Adrian Immenhauser

Bunker Cave stalagmites: an archive for central European Holocene climate variability

Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present highresolution records of δ18O, δ13C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric precipitation variability. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation, and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 8 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 and 0.2 ka. The proxy signals in the Bunker Cave stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker Cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the thermohaline circulation.

Outcrop analog for an oolitic carbonate ramp reservoir: A scale-dependent geologic modeling approach based on stratigraphic hierarchy

Considerable effort has been devoted to the development of simulation algorithms for facies modeling, whereas a discussion of how to combine those techniques has not existed. The integration of multiple geologic data into a three-dimensional model, which requires the combination of simulation techniques, is yet a current challenge for reservoir modeling. This article presents a thought process that guides the acquisition and modeling of geologic data at various scales. Our work is based on outcrop data collected from a Jurassic carbonate ramp located in the High Atlas mountain range of Morocco. The study window is 1 km (0.6 mi) wide and 100 m (328.1 ft) thick. We describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest: (1) stacking pattern of high-frequency depositional sequences, (2) facies association, and (3) lithofacies. Five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data. The surface-based model shows a low-angle profile with modest paleotopographic relief at the inner-to-middle ramp transition. Facies associations were populated using truncated Gaussian simulation to preserve ordered trends between the inner, middle, and outer ramps. At the lithofacies scale, field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation. This study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks. The selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings. This study demonstrates that a scale-dependent modeling approach should be a common procedure when building subsurface and outcrop models.

Early Aptian algal bloom in a neritic proto–North Atlantic setting: Harbinger of global change related to OAE 1a?

Pervasive growth of microencrusters ( Lithocodium/Bacinella ) characterizes short-lived stratigraphic intervals in Lower Aptian shallow-water carbonate platform settings of the central and southern Tethys. Although a causal relationship between this peculiar shallow-water facies and the early Aptian oceanic anoxic event (OAE) 1a seems likely, the temporal and spatial distributions of Lithocodium and Bacinella mass occurrences in the rock record point to a rather complex pattern. Possible controls include various global and regional drivers expressed in environmental perturbation of neritic ecosystems. Microencruster blooms have hitherto been reported to occur at the onset and in the aftermath of oceanic anoxic event (OAE) 1a, slightly pre- or postdating the deposition of dark organic-rich black shales in pelagic basins. This study presents evidence for a punctuated and well-expressed early Aptian bloom of the ulvophycean green algae Lithocodium aggregatum observed at the proto-North Atlantic margin, Lusitanian Basin, Portugal. Similar to southern and central Tethyan sections, a Lithocodium -dominated interval temporally replaces the rudist-dominated platform ecosystem. This Lithocodium -rich horizon is composed of oncoidal floatstones and boundstones, including a well-exposed biohermal level, and reaches a thickness of up to 6 m. High-resolution carbon-isotope stratigraphy shown here clearly argues for Lithocodium to represent a biotic harbinger of environmental change in the run-up of OAE 1a. Chemostratigraphy provides evidence that the subsequent carbonate platform breakdown in the proto∼North Atlantic was coeval with an early Aptian carbonate platform drowning episode observed in the northern Tethys prior to OAE 1a. A regionally enhanced nutrient level and a relative sea-level rise are suggested to have triggered the transient mass occurrence of Lithocodium microencrusters, which also may have been influenced by elevated atmospheric CO2 concentrations related to the emplacement of the Ontong Java large igneous province. Upwelling water masses and enhanced terrigenous runoff due to increased weathering may have served as possible sources of the required nutrients, which tentatively diminished and finally interrupted the metazoan carbonate platform factory.

Determination of Methanogenic Pathways through Carbon Isotope (δ13C) Analysis for the Two-Stage Anaerobic Digestion of High-Solids Substrates

This study used carbon isotope (δ(13)C)-based calculations to quantify the specific methanogenic pathways in a two-stage experimental biogas plant composed of three thermophilic leach bed reactors (51-56 °C) followed by a mesophilic (36.5 °C) anaerobic filter. Despite the continuous dominance of the acetoclastic Methanosaeta in the anaerobic filter, the methane (CH4) fraction derived from carbon dioxide reduction (CO2), fmc, varied significantly over the investigation period of 200 days. At organic loading rates (OLRs) below 6.0 gCOD L(-1) d(-1), the average fmc value was 33%, whereas at higher OLRs, with a maximum level of 17.0 gCOD L(-1) d(-1), the fmc values reached 47%. The experiments allowed for a clear differentiation of the isotope fractionation related to the formation and consumption of acetate in both stages of the plant. Our data indicate constant carbon isotope fractionation for acetate formation at different OLRs within the thermophilic leach bed reactors as well as a negligible contribution of homoacetogenesis. These results present the first quantification of methanogenic pathway (fmc values) dynamics for a continually operated mesophilic bioreactor and highlight the enormous potential of δ(13)C analysis for a more comprehensive understanding of the anaerobic degradation processes in CH4-producing biogas plants.

