The fossil record of Mexican freshwater fishes, although scarce, has increased in recent years. These fossils are known in 39 localities, 4 of which are Cretaceous and carry remains of cf. †Melvius sp., Amiidae, Lepisosteidae and †Ceratodus sp., groups no longer recorded as fossil material in subsequent periods. The remaining localities belong to the Cenozoic Era (Oligocene to Pleistocene) and contain modern faunas; most of them are located in the Mexican Volcanic Belt and most are from Pleistocene deposits. The diversity of fossil fish includes 12 families and at least 26 genera, and 39 species. Only some of the latter are known as fossils. The position of the Cenozoic localities in relation to existing drainage and fish communities suggests events of change in the hydrology for some recent basins. In order to broaden the knowledge on this group of fishes, it is required to perform active prospective work in less explored areas such as Northern endorheic drainages and Southern tropical basins of Mexico, in addition to applying finer recovery and study techniques, as well as incorporating new procedures for, among others, molecular and isotopic analyses.

Pliocene deposits cropping out in the Agua Amarga subbasin (Almería, SE Spain) include a composite shell bed made up of variously preserved and densely packed mollusks. The characteristics of the shell bed indicate deposition in shallow marine settings under a changeable sedimentation rate. The composite shell bed was formed through the amalgamation of several depositional events, mostly connected with storm events. During relatively slow sedimentation the bivalve Panopea colonized the substratum. The colonization took place over different stages of the shell bed formation, as reflected by differently preserved Panopea scattered throughout the shell bed. The upper part of the shell bed contains several tens of Panopea preserved within their burrows: Scalichnus cf. phiale Hanken et al., 2001. All bivalves in S. cf. phiale are articulated and preserved in life position. They are confined to a single horizon and most probably represent a single fossil population composed of adult individuals of Panopea resulting from anastrophic burial by storm deposits. As a consequence, the bivalves in their burrows succumbed at the same time; that is, the study case represents an “ecological snapshot” or ecological census.

Regional three-dimensional groundwater-flow and saltwater transport models were built to analyse saltwater intrusion in the Great Maputo area, southern Mozambique. Increased water demand has led to many private groundwater abstractions, as the local public water supply network has already reached maximum capacity. Pushing for new strategies to tackle the water-supply shortages exposes the aquifer system to saltwater intrusion from entrapped fossil saline groundwater and seawater. Previous attempts at modelling have been frustrated by data limitations. This study compiled all the available data to build the models, which were subsequently calibrated with observed heads, discharges and salt concentrations. The transport models were used to test hypotheses of potential sources of saltwater resulting in the current salinity distribution. Furthermore, scenarios were simulated to assess the impacts of sea-level rise and projected groundwater abstractions. Results show that saline groundwater is widely distributed in the aquifer’s western sector, where it is a limiting factor for groundwater development, and seawater intrusion is a risk along the coastline. Newly constructed wells (46) along the Infulene River can be operated with some impacts of saltwater upconing and must be closely monitored. Although current groundwater abstractions (60,340 m³/day) are still small compared with groundwater recharge (980,823 m³/day), larger volumes of abstraction are feasible only when using a high number of production wells further away from the city with relatively low yields to avoid saltwater upconing. Capture of fresh groundwater upstream of discharge areas by wells for water supply is possible while maintaining groundwater discharges for groundwater dependent ecosystems.

Hydrogeological models of mountain regions present the opportunity to understand the role of geological factors on groundwater resources. The effects of sedimentary facies and fracture distribution on groundwater flow and resource exploitation are studied in the ancient fan delta of Sant Llorenç de Munt (central Catalonia, Spain) by integrating geological field observations (using sequence stratigraphy methods) and hydrogeological data (pumping tests, hydrochemistry and environmental isotopes). A comprehensive analysis of data portrays the massif as a single unit, constituted by different compartments determined by specific layers and sets of fractures. Two distinct flow systems—local and regional—are identified based on pumping test analysis as well as hydrochemical and isotopic data. Drawdown curves derived from pumping tests indicate that the behavior of the saturated layers, whose main porosity is given by the fracture network, corresponds to a confined aquifer. Pumping tests also reflect a double porosity within the system and the occurrence of impervious boundaries that support a compartmentalized model for the whole aquifer system. Hydrochemical data and associated spatial evolution show the result of water–rock interaction along the flow lines. Concentration of magnesium, derived from dolomite dissolution, is a tracer of the flow-path along distinct stratigraphic units. Water stable isotopes indicate that evaporation (near a 5% loss) occurs in a thick unsaturated zone within the massif before infiltration reaches the water table. The hydrogeological analysis of this outcropping system provides a methodology for the conceptualization of groundwater flow in similar buried systems where logging and hydrogeological information are scarce.

Assessment of the level of activity of advective transport through faults and fractures is essential for guiding the geological disposal of radioactive waste. In this study, the advective flow (active, inactive) of meteoric water through fractures is assessed by comparing stable isotopes (δD and δ¹⁸O) between fracture and pore waters obtained from four boreholes in marine deposits in the Horonobe area, Japan. At 27–83-m depth in one borehole and 28–250 m in another, the isotopic compositions of pore and fracture water reflect mixing with meteoric water, with stronger meteoric-water signatures being observed in the fracture water than in pore water of the rock matrix. At greater depths in these boreholes and at all sampling depths in the other two studied boreholes, the isotopic compositions of fracture and pore waters are comparable. These results suggest that the advective flow of meteoric water is active at shallow depths where fossil seawater is highly diluted in the two boreholes. This interpretation is compatible with the occurrence of present or paleo meteoric waters and tritium, whereby present meteoric water and tritium are limited to those depths in the two boreholes. This difference in the level of activity of advective flow is probably because of the glacial–interglacial difference in hydraulic gradients resulting from sea-level change. Although fractures are hydraulically connected to the surface through the sedimentary rock, advective flow through them is inferred to remain inactive so long as sea level does not fall substantially.