Triassic carbonate buildup flanks in the Dolomites, northern Italy: breccias, boulder fabric and the importance of early diagenesis

The flanks of Middle Triassic carbonate buildups in the Dolomites show well‐developed clinostratification, with typical angles of 30–40°. This paper focuses on the metre‐scale fabric of these clinoforms and sets these within the context of their large‐scale and microscopic features. Clinoform stratification is caused by fibrous cement crusts, by stylolites paralleling a vague stratification and by pelagic limestone interbedded with the lower portions of the clinoforms. These parts of the clinoforms locally exhibit a boulder fabric. A fracture system, subvertical to clinostratification, is filled by fibrous cements and marine internal sediment. The analysis of clinoform fabric indicates that parts consist of in situ automicrite. Other parts of the clinoforms are made up of breccia. The breccias occur as isolated pockets and lenses with random orientation and dimensions ranging from a few square decimetres to hundreds of square metres. The breccias have gradual contacts with the unbrecciated host rock. Breccia components are mostly angular, show a microfacies similar to that of the unbrecciated host rock and are composed of millimetre‐ to decimetre‐sized particles that generally float in radiaxial‐fibrous cement. Matching grain boundaries are common. Calcite cement typically makes up 20 and 40 vol.% of the brecciated areas. Clinostratification, the fracture system, brecciation and boulder fabric point to gravity induced deformation of in situ flank deposits rather than gravity induced depositional processes. Brecciation appears to result from translational sliding (millimetres to metres) on the steep buildup flanks, which caused fracturing of the vaguely stratified automicrite, followed by displacive growth of fibrous cement. Cementation occurred in a (shallow) burial, marine phreatic environment, because cement clasts are virtually absent from the flank‐derived gravity flows in the adjoining basinal sediments. Displacive cement growth indicates a volume increase of the clinoforms during diagenesis of up to 20–40 vol.% and can account for the local drag of buildup interior limestones. Similarly, the boulder fabric appears to be a diagenetic feature, which resulted from differential settling of incompletely lithified boundstone and grainstone, and the interbedded pelagic limestone.     

Reef Fabrics, biotic crusts and syndepositional cements of the Latemar reef margin (Middle Triassic), northern Italy

The Latemar reef buildup of the central Dolomites (northern Italy) provides a rare opportunity to examine an in-place Middle Triassic (Upper Anisian to Lower Ladinian) platform margin that is not strongly deformed or dolomitized. The margin lies between the flat lying platform interior and steeply dipping foreslope clinoforms. Across this transition, the depositional profile relates directly to a consistent lateral facies pattern: (1) restricted-biota grainstone of the platform interior, (2) ‘Tubiphytes’-rich boundstone and (3) diverse-biota grainstone that grades into (4) foreslope breccia beds. The boundstone and diverse-biota grainstone facies comprise the platform margin. The boundstone facies consists of a framework of small (< 10 cm) skeletal remains (< 10% by volume) with associated biotic crusts, internal sediments and syndepositional cements. Crusts and cements constitute most of the rock volume and created the boundstone fabric. Biotic crusts exhibit gravity-defying geometries and range from a light grey, ‘structure grumeleuse’ rind to dark grey, micritic laminae. Both cements and biotic crusts occur as redeposited talus in the foreslope talus deposits, indicating a syndepositional origin. The diverse-biota grainstone facies primarily consists of skeletal-peloidal grainstone with a diverse open marine biotic assemblage, in contrast to the restricted biota grainstones of the platform interior that have a low diversity, restricted marine biota. Metre scale hexacoral boundstone and centimetre-scale sponge boundstone and microbial boundstone occur as isolated patches (tens to hundreds of metres apart) within the diverse-biota grainstone facies. The depositional profile, facies zonation and biotic constituents all indicate that the Latemar buildup had a shallow water reef margin, in contrast to previous interpretations that these were upper slope reefs. The syndepositional biotic crusts and inorganic cementation played key roles in stabilizing the boundstone fabric to form a wave-resistant reef fabric.     

