Mid-oceanic carbonate platforms as oceanic dipsticks: examples from the Pacific

Framebuilders of Cenozoic coral reefs are limited by their photic requirements to the contemporaneous sea-level, and therefore shallow water reef facies are reliable paleo sea-level indicators. Sea-level lowstands leave no record on coral reefs in areas subject to tectonic uplift, such as the Huon Peninsula, New Guinea, but are recorded by coral reefs in areas subject to tectonic subsidence. A eustatic sea-level fall which exceeds the rate of subsidence subaeriallyexposes the upper section of the reef complex, creating a meteoric ground water system whose diagenetic imprint on the reef carbonates offers a good indicator of a sea-level stillstand. Cenozoic reef platforms thus may contain records of sea-level fluctuations, whether eustatic and global, or tectonic and local. Those reef platforms which developed on seamounts formed in mid-oceanic plate settings are particularly useful for the study of eustatic sea-level changes because their subsidence history is relatively simple, and the tectonic factor can be accounted for when estimating the eustatic sea-level component. Conventional petrographic and biostratigraphic methods used to delineate erosional unconformities in Cenozoic carbonate sections are often deficient. We demonstrate here that stable oxygen and carbon isotopes of the carbonates can reveal the location of both the exposure surface and the paleo water table with greater confidence on account of the specific imprint of meteoric diagenesis. In addition, the⁸⁷Sr/⁸⁶Sr isotope technique offers a promising dating tool of disconformities linked to sea-level lowstands with a resolution superior to the conventional biostratigraphic techniques. Although oxygen, carbon, and strontium isotopes monitor different aspects of global sea-level changes, when used in conjunction they provide deeper insights into the past than either one could achieve alone. Examples from previous and ongoing studies of Pacific mid-oceanic carbonate platforms illustrate the potential of the isotope techniques to unravel sea-level changes. At Midway Atoll, stable carbon and oxygen isotopes along with lithologic and biostratigraphic data suggest a sharp eustatic sealevel fall during the Early Miocene and a series of rapid, brief eustatic fluctuations during the Pliocene-Quaternary. The frequency and timing of the latter is supported by sea-level data from Enewetak Atoll obtained on the basis of detailed strontium isotopes and lithology. The Enewetak data also indicate a series of rapid, brief eustatic fluctuations around the Early-Middle Miocene boundary. At Niue, a carbonate platform about 500 km south of Samoa, oxygen, carbon, and strontium isotope records cover the critical interval of the Miocene-Pliocene boundary and show two distinct disconformities. The mid-oceanic carbonate platforms offer a testing ground of Vail-Haq type eustatic sea-level curves derived primarily from sections along passive continental margins and continental interiors. We show that Neogene sea-level data obtained from Midway, Enewetak, and Niue differ from Vail and Hardenbol's contemporaneous sea-level curve and support Haq et al.'s version.     

Response of triassic reef coral communities to sea-level fluctuations, storms and sedimentation: Evidence from a spectacular outcrop (Adnet, Austria)

