Ichnology of the Callovian-Oxfordian rocks of the Katrol hill range,Kachchh, western India

On the basis of distinct lithologic features such as composition, grain size, bedding characteristics and sedimentary structures, six facies were identified in Callovian to Oxfordian rocks exposed southwest of Bhuj, Kachchh. They are interbedded calcareous shale-siltstone (ICSSF), limestone (LF), ferruginous sandstone (FerSF), felspathic sandstone (FelSF), grey shale (GSF) and oolitic limestone (OLF) facies. The rich and highly diversified trace fossils reveal a wide range of animal behaviours represented by dwelling, feeding, crawling and resting structures. Horizontal feeding structures are found abundantly in all lithofacies indicating low wave and current energy and deposition of poorly sorted muddy to sandy sediments. A few coarse layers containing Arenicolites, Ophiomorpha and Skolithos indicate the presence of opportunistic animals (due to their first appearance under harsh conditions) under -intermittently moderate wave and current energy or storm wave conditions (due to coarse grain size and dominance/presence of only vertical trace fossils) in the shoreface zone. Taenidium occurs mainly in the lower shoreface to transitional zone suggesting low to moderate energy conditions. Thalassinoides occurs in middle to lower shoreface settings under relatively low-energy conditions. Zoophycos represents offshore environment, where it occupies the deepest bioturbation levels.The characteristic lithofacies and assemblages of trace fossils in the rocks of the Chari/Jumara Formation indicate a depositional environment fluctuating from the upper shoreface to offshore zone.     

Zoophycos and related trace fossils from the Chefar El Ahmar Formation,Upper Emsian-Frasnian Ia-Ib (Ougarta,SW Algeria)

The Upper Emsian to Frasnian Ia-Ib strata of the Marhouma area (or “km 30” outcrop), exposed in the Ougarta Range (SW Algeria) belong to the Chefar El Ahmar Formation. On the basis of distinct lithological and palaeontological features, this formation is subdivided into three members (Lower Marly Limestones Member, Middle Marly Limestones Member, and Upper Marly Limestones Member). The studied beds show low to moderate diversity of trace fossil assemblage which contains thirteen ichnotaxa: Chondrites intricatus, Chondrites isp., Chondrites cf. targionii, Circulichnis cf. montanus, Cochlichnus isp., Neonereites biserialis, Neonereites multiserialis, Nereites isp., Palaeophycus isp., Planolites isp., Thalassinoides isp., Zoophycos aff. cauda-galli, and Zoophycos isp. A. The two latter ichnotaxa are the most common trace fossils in the assemblage and occur at three different levels showing different bioturbation intensities. The first Zoophycos-bearing level (Zl 1) is characterised by an overall high bioturbation intensity reflecting a very high oxygenation rate and nutrient supply, allowing the development of large and dense Zoophycos specimens. The second Zoophycos-bearing level (Zl 2) has a considerable reduction of bioturbation intensity as compared to the previous level, with an abundance of Chondrites, which is probably due to radical palaeoecological changes that suggests dysoxic and stressful conditions. The third Zoophycos-bearing level (Zl 3) is characterised by an overall moderate bioturbation intensity. The distribution of trace fossils was influenced by lithology, sedimentation rate, energy level (storm events), bottom oxygenation, and nutrient supply. The lithofacies and trace fossils of the Chefar El Ahmar Formation both indicate a depositional environment fluctuating from the lower shoreface to lower offshore zone.     

The Faraoni event (latest Hauterivian) in ichnological record: The Río Argos section of southern Spain

