Depositional Sedimentary Facies, Stratigraphic Control, Paleoecological Constraints, and Paleogeographic Reconstruction of Late Permian Chhidru Formation (Western Salt Range, Pakistan)

The Upper Indus Basin, in Pakistan’s western Salt Range, is home to the Zaluch Gorge. The sedimentary rocks found in this Gorge, belonging to the Chhidru Formation, were studied in terms of sedimentology and stratigraphy, and provide new insights into the basin paleogeographic evolution from the Precambrian to the Jurassic period. Facies analysis in the Chhidru Formation deposits allowed the recognition of three lithofacies (the limestone facies—CF1, the limestone with clay interbeds facies—CF2, and the sandy limestone facies—CF3) with five microfacies types (mudstone biomicrite—MF-1, wackestone-biomicrite—MF-2, wackestone-biosparite—MF-3, pack-stone-biomicrite—MF-4, and packstone-biosparite—MF-5), as well as their depositional characteristics. The identified carbonate and siliciclastic formations display various facies in a shallow marine environment, with different lithologies, sedimentary features, and energy conditions. It is thought that the depositional characteristics of these microfacies are closer to those of the middle to outer shelf. Because of the progressively coarsening outcrop sequence, this formation seems to be at the very top of the high stand system tract (HST). A modified dynamic depositional model of the Chhidru Formation is further built using outcrop data, facies information, and stratigraphy. According to this concept, the formation was deposited in the middle to inner shelf area of the shallow marine environment, during the Late-Permian period. The Permo-Triassic Boundary (PTB), which is the end of the type-1 series, is marked by this formation’s top.

Determination of functional structure of soft-bottom marine macrobenthic communities of the Samsun Shelf Area using biological traits analysis

Biological Traits Analysis (BTA) was used to investigate the functional structure of marine macrobenthic communities along the Samsun Shelf Area (SSA). Benthic samples were collected seasonally from five different locations and at four different depths using a Van Veen grab sampler. Macrofaunal communities distributed in the SSA were assessed using 10 biological traits to identify characteristic traits for each depth and location. It was found that variability of benthic ecosystem functions in the SSA was driven by biological traits such as maximum size, living habit, sediment position, feeding mode and type of reproductive behavior. Bivalves, polychaetes and crustaceans of small to medium size, biodepositing, burying themselves in the sediment (burrowers) and feeding in suspension were relatively more abundant at depths of 0–60 m. However, the biomass of Amphiura, Abra, Papillicardium and some polychaetes characterized by medium to large sizes, diffusive mixing, free living and feeding on deposit and subsurface deposit showed higher values at depths below 60 m. In general, it is concluded that the functional structure of the benthic infauna in the SSA has adapted to physical disturbance, and communities distributed in this area consist mainly of taxa resistant to mechanical pressure.

