Wyniki wyszukiwania - BazTech

1

Geochemistry of siliciclastic rocks from the Shemshak Group (Upper Triassic-Middle Jurassic), northeastern Alborz, northern Iran : implications for palaeoweathering, provenance, and tectonic setting

Taheri A., Jafarzadeh M., Armstrong-Altrin J. S., Mirbagheri S. R.

Geological Quarterly

|

2018

|

Vol. 62, No. 3

522--535

EN

Combined petrographic and geochemical data of the siliciclastic sedimentary rocks from the Shemshak Group in the northeastern Alborz Mountains, north of Iran are described, together with their implications for palaeoweathering, their provenance, and tectonic setting. Based on field observations and modal composition, the sandstones are classified as litharenites. The chemical index of alteration (CIA) indicated that the source terrains underwent a moderate intensity of chemical weathering. The index of chemical variation (ICV) values indicated that the Shemshak Group rocks were immature and related to a source area with an active tectonic regime. Major, trace and rare earth element (REE) data suggested the domination of mixed sedimentary (recycled) and igneous rocks in the source area of the Shemshak Group. Petrographic and geochemical characteristics of Shemshak Group rocks suggest an active continental margin (ACM), which corresponds to the collision of the Iran plate with the Turan plate.

2

Petrographic and geochemical study of the Maastrichtian Ajali Sandstone, North Central Nigeria

Ogala J. E., Olobaniyi S. B., Omo-Irabor O. O., Adaikpoh E. O.

Geological Quarterly

|

2015

|

Vol. 59, No. 1

79--90

EN

he Upper Cretaceous Ajali Sandstone is an extensive stratigraphic unit of the Anambra Basin in southern Nigeria. It consists of friable, white cross-bedded sandstones exhibiting a fining upward sequence. Structures such as bioturbation, planar and herringbone cross beds indicate variability in depositional environment ranging from fluviatile to deltaic. Petrographic and geochemical compositions (major and trace elements) of these sandstones have been investigated to determine their provenance, tectonic setting and weathering conditions. Fifteen sandstone samples examined are rich in quartz but poor in feldspar and lithic fragments. Texturally, the framework grains of the sandstones are fine- to medium-grained, sub-angular to sub-rounded, moderately sorted to poorly sorted, positively skewed and leptokurtic. The sandstones are texturally immature as depicted by their sub-angular edges of grains, but mineralogically mature in terms of high percentage of quartz. The high chemical index of alteration (CIA) values (71.0–99.2%) for these sandstones suggests that they were derived from highly weathered rocks in the source area. The composition of the major oxides in the sandstones revealed that SiO2 (49.1–99.7%), Al2O3 (0.2–30.3%), Fe2O3 (0.4–1.8%) and TiO2 (0.06–3.2%) were the most abundant elements in all sandstone samples indicating a high detrital quartz and clay mineral content. The Al2O3/TiO2 ratios (1.47 to 12.48), Ti/Zr (6.48–18.63) and Zr/Cr (2.24–22.36) suggest that the sandstones were derived from variable basement complex rocks, including some contribution from mafic or ultramafic components. Inferences from the plots of K2O/Na2O versus SiO2 indicated a passive margin tectonic setting for the sandstones. The high loading of CaO and Na2O in more than 50% of the samples is indicative of terrigenous input, mainly in the form of carbonates and silicates. These results are generally consistent with a derivation of the sandstones from adjacent igneous and metamorphic basement complexes (Cameroon–Adamawa highlands and Oban Massif) while the extensive and blanket-like geometry of the Ajali Sandstone is indicative of an excellent reservoir for groundwater in the Anambra Basin.

3

Utwory jury środkowej i ?dolnej w rejonie Księżpol-Lubaczów (SE Polska)

Moryc W.

Biuletyn Państwowego Instytutu Geologicznego

|

2004

|

nr 408

5-71

PL

Obszar Księżpol-Lubaczów w dolnej i środkowej jurze należał do północnego skłonu, wschodniego przedłużenia bruzdy środkowopolskiej. Opisane utwory środkowej i przypuszczalnej dolnej jury to osady klastyczne o maksymalnej miąższości rzeczywistej około 400 m. W ich najniższej części występuje cienka, około 20 m grubości seria ilasto- piaszczysta, zaliczona do dolnej jury. Środkową jurę reprezentują, od dołu, utwory piaskowcowe, którym przypisuje się wiek od aalenu do kujawu dolnego oraz leżące wyżej osady ilasto-mułowcowe, miejscami z wkładkami piaskowców, należące do kujawu środkowego i górnego, batonu oraz keloweju. W pracy przedstawiono również tektonikę i układ strukturalny badanych utworów oraz uwagi dotyczące paleogeografii. Ponadto określono związek tych osadów z podobnymi utworami występującymi na obszarach graniczących z rejonem badań.

EN

In the Early and Middle Jurassic, the area of Księżpol-Lubaczów constituted the northern margin of the eastern continuation of the Mid-Polish Trough. Middle and probably Lower Jurassic deposits consist of clastic rocks, approximately 400 metres thick. In its lowermost part, the thin (ca 20 m thick) clay-sandy series is considered to be of Early Jurassic age. The basal layer of the Middle Jurassic lithostratigraphic succession consists of sandstones, whose age was established as Aalenian-early Kuiavian. The upper layers of the succession are composed of clayey and muddy sediments with sandstone intercalations, representing the middle and upper Kuiavian, Bathonian and Callovian. The present study focuses on the Middle Jurassic deposits as well as the tectonic, structural and palaeogeographic problems of the area. Moreover, a comparison is made of the discussed sediments and stratigraphic index-fossils with those of the neighbouring regions.