Summary The Upper Rhaetian coral limestone of Adnet, southeast of Salzburg Austria has been repeatedly referred to as one of the most spectacular examples of an ancient ‘autochthonous’ coral reef structure. The ‘Tropfbruch’ quarry is probably the best outcrop for interpreting the distributional patterns of biotic successions and communities of a late Triassic patch reef. Our study is based on the interpretation of a) outcrop photographs, b) reef maps resulting from quadrat transects, and c) the analysis of quantitative data describing the distribution and frequency of reef organisms and sediment. A new methodological approach (combination of reef mapping and photo-transects) is used to obtain quantitative field data which can be compared in greater detail with data from modern coral reefs investigated by corresponding quantitative surveys. Three unconformities and three well-defined ‘reef growth stages’ reflecting the vertical and lateral development of the reef structure were differrentiated using transects: Stage 1, representing the reef growth optimum, is characterized by laterally differentiated coral reef knobs with corals in growth position. Criteria supporting this interpretation are the extraordinary size of the corals, their preservation in situ and the great thickness of this interval. The massive coralPamiroseris grew under higher energy conditions at the rim of the reef knob, whereas branchingRetiophyllia colonies preferred less agitated water in the center. Vertical changes are reflected by an increase in frequency of the dasycladacean algaDiplopora adnetensis and by the decreasing size ofRetiophyllia. These sedimentological and biological criteria together with the unconformity above indicate a fall in the sea level as a major control mechanism. Stage 2, separated from stage 1 by an unconformity caused by partial subaerial exposure and karstification, is characterized by vertically stacked coral successions with diverse reef debris. Facies heterogeneity is reflected by differences in the diversity, taphonomy and packing density of reef-building organisms as well as by differences in sediment input from the platform. Water depths and accommodation space were lower, therefore minor sea level fluctuations had a stronger effect on the biotic composition. The high percentage of coral debris and corals reworked by storms and the increase in the input of platform sediment led to a reduction of reef growth. Stage 3, again separated at the base by an unconformity associated with karstification, is characterized by bioclastic sediments with isolated reefbuilders forming a level-bottom community. The distribution of different coral morphotypes suggests that sea level fluctuations were not the only controlling factor. Variations in the substrate were caused by differences in the input of platform sediment. The three-step development seen in Adnet documents the response of low-diverse coral associations to variations caused by small-scale sea level changes, storm activity and sedimentation. The vertical changes in reef community structures correspond to a sequence of ‘allogenic replacements’. The Adnet reef structure should not be regarded as a general model of Alpine Upper Rhaetian reefs, because of the particular setting of the patch reef. Only the ‘capping beds’ of the Upper Rhaetian Reef Limestone of the Steinplatte exhibit criteria similar to Adnet. Potential modern analogues of features seen in the coral communities of Adnet are the internal structure of theRetiophyllia thickets, the key role of branching corals within the communities, the scattered distribution and low and even diversity of corals subsequent to breaks in settlement, segration patterns of corals indicating ‘contact avoidance’, toppling of large coral colonies by intensive boring, and decreasing coral coverage from deeper and sheltered settings to more shallower water depths.     

Upper Triassic reef facies in the Asher-Atlit-1 borehole, Northern Israel: Microfacies, cement stratigraphy and paleogeographic implications

Summary  The late Triassic succession of the Asher-Atlit 1 borehole is over 1000 m thick, and is composed of reefal and associated facies interbedded with volcanics of Norian age. Only borehole cuttings are available. Microfacies classification and cement stratigraphy determined by optical and CL microscopy, allowed discrimination of six episodes of reef establishment, progradation, shallowing, and termination. Organic buildups are constructed of reef-building biota (sponges, possible corals, encrusting organisms) typical for the late Triassic of the Tethys. Reef-associated facies include fore-slope, central reef, ooid shoal, lagoonal, and supratidal environments. Cement zoning patterns trace diagenetic signatures which range from early neomorphic skeletal replacements and original marine cements, via characteristic burial sequences; depositional and diagenetic sequences are terminated by marginal marine intra- or supratidal conditions, and subaerial exposure with pedogenic overprints. Volcanic episodes tend to be associated with termination of carbonate sedimentation episodes, while volcanic quiescence and subsidence permit vertical progradation of reefal and associated facies. The depositional and progradational environment, rapid rate of sedimentation, periodicity, association with volcanics, and regional considerations, suggest a depositional setting on the rifted shelf-margin of the nascent Neo-Tethys, with a possible eustatic overprint.     

Sponge communities from the Lower Liassic of Adnet (Northern Calcareous Alps, Austria)

The lower slope of the drowned Alpine Adnet Reef was recolonized in Hettangian time by sponge communities of hexactinellid (hexactinosid and lyssacinosid) taxa and a few demosponges. Special taphonomic processes caused an excellent preservation of these sponges. The preservation allows to define several growth forms and to study original spicule configurations of the mainly non-rigid skeletons. Sponge faunas of presumably similar associations are known from adjacent basins, but only by isolated spicules of completely collapsed specimens. In Adnet the sponges are embedded in biodetrital limestones of the Schnöll Formation. Orientation and distribution of the sponges reflect autochthonous faunas that have been mixed with dislocated individuals by local water currents. The predominance of erect sponge types indicates intermediate sedimentation rates and/or occasional high-energy events. Sponge types and community structures are comparable with those ones from Middle Paleozoic mud mounds. Several hiatuses, mostly characterized by ferromanganese crusts have been kept free of sponge settlement. Carbon stable isotopes of the sponge-rich sequence show a small negative δ¹³C_carb excursion that covers the period from Lower Hettangian to Lower Sinemurian.This revised version was published online in May 2005 because several displayed passages had been inadvertently deleted in the original published version.     