Three-dimensional modelling of an isolated carbonate buildup (Triassic, Dolomites, Italy)

The Middle Triassic carbonate buildups of the Dolomites show facies similarities with mud mounds but display apparent architectural elements of flat‐topped carbonate platforms. In order to test whether the facies similarities to mounds are also reflected in the internal buildup architecture, a three‐dimensional modelling study of the Middle Triassic Monte Cernera buildup has been carried out. The Cernera buildup exhibits apparent geometries suggesting a mounded platform in the lower and uppermost part of the buildup, separated by an interval with apparent platform geometry and a retrogradational platform interior, which is difficult to explain with a flat top platform model. For this purpose, a number of three‐dimensional models were constructed using the three‐dimensional modelling programme petrel ^TM. Key geological horizons were constructed based on outcrop measurements, intermediate horizons were calculated in the modelling program, and the intersections of the modelled layers with a digital topography surface were displayed and compared with outcrop photographs. The models were refined stepwise until a best fit with the actual bedding architecture was achieved. The best fit model shows that the mounded geometries in the lower and uppermost part of the buildup are real architectural elements. The intermediate platform stage, about 1·5 km across, had probably retained a mounded top with a relief of up to 50 m, which is difficult to distinguish from an absolutely flat top, but necessary to explain the retrogradational platform interior. The present study shows that Monte Cernera was dominated by mounded geometries at all stages of platform development. The mounded geometry plus facies data suggest that the platform is a deep‐water accumulation, below the zone of intense wave energy, but within the photic zone. The Cernera represents a tropical buildup type, which did not have the capacity to grow into continuously wave‐swept environments because of the small size and the absence of a wave‐resistant energy barrier. Such buildup types are probably common after major crises in earth history, when reef organisms were virtually absent.     

Compositional changes in sigmoidal carbonate clinoforms (Late Tithonian,eastern Sardinia,Italy): insights from quantitative microfacies analyses

Quantitative analysis of sediment composition was performed on a kilometre wide section of Upper Tithonian low relief (up to 70 m), gently inclined (3° to 15°), sigmoidal carbonate clinoforms (eastern Sardinia) to identify changes in sediment composition along the slope and across the studied succession. These changes may reflect modifications of the carbonate factory and of processes responsible for sediment transport. Point‐count analysis of carbonate microfacies, Q‐mode/R‐mode cluster analysis and Spearman’s rank provided a composition‐based classification of microfacies and highlighted relationships among sediment components. The studied clinoforms are mainly composed of non‐skeletal grains (70%), such as peloids and lithoclasts, together with micrite and cements and only a limited contribution from coated grains (2%). Among skeletal grains (28%), the greatest contribution derives from a coral–stromatoporoid–encruster reef that provided 15% of the components. Crinoids, brachiopods and other along‐slope thriving biota provided nearly 5% of the allochems, whilst fragments of molluscs (gastropods, bivalves and diceratids) from the backreef sourced another 2%. The contribution of platform interior biota is negligible (1%). The association of composition‐based facies varies along the slope. The upper slope beds consist of coral‐stromatoporoid grainstone to rudstone; the middle slope deposits are dominated by encruster‐lithoclast grainstone and packstone. At the lower slope, peloidal lithoclastic packstone as well as brachiopod–crinoidal wackestone prevail. Also the association of skeletal grains changes along the slope. The encruster–frame builder association typifies the upper slope whilst encrusters characterize the middle slope sediments. In the lower slope encrusters are equally represented as the brachiopod–crinoid association. Along‐slope compositional changes evidence a scarce downslope transport of frame builders and a progressive enrichment in along‐slope thriving biota. Quantitative analysis of microfacies allowed the sigmoidal clinoforms to be grouped into six sets. Each set gathers sigmoids with a similar sediment composition. Coated grains are dominant in the first set whilst they are lacking in the overlying sets reflecting a change in the carbonate factory. Other major compositional changes among the sets concern the relative amounts of peloids, micrite, frame builders (corals and stromatoporoids) and encrusters. The contribution of peloids varies inversely to that of cements and micrite as evidenced in the third and fifth sets which, respectively, record the highest occurrence of peloids or cement and micrite. Variations in the amount of frame builders and encrusters are instead non‐linear. High percentages of both frame builders and encrusters, as recorded in the second and fifth sets, are related to low amounts of peloids and lithoclasts that probably reflect episodes of reduced background sedimentation. This study demonstrates that quantitative analysis of carbonate microfacies represents a powerful tool that can improve the reconstruction of the stacking pattern in carbonate slope successions both in outcrop and in subsurface settings.     