The Early Cretaceous (latest Hauterivian) Faraoni Oceanic Anoxic Event (F-OAE) in the Río Argos section (Caravaca region, southern Spain), the candidate for the Global Boundary Stratotype Section and Point (GSSP) of the Hauterivian–Barremian transition, has been studied. Its ichnological bed-by-bed analysis allows for interpretation of oxygenation changes through the Faraoni Level interval and improvement upon previous characterization of oxygen conditions prior, during and after the F-OAE. The trace fossil assemblage belongs to the Zoophycos ichnofacies and it includes Chondrites intricatus, Chondrites targionii, Halimedides isp., Palaeophycus isp., ?Patagonichnus isp., Planolites isp., Rhizocorallium isp., Taenidium isp., Thalassinoides isp., Trichichnus linearis, Zavitokichnus fusiformis, and Zoophycos isp. Their diversity in particular beds fluctuates. Beds with four to six ichnotaxa reflect a multi-tiered macrobenthic trace maker assemblage living in good oxic and trophic conditions. In one bed below and one bed above the Faraoni Level (both marls without primary lamination), there are only two or three, mostly opportunistic ichnotaxa (Trichichnus, Chondrites, Planolites). They record dysoxic conditions. At the base of the Faraoni Level, one thicker and two thinner beds of marly mudstones (21.2 and 3.5 cm thick, respectively) are characterized by primary lamination. At the top and in the basal part of the thicker bed and in the thinner beds some trace fossils are present. These beds were deposited under anoxic conditions and later colonized by trace makers either from overlying beds deposited under oxic conditions or from the level of a greenish lamina in the lower part of the thicker bed, recording short episodes of dysoxic conditions. The thinner anoxic beds are separated by marls deposited under dysoxic conditions.     

Geochemical and isotopic characterization of trace fossil infillings: New insights on tracemaker activity after the K/Pg impact event

Geochemical and isotopic analyses of the Cretaceous–Paleogene (K/Pg) boundary deposits were conducted at the Caravaca section (External Subbetic, southeast of Spain) in order to evaluate the recovery of the macrobenthic tracemaker community and the bioturbational disturbance. Samples from the infilling material of several lower Danian dark-colored trace fossils (Chondrites, Planolites, Thalassinoides and Zoophycos) located in the uppermost 8-cm of the light upper Maastrichtian strata, as well as samples from the host sedimentary rock of these trace fossils, were analyzed and compared with data from the lower Danian deposits. The values of element ratios indicative of extraterrestrial contamination (Cr/Al, Co/Al and Ni/Al) are higher in the infilling trace fossil material than in the upper Maastrichtian and lower Danian deposits, which suggests a contribution of the ejecta layer. Regarding the isotope composition, the δ¹³C values are lower in the infilling material than in the Maastrichtian host sedimentary rocks surrounding the traces, while the δ¹⁸O are higher in the infilling material. The geochemical and isotopic compositions of the infilling material evidence the unconsolidated character of the sediment, including the red boundary layer. Softground conditions confirm a relatively rapid recovery by the macrobenthic tracemaker community, starting a few millimeters above the K/Pg boundary layer. The mixture of the infilling material of the trace fossils moreover reveals a significant macrobenthic tracemaker activity affecting K–Pg boundary transition sediments that may have significantly altered original signatures.     

Exceptionally favourable life conditions for macrobenthos during the Late Cenomanian OAE-2 event: Ichnological record from the Bonarelli Level in the Grajcarek Unit,Polish Carpathians

Pelagic and hemipelagic sediments of the Bonarelli Level (uppermost Cenomanian) in the Sztolnia section (Grajcarek Unit, Polish Carpathians) contain trace fossils of the Zoophycos ichnofacies, including (in descending order of abundance): Chondrites (smaller and larger forms), Planolites, Thalassinoides, Palaeophycus, Taenidium, Teichichnus, and Zoophycos. They occur in thick bioturbated layers, which are interbedded with rare, thin layers of unbioturbated black shales. The black shale layers mark the Bonarelli Level and are interpreted as a record of anoxia or dysoxia. Coeval sections in the Western Tethys contain similar trace fossils but they are less abundant and these sections are characterized by thicker unbioturbated black shale layers and thinner bioturbated layers. This confirms the exceptionally favourable life conditions in sediments of the Sztolnia section, which do not record strong global anoxia during the OAE-2 event. Such favourable conditions were probably caused by effective oxygenation of pore waters and deep burial of organic matter, which are a consequence of high rates of accumulation and the palaeogeographical location of the section on a flank of a submarine high, under strong circulation.     

