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Low biostratigraphic resolution and lack of chronostratigraphic calibration hinder precise correlations between platform carbonates and coeval deep-water successions. These are the main obstacle when studying the record of Mesozoic oceanic anoxic events in carbonate platforms. In this paper carbon and strontium isotope stratigraphy are used to produce the first chronostratigraphic calibration of the Barremian-Aptian biostratigraphy of the Apenninic carbonate platform of southern Italy. According to this calibration, the segment of decreasing delta C-13 values, leading to the negative peak that is generally taken as the onset of the Selli event, starts a few metres above the last occurrence of Palorbitolina lenticularis and Voloshinoides murgensis. The following rise of delta C-13 values, corresponding to the interval of enhanced accumulation of organic matter in deep-water sections, ends just below the first acme of Salpingoporella dinarica, which roughly corresponds to the segment of peak delta C-13 values. The whole carbon isotope excursion associated with the oceanic anoxic event 1a is bracketed in the Apenninic carbonate platform between the last occurrence of Voloshinoides murgensis and the "Orbitolina level", characterized by the association of Mesorbitolina parva and Mesorbitolina texana. Since these bioevents have been widely recognized beyond the Apenninic platform, the calibration presented in this paper can be used to pinpoint the interval corresponding to the Early Aptian oceanic anoxic event in other carbonate platforms of central and southern Tethys. This calibration will be particularly useful to interpret the record of the Selli event in carbonate platform sections for which a reliable carbon isotope stratigraphy is not available.
The occurrence of mounds dominated by siliceous sponges and microbialites is often related to distal, deep settings of middle ramps and shelves. This paper presents evidence for Bajocian (Garanliana garantiana Zone) microbial-siliceous sponge mounds formed in open marine but relatively shallow settings of a ramp from the Iberian Basin of eastern Spain. Marked differences in mound spacing, morphology, and composition of the related intermound facies are observed from distal to more proximal settings. The distal (below storm wave base) settings are characterized by alternating tabular-bedded marls and limestones rich in pelagic fossils (ammonites, belemnites), open-marine thin-shelled bivalves (Bositra-like), as well as peloids, which include widely or randomly spaced isolated, small (up to 0.4 m high) and larger (up to 2.5 m high) mounds with upward accretion. The intermediate (near to above storm wave base) settings show tabular, thickened beds of peloidal and/or intraclastic limestones with closely spaced mounds (similar to 1 m high), which often coalesce laterally, forming extensive lenticular structures (up to 10 m wide). The proximal (above storm wave base) depositional settings consist of tabular to irregular beds of intraclastic limestones with widely spaced small (up to 0.4 m high) mounds with mainly tabular geometries. The mound framework contains variable proportions of microbialites (dense to clotted peloidal thrombolitic fabrics) and siliceous sponges (hexactinellids and lithistids in similar proportion) ranging from planar to conic shapes. These morphological and compositional changes allow characterizing three shallowing-upward sequences (sequences 1-3) developed in the overall regressive trend of a basin-wide, upper Bajocian T-R cycle. Episodic wave reworking of the early-cemented mounds resulted in the formation of peloids, small rounded intraclasts, and large, rounded or subangular intraclasts. These nonskeletal micritic grains show internal fabrics related to those of the mound and/or microbialites. A progressive textural gradation towards greater size and lesser roundness of the nonskeletal grains in the areas in the vicinity of the main mound factory is documented (i.e., from large, subangular intraclasts in the areas close to the main mound factory to peloids in the areas that are far from it). We discuss the alternative model of internal waves (instead of storm-induced waves) as the hydrodynamic agent providing the high-energy events needed to explain the origin of the peloidal-intraclastic intermound facies and, likely, also the nutrients needed by the microbialites and siliceous sponges to grow.
