Abstract The geological paradox of at least two Neoproterozoic glacial intervals at tropical latitudes intercalated within carbonates remains an unsolved puzzle. Several conceptual models have been proposed to explain these apparent rapid swings between climatic extremes and the associated isotopic changes in sea-water chemistry. In Oman, post-glacial transgressive sedimentary successions represent important hydrocarbon source rocks. Source rock characteristics of Neoproterozoic post-glacial successions in other parts of the world (even if not directly correlatable) are, therefore, of special economic interest. This paper concentrates on the Ghaub Formation diamictite interval in northern Namibia and the major environmental change in the aftermath of the assumed glaciation. The relationship of the post-glacial sediments with the underlying different types of cap carbonate and diamictite successions is discussed, and a model of the succession of events is presented. The palaeotopography, caused mostly by ongoing tectonic activity including uplift on the scale of thousands of metres, strongly influenced the petroleum system created and played an important role for the hydrocarbon prospectivity of this post-glacial succession. Tectonic activity on the shelf of the southern margin of the Congo Craton was repeated, and different sub-basins were created before, during and after the Ghaub glaciation. The newly formed relief was flooded, and the different sub-basins were affected by restricted circulation for quite some time. This general scenario bears many similarities to the late Ordovician–early Silurian petroleum system, also formed during post-glacial sea-level rise.

Abstract During Triassic times, the Northern Calcareous Alps were situated at the northwestern margin of the Tethys ocean. Succeeding the Permian and Lower Triassic red bed stage, shallow-water carbonates were the main constituents of the Middle and Late Triassic strata, in addition to some mixed carbonate-clastic deposits and basin carbonates. Biostratigraphic data enables exact positioning of the depositional sequences. Despite many good correlations with other Alpine regions as well as with epicontinental Triassic units of central, northwestern and northern Europe, no correlative sequences exist in the Northern Calcareous Alps during late Anisian, late Ladinian, early Carnian and probably Norian times. Variations resulted from local (basin-wide) controls, mainly caused by diverging subsidence patterns. While second-order trends roughly correspond with other Triassic basins, peak transgressions and maximum regressions show some differences. Separated by postdepositional Alpine strike-slip and thrust tectonics from the stable European northern hinterland, definition of third-order sequence boundaries is often problematic in the Northern Calcareous Alps. Without unconformities, sequence stratigraphy sensu Vail and coworkers cannot be applied in a strict sense. Transgressive and maximum flooding surfaces comprised the best marker horizons for correlationing sequences. A working procedure that incorporates at least parts of the genetic stratigraphic sequence model of Galloway (1989) proved extremely helpful in working with these successions.

Abstract A succession of deep burial carbonate cements with two types of saddle dolomite and three types of blocky calcite was investigated in Permian to Tertiary sedimentary rocks in different nappes of the Eastern Alps. The first generation of saddle dolomite occurs only in rocks of Permian to Late Triassic/Early Jurassic age. All otlier carbonate cements occur within rocks of Permian to Early Tertiary age. Carbon and oxygen isotopic compositions of the carbonate cements and of the Triassic to Tertiary host rocks exhibit regional trends as well as trends to more negative δ 18 O with increasing burial. Fluid inclusion data show homogenization temperatures between 90° and 250°C for the carbonate cements. Temperatures decrease from the bottom to the top of the stratigraphic column, and regional trends are also exhibited. Calculated oxygen isotopic compositions of fluids precipitating the carbonate cements suggest strong positive 8’“0 values, which are characteristic of saline formation waters or metamorphic waters. The first generation of saddle dolomite is inferred to have formed in the same paleo-fluid system as Late Triassic/Early Jurassic Pb-Zn ores by fluid flow directed from the hinterland in the north (Vindelician high, Bohemian massif) to the East Alpine area. The fluids ascended and precipitated saddle dolomite and, under certain conditions, Pb-Zn ores. All other carbonate cements formed post-Oligocene time after the peak of metamorphism in the Central Eastern Alps and during uplift of this area. Results suggest that meteoric fluids descended and equilibrated with metamorphic rocks subsequently mixed with metamorphic waters in this uplifted area and flowed northwards and southwards, ascending through the rock pile. Fluid mixing with a second, near surface, meteoric groundwater system could explain a renewed decrease in carbonate cement δ 18 O values at the top of the sedimentary succession and in northern parts of the Alpine realm.

Abstract The Lower to Middle Cambrian sequence of southwestern Sardinia shows different stages of platform evolution through time, from a ramp to an isolated carbonate platform: (1) terrigenous carbonate homoclinal ramp with algal-archaeocyathan mounds ( Epiphyton/Renalcis ) in the west and terrigenous, shallow-marine to tidal sequences in the east; (2) carbonate terrigenous ramp or rimmed shelf with an ooid shoal complex, prograding toward the west; the back-shoal area contains peloidal mudstones, algal-archaeocyathan biostromes ( Girvanella ), and increasingly tidal deposits (siliciclasts and carbonates) toward the east; (3) isolated platform, aggraded to sea level, with an intra-shelf basin in the southeast and slopes to the north and west; (4) isolated, flooded platform; barriers toward the open sea partly broken down; (5) isolated platform with raised margins and deep interior, often with thick breccia beds in uppermost parts; (6) segmentation and drowning of the platform with deposition of nodular limestones and intercalated limestones and shales; and (7) siliciclastic deposits covering the former platform. Evidence of tensional tectonics (slumping, debris flows, internal breccias, neptunian dykes, intraplatform basins and ponds) is abundant. Subsidence rates, however, are relatively low; the stratigraphic horizons are largely continuous. Rifting terminated by late Early Cambrian to Mid-Cambrian time, when plate-tectonic setting changed to a drift phase.

Abstract Lead and zinc ores of the Alpine Triassic occur mainly within shallow water sediments of lower Carnian age; these sequences underwent emersion periods and were affected by weathering and meteoric karstification (Lagny, 1975; Bechstadt, 1975a, b, 1979; Assereto et al, 1976). The Bleiberg-Kreuth mineralization within the Wetterstein limestone is controlled by at least four geologic factors: (1) it occurs on lagoonal platforms, situated some distance from the mainland to the north, which might have been the original source of the metal; (2) on these platforms it is localized within areas where an extensive cavity network had been formed by karstic weathering; (3) the mineralization is bound to areas close to or with peritidal cyclic and evaporitic sedimentation (“special facies” of Schneider, 1964); and (4) it occurs below sealing shales (Raibl beds). Only the subaerial exposure facies is described in more detail, whereas the conflicting theories concerning lead-zinc mineralization are mentioned only briefly (Figs. 1,2).