Palaeoecology of Late Triassic marine assemblages from the proto-Atlantic Basin (Ayamonte,SW Spain)

The Triassic represents a critical period that attests to the diversification of marine ecosystems. This paper analyses the stratigraphy of the easternmost Mesozoic series of the Algarve Basin in the Ayamonte sector (SW Spain). Two sets forming this series are described. The first, mainly siliciclastic, was deposited in continental contexts represented by fluvial and lacustrine environments with bioturbation associated with swamp-like environments (Taenidium) or with plain alluvial sediments (Labyrintichnus terrerensis, Planolites). This ichnoassemblage corresponds to the ichnofacies of Scoyenia. The second set, is carbonate-dominated and shows a remarkable palaeontological content comprising bivalves and gastropods, which made it possible to review our current knowledge of the regional stratigraphy of the Triassic in this area. Trigonodus-Isocyprina form this association for bivalves and Coeslostylina and Coeslostylina-Spirostylus-Mathilda for gastropods allowing to infer a Late Triassic (Carnian-Rhaetian) age for the Ayamonte area. The characteristic trace fossils of the carbonate sections are represented by Thalassinoides Treptichnus pollardi and Helminthoidichnites tenuis, which belong to the proximal expression of the Cruziana ichnofacies. Shallow marginal, low energy, and brackish and locally lacustrine conditions are inferred for this carbonate-dominated set, alternating with episodes of normal salinity, and towards the top, with punctuated episodes of higher energy. This palaeoenvironmental context is congruent with the palaeogeographical scenario conditioned by the existence of a threshold of major order that would indicate the initial breaking of Pangea and the opening of the Tethys in the eastern Mediterranean.     

豫西登封地区寒武系张夏组中部生物扰动构造及其地质意义

掘穴生物作为生态系统工程的建造者,其对沉积物进行的改造直接影响了沉积物的物理化学性质,进而影响了底栖生态系统。豫西登封地区寒武系苗岭统张夏组中部薄层微晶灰岩中发育大量的生物扰动构造,利用地球生物学、古生物学和生物扰动指数等方法,探讨了生物扰动构造的形成环境及其对沉积物的影响。研究表明,研究区张夏组中部生物扰动构造特征多为扰动边界模糊不清,生物扰动指数（BI）为2 ~ 5,说明该沉积期食物充足,氧气含量高。此外,在生物扰动中识别出3种遗迹化石：Thalassinoides bacae,Planolites isp.和Rhizocorallium isp.,说明生物扰动构造为多种生物造迹形成的。依据寒武系苗岭统张夏组中部的遗迹化石以及沉积特征,可知其整体处于偶尔受到风暴影响的滩间局限台地环境。     

东濮凹陷沙三段正常三角洲沉积中遗迹化石及意义

通过对钻井岩心的观察和遗迹化石的鉴定,在东濮凹陷古近纪沙河街组沙三段发现遗迹化石10属15种,包括:Skolithos vertivalis,Skolithos linearis,Skolithos isp.,Palaeophycus tubularis,Palaeophycus isp.,Planolites montanus,Planolites beverlegensis,Planolites isp.,Mermoides isp.,Taenidium isp.,Teichichnus isp.,Helminthoidichnites tenuis,Helminthopsis isp.,Beaconites isp.和Thalassinoides isp.。根据岩性特征、沉积构造和遗迹化石的组成、分布特征,研究区沙三段主要发育正常三角洲前缘亚相、前三角洲亚相,并划分了反映不同沉积环境和水体深度的2种遗迹组合,分别为Palaeophycus-Planolites遗迹组合和Planolites-Helminthoidichnites遗迹组合。     