Controls on carbonate platform architecture and reef recovery across the Palaeozoic to Mesozoic transition: A high-resolution analysis of the Great Bank of Guizhou

Carbonate platforms spanning intervals of global change provide an opportunity to identify causal links between the evolution of marine environment and depositional architecture. This study investigates the controls on platform geometry across the Palaeozoic to Mesozoic transition and yields new stratigraphic and palaeoenvironmental constraints on the Great Bank of Guizhou, a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of south China. Reconstruction of platform architecture was achieved by integrating field mapping, petrography, biostratigraphy, satellite imagery analysis and δ¹³C chemostratigraphy. In contrast to previous interpretations, this study indicates that: (i) the Great Bank of Guizhou transitioned during Early Triassic time from a low-relief bank to a platform with high relief above the basin floor (up to 600 m) and steep slope angles (preserved up to 50°); and (ii) the oldest-known platform-margin reef of the Mesozoic Era grew along steep, prograding clinoforms in an outer-margin to lower-slope environment. Increasing platform relief during Early Triassic time was caused by limited sediment delivery to the basin margin and a high rate of accommodation creation driven by Indosinian convergence. The steep upper Olenekian (upper Lower Triassic) slope is dominated by well-cemented grainstone, suggesting that high carbonate saturation states led to syndepositional or rapid post-depositional sediment stabilization. Latest Spathian reef initiation coincided with global cooling following Early Triassic global warmth. The first Triassic framework-building metazoans on the Great Bank of Guizhou were small calcareous sponges restricted to deeper water settings, but early Mesozoic reef builders were volumetrically dominated by Tubiphytes, a fossil genus of uncertain taxonomic affinity. In aggregate, the stratigraphic architecture of the Great Bank of Guizhou records sedimentary response to long-term environmental and biological recovery from the end-Permian mass extinction, highlighting the close connections among marine chemistry, marine ecosystems and carbonate depositional systems.     

贵州玉屏彰寨奥陶纪红花园期障积岩隆礁

该障积岩隆礁的造礁生物主要为海绵和藻,岩石类型有海绵灰岩、藻席岩、核形石凝决石灰岩、生物屑灰岩等。本文系统介绍其造礁生物的生态特征、岩石组合并分析其沉积相和礁的生长发育阶段,最后运用马尔柯夫概型分析研究期旋回沉积发育较好的礁核相地层的学积特征。     

Quantitative compositional analysis of a Triassic carbonate platform (Southern Alps,Italy)

We have estimated abundance and distribution of automicrite, marine cements and skeletal grains in the Triassic Sella massif, an isolated platform flanked by steep (25–35°) clinoforms. 108 samples were taken at constant intervals from measured sections of the major zones of the platform edifice: the platform top, margin–upper slope, and lower slope. In a first step, carried out in the field and on hand specimen, purely detrital deposits were separated from automicrite facies, i.e. beds with automicrite, cement-filled, primary vugs and admixtures of skeletal carbonate and lithoclasts. In the second step, samples with automicrite facies were thin-sectioned and point counted. The categories used for point counting were (a) automicrite, (b) vugs and cement, (c) microspar or neomorphic spar, (d) skeletal grains and (e) internal sediments. At the platform top 46% of samples are pure detrital deposits, 27% consist of automicrite facies and 27% are too strongly altered by dolomitization to allow classification. At the margin–upper slope 68% of samples consist of automicrite facies, 22% are pure detrital sediments and 10% are strongly altered. At the lower slope 63% are detrital deposits, 10% automicrite facies and 27% are extensively dolomitized. The most important contributors to the automicrite facies are automicrite (41% on the platform top, 29% on the margin–upper slope, 28% on the lower slope) and early marine cement (35% on the platform top, 48% on the margin–upper slope, 27% on the lower slope). The amount of skeletal grains is less than 10%.The automicrite facies stabilized the platform margin and upper slope. Automicrite, abundant early marine cements and micro-organisms such as Tubiphytes, formed a rigid framework, thus substituting for the lack of a metazoan reef. On the upper slopes, the framework of automicrite facies stabilized the slope but intermittently. The automicrite layers are frequently dissected by sediment-filled fractures or are broken into clasts. We assume that they slid on the layers of loose detritus. Bigger slides turned into rubbly debris flows that formed metre-thick breccias at the lower slope and the proximal basin floor. The planar shape and steep angle of the clinoforms indicate that the large-scale geometry of the slope was not controlled by the automicrite but rather by non-cohesive layers of sand and rubble piled up to the angle of repose.The production mode of the Sella is comparable of that of a (mud) mound factory. This factory was highly productive: in 1 Ma, the platform aggraded over 300 m and prograded over 2000 m in all directions.     