Carnian (Triassic) aridization on the Levant margin: evidence from the M1 member, Mohilla Formation, Makhtesh Ramon, south Israel

The Carnian Pluvial Event was followed by extreme aridity around the Mediterranean region, but the relationship between these climatic modes and the evaporite deposits of the north Arabian margin has not been established. The Mohilla Formation in Israel was deposited on the rifted Levant margin of the Neotethyan seaway during the Carnian (Late Triassic). The lowermost member, M1 (carbonate, shale, minor evaporite), records sea-level and climate change of the transition from open-marine deposits to the thick evaporite of the overlying M2 member. Field, petrographic and cathodoluminescence investigation of the M1 member exposed at Makhtesh Ramon, southern Israel, enabled tracking of changing paleoenvironments. The M1 member can be subdivided into six sea-level controlled sedimentary cycles, each terminating in subaerial exposure. Open-marine, lagoonal, and supratidal belts are represented, but environments become increasingly restricted upwards. Three of the exposure horizons are marked by well-developed early diagenetic features, including dissolution porosity and meteoric cements. These changing facies belts and the superposed diagenetic modes formed under an oscillating climate regime of three relatively humid episodes dominated by deposition of carbonate, alternating with evaporitic sediments indicating aridity. Deposition of the M1 member can be correlated with the transition in the western Tethys from the Carnian pluvial episode to aridity. This transition in the Levant region is characterized by an oscillatory climate that culminated in a thick evaporite unit from the extreme arid phase. The oscillations may be attributed to shifting global climate belts, overprinted by monsoonal strengthening and weakening, in the equatorial belt.     

Generation and evolution of oolitic shoal reservoirs in the Permo-Triassic carbonates,the South Pars Field,Iran

Ooid grainstone is the main reservoir rock in the Permo-Triassic Dalan and Kangan formations (Khuff equivalents) in many gas fields of the Persian Gulf and neighbouring areas. Ooids with a dominant aragonite mineralogy accumulated in a series of linear shoals and sand banks parallel to the shoreline, on the shallow parts of a vast epeiric carbonate platform. On the basis of the sequence stratigraphic analysis, these reservoir facies mainly developed during relative sea-level rises and increases in accommodation space. Integrated petrographic and geochemical studies reveal that ooid grainstone was altered through a complex diagenetic history, largely controlled by water chemistry, as a result of relative sea-level fluctuations. Two main types of ooid grainstone are the result: dolomitised grainstone or type H and oomouldic grainstone or type M. Dolomitised grainstone is commonly associated with the transgressive systems tract (TST), and developed under hypersaline conditions. In comparison, oomouldic grainstone is predominant in the early highstand systems tract (HST), which was affected by intensive meteoric diagenesis. Petrophysical study indicates that the reservoir properties of these rocks are largely a function of diagenesis. On the basis of their dominant pore types and diagenetic modifications, the ooid grainstone facies of the studied formations are grouped into five reservoir rock types. The spatial and temporal distribution of these rock types and their diagenetic evolution can be predicted within the sequence stratigraphic framework. Among these rock types, porosity has been greatly enhanced by dolomitisation and dissolution in the dolomitised grainstone (DG) and oomouldic grainstone (MG). On the other hand, it has been reduced by cementation and compaction in tightly cemented and compacted grainstones (CEG and COG rock types). The primary porosity has been relatively well preserved in grainstone with interparticle porosity (IPG rock type). The later porosity reduction during burial was also controlled by rock type. This study shows that despite the great burial depth, a significant amount of porosity is still preserved in oomouldic grainstone.     