New Technology Yields High-Resolution 3D Modeling for Fracture Analyses

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 203108, “High-Resolution Fracture Analyses and 3D DMX DFN Modeling of Triassic Dolomites, Wadi Bih, Ras Al Khaimah, UAE,” by Janpieter van Dijk and Raffik Lazzar, GeoModl, prepared for the 2020 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, held virtually 9–12 November. The paper has not been peer reviewed. The complete paper outlines a high-resolution 3D fracture modeling exercise using the DMX protocol applied to Triassic dolomites of the United Arab Emirates. The outcropping rocks show a low primary porosity, are well bedded, and are highly fractured (jointed) up to centimeter scale. The exercise shows the relevance of applying new technologies to outcrop observations and shows several elements and related technologies that, to the authors’ knowledge, have not been presented previously. Introduction The focus area of the complete paper is a small outcrop situated in Wadi Bih in the territory of Ras Al Khaimah (Fig. 1) along a small road near a recently constructed artificial lake. This outcrop, which is approximately 150 m2 in size, shows well-bedded, highly fractured Triassic dolomites. Both section views and bedding-plane views can be observed. The outcrop was selected because it represents an analog of the Triassic Khuff formation, an important hydrocarbon-producing reservoir in the region. The outcrop is easily accessible and displays a clearly defined fracture (joint) network with recognizable sets, also showing truncation relationships between fractures, joints, and bedding that can be examined. Geological Context The area shows a complete series of Permian to Cretaceous, mostly carbonate sediments, outcropping in a series of north/south to north-northeast/south-southwest anticlines and synclines bounded by mostly west-vergent thrust faults. The Wadi Bih outcrop is situated on the moderately east-dipping flank of the north/south-trending Hagab Anticline, also called the Hagil Window after the area of the nearby Wadi Hagil, where the deepest Permian series are outcropping in the core of the anticline. This anticline is situated on the foot-wall of a major north/south-trending thrust fault. The geological history of the area is connected to the initial Mesozoic deposition of the series on the shelf area along the northeast flank of the Arabian shield. In the outcrop study, the focus is on the joint network. The authors write that this network is tilted together with the bedding as part of the flank of the anticline. No relation can be detected between the joint network sets and the fault and anticline axis pattern dominating the area. The joint network, therefore, most probably was formed in the early stages after lithification and dolomitization of the rock.

Characterization of Pliocene Biogenic Gas Reservoirs from the Western Black Sea Shelf (Romanian Offshore) by Integration of Well Logs and Core Data

The successful interpretation of open-hole well logging data relies on jointly using all available petrophysical and geological information. This paper presents relevant case studies related to the integration of well logs with core measurements for exploration wells drilled in the Romanian continental shelf area of the Western Black Sea basin. The analyzed wells targeted gas-bearing sands and silts complexes of Early Pliocene (Dacian) age, developed in a deltaic to shallow marine sedimentary environment in two distinct fields. The wireline logging programs included conventional formation evaluation logs, pressure surveys, nuclear magnetic resonance, and borehole electrical imaging logs. The core dataset comprised routine and special measurements (porosity, grain density, permeability, water saturation, and Archie parameters) carried out at quasi-reservoir confining pressure. The wireline logging suites were interpreted via a deterministic workflow, including core-derived interpretation parameters. Other core-derived parameters were used for constraining and validating the log interpretations. The results show that a problem related to the ambiguity of formation water resistivity can be overcome through resistivity–porosity dependencies constructed to include potential aquifer zones in the proximity of the Dacian gas-bearing reservoirs. This study also revealed and quantified uncertainties regarding the estimation of gas–water contacts from formation pressure surveys, which can be mitigated by the confirmation or correction of pressure-derived fluid contacts via the well log interpretation results. Lastly, we identified a probable resistivity logs suppression effect related both to high contents of capillary-bound water and also to the limited resolution of electrical logging tools in the presence of sand-shale thin bedding or laminations.

Imaging of shallow structures around Küçükçekmece Lake in Istanbul land area with high resolution geophysical data.

Küçükçekmece Lake and surrounding land area play an important role to understand the active tectonism of the southern land area of Istanbul. This study gives the results of a geophysical survey to understand the structural features of the study area. We collected geo-electrical data on the surrounding Küçükçekmece Lake. Totally 14 different VES values were inverted and evaluated variation of resistivity with depth. Additionally, the obtained apparent resistivity cross-sections for 3 profiles of VES points. All of them are interpreted considering geological well data from the study area and previous geophysical studies, which included especially high resolution shallow seismic data and chirp seismic data from the lake and shelf area in the Sea of Marmara close to the lake. The resistivity sections and inverted VES data show that faults cut the recent units and also cause resistivity changes in these units in the land area. These faults are consistent with the orientation of active faults observed from the seismic section on the lake and deforming the lake floor. This data set can be given as geophysical evidence for the existence of faults in the Istanbul land area.

