The ca. 1730 Ma Wollogorang Formation is a mixed carbonate-siliciclastic unit in the southern McArthur Basin of northern Australia. It is an exploration target for base metals and may be a petroleum source unit and unconventional reservoir. Facies analysis indicates that the Wollogorang Formation records deposition in supratidal to offshore environments. Lateral consistency in facies, thickness, and stratigraphic architecture suggests deposition on an east-west trending (present coordinates) epeiric platform. According to recent tectonic models for northern Australia, this epeiric platform likely deepened to the present-day east. The Wollogorang Formation comprises one second-order and five nested third-order sequences. Despite the unavailability of biostratigraphy and biofacies, and the general poor time control in Precambrian basins, we are able correlate third-order (i.e., our lowest rank) sequences over tens to hundreds of kilometers using high-resolution facies and petrophysical logs. As the distinction between stratigraphic sequences (related to shoreline shifts) and sedimentological bedsets (not related to shoreline shifts) becomes more difficult with decreasing hierarchical level, sedimentological, stratigraphic, paleontological, and mineralogical (including diagenetic) criteria were recently proposed to distinguish these cycles. Our study suggests that sedimentological and stratigraphic criteria are the most useful in Precambrian sequence stratigraphy. In contrast, paleontological criteria are irrelevant in Precambrian successions. Mineralogical (including diagenetic) criteria have not been tested in this study. In addition to further study these criteria, we suggest testing geochemical criteria, such as the enrichment of redox-sensitive trace elements and minor carbonate carbon isotope variation, to distinguish stratigraphic sequences from sedimentological bedsets.

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.

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.

Basin-scale stratigraphic correlation is the fundamental base for successful reservoir exploration, and especially when dealing with cross-border areas. Differences in lithostratigraphic and chronostratigraphic nomenclature between sub-basins and countries often result in problematic estimations of reservoir geometries and potential. This study combines available biostratigraphic, biofaunal and lithofacies data, together with sequence-stratigraphical correlations of the Lower Jurassic from the Central European Basin (CEB), to propose a genetic-based framework of transgressive and regressive depositional units. The determination of four major biofacies environments, composed of (I) polyhaline open-marine/ offshore environments, (II) upper mesohaline marine-brackish environments, (III) lower mesohaline brackish environments and (IV) low oligohaline to freshwater continental environments comprising very rare marine phytoplankton and terrestrial spores and pollens, were translated into 12 biofacies reconstructions of ammonite (sub-) chronozone levels. Variations of biofacies reconstructions in time and space were supplemented by biostratigraphically constrained large-scale progradational and retrogradational sedimentary architecture. Retrogradation is accompanied by increasing polyhaline environments and pinpoint basin-wide third-order flooding events, whereas progradation is accompanied by decreasing polyhaline environments pointing to third-order regressions. The outcomes of this study support exploration of Lower Jurassic deep geothermal reservoirs or CO2 storage sites in the eastern CEB (especially Germany and Poland).

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.

The historic Late Triassic outcrops at Fuchsberg and Langenberg near Seinstedt (Lower Saxony, Germany) are constrained to the Norian/Rhaetian boundary interval by means of conchostracan and palynomorph biostratigraphy. A comprehensive revision revealed a fluvial-dominated delta plain that formed in response to the successive transgression of the 'Rhaetian Sea' and received siliciclastics from southern source areas. At Fuchsberg and Langenberg, the distal lower delta plain is exposed and brackish subaqueous delta plain wetlands, mouthbar/distributary channel complexes and interdistributary bay subenvironments are reconstructed. Delta formation was controlled by bifurcation of distributary channels and avulsion of delta lobes. A diverse ecosystem is documented: a rich invertebrate fauna of limulids (1 taxon), insects (at least 20 taxa of 9 orders), malacostracans and conchostracans (several taxa) and a vertebrate fauna of amphibians (at least 1 taxon), sharks (9 taxa) and osteichthyan fishes (at least 6 taxa). In particular, fossiliferous interdistributary bay lithologies detail trophic systems of autochthonous subaqueous and parautochthonous riparian habitats. Abundant remnants of cycadophytes, ferns, horsetails and large vertebrates from Fuchsberg and adjacent outcrops of the Seinstedt area enable the reconstruction of vegetated upstream environments at the upper delta plain and floodplain.

ABSTRACTTwo new well preserved odonate (damsel-dragonflies) insect wings from the latest Norian (Upper Triassic) of two different localities are described. Although the rather long distance of more than 250 km separates the localities, the holotypes occur in comparable lithologies and are thus described together. We describe an odonate forewing, Italophlebia baueri sp. n., from an abandoned quarry at Langenberg near Seinstedt north of the Harz Mountains (Lower Saxony), which is the first occurrence of this genus outside Italy. The second wing, Triassothemis gartzii sp. n., was found in the cored well Gartz 1 (NE Germany). In both occurrences the insect wings were associated with abundant autochthonous as well as allochthonous faunal and floral remnants of shallow subaquatic environments.

First record of the genusIpsvicia(Hemiptera: Ipsviciidae) outside Gondwana - an Australian genus from the Upper Triassic of GermanyIpsvicia langenbergensissp. n. (Hemiptera: Ipsviciidae) from the Upper Norian (Upper Triassic) deposits of the Langenberg near Seinstedt, Lower Saxony (Germany) is described and illustrated. This is the first definite record of the genusIpsviciaTillyard, 1919 outside Gondwana. The stratigraphy and palaeoenvironment of the Langenberg and the nearby Fuchsberg localities are briefly discussed.