Reworked marine sandstone concretions: a record of high-frequency shallow burial to exhumation cycles

Concretions, with abundant calcite-dolomite cement-replacement textures originally hosted in shallow-marine sandstones, were reworked into Lower Cretaceous fluvio-deltaic conglomerates and shoreface sandstones (External Zones, Betic Cordillera). A cycle of host sand deposition, early diagenetic concretion formation and concretion reworking is documented: (1) Well-sorted shoreface sandstone deposited. (2) Spherical to ovoid, non-ferroan calcite-cemented concretions formed below flooding surfaces at shallow-burial depths during early eodiagenesis. Non-ferroan calcite cements were precipitated from the bicarbonate derived from seawater and from dissolution of marine bioclasts, as shown by isotope analyses. (3) Concretions were reworked and exposed on the seafloor in a high-energy setting as indicated by the presence of numerous bivalve borings (Entobia ichnofacies), laminated micritic microbial crusts around the concretions, and epilithobionts (oysters, barnacles and corals) on the concretion surface. Concretions also appear as erosional remnants on the floor of channels which were incised into the shoreline sandstone when sea-level fell. (4) The fluvio–deltaic channels were filled with sediment during flooding in the late lowstand of sea-level. (5) The concretions are partly dolomitized, and the presence of siderite, pyrite and barite in the outer part of the concretions precipitated before the dolomite, suggests that the latter formed during shallow burial.     

Deep-water coral banks: an example from the “Calcare di Mendicino” (Upper Miocene, Northern Calabria, Italy)

Summary The “Calcare di Mendicino” is a mixed carbonatesiliciclastic informal unit of Miocene (Late Tortonian-Early Messinian age), that crops out extensively in the northwestern part of the Calabria. In the Scannelle quarry near Belsito (Cosenza), four stratigraphic sections were studied to define the sedimentological and paleoecological setting. The carbonate body records the development of a deep-water coral bank characterized by a low-diverse community of azooxanthellate scleractinian (Oculina andDendrophyllia) and stylasterine hydrozoans colonies. Two main stages of bioconstruction development can be distinguished: a thicket and a bank stage. Among the biostromal dwellers the more common are bryozoans, echinoids, benthic foraminifers, gastropods, and bivalves. A higher content of planktonic foraminifers occur in the thicket stage. The coral bank flourished within the aphotic zone, with deep currents loaded with nutrients and siliciclastic sediments. The upper part of the “Calcare di Mendicino” carbonate body has been affected by a pervasive dolomitization destroying almost completely the sedimentary structures and the biofacies. The lower part, the main object of this paper, preserves the microfacies but it experienced a widespread recrystallization obliterating the primary geochemical characteristics. The diagenetic history, partly hidden, reveals three main stages: primary marine with isopachous fibrous cements, deep burial with cavities infilled by sparry calcite, and meteoric-phreatic with dog-tooth cements.     

Biostratigraphic correlation,paleoenvironment stress,and subrosion pipe collapse: Dutch Rhaetian shales uncover their secrets

A subrosion pipe or sinkhole is a geologic phenomenon that occurs due to dissolution of strata in the subsurface causing the overlying sediments to collapse. The subrosion pipe in the Winterswijk quarry complex in the eastern Netherlands yielded rare, dark-colored shales. Bivalves and palynomorphs indicate that the shales were deposited during the Rhaetian (uppermost Triassic). In addition, detailed correlation with other NW European localities in Great Britain, Austria, and Germany further constrained the age of the shales to the middle of the Rhaetian. The shales were deposited in a near-coastal environment and contained a low diverse macroinvertebrate fauna with bivalves and some brittle stars that lived in a hostile environment, probably caused by low salinity and oxygen levels. These middle Rhaetian shales were mixed with dark-colored middle to late Hettangian sediments, both overlying Middle Triassic (Anisian) strata, which is present in the pipe as well. The presence of Rhaetian sediments in the subrosion pipe reopened the discussion on its age of formation. We suggest that a collapse in the Middle Eocene is most likely. This research expands the knowledge of the marine realms in the uppermost Triassic in Europe, just prior to the Permian–Triassic extinction event.     