The Upper Cretaceous (Campanian-Maastrichtian) bioclastic wedge of the Orfento Formation in the Montagna della Maiella, Italy, is compared to newly discovered contourite drifts in the Maldives. Like the drift deposits in the Maldives, the Orfento Formation fills a channel and builds a Miocene delta-shaped and mounded sedimentary body in the basin that is similar in size to the approximately 350 km(2) large coarse-grained bioclastic Miocene delta drifts in the Maldives. The composition of the bioclastic wedge of the Orfento Formation is also exclusively bioclastic debris sourced from the shallow-water areas and reworked clasts of the Orfento Formation itself. In the near mud-free succession, age-diagnostic fossils are sparse. The depositional textures vary from wackestone to float-rudstone and breccia/conglomerates, but rocks with grainstone and rudstone textures are the most common facies. In the channel, lensoid convex-upward breccias, cross-cutting channelized beds and thick grainstone lobes with abundant scours indicate alternating erosion and deposition from a high-energy current. In the basin, the mounded sedimentary body contains lobes with a divergent progradational geometry. The lobes are built by decametre thick composite megabeds consisting of sigmoidal clinoforms that typically have a channelized topset, a grainy foreset and a fine-grained bottomset with abundant irregular angular clasts. Up to 30 m thick channels filled with intraformational breccias and coarse grainstones pinch out downslope between the megabeds. In the distal portion of the wedge, stacked grainstone beds with foresets and reworked intraclasts document continuous sediment reworking and migration. The bioclastic wedge of the Orfento Formation has been variously interpreted as a succession of sea-level controlled slope deposits, a shoaling shoreface complex, or a carbonate tidal delta. Current-controlled delta drifts in the Maldives, however, offer a new interpretation because of their similarity in architecture and composition. These similarities include: (i) a feeder channel opening into the basin; (ii) an excavation moat at the exit of the channel; (iii) an overall mounded geometry with an apex that is in shallower water depth than the source channel; (iv) progradation of stacked lobes; (v) channels that pinch out in a basinward direction; and (vi) smaller channelized intervals that are arranged in a radial pattern. As a result, the Upper Cretaceous (Campanian-Maastrichtian) bioclastic wedge of the Orfento Formation in the Montagna della Maiella, Italy, is here interpreted as a carbonate delta drift.
Oceanic Anoxic Event-2 (OAE-2; Cenomanian-Turonian) is characterized by extensive deposition of organic carbon-rich deposits (black shales) in ocean basins worldwide as result of a major perturbation of the global carbon cycle. While the sedimentological, geochemical, and paleontological aspects of deep water expressions of OAE-2 have been intensively studied in the last few decades, much less attention has been given to the coeval shallow water deposits. In this study, we present the results of a detailed facies and petrographic (optical microscope and scanning electron microscopy) and geochemical studies (delta C-13(carb), delta C-13 (org), delta N-15(bulk), TOC, and Rock-Eval pyrolysis) on two key shallow marine sections from the Apennine Carbonate Platform (ACP; Italy). Here a continuous record of shallow water carbonates through the OAE-2 interval is preserved, offering the unique opportunity to document the archive of paleoenvironmental changes in a neritic setting, at a tropical latitude and far from the influence of a large continental block. Two conspicuous intervals are characterized by abundant and closely spaced dark microbial laminites found at correlative stratigraphic horizons in the two stratigraphic sections. These laminites contain elevated concentrations of TOC (up to 1%) relative to microbial capping cycles laminites stratigraphically above and below. The organic matter preserved in these fine-grained laminites is dominated by cyanobacteria remains, which accounted for most of the organic matter produced on the ACP in these intervals. Our study suggests that Tethyan carbonate platforms experienced significant biological changes during OAE-2, alternating, in few kiloyears, between eutrophic phases dominated by microbial communities and mesotrophic/oligotrophic conditions favoring normal carbonate production/sedimentation. The synchronous occurrence of microbialite facies at different locations across the ACP and on other platforms worldwide (e.g., Mexico and Croatia) suggests a causal link between Large Igneous Province volcanism and the environmental conditions necessary to trigger cyanobacterial proliferation on shallow carbonate platforms.
Following the Middle Permian (Capitanian) mass extinction there was a global ‘reef eclipse’, and this event had an important role in the Paleozoic-Mesozoic transition of reef ecosystems. Furthermore, the recovery pattern of reef ecosystems in the Wuchiapingian of South China, before the radiation of Changhsingian reefs, is poorly understood. Here, we present a detailed sedimentological account of the Tieqiao section, South China, which records the only known Wuchiapingian reef setting from South China. Six reef growing phases were identified within six transgressive-regressive cycles. The cycles represent changes of deposition in a shallow basin to a subtidal outer platform setting, and the reefal build-ups are recorded in the shallowest part of the cycles above wave base in the euphotic zone. Our results show that the initial reef recovery started from the shallowing up part of the 1st cycle, within the Clarkina leveni conodont zone, which is two conodont zones earlier than previously recognized. In addition, even though metazoans, such as sponges, do become important in the development of the reef bodies, they are not a major component until later in the Wuchiapingian in the 5th and 6th transgressive-regressive cycles. This suggests a delayed recovery of metazoan reef ecosystems following the Middle Permian extinction. Furthermore, even though sponges do become abundant within the reefs, it is the presence and growth of the encrusters Archaeolithoporella and Tubiphytes and abundance of microbial micrites that play an important role in stabilizing the reef structures that form topographic highs.