古海洋氧化还原条件的遗迹化石定量表征特征:以华南二叠纪末生物大灭绝事件为例*

地质历史时期的重大生物—环境事件往往伴随着古海洋海水氧化还原条件的改变,而遗迹化石作为原位保存的生物成因沉积构造,对于解读古海洋氧化还原条件具有显著的优势。通过对前人常用的遗迹学参数进行分析总结,发现遗迹化石多样性、生物扰动强度、潜穴直径、特征遗迹化石组合这4项定量参数可以表征古海洋氧化还原条件的变化。文中以华南二叠系乐平统遗迹化石及生物扰动构造作为研究对象,系统分析了二叠纪末生物大灭绝事件前后遗迹化石参数表征的古海洋氧化还原条件变化特征:自吴家坪期晚期华南古海洋开始出现缺氧,然而该缺氧状态在长兴期不具有持续性,而是呈现出周期性缺氧/贫氧→富氧/有氧的波动特征;在二叠纪末生物大灭绝之前,煤山剖面高精度的定量遗迹学参数指示长兴组24e层顶部存在缺氧事件,并与大灭绝事件有着良好的对应关系。这一实例具体展示了遗迹学参数在古海洋水体氧化还原条件重建中应用前景广阔。     

Depositional environments and ichnology of Upper Cretaceous deep-marine deposits in the Sistan Suture Zone,Birjand, Eastern Iran

The palaeoenvironmental significance of trace fossil assemblages in the flysch deposits of the Upper Cretaceous of the Sistan ocean – the Sefidabeh basin in the Sistan Suture Zone SSZ in Eastern Iran – has been assessed for the first time. The Sefidabeh basin of turbidite origin consists of 10 sedimentary facies, which can be grouped into 3 facies associations (FA) representing submarine channel-related facies associations (FA1), lobe-related facies associations (FA2), distal fan-basin floor facies associations of a deep-water turbidite system (FA3). Thirty three ichnogenera, with many ichnospecies, have been identified in this deep sea succession: Alcyonidiopsis, Arthrophycus, Asterostoma, Belorhaphe, Bergaueria, Cardioichnus, Chondrites, Cosmorhaphe, Desmograpton, Gyrophyllites, Halopoa, Helminthopsis, Helminthorhaphe, Laevicyclus, Lophoctenium, Mammilichnis, Megagrapton, Multina, Nereites, Ophiomorpha, Palaeophycus, Planolites, Phycodes, Phycosiphon, Paleodictyon, Rutichnus, Scolicia, ?Strobilorhaphe, Taenidium, Teichichnus, Thalassinoides, Zoophycos and Urohelminthoida. Their distribution is clearly linked with lithofacies and depositional palaeoenvironments. Changes in trace fossil assemblages and ichnocoenoses follow different environments of the turbidity system of the submarine channel to fan system of the Sefidabeh basin and are associated with variations in environmental controlling factors. Environmental controlling factors including hydrodynamic regime, oxygen level, organic content and sedimentation rates. Ten ichnocoenoses were recognized in the facies associations of the deep-sea fan system of this study. Taking into consideration the diversity, bioturbation level, and colonization order of bioturbated beds and the obvious deepening of the deep-sea depositional system from inner to outer parts of the succession, ichnocoenoses can express a bathymetric trend from shallower to deeper parts, and from higher-to-lower hydrodynamic condition of deep-sea fan systems of the Sefidabeh basin. This study reveals important sedimentological and ichnological features of turbiditic systems in deep sea settings of Iran and permits the development of predictive models for the palaeoenvironmental significance of trace fossil assemblages that can be readily translated to analogous depositional systems in the surface/subsurface.     

Invertebrate trace fossils from the Alveley Member,Salop Formation (Pennsylvanian,Carboniferous), Shropshire,UK

