Jürgen Grötsch

Bio: Jürgen Grötsch is an academic researcher from Royal Dutch Shell. The author has contributed to research in topics: Aptian & Cretaceous. The author has an hindex of 14, co-authored 25 publications receiving 956 citations. Previous affiliations of Jürgen Grötsch include Abu Dhabi Company for Onshore Oil Operations & University of Erlangen-Nuremberg.

Ecological succession, palaeoenvironmental change, and depositional sequences of Barremian–Aptian shallow‐water carbonates in northern Oman

Abstract: Barremian and Aptian shallow-water carbonate facies (uppermost Lekhwair, Kharaib and Shuaiba Formations) are described from outcrops in northern Oman Based on facies analysis and bedding pattern, three orders of depositional sequences are defined (third to fifth order) and correlated between sections Over the course of three third-order sequences, covering the Barremian to Lower Aptian, a third-order depositional pattern is documented that consists of a succession of three distinct faunal assemblages: discoidal orbitolinids and calcareous algae were deposited during early transgression; microbialites and microencrusters dominate the late transgressive to early highstand facies; and a rudist- and miliolid-dominated facies is typical of the highstand This ecological succession was controlled largely by palaeoenvironmental changes, such as trophic level and clay influx, rather than sedimentological factors controlled by variations in accommodation space Orbitolinid beds and carbonates formed by microbialites and microencrusters seem to be the shallow-water carbonate response to global changes affecting Late Barremian to Aptian palaeoclimate and palaeoceanography

Carbon-isotope stratigraphy in shallow-water carbonates: implications for Cretaceous black-shale deposition

Abstract: A Barremian to Albian succession on Mount Kanala, part of a Tethyan isolated carbonate platform, was investigated for its δ13C variations. The limestone sequence is composed of a series of peritidal shallowing-upward cycles with clear petrographic evidence for strong early diagenetic overprinting related to repeated subaerial exposure. Despite significant impact of diagenesis, the observed changes in δ13C can be very well correlated with deep-water sections from different ocean basins and shallow water carbonate platforms in the Middle East. This lends further support to the applicability of δ13C variations for stratigraphic purposes in shallow-water limestones. Using the δ13C signal, time resolution in Lower Cretaceous platform carbonates can be significantly increased, independent of bio-zonations often hampered by ecological variability. Cyclostratigraphic analysis of the Aptian part of the section shows that strong positive excursions of the cumulative departure from mean cycle thickness of the peritidal shallowing-upward cycles coincide with global positive δ13C excursions. This, and the fact that positive shifts in the δ13C record are preserved within shallow water limestones, provide evidence that black-shale accumulation in the ocean basins occurred during sea-level rise and flooding of platform tops. Integration of carbon-isotope-, cyclo- and sequence-stratigraphic results from different carbonate platforms indicate that strong positive global δ13C shifts and concurrent organic-carbon burial during black-shale deposition are ultimately caused by rapid rises of eustatic sea level. Hence, the rate of change of eustatic sea level is considered to play a crucial role in black-shale accumulation in the global ocean basins during the Cretaceous.

The Barremian-Aptian Evolution of The Eastern Arabian Carbonate Platform Margin (Northern Oman)

Abstract: Carbonate platform margins are sensitive recorders of changes in sea level and climate and can reveal the relative importance of global and regional controls on platform evolution. This paper focuses on the Barremian to Aptian interval (mid Cretaceous), which is known for climatic and environmental changes towards more intensified greenhouse conditions. The study area in the northern Oman mountains offers one of the very few locations where the Cretaceous carbonate margin of the Arabian Plate can be studied along continuous outcrops. Our detailed sedimentological and sequence stratigraphic model of the platform margin demonstrates how major environmental and ecological changes controlled the stratigraphic architecture. The Early Cretaceous platform margin shows high rates of progradation in Berriasian to Hauterivian times followed by lower rates and some aggradation in the Late Hauterivian to Barremian. High-energy bioclastic and oolitic sands were the dominant deposits at the margin. Turbidites were deposited at the slope and in the basin. The Early Aptian platform margin shows a marked change to purely aggradational geometries and a welldeveloped platform barrier that was formed mainly by microbial buildups. The sudden dominance in microbial activity led to cementation and stabilization of the margin and slope and, therefore, a decrease of downslope sediment transport by turbidites. In the Late Aptian, large parts of the Arabian craton were subaerially exposed and a fringing carbonate platform formed. Seven Barremian to Early Albian large-scale depositional sequences reflecting relative sea-level changes are identified on the basis of time lines constrained by physical correlation and biostratigraphy. The reconstruction of the margin geometries suggests that tectonic activity played an important role in the Early Aptian. This was most likely related to global plate reorganization that was accompanied by increased volcanic activity in many parts of the world. Along the northeastern Arabian platform the associated global changes in atmospheric and oceanic circulation are recorded with a change in platform-margin ecology from an ooid-bioclast dominated to a microbial dominated margin. Time-equivalent argillaceous deposits suggest an increase in rainfall and elevated input of nutrients onto the platform. This process contributed to the strongly diminished carbonate production by other organisms and favored microbial activity. The platform margin may thus represent a shallow-marine response to the Early Aptian global changes, commonly associated with an oceanic anoxic event in basinal environments.