The geometry of carbonate platforms reflects the interaction of several factors. However, the impact of carbonate-producing organisms has been poorly investigated so far. This study applies stratigraphic forward modelling (SFM) and sensitivity analysis to examine, referenced to the Miocene Llucmajor Platform, the effect of changes of dominant biotic production in the oligophotic and euphotic zones on platform geometry. Our results show that the complex interplay of carbonate production rates, bathymetry and variations in accommodation space control the platform geometry. The main driver of progradation is the oligophotic production of rhodalgal sediments during the lowstands. This study demonstrates that platform geometry and internal architecture varies significantly according to the interaction of the predominant carbonate-producing biotas. The input parameters for this study are based on well-understood Miocene carbonate biotas with characteristic euphotic, oligophotic and photo-independent carbonate production in which it is crucial that each carbonate-producing class is modelled explicitly within the simulation run and not averaged with a single carbonate production-depth profile. This is important in subsurface exploration studies based on stratigraphic forward models where the overall platform geometry may be approximated through calibration runs, and constrained by seismic surveys and wellbores. However, the internal architecture is likely to be oversimplified without an in-depth understanding of the target carbonate system and a transfer to forward modelling parameters.
Integration of digital elevation models and satellite images to investigate geological processes.
(2006)
In order to better understand the geological boundary conditions for ongoing or past surface processes geologists face two important questions: 1) How can we gain additional knowledge about geological processes by analyzing digital elevation models (DEM) and satellite images and 2) Do these efforts present a viable approach for more efficient research. Here, we will present case studies at a variety of scales and levels of resolution to illustrate how we can substantially complement and enhance classical geological approaches with remote sensing techniques. Commonly, satellite and DEM based studies are being used in a first step of assessing areas of geologic interest. While in the past the analysis of satellite imagery (e.g. Landsat TM) and aerial photographs was carried out to characterize the regional geologic characteristics, particularly structure and lithology, geologists have increasingly ventured into a process-oriented approach. This entails assessing structures and geomorphic features with a concept that includes active tectonics or tectonic activity on time scales relevant to humans. In addition, these efforts involve analyzing and quantifying the processes acting at the surface by integrating different remote sensing and topographic data (e.g. SRTM-DEM, SSM/I, GPS, Landsat 7 ETM, Aster, Ikonos…). A combined structural and geomorphic study in the hyperarid Atacama desert demonstrates the use of satellite and digital elevation data for assessing geological structures formed by long-term (millions of years) feedback mechanisms between erosion and crustal bending (Zeilinger et al., 2005). The medium-term change of landscapes during hundred thousands to millions years in a more humid setting is shown in an example from southern Chile. Based on an analysis of rivers/watersheds combined with landscapes parameterization by using digital elevation models, the geomorphic evolution and change in drainage pattern in the coastal Cordillera can be quantified and put into the context of seismotectonic segmentation of a tectonically active region. This has far-reaching implications for earthquake rupture scenarios and hazard mitigation (K. Rehak, see poster on IMAF Workshop). Two examples illustrate short-term processes on decadal, centennial and millennial time scales: One study uses orogen scale precipitation gradients derived from remotely sensed passive microwave data (Bookhagen et al., 2005a). They demonstrate how debris flows were triggered as a response of slopes to abnormally strong rainfall in the interior parts of the Himalaya during intensified monsoons. The area of the orogen that receives high amounts of precipitation during intensified monsoons also constitutes numerous landslide deposits of up to 1km<sup>3 volume that were generated during intensified monsoon phase at about 27 and 9 ka (Bookhagen et al., 2005b). Another project in the Swiss Alps compared sets of aerial photographs recorded in different years. By calculating high resolution surfaces the mass transport in a landslide could be reconstructed (M. Schwab, Universität Bern). All these examples, although representing only a short and limited selection of projects using remote sense data in geology, have as a common approach the goal to quantify geological processes. With increasing data resolution and new sensors future projects will even enable us to recognize more patterns and / or structures indicative of geological processes in tectonically active areas. This is crucial for the analysis of natural hazards like earthquakes, tsunamis and landslides, as well as those hazards that are related to climatic variability. The integration of remotely sensed data at different spatial and temporal scales with field observations becomes increasingly important. Many of presently highly populated places and increasingly utilized regions are subject to significant environmental pressure and often constitute areas of concentrated economic value. Combined remote sensing and ground-truthing in these regions is particularly important as geologic, seismicity and hydrologic data may be limited here due to the recency of infrastructural development. Monitoring ongoing processes and evaluating the remotely sensed data in terms of recurrence of events will greatly enhance our ability to assess and mitigate natural hazards. <hr> Dokument 1: Foliensatz | Dokument 2: Abstract <hr> Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006
The paleo-Loppa High in the SW Barents Sea is a ridge structure, which developed during the late Paleozoic when the earliest phase of the Atlantic rifting between Greenland and Norway occurred. The southwest of the Barents Sea, located at the northern margin of Pangaea during the Carboniferous and Permian, was characterized by a structural style of half-graben geometries. The northward drift of the northern Pangaea triggered changes in regional climatic conditions that are reflected in the preserved sedimentary deposits. 2D/3D seismic combined with well and core data were used to define depositional seismic sequences and to understand the stratigraphic evolution of the paleo-Loppa High during the late Paleozoic. Based on the geometry of the defined seismic sequences and the character of observed sedimentary facies, a paleogeographic reconstruction of the key stages in the paleo-Loppa High evolution is also proposed and discussed in relation to local tectonic, global sea-level oscillations, and climatic changes. A total of seven seismic sequences, ranging from clastic-dominated to transitional elastic-carbonate sedimentation followed by an evaporitic drawdown phase, then shifting to carbonate-dominated sequences and finally capped by silica- and chert-dominated deposits, have been defined and represent the infill evolution of the paleo-Loppa High. Tectonics processes associated with the rifting are the principal controls in the 3-D morphology of the defined sequences. Sea-level fluctuations and climate changes have modified the biotic evolution and were responsible of the small-scale features inside each sequence. A renewed interest, in the study of the late Paleozoic sedimentary deposits of the paleo-Loppa High, has been manifested due to the recent discoveries of hydrocarbons in the Gohta and Alta prospects.
