The biotic recovery process following the Frasnian–Famennian (F–F) mass extinction played an important role in reestablishing the late Palaeozoic marine ecosystem. The Nehden event is assumed as the ...global biotic recovery process in the aftermath of the F–F mass extinction, but the timing and pattern of this event is still in dispute due to lack of consistent geological records. In order to recognize the Nehden event and elucidate its timing and pattern, a newly refined conodont biostratigraphic framework spanning the Palmatolepis minuta minuta Zone to the Pa. rhomboidea Zone (370.8–367 Ma) has been established in the Yangdi section, Guangxi, South China. Based on a detailed analysis of microfacies and carbon isotope of carbonates (δ13Ccarb), the start of the Nehden event has been placed at the upper part of the Pa. m. minuta Zone, marked by deposition of calcareous shales and proliferation of palmatolepid conodonts and ostracods. Two episodes of the Nehden event are recognized in this study according to integrated palaeontological, sedimentological, and geochemical data from South China and other continents. The first phase of the Nehden event is assigned at the upper part of the Pa. m. minuta Zone, characterized by radiation of conodonts, ostracods, and brachiopods, which is coincident with the minimum value of negative δ13Ccarb excursion and climate warming. The second phase is placed at the Pa. termini to Pa. glabra pectinata zones, documented by biodiversification of cheiloceratid ammonoids and phacopid trilobites, which is concurrent with climate warming and the maximum transgression during the early Famennian. The extensive development of microbial bindstone in the lower Famennian succession at Yangdi demonstrates that microbial communities occupied the vacant ecological niches left behind by metazoans after the F–F biotic crisis. The expansion of ecological niches of microbial communities and depauperation of metazoan reefs implies the bioconstructor turnover from metazoan to microbial communities following the F–F extinction. The time equivalence of biotic radiation, climate change and sea-level fluctuation in two episodes of the Nehden event indicates the early Famennian biotic recovery was favored by climate warming and transgression. The results in this study not only offer important data to constrain the timing of the Nehden event, but also provide an insight on the process of biotic recovery following the F–F mass extinction event.
•The Lower Famennian conodont biostratigraphy was erected in slope facies.•The Nehden event was recognized in a deep-water setting for the first time in South China.•Timing and pattern of the Nehden event was elucidated.•The Nehden event was associated with transgression and climate warming.
Malang and Wonosari areas are located in Southern Mountains of Java, and their rock variations are comparable. Study focuses on limestone found at Sumbermanjing Wetan, Malang, that has been ...identified as part of Wonosari Formation. This place is closer to Punung area as viewed from the type location. Limestone microfacies approach is used to determine whether the limestone belongs to Wonosari or Punung formations. Methods used to identify standard microfacies types and facies zone are measured stratigraphy, petrographic analysis, and microfossil analysis. Measured stratigraphy was conducted along Bangbang River, and seven limestone samples were collected for analysis. Findings showed three standard microfacies types: SMF-5 characterized by packstone or rudstone with a mudstone matrix, SMF-8 characterized by wackstone or floatstone with complete fossils, and SMF-18 characterized by grainstone or packstone with abundant foraminifera or algae. Limestone belongs to facies zone (FZ) 7 - 8, which is characterized by presence of packestone, wackestone, clay sized limestone, and benthic algae foraminifers. Limestone ages range from Middle to Upper Miocene (N12 - N16), were formed in an inner Neritic. Limestone is equivalent to Wonosari and Punung Formations, based on standard microfacies type, facies zone, and age range. When lignite intercalation are present, the limestone is equivalent to the Punung Formation.
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•Sandstone in the upper part of the Qawasim Formation is the main reservoir in the El Tamad field.•Primarily, the sandstone is arenite in composition, well sorted with sub-rounded to ...rounded grains.•Diagenesis enhanced the reservoir quality of the sandstone with low-cement content, poor compaction and weak fracturing.•Clastic rocks of the Qawasim Formation were deposited in a shelf environment as stacked barrier-island bars.•Carbonate rocks of the Qawasim Formation were deposited in a shelf lagoon with open circulation.
The Nile Delta region is the main gas-producing province in Egypt. Late Miocene sediments are the target of drilling in the onshore Nile Delta where it has the potentiality to store and produce hydrocarbons. Five wells of the Messinian Qawasim Formation at El Tamad Field were selected for the present study. Detailed petrographic investigations were carried out to reveal the depositional and diagenetic features of the Qawasim Formation rock units. Two main facies were distinguished in the studied formation: clastic and carbonate facies. The clastic rocks include conglomerate, sandstone and shale, while the carbonate rocks include limestone and dolostone. Depositional, diagenetic and petrophysical parameters of the sandstones of the Qawasim Formation reflect that this rock unit an excellent reservoir for hydrocarbon. These microfacies display depositional features such as well sorting, open packing and poor cementation in both coarse and fine-grained microfacies. The porosity of sandstone was enhanced by diagenetic processes such as dolomitization of calcite cement and low compaction that resulted in grain cracking, while the dissolution of feldspars had a subordinate impact on increasing porosity due to their low abundance and the resultant authigenic clay minerals.
