Wyniki wyszukiwania - BazTech

1

Skały silikoklastyczne triasu i jury niecki łódzko-miechowskiej w aspekcie rozwoju ich przestrzeni porowej

Kuberska Marta, Kozłowska Aleksandra, Wołkowicz Krystyna

Przegląd Geologiczny

|

2023

|

Vol. 71, nr 4

212--218

EN

Triassic and Jurassic siliciclastic rocks from boreholes drilled in the Łódź and Miechów troughs to the SW of the Mid Polish Anticlinorium have been subjected to petrologic studies. The are represented by claystones, mudstones, sandstones, and less frequently by conglomerates. The studies shows that the filtration and reservoir properties of the Triassic deposits not good due to diagenetic processes (compaction, cementation, replacement, dissolution). Only some Lower Triassic sandstones, occurring among others, as intelayers, display increased values of permeability and porosity (to about 27 vol. %). The best properties are display ed by sandstones from the Brzegi IG 1 borehole, in which macropore intergranular space is present. The Lower Jurassic rocks are characterized by the best properties within the Jurassic complex. They show increased values of mostly secondary porosity, which results from the dissolution of grains and cements. The pore space is developed homogenously. It has a micropore character in the Middle and Upper Jurassic deposits.

2

Permian versus Jurassic geotectonic position of the Lhasa block – facts and controversies

Krobicki Michał, Golonka Jan, Starzec Krzysztof, Iwańczuk Joanna

Geotourism / Geoturystyka

|

2023

|

nr 1-2 (72-73)

38--38

EN

The Cimmerian Continent (or Cimmeria, Cimmerian terrane, Cimmerian blocks) was detached from eastern Gondwana in the Late Paleozoic as a sliver/ribbon of continental strip rifting elements. Recently, these elements belong to an almost continuous long belt (ca. 13,800 km) from central Italy trough Greece, Turkey, Iran, Afghanistan, Tibet, SW China, Myanmar, Thailand up to Indonesia (Sumatra). The palaeogeographic position and relationship of some elements during Permian-Mesozoic times is still matter of discussion. The Qiangtang and Lhasa blocks (present-day Tibet) belong to these elements and their location in space and time and their relationship causes a lot of controversies. Their position alongside eastern Gondwana in the mid-Early Permian (ca. 290–285 Ma) are suggested both by palaeomagnetic and facies studies. Palaeomagnetic studies indicated this position one decade ago, which has been confirmed by recent studies. The Cimmerian Continent [Iran (Alborz)-Qiangtang-Baoshan-Tengchong-Sibumasu] was separated from the Gondwanian part of Pangea during mid-Early Permian time by rifting and drifting. Northwards migration of it took place during Permian-Triassic times caused wide opening of the Bangong‐Nujiang Tethyan Ocean and closing of the Paleotethys Ocean but the Lhasa block was still southern margin of the Bangong‐Nujiang Ocean. The Triassic Indosinian Orogeny has been one of the most spectacular geotectonic event reflecting collision of this continent with Indochina block and closure of the Paleotethys Ocean. The separation of the Lhasa block from Gondwana is enigmatic but most probably took place during earliest Jurassic times. This separation was followed by quick shift northward. Intensive sedimentological studies of the Late Triassic (Carnian-Norian) several flysch-type turbidites in the eastern Tethyan Himalaya (e.g. Qulonggongba, Pane Chaung, Langjiexue, Quehala, Duoburi formations/groups) indicate that their provenance was connected with Lhasa block, which has been their source area during early-stage evolution of the Neotethys. The late Early Permian rift-related basaltic magmatism in northern Baoshan (in SW China) and sourrounding regions was connected with first step of separation from Gondwana margin of this block (together with South Qiangtang and Sibumasu blocks and simultaneously with opening of the Bangong‐Nujiang Ocean before the Middle Permian) – independently of Lhasa block which was separated later, the most probably during Late Triassic or Triassic/Jurassic transition time with very wide space of the Bangong‐Nujiang Tethyan Ocean between Qiangtang and Lhasa blocks (2,600 km ±710 km – 23.4° ±6.4° during the Middle Jurassic with its maximum width in the Late Triassic). From the palaeobiogeographic point of view, the worldwide distribution of Pliensbachian-Early Toarcian large bivalves of the so-called Lithiotis-facies, dominated by Lithiotis, Cochlearites, Litioperna genera revealed by the authors’ studies, indicates very rapid expansion of such type of bivalves alongside southern margin of Neotethys, and could be good evidence of palaeogeographic position of the Lhasa block in this time. Himalayan and Tibetan (Nyalam area) occurrences of Lithiotis and/or Cochlearites bivalves could help to place the Lhasa block nearby the Gondwana during Early Jurassic times. This palaeobiogeographic research contradict another interpretation based on different fossils (Permian fusulinids and brachiopods) interpreted as subtropical fauna, which could occur in low subtropical latitudes together with other parts of the Cimmerian Continent.

3

Jurassic and Cretaceous evolution of Tethys: Palaeoceanographic events

Yilmaz İsmail Ömer

Geotourism / Geoturystyka

|

2023

|

nr 1-2 (72-73)

