The geothermal reservoir in the Eastern Molasse Basin is mainly located in Kimmeridgian dolomites, which have different genesis, as documented in the present study. Different diagenetic pathways from primary carbonate sediments with associated sponge-algal mound facies to deep buried dolomite in the Molasse Basin lead to dolomite with different reservoir properties (porosity, permeability). Based on five previous studies that provide data on microthermometry isotope ratios (delta O-18, delta C-13) and burial depths, the formation of dolomite can be assigned to different eogenetic and mesogenetic phases. Early matrix dolomite and dolomite bound to organic material (sponges, microbial layers) were formed during eo-to shallow mesogenesis at a burial depth of up to 1,000 m and at temperatures of 40-70 degrees C and 60-90 degrees C. The first light overgrowths on dolomite crystals are also assigned to this phase. In the shallow mesogenetic phase, intensive dolomite formation took place at depths of up to 2,500 m and temperatures between 70-100 degrees C. Dolomite overgrowth is ongoing, resulting in zoned dolomite crystals with fine-crystalline, inclusion-rich cores and light seams of overgrowth. Deep mesogenesis is characterised by intensive recrystallisation of the dolomites at > 2,500 m depth and temperatures of 100-150 degrees C. Intense compaction also takes place, which leads to the partial dissolution of dolomite crystals including their overgrowths seams. The dolomite structure is compacted and porosity and permeability are extremely reduced, as can be concluded from microstylolites on dolomite crystals. The investigation results from four boreholes (Unterf & ouml;hring Th3, Pullach Th3, Sauerlach Th3 and Geretsried Gt1), which lie approximately on a N-S line, reveal the spatial effects of these processes. The Mg-rich pore solutions due to the pressure solution migrate to northern, structurally higher positions and lead to the formation of dolomite cements ("overdolomitisation"), which close still open intergranular pores. Therefore, the dolomite reservoirs in the northern, less submerged area of the Eastern Molasse Basin still have favourable reservoir characteristics, while to the south the dolomites become denser with increasing burial. The reservoir properties are extremely reduced at depths of > 5,000 m and only dense dolomite is present. Here, only fissures serve as pathways for geothermal water. These processes are also strongly dependent on the early facies and genetic parameters, which were effective down to a depth of about 1,000 metres. Therefore, it is dolomite formation in the Eastern Molasse Basin represents a complex system of early facies influences, overprinting, alteration and cementation in the different phases of subsidence, which is still active today. Therefore, is important to recognise the early genetic parameters to understand the subsequent burial development, even if only ghosts structures are preserved.

This paper focuses on the correlation of two different marble units from an approximately 3,900 m deep geothermal exploration well (GP-1) in western Turkey by petrographical and geochemical data. Future geothermal exploration drilling in that area will benefit from a better (tectono) stratigraphic correlation and a better definition of the reservoir geometry in the basin. It is an innovative approximation in many settings to correctly correlate marble units without clear stratigraphic markers or fossil record, in particular, when sample material is restricted to cuttings. The most distinctive petrographical and geochemical properties in this study are colour, light transmission along with rare-earth element + yttrium (REY) geochemistry, and stable carbon and oxygen isotope data. Two stratigraphic correlations can be maintained for two different marble horizons of the GP-1 well to different stratigraphic horizons outcropping in the study area. Additional Rb-Sr geochronology yields an age of the last metamorphic overprint of the marbles of approximately 30 Ma. This study shows that a multiproxy approach is required to yield a reliable stratigraphic correlation as an important component of geothermal exploration, which supports the conceptual geological model prior to further geothermal drilling.

The Bavarian Molasse Basin and especially the region of Munich is the first and successfully exploited orogenic foreland basin for geothermal energy in the world. It might serve as a type locality for the orogenic belt – foreland basin type related to the geothermal play type concept introduced by Moeck (2014). At present (status 9/2018) there are 22 operating deep geothermal projects and 2 projects in the construction phase in the Bavarian Molasse Basin. Typical exploration targets in the 2 to 5 km deep carbonate reservoir of the Upper Jurassic are faults –favorably located in reef or massive reef detritus facies. With their heterogeneity caused by deposition, biogenic content, diagenetic alteration and facies-selective fracture pattern, carbonate rocks belong to the most challenging reservoir types. In particular south of Munich, the causes, effects and prediction of this reservoir heterogeneity is an understudied topic. Predicting fault attributes in subsurface carbonate reservoirs requires fault zone drilling and reservoir diagnostics through pore space evaluation in particular from drill cores analysis to identify chemical, mechanical, biological, or depositional processes affecting porosity, permeability and flow units. The sidetrack GEN-1ST-A1 at the project site Geretsried drilled in 2017 is one of the deepest geothermal wells in the South German Molasse Basin and serves as research site. VSP optimized 3D fault zone interpretation, depth specific total mud loss while drilling, hydraulic testing, core analyses and logcore correlation aims to better understand the permeability structure and reactivation potential of a deep fault zone in Upper Jurassic carbonates. The results indicate a high fracture density in low-porosity rock with partly open partly sealed fractures.

