Silica diagenesis of Neogene diatomaceous and volcaniclastic sediments in northern Japan*

Marine diatomaceous siliceous sediments in Neogene sections of northern Japan contrast with the Monterey Shale of California in containing many intercalations of acidic volcaniclastic sediments. Diagenesis of these sediments from deep boreholes and surface sections was investigated. Three diagenetic zones—biogenic opal, opal-CT and quartz zones—are recognized in siliceous sediments, corresponding roughly to amorphous silica, low cristobalite and quartz zones in acidic vitric volcaniclastic sediments. Opal-CT consists almost exclusively of silica and water, while low cristobalite contains appreciable amounts of A1, Ca, Na and K. In subsurface sections, values of d(101) spacing of opal-CT decrease progressively with increasing burial depth. The progressive ordering is not associated with additional silica cementation. In surface sections, the behaviour of d(101) spacing is complicated owing to the modification of the progressive ordering developed during burial diagenesis by later silica cementation during uplift. The cementing opal-CT is probably precipitated from percolating groundwater which dissolves siliceous skeletons in porous diatomaceous mudstones overlying the opal-CT porcellanite. Opaline cherts that form during burial diagenesis are designated as early opaline chert, while those which form during uplift are later opaline chert. The later opaline chert contains two groups of opal-CT; one is progressively ordered opal-CT and the other is additionally cemented opal-CT with higher d(101) spacing than that in the host porcellanite. In diatomaceous siliceous sediments, early opaline chert is scarce. Most, if not all, opaline cherts in surface sections are of later origin.     

Fukuititan nipponensis, A New Titanosauriform Sauropod from the Early Cretaceous Tetori Group of Fukui Prefecture,Japan

<正>A titanosauriform dinosaur:Fukuititan nipponensis gen.et sp.nov.is erected based on the incomplete skeleton.It is characterized by elongated asymmetric tooth crown with a weak or absent labial groove and without lingual concavity;stalk-like epipophysis of cervical vertebra;the transverse width of the proximal end of the humerus approximately 32%of the humerus length;metacarpal longer,approximately 48%of the radius and the distal end of the ischia slightly expanded.It represents the first relatively complete titanosauriform skeleton found from Japan.The discovery of Fukuititan indicates that the diversity and geographical distribution of Titanosauriformes are much higher than the previous thought.     

Origin and diagenetic evolution of Ca–Mg–Fe carbonates in some coalfields of Japan

Carbonate concretions, lenses and bands in the Pleistocene, Palaeogene and Upper Triassic coalfields of Japan consist of various carbonate minerals with varied chemical compositions. Authigenic carbonates in freshwater sediments are siderite > calcite > ankerite > dolomite >> ferroan magnesite; in brackish water to marine sediments in the coal measures, calcite > dolomite > ankerite > siderite >> ferroan magnesite; and in the overlying marine deposits, calcite > dolomite >> siderite. Most carbonates were formed progressively during burial within a range of depths between the sediment-water interface and approximately 3 km. The mineral species and the chemical composition of the carbonates are controlled primarily by the initial sedimentary facies of the host sediments and secondarily by the diagenetic evolution of pore water during burial. Based on the regular sequence and burial depth of precipitation of authigenic carbonates in a specific sedimentary facies, three diagenetic stages of carbonates are proposed. Carbonates formed during Stage I (< 500 m) strongly reflect the initial sedimentary facies, e.g. low Ca-Mg siderite in freshwater sediments which are initially rich in iron derived from lateritic soil on the nearby landmass, and Mg calcite and dolomite in brackish-marine sediments whose pore waters abound in Ca²⁺ and Mg²⁺ originating in seawater and calcareous shells. Carbonates formed during Stage II (500–2000 m) include high Ca-Mg siderite, ankerite, Fe dolomite and Fe–Mg calcite in freshwater sediments. The assemblage of Stage II carbonates in brackish-marine sediments in the coal measures is similar to that in freshwater sediments. This suggests similar diagenetic environments owing to an effective migration and mixing of pore water due to the compaction of host sediments. Carbonates formed during Stage III (> 2000 m) are Fe calcite and extremely high Ca-Mg siderite; the latter is exclusively in marine mudstones. The supply of Ca is partly from the alteration of silicates in the sediments at elevated burial temperatures. After uplift, calcite with low Mg content precipitates from percolating groundwater and fills extensional cracks.     

ZEOLITES IN SEDIMENTARY ROCKS, WITH REFERENCE TO THE DEPOSITIONAL ENVIRONMENTS AND ZONAL DISTRIBUTION

The authors have studied alterations of Cenozoic and Mesozoic pyroclastic rocks of Japan, which contain several kinds of zeolites in abundance. This paper summarizes zeolites in sedimentary rocks, with reference to the depositional environments and zonal distribution, by a survey of the literature in addition to the authors’ data. The zonal distribution of zeolites is recognized in buried sedimentary rocks as follows: The zeolites in syngenetic or early diagenetic origin depend strongly upon a specific sedimentary environment. Phillipsite occurs largely in pelagic sediments of the younger geologic age. Analcime is found in saline-lake and terrestrial sediments in a warm, rather arid region, frequently associated with phillipsite, chabazite and natrolite. The zeolites are not influenced by the sedimentary environments but depend upon the depth of burial, i.e., increasing temperature and pressure. Most of clinop- tilolite, mordenite and erionite, forming at a relatively shallow depth, occur only as an alteration product of acidic to intermediate volcanic glass and cement of the post- Jurassic pyroclastic rocks. Laumontite, forming at a greater depth, on the other hand, is widely distributed in the pre-Pliocene various sedimentary rocks.     