Orbitolinids are larger foraminifera widespread in Lower Cretaceous shallow-water carbonates of the Tethyan realm. They are among the most important fossil groups used for Biostratigraphy. Despite this and although the structural features of the group have been described in detail, very little is known about the composition of their agglutinated test and the process by which they selected foreign grains. In this study, the test of Orbitolina d'Orbigny, 1850 (subgenus Mesorbitolina Schroeder, 1962) from Aptian shallow-water carbonate deposits of southern Italy has been studied in detail. We combine petrographic techniques (optical microscope and SEM) with energy-dispersive x-ray spectrometry (EDS), electron probe microanalyzer (EPMA), X-ray diffraction and Raman spectroscopy analyses.
The results show that the test of Mesorbitolina is composed of carbonate and non-carbonate agglutinated grains with the latter distributed across the test with a specific pattern, moving from the marginal to the central zone. In the marginal zone, non-carbonate grains are found only in the epidermis and along the septa which are composed of quartz, with smaller amounts of illite/muscovite and K-feldspar grains. In the central zone of the test, non-carbonate grains are distributed in two ways. Coarse grains of quartz and K-feldspar are abundant and randomly placed in the endoskeleton embedded in a mosaic of minute carbonate grains. Flat grains, mainly of illite/muscovite constitute the external part of the septa. Our observations indicate that Mesorbitolina did select and place agglutinated grains across its test, mainly according to their shape, whereas it did not select particles according to grain size. The distribution of agglutinated particles according to their mineralogical composition shows some contradictory evidence and therefore, at the moment, grain selection in function of mineralogy cannot be completely confirmed or ruled out. Analogies in the test composition of Mesorbitolina specimens from coeval deposits from different areas of southern Italy indicate that the features of their agglutinated test are typical characters of the genus Mesorbitolina. However, it is still unclear what advantage was obtained by the foraminifer by the described test features.
Each simulation algorithm, including Truncated Gaussian Simulation, Sequential Indicator Simulation and Indicator Kriging is characterized by different operating modes, which variably influence the facies proportion, distribution and association of digital outcrop models, as shown in clastic sediments. A detailed study of carbonate heterogeneity is then crucial to understanding these differences and providing rules for carbonate modelling. Through a continuous exposure of Bajocian carbonate strata, a study window (320 m long, 190 m wide and 30 m thick) was investigated and metre-scale lithofacies heterogeneity was captured and modelled using closely-spaced sections. Ten lithofacies, deposited in a shallow-water carbonate-dominated ramp, were recognized and their dimensions and associations were documented. Field data, including height sections, were georeferenced and input into the model. Four models were built in the present study. Model A used all sections and Truncated Gaussian Simulation during the stochastic simulation. For the three other models, Model B was generated using Truncated Gaussian Simulation as for Model A, Model C was generated using Sequential Indicator Simulation and Model D was generated using Indicator Kriging. These three additional models were built by removing two out of eight sections from data input. The removal of sections allows direct insights on geological uncertainties at inter-well spacings by comparing modelled and described sections. Other quantitative and qualitative comparisons were carried out between models to understand the advantages/disadvantages of each algorithm. Model A is used as the base case. Indicator Kriging (Model D) simplifies the facies distribution by assigning continuous geological bodies of the most abundant lithofacies to each zone. Sequential Indicator Simulation (Model C) is confident to conserve facies proportion when geological heterogeneity is complex. The use of trend with Truncated Gaussian Simulation is a powerful tool for modelling well-defined spatial facies relationships. However, in shallow-water carbonate, facies can coexist and their association can change through time and space. The present study shows that the scale of modelling (depositional environment or lithofacies) involves specific simulation constraints on shallow-water carbonate modelling methods.