Lithostratigraphy and depositional environments of the upper cretaceous deposits in the central Taurides (S Turkey)

The study area is located in the Central Taurides (southern Turkey), which is bounded by the K?rkkavak fault to the west and Ecemi? fault to the east. The sequences are studied in detail based on measured sections composed of the rocks deposited during the Cenomanian–Maastrichtian and located within different tectonic units previously described in the Taurides. The study materials include 217 thin section data from seven Cenomanian–Maastrichtian sequences of outcropping in different parts of the Central Taurides. The sediments deposited during the Cenomanian–Maastrichtian period in the Central Taurides are subdivided into eight units based on their lithological, paleontological, and textural properties. The lower boundaries of the upper Santonian and Campanian are unconformable contacts. The Upper Cretaceous sequence starts with the middle Cenomanian and represents a continuation of the Lower Cretaceous tidal flat and shelf lagoon sequence. Upper Turonian–Coniacian sediments are not observed due to the eustatic sea level drop. The second main transgression period of the Upper Cretaceous platform took place in the Santonian. This unit is represented by limestones composed of wackestones/packstones containing benthic foraminifera and rudist fragments, which are deposited in tidal flats and subtidal environments. The late Campanian starts with a transgression, and the environment transformed transitions into slope facies from inner platform facies, as a result of the thrust of ophiolitic rocks. In the following period, slope front and basin plain environments were dominant due to the increasing slope. Slumped pelagic limestones were deposited on the slope. Planktonic foraminiferal pelagic limestones were unconformably deposited on plaque limestone in the slope front environment depending on the increase in slope gradient and local faulting. As a result of decreasing tectonic activity, the sediments were deposited onto a stable basin plain. They were initially fed from the nearby carbonate platform and then by siliciclastic turbidites derived from the thrusted ophiolitic rocks. In this study, the lithostratigraphic properties of the Cenomanian–Maastrichtian units outcropping in various parts of the Central Taurides are described. The sedimentary deposits described here suggest different basinal conditions in the region.     

The Cenomanian–Turonian boundary on the Saharan Platform (Tunisia and Algeria)

Several transects made of correlated stratigraphic sections and well logs have been constructed spanning southern Tunisia and the Algerian Sahara (Tinrhert) for comparison with earlier results obtained in the Saharan Atlas. The study is based on facies analysis, sedimentology, biostratigraphy focused on ammonites and foraminifers) as well as whole rock geochemistry (δ¹³C). These suggest that the entire northern Sahara Platform underwent marine flooding that commenced just prior to the onset of the global positive δ¹³C shift documented for the Cenomanian–Turonian boundary. This flooding occurred in two phases. The first phase is expressed by the deposition of deeper-water, light-coloured bioturbated mudstones overlying the shallow-water deposits comprising the local Cenomanian successions. But in some places in the Central Sahara (Hassi Messaoud area, Tihemboka Arch) as well as in the Saharan Atlas, shallow-water carbonates kept up locally with the relative sea-level rise to build up isolated carbonate platforms. The topographic lows or saddles between these areas could have been formed through differential accumulation rates. During the second phase, flooding resumed and black shales were deposited over the mudstones in the saddles. The occurrence of black shales in these saddles is limited to the northern edge of the platform (Saharan Atlas of Algeria, Gafsa Trough in southern Tunisia). On the platform, this phase is represented by the same kind of mudstones deposited during the first phase of the flooding (southern Tunisia), or by ammonite-rich chalks in the intra-cratonic basin of the Tinrhert (southern Algeria). Black-shale deposition ceased in the early Turonian. Based on the δ¹³C curve, the latest Cenomanian flooding of the Sahara Platform is roughly coeval with that documented for the US Western Interior.During the first phase of the transgression, that is before the occurrence of the large Whiteinella of the W. archeocretacea Zone in the black shale unit, planktic foraminifers are dominated by small globulose forms of the Hedbergella delrioensis type, associated with Heterohelicidae. Keeled forms (rotaliporids, dicarinellids) are scarce and always very small when present. Perhaps these dwarfed forms were adapted to the restricted environments of the extensive intracratonic seaways crossing the Saharan Platform to the Benoué Trough in Nigeria.     

