Upper Ordovician sequences of western Estonia

The Upper Ordovician (uppermost Caradoc-Ashgill) section of western Estonia consists of a series of seven open-shelf carbonate sequences. Depositional facies grade laterally through a series of shelf-to-basin facies belts: grain-supported facies (shallow shelf), mixed facies (middle shelf), mud-supported facies (deep shelf and slope) and black shale facies (basin). Locally, a stromatactis mud mound occurs in a middle-to-deep shelf position. Shallow-to-deep shelf facies occur widely across the Estonian Shelf and grade laterally through a transitional (slope) belt into the basinal deposits of the Livonian Basin.

Each sequence consists of a shallowing-upward, prograding facies succession. Sequences 1 (Upper Nabala Stage) and 2 (Vormsi Stage) record step-wise drowning of underlying shelf units (lower Nabala) that culminated in the deposition of the most basinal facies (Fjäcka Shale) in the Livonian Basin. Sequences 3–6 comprise the overlying Pirgu Stage and record the gradual expansion of shallow and middle-shelf facies across the Estonian Shelf. The Porkuni Stage (sequence 7) is bracketed by erosional surfaces and contains the shallowest-water facies of the preserved strata. The uppermost part of the section (Normalograptus persculptus biozone) is restricted to the Livonian Basin, and includes redeposited carbonate and siliciclastic grains; it is the lowstand systems tract of the lowest Silurian sequence 8. Sequence 7 and the overlying basinal redeposited material (i.e., the lowstand of sequence 8) correspond to the latest Ordovician (Hirnantian) glacial interval, and the bracketing unconformities are interpreted as the widely recognized early and late Hirnantian glacial maximums.

The sequences appear correlative to Upper Ordovician sequences in Laurentia. Graptolite biozones indicated that the Estonian sequences are equivalent to carbonate ramp sequences in the western United States (Great Basin) and mixed carbonate-siliciclastic sequences in the eastern United States (Appalachian Basin–Cincinnati Arch region). These correlations indicate a strong eustatic control over sequence development despite the contrasting tectonic settings of these basins.     

Late Ordovician (Turinian–Chatfieldian) carbon isotope excursions and their stratigraphic and paleoceanographic significance

Five positive carbon isotope excursions are reported from Platteville–Decorah strata in the Upper Mississippi Valley. All occur in subtidal carbonate strata, and are recognized in the Mifflin, Grand Detour, Quimbys Mill, Spechts Ferry, and Guttenberg intervals. The positive carbon isotope excursions are developed in a Platteville–Decorah succession in which background δ¹³C values increase upward from about −2‰ at the base to about 0‰ Vienna Pee Dee belemnite (VPDB) at the top. A regional north–south δ¹³C gradient, with lighter values to the north and heavier values to the south is also noted. Peak excursion δ¹³C values of up to +2.75 are reported from the Quimbys Mill excursion, and up to +2.6 from the Guttenberg excursion, although there are considerable local changes in the magnitudes of these events. The Quimbys Mill, Spechts Ferry, and Guttenberg carbon isotope excursions occur in units that are bounded by submarine disconformities, and completely starve out in deeper, more offshore areas. Closely spaced chemostratigraphic profiles of these sculpted, pyrite-impregnated hardground surfaces show that they are associated with very abrupt centimeter-scale negative δ¹³C shifts of up to several per mil, possibly resulting from the local diagenetic effects of incursions of euxinic bottom waters during marine flooding events.     

Late Devonian carbon isotope stratigraphy and sea level fluctuations, Canning Basin, Western Australia

The Upper Devonian reef complexes of the Canning Basin contain some of the world’s best exposed, continuous stratigraphic sections through the Frasnian-Famennian boundary. The facies distribution and composition of these reef complexes record interactions among sea level changes, sediment supply, ocean chemistry, and paleoecology. Changes in relative sea level produced spatial shifts in reef platform development and regional changes in sediment supply that can be correlated across facies boundaries using a combination of sequence stratigraphy, biostratigraphy, and carbon isotope stratigraphy. During the lowstand interval below the Frasnian-Famennian boundary, the reef margin advanced down the reef slope in shallow-water environments, and siliciclastics locally dominated in the marginal slope environment. Compilation of a broad late Frasnian to early Famennian sequence stratigraphic framework for the Canning Basin demonstrates that transgressive intervals correlate to positive carbon isotopic excursions within the basin. These isotopic shifts also can be correlated to time-equivalent positive carbon isotopic excursions reported from transgressive intervals in Europe. Thus, the late Frasnian transgressions in the Canning Basin were primarily eustatic rather than tectonic in origin, and positive carbon isotopic signatures of the Kellwasser horizons are globally correlative.     