A New Species of Huaxiapterus （Pterosauria： Pterodactyloidea） from the Lower Cretaceous of Western Liaoning, China with Comments on the Systematics of Tapejarid Pterosaurs

A new species of tapejarid pterosaur, Huaxiapterus coroUatus sp. nov. is erected on the basis of a nearly complete skull and postcranial skeleton from the Lower Cretaceous Jiufotang Formation of Liaoning Province, China. Huaxiapterus coroUatus sp. nov. is characterized by a hatchet-shaped rectangular process on the premaxilla, whose short axis is perpendicular to the anterior margin of the premaxillae. Except for this process, other characters of the skull such as the breadth of the snout between the anterior margin of the nasoantorbital fenestra and the anterior margin of the premaxilla are similar to that of Huaxiapterus jii. Huaxiapterus and a second Chinese tapejarid, Sinopterus, share several unique cranial characters in common with Tapejara and these three genera appear to be more closely related to each other than to other azhdarchoids. The Chinese tapejarids （Sinopterus and Huaxiapterus） have relatively elongate skulls and weakly developed cranial crests and seem to be less derived than Tapejara, with its shorter, deeper skull and large cranial crest. Tupuxuarids （Tupuxuara and Thalassodromeus） have often been associated with tapejarids in the family Tapejaridae, but this relationship is controversial because some phylogenetic analyses have supported the pairing of tupuxuarids with Azhdarchidae. We propose that Tapejaridae be restricted to Tapejara, Sinopterus and Huaxiapterus.     

New Nodosaurid Dinosaur from the Late Cretaceous of Lishui, Zhejiang Province, China

A new genus and species of nodosaurid dinosaur： Zhejiangosaurus lishuiensis gen. et sp. nov. is erected herein. It is characterized by the sacrum consisting of at least three true sacral vertebrae, 5 caudal dorsal vertebrae fused to form the presacral rod, wide divergence of long slender preacetabular process of the ilium from the middle line of the body, and the fourth trochanter located at the femoral mid-length.     

A New Iguanodontian Dinosaur from the Lower Cretaceous Khok Kruat Formation,Nakhon Ratchasima in Northeastern Thailand

Here we report a new iguanodontian dentary found from the Lower Cretaceous Khok Kruat Formation, Nakhon Ratchasima, northeast Thailand. A unique character, which is an elongated and flat shape of the dentary ramus, makes it possible to assign the specimen to the new genus of non‐hadrosaurid iguanodontian, Ratchasimasaurus suranareae gen. et sp. nov. R. suranareae shows both primitive and derived characters, such as a caudally inclined coronoid process and alveolar trough with a primitive crown impression, and a derived buccal shelf between tooth row and coronoid process. The discovery of a new iguanodontian from the Indochina Terrene, considering that the previously reported “Probactrosaurus‐like” iguanodontian, points out a great diversity of this group in the late Early Cretaceous in Thailand, and corresponds to the Asian iguanodontian diversity at that time.     

A New Nodosaurid Ankylosaur from the Chaochuan Formation of Dongyang, Zhejiang Province, China

Dongyangopelta yangyanensis gen. et sp. nov. from the Chaochuan Formation (Albian-Cenomanian) of Dongyang, Zhejiang Province, China is characterized: the convex anterior surface of the first presacral rod centrum strongly inflates laterally and slightly curves posteriorly; the fused pelvic shield composes of larger pebble-shaped bosses, defined by smaller tubercles or flat stretches of bone; most osteoderms are heavily roughened with notches and grooves for dermal attachment along the edge; domed triradiate osteoderm is present; sigmoid curvature of the dorsal surface of the ilium is present; the preacetabular process curves lateroventrally at the anterior end and has a shallow groove in the edge of the lateral and anterior ends and strong lateromedial expansion of the distal femur. The femoral head is well separated from the greater trochanter, indicating that Dongyangopelta is a nodosaurid ankylosaur, the second from southeast China. Phylogenetic analysis also positions this taxon in the Nodosauridae clade. Dongyangopelta differs from Zhejiangosaurus in the characters of presacral rod, ilium, and femur. Dongyangopelta represents the first ankylosaur outside North America and Europe that definitively possesses a pelvic shield with fused armor.     

A New Titanosauriform Sauropod from the Early Late Cretaceous of Dongyang, Zhejiang Province

A new titanosauriform sauropod Dongyangosaurus sinensis gen. et sp. nov. from the early Late Cretaceous of Dongyang County, Zhejiang Province, is erected based on a partial postcranial skeleton. It is characterized by complex laminae on the lateral surface of the neural spines and postzygapophyses of dorsal vertebrae, a distinct fossa on the ventral surfaces of the prezygapophyses of dorsal vertebrae, distinct fossae are also present on the lateral surface of the postzygapophysis of anterior caudal vertebrae; pubis is shorter than ischium, the small obturator foramen of pubis elongated, and nearly closed. The lamina complexity of dorsal vertebrae in Dongyangosaurus indicates that a higher diversity of titanosauriformes occurred during the early Late Cretaceous in China.