81--81

EN

Jurassic and Cretaceous evolution of Tethys Ocean is characterized by extension of oceans basins, rifting, development of carbonate platforms and sea level fluctuations. Ocean basins and platform margins were sides of records of collaboration of oceanic, sea level and climate changes in different scales. Deposition of organic sediment increased on the margins of the ocean basins at certain time intervals due to changes in oceanic circulation and chemistry, productivity, climate and sea level. Oceanic Anoxic Events (OAE) stated to took place at aperiodic time intervals and generally associated with organic matter deposits and anoxic water columns. Records of oceanic anoxic event can also be associated by potential source rocks in Jurassic and Cretaceous along Tethys Ocean basins and can be tracked by stable isotope shifts, turnover of fossil groups, presence of black shales/organic rich mudstones, change in redox sensitive elements. Volcanic contribution in oceans is also considered as one of the collaborators of OAE generations. OAE records in Jurassic is seen in Toarcian interval and stated as Toarcian OAE. In Cretaceous, OAE records can be stated as Weissert, Faraoni, Selli (OAE1a), Noir, Fallot, Jacop, Kilian, Paquier (OAE1b), Leenhardt, Amadeus (OAE1c), Breistroffer (OAE1d), Bonarelli (OAE2), and OAE3. Generally, Cretaceous OAE are globally correlated or at least hemispherical. Some of them can be weakly correlated due to different duration and magnitude. Stratigraphic positions of OAE can also be used better marker levels in sequence stratigraphic interpretations. Therefore, positions of OAE are very important in terms of higher resolution for platform to basin correlations and even basin to basin. Cretaceous Oceanic Anoxic Events in eastern Tethys Ocean in Pontides and Taurides can be seen in Cretaceous successions (Mid-Barremian, Aptian, Albian, Cenomanian-Turonian) of Central Pontides (NW Turkey) and Central Taurides (S Turkey) (Yilmaz et al., 2004, 2010, 2012) as presence of black shales. The Mid-Barremian black shales (MBE) have been recorded within turbidite succession in deep marine setting in central Sakarya zone of Pontides following the drowning of the platform (Yilmaz et al., 2012). 2‰ shifts in carbon isotope curve is recorded in parallel with European basins, but with low TOC value. The Aptian black shales (OAE1a) are recorded in pelagic carbonate slope environments in central and north of Sakarya zone of Pontides and represented by a negative carbon isotope shift with 2‰, and TOC around 2% (Yilmaz et al., 2004; Hu et al., 2012). In Sakarya zone of Pontides, OAE2 is recorded in pelagic slope carbonates with carbon isotope curve more than 1‰ positive shift and >2% TOC. Another OAE2 was recorded in Antalya Nappes of Taurides without carbon isotope curve but TOC > 20% (Yurtsever et al., 2003, Bozcu et al., 2011). OAE1a equivalent in Tauride Carbonate platform can be interpreted as presence of dark colored thick stromatolite bearing platform carbonates transgressivley overlying the karstic sequence boundary. The OAE1a and OAE2 levels recorded in Turkey can easily be correlated with European examples and mainly controlled by sea level and tectonics in largescale and climate and oceanographic changes in small-scale. The most extensive distribution of the OAE records in Turkey belong to OAE1a and OAE2, and display potential for source rocks for hydrocarbon exploration.

4

O ochronie starych kamieniołomów skał jurajskich na Wyżynie Wieluńskiej, czyli o konieczności współdziałania nauki, górnictwa i lokalnej administracji

Wierzbowski Andrzej

Przegląd Geologiczny

|

2022

|

Vol. 70, nr 11

800--805

EN

Abandoned quarries in the Wieluń Upland at Działoszyn and Wieluń in central Poland are of unique value for the detailed stratigraphical, palaeontological, sedimentological and palaeogeographical studies of the Oxfordian and Kimmeridgian stages (especially the Upper Oxfordian and Lower Kimmeridgian substages) of the Jurassic System in Europe. It is because they yield the successions of deposits containing diverse assemblages of ammonites of a great significance for stratigraphical correlation, including that corresponding to the stratigraphical interval at the newly accepted global stratotype (GSSP) between the Oxfordian and the Kimmeridgian. Moreover, the quarries show the last Late Jurassic deposits placed towards the west in central Poland and preserved against the erosion, thus of high importance for the palaeogeographical reconstructions. The quarries offer also a special opportunity for educational purposes, and might become local geological attractions as they contain abundant fossils. Additionally, due to the fact that the Wieluń Upland, especially the environs of Działoszyn, has been one of the main areas of exploitation of limestones in Poland - the scientific value of the collected material and the history of the limestone mining could be presented in a specially prepared exhibition at the local museum, supported by geo-educational paths marked out in the abandoned quarries. Cooperation between the scientific community, local administration centers, and the owners of the quarries is of fundamental importance for the subject.

5

Textural characteristics, mode of transportation and depositional environment of the Stormberg Group in the Eastern Cape, South Africa: evidence from grain size and lithofacies analyses

Chima Priscilla, Baiyegunhi Christopher

Geologos

|

2022

|

Vol. 28, No. 1

61--78

EN

The Stormberg Group comprises the Molteno, Elliot and Clarens formations and is one of four stratigraphical groups that make up the Karoo Supergroup in South Africa. The group is the highest unit in the Karoo Basin, representing the final phase of preserved sedimentation. The major problem with the Stromberg Group is that the mode of transport, hydrodynamic energy conditions and depositional environment are still poorly understood. For the present paper, grain size and lithofacies studies on selected sandstones from the Molteno, Elliot and Clarens formations were performed so as to elucidate their textural characteristics, depositional processes, sedimentation mechanisms and hydrodynamic energy conditions and to discriminate different depositional environments. The statistical parameters of grain size distribution (mean grain size, standard deviation, skewness and kurtosis) show that the sandstones are predominantly unimodal, fine grained, moderately well sorted, mesokurtic and near symmetrical. The bivariate diagrams of the aforementioned statistical parameters demonstrate that river and aeolian dune had the greatest impact on the depositional environments. Likewise, the C-M pattern (Passega diagram) shows that the sandstones were mostly deposited through tractive current process. Furthermore, the C-M diagram reveals the prevalence of rolling, suspension and graded suspension modes of sediment transportation. Seventeen sedimentary lithofacies were identified and grouped into seven lithofacies associations. These lithofacies associations indicate braided channel, overbank and swamp deposits for the Molteno Formation, alluvial fan/floodplain and playa deposits for the Elliot Formation and aeolian deposits for the Clarens Formation.

6

Terrigenous organic matter and formation of siderite in the Bathonian Ore-Bearing Clay Formation at Gnaszyn, Poland : a petrochemical study