New constraints on the last aragonite–calcite sea transition from early Jurassic ooids

Calcite and aragonite seas are commonly distinguished based on the prevailing primary mineralogy of ooids and carbonate cements over time. Secular oscillations of these seas are usually attributed to changes in ocean chemistry and paleoclimate. While the veracity of such oscillations has been verified by independent data and modeling approaches, the timing of the transition from one ocean state to the other remains poorly resolved. Here, the timing of the last aragonite–calcite sea transition is estimated by assessing the preservation of Early Jurassic ooids from the Trento Platform in northern Italy. Point counting of ooid-bearing limestones from four distinct stratigraphic levels provides a contrasting pattern: Hettangian and Sinemurian ooids are all poorly preserved and were probably predominantly originally aragonitic, whereas Pliensbachian and Toarcian ooids are excellently preserved, suggesting a primary calcitic mineralogy. Although calcitic ooids may have already been common in the Late Triassic, it is proposed that the last aragonite–calcite sea transition occurred in the Early Jurassic between the Sinemurian and Pliensbachian, at least in this subtropical region. Therefore, the selective extinction of aragonite-secreting organisms at the end-Triassic mass extinction cannot be attributed to secular changes in ocean chemistry.     

Triassic reefs in Slovenia

The paper deals with the distribution, paleogeography, age and biota of Triassic reefs in Slovenia. Most of these reefs have not been studied in detail up to now, but the paleographical distributional pattern can be outlined (Figs. 1 and 2). Triassic reefs are known from Central and Northern Slovenia, predominantly occurring at the margins of the “Slovenian trough” (which separates the northern Julian Platform and the southern Dinaric Platform) and at the margins of an intraplatform trough within the Julian platform. Reef growth started in the Ladinian and Cordevolian and continued (with interruptions during the Upper Carnian ?) to the Norian and Rhaetian. Anisian environments are characterized by the predominance of algal mats and dasycladacean algae. Cordevolian patch reefs as well as Norian and Rhaetian reefs were built during the Late Triassic by calcareous sponges and corals, which belong to different species (Tab. 1 and 2). Some smaller Cordevolian patch reefs may have been formed within deeper-water sediments. An interesting facies sequence is developed in the Norian Dachstein Limestone reef of Pokljuka (Julian Alps), starting with deeper-marine cherty limestones, which gradually succeeded by crinoidal limestones followed by reef limestones and lagoonal Dachstein Limestones.     

Miliolipora species (Foraminifera,Miliolina) from the Rhaetian Dachstein Limestone of Karavanke Mts (Slovenia): Palaeoecological and palaeobiogeographic implications

The Carnian-Rhaetian genus Miliolipora (Soritoidea, Milioliporidae) is characterised by a coarsely perforated porcelaneous wall and a quinqueloculinoid arrangement of semi-tubular chambers. Miliolipora tamarae nov. sp. has been documented in the Rhaetian Dachstein reef limestone of Mt. Begunj??ica (Karavanke Mts., northern Slovenia). This new species differs from Miliolipora cuvillieri Brönnimann and Zaninetti in its costate outer chambers and evolute coiling. Both species are abundant in an oncoid rudstone/grapestone facies located immediately behind the central reef zone. In this depositional context, Miliolipora spp. were subjected to mechanical sorting and are believed to have been transported a short distance from their habitat. The costae and the overall less rounded shape of the test helped to stabilize M. tamarae nov. sp. on the sea floor. Both species were widely spread in the Tethyan realm confirming the broad palaeobiogeographic distribution of the Late Triassic foraminifera.     

Numerical modeling of the impact of sea-level rise on fringing coral reef hydrodynamics and sediment transport