Numerical simulation of fluid-flow processes in a 3D high-resolution carbonate reservoir analogue

A high-resolution three-dimensional (3D) outcrop model of a Jurassic carbonate ramp was used in order to perform a series of detailed and systematic flow simulations. The aim of this study was to test the impact of small- and large-scale geological features on reservoir performance and oil recovery. The digital outcrop model contains a wide range of sedimentological, diagenetic and structural features, including discontinuity surfaces, shoal bodies, mud mounds, oyster bioherms and fractures. Flow simulations are performed for numerical well testing and secondary oil recovery. Numerical well testing enables synthetic but systematic pressure responses to be generated for different geological features observed in the outcrops. This allows us to assess and rank the relative impact of specific geological features on reservoir performance. The outcome documents that, owing to the realistic representation of matrix heterogeneity, most diagenetic and structural features cannot be linked to a unique pressure signature. Instead, reservoir performance is controlled by subseismic faults and oyster bioherms acting as thief zones. Numerical simulations of secondary recovery processes reveal strong channelling of fluid flow into high-permeability layers as the primary control for oil recovery. However, appropriate reservoir-engineering solutions, such as optimizing well placement and injection fluid, can reduce channelling and increase oil recovery.

The Impact of Hierarchical Fracture Networks on Flow Partitioning in Carbonate Reservoirs: Examples Based on a Jurassic Carbonate Ramp Analog from the High Atlas

Hydrocarbon reservoirs commonly contain an array of fine-scale structures that are below the resolution of seismic images. These features may impact flow behavior and recovery, but their specific impacts may be obscured by the upscaling process for sector and field-scale reservoir simulations. It is therefore important to identify those situations in which subseismic structures can introduce significant departures from full-field flow predictions. Using exposures of Jurassic carbonate outcrops near the village of Amellago in the High Atlas Mountains of Morocco, we have developed a series of flow simulations to explore the interactions of a hierarchical fracture network with the rock matrix of carbonate ramp strata. Model geometries were constructed in CAD software using field interpretations and LiDAR1 data of an outcrop area that is 350 m long by 100 m high. The impact of water injection on oil recovery between an injector and producer pair was investigated. Simulations were performed by a single medium reservoir simulator using a single mesh to represent fracture planes as well as rock-matrix volumes. The effects of changing scenarios for rock permeability and porosity as well as facture permeability distributions were investigated. First-order results show that the best recovery was achieved by a model with a high permeability, homogeneous matrix combined with a heterogeneous fracture network. The worst recovery scenario was given by a model with low, homogeneous permeability and high fracture permeabilities. The results highlight the importance of the permeability contrasts between the matrix and the fractures for overall recovery and the very significant impact that fractures can have on recovery by creating shadow zones and providing critical connections between permeable layers. The presence of the hierarchical fracture network developed strong fingering even in homogeneous matrix cases and evolving velocity patterns reveal competing fluid pathways among matrix and fracture routes. Insights from these models can help to develop production strategies to improve recovery from fractured carbonate reservoirs and provide an initial platform from which to extend further evaluations of different populations of conductive and baffling structures, spatial variations in wettability and capillary pressures and well positions.

Modelling and simulation of a Jurassic carbonate ramp outcrop, Amellago, High Atlas Mountains, Morocco

Carbonate reservoirs pose significant challenges for reservoir modelling and flow prediction due to heterogeneities in rock properties, limits to seismic resolution and limited constraints on subsurface data. Hence, a systematic and streamlined approach is needed to construct geological models and to quickly evaluate key sensitivities in the flow models. This paper discusses results from a reservoir analogue study of a Middle Jurassic carbonate ramp in the High Atlas Mountains of Morocco that has stratigraphic and structural similarities to selected Middle East reservoirs. For this purpose, high-resolution geological models were constructed from the integration of sedimentological, diagenetic and structural studies in the area. The models are approximately 1200×1250 m in size, and only faults (no fractures) with offsets greater than 1 m are included. Novel methods have been applied to test the response of flow simulations to the presence or absence of specific geological features, including proxies for hardgrounds, stylolites, patch reefs, and mollusc banks, as a way to guide the level of detail that is suitable for modelling objectives. Our general conclusion from the study is that the continuity of any geological feature with extreme permeability (high or low) has the most significant impact on flow.