The late Carboniferous–early Permian was a period of major environmental change, with the rainforests that covered the equatorial zone during the Carboniferous disappearing due to increasing aridification. This environmental transition had significant impacts on the terrestrial biota, including a major extinction event among plant and vertebrate groups. A rich and unique ichnofauna from the Alveley Member (Moscovian: Westphalian D) of the Salop Formation at Alveley in Shropshire (England) has yielded important insights into late Carboniferous terrestrial communities. However, research to date has focused entirely on the vertebrate footprints. Abundant invertebrate ichnofossils also occur at Alveley, typically on the rippled upper surfaces of beds assigned to a floodplain facies that preserve the vertebrate tracks in hyporelief on their base. We provide the first detailed examination of the invertebrate ichnofauna from Alveley, identifying six ichnospecies within five ichnogenera (Diplichnites, Gordia, Paleohelcura, Palmichnium, Protichnites), including a new species of the common arthropod ichnogenus Diplichnites. This moderately diverse invertebrate ichnofauna is dominated by arthropod repichnia. There is no evidence of infaunal bioturbation and the single example of Gordia indicates limited sediment grazing activity. The Alveley ichnofauna is typical of Euramerican continental ichnoassemblages from the very latest Carboniferous, and indicates a moderate diversity of arthropods (crustaceans, arachnids and chelicerates) living alongside the marginal freshwater to terrestrial assemblage of temnospondyl amphibians, and basal synapsid, diadectomorph and captorhinomorph amniotes.     

大民屯凹陷古近系沙河街组三段扇三角洲前缘沉积生物扰动特征

为探究陆相扇三角洲前缘沉积生物扰动特征,以辽河拗陷大民屯凹陷沈检5井古近系沙河街组三段扇三角洲前缘沉积岩芯为研究对象,对生物遗迹化石进行了鉴定,统计了垂向剖面上生物扰动层厚度和扰动指数的分布特征.依据主微量元素参数反映的沉积条件,探讨了生物扰动层厚度和扰动指数与沉积环境的响应关系.研究结果表明,沈检5井S34Ⅱ和S34...     

The ichnology of carbonate drifts

Carbonate drifts have so far not been as intensely investigated as their siliciclastic equivalents, especially from an ichnological perspective. The aim of this work is therefore to provide an overview of the different bioturbation styles in carbonate drifts for ichnologists and sedimentologists working in such deposits. Different types of carbonate drifts from the Maldives were studied to address this objective. The cores recovered during International Ocean Discovery Program Expedition 359 were examined to provide the sedimentological and ichnological data for a detailed analysis of the ichnology of carbonate drifts. The ichnological characteristics of the Maldives drifts are compared to other carbonate drifts in order to discuss similarities and differences, and thus provide an overview of the general characteristics of carbonate drift ichnology. These drifts are located in the Santaren Channel which lines Great Bahama Bank, along the Marion Plateau in Australia, in the Limassol and Larnaca basins in Cyprus and in the Danish Basin in Denmark. The common characteristics of bioturbation in carbonate drifts are: (i) the complete bioturbation of the sediment with bioturbation indexes between four and six; (ii) the occurrence of distinctive trace fossils limited to facies contacts or condensed intervals; (iii) a typical ichnoassemblage consisting of Thalassinoides, Scolicia, Planolites, Zoophycos, Chondrites, Phycosiphon and Palaeophycus; (iv) the contiguous occurrence of ichnogenera from different tiers, with only Zoophycos and Chondrites as deep tiers; and (v) distinct infills of the traces including particulate organic matter, pyrite, silica and celestine. In addition, the main ichnofacies of carbonate drifts is the Zoophycos ichnofacies. Ichnofabrics grade from coarse‐grained and completely bioturbated to ichnofabrics with present to rare trace fossils and preserved sedimentary structures. The type and intensity of the bioturbation is controlled by the amount of organic matter and the oxygenation at the sea floor that is determined by the action of bottom currents and the sea‐level fluctuations affecting the carbonate factory in carbonate platforms bordering the basins where the carbonate drifts form. The study of the bioturbation in core and outcrop provides palaeoenvironmental information about carbonate‐drift deposits that complement the classical sedimentological data.     