•Combination of different dating methods provides robust and accurate chronology.•Varve microfacies structure reflects sedimentation conditions.•Rapid ecological shifts were caused mainly by ...anthropogenic pressure.•Lake water level was affected by climate change and human activity.
Sediments from Lake Lubińskie, western Poland, were investigated to determine the limnological responses to environmental changes during the last 3,000 years. To identify the mechanisms driving the eutrophication in the lake, we distinguished six lithozones along with five major varve microfacies. An age-depth model based on varve counting and radiometric measurements was established resulting in final age of 946 +113/-144 before the Common Era at the bottom of the composite profile. Varve microfacies as well as geochemical, pollen, and diatom data was used to determine major phases of landscape and lake ecosystem transformations. Our data shows that until the 4th century of the Common Era, conditions in the lake were stable. Several shifts occurred before the first millennium, when changes were observed in every proxy as a response to the increased agricultural activity in the area as well as climate fluctuations. The highest frequency of shifts was observed from the 17th century onward and mirrored further deforestation (decrease in arboreal pollen), accelerated erosion (increase in Ti), increased nutrient delivery (increased total nitrogen content), and better ventilation of the water body (higher Mn/Fe ratio). Simultaneously, the lake became more eutrophic as a response to changes in the lake catchment area. Our study suggests that inferred lake-level changes are primarily related to human activity in the catchment area.
Petrographically, the Lower Miocene Rudeis reservoir rock samples in October oil field can be summed up into three reservoir rock types RRTs. The RRT1 samples are mostly calcareous to ferruginated ...sandstones, sometimes are fossiliferous, whereas the RRT2 and RRT3 samples are carbonate rocks of grainstone and packstone microfacies, respectively. Cementation by sparite and compaction are the most important porosity-reducing diagenetic factors, whereas dissolution and leaching out as well as fracturing are the most dominant porosity-enhancing factors.
The petrophysical and reservoir quality studies include measuring density, porosity, permeability measurements as well as reservoir quality index (RQI), flow zone indicator (FZI) and reservoir potential index (RPI) calculations. The permeability-porosity plot is the key-factor for discriminating the petrophysical behaviour into these three rock reservoir types.
Petrophysically, the studied sandstone RRT1 samples have the best storage capacity and reservoir quality (the RQI, FZI and the RPI indicate poor to very good reservoir quality), whereas the RRT3 samples have the least prospective properties (the RQI, FZI and the RPI indicates impervious reservoir quality).
Based on the FZI values, the studied Rudeis Formation was discriminated into a number of hydraulic flow units (6 HFUs). HFU 5–6 are the best reservoir zones; they are assigned in the central parts of the studied area, whereas the least quality (HFU 1–3) was assigned to the south. In addition, the mercury injection capillary pressure tests (MICP) indicates that, the RRT1 samples are ranked as IV (fair) to VI (impervious) ranks, the RRT2 as V (poor) to VI, whereas the RRT3 samples are impervious samples. Wettability of the studied RRT1 samples is mostly neutral.
•The studied rock samples can be summed up into three reservoir rock types RRTs.•The RRT1 samples are mostly fossiliferous sandstones, whereas the RRT2 and RRT3 are carbonates.•Permeability is the key-control factor for the reservoir quality RQI and FZI parameters.•RRT1 samples are ranked as IV (fair) to VI (impervious) ranks, as the RRT2 and RRT3 as V (poor) to VI ranks.•Wettability of the studied RRT1 samples is mostly neutral.
This study aims to diagnose microfacies of the Jeribe Formation to determine depositional environments and derivation depositional model for this formation. The study consisted of two wells in the ...Hamrin anticline north of the Saladin Governorate within the foothill zone. In the study area, the lower contact of the Jeribe Formation is unconformable with the Dhiban Formation, whereas the upper contact is conformable with the Fatha Formation. Depending on the microfacies analysis, four significant microfacies were distinguished, including mudstone, wackestone, packstone, and grainstone, and then divided into eight submicrofacies types depending on grain types. The microfacies analysis of the Jeribe Formation revealed the recognition of five environments: open-marine (middle ramp to inner ramp), restricted, shoal, lagoon, and partial environments. The majority of microfacies are determined within the inner ramp setting. The Jeribe Formation was deposited in a shallow marine environment.