The majority of running geothermal plants worldwide are located in geological settings with convection- or advection-dominant heat transport. In Germany as in most regions in Europe, conduction is the dominating heat transport mechanism, with a resulting average geothermal gradient. The geothermal play type concept is a modern methodology to group geothermal resources according to their geological setting, and characteristic heat transport mechanisms. In particular, the quantity of heat transport is related to fluid flow in natural or engineered geothermal reservoirs. Hence, the permeability structure is a key element for geothermal play typing. Following the existing geothermal play type catalogue, four major geothermal play types can be identified for Germany: intracratonic basins, foreland basins and basement/crystalline rock provinces as conduction-dominated play types, and extensional terrains as the convection-dominated play type. The installed capacity of geothermal facilities sums up to 397.1 MWth by the end of 2018. District heating plants accounted for the largest portion, with about 337.0 MWth. The majority of these installations are located in the play type 'foreland basin', namely the Molasse Basin in southern Germany. The stratigraphic unit for geothermal use is the Upper Jurassic, also known as 'Malm' formation, a carbonate reservoir with high variability in porosity and permeability. Recently drilled wells in the southernmost Molasse Basin indicate the Upper Jurassic as a tight, fracture-controlled reservoir, not usable for conventional hydrothermal well doublets. Our new data compilation including the recently drilled deep geothermal well Geretsried reveals the relation of porosity and permeability to depth. The results suggest that obviously diagenetic processes control permeability with depth in carbonate rock, diminishing the predictability of reservoir porosity and permeability. The play type concept helps to delineate these property variations in play type levels because it is based on geological constraints, common for exploration geology. Following the general idea of play typing, the results from this play analysis can be transferred to geological analogues as carbonate rock play levels in varying depth.

The development of Mesozoic hydrothermal reservoirs in the North German Basin requires precise prediction of reservoir qualities as well as reliable assessments of the exploration risk in order to insure stakeholders and financial partner against the geological risk. So far, the risk assessment by means of so-called Probability of Success (POS) studies employed only mathematical methods to derive probabilities of reservoir thicknesses, fluid temperatures and productivity indexes. This has resulted in mismatches of reservoir parameters proposed by POS studies before drilling and reservoir test data measured after drilling. Here, we present an approach combining sedimentological and mathematical methods to enable more realistic assessments of the exploration risk. For a potential geothermal site in western Mecklenburg-Vorpommern (Germany), where the development of a Rhaetian (Triassic) hydrothermal reservoir at a depth of about 2800 m is planned, the risk assessment was done combining results of subsurface reservoir mapping and Monte Carlo Simulation (MCS). Compared to ordinary Kriging, the herein applied approach results in more realistic distribution pattern of reservoir thicknesses and, consequently, enable more reliable risk assessments of flow rates and productivity indexes.