Lis Kacper, Wojtulek Piotr, Lis Grzegorz, Jelonek Iwona

Annales Societatis Geologorum Poloniae

|

2022

|

Vol. 92, No. 3

295--312

EN

The Bathonian Ore-Bearing Clay Formation, outcropping in the Gnaszyn open-pit mine at Częstochowa (Poland), includes several horizons of abundant iron carbonate concretions. The cores of the concretionary bodies commonly contain organic matter (OM), dominated by fragments of wood. These organic particles usually display well-preserved primary structures and occur rarely as more deformed and/or completely degraded fragments. Their original structures are frequently replaced by or filled with secondary mineralization, mostly represented by pyrite. The maceral composition of the OM of the wood fragments is dominated by huminite with subordinate inertinite and resinite. Vitrinite reflectance analyses revealed values lower than 0.45%. The total organic carbon content (TOC) displayed variable results between 2% and 18%. Rock-Eval analyses revealed low amounts of hydrogen (< 45 mg HC/g TOC) and relatively high amounts of oxygen (up to 136 mg CO2/g TOC). Analysed samples contained small quantities of free hydrocarbons (S1 peak < 0.26 mg HC/g rock) as well as hydrocarbons, generated during pyrolysis (S2 peak < 7.05 mg HC/g rock). These features are characteristic for immature type IV kerogen of terrigenous origin. However, the maceral composition and frequent occurrence of siderite affecting the Rock-Eval parameters may indicate that the original kerogen belonged to type III. According to previous authors, the OM of terrigenous origin was delivered to well-oxygenated water of the palaeo-basin in the Częstochowa area. The present data indicate that intensive biodegradation of this OM at shallow burial depleted the oxygen supply within the sediment, driving the pore water into dys- or anoxic conditions. The activity of microorganisms in reducing iron and/or sulphates became the dominant biodegradation reaction, introducing Fe2+ and HCO3- ions into the system. Negative δ13C values in the cortex of the concretions analysed indicate that the bicarbonate consumed in siderite precipitation was supplied by this microbial activity. The reducing microenvironments developed in the sediment and wood fragments acted as nucleation sites for siderite precipitation.

7

Carbon, oxygen and strontium isotope composition of Plattenkalk from the Upper Jurassic Wattendorf Konservat-Lagerstätte (Franconian Alb, Germany)

Blendinger Wolfgang, Mäuser Matthias

Volumina Jurassica

|

2021

|

Vol. 19, no. 1

1--20

EN

The oldest Jurassic (Kimmeridgian) Plattenkalk occurs in Wattendorf on the northern Franconian Alb (southern Germany). It is a 15 m thick alternation of laminated dolomite and limestone, interbedded with carbonate debris layers in a depression ~2 km across and a few tens of metres deeper than the surrounding microbial-sponge reefs. The Plattenkalk overlies a few tens of metres of microbialsponge biostrome facies and bedded, micritic basinal limestone. The bulk-rock stable isotopes of the micritic basinal facies gradually change from normal marine (δ13C ~ +2‰, δ18O ~ –2‰ VPDB) to lower values (δ13C ~ 0‰, δ18O ~ –6‰) in a ~ 40 m thick interval including Plattenkalk and suggest ageing of the bottom waters. The surrounding reefs are isotopically nearly invariant (δ13C ~ +2‰, δ18O ~ –2‰ VPDB). An isotope anomaly (δ13C of > ~ –9‰) is restricted to the basinal facies and is most pronounced in the biostrome facies. This indicates methanogenesis, which is documented in negative δ13C in dedolomite, calcite-cemented dolomite and calcite concretions and occurred probably mainly below seabed. The Konservat-Lagerstätte was probably deposited near an oxygen minimum zone in a water column with low productivity of organic material. Dolomite is in isotopic equilibrium with Plattenkalk and was probably deposited as protodolomite from chemically modified, aged seawater. 87Sr/86Sr ratios of bulk carbonate are often slightly radiogenic, probably due to random analytical sample contamination by clay minerals. Belemnite and some matrix 87Sr/86Sr is slightly lower than that of Kimmeridgian seawater, either caused by basin restriction or by fluids derived from the diagenesis of Oxfordian rocks below. An equivalent Upper Kimmeridgian depression ~23 km distant and a somewhat younger Konservat-Lagerstätte in Poland show a δ13C isotope anomaly below the main fossil beds. Isotopic evidence for saline bottom waters, the current interpretation, is lacking. This study also shows that micritic carbonates can preserve their early diagenetic, marine δ18O signal, which is correlatable over tens of kilometres

8

Charakterystyka litofacjalna utworów jury górnej i kredy dolnej w rejonie Dąbrowa Tarnowska – Dębica w oparciu o interpretację danych sejsmicznych i otworowych