Chemostratigraphy of the Cenomanian-Turonian shallow-water carbonate: new correlation for the rudist levels from north Sinai,Egypt

The present study aims to provide carbon-isotope curves for the Cenomanian to Turonian rudist-dominated successions in north Sinai. The high-resolution carbon-isotope curves obtained from north Sinai sections provide new insight for calibrating the age of rudists as well as for evaluating the effects of the oceanic anoxic event 2 (OAE2) on rudist communities. The primary goals are (1) to provide a high-resolution sequence stratigraphic framework for the Cenomanian-Turonian succession, (2) to use rudist and ammonite biostratigraphic data to distinguish the stratigraphic levels of the rudist species, and (3) to integrate the chemostratigraphic (δ¹³C) profile and the rudist levels to improve the biostratigraphy based on the rudist distributions and the carbon-isotope data. The recognition of three ammonite zones through the Cenomanian-Turonian succession was utilized to identify four temporally significant rudist levels indicative of the Lower Cenomanian, Middle Cenomanian, Upper Cenomanian, and Middle Turonian, respectively. Most of the rudists occur in the highstand deposits of medium-scale sequences. Carbon- and oxygen-isotopic analyses were carried out on both rudists and surrounding carbonate units. Based on the variations in the carbon-isotope signals, 12 chronostratigraphic segments were identified in the studied sections. The Cenomanian carbon-isotope segments (C23–C30) were obtained from the Halal Formation at Gabal Yelleg and Gabal Maaza sections, while the Turonian segments (C30–C34) were measured from the Wata Formation at Gabal Yelleg section. The carbon-isotope record from the studied sections is consistent with the trends documented in previous studies of the Tethyan realm. The Cenomanian-Turonian boundary is placed at the onset of falling carbon-isotope values (δ¹³C) from 2.61 to ?0.25‰ in the upper part of OAE2 with the carbon-isotope segment C30 at Gabal Yelleg. The negative shift in δ¹³C values (C33) occurred in the Middle Turonian lowstand deposits characterizing the global sea level fall during this interval.     

ASD field hyperspectral measurements for discrimination of the ferruginous rocks and the iron ore types at El Gedida-Ghorabi area,Bahariya Oasis,Western Desert,Egypt

The ironstone succession at El Gedida-Ghorabi-Naser area of El Bahariya depression is subdivided into lagoonal manganiferous mud and fossiliferous ironstone consisting mainly of hematite and goethite-hydrogoethite. The application of the ASD field spectroradiometer measurements (spectral range) in the ASTER data led to the interpretation of the presence of ferruginous units as quartzitic sandstone, gluconitic sandy clay, and pink marly limestone. The existing iron ore minerals in the iron ore localities were also classified into high Mn hematite, low Mn hematite, goethite, hydrogoethite as well as low- and high-grade Hematite and Barite. Quartz, feldspars, rutile, and clay minerals (e.g., kaolinite and illite) are mainly associated with the iron ore. Accessory minerals of manganese, e.g., psilomelane and pyrolusite, were also present. The Barite mineral is recorded as a common mineral association with the iron ore deposits at El Gedida and Ghorabi localities. The stratigraphical units investigated in the study area include the oldest gravely clayey sandstones of the Bahariya Formation overlain by the fossiliferous and oolitic limestones of the El-Hamra, Qazzun, and Naqb Formations. Quartztic sandstones and clayey sandstones of the Radwan Formation and youngest Quaternary sediments of sandy-clayey materials were often found as intermittent cover and overburden in unconformity surfaces over the iron ore bands.     

The genesis, mineralization, and stratigraphic significance of phosphatic/glauconitic condensed limestone unit in the Manavgat Basin, SW Turkey

A condensed hemipelagic limestone unit with glauconite and phosphate separates a drowned Late Burdigalian carbonate platform from overlying Langhian pelagic mudstones, marls, and calcarenitic tempestites within the Neogene Manavgat Basin of southwestern Anatolia, Turkey. The unit consists of coeval lenticular limestone bodies, between 1 cm and 15 m in thickness, ranging from 10 m to 3 km in lateral extent. The P2O5 content of this limestone ranges from 0.2 to 10% by weight and the iron-oxide, clay, and other metal-oxide contents of this unit substantially exceed those of the underlying and overlying rocks.This condensed stratigraphic unit was deposited on the southwesterly outer shelf portions of drowned horsts that directly faced upwelling currents. The unit displays three main facies: 1) glauconitic phosphate crusts associated with hardgrounds; 2) bedded glauconitic-phosphatic limestones; and 3) glauconitic-phosphatic limestones interbedded with resedimented limestones. Facies (1) forms the thinnest units whereas facies (3) is the thickest, since the thickness and spatial distribution of this facies are related to environmental contrasts caused by block faulting of the underlying carbonate platform.This lithostratigraphic unit of hemipelagic glauconite–phosphate deposition represents an interval of maximum flooding in tectonically active situations and depositional hiatus on submarine highs that separate the carbonate transgressive systems tract from the overlying terigenic tempestite highstand systems tract. This appears to be the sole condensed unit within the Miocene Manavgat Basin; and is here ascribed to a third-order (2.3) eustatic rise in sea level comprising the maximum flooding of the first-order cycle. This is also the time for early–Mid Miocene major changes in Mediterranean climate from tropical to temperate.     