The recent interest on environmentally friendly energy resources has increased the economic interest on the Upper Jurassic carbonate rocks in the North Alpine Foreland Basin, which serves as a hydrogeothermal reservoir. An economic reservoir use by geothermal fluid extraction and injection requires a decent understanding of porosity–permeability evolution of the deep laying Upper Jurassic strata at depths greater than 2000 m. The analysis of paleofluids caught in cements of the rock mass helps to determine the postdepositional reservoir evolution and fluid migration. Therefore, the high- and low-permeability areas of the Upper Jurassic in the North Alpine Foreland Basin referred to as Molasse Basin were analyzed by means of encountered postdepositional cements to determine the reservoir evolution. The cements were sampled at different hydrocarbon and geothermal wells, as well as at outcrops in the Franconian and Swabian Alb. To determine the composition and temperature of the paleofluids, fluid inclusions and cements of the Upper Jurassic carbonate rocks were analyzed by microthermometry and stable isotope measurements. Since drill cuttings are a rather available sample material compared to drill cores, a new microthermometry measurement method was achieved for the around 1 mm drill cuttings. Salinity and formation temperature of paleofluids in fluid inclusions and isotope data are consistent with previous studies and reveal a 5-stage evolution: the main cementation phases are composed of (I) the early diagenesis in limestones (200-400 m, 40-50°C), (II) early diagenetic dolomitization, and (III) burial dolomitization (1-2 km, II: 40-90°C; III: 70-100°C; 40 g/L NaCl equiv.), and (IV) late burial calcification (IIIa: 110-140°C, IIIb: 140-200°C) linked to tectonic features in the Molasse Basin. In the outcrop samples, a subsequent (V) cementation phase was determined controlled by karstification. In the southwest, an increase in salinity of the fluid inclusions in vein calcites, above the salinity of the Jurassic seawater, highlights the influence of basin fluids (diagenetic, evaporitic). In the other eastern wells, vein calcites have precipitated from a low saline fluid of around 10-20 g/L NaCl equiv. The low salinity and the isotope values support the theory of a continuous influence of descending meteoric fluids. Consequently, the Upper Jurassic seawater has been diluted by a meteoric fluid to a low saline fluid (<1 g/L), especially in areas with high permeability. Here, we show how a better understanding of cementation trajectory at depth can help to generate a better understanding of geothermal usability in deep carbonate reservoirs.

Abstract The North German Basin yields enormous geothermal resources of more than 13 000 EJ (exajoule: 1 EJ = 1 × 1018 J) heat in place bound to Paleozoic petrothermal and Mesozoic hydrothermal reservoirs. So far, these resources are only exploited at a few localities. Thus, geothermal energy is considered an underutilized energy resource. Despite long-term experience in exploiting Rhaetian hydrothermal reservoirs, the exploration risk remains high, which is mainly related to high expectations on reservoir thickness and quality. Previous exploration campaigns have identified potential hydrothermal reservoirs in six Mesozoic reservoir complexes. But, as high-resolution subsurface maps are not available, the reliable prediction and targeting of reservoirs remains an unsolved problem. As such, an exploration strategy integrating methods of sedimentology, palaeontology, petrography and reservoir characterization was applied to a large database of cores and wireline logs. This contribution details the key results of the exploration of Upper Keuper and Middle Jurassic reservoir complexes, including high-resolution subsurface facies, sandstone thickness and reservoir quality maps. Sets of these maps enable the reliable prediction and targeting of individual hydrothermal reservoirs, and, thus, make a significant contribution to a lowered exploration risk.

The enormous geothermal resources of the North German Basin are bound to Palaeozoic petrothermal and Mesozoic hydrothermal reservoirs. Based on previous exploration campaigns, six Mesozoic reservoir complexes were identified among which the hydrothermal reservoirs of the Stuttgart Formation were underexplored so far. To evaluate the potential of these reservoirs, an interdisciplinary exploration strategy was applied to a large database of cores, wireline logs and seismic data. Repeated transgressions from Tethyan waters resulted in formation of inland seas covering large parts of the basin. Accordingly, the deposition of the Stuttgart Formation was primarily controlled by 3rd- and 4th-order T-R sequences; in particular the basinwards-directed progradation of the tluvio-deltaic Lower and Upper Schilfsandstein members are related to lowstands. Within both members, fine- to medium-grained sandstones of channel fills and levee/crevasse splay complexes form compound reservoirs representing the main target of geothermal exploration. For the Lower Schilfsandstein, this channel belt reservoir type is characterised by a median thickness of 23 m, median porosity of 22.7 % and median permeability of 443 mD. For the Upper Schilfsandstein, the channel belt reservoir type is characterised by a median thickness of 17 m, median porosity of 24 % and median permeability of 546 mD. The quality of these reservoirs is limited by the generally low compositional maturity of sandstones being lithic arkoses and feldspatic litharenites, the partly high content of detrital matrix within pores and substantial diagenetic cementation. The resulting high lateral variability of reservoir qualities contributes to considerable exploration risks. Despite this, reservoirs of high quality could be proven for individual localities where they may be considered an alternative option if the development of Upper Keuper or Middle Jurassic hydrothermal reservoirs fails.