Most climate projections suggest that sea level may rise on the order of 0.5–1.0 m by 2100; it is not clear, however, how fluid flow and sediment dynamics on exposed fringing reefs might change in response to this rapid sea-level rise. Coupled hydrodynamic and sediment-transport numerical modeling is consistent with recent published results that suggest that an increase in water depth on the order of 0.5–1.0 m on a 1–2 m deep exposed fringing reef flat would result in larger significant wave heights and setup, further elevating water depths on the reef flat. Larger waves would generate higher near-bed shear stresses, which, in turn, would result in an increase in both the size and the quantity of sediment that can be resuspended from the seabed or eroded from adjacent coastal plain deposits. Greater wave- and wind-driven currents would develop with increasing water depth, increasing the alongshore and offshore flux of water and sediment from the inner reef flat to the outer reef flat and fore reef where coral growth is typically greatest. Sediment residence time on the fringing reef flat was modeled to decrease exponentially with increasing sea-level rise as the magnitude of sea-level rise approached the mean water depth over the reef flat. The model results presented here suggest that a 0.5–1.0 m rise in sea level will likely increase coastal erosion, mixing and circulation, the amount of sediment resuspended, and the duration of high turbidity on exposed reef flats, resulting in decreased light availability for photosynthesis, increased sediment-induced stress on the reef ecosystem, and potentially affecting a number of other ecological processes.     

Drowned reefs and antecedent karst topography,Au'au Channel,S.E. Hawaiian Islands

During the last glacial maximum (LGM), about 21,000 years ago, the Hawaiian Islands of Maui, Lanai, and Molokai were interconnected by limestone bridges, creating a super-island known as Maui-Nui. Approximately 120 m of sea-level rise during the Holocene Transgression flooded, and then drowned, these bridges separating the islands by inter-island channels. A new multibeam high-resolution bathymetric survey of the channels between the islands, coupled with observations and video-transects utilizing DeepWorker-2000 submersibles, has revealed the existence of numerous drowned reef features including concentric solution basins, solution ridges (rims), sand and sediment plains, and conical-shaped reef pinnacles. The concentric basins contain flat lagoon-like bottoms that are rimmed by steep-sided limestone walls. Undercut notches rim the basins at several depths, marking either sea-level still stands or paleo-lake levels. All of the solution basins shallower than 120 m were subaerial at the LGM, and at one stage or another may have been shallow shoreline lakes. Today, about 70 drowned reef pinnacles are scattered across the Maui–Lanai underwater bridge and all are situated in wave-sheltered positions. Most drowned during the interval between 14,000 and 10,000 years ago when sea-level rise averaged 15 mm/year. Virtually all of the surficial topography in the Au'au Channel today is a product of karst processes accentuated by marginal reef growth during the Holocene. Both the submerged basins and the drowned reefs represent an archive of sea-level and climate history in Hawaii during the late Quaternary.     

Synchronous Wildfire Activity Rise and Mire Deforestation at the Triassic–Jurassic Boundary

The end-Triassic mass extinction event (∼201.4 million years ago) caused major faunal and floral turnovers in both the marine and terrestrial realms. The biotic changes have been attributed to extreme greenhouse warming across the Triassic–Jurassic (T–J) boundary caused by massive release of carbon dioxide and/or methane related to extensive volcanism in the Central Atlantic Magmatic Province (CAMP), resulting in a more humid climate with increased storminess and lightning activity. Lightning strikes are considered the primary source of wildfires, producing charcoal, microscopically recognized as inertinite macerals. The presence of polycyclic aromatic hydrocarbons (PAHs) of pyrolytic origin and allochthonous charcoal in siliciclastic T–J boundary strata has suggested widespread wildfire activity at the time. We have investigated largely autochthonous coal and coaly beds across the T–J boundary in Sweden and Denmark. These beds consist of predominantly organic material from the in situ vegetation in the mires, and as the coaly beds represent a substantial period of time they are excellent environmental archives. We document a remarkable increase in inertinite content in the coal and coaly beds across the T–J boundary. We show estimated burning temperatures derived from inertinite reflectance measurements coupled with palynological data and conclude that pre-boundary late Rhaetian mire wildfires included high-temperature crown fires, whereas latest Rhaetian–Sinemurian mire wildfires were more frequent but dominated by lower temperature surface fires. Our results suggest a major change in the mire ecosystems across the T–J boundary from forested, conifer dominated mires to mires with a predominantly herbaceous and shrubby vegetation. Contrary to the overall regional vegetation for which onset of recovery commenced in the early Hettangian, the sensitive mire ecosystem remained affected during the Hettangian and did not start to recover until around the Hettangian–Sinemurian boundary. Decreasing inertinite content through the Lower Jurassic suggests that fire activity gradually resumed to considerable lower levels.     