Radiolarians of the upper Cenomanian and lower Turonian from deposits of the Ananuri Formation, the western Caucasus (Lazarevskoe area)

Diverse radiolarians (over 70 species) are detected in cherty rocks above the bituminous shale horizon, the marker of anoxic event OAE-2 recorded across the Cenomanian-Turonian boundary in the upper part of the Ananuri Formation of flyschoid deposits, the Lazarevskoe area of the western Caucasus. The radiolarian assemblages studied are comparable in composition with radiolarians from concurrent Cenomanian-Turonian boundary strata in other Mediterranean regions (e.g., in the Crimea and Turkey). The lower radiolarian assemblage includes index species Dactyliosphaera silviae of synonymous Cenomanian zone. Alievium superbum present in the upper assemblage is index species of the relevant Turonian zone. Within the studied flyschoid sequence, sediments indicative of the above event (bituminous shales and cherts) are confined to upper elements of flysch rhythms.     

Siliciclastic deposit of the Nahr Umr Formation, sedimentological and depositional environment studies, central and southern Iraq

The depositional facies and environments were unraveling by studying 21 subsurface sections from ten oilfields in the central and southern Iraq and a large number of thin sections of the Nahr Umr (siliciclastic deposit) Formation (Albian). This formation is mainly composed of sandstone interlaminated with minor siltstone and shale, with occurrence of thin limestone beds. Nahr Umr Formation is subdivided into three lithostratigraphic units of variable thicknesses on the basis of lithological variations and log characters. Mineralogically and texturally, mature quartz arenite and sandstones are the common type of the Nahr Umr Formation. The sandstones are cemented by silica and calcite material and have had a complex digenetic history. Compaction, dissolution, and replacements are the main diagenetic processes. Prodelta, distal bar, distributary mouth bar, distributary channel, over bank, and tidal channel are the main depositional environments recognized for the Nahr Umr Formation, within the studied wells. This formation was deposited in shallow marine and fluvial–deltaic environments and exhibit progradational succession of facies. Eight sedimentary facies that have been identified in the Nahr Umr Formation include claystone lithofacies, claystone siltstone lithofacies, lenticular-bedded sandstone–mudstone lithofacies, wavy-bedded sandstone–mudstone lithofacies, flaser-bedded sandstone–mudstone lithofacies, parallel and cross lamination sandstone lithofacies, trough cross-bedded sandstone lithofacies, and planar cross-bedded sandstone lithofacies. The depositional model of the Nahr Umr Formation environment was built based on the lithofacies association concepts.     

Storm activities during the sedimentation of late Paleocene-middle Eocene Subathu Formation,western Himalayan foreland basin

Late Paleocene-middle Eocene Subathu Formation represents the earliest deposits of the western Himalayan foreland basin. A large part of this formation is comprised of impure limestone and grey shale intercalations. The limestones contain sole marks, intraformational conglomerates, hummocky cross stratification and wave ripples. The occurrence of sole marks suggests that they are developed by the unidirectional currents at the initial phase of the storm that resulted erosion and subsequent deposition. The intraformational limestone conglomearate also suggests erosion of the earlier deposited limestone hardgrounds as a consequence of storm associated transgression. The hummocky cross stratification formed by the oscillatory flows during the long-shore littoral drift. The depth of formation of the hummocky cross stratified limestone facies was less than 40 m and most likely deposited between shore-face to backshore regions of the gulf similar to present day Persian Gulf. The identification of deeper facies (shelf facies) from Pakistan and coastal facies from India suggest that the gulf was open from the west and closed from the east.     