Upper Jurassic carbonates serve as a geothermal reservoir within the north Alpine foreland basin (so-called Molasse basin). The pore space development of the Upper Jurassic is an important factor for the success of geothermal projects or any other reservoir production. Hitherto, successful geothermal projects have cumulated in the area around Munich (Germany), as porosity and permeability of the southward dipping strata decrease with depth towards the Alps. The porosity decline can be caused by a change in facies or by a different grade in diagenesis, which has not been sufficiently analyzed yet. The diagenesis of the Upper Jurassic, especially the porosity, was analyzed in the southern part of the Molasse basin at depths less than 3.500 m. The first step in our approach was the microfacies analysis of rock samples to characterize the primary pore space. The microfacies results show a change in facies (transition zone) southwards, indicated by planktonic organisms in black, low porose carbonate rocks. Due to Alpine tectonics and the formation of the typical wedge shaped north Alpine foreland basin, synsedimentary fractures and fault zones developed in the carbonates. Compared to the matrix those fracture and fault systems provide the main pathways for fluid flow. In the second step, diagenetic fluids were analyzed by fluid inclusion and cathodoluminescence measurements within calcite and dolomite crystals at different cement phases to understand the diagenesis of those deep buried carbonates. The microfacies analysis is important for the identification of high porosity domains and should be considered in reservoir exploration.

Research focussing on the morphology and morphodynamics of modern river deltas has contributed much to the understanding of reservoir geometry and prediction of hydrocarbon splays and deep geothermal aquifers. The interplay of allogenic and autogenic controls results in complex histories of modern river deltas comprising subsequent regressive and transgressive stages of delta formation. The application to ancient examples is still ambiguous and in particular the detailed morphological description of ancient deltas is often hampered by limited subsurface data. This basin‐scale study employs a data set of 15 cored wells and more than 450 logged wells in combination with lithofacies, biofacies and architectural analysis to reconstruct high‐resolution subsurface facies and sand thickness maps of the Toarcian–Bajocian deltaic system in the North German Basin. The results of this study show the evolution from smaller elongate river‐dominated delta types in the Lower and Upper Toarcian (15 000 to 20 000 km²), and a larger lobate river‐dominated delta in the Upper Aalenian (40 000 km²) to a cuspate mixed river‐dominated and wave‐modified delta in the Upper Bajocian (25 000 km²). River‐dominated deltas are formed of distributary deltaic channel belts and associated sheetsands of the delta plain and distributary‐mouth bar complexes with bar‐finger sand architectures of the delta front. Increasing marine processes in the Bajocian resulted in modification of delta complexes forming a shoreface setting with foreshoals, arc‐like chains of ooid‐bearing barrier shoals and back barrier lagoons. The complex history of the Toarcian–Bajocian deltaic system was mainly controlled by allogenic sea‐level fluctuations that triggered the delta progradation and subordinately by allogenic basin reorganization. Autogenic process change of channel avulsion led to locally reduced sediment flux and culminated in lobe abandonment and transgressive shorelines. Differential compaction of underlying deltaic deposits result in strong differences in accommodation space and contributed greatly to large‐scale delta shifts (>300 km).