The Middle Caradoc Facies and Faunal Turnover in the Late Ordovician Baltoscandian palaeobasin

A Late Ordovician episode of remarkable biotic, climatic, sea level and facies changes, named here as the Middle Caradoc Facies and Faunal Turnover, took place in the Baltoscandian area. This paper presents an integrated overview of these changes in the critical middle Caradoc interval. Data are given on carbonate rock composition, distribution and grain-size composition of the siliciclastic material and the carbon isotopic composition of whole-rock carbonates in cores of Estonia and Sweden.

The Middle Caradoc Facies and Faunal Turnover can be described as a succession of related environmental changes. The turnover began with a positive excursion in carbonate δ¹³C and continued with sea level changes that led to a sedimentary hiatus on the shelf and a change from carbonate-dominated to siliciclastic-dominated sedimentation in the basin. The turnover ended with an extinction event and associated microfaunal crisis.

The middle Caradoc turnover in Baltoscandia is comparable to a similar succession of changes in North America. The turnover affected two palaeocontinents, and reflects a widespread, possibly global environmental change. Onset of glaciation on Gondwana and/or increased orogenic activity might have initiated the changes in ocean circulation and led to the initial carbon isotope excursion. The following sea level rise and faunal changes affected several different continents.     

Aspects of recent advances in the Ordovician stratigraphy and palaeontology of China

The continuous and richly fossiliferous Ordovician succession of China (particularly South China) comprises a heterogeneous suite of litho- and bio-facies, which has been a main focus of stratigraphical and palaeontological research in recent years. Among the seven GSSPs established in China, three are within the Ordovician System, and the GSSP of the Darriwilian Stage at Huangnitang, Changshan County, western Zhejiang Province, was the first “golden spike” in China and the first for the Ordovician System. A series of case studies have revealed that: (1) the Ordovician radiation of some fossil groups on the Upper Yangtze Platform (e.g., brachiopods and graptolites) reached their first α-diversity acme in the Didymograptellus eobifidus Biozone, four zones earlier than the global trend; (2) the β-diversity peak was attained 3–4 zones later than the α-diversity peak; (3) many brachiopod communities or faunas first occurred in the central part of the Upper Yangtze Platform and subsequently expanded to both more offshore and near-shore facies; (4) diachroneity existed in many aspects of the radiation. The end-Ordovician mass extinction was a severe event in South China. Two pulses of the extinction are recognized for a number of major fossil groups, some being most strongly affected during the first pulse whereas the others suffered during the second pulse. Macroevolution during the Ordovician–Silurian transition has been investigated in detail, and the role of the Lazarus effect has been found to be less important than previously believed.     

Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control

The evolution of borings has shown that the morphology of borings is a function of both the borer and its substrate. This study investigated the effect of bryozoan internal skeletal morphology on the dimensions and distribution of borings. One hundred and forty-three trepostome colonies from the Middle and Upper Ordovician strata of northern Estonia were examined. Of these, 80% were matrix entombed, longitudinally sectioned ramose and hemispherical colonies, and 20% were matrix-free hemispherical colonies that allowed examination of the colony surfaces. Seventy-one percent of the ramose colonies were bored, whereas 88% of the hemispherical colonies were bored. On average, only 8% of colony surface areas were bored out. Borings were more randomly oriented in the hemispherical colonies. In contrast in the ramose colonies, the borings tended to more restricted to the thin-walled endozone and thus parallel to the branch axis. This is interpreted to be a function of the thick-walled exozones controlling to some extent where the borer could bore. Based on morphology, the borings in the hemispherical colonies are referred to Trypanites and those in the ramose colonies to Sanctum . Sanctum is revised to include two possible openings and to recognize that boring shapes were inherently constrained by the thick-walled exozones of the host bryozoan colonies. Both trace fossils were probably produced by a boring polychaete that used the tubes as domiciles.     