Urbaniec Andrzej

Prace Naukowe Instytutu Nafty i Gazu

|

2021

|

nr 232

1--240

PL

Głównym celem monografii jest odtworzenie historii depozycji i rozwoju facjalnego utworów górnej jury i dolnej kredy, występujących w podłożu zapadliska przedkarpackiego, w oparciu o dostępne dane z otworów wiertniczych oraz sejsmikę 3D. Rejon badań usytuowany jest w środkowej części przedgórza Karpat, pomiędzy miastami Dąbrowa Tarnowska na północnym zachodzie i Dębica na południowym wschodzie. Nowe dane, uzyskane w roku 2015, w postaci zdjęcia sejsmicznego 3D, jak również informacji z głębokiego otworu O-1 przewiercającego pełen profil utworów mezozoiku, pozwoliły na znacznie lepsze rozpoznanie i udokumentowanie wielu szczegółów budowy geologicznej tego, dotąd słabo rozpoznanego, rejonu. Sedymentacja badanych utworów węglanowych przedgórza Karpat w epokach późnojurajskiej i wczesnokredowej odbywała się w strefie szelfowej północnego, pasywnego brzegu oceanu Tetydy. Cechą charakterystyczną utworów górnej jury jest ich duże zróżnicowanie facjalne, wynikające głównie z obecności rozbudowanych kompleksów biohermowych oraz pakietów warstwowanych osadów marglisto-wapiennych. W rozdziale 2 przedstawiono budowę geologiczną rejonu badań, uwzględniając wszystkie piętra strukturalne, rozwój litologiczny utworów poszczególnych jednostek, stosowane podziały litostratygraficzne i regionalne ramy paleogeograficzne. W rozdziale 3 szczegółowo omówiona została historia badań oraz aktualny stan rozpoznania kompleksu węglanowego górnej jury i dolnej kredy przedgórza Karpat. Rozdział 4 zawiera charakterystykę litologiczną badanych utworów węglanowych z podziałem na jednostki litostratygraficzne. Charakterystyka ta opracowana została na podstawie analizy cech makroskopowych dostępnego materiału rdzeniowego oraz profilowań geofizyki otworowej. Zamieszczone profile litostratygraficzne wybranych głębokich otworów wiertniczych z obszaru badań lub jego bliskiego sąsiedztwa dokumentują obecny stan wiedzy na temat litostratygrafii i rozwoju facjalnego utworów górnej jury i dolnej kredy. W rozdziale 5 przedstawiono charakterystykę mikrofacjalną i mikropaleontologiczną badanych utworów węglanowych, jak również przeprowadzono dyskusję dotyczącą możliwości określenia zasięgu wiekowego poszczególnych wydzieleń litostratygraficznych w oparciu o wyniki wieloletnich badań oraz dane literaturowe. W rozdziale 6 zaprezentowano wyniki analizy obrazu sejsmicznego, wykonanej w oparciu o wybrane atrybuty sejsmiczne. W ramach pracy omówiono następujące atrybuty: RMS Amplitude, Envelope, Instantaneous phase, Dominant frequency, Instantaneous bandwidth, Apparent polarity, Relative acoustic impedance, First derivative, Iso-frequency component, Time gain, Chaos, Variance (Edge method), Local flatness. Przeprowadzona analiza pozwoliła na uzyskanie dodatkowych istotnych informacji odnośnie wykształcenia litologicznego i rozprzestrzenienia utworów poszczególnych ogniw litostratygraficznych, jak również dała możliwość uszczegółowienia lokalizacji dyslokacji. Na podstawie interpretacji zapisu sejsmicznego w obrębie badanego kompleksu skalnego udokumentowano również występowanie niezgodności kątowych, stref zaburzeń i deformacji związanych z tektoniką synsedymentacyjną oraz przypuszczalnych osadów spływów grawitacyjnych. W rozdziale 7 zamieszczono przekroje litofacjalne, skonstruowane wzdłuż wybranych przekrojów sejsmicznych, prezentujące przestrzenny rozkład i wzajemne relacje pomiędzy utworami poszczególnych ogniw litostratygaficzych. W rozdziale 8 przeanalizowano rozmieszczenie kompleksów biohermowych górnej jury względem morfologii podłoża jury. Analiza rozmieszczenia wykartowanych na podstawie zapisu sejsmicznego budowli organicznych, należących do serii wielkich bioherm gąbkowo-mikrobialnych, wskazuje na dwa główne obszary ich występowania, tj. rejon NW (kompleks biohermowy „N”), w którym występuje dosyć rozległy kompleks biohermowy, a jego dokładny zasięg jest trudny do ustalenia ze względu na późniejsze procesy regionalnej dolomityzacji oraz rejon centralny (kompleks biohermowy „S” w okolicach otworu O-1), w którym stwierdzono kompleks kilku wysokich budowli o dosyć stromych krawędziach. Rozdział 9 poświęcony jest zagadnieniu historii depozycyjnej późnojurajsko-wczesnokredowego basenu sedymentacyjnego przedgórza Karpat oraz omówieniu roli najważniejszych czynników wpływających na rozkład facji w obszarze badań. Wykazano, że cechą charakterystyczną znacznej części osadów jurajskich jest silnie diachroniczny charakter rozprzestrzenienia poszczególnych facji, uwarunkowany głównie paleogeomorfologią dna zbiornika sedymentacyjnego, jak również czynnikami lokalnymi, związanymi z tektoniką synsedymentacyjną. Seria gąbkowo-globuligerinowa, rozpoczynająca profil utworów górnej jury i reprezentująca najgłębszy etap sedymentacji w warunkach otwartego szelfu, cechuje się stosunkowo dużą jednorodnością wykształcenia na całym obszarze przedgórza. Kompleks biohermowy „S” rozwinął się w nadkładzie elewowanej strefy, złożonej z kilku mniejszych elementów tektonicznych, natomiast kompleks biohermowy „N” wykształcił się na rozległej, wyniesionej części strefy zrębowej, gdzie w podłożu występuje jeden główny blok tektoniczny. Intensywnie rozwijające się kompleksy biohermowe „N” i „S” wywierały coraz większy wpływ na dalszy rozwój sedymentacji osadów górnej jury w badanym rejonie, dostarczając jednocześnie materiału dla osadów redeponowanych w głębsze partie zbiornika w wyniku podmorskich spływów grawitacyjnych. W strefie przylegającej od SE do kompleksu biohermowego „S”, na profilach sejsmicznych dostrzegalny jest charakterystyczny, wysokoamplitudowy zapis obejmujący cały pakiet refleksów sejsmicznych o zmiennych kątach upadów. Częste zmiany polarności, dostrzegalne w obrębie tej strefy w odtworzeniu atrybutu Apparent polarity, podobnie jak i skrajnie zmienny zakres wartości atrybutu Relative acoustic impedance, świadczą o silnym zróżnicowaniu litologicznym tego kompleksu skalnego. W tytonie, w trakcie sedymentacji utworów serii koralowcowo-onkolitowej, nastąpiło wyraźne ujednolicenie warunków sedymentacji na całym obszarze przedgórza Karpat, związane głównie z zanikiem paleomorfologicznego zróżnicowania powierzchni dna morza. Przypuszczalnie w tym samym czasie miał miejsce kolejny etap reaktywacji dyslokacji, o czym świadczy powierzchnia niezgodności kątowej, i związane z nią efekty erozji osadów starszych. Rozprzestrzenione na całym obszarze badań utwory serii muszlowcowo-oolitowej dolnej reprezentują różnego typu płytkowodne środowiska sedymentacji (w tym środowisko równi pływowej, lagunowe i stref barierowych), jakie wykształciły się na obszarze przedgórza Karpat, na pograniczu późnej jury i wczesnej kredy. Środowisko sedymentacji utworów serii marglisto-muszlowcowej, datowanej na berias, określić można jako skrajnie płytkowodne, z facjami lagunowymi i wpływem środowisk brakicznych. Utwory najwyższych serii dolnej kredy (tj. mułowcowo-wapiennej i muszlowcowo-oolitowej górnej) reprezentują facje płytkomorskie związane z transgresją morską, która miała miejsce w walanżynie. Przedstawiona historia depozycyjna późnojurajsko-wczesnokredowego basenu sedymentacyjnego przedgórza Karpat, w połączeniu z opisem cech makroskopowych rdzeni wiertniczych, analizą mikrofacjalną i mikropaleontologiczną poszczególnych jednostek litostratygraficznych oraz interpretacją obrazu sejsmicznego, pozwala na kompleksową charakterystykę analizowanych utworów oraz wskazanie procesów mających największy wpływ na obecny charakter i stan zachowania badanych serii skalnych.

