied to the dicot leaf collection and indicate warm temperate paleotemperatures (~11–15±~4°C MAT) and elevated paleoprecipitation (~120cm/yr MAP) estimates as compared to modern conditions; results that are parallel with previously published estimates from the partly coeval Chickaloon Formation deposited in more distal depositional environments in the same basin. The low abundance of leaf herbivory in the Box Canyon dicot assemblage (~9% of leaves damaged) is also similar to the results from assemblages in the meander-plain depositional systems of the Chickaloon. This new suite of data informs models of the tectonostratigraphic evolution of southern Alaska and the developing understanding of terrestrial paleoecology and paleoclimate at high latitudes during the Late Paleocene–Early Eocene greenhouse climate phase.

Paleocene–Eocene stratigraphy and paleoenvironment at Tora, Southeast Wairarapa, New Zealand

The Upper Cretaceous and Lower Paleogene sedimentary rocks at Tora, southeast Wairarapa, are considered to form a transitional sedimentary succession within the East Coast Basin, containing elements of both the siliciclastic succession to the north in the eastern North Island and the pelagic succession to the south in eastern Marlborough. However, the Tora succession is complicated by rapid lateral facies changes, numerous unconformities and unusual occurrences of coarse-grained facies in what is more typically a rather monotonous fine-grained passive-margin sequence. We interpret the uppermost Cretaceous and Paleocene units (Manurewa, Awhea, Mungaroa and Awheaiti formations) as components within a middle to lower bathyal, submarine channel and fan complex that unconformably overlies the Upper Cretaceous Rakauroa Member of the Whangai Formation. The two overlying Lower–Upper Eocene units (Pukemuri Siltstone, Wanstead Formation) both consist of a basal debris-flow deposit grading into middle bathyal mudstone, deposited during progressive marine transgression and deepening to lower bathyal–abyssal depths.