Conodont biostratigraphy and carbon isotope chemostratigraphy of the Middle to Upper Ordovician on the western Yangtze Platform,South China

Middle and Late Ordovician strata in the nearshore area of the western Yangtze Platform are investigated. In total, 241 δ¹³C_carb samples and 108 conodont samples from the Songliang and Tuanjie sections in the northeastern Yunnan Province were collected for chemostratigraphic and biostratigraphic studies. Altogether, 21 species belonging to 16 conodont genera were recovered from the two sections, among which Ansella jemtlandica, Drepanoistodus basiovalis, Hamarodus brevirameus, and Microzarkodina hagetiana are important age indicators within the Dapingian to early Katian interval. Four carbon isotope shifts are recognized in the studied sections: a negative shift in the early Darriwilian, the middle Darriwilian carbon isotope excursion (MDICE), the early Katian Guttenberg carbon isotope excursion (GICE), and a further positive carbon isotope shift later in the early Katian which is a new record of this event in South China. Integrated carbon chemostratigraphy and conodont biostratigraphy indicate early Darriwilian and early Katian ages for the base and top, respectively, of the Huadan Formation at the Songliang section, and a Darriwilian to early Katian age for the Shihtzupu Formation at the Tuanjie section.     

Late Ordovician extinction of North American and British crinoids

After reaching a diversity peak in the Caradocian, North American Ordovician crinoids underwent a gradual decline to a nadir in the early Ashgillian (Maysvillian). This interval, recording extinction of the Cleiocrinidae, Merocrinidae, Ottawacrinidae, Hybocystitidae, and several lineages of camerate crinoids, was apparently caused by major environmental shifts in seas of eastern North America resulting from a westward-prograding wedge of terrigenous clastics derived from the Taconic Highlands, possibly coupled with a marine transgression in the Maysvillian that allowed colder water slope biofacies to invade the craton. Crinoids suffered a major episode of extinction in the late Ashgillian (late Richmondian/Rawtheyan). This event, preceding the end of the Ordovician by at least one stage or 2 to 4 million years, resulted in extinction of 12 families of crinoids including the Xenocrinidae, Tanaocrinidae, Reteocrinidae, Archaeocrinidae, Anthracocrinidae, Cincinnaticrinidae, Iocrinidae, Anomalocrinidae, Carabocrinidae, Cupulocrinidae, Porocrinidae, and Hybocrinidae. Glacio-eustatic lowering of sea level may have triggered this crisis by partially draining the North American craton, resulting in changes in oceanic circulation, salinity, and temperature. Latest Ordovician (Hirnantian) carbonates of the North American mid-continent region contain pelmatozoan assemblages from which Silurian crinoids radiated. These taxa were largely unaffected by a minor extinction event at the Ordovician/Silurian boundary.     

Late Ordovician brachiopods from Peru and their palaeobiogeographical relationships

A Sandbian brachiopod association from the Calapuja Formation, in the Peruvian Altiplano, north‐west of Lake Titicaca, has allowed a re‐examination of the palaeobiogeographical relationships between Gondwana and Avalonia during the Late Ordovician, when the palaeocontinents are considered to be already very distant from one another. The brachiopod fauna includes the new species Onnizetina calapujensis sp. nov., Horderleyella chacaltanai sp. nov., Drabovinella minuscula sp. nov. and Tasmanella curtiseptata sp. nov., as well as Caeroplecia sp., Dinorthis cf. flabellulum and Tunariorthis cardocanalis. In addition, Colaptomena expansa expansa and Heterorthis retrorsistria, known from the British Burrellian Stage of the Caradoc Series (late Sandbian) in Wales and the Welsh Borderlands, have also been identified. The brachiopod collection is the most diverse known from a single locality in the whole Central Andean Basin. Within it, forms with clear Gondwanan links occur, such as the new species of Onnizetina, Drabovinella and Horderleyella, and typical representatives of the Avalonian faunas, such as the Welsh Colaptomena expansa expansa and Heterorthis retrorsistria. The brachiopod species exchange between the Proto‐Andean margin of Gondwana and Avalonia, now believed to be possible during the late Sandbian, allows a reconsideration of the global taxonomic affinities of both regions. With this in mind, detrended correspondence analysis (DCA) and cluster analysis have been applied to an updated rhynchonelliformean brachiopod matrix consisting of presence/absence data. The scatter plot resulting from the DCA allows a vivid visualization of the grouping and geographical trends of the South American localities with respect to Avalonia–Baltica and the Mediterranean margin of Gondwana during the Sandbian. Our results agree with previous palaeogeographical reconstructions, depicting Avalonia very close to Baltica and already distant from Gondwana. As a few brachiopod species, with low dispersal potential, would have been able to migrate between those distant palaeocontinents, the existence of intermediate islands in the Rheic Ocean, permitting the transit by island hopping of eurythermal species, must be considered.     