Paleocirculation and foraminiferal assemblages of the Cenomanian–Turonian Bridge Creek Limestone bedding couplets: Productivity vs. dilution during OAE2

The limestone–marlstone (or limestone–calcareous shale) bedding couplets of the lower Bridge Creek Member of the Greenhorn Formation coincide with Oceanic Anoxic Event 2 and the Cenomanian–Turonian stage boundary at 93.9 Ma, and are characterized by fluctuations in microfossil and macrofossil biofacies, and organic carbon. Since G.K. Gilbert (1895), these strongly alternating lithofacies have been attributed to climate and/or productivity cycles. Heretofore, only the calcareous shale and marlstone parts of the Bridge Creek bedding couplets have been quantitatively analyzed for planktic and benthic foraminiferal assemblages. In this study, foraminiferal assemblages extracted from the hard limestone beds are comparable with the muddier lithologies thereby allowing a quantitative evaluation of the foraminiferal response to cyclically changing conditions in the U.S. Western Interior Sea (WIS) that resulted in the deposition of these lithologic couplets. The results reveal a modest cyclical response of foraminiferal assemblages extracted from limestone beds compared to adjacent calcareous shale or marlstone. These include the absence of planktic planispiral morphotypes (Globigerinelloides), increase in the proportion of planktic biserial and triserial morphotypes (Heterohelix and Guembelitria, respectively), and an increase in the proportion of benthics relative to total foraminifera (decrease in percent planktics) in the limestone beds. Such conditions suggest that the limestones may have been more productive than the adjacent shales and marlstones. Reduced surface salinity and greater stratification of the upper water column may have also contributed to the differences in assemblages preserved in the marlstones and calcareous shales. The onset of OAE 2 in the late Cenomanian is marked by an abrupt benthic oxygenation event (‘Benthonic Zone’) as Tethyan waters were drawn well north into the WIS, and cool Boreal waters spread across northwest Europe, known as the Plenus Cold Event. At this time, the WIS became an important ocean gateway for surface ocean circulation with rising sea level that helped facilitate the development and spread of OAE 2. A cyclonic (counterclockwise) gyre circulation in the WIS during deposition of the lower part of the Bridge Creek was driven by the difference between precipitation in the north and evaporation in the south. The gyre is represented by two modes, strong and weak, responsible for deposition of the limestone and marlstone, respectively. For the middle and upper parts of the studied section representing the plateau of OAE 2 and subsequent peak transgression of the WIS, the counterclockwise gyre was driven less by E-P gradient but by the amount of surface runoff from both margins of the WIS with deposition of limestone beds during the wetter (strong) phase and marlstones during the drier (weak) phase. Highest levels of TOC redevelop after OAE 2 in the early Turonian with the incursion or development of an oxygen minimum zone at the time of peak transgression.     

Biostratigraphy of the Garau Formation (Berriasian?–lower Cenomanian) in central part of Lurestan zone,northwest of Zagros,Iran

Deposition of organic rich black shales and dark gray argillaceous limestones in the Berriasian–Turonian interval has been documented in many parts of the world. Northwest of Zagros, Iran (Lurestan zone), thin bedded black shales and marls, dark gray argillaceous limestones and fissile limestone layers, having bitumen, of the Garau Formation are deposited. For biostratigraphic studies two stratigraphic sections including one surface section (Kuzaran) and one subsurface section (Naft well) were selected, respectively. In this study, 61 foraminiferal species belonging to 17 genera have been identified, and 12 biozones were recognized. Based on fossils distribution and biozones identification, the age of the Garau Formation is Berriasian?–early Cenomanian. In addition, the micropalaeontological study demonstrated a variety of widespread morphological changes in planktonic foraminifera assemblages (e.g., the elongation of the final chambers, appearance of twin chambers in the last whorl). These changes coincide with deposition of argillaceous limestones and marls rich in organic matter, indicating oceanic anoxic events. On this basis, three oceanic anoxic events such as OAE1a, OAE1b and OAE1d were recognized in Naft well section and two (OAE1b and OAE1d) in Kuzaran section.     

The Cretaceous marine onlap on Palaeozoic deposits (Smara–Lâayoune Basin,South Morocco). Comparison with neighbouring regions

The Cretaceous marine transgression proceeded through successive steps from the Albian to the Turonian (dated with ammonites). The onlapping wedge begins with coastal transgressive–regressive short-term sequences on massive, probably fluvial sandstones to be correlated with the very thick continental Lower Cretaceous succession found in the Puerto Cansado well in the Tarfaya sub-basin to the north. A second step, of probable Cenomanian age, reached the Palaeozoic basement. A third, more pronounced step occurred during the earliest Turonian with platy laminated limestone overlain by marlstone bearing pyritized ammonites. At early Turonian peak transgression, a marine connection was possibly established between the Atlantic and the Tethyan margins, between the Anti-Atlas and the Reguibat Shield. From large-scale correlation integrating what occurred along the southwestern shoulder of the Atlas rift, the South Moroccan Atlantic margin may have undergone a short-lived tectonic uplift around the Cenomanian–Turonian boundary.     