EN

The main subject of this monograph is a reconstruction of the history of deposition and facial development of Upper Jurassic and Lower Cretaceous deposits in the basement of the Carpathian Foredeep, based on data available from boreholes and a 3D seismic survey. The research area is located in the central part of the Carpathian Foreland, between two cities: Dąbrowa Tarnowska in the north-west and Dębica in the south-east. The new 3D seismic survey made in 2015 and the O-1 deep borehole – drilled in the same year and portraying a full profile of the Mesozoic sediments – allowed for much better recognition and documentation of many details of the geological structure of this previously poorly mapped area. The sedimentation of the carbonate formations of the Carpathian Foreland during the Late Jurassic and the Early Cretaceous took place in the shelf zone of the northern, passive margin of the Tethys Ocean. A characteristic feature of the Upper Jurassic sediments is their high facies diversity, due mainly to the presence of biohermal complexes and sets of layered marly-limestone sediments. Chapter 2 presents the geological structure of all structural stages in the area under study, including the lithological development, the lithostratigraphic divisions applied, and the regional palaeogeographic frameworks. Chapter 3 discusses both the history of research and the current state of knowledge regarding the Upper Jurassic and Lower Cretaceous carbonate sediments of the Carpathian Foreland. Chapter 4 describes the lithological characteristics of the carbonate sediments, considering lithostratigraphic units. This characterisation is based on a macroscopic examination of the available core material and analysis of the well logs. The lithostratigraphic profiles of selected deeper boreholes from the research area and its close vicinity document the current state of knowledge on lithostratigraphy and the facies development of the Upper Jurassic and Lower Cretaceous deposits. Chapter 5 features the microfacies and micropalaeontological characteristics of the carbonate sediments under study. Based on the results of many years of research and literature data, the possibilities of determining the age of every lithostratigraphic unit are discussed. Chapter 6 presents the analysis of the seismic 3D image based on selected seismic attributes. As part of the work, the following attributes are discussed: RMS Amplitude, Envelope, Instantaneous phase, Dominant frequency, Instantaneous bandwidth, Apparent polarity, Relative acoustic impedance, First derivative, Iso-frequency component, Time gain, Chaos, Variance (Edge method), and Local flatness. The analysis revealed additional important information regarding both the lithological development and the spatial range of sediments of individual lithostratigraphic units, at the same time facilitating the detailed location of fault zones. Based on the interpretation of the seismic image within the studied rock complex, the occurrence of angular unconformity, disturbance, and deformation zones related to synsedimentary tectonic as well as probable gravity-flow deposits are also documented. Chapter 7 presents lithofacial cross-sections constructed along selected seismic sections reflecting the spatial distribution and relationships between the sediments of individual lithostratigraphic units. Chapter 8 analyses the distribution of Upper Jurassic biohermal complexes in relation to the morphology of the Jurassic base surface. An analysis of the distribution of organic buildups belonging to the Huge Sponge-Microbial Bioherms Series, interpreted indirectly from seismic image, indicates two main areas where they can be found. These are the north-west part of the study area – where a quite extensive biohermal complex occurs (‘Complex N’), the exact range of which is difficult to determine due to later regional dolomitisation processes – and the area located in the central part of the seismic survey, where a complex of several very tall buildups with steep edges was found (‘Complex S’). Chapter 9 is devoted to the issue of the depositional history of the Late Jurassic–Early Cretaceous sedimentary basin of the Carpathian Foreland and to a discussion of the role of the most important factors influencing facies distribution in the research area. It has been shown that a characteristic feature of a large part of the Jurassic sediments is the strongly diachronic nature of the distribution of facies controlled by the varying bottom relief of the sedimentation basin and by some local factors related to synsedimentary tectonic episodes. The Sponge-Globuligerinid Series, beginning the profile of the Upper Jurassic sediments and representing the deepest sedimentation stage in the open shelf conditions, is characterised by a relatively high homogeneity of lithology in the whole Carpathian Foreland area. The ‘S’ biohermal complex developed over the elevated zone composed of several smaller tectonic elements, whilst the ‘N’ biohermal complex developed on a large, elevated part of the horst zone. The intensively developing ‘N’ and ‘S’ biohermal complexes affected successive deposition of the Late Jurassic sedimentary basin in the study area more and more. Those biohermal complexes were the source of the material redeposited into deeper parts of the sedimentary basin. On seismic profiles in the south-east neighbourhood of the ‘S’ biohermal complex, there is a characteristic high-amplitude record including the entire reflection set of variable dip angles. The frequent polarity changes which are visible within this zone in the Apparent polarity attribute, as well as the extremely variable range of values the Relative acoustic impedance attribute, prove the strong lithological differentiation of this rock complex. During the Tithonian time (sedimentation of the Coral-Oncolite Series), there was clear unification of the sedimentation conditions in the entire Carpathian Foreland area, mainly due to disappearance of the bottom relief diversity. At the same time another stage of dislocation reactivation occurred, as evidenced by the angular unconformity and the erosion traces of older sediments associated with this unconformity. The deposits of the Lower Shellbed-Oolite Series scattered throughout the research area represent various types of shallow-water sedimentation environments (including tidal, lagoon, and barrier zones) that developed in the Carpathian Foreland area on the borderline between the Late Jurassic and the Early Cretaceous. The sedimentation environment of the Marly-Shellbed Series dated to the Berriasian can be described as extremely shallow-water, with lagoon facies and under the influence of brackish environments. The sediments of the last two series of the Lower Cretaceous (i.e. the Mudstone-Limestone and Upper Shellbed-Oolite Series) represent the shallow-marine facies associated with marine transgression that took place during the Valanginian. The processes that have had the greatest impact on the current character and preservation of the rock series under study can be pinpointed and a comprehensive characterisation of these formations can be undertaken thanks to the depositional history of the Late Jurassic – Early Cretaceous sedimentary basin of the Carpathian Foreland presented herein, the macroscopic examination of the available core material, the microfacial and micropalaeontological analysis of individual lithostratigraphic units, and the interpretation of the seismic image.