The Büdöskút Olistolith,an exotic limestone block from the Bükk mountains (NE-Hungary)

Summary The present paper presents results of stratigraphical, sedimentological and micropalaeontological investigations of an olistolith from the Büd?skút area in the Bükk Mts (NW Hungary). The olistolith consists of Norian sub- and peritidal platform carbonates (Büd?skút lime-stone). During early diagenesis dissolution cavities originated which where filled by ostracodal mudstones. Other cavities first were wallpapered by evinospongial crusts and later filled either by ostracodal mudstones or by brick-red haematitic material (weathered bauxite). The evinospongial crusts show stromatolite-like structures and their forming therefore is supposed to be organically (microbially) induced. During the Early up to the Late Jurassic the host rock was dissected by neptunian dykes. The internal sediment's faunal content reveals that the dykes formed during the (?) Hettangian/Sinemurian and the Toarcian— Oxfordian age. A comparison of the Büd?skút limestone neptunian dyke internal sediments with the Bükk parautochthonous and the Szarvasko-Mónosbél nappe complex sedimentary columns shows no similarities. Therefore the Büd?skút olistolith is interpreted as an exotic body within the Bükk Mts.     

Patch-reef morphology as a proxy for Holocene sea-level variability,Northern Florida Keys,USA

A portion of the northern Florida Keys reef tract was mapped with the NASA Experimental Advanced Airborne Research Lidar (EAARL) and the morphology of patch reefs was related to variations in Holocene sea level. Following creation of a lidar digital elevation model (DEM), geospatial analyses delineated morphologic attributes of 1,034 patch reefs (reef depth, basal area, height, volume, and topographic complexity). Morphometric analysis revealed two morphologically different populations of patch reefs associated with two distinct depth intervals above and below a water depth of 7.7 m. Compared to shallow reefs, the deep reefs were smaller in area and volume and showed no trend in topographic complexity relative to water depth. Shallow reefs were more variable in area and volume and became flatter and less topographically complex with decreasing water depth. The knoll-like morphology of deep reefs was interpreted as consistent with steady and relatively rapidly rising early Holocene sea level that restricted the lateral growth of reefs. The morphology of shallow “pancake-shaped” reefs at the highest platform elevations was interpreted as consistent with fluctuating sea level during the late Holocene. Although the ultimate cause for the morphometric depth trends remains open to interpretation, these interpretations are compatible with a recent eustatic sea-level curve that hindcasts fluctuating late Holocene sea level. Thus it is suggested that the morphologic differences represent two stages of reef accretion that occurred during different sea-level conditions.     

THE EARLY JURASSIC AMMONITE BADOUXIA FROM BRITISH COLUMBIA, CANADA

Abstract:  Most species of the Lower Jurassic ammonite genus Badouxia are restricted to the eastern Pacific where they are of fundamental importance to the Hettangian/Sinemurian ammonite zonation of North America. The fauna from the type area for the genus has been restudied and four species and two transitional forms are now recognized. Badouxia forticostata and Badouxia castlensis are new. Badouxia occidentalis (Frebold) and Badouxia oregonensis Taylor are placed in synonymy with Badouxia canadensis (Frebold). These major taxonomic changes and subsequent modification to the range of B . canadensis require revisions to the current zonation for the Western Cordillera of North America. The Oregonensis Zone is re-named the Mineralense Zone. The Canadensis Zone is abandoned and its previously defined Rursicostatum and Columbiae subzones are elevated to the level of full zones. Large samples indicate that most species of Badouxia display a remarkable range of continuously variable morphology. In addition, the genus shows some of the best-documented evidence of sexual dimorphism in Early Jurassic ammonites. Badouxia spans the Hettangian/Sinemurian boundary and based on the range of different species, five stratigraphic intervals are recognized. Intervals 1–3 correlate with the north-west European Angulata Zone. The majority of interval 4 and the whole of interval 5 correlate with the north-west European Bucklandi Zone. The age of the base of interval 4 is uncertain.     