Upper Jurassic Rock Depositional Settings in the Baidar Valley and Evolution of the Crimean Carbonate Platform

The paper presents results of the lithological study of Upper Jurassic limestones, flyschoids and limestone breccias on the southern side of the Baidar Valley in the Crimean Mountains. Study of the microfacies revealed that the limestones are represented by deposits on lagoons, platform edge shoals, reefs, and forereef aprons on the carbonate platform slope. Flyschoids include deposits in the distributive turbidite channels and hemipelagic sediments in the deep-water part of the basin. Limestone breccias were formed by gravitation flows on the carbonate platform toe-of-slope and slope. The presence of gravitation deposits in the Upper Jurassic carbonate complexes of the Crimean Mountains can testify to the primary clinoform structure of this sedimentary sequence. Comparison of the obtained sedimentological data made it possible to reconstruct the facies model of the Crimean carbonate platform and main episodes of its formation. Development of the carbonate shelf was related to two transgressive-regressive cycles. A dome-shaped reef was formed away from the coast at the initial (Oxfordian) stage. The carbonate platform was formed at the early Kimmeridgian lowstand stage when sediments were deposited in the internal part of the platform adjacent to land. In the late Kimmeridgian and early Tithonian, configuration of the carbonate platform profile resembled a distally steepened ramp, and its active progradation and shelf expansion took place in the course of transgression. Regression in the late Tithonian–early Berriasian led to regressive transformation of the ramp into platform with a flattened shallow-water shelf. Tectonic deformations at the Jurassic/Cretaceous transition promoted the formation of megabreccias on the carbonate platform foreslope. The tectonically reworked rock sequence of the “extinct” carbonate platform was overlapped transgressively by the upper Berriasian or lower Valanginian, relatively deep-water deposits of the Cretaceous platform cover.     

Feldspar concentrations in lower Cambrian limestones of the Moroccan Atlas: Pyroclastic vs authigenic processes

Carbonate strata containing abundant euhedral feldspar, usually considered as authigenic, are characteristic of some lower Cambrian exposures in the Atlas Mountains, Morocco. Impure limestones are abundant in the Issendalenian Amouslek Formation of the western Anti-Atlas, and in the Banian Lemdad Formation of the southern High Atlas. Some of their limestone beds contain up to 40% acid insoluble residue, of which feldspar comprises as much as 65% in some samples, the remainder consisting of detrital and authigenic quartz, apatite, pyrite, and clay minerals. The host limestones are bioclastic tempestites, ooidal–oncoidal–bioclastic shoal complexes, archaeocyathan-microbial peri-reef settings (mainly flanks but not reef cores), and microbial reefs. A volcanic origin is adopted for the feldspars based on: (i) fluctuations in feldspar concentration paralleling bedding, but unrelated to host-facies (except for the aforementioned archaeocyathan-microbial reef cores that were controlled by turbidity); (ii) the local association with glassy fragments (with feldspars embedded in glass shards); and (iii) the scattered occurrence of gradational lithofacies from silty tuff to tuffitic limestone.The mineral and chemical composition of the host-rock and diagenetic fluids was the determining factor for the kind of feldspar preservation. Although the primary type of K–feldspar replacement is albitization, secondary albite subsequently suffered from illitization, chloritization, and/or replacement by calcite. A direct implication of this work is the possible geochronological dating of both volcanic eruptions and archaeocyath- and trilobite-bearing host-rocks based on radiometric analyses within unaltered K–feldspar pyroclasts extracted after etching.     

Sea level changes in the upper Aptian-lower/middle(?) Turonian sequence of Cauvery Basin,India – An ichnological perspective