9

Early and Middle Jurassic tectonically controlled deposition in the High-Tatric succession (Tatricum), Tatra Mountains, southern Poland : a review

Łuczyński Piotr

Geological Quarterly

|

2021

|

Vol. 65, No. 1

art. no. 16

EN

The High-Tatric succession of the Tatra Mountains represents the Tatricum domain of the Central Western Carpathians, which in the Jurassic was located on the southern margin of the incipient and expanding Vahic Ocean – a branch of Western Tethys. This paper describes the various depositional consequences of extensional tectonic activity as it impacted on sedimentation in the High-Tatric succession of the Tatra Mountains during the Early and Middle Jurassic. Evidence of such impacts on depositional style and facies development are present within the Dudziniec, Smolegowa and Krupianka formations, in all the High-Tatric tectonic units. These impacts also include erosional surfaces and sedimentary gaps separating particular formations, commonly associated with minor angular unconformities. The Lower Jurassic, pre-Bajocian, Dudziniec Formation of the Kominy Tylkowe (autochthonous) Unit is developed in mixed carbonate-clastic facies. The occurrence and proportion of sand-dominated and carbonate-dominated facies, as well as their thickness differences, were controlled by syndepositional tilt-block tectonics, taking place both in depositional and in neighbouring source areas. The Smolegowa and Krupianka formations (Bajocian-Bathonian) occur in all High-Tatric tectonic units, but in the Czerwone Wierchy and Giewont units they are represented mainly by laterally discontinuous bodies of crinoidal limestone of very limited thickness. The preservation of these deposits only in some areas, as well as their thickness reductions, are effects of differentiated subsidence and uplift of isolated blocks taking place in an extensional regime. Moreover, the Krupianka Formation abounds in condensed facies with ferruginous crusts and stromatolites – a feature characteristic of rapidly drowning ocean margins. Deposits of the Dudziniec, Smolegowa and Krupianka formations are also preserved as infills of extensive systems of neptunian dykes penetrating mainly the Triassic substrate, which is yet another classic symptom of synsedimentary extension. The dominant influence of tectonics on sedimentary development ceased with the onset of deposition of the Raptawicka Turnia Formation in the Callovian.

10

Structure of the calcitic layer of the aptychus of the ammonite genus Peltoceras

Mironenko Aleksandr A.

Annales Societatis Geologorum Poloniae

|

2021

|

Vol. 91, No. 4

397--404

EN

The aptychi of ammonites combined the functions of lower jaws and protective opercula. They consist of two parts: an inner organic layer and an outer calcitic lamella. In different evolutionary lineages of ammonites, the shape of aptychi, the sculpture of their surface and the microstructure of the calcitic layer vary greatly. However, the structure of the aptychi is not known for all evolutionary lineages of ammonites. Although numerous aptychi have been described for the Jurassic family Aspidoceratidae, almost all of them belong to only one evolutionary branch of this family – the Aspidoceratinae (sensu lato). For the second branch – the Peltoceratinae, only one aptychus had been described to date and the structure of its calcitic layer remained unknown. In this article, for the first time, the structure of the aptychus of the Peltoceratinae (upper Callovian Peltoceras) is described. The surface of this aptychus is covered with rough ribs and the calcitic part consists of only one layer of dense calcite. The thickness of the aptychus is much greater than that of the aptychi of supposed ancestors of the Peltoceratinae. The increase in the thickness of the aptychi in both the Aspidoceratinae and the Peltoceratinae, contemporaneously with the appearance of spines on their shells, is most likely related to increasing the protective function of the aptychi of these ammonites in the late Callovian.

11

New dimorphic species of the genus Rollierites Jeannet from southern Poland

Jain Sreepat, Mazur Marek

Annales Societatis Geologorum Poloniae

|

2021

|

Vol. 91, No. 4

405--418

EN

A new ammonite assemblage from the lower beds of the Ogrodzieniec Quarry (southern Poland), the only Callovian section in the middle part of the Polish Jura Chain, is described. It includes the presence of Kosmoceras rotundum (Quenstedt), followed by the first example of co-occurring micro- and macroconchs in the genus Rollierites (R. biplicatum sp. n.) and above it, the association of Euaspidoceras sp. and Peltoceratoides (Parawedekindia) gerberi Prieser. Both R. biplicatum sp. n. (m and M; microconch and macroconch) and K. rotundum are assigned to the late Callovian Lamberti Zone. P. (P.) gerberi characterizes the early Oxfordian Cordatum Zone. This is the first record of the genus Rollierites from Poland. This study extends the upper age limit of the middle Callovian Rollierites up to the late Callovian Lamberti Zone. On the basis of morphological and stratigraphical data, it is tentatively proposed that the origin of the early–middle Oxfordian Tornquistes may be in the middle–late Callovian Rollierites, rather than the previously proposed late Callovian Pachyceras. However, this is speculation, as the present data set is insufficient.

12

Callovian and Kimmeridgian fossils and stratigraphy of the Blue Nile Basin (central western Ethiopia)

Jain Sreepat, Schmerold Roland

Annales Societatis Geologorum Poloniae

|

2021

|

Vol. 91, No. 3

287--307

EN

A refined, stratigraphic and biostratigraphic framework for Ethiopia has a strong bearing on the Jurassic sedimentary evolution, not only for the Horn of Africa, but also for the North African region. The present contribution provides an updated Callovian-Kimmeridgian stratigraphy and biostratigraphy, on the basis of the occurrences of age-diagnostic ammonites from Dejen (Blue Nile Basin; central western Ethiopia). Here, the late Callovian (Lamberti Zone) ammonite Pachyceras cf. lalandeanum (d'Orbigny) is associated with the nautiloid Paracenoceras cf. giganteum (d'Orbigny). The early Kimmeridgian Orthosphinctes aff. tiziani (Oppel) is associated with the nautiloids Paracenoceras cf. kumagunense (Waagen) and P. cf. ennianus (Dacqué) and a large gastropod Purpuroidea gigas (Étallon). The previously recorded middle Callovian ammonite Erymnoceras cf. coronatum (Bruguiere) is associated with the now recorded P. gigas (Étallon). Additionally, the age of the Antalo Limestone Fm is also reassessed on the basis of the ammonite records from the three basins - Ogaden, Blue Nile and Mekele. The Ogaden Basin strata span from the late Callovian to the late Tithonian (from ammonite records), the Blue Nile Basin from the early Callovian to the late Tithonian (calcareous nannofossils) and the Mekele Basin from the uppermost middle Oxfordian to the early Kimmeridgian (ammonite records). However, the upper age assignments should be considered tentative, as much of the previously recorded Oxfordian-Kimmeridgian ammonite fauna needs taxonomic re-evaluation and precise resampling. Contextually, it should be mentioned that in all the three sedimentary basins, the top part of the Antalo Limestone Fm did not yield any ammonites.