Radiaxial-fibrous and fascicular-optic Mg-calcitic cave cements: a characterization using electron backscattered diffraction (EBSD)

c-axes in growth direction (“fascicular-optic”), (ii) such with converging c axes in growth direction (“radiaxialfibrous”) and (iii) such with uniform c-axes (“radialfibrous”). Following this classification, Neuser & Richter (2007) have presented oblong calcite crystals with converging and diverging c-axes in growth directions within stalagmites from caves located in dolostone host rock lithologies. Data obtained at these sites clearly documented that the Mg content of the drip waters is significant (Richter et al., 2011).

The architecture and associated fauna of Perouvianella peruviana, an endemic larger benthic foraminifera from the Cenomanian–Turonian transition interval of central Peru

During the Cenomanian–Turonian transition interval, larger benthic foraminifera became extinct or suffered decreases in terms of their diversity. Anoxic/dysoxic conditions of oceanic bottom water masses and potentially seawater acidification during this pivotal time also affected ecological niches in the shallow epeiric domain and resulted in the demise of many taxa of benthic foraminifera worldwide. Nevertheless, exceptions to this pattern have been reported too. Here, evidence is presented for mass occurrences of larger benthic foraminifera (Perouvianella peruviana) from the Western Platform in Peru that were not affected by environmental conditions related to the Cenomanian–Turonian transition. A new architectural analysis of P. peruviana tests found in abundance in central Peru has permitted a detailed update on its systematic and functional morphology. The paleoenvironment associated with the P. peruviana mass occurrence was characterized by mesotrophic conditions, perhaps in one way or another similar to the environmental parameters that lead to Aptian and Albian larger benthic foraminifera mass occurrences at the southern Tethyan margin (‘Orbitolina levels’). Algae and small, cosmopolitan r-strategist foraminifera coexisted with P. peruviana. Moreover, a first description of the soritid taxa Pseudopeneroplis oyonensis n. gen., n. sp. is provided. Interestingly, the superposition of local and global environmental patterns onto the Western Peruvian shelf water masses triggered a mass development of the Perouvianella population coincident with Oceanic Anoxic Event 2. Conversely, the migration of foreign complex-shelled K-strategist larger benthic foraminifera from neighboring realms was inhibited.

Editorial: The Depositional Record

Many of you will have already heard about the launch of a major new journal ‘The Depositional Record’ to be published alongside the flagship journal ‘Sedimentology’. The new journal, owned by the International Association of Sedimentologists (IAS) and published by Wiley, will be Open Access and digital only. The journal was launched at the 19th International Sedimentological Congress in Geneva and the web site has been ‘live’ since 19 August 2014. Our aim is to publish the first issue by May 2015 and obtain an Impact Factor by July 2017. Over this period, the authors’ publication charges will be met by the IAS. The purpose of this editorial is to define how we, the Editors, envisage that The Depositional Record will differ from Sedimentology. Historically, the journal Sedimentology has emphasized classic sedimentology, such as the description of sedimentary sequences and processes. While Sedimentology will continue to publish such studies and others, new analytical methods and approaches have been developed over the past 50 years. New geochemical and geobiological techniques, in particular, can provide information on climate, carbon dynamics, evolution of the oceans, formation of sediments and diagenesis within the depositional record. In addition, there are many types of deposits often not considered within the remit of classic sedimentology, yet they utilize the geological principles on which our science is based. Through environmental reconstruction using such proxies, the depositional record at all scales can be used to better understand anthropological, archaeological, palaeobotanical and palaeofaunal histories, including extinction events and environmental modelling more generally. Although papers on new methods and different types of geo-records have been published in Sedimentology, many of the fundamental papers in the areas listed above are published in journals such as Earth and Planetary Science Letters, Geobiology, Geochimica et Cosmochimica Acta, Paleoceanography, Biogeosciences, Quaternary Science Reviews and many others. The Depositional Record is aimed at such papers. We want to attract high-impact research papers that address processes which affect, or which are recorded in, the depositional record over all time and physical scales. We would be equally happy with studies addressing the impacts of ocean acidification upon the growth rate and chemical composition of a modern coral, the application of next-generation gene sequencing data to understand the role of microbes in carbonate mineral precipitation, investigations into the Neoproterozoic carbon cycle, the geological records of the Mg/Ca ratio of the oceans, the sedimentary record of ancient Roman harbour utilization or the reconstruction of past and future ice-sheet dynamics using glacial sediments. We encourage you to submit your exciting papers in these areas to The Depositional Record. A more detailed description of the scope and goals of the journal can be found at http://onlinelibrary. wiley.com/journal/10.1002/(ISSN)2055-4877.