Facies and evolution of the carbonate factory during the Permian–Triassic crisis in South Tibet,China

The nature of Phanerozoic carbonate factories is strongly controlled by the composition of carbonate‐producing faunas. During the Permian–Triassic mass extinction interval there was a major change in tropical shallow platform facies: Upper Permian bioclastic limestones are characterized by benthic communities with significant richness, for example, calcareous algae, fusulinids, brachiopods, corals, molluscs and sponges, while lowermost Triassic carbonates shift to dolomicrite‐dominated and bacteria‐dominated microbialites in the immediate aftermath of the Permian–Triassic mass extinction. However, the spatial–temporal pattern of carbonates distribution in high latitude regions in response to the Permian–Triassic mass extinction has received little attention. Facies and evolutionary patterns of a carbonate factory from the northern margin of peri‐Gondwana (palaeolatitude ca 40°S) are presented here based on four Permian–Triassic boundary sections that span proximal, inner to distal, and outer ramp settings from South Tibet. The results show that a cool‐water bryozoan‐dominated and echinoderm‐dominated carbonate ramp developed in the Late Permian in South Tibet. This was replaced abruptly, immediately after the Permian–Triassic mass extinction, by a benthic automicrite factory with minor amounts of calcifying metazoans developed in an inner/middle ramp setting, accompanied by transient subaerial exposure. Subsequently, an extensive homoclinal carbonate ramp developed in South Tibet in the Early Triassic, which mainly consists of homogenous dolomitic lime mudstone/wackestone that lacks evidence of metazoan frame‐builders. The sudden transition from a cool‐water, heterozoan dominated carbonate ramp to a warm‐water, metazoan‐free, homoclinal carbonate ramp following the Permian–Triassic mass extinction was the result of the combination of the loss of metazoan reef/mound builders, rapid sea‐level changes across Permian–Triassic mass extinction and profound global warming during the Early Triassic.     

贵州汞、铅-锌层控矿床成矿机制的初步探讨

汞、铅-锌层控矿床均产于一定地层、岩相和岩性中,它们的分布远离岩浆岩体,成矿温度低。多年来,不少中外地质工作者把这类矿床列为低温热液矿床(岩浆期后热液或远温式矿床)。近年来,随着层控矿床研究的进展,对它的成因也有了一些新认识和突破。本文在综合研究贵州汞、铅-锌矿床的地质特征的基础上,对矿质的初始来源、沉积环境、成矿作用方式作一初步探讨。     

贵州关岭中三叠统坡段组沉积特征及其形成环境

贵州中三叠世碳酸盐台地边缘的“堤礁”向来受到人们的关注,并成为研究的热点。当前对台地边缘沉积的性质存在着不同的观点。某些人认为这些沉积是在浅水和拢动环境下形成的滩相沉积;而另外一些研究者则仍坚持它们代表典型的礁相沉积,因为它含有丰富的造型生物,如六射珊瑚、苔藓虫、钙质海绵和龙介类等。在贵州中部关岭县扒子场出露了一套巨厚的和属于台地边缘的中三叠统。扒子场在关岭县城的东南,直距约22km。三叠系中下统沿着公路断面连续出露。中统包括安尼阶的坡段组及拉丁阶的垄头组和竹杆坡组。坡段组主要由砂砾屑－生屑颗粒岩组成,约占全剖面的2／3。它们形成于水流激荡的滩相环境。其他岩石为骨屑－球粒粒泥岩和泥粒岩,约占全剖面的1／3。根据该组的岩石结构、沉积构造和生物组分,坡段组代表由砂砾屑、生屑组成的粒屑滩,而非生物礁相沉积。仅在底部或下部出现少量的Tubiphytes-蓝细菌造礁骨架,组成局部的礁丘。     

西藏改则热那错上三叠统日干配错组碳酸盐岩岩石学特征与沉积环境*

西藏改则县热那错东沟剖面上三叠统卡尼阶至瑞替阶日干配错组沉积了厚度较大的碳酸盐岩地层,其中化石丰富。在碳酸盐岩中识别出11种主要的岩石类型：灰泥灰岩﹑含生物碎屑灰泥灰岩、生物碎屑粒泥灰岩、生物碎屑泥粒灰岩、内碎屑泥粒灰岩、内碎屑颗粒灰岩、藻颗粒灰岩、多种类型鲕粒灰岩、单一类型鲕粒灰岩、球粒泥粒灰岩和生物礁灰岩。根据岩石特征及组合类型可划分为5种沉积相：陆源碎屑滨岸相、局限台地相、开阔台地相、台地边缘浅滩相和台地边缘礁相,它们共同构成了日干配错组4个有序的海侵—海退旋回,整体显现出海侵的相序结构。     