Balanoglossites ichnofabrics from the Middle Ordovician Volkhov formation (St. Petersburg Region, Russia)

The limestone succession of the Middle Ordovician Volkhov Formation in the St. Petersburg region (Russia) exposes numerous horizons with firm- and hardgrounds below omission surfaces, which contain trace fossils attributable to the ichnogenus Balanoglossites Mägdefrau, 1932. Although known from the literature since 75 years, such trace fossils were previously only informally described as “Korrosionsgruben”, “Karandashi”, or ascribed to different ichnotaxa such as Trypanites, Arenicolites and Pseudopolydorites. Owing to their complexity and often high bioturbation density, the morphology of these trace fossils is difficult to capture. Ichnofabrics containing Balanoglossites triadicus were studied in detail from sawn rock faces, broken rock blocks and sectioned slabs, including those from historical buildings in St. Petersburg. Accordingly, different trace-fossil elements can be revealed in dependence on the original substrate consistency, reflecting various stages of lithification: Mineral-stained and Trypanites-perforated hardground surfaces are bioeroded with long elongated grooves which are assigned to the ichnogenus Sulcichnus. Subtle openings lead into the partly lithified limestone where they branch into complex galleries of B. triadicus. They are characterized by J-, U- and Y-shaped shafts and multiply branched tunnels, which gradually continue into the underlying firmground. Other portions of the ichnofabric only exhibit biodeformational structures or the strongly compacted and branched burrow networks Labyrintichnus, which is due to the original soft sediment consistency. Balanoglossites ichnofabrics demarcate certain omission surfaces within the Dikari Limestone and can be traced for more than 300 km, supporting the regional lithostratigraphical correlation. The trace maker of B. triadicus and related trace fossils is interpreted to be a eunicid polychate with the ability to bioerode and burrow the sediment. The studied material from the Ordovician is similar to the Balanoglossites from the type area, the Triassic of Germany, in many respects. B. triadicus is a very common trace fossil in Ordovician and other Palaeozoic rocks of Baltoscandia and North America but so far has been seldom identified as such but instead is commonly confused with Thalassinoides, from which, however, it differs in several aspects.     

Effect of discharge on the chlorophylla distribution in the tidally-influenced Potomac River

In the tidal Potomac River, high river discharges during the spring are associated with high chlorophylla concentrations in the following in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophylla (less than 50 μg l^?1 occurred in the tidal river if average monthly discharge during July or August exceeded 200 m³s^?1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophylla (greater than 100 μg l^?1 approximately one year out of four. Chlorophylla maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m³ s^?1, but sustained discharges greater than 1,100 m³ s^?1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981.     

Paleoenvironmental conditions across the Cretaceous–Paleogene transition at the Apennines sections (Italy): An integrated geochemical and ichnological approach

Two distal Cretaceous–Paleogene (K/Pg) boundary sections in the Central Apennine region (Italy) have been studied: Bottaccione Gorge and Contessa Highway. Geochemical and carbon isotope analyses on the infilling of trace fossils and on the host sedimentary rocks were performed to determine paleoenvironmental conditions during the Cretaceous–Paleogene transition. Major and trace element contents were measured in a 63 cm-thick interval at Bottaccione Gorge (from 22 cm below to 41 cm above the K/Pg boundary) and in a 72 cm-thick interval at Contessa Highway (from 43 cm below to 29 cm above the K/Pg boundary). Even though the K/Pg ejecta layer is now depleted at these sections due to continuous oversampling, the uppermost Maastrichtian and lowermost Danian deposits record the paleoenvironmental conditions prior to and after the K/Pg event. We used redox-sensitive element ratios (V/Al, Cr/Al, Co/Al, Ni/Al Cu/Al, Zn/Al, Mo/Al Pb/Al and U/Mo) and detrital element ratios (K/Al, Rb/Al, Zr/Al and ƩREE/Al) as proxies of certain environmental parameters, used for paleoenvironmental reconstruction. In general, similar values for elemental ratios are registered within Maastrichtian and Danian deposits, which supports similar paleoenvironmental conditions prior to and after the K/Pg event as well as the rapid reestablishment of the pre-impact conditions (i.e., oxygenation, nutrient availability, and/or sedimentary input). An enrichment in certain redox-sensitive elements above the K/Pg at the Bottaccione Gorge section suggests lower oxygenation, as also evidenced by the tracemaker community. Carbon isotope composition data from the infilling material of trace fossils furthermore reveals values similar to those of the host rocks at the corresponding depth, which supports an active infilling by nearly contemporaneous bioturbation during sediment deposition.     