The global Mesozoic sea-level rise contributed to the stepwise flooding of the Central European Basin (CEB) across the T-J transition and transformed the CEB from a late Triassic inland playa to an early Jurassic semi-enclosed inland sea. The calibration of sections from North Germany and Thuringia using high-resolution palynomorph and ammonite biostratigraphy contributes to the improved temporal and spatial resolution of this decisive period. The herein proposed Deltoidospora-Concavisporites (DC) Zone, placed between the Rhaetian Ricciisporites-Polypodiisporites (RP) Zone and the Hettangian Pinuspollenites-Trachysporites Zone, marks the transitional zone of overlapping Rhaetian and Hettangian palynomorphs in brackish-marine, brackish and terrestrial environments of the North German Basin (NGB). Thus, the DC Zone enables the identification of the T-J transition in the NGB. Following a short-term ingression in the late Norian Corollina-Porcellispora Subzone, the first Rhaetian transgression contributed to substantial marine-terrestrial facies shifts. The diachronous transgressive onlap of brackish-marine strata culminated in a first Rhaetian maximum flooding in the upper Corollina-Enzonalasporites Zone to lower Rhaetipollis-Limbosporites (RL) Zone. After a regressive maximum in the middle RL Zone, the next transgression culminated in a second Rhaetian maximum flooding in the upper RL Zone. Following the end-Triassic regression, herein assigned to the upper RP Zone, the diachronous transgressive onlap of marine shales marks the change to marine Jurassic environments. The herein proposed Deltoidospora-Concavisporites (DC) Zone, placed between the Rhaetian Ricciisporites-Polypodiisporites (RP) Zone and the Hettangian Pinuspollenites-Trachysporites Zone, marks the transitional zone of overlapping Rhaetian and Hettangian palynomorphs in brackish-marine, brackish and terrestrial environments of the North German Basin (NGB). Thus, the DC Zone enables the identification of the T-J transition in the NGB. At the western gate of the CEB, the onset of marine Hettangian strata with ammonites, dated as the P. erugatum Biohorizon at St. Audrie's Bay, postdates the base Hettangian GSSP by ~250kyr. From there to Thuringia, the diachronous onlap of marine Hettangian strata with ammonites, herein dated as the P. plicatulum Biohorizon, took place over ~100kyr. The first Jurassic maximum flooding is dated as the interval of the P. psilonotum to P. plicatulum Biohorizons (lower Planorbis Zone). Rhaetian–Hettangian 3rd-order sequences of the CEB correlate with contemporaneous sequences described from Tethyan and peri-Tethyan basins pointing to circum-Tethyan eustatic cycles. The 4th-order sequences are evident in the Rhaetian-Hettangian, but only a set of Rhaetian 4th-order sequences can be correlated in the NGB so far.

At geothermal plants, process failures often occur due to corrosion and scaling processes. Especially after heat extraction, sulfate reducing bacteria contribute to corrosion processes by producing reduced sulfur compounds. In biofilms containing scales such as iron sulfides, corrosion processes are enhanced. In a mobile bypass system located at the geothermal plant in Neubrandenburg (North German Basin), the influence of biofilm formation on corrosion and scaling was investigated. Short-term heat shocks were successfully tested in the bypass system in order to reduce biofilm formation and thus to diminish corrosion and scaling processes.

(1) GFZ German Research Centre for Geosciences, Section 5.3 Geomicrobiology, Telegrafenberg, 14473 Potsdam, Germany (anne.kleyboecker@gfz-potsdam.de), (2) Jagiellonian University, Institute of Geological Sciences, Oleandry 21, 30-063 Krakow, Poland (monika.kasina@uj.edu.pl), (3) Hydroisotop GmbH, Woelkestr. 9, 85301 Schweitenkirchen, Germany (fe@hydroisotop.de), (4) BWG Geochemische Beratung GmbH, Seestr. 7A, 17033 Neubrandenburg, Germany (aseibt@bwg-geochemie.de), (5) GTN Geothermie Neubrandenburg GmbH, Seestr. 7A, 17033 Neubrandenburg, Germany (Markus.Wolfgramm@gtn-online.de), (6) Merseburg University of Applied Sciences, Eberhard-Leibnitz-Str. 2, 06217 Merseburg, Germany (hilke.wuerdemann@hs-merseburg.de)

The structural evolution of faults in foreland basins is linked to a complex basin history ranging from extension to contraction and inversion tectonics. Faults in the Upper Jurassic of the German Molasse Basin, a Cenozoic Alpine foreland basin, play a significant role for geothermal exploration and are therefore imaged, interpreted and studied by 3D seismic reflection data. Beyond this applied aspect, the analysis of these seismic data help to better understand the temporal evolution of faults and respective stress fields. In 2009, a 27 km(2) 3D seismic reflection survey was conducted around the Unterhaching Gt 2 well, south of Munich. The main focus of this study is an in-depth analysis of a prominent v-shaped fault block structure located at the center of the 3D seismic survey. Two methods were used to study the periodic fault activity and its relative age of the detected faults: (1) horizon flattening and (2) analysis of incremental fault throws. Slip and dilation tendency analyses were conducted afterwards to determine the stresses resolved on the faults in the current stress field. Two possible kinematic models explain the structural evolution: One model assumes a left-lateral strike slip fault in a transpressional regime resulting in a positive flower structure. The other model incorporates crossing conjugate normal faults within a transtensional regime. The interpreted successive fault formation prefers the latter model. The episodic fault activity may enhance fault zone permeability hence reservoir productivity implying that the analysis of periodically active faults represents an important part in successfully targeting geothermal wells.