Lower Aptian carbon isotope stratigraphy from a distal carbonate shelf setting: the Cau section, Prebetic zone, SE Spain

A δ¹³C curve is reported for the latest Barremian to Early Aptian at a section located in the Prebetic zone (Cau section, SE Spain). The studied section records a hemipelagic succession of dark shales, deposited on a distal carbonate ramp with a high subsidence rate, adjacent to shallow carbonate environments. The integrated biostratigraphy of the section is based on ammonites, planktonic foraminifera and calcareous nannofossils, and it has allowed an accurate dating of the succession. The δ¹³C curve presented shows a distinctive evolution, leading to the recognition of three major excursions, as well as a subdivision into eight segments, which represents an improvement of the current biostratigraphic resolution. The correlation, both isotopic and biostratigraphical, with other well resolved sections is very accurate even at the higher resolution attained. Correlation with sections with low-resolution biostratigraphic characterisation from shallow platform limestones also gives good results, which supports the effectiveness of carbon isotope stratigraphy as a correlation tool.     

Huemacaspis (Trilobita, Kerfornellinae) from the Late Ordovician of the Argentine Cordillera Oriental

The trilobite genus Huemacaspis P?IBYL and VANěK, 1980 is redescribed from well-preserved material from the Santa Gertrudis Formation (early Caradoc), Argentine Cordillera Oriental. The new species H. gallinatoensis is described and figured. Huemacaspis is widely distributed in the southern part of the Central Andean basin during the early Caradoc and it is a key taxon for the correlation of different units from the Cordillera Oriental and Sierras Subandinas of Argentina and the Cordillera Oriental of Bolivia. This taxon is one of the few records of trilobites of early Caradoc age found in the shallow shelf environments of southwestern Gondwana. Huemacaspis is accommodated within the Kerfornellinae, a subfamily otherwise known from southern Central Europe and northern Africa. The trilobite fauna from the early Caradoc of the Central Andean basin suggests a faunal exchange with the latter regions indicating the persistence of a broadly similar biogeographic pattern to that documented in earlier Ordovician times.     

Effects of fixation on freshwater invertebrate carbon and nitrogen isotope composition and its arithmetic correction

Retrospective investigations using carbon and nitrogen stable isotope composition of archived material have a great potential for describing past effects of anthropogenic ecosystem alterations or natural shifts in ecosystems. In this study, we examined the effects of two commonly used preservation substances of freshwater invertebrates, ethanol and lugol, on δ¹³C and δ¹⁵N of various planktonic and benthic taxa. For both isotopes, the average effect of fixation in ethanol was stronger than in lugol, and the effects on δ¹³C were stronger than on δ¹⁵N (average ± SD: 1.18 ± 0.94 and −0.47 ± 0.99 for δ¹³C ethanol and lugol fixed samples, respectively, and 0.39 ± 0.68 and 0.17 ± 0.77 for δ¹⁵N, respectively). The changes in the isotopic composition were not dependent on the initial isotopic composition of each taxon, but were related with concomitant changes in the carbon or nitrogen content. Application of a mass balance correction equation to the fixed samples resulted in a significantly lower average effect of fixation in ethanol (0.01 ± 0.59 and 0.44 ± 0.65 for δ¹⁵N and δ¹³C, respectively), while corrections had little effect for lugol fixed samples (0.24 ± 0.53 and −0.39 ± 0.85, respectively). For both isotopes and fixatives, corrections resulted in linear relationships between fixed vs. control samples, with slopes and intercepts not significantly different from 1 and 0, respectively. Therefore, mass balance correction of stable isotopes in fixed invertebrates is recommended for minimising the effects of fixation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: M. Power     