Carbon and oxygen isotope evidence for high-frequency (104–105 yr) and My-scale glacio-eustasy in Middle Pennsylvanian cyclic carbonates (Gray Mesa Formation), central New Mexico

We combine cyclo- and sequence stratigraphy along with whole rock δ¹³C and conodont apatite δ¹⁸O analysis to document high-frequency (10⁴–10⁵ yr) and My-scale sea-level changes for the Middle Pennsylvanian (Desmoinesian or Moscovian) Gray Mesa Formation of central New Mexico. Approximately 75 subtidal cycles (1–8 m) are grouped into 4 1/2 My-scale depositional sequences (40–80 m). About 50% of the cycles show evidence of prolonged subaerial exposure at cycle tops with the development of calcretes, diagenetic mottling, and regolith intraclasts. High-resolution δ¹³C analysis of whole rock limestones across nine of the cycles indicates that the cycle tops were diagenetically altered by isotopically light, meteoric fluids during sea-level fall and lowstand. These δ¹³C trends support the interpretation that high-frequency sea-level changes were responsible for cycle development.Conodont apatite δ¹⁸O values from sampled cycles indicate that the high-frequency sea-level changes were driven by glacio-eustasy combined with changes in surface seawater temperature (SST). δ¹⁸O values from conodont apatite, spanning parts of three depositional sequences indicate that My-scale glacio-eustasy and/or SST changes controlled sequence development. δ¹⁸O shifts indicate that the magnitudes of 10⁴–10⁵ yr glacio-eustasy were between ～ 55 and 170⁺ m combined with tropical SST changes of ～ 1.5°–6 °C. Calculated My-scale glacio-eustatic oscillations were between ～ 60 and 140 m with SST changes of < 3.5 °C. The most plausible driver for the My-scale paleoclimate changes is long-period obliquity (～ 1.2 My) variations. These calculated high-frequency, glacio-eustatic values are similar or greater than Pleistocene values, and lie within the range estimated for other Middle Pennsylvanian successions using a variety of independent eustatic proxies. The similarity in range of magnitudes between high-frequency and My-scale sea-level changes combined with the large differences in magnitudes between individual high-frequency sea-level oscillations helps explain the lack of systematic cycle-stacking patterns within these Pennsylvanian icehouse sequences.     

Quaternary dune carbonates from the Mediterranean Coast of Egypt: Petrography and diagenesis

Summary The Quaternary carbonates of the Mediterranean coast of Egypt between Alexandria and Salum appear as parallel limestone ridges rising up to 100 m above sea level. These ridges are dominated by dunal carbonates which differ not only in their primary composition but also by distinct grades of meteoric water diagenesis. Oolitic facies dominates the younger aeolianites of the first and second ridges. Bioclastic facies with abundant coralline algae, benthonic foraminifers, molluscs, echinoderms and intraclasts represents the major rock type in the older aeolianites. Features of meteoric water diagenesis include precipitation of increasing amounts of avoid-filling low Mg-calcite spar, dissolution of aragonite and stabilization of aragonite and high Mg-calcite to low Mg-calcite. Aeolianites below paleosol horizons contain abundant calcrete cements, micritized fossils and detrital grains which are commonly corroded and replaced by calcite. Three stages of progressive meteoric diagenesis are recognised in the Egyptian Quaternary aeolianites. In stage 1 minor precipitation of low Mg-calcite occurs at the grain boundaries. Stage 2 is marked by partial dissolution of aragonite, partial loss of high Mg-calcite and precipitation of low Mg-calcite in some pore spaces. In stage 3, most of the remaining pores are occluded by cementation. At the end of stage 3, Mg is removed from high Mg-calcite but some aragonite still persists. The early vadose cements are represented by miniscus, bridge and pendant cements. The phreatic cements were precipitated as bladed spar in the isopachous rims and equant spar in the intergranular and mouldic porosity. The late vadose cements are represented by micritic cements that were related to calcrete formation. Elemental behaviour during meteoric water diagenesis indicates that it leads to a gradual decrease in bulk Sr along with Na in progressively altered aeolianites. Mn distribution is controlled by the carbonate mineralogy (aragonite versus calcite) as well as the proximity of the aeolianites to the overlying paleosol horizons.