Carbonate platform evolution: from a bioconstructed platform margin to a sand-shoal system (Devonian, Guilin, South China)

ABSTRACT The depositional organization and architecture of the middle–late Devonian Yangdi rimmed carbonate platform margin in the Guilin area of South China were related to oblique, extensional faulting in a strike‐slip setting. The platform margin shows two main stages of construction in the late Givetian to Frasnian, with a bioconstructed margin evolving into a sand‐shoal system. In the late Givetian, the platform margin was rimmed with microbial buildups composed mainly of cyanobacterial colonies (mostly Renalcis and Epiphyton). These grew upwards and produced an aggradational (locally slightly retrogradational) architecture with steep foreslope clinoforms. Three depositional sequences (S3–S5) are recognized in the upper Givetian strata, which are dominated by extensive microbialites. Metre‐scale depositional cyclicity occurs in most facies associations, except in the platform‐margin buildups and upper foreslope facies. In the latest Givetian (at the top of sequence S5), relative platform uplift (± subaerial exposure) and associated rapid basin subsidence (probably a block‐tilting effect) caused large‐scale platform collapse and slope erosion to give local scalloped embayments along the platform margin and the synchronous demise of microbial buildups. Subsequently, sand shoals and banks composed of ooids and peloids and, a little later, stromatoporoid buildups on the palaeohighs, developed along the platform margin, from which abundant loose sediment was transported downslope to form gravity‐flow deposits. Another strong tectonic episode caused further platform collapse in the early Frasnian (at the top of sequence S6), leading to large‐scale breccia release and the death of the stromatoporoid buildups. Siliceous facies (banded cherts and siliceous shales) were then deposited extensively in the basin centre as a result of the influx of hydrothermal fluids. The platform‐margin sand‐shoal/bank system, possibly with gullies on the slope, persisted into the latest Frasnian until the restoration of microbial buildups. Four sequences (S6–S9), characterized by abundant sand‐shoal deposits on the margin and gravity‐flow and hemipelagic deposits on the slope, are distinguished in the Frasnian strata. Smaller‐scale depositional cyclicity is evident in all facies associations across the platform–slope–basin transect. The distinctive depositional architecture and evolution of this Yangdi Platform are interpreted as having been controlled mainly by regional tectonics with contributions from eustasy, environmental factors, oceanographic setting, biotic and sedimentary fabrics.     

中韩第五次《东北亚地壳演化》学术研讨会在北京举行

新疆天山东部广泛发育晚石炭世碳酸盐岩隆。这些岩隆主要为生物丘,少数为生物滩及与岩隆有关的生物层,其中生物丘含大量灰泥和内碎屑。基本岩石类型为泥粒状灰岩、粒泥状灰岩、粒泥状－泥粒状灰岩,少量岩石类型包括颗粒岩、骨架岩和障积岩。成岩作用是碳酸盐岩隆发展演化的重要阶段和过程,在生物丘内,已经识别出四种重要的胶结物,即球粒泥晶、纤状方解石、放射轴状方解石和粒状方解石。尽管缺失典型的造礁生物,但通过岩石类型研究和微相分析,认为碳酸盐岩隆的形成主要取决于生物作用及古环境格局。本区碳酸盐岩隆可以同欧洲瓦尔索坦的岩隆对比     