Ordovician meteoric carbon and oxygen isotopic values: implications for the latitudinal variations of ancient stable isotopic values

Columnar and clear blocky calcite cement from a Middle Ordovician carbonate succession in east Tennessee is interpreted as meteoric in origin. Columnar and clear blocky calcite from this succession does not show extremely large ¹³C depletions reported from meteoric phases of younger rocks. Meteoric fluid δ¹⁸O values calculated from clear blocky calcite are 2 to 3‰ more negative than approximately coeval sea water; a relationship typical of modern, low-latitude, coastal meteoric water. Comparison with meteoric δ¹⁸O values from Ordovician units elsewhere suggests that the geographic distribution of these values may be broadly similar to that observed today. Therefore, we tentatively suggest that geographic distribution of meteoric δ¹⁸O values during both icehouse and greenhouse eras are similar.     

Seasonal carbon isotope discrimination in a grassland community

Summary Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture.     

Magnesian calcite and chamositic ooids forming shoals peripheral to Late Ordovician (Ashgill) muddy siliciclastic shores: southern Ontario

In southern Ontario, ooids are associated with two distinct facies associations in the Queenston Formation, the final stage of Late Ordovician (Ashgill) Taconic basin fill. One facies consists of thin ooid and bioclastic grainstones interbedded with mudrock, and lies near the base of the formation, and, in southwestern Ontario, also forms a local NW-thickening wedge near the middle of the formation. Ooids have radial-fibrous and radial-concentric fabrics (Type A), with chamosite, illite, and Fe-oxide laths at intercrystalline sites. Vertical lithologic and ooid abundance patterns indicate that thresholds to carbonate production were sensitive to changes in terrigenous sediment supply, sea level, circulation, accommodation space, and tectonism.

Ooids in the second facies association are admixed with abraded fragments of open-marine biota, or occur burrow fills, within a <30-cm-thick interval of mudrock near the top of the preserved Queenston succession, a few metres below the Ordovician–Silurian unconformity. Ooids have radial concentric and crosscutting patchy microcrystalline fabrics (Type B). This unit may represent a transgressive or stillstand deposit modified by bioturbation.

The extent of preserved fabric suggests that both ooid types were originally magnesian calcite, but Type A ooids underwent greater burial alteration. This is shown by crystalline mosaics that cross-cut relict primary fabrics; δ¹³C values (−1.82‰ to +0.67‰) and δ¹⁸O values (−4.46‰ to −10.57‰) more negative than marine calcite of similar age; Mn and Fe concentrations more elevated above expected marine values; and a luminescence similar to that of intergranular cements. Burial meteoric diagenesis was likely promoted by excellent permeability of the host sand. We interpret authigenic chamosite and Fe-oxide to reflect diagenesis of iron-bearing and clay detritus trapped during ooid growth. Type B ooids suffered less alteration: δ¹³C (+1.1‰ to +6.64‰) and δ¹⁸O (−3.04‰ to −4.81‰) values overlap the expected marine range, including ¹³C enrichment that occurs within the Hirnantian (latest Ordovician) excursion. Although Mn and Fe values are still higher than those of modern calcitic ooids, negligible luminescence suggests that recrystallization occurred in the presence of marine-derived pore fluids. Further burial alteration was inhibited due to low permeability of the host mud.

Type A ooid facies in the Queenston Formation forms an ancient analogue for lesser known Quaternary ooid shoals peripheral to tropical deltaic systems. The facies of Type B ooids, while more enigmatic, may preserve a geochemical herald of latest Ordovician climate change. The presence of minor chamosite in Type A ooids defines a possible distal facies of the well-known oolitic ironstones of similar age in the mid-continental USA.     

Early–Mid Ordovician Yangtzeella (Syntrophiidina, Brachiopoda) and its evolutionary significance