13

A lost carbonate platform deciphered from clasts embedded in flysch : Štramberk-type limestones, Polish Outer Carpathians

Hoffmann Mariusz, Kołodziej Bogusław, Kowal-Kasprzyk Justyna

Annales Societatis Geologorum Poloniae

|

2021

|

Vol. 91, No. 3

203--251

EN

Limestones designated the Štramberk-type are the most common carbonate exotic clasts (exotics) embedded in the uppermost Jurassic–Miocene flysch deposits of the Polish Outer Carpathians. About 80% of stratigraphically determinable carbonate exotics from the Silesian, Sub-Silesian and Skole units (nappes) are of Tithonian (mostly)–Berriasian (sporadically Valanginian) age. A study of these exotics revealed eight main facies types: coral-microbial boundstones (FT 1), microencruster-microbial-cement boundstones (FT 2), microbial and microbial-sponge boundstones (FT 3), detrital limestones (FT 4), foraminiferal-algal limestones (FT 5), peloidalbioclastic limestones (FT 6), ooid grainstones (FT 7), and mudstones-wackestones with calpionellids (FT 8). Štramberk-type limestones in Poland and the better known Štramberk Limestone in the Czech Republic are remnants of lost carbonate platforms, collectively designated the Štramberk Carbonate Platform. Narrow platforms were developed on intra-basinal, structural highs (some of them are generalized as the Silesian Ridge), with their morphology determined by Late Jurassic synsedimentary tectonics. An attempt was made to reconstruct the facies distribution on the Tithonian–earliest Cretaceous carbonate platform. In the inner platform, coral-microbial patch-reefs (FT 1) grew, while the upper slope of the platform was the depositional setting for the microencruster-microbial-cement boundstones (FT 2). Microbial and microbial-sponge boundstones (FT 3), analogous to the Oxfordian–Kimmeridgian boundstones of the northern Tethyan shelf (also present among exotics), were developed in a deeper setting. In the inner, open part of the platform, foraminiferal-algal limestones (FT 5) and peloidal-bioclastic limestones (FT 6) were deposited. Poorly sorted, detrital limestones (FT 4), including clastsupported breccias, were formed mainly in a peri-reefal environment and on the margin of the platform, in a high-energy setting. Ooid grainstones (FT 7), rarely represented in the exotics, were formed on the platform margin. Mudstones-wackestones with calpionellids (FT 8) were deposited in a deeper part of the platform slope and/or in a basinal setting. In tectonic grabens, between ridges with attached carbonate platforms, sedimentation of the pelagic (analogous to FT 8) and allodapic (“pre-flysch”) Cieszyn Limestone Formation took place. The most common facies are FT 4 and FT 1. Sedimentation on the Štramberk Carbonate Platform terminated in the earliest Cretaceous, when the platform was destroyed and drowned. It is recorded in a few exotics as thin, neptunian dykes (and large dykes in the Štramberk Limestone), filled with dark, deep-water limestones. Reefal facies of the Štramberk Carbonate Platform share similarities in several respects (e.g., the presence of the microencrustermicrobial-cement boundstones) with reefs of other intra-Tethyan carbonate platforms, but clearly differ from palaeogeographically close reefs and coral-bearing facies of the epicontinental Tethyan shelf (e.g., coeval limestones from the subsurface of the Carpathian Foredeep and the Lublin Upland in Poland; the Ernstbrunn Limestone in Austria and Czech Republic). Corals in the Štramberk Limestone and Štramberk-type limestones are the world’s most diverse coral assemblages of the Jurassic–Cretaceous transition. The intra-basinal ridge (ridges), traditionally called the Silesian Cordillera, which evolved through time from an emerged part of the Upper Silesian Massif to an accretionary prism, formed the most important provenance area for carbonate exotic clasts in the flysch of the Silesian Series. They are especially common in the Lower Cretaceous Hradiště Formation and the Upper Cretaceous–Paleocene Istebna Formation. The Baška-Inwałd Ridge and the Sub-Silesian Ridge were the source areas for clasts from the Silesian and Sub-Silesian units (e.g., in the Hradiště Formation), while the Northern (Marginal) Ridge was the source for clasts from the Skole Unit (e.g., in the Maastrichtian–Paleocene Ropianka Formation).

14

Evidence that the fossil insect trackway Bifurculapes laqueatus Hitchcock, 1858 was made underwater

Getty Patrick R.

Acta Geologica Polonica

|

2020

|

Vol. 70, no. 1

125--133

EN

Three trackways attributable to the ichnospecies Bifurculapes laqueatus Hitchcock, 1858 found in Lower Jurassic rocks of the Newark Supergroup in northeastern North America are preserved in association with current lineations. Each trackway takes turns so that parts of the trackway parallel the current lineations. This parallelism is interpreted as evidence that the trackmakers were entrained in flowing water and had to change course due to the current. If this interpretation is correct, then morphological differences between B. laqueatus and terrestrial insect trackways could be explained by the trackmaker moving subaqueously. Further, B. laqueatus would constitute only the second insect trackway from this region to be recognized as being made subaqueously. From an ecological standpoint, the aquatic insects that made B. laqueatus were probably near the base of the local food chain, the apex predators of which were piscivorous theropod dinosaurs.

15

An experimental study of selected Jurassic carbonate samples from north-eastern Tunisia

Dhahri Rima, Ezzine Ines, Ghanmi Mohammed

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

|

2019

|

Vol. 28, No. 4

547--556

EN

The industrial development of the outcrops in the Tunis-Zaghouane area could represent an important economic driver for the country. The main structures are introduced and illustrated with onsite field observations. Moreover, samples which were extracted from the selected regions and are characterized based on measurements of porosity, water absorption and abrasion loss coefficients. The experimental results showed a negligible variation of densities, demonstrated a linear correlation between connected porosity and overall water absorption. In addition, experimental result confirms that outcrops from Jebel Zaghouane, Jebel Hammam Zriba and Jebel Hammam Jedidi could be developed as construction materials.

