Petrography and temporal changes in petrofacies of deep-marine Ainsa–Jaca basin sandstone systems, Early and Middle Eocene, Spanish Pyrenees

A petrographic study of 157 samples from the Early to Middle Eocene deep-marine sandy systems, Ainsa–Jaca basin, Spanish Pyrenees, shows that each system has a characteristic petrofacies. Three main petrofacies are recognized. Petrofacies 1 sandstones comprise mainly siliciclastic grains (≥80%), subordinate terrigenous carbonate grains and negligible intrabasinal grains. Petrofacies 2 hybrid arenites are characterized by significant amounts (≥10%) of intrabasinal carbonate grains. Petrofacies 3 calcilithites contain relatively abundant (≥10%) extrabasinal carbonate grains. On the basis of these petrofacies, a revised correlation of the sandy systems is proposed between the more proximal Ainsa basin, and the more distal Jaca basin sediments, now separated by the Boltaña anticline, across which it is impossible to actually trace out individual beds or sandstone packages between both basins. The arenite composition in the Ainsa and Jaca basins is interpreted as being controlled mainly by synsedimentary tectonic processes that led to changes in sediment sources during basin evolution.     

Responsible Geographies: Co-oreating Knowledge in Aotearoa

We examine in this paper the potential for (reforming the relations of social scientific research in Aotearoa. Drawing upon our experience of undertaking historical geographical research with and for Ngati-Toa Rangatira, we argue for the need to develop responsible geographies in Aotearoa. We suggest that the metaphors of ‘crossing borders’ and ‘building structures’ might offer one route into the development of such a responsible geography.     

Cross-stratified calcarenites from New Zealand: subaqueous dunes in a cool-water, Oligo-Miocene seaway

Cross-bedded, cool-water, bioclastic limestones of the Te Kuiti Group on the North Island of New Zealand are composed primarily of bryozoans, echinoderms, and benthic foraminifers. Their prominent, large-scale, unidirectional cross-stratification is interpreted as produced by migrating subaqueous dunes on the floor of a 50–100 km wide, north-east-trending seaway in water depths of 40–60 m. These dunes are thought to have developed in response to strong, seaway-parallel, tidal currents combined with a north-east-directed, set-up or oceanic current. Cross-stratification is organized into four hierarchical levels: (1) cross-lamination; (2) first-order sets; (3) second-order sets; and (4) cross-stratified successions. The levels are based on increasing degrees of internal complexity. Distinct attributes such as internal organization, cross-set thickness, foreset shape, and lower bounding-surface shape are used to describe and interpret the cross-stratification. All these attributes are here integrated in a new and expanded classification of unidirectional cross-stratification that emphasizes flow and bedform dynamics rather than overall set shape. Individual cross-stratified successions are interpreted to have formed by dunes with varying sinuosity, superposition, and flow history, under conditions of different current strength but constant sediment production. Horizontally bedded successions are the result of robust, active dune fields that grew during times of vigorous sediment transport. Formset successions were produced from large compound dunes and are the expression of languid and decaying dune fields that developed during times of decreasing sediment transport. These decaying dunes were gradually smothered by continuously and locally produced bioclastic sediment. Formset cross-stratified successions are most likely to develop in carbonates, where the sediment is produced in place, than in terrigenous clastics where the sediment is imported.     

Microbial micritic carbonates in uppermost Permian reefs, Sichuan Basin, southern China: some similarities with Recent travertines

The uppermost Permian Chuenmuping reef formed on the western side of a carbonate platform situated in the eastern Sichuan Basin, southern China. Contrasts exist between this western patch reef and the better known Jiantianba barrier reef complex on the eastern platform margin in western Hubei Province, 250 km to the east. Microbial micritic carbonates form significant components of the Chuenmuping reef limestones. Three types of fabric can be identified: irregular, clotted and scalloped-laminated. An additional, cuneiform fabric has been found only in fore-reef facies at Jiantianba. Irregular fabric is comparable with the surface of presently forming travertines at Rapolano Terme, central Italy, which are produced by calcification of cyanobacteria. Clotted fabric shows indistinct peloids which tend to lack rims, and are amalgamated into irregular masses, some of which exhibit bush-like arrangements where traces of filaments can be seen. Traces of filaments are observed in both dark and light layers in the scalloped-laminated fabric, again suggesting a microbial origin. Cuneiform fabric consists of peloids and filaments, and closely resembles deposits in Quaternary travertines which may have been caused by bacterial action. Chuenmuping reef shows a shallowing sequence in normal marine conditions. The micritic fabrics interpreted here as microbial occur more commonly in the upper part of the reef. This indicates that microbial micrites, with a cementing role, formed coevally with reef growth within the upper part of the photic zone.     

Changes in velocity profiles at roughness transitions in coarse grained channels

Heterogeneous coarse grained channels are often characterized by local transitions in bed surface roughness. Distinct spatial zones in terms of grain size have been reported, for example sand ribbons and bedload sheets. The transition from areas of finer to coarser grained surface sediment is often abrupt. However, the effects of these transitions on the shape of the velocity profile and associated shear velocity and roughness length estimates have not been investigated in detail in coarse grained channels. This paper therefore examines the combined effects of a sudden change in surface roughness and of superimposed scales of resistancé on the structure of the turbulent boundary layer. Measurements along roughness transitions from smooth to rough beds were conducted in a flume using artificial roughness features and in a natural gravel bed river. Immediately at the transition from a zone of close packed roughness to a rougher section dominated by obstacles superimposed on the more or less uniform roughness surface, boundary shear stress and roughness length increase considerably. Downstream from this transition, velocity profiles become concave upwards. Downstream and upstream sections show significant differences in terms of near bed velocities (deceleration downstream of the transition), velocity gradient and turbulence intensity of the streamwise velocity component. Comparing the mean velocity profiles corresponding to these two different roughness surfaces gives some indication of the proportion of total shear velocity (or shear stress) associated with the pressure drag produced by large and isolated obstacles.     

Coral-stromatolite reef framework, Upper Miocene, Almería, Spain

Stromatolitic crusts on stick-like and platy Porites corals forming Messinian reefs in Almería played an important role in supporting and binding the brittle corals. The crusts were previously regarded as probable marine cements. However, their clotted, peloidal, and micritic fabrics are directly comparable with those of stromatolites. They accreted allochthonous grains even on vertical faces, and include bushy fabrics closely comparable with those produced by cyanobacterial calcification. They contain numerous fenestrae, exhibit rapid fabric variation, and locally form micro-columns and laminated domes. Their similarities to peloid micrite crusts in Recent reefs suggest that at least some of these Recent crusts are microbial in origin, even though they have widely been interpreted as marine cements. The sedimentary effects of crust development substantially affected both the morphology and relief of the reefs and the generation of reefal clasts. Binding of the reef-frame in the Pinnacle and Thicket zones in the lower and middle parts of the reef created a rigid margin which shed large (commonly up to 5 m) cuboidal blocks of coral-stromatolite frame. The blocks broke along planes of weakness provided by the vertical Porites sticks and were deposited on the Fore-Reef Slope. In the uppermost parts of the reefs crusts dominate the structure, constituting 80% or more of the rock. Veneers up to 15 cm thick encrust thin irregular Porites plates to create a solid Reef Crest Zone which has not been recognized before. The coral-stromatolite framework is associated with echinoids, crustose corallines and halimedacean algae which, together with the scleractinians, indicate normal marine salinity throughout reef growth.