海西—印支期上扬子南缘碳酸盐岩台地边缘沉积特征、演化及其控制因素

海西—印支期上扬子地块发育稳定型的碳酸盐岩大台地,在碳酸盐岩台地南缘台地边缘沉积体系发育,主要包括4种沉积类型:台地边缘滩,台地边缘礁、台地前缘斜坡、滩(礁)间海。据海西—印支期台缘沉积发育及分布特征,可分为4个沉积演化阶段:中泥盆世—晚泥盆世(SS1),台缘沿弥勒—师宗—晴隆—南丹—河池一线呈带状分布,台缘礁滩发育;早石炭世—早二叠世早期(SS2-SS3),台缘沿晴隆—六盘水—安顺呈带状分布,台缘生屑滩发育;早二叠世晚期—晚二叠世(SS4),沿贞丰—紫云—罗店—河池—柳州—娄底呈带状分布,台缘滩、台缘礁交互发育;早三叠世—中三叠世(SS5),沿贞丰—镇宁—贵阳—福泉一线呈带状分布,早三叠世主要发育台缘鲕粒滩,中三叠世台缘礁占优势。这4个阶段的台缘沉积特征表明:台地边缘礁滩沉积体系垂向演化受海平面变化控制,横向迁移主要受同沉积断裂控制,不同类型生物的出现和绝灭控制台缘生物礁滩的类型及特征。     

Early to mid-Viséan shallow water platform buildups,north Co. Dublin,Ireland

A number of carbonate buildups in north Co. Dublin, long assigned to the late Viséan (Asbian), are shown on the basis of coral, foraminiferal and algal evidence to be early to mid-Viséan (late Chadian to Holkerian) in age. They are equivalent in age to beds ranging from the upper part of the Lane Formation to the top of the Holmpatrick Formation. The buildups are poorly exposed and relatively small, probably only a few tens of metres across at most. Buildup sediments are massive to crudely bedded and dominated by peloidal, clotted and dense uniform micrites displaying lime mudstone and bioclastic wackestone textures. Dasycladacean algae are common in the buildups and cryptalgal fabrics are locally important. Cavities in the buildups are generally small (< 5 cm) and lined with inclusion-rich radiaxial calcite cements. Micritization of bioclasts and cements is ubiquitous. Enclosing off-buildup limestones are skeletal and intraclastic grainstones possessing sedimentary structures indicative of deposition in moderate to high energy environments. Fossil and petrographic evidence from the buildups also indicate a shallow water origin for the north Co. Dublin buildups. Compared with the slightly older Tournaisian (Courceyan to early Chadian) Waulsortian buildups which developed extensively in the Dublin Basin, these younger platform buildups are smaller and more isolated and possess a diverse suite of algal components and cryptalgal fabrics. Nevertheless, components in the north Co. Dublin buildups most closely resemble the shallowest phase D Waulsortian buildups, particularly in the presence of abundant peloids and micritized cements. The north Co. Dublin buildups developed on a carbonate platform (the Milverton Platform), adjacent to the Dublin Basin, whereas the Waulsortian developed in a deeper ramp setting. Following the demise of the Waulsortian in early Chadian time carbonate buildups established themselves on the shallow platforms. It is suggested that the microbial communities responsible for these buildups may have ‘evolved’ from older phase D Waulsortian communities and that he north Co. Dublin platform buildups represent the shallow water end of a spectrum of Viséan buildups.     

Tectonic significance of mafic volcanic rocks in a Mesozoic sequence of the Menderes Massif, West Turkey

The Mesozoic platform sequence of the Menderes Massif consists of thick succession of detrital and carbonate rocks. In this sequence there are mafic metavolcanic rocks at two different levels. The first level of mafic metavolcanic intercalations is in the Late Triassic detrital-rich series located in the ÇaltayL Formation, which is the lowermost unit of the Mesozoic platform. The second level of the mafic metavolcanic rocks is located in the Late Cretaceous-(?)Paleocene Selçuk Formation laying on top of the platform sequence. The ÇaltayL Formation, which is composed of mica-schists, thinly-bedded cherts, calc-schist and mafic volcanic intercalations unconformably overlie the BayLndLr Formation, which consists of mica-schists, phyllites, and white quartzites of Palaeozoic or probably older age. The mafic volcanic rocks in the ÇaltayL Formation are alkaline basalts with within plate characteristics and are formed during an intraplate extension. The ÇaltayL Formation is conformably overlain by the KayaaltL Formation represented by calc-schists, dolomitic marbles, and rudist- and emery-bearing massive marbles in ascending order. The Selçuk Formation overlies the KayaaltL Formation and consists of a mica-schist matrix with allochthonous blocks of mafic volcanic rocks, metaperidotites, metagabbros and massive marbles. The mafic volcanic rocks in the Selçuk Formation are tholeiitic basalts and are petrologically similar to mid-oceanic basalts. The geological and geochemical characteristics of the mafic metavolcanic rocks in the ÇaltayL Formation indicate that during the Late Triassic, the Menderes platform was segmented, probably by the opening of a branch of the Neotethyan Ocean. Between the Late Triassic and the Late Cretaceous, the Menderes carbonate platform was built up. During the Latest Cretaceous-Early Paleocene, a slab of oceanic crust obducted on this platform and provided slices of mafic metavolcanic rocks into the Selçuk Formation.     