Abstract:  Re-examination of newly collected topotype material confirms that the type species of Yangtzeella , Y .  poloi , a widespread Early and Mid Ordovician syntrophiidine brachiopod in South China, has a finely costellate shell rather than being smooth as previously thought. Thus, the subgenus Yangtzeella ( Vadimella ) Nikitina et   al ., established on the basis of fine costellae, is invalidated. Among 15 species of Yangtzeella , five species are recognized as valid based on multivariate analyses: Y .  poloi , Y .  unsulcata , Y .  songziensis , Y .  kueiyangensis and Y .  igori , among which the type species was the oldest known. Six are synonymized: Y .  septata , Y .  reticulata , Y .  lensiformis , Y .  depressa , Y .  yichangensis and Y .  minuta . Four are rejected from Yangtzeella : Y .  extensa , Y .  similior , Y .  yohi and Y .  poloi var. minor . Regional biostratigraphy indicates that Yangtzeella first appeared in a relatively deep-water setting on the Lower Yangtze Platform (South China palaeoplate) during late Tremadoc time ( Scolopodus warendensis conodont biozone) and then expanded to the deeper Jiangnan Slope as well as to the shallower Upper Yangtze Platform. The genus experienced two episodes of heightened abundance and diversity on the Upper Yangtze Platform during late Dapingian and mid Darriwilian times, respectively. Outside South China, Yangtzeella occurs sporadically in a few microplates or terranes, such as Tarim, Chu-Ili (southern Kazakhstan) and Taurides (southern Turkey) during the Dapingian and Darriwilian. Worldwide, Yangtzeella became extinct by the end of the Darriwilian.     

Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions

Four whole-lake inorganic ¹³C addition experiments were conducted in lakes of differing trophic status. Inorganic ¹³C addition enriched algal carbon in ¹³C and changed the C-DOC by +1.5‰ to +9.5‰, depending on the specific lake. This change in C-DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in C-DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about 20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and 5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient enriched lake. Natural abundance measurements of the C of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results, we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters.     

Resource allocation to reproduction and soma in Drosophila: a stable isotope analysis of carbon from dietary sugar

Metabolic resources in adults of holometabolous insects may derive either from larval or adult feeding. In Drosophila melanogaster, reproduction and lifespan are differently affected by larval vs. adult resource availability, and it is unknown how larval vs. adult acquired nutrients are differentially allocated to somatic and reproductive function. Here we describe the allocation of carbon derived from dietary sugar in aging female D. melanogaster. Larval and adult flies were fed diets contrasting in sucrose (13)C/(12)C, from which we determined the extent to which carbon acquired at each stage contributed to adult somatic tissue and to egg manufacture. Dietary sugar is very important in egg provisioning; at every age, roughly one half of the carbon in eggs was derived from sugar, which turned over from predominantly larval to entirely adult dietary sources. Sucrose provided approximately 40% of total somatic carbon, of which adult dietary sucrose came to supply approximately 75%. Unlike in eggs, however, adult acquired sucrose did not entirely replace the somatic carbon from larvally acquired sucrose. Because carbon from larval sucrose appears to be fairly "replaceable", larval sucrose cannot be a limiting substrate in resource allocation between reproduction and lifespan.     

Ramp morphology controlling the facies differentiation of a Late Ordovician reef complex at Bachu,Tarim Block,NW China

A carbonate ramp in the shallow‐marine northwestern part of the Central Tarim Uplift, Bachu, NW China, exhibits an extraordinary Late Ordovician reef complex along the Lianglitag Mountains, exposed for a distance of about 25 km. Seven localities within the ‘Middle Red Limestone’ of the Upper Member of the Lianglitag Formation (Katian, Late Ordovician) illustrated the changes in biofacies and lithofacies: northern, seaward‐directed patch reefs are replaced towards the south by coeval grain banks. The patch reef units are dominated by microbial and calcareous algal components. The reefs at the northernmost locality are knoll‐shaped, kalyptra‐shaped or irregularly shaped with sizes of individual reefs increasing from about 2 m in height and diameter. Stratigraphically upward, reefs notably expand to larger structures by several mounds coalescing; they are generally about 10 m thick and tens of metres in lateral extent. The maximum thickness of the main patch reef is more than 30 m, and its diameter is around 100 m. The reefal units turn into biostromes with gentler relief southward and still further south grade into banks composed of peloids and coated grains. The southernmost locality is still a shallow‐water bank, and the coastline is not documented in the study area. The present evidence indicates that the Late Ordovician palaeo‐oceanography provided a number of environments for the optimal growth of carbonate build‐ups; microbial‐calcareous algal communities could thrive in areas where the innovative metazoan reef frameworks consisting of corals and stromatoporoids did not play a significant role. The ramp morphology, especially changes in water depth, controlled the configuration of the reef complex.