Integrated 3-D Reservoir Modeling Based on 3-D Seismic: The Tertiary Malampaya and Camago Buildups, Offshore Palawan, Philippines

Abstract: Three-dimensional (3-D) seismic interpretation and drilling results indicate complex sedimentary geometries of the Malampaya and Camago build ups (offshore Palawan, Philippines) with localized progradation due to unidirectional offbank transport alternating with vertical aggradation. Successive reduction of size during buildup growth and backstepping of the protected landward margin in response to transgression ultimately appear to have triggered the demise of carbonate production and platform drowning. The shallow-water platform top sediments repeatedly show signs of subaerial exposure before reflooding. A modeling functionality was developed to allow development of multiple-scenario 3-D reservoir models in an exploration or appraisal stage. The model enables merging of seismic-scale observations based on 3-D volume and horizon analyses with subseismic scale information from well data; however, inherent noise within the seismic data introduced by the complex buildup morphology has resulted in inconsistent attribute distribution and fault dimming. These difficulties are compounded by erratic velocity distribution within the limestone, nonhyperbolic move out, and a narrow relatively low-frequency spectrum, all of which prevent the use of the 3-D seismic volume as hard data but rather allow its use as a soft constraint for guiding the geological interpretation and ultimately the modeling process. Seismic data quality in such complex morphologic settings and scarcity of well data hamper greatly the use of geostatistically driven modeling approaches; therefore, a new functionality was developed within Shell's proprietary integrated 3-D modeling suite (GEOCAP), which allows deterministic model reservoirs using seismic horizon and volume interpretation, sequence- and cyclo-stratigraphic architecture, and the concept of reservoir rock type. Seismic velocity in clean carbonate formations is predominantly a function of porosity distribution. To assess time-to-depth conversion uncertainty, the reservoir rock type based models were first produced in the time domain. Only after differential 3-D depth conversion of these models could the scenarios be reconstructed in the depth domain. The depth models subsequently were used to derive permeability and saturation 3-D distortions, and thus hydrocarbon volumes for each deterministic scenario. The models were then used for simulation purposes.

Sequence stratigraphy: methodology and nomenclature

Abstract: The recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply, which correspond to sequences in the rock record. These cycles may be symmetrical or asymmetrical, and may or may not include all types of systems tracts that may be expected within a fully developed sequence. Depending on the scale of observation, sequences and their bounding surfaces may be ascribed to different hierarchical orders. Stratal stacking patterns combine to define trends in geometric character that include upstepping, forestepping, backstepping and downstepping, expressing three types of shoreline shift: forced regression (forestepping and downstepping at the shoreline), normal regression (forestepping and upstepping at the shoreline) and transgression (backstepping at the shoreline). Stacking patterns that are independent of shoreline trajectories may also be defined on the basis of changes in depositional style that can be correlated regionally. All stratal stacking patterns reflect the interplay of the same two fundamental variables, namely accommodation (the space available for potential sediment accumulation) and sediment supply. Deposits defined by specific stratal stacking patterns form the basic constituents of any sequence stratigraphic unit, from sequence to systems tract and parasequence. Changes in stratal stacking patterns define the position and timing of key sequence stratigraphic surfaces. Precisely which surfaces are selected as sequence boundaries varies as a function of which surfaces are best expressed within the context of the depositional setting and the preservation of facies relationships and stratal stacking patterns in that succession. The high degree of variability in the expression of sequence stratigraphic units and bounding surfaces in the rock record means ideally that the methodology used to analyze their depositional setting should be flexible from one sequence stratigraphic approach to another. Construction of this framework ensures the success of the method in terms of its objectives to provide a process-based understanding of the stratigraphic architecture. The purpose of this paper is to emphasize a standard but flexible methodology that remains objective.