Evolutionary drivers of the hump-shaped latitudinal gradient of benthic polychaete species richness along the Southeastern Pacific coast

Latitudinal diversity gradients (LDG) and their explanatory factors are among the most challenging topics in macroecology and biogeography. Despite of its apparent generality, a growing body of evidence shows that ‘anomalous’ LDG (i.e., inverse or hump-shaped trends) are common among marine organisms along the Southeastern Pacific (SEP) coast. Here, we evaluate the shape of the LDG of marine benthic polychaetes and its underlying causes using a dataset of 643 species inhabiting the continental shelf (<200 m depth), using latitudinal bands with a spatial resolution of 0.5°, along the SEP (3–56° S). The explanatory value of six oceanographic (Sea Surface Temperature (SST), SST range, salinity, salinity range, primary productivity and shelf area), and one macroecological proxy (median latitudinal range of species) were assessed using a random forest model. The taxonomic structure was used to estimate the degree of niche conservatism of predictor variables and to estimate latitudinal trends in phylogenetic diversity, based on three indices (phylogenetic richness (PDSES), mean pairwise distance (MPDSES), and variation of pairwise distances (VPD)). The LDG exhibits a hump-shaped trend, with a maximum peak of species richness at ca. 42° S, declining towards northern and southern areas of SEP. The latitudinal pattern was also evident in local samples controlled by sampling effort. The random forest model had a high accuracy (pseudo-r2 = 0.95) and showed that the LDG could be explained by four variables (median latitudinal range, SST, salinity, and SST range), yet the functional relationship between species richness and these predictors was variable. A significant degree of phylogenetic conservatism was detected for the median latitudinal range and SST. PDSES increased toward the southern region, whereas VPD showed the opposite trend, both statistically significant. MPDSES has the same trend as PDSES, but it is not significant. Our results reinforce the idea that the south Chile fjord area, particularly the Chiloé region, was likely the evolutionary source of new species of marine polychaetes along SEP, creating a hotspot of diversity. Therefore, in the same way as the canonical LDG shows a decline in diversity while moving away from the tropics; on this case the decline occurs while moving away from Chiloé Island. These results, coupled with a strong phylogenetic signal of the main predictor variables suggest that processes operating mainly at evolutionary timescales govern the LDG.

Revision of the genus Attaphila (Blattodea: Blaberoidea), myrmecophiles living in the mushroom gardens of leaf-cutting ants

The genus Attaphila, comprising minute myrmecophilous cockroaches, is revised, including now six previously known (A. aptera, A. bergi, A. flava, A. fungicola, A. schuppi, A. sexdentis) and three new species (A. multisetosasp. nov. Bohn and Klass, A. paucisetosasp. nov. Bohn and Klass, A. sinuosocarinatasp. nov. Bohn and Klass). All species are described or redescribed and depicted with their main characteristics; determination keys allow the identification of males and females. Especially the male characters allow a distribution to two species-groups with differing host specificity: bergi-group associated with Acromyrmex (and possibly Amoimyrmex) ants, fungicola-group associated with Atta ants; the former appears paraphyletic, the latter monophyletic. The genus Attaphila is characterised emphasising its unique features: (1) insertion of antennae at the bottom of a wide funnel-shaped deepening; (2) antenna with the possibility of a rectangular bending between scapus and pedicellus (associated with a distal excavation of the scapus) and (3) with an unusual shape and low number of antennomeres; (4) femora of legs with a ventral groove allowing a close spacing of femur and tibia during a strong flexion; (5) a complex and unusual shape of the laterosternal shelf area of the female genitalia (lack of shelf, presence of a pair of complicated tubular invaginations); and (6) lateral parts of abdominal tergite T9 of male ending in a pair of ventromesally directed arms, which contact the lateral margins of the subgenital plate. Functional aspects and the possible biological roles of these features are discussed. Older biological data are summarised and new observations are presented. The position of Attaphila within Blattodea is discussed. Like a recent molecular study, the morphology of the male genitalia places the genus in the Blaberoidea. The molecular result of Attaphila being closest to three particular blattellid genera, however, is conflictual from the morphological perspective.