风暴沉积的遗迹学研究

遗迹化石正在证明其在鉴别和解释事件地层中的作用。风暴沉积含有一套混合的、与能量水平变化相适应的遗迹化石组合,两种不同的遗迹群落反映变化着的行为方式对生物所移居的两种连续的,但是单个性质不同的生境所作出的反应:常住的或平常天气的遗迹群落可以作为一种稳定的底栖群落的代表,在这一群落里单个的居群达到或接近它们的承载能力;而周期性产生的风暴遗迹群落则代表着在一种不稳定的、生态环境恶化的、机械控制的环境下繁盛的机会主义生物的群落。典型的陆源碎屑的风暴沉积中的遗迹群落可以加拿大艾伯塔上白垩统卡迪组中的遗迹群落为例,而碳酸盐风暴沉积中的遗迹群落则可以中国华北地台东部上寒武统崮山组中的碳酸盐风暴沉积序列中的遗迹群落为例,本文详细介绍这两种类型的成因及结构、构造特点。     

Combining in situ isotopic, trace element and textural analyses of quartz from four magmatic-hydrothermal ore deposits

This study couples in situ ¹⁶O, ¹⁷O and ¹⁸O isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic-hydrothermal quartz crystals. Euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic-hydrothermal ore deposits: El Indio Au–Ag–Cu deposit; Summitville Au–Ag–Cu deposit; North Parkes Cu–Au deposit and Kingsgate quartz-Mo–Bi–W deposit. The internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps. Quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry (for 40 trace elements in quartz) and sensitive high-resolution ion microprobe (for 3 isotopes in quartz). Imaging revealed fine oscillatory zoning, sector zoning, complex “macromosaic” textures and hidden xenocrystic cores. In situ oxygen isotope analyses revealed a δ¹⁸O range of up to 12.4 ± 0.3 ‰ in a single crystal—the largest isotopic range ever ascribed to oscillatory zonation in quartz. Some of these crystals contain a heavier δ¹⁸O signature than expected by existing models. While sector-zoned crystals exhibited strong trace element variations between faces, no evidence for anisotropic isotope fractionation was found. We found: (1) isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis (e.g., δD–δ¹⁸O) using bulk analytical techniques, (2) the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and (3) in three of the four samples, both textural and isotopic data indicate non-equilibrium deposition of quartz.     

Rhizocorallium in estuarine Ingersoll shale (Upper Cretaceous Eutaw Formation,Eastern Alabama coastal plain)

The ichnofossil Rhizocorallium—an oblique to horizontal U-shaped spreiten burrow—has been recognized in a broad range of Phanerozoic continental, marginal marine, and shallow to deep marine facies. Nonetheless, occurrences of this ichnotaxon in Cretaceous estuarine deposits are rarely described. Herein we document Rhizocorallium in the Ingersoll shale, a carbonaceous clay lens within an estuarine succession contained in the Upper Cretaceous (Santonian) Eutaw Formation exposed in the eastern U.S. Gulf coastal plain. The Ingersoll Rhizocorallium specimens, assigned to R. commune var. irregulare based on their basic morphology, horizontal disposition, dimensions, and actively filled spreiten, record a change in depositional conditions and substrate consistency linked to transgression. The Ingersoll shale accumulated rapidly in a restricted tidal channel in a bayhead delta setting and hosts an impoverished resident ichnofauna reflecting soupground conditions. In contrast, attributes of Rhizocorallium (e.g., burrow wall bioglyphs) and associated Thalassinoides in the upper part of the Ingersoll shale reflect firm substrates (i.e., Glossifungites ichnofacies). Firmground development and colonization reflect burial dewatering and subsequent exhumation by bay-shoreline ravinement of clays and the concomitant shift to estuarine central bay deposition. The biological affinity of the Rhizocorallium trace makers cannot be confidently established. However, based on relatively straight and seemingly current-aligned axes, passive burrow fills, lack of associated fecal pellets, and emplacement in firm clay, these structures were likely produced by suspension-feeding organisms—either crustaceans or worms—that took advantage of wave- or tide-induced currents in shallow areas near the estuary head.