Compositional variations during phases of progradation and retrogradation of a Triassic carbonate platform (Picco di Vallandro/Dürrenstein, dolomites, Italy)

In this paper data are presented on the composition of sediments deposited at the toe of slope during progradation or retreat of Triassic carbonate platforms in the Dolomites (Italy). For this purpose a succession was studied from the toe of slope of a Triassic (Carnian) carbonate platform (Picco di Vallendro/Dürrenstein, Dolomites, Italy). The microfacies analysis of selected calciturbidites sequences revealed a reduced input of oncolites and ooids during progradation and an increase in clasts. The main input, however, was derived from the reefs on the platform. Retrogradation of the platform showed an increase of filaments and radiolarians (open ocean biota) as well as carbonate mud and a reduced input of grains that originated within the reefs on the platform. Both during progradation and retrogradation parts of the platform were flooded and could produce excess sediment that could be exported to the surrounding basins. However, the absence of platform interior biota documents that progradation occurred from sediments of the reefal belt, probably during relative sea-level lowstands. Carbonate composition varies systematically with toe-of-slope progradation/retrogradation and, thus, argues for carbonate production as the main driver of the geometries observed at the toe of slope.     

桂林泥盆纪碳酸盐台地的发育

桂林地区中、晚泥盆世大量发育的碳酸盐岩构成了一个东西宽近４０ｋｍ、南北长近８０ｋｍ的浅海碳酸盐台地，其岩相变化复杂，生物群落丰富。本文论述了碳酸盐台地形成各阶段的岩相和生物相特征，阐明了影响碳酸盐台地形成的因素，认为从滨岸碎屑环境变为成熟碳酸盐台地中间阶段的沉积物──混积岩及滩（补丁礁）和滩间沉积物在碳酸盐台地形成过程中不可忽视。     

黔南晚石炭世礁相地层中造礁生物Tubiphytes研究

广泛分布在黔南晚石炭世礁相地层中,具有多样的生物形态。其造礁作用以粘结方式为主,可以集中密集形成粘结岩礁块,也可以与其它造礁生物共同建造礁体。其建造的礁体分布局限,礁体一般规模不大。Tubiphytes在工作区除形成礁体外,还通过包覆其它生物碎屑和粘连灰泥和碎屑颗粒形成粘结岩,构成珊瑚礁体的基底,起到固结基底的作用;也可以在其它礁体内部粘结充填在礁骨架中的灰泥和碎屑颗粒形成块状粘结岩,起到加固礁体的作用。Tubiphytes与其它生物碎屑一起作为碳酸盐岩造岩的重要组成部分,在礁相地层中也广泛存在。Tubiphytes在黔南晚石炭世礁相地层中是一类具有特色的生物。     

上扬子地台南缘早志留世埃隆期碳酸盐岩岩石学特征及沉积环境

上扬子地台南缘早志留世埃隆期发育的碳酸盐岩,近期揭示具有较好的油气勘探前景,但有关该套岩层的岩石学特征及其沉积环境研究需要进一步深入。论文以野外地质剖面和室内薄片鉴定为基础,对上扬子地台南缘早志留世埃隆期碳酸盐岩开展系统的岩石颗粒组分、岩石类型和沉积环境分析。发现早志留世埃隆期碳酸盐岩颗粒类型主要为生物碎屑,含少量内碎屑与鲕粒;根据曾允孚先生等的碳酸盐岩结构成因分类方案,该地区碳酸盐岩主要有7种类型:包括亮晶鲕粒灰岩、亮晶生物屑灰岩、珊瑚礁灰岩、亮晶砂屑灰岩、砂屑-生物屑微晶灰岩、微晶砂屑灰岩和微晶灰岩。根据岩石学特征和野外露头分析,认为在早志留世埃隆期研究区从早期到晚期沉积环境经历了碳酸盐缓坡到碳酸盐台地的转变,并发育了外缓坡、内缓坡、台地边缘斜坡、台地边缘滩、台地边缘生物礁、开阔台地等亚相。以三级层序为编图单元,揭示了礁滩沉积区域展布特征,生物礁滩体主要发育于SQ2层序,具有环带状展布的特征。