16

Bajocian transgressive-regressive sequences of the Tecocoyunca Group, southern Mexico, with maximum flooding surfaces marked by Thalassinoides

Pieńkowski Grzegorz, Martini Michelangelo, Zepeda-Martínez Mildred

Geological Quarterly

|

2019

|

Vol. 63, No. 3

449--459

EN

Bajocian (Middle Jurassic) transgressive-regressive sequences (TRS), outcropping in the Rosario Nuevo Creek (Tezoatlán Basin, Tecocoyunca Group) in Oaxaca State, Mexico, represent one of the Jurassic phases of opening and widening of a trans-Pangaean marine corridor (called also the Hispanic Corridor) and show a retrogradational-progradational set of sedimentary successions with decipherable and diverse facies. Two TRSs have been distinguished. The lower one starts with fluvio-deltaic sandstones including pedogenic horizons. Drowning of the deltaic plain and gradual rising of the water table is marked by change in vegetation: from large trees to low-rise vegetation with characteristic clumps of dense roots cemented by siderite. The delta plain succession is topped by a thin coal seam, followed by a transgressive surface. Ensuing laminated mudstones of restricted marine origin pass into open marine deposits, represented by bioturbated heterolithic strata with ammonites followed by nearshore sandstones, deposited in a storm-dominated basin. A similar succession, although without the deltaic part, is repeated in the next TRS. Of note are two thin (15-20 cm) continuous beds with Thalassinoides isp. networks, present within open marine deposits. Although large Thalassinoides networks are mostly known from shallow-marine and coastal environments, the case from Mexico represents less common occurrences from a deeper marine (offshore) setting, associated with maximum flooding surfaces, sediment starvation and firmgrounds (Glossifungites ichnofacies). Occurrences of Thalassinoides meshes, precisely marking maximum flooding surfaces, are helpful in defining the hierarchy of sequence stratigraphic cycles.

17

Nowe odkrycie w krach mezozoicznych w okolicach Łukowa i jego znaczenie dla promocji geoturystycznej regionu

Wierzbowski A., Świder M., Krzeczyńska M., Szczygieł W.

Przegląd Geologiczny

|

2018

|

Vol. 66, nr 11

706--712

EN

An excavation dug out in the glacially transported rock masses at Golaszyn near Łuków (eastern Poland), revealed the presence of deposits unknown so far in this area. These are older than the only known so far here glacially transported clays containing concretions with splendidly preserved ammonites of late Callovian at Łapiguz brickyard of Łuków. The succession exposed consists of sands and sandstones of Middle Callovian age which rest on red-brownish clays. The latter may be compared with the Triassic - Buntsandstein deposits of the northwestern Lithuania, that is the home area of glacially transported rock masses, commonly occurring in eastern Poland in the Łuków area. The new geological discoveries markedly increase a set of attractions for the promotion of the Łuków region for the education and geotourism purposes.

18

New palynological data for Toarcian (Lower Jurassic) deep-marine sandstones of the Western Caucasus, southwestern Russia

Goryacheva A. A., Zorina S. O., Ruban D. A., Eskin A. A., Nikashin K. I., Galiullin B. M., Morozov V. P., Mikhailenko A. V., Nazarenko O. V., Zayats P. P.

Geologos

|

2018

|

Vol. 24, No. 2

127--136

EN

Information on Jurassic palynomorphs from the Greater Caucasus is potentially of great importance, but its availability to the international research community is severely limited. New palynological data for Toarcian deposits of the Western Caucasus are recorded in the present paper. Particularly, dinoflagellate cysts are described for the first time from the Bagovskaja Formation; palynomorphs are found in sandstone levels within this unit. The most representative assemblage includes pollen (with predominant bisaccate pollen), spores (Cyathidites being commonest), and dinoflagellate cysts amongst which the predominant taxon is Nannoceratopsis spiculata. The dinocyst assemblage implies a late Toarcian age for the upper part of the Bagovskaja Formation. On the basis of these new palynostratigraphical results, the range of the formation is extended; previously, only the lower part had been dated on ammonite evidence.

19

Crinoids (Crinoidea, Echinodermata) from the Middle Jurassic (Callovian) of eastern Poland : a case study from the Żebrak IG 1 borehole

Salamon M. A., Feldman-Olszewska A.

Annales Societatis Geologorum Poloniae

|

2018

|

Vol. 88, No. 3

273--283

EN

A taxonomic account of the Callovian crinoid fauna from the Żebrak IG 1 borehole (eastern Poland) is presented. The assemblage contains numerous isocrinid ossicles (Isocrinidae) assigned to the following taxa: Isocrinus cf. nicoleti (Desor), Isocrinus sp., Chariocrinus andreae (Desor), Balanocrinus cf. subteres (Münster in Goldfuss) and Pentacrinites sp. These isocrinids are associated with a few ossicles of cyrtocrinids (Cyrtocrinida; Cyrtocrinida indet.). The crinoid remains are poorly preserved; they all are isolated ossicles, showing broken margins and/or abraded surfaces. Such a state of preservation documents a long distance of transportation and/or re-deposition in a high-energy, shallow-water setting. The crinoid assemblage differs significantly from those of southern Poland (the Polish Jura Chain and the Mesozoic margin of the Holy Cross Mountains), in which sessile crinoids, such as cyrtocrinids (Cyrtocrinida), inhabiting mostly deeper-water carbonate facies, are predominant.

20

Pinnidae (Bivalvia) from the Reuchenette Formation (Kimmeridgian, Upper Jurassic) of northwestern Switzerland

Koppka J.

Acta Geologica Polonica

|

2018

|

Vol. 68, no. 1

21--51

EN

The shallow-marine carbonate deposits of the Reuchenette Formation (Kimmeridgian, Upper Jurassic) in northwestern Switzerland and adjacent France yield highly diverse bivalve associations, but only rarely contain remains of pinnid bivalves. The three occurring taxa Pinna (Cyrtopinna) socialis d’Orbigny, 1850, Stegoconcha granulata (J. Sowerby, 1822) and Stegoconcha obliquata (Deshayes, 1839) have been revised. A lectotype for Pinna (C.) socialis was designated and the taxon is assigned herein to P. (Cyrtopinna) Mörch, 1853, the first record of the subgenus from the Jurassic. A brief review of Stegoconcha Böhm, 1907 revealed two species groups within the genus. Species close to the type species S. granulata are characterized by a nearly smooth anterior shell, followed posteriorly by deep radial furrows and rows of pustules covering the dorsal flank. Another group comprises radially ribbed species related to S. neptuni (Goldfuss, 1837). It includes among others the Paleogene species S. faxensis (Ravn, 1902), extending the known range of Stegoconcha from the Middle Jurassic into the Paleogene. The paper suggests a relationship between Stegoconcha and the Cretaceous Plesiopinna Amano, 1956, with S. obliquata as a possible intermediate species leading to Plesiopinna during the Early Cretaceous. Furthermore, a possible relationship between Stegoconcha and Atrina Gray, 1842 is discussed.