The microbial biocenosis in highly saline fluids produced from the cold well of a deep geothermal heat store located in the North German Basin was characterized during regular plant operation and immediately after plant downtime phases. Genetic fingerprinting revealed the dominance of sulfate-reducing bacteria (SRB) and fermentative Halanaerobiaceae during regular plant operation, whereas after shutdown phases, sequences of sulfur-oxidizing bacteria (SOB) were also detected. The detection of SOB indicated oxygen ingress into the well during the downtime phase. High 16S ribosomal RNA (rRNA) and dsrA gene copy numbers at the beginning of the restart process showed an enrichment of bacteria, SRB, and SOB during stagnant conditions consistent with higher concentrations of dissolved organic carbon (DOC), sulfate, and hydrogen sulfide in the produced fluids. The interaction of SRB and SOB during plant downtimes might have enhanced the corrosion processes occurring in the well. It was shown that scale content of fluids was significantly increased after stagnant phases. Moreover, the sulfur isotopic signature of the mineral scales indicated microbial influence on scale formation.

In geothermischen Anlagen können Biofilme die Mineralbildung und die Injektivität von Bohrungen sowie die Materialbeständigkeit beeinträchtigen. In drei bezüglich Temperatur und Salinität sehr unterschiedlichen Anlagen waren Organismen des Schwefelkreislaufs an Betriebsstörungen beteiligt: Die erhöhte Abundanz von Sulfat-reduzierenden Bakterien (SRB) auf der kalten Seite eines Wärmespeichers wies auf deren Beteiligung an der Korrosion und der Abnahme der Injektivität hin. In allen Anlagen führte der Zutritt von Sauerstoff bzw. der Eintrag von Nitrat zu einer temporären Zunahme Schwefel-oxidierender Bakterien (SOB) und hat vermutlich Korrosionsprozesse beschleunigt. Außerdem hatte in einem Kältespeicher die temporäre Zunahme der SOB ein Filterclogging zur Folge. Aufgrund ihrer entscheidenden Rolle bei mikrobiell induzierter Korrosion (MIC) weisen Änderungen in der Abundanz von SOB und SRB auf die Ursachen mikrobiell bedingter Störungen hin. Zur Beseitigung der Störungen wurden temporäre Erhöhungen der Temperatur, Säuerungen sowie die Zugabe von Wasserstoffperoxid (H2O2) oder Nitrat in den Anlagen getestet und aus mikrobiologischer Sicht bewertet.

In the Early Jurassic, the epicontinental Central European Basin (CEB), including the North German Basin (NGB), was covered with a semi-enclosed inland sea that was in the late Middle Jurassic transferred to a continental shelf sea connected with the Boreal and the Tethyan oceans. The pronounced facies architectures of Lower to Middle Jurassic coastal-deltaic and basinal deposits challenged many workers to apply sequence stratigraphic methods. However, resulting regional schemes are in places contradicting, which is caused by both common problems with precise dating and processes of regional to local scale obliterating the sea-level signal, such as tectonically enhanced subsidence, enhanced sediment supply, thermal doming, or salt diapirism. This paper proposes a Lower to Middle Jurassic sequence stratigraphic framework of the NGB. The application of a multi-method approach, including intensive macro- and micropalaeontological dating as well as mapping of biofacies and lithofacies architecture to an extensive data set of cored and logged wells resulted in a hierarchical framework of 2nd-, 3rd-, and 4th-order epicontinental sequences. This approach enabled the identification and exclusion of areas and locations where subordinated controls, such as salt diapirism, superimposed the signature of sea-level fluctuations within stratal pattern architectures. The proposed sequence stratigraphic framework correlates well with the Boreal Standard but to much lesser extent with the Tethyan Standard and, thus, demonstrates the principle control of Boreal cycles on epicontinental stratal pattern architectures of the NGB. This coincides with more significant faunal exchanges between the Boreal and Subboreal provinces. In particular, the opening of a marine strait via the Russian Platform in the late Middle Jurassic enabled the immigration of Boreal ammonites and ostracods into the NGB and the northern CEB and illustrates the change from a semienclosed inland sea to a continental shelf sea. Furthermore, the recognition of Lower and Middle Jurassic 4th- order sequences supports suggestions of glacio-eustatic sea-level changes in the Jurassic. (C) 2015 Elsevier B.V. All rights reserved.