Cauvery Basin, a pericratonic rift basin along the Eastern Continental Margin of India, evolved during the breakup of the Eastern Gondwanaland. It exposes both syn-rift and later post-rift passive margin deposits ranging from Barremian to Miocene. The Karai Formation, upper Aptian-lower/middle (?) Turonian represents the oldest passive margin in the Cauvery Basin. It is bounded at both contacts by major sequence boundaries viz. the break-up unconformity and the Turonian tilt event. The present communication deals with the ichnology of the Karai Formation and its integration with sedimentary facies and biostratigraphy to interpret the sea level changes during deposition. A traverse between the villages Karai and Kulakkalnattam was studied in detail for this purpose. Based on the lithological position, characters and internal grain size trends, the Karai Formation is sub-divided into four informal lithologic units; the lower three units, constitute a lithostratigraphic unit known in literature as the Gypsiferous Clay Member, while the uppermost, corresponds to the Sandy Clay Member. At the base, clays of the Karai Formation unconformably onlap onto the Precambrian basement or the fluvial syn-rift deposits across the break-up unconformity. Upper Aptian to middle Cenomanian, units I and II showing the distal Cruziana ichnofacies, deepening of the basin and a retrogradational stacking pattern represent a transgressive system tract (TST). This long phase of transgression is attributed to continuous accommodation created by the post-breakup thermal subsidence. The upper part of unit II (middle Cenomanian) shows condensation, with its top representing the maximum flooding surface (MFS). Upper Cenomanian to lower/middle (?) Turonian, units III and IV characterised by a shift from the distal Cruziana to the Skolithos ichnofacies, an initial aggradational and later deltaic, progradational stacking pattern resulting from a fall in the relative sea level and filling up of accommodation space represent the highstand system tract (HST). A further fall in the relative sea level led to the exposure, incision and erosion of the Karai Formation over which the younger transgressive sequence of the Trichinopoly Group was deposited with an angular unconformity.     

Biostratigraphy and facies analysis of the Upper Cretaceous–Danian? platform carbonate succession in the Kuyucak area,western Central Taurides,S Turkey

The Upper Cretaceous succession outcropping in the Anamas–Akseki Autochton, consists of approximately 500 m thick purely platform carbonate sediments. It begins with Cenomanian limestones intercalated with limestone breccias (Unit-1) containing mainly Pseudorhapydionina dubia, Pseudonummoloculina heimi, Spiroloculina cretacea (Assemblage I) and unconformably overlies the Lower Cretaceous (Barremian–Aptian) limestones with Vercorsella laurentii, Praechrysalidina infracretacea and Salpingoporella hasi. The Cenomanian limestones include foraminiferal packstone–wackestone, peloidal packstone–wackestone and mudstone microfacies deposited in restricted platform conditions. The Cenomanian succession is truncated by an unconformity characterised by locale bauxite deposits. Immediately above the unconformable surface, dolomitic limestones and rudistid limestones (Unit-2) are assigned to the upper Campanian based on the benthic foraminiferal assemblage (Assemblage II) comprising mainly Murciella gr. cuvillieri, Pseudocyclammina sphaeroidea, Accordiella conica, Scandonea samnitica and Fleuryana adriatica (smaller-sized populations). The upper Campanian limestones composed of dominantly foraminiferal-microbial packstone–wackestone microfacies deposited in shallow water environment with low energy, restricted circulation. The following limestones of the Unit-2 is characterised by sporadic intercalation of “open shelf” Orbitoides, Omphalocyclus, Siderolites assemblage (Assemblage III), assigned to the Maastrichtian, in addition to pre-existing “restricted platform” species. In the upper part of this biozone, the Rhapydionina liburnica/Fleuryana adriatica concurrent range subzone (Assemblage IIIb) is distinguished by the presence of Valvulina aff. triangularis, Loftusia minor as well as the nominal species. The Maastrichtian limestones with sporadically open marine influence consist of bioclastic (rudist-bearing) packstone–floatstone, foraminiferal packstone–wackestone with rudist fragments and peloidal/intraclastic packstone–wackestone microfacies deposited in shallow subtidal–subtidal (lagoonal) environments. The Upper Cretaceous succession passes upwardly into 70 m thick limestones and clayey limestones (Unit-3) which do not contain rudists and pre-existing foraminiferal assemblage with one exception Valvulina aff. triangularis. Variable amounts of ostracoda, discorbids, miliolids, dasycladacean algae and Stomatorbina sp. (Assemblage IV) occur into mud-rich microfacies suggesting restricted conditions with low water energy. A probable Danian age is proposed for the Unit-3 based on the occurrence of Valvulina aff. triangularis and Stomatorbina sp. which were previously recorded from Danian of peri-Tethyan platforms.     

河南登封地区寒武系第三统张夏组米级旋回及其演化

河南登封地区寒武系第三统张夏组是一套167m厚的碳酸盐岩地层,出露连续且完整,发育以微生物岩主导和以后生动物扰动灰岩主导的两种米级旋回类型。通过对米级旋回的演化及其沉积学和古遗迹学特征分析,张夏组自下而上由以微生物岩主导的米级旋回逐渐让位于以后生动物扰动灰岩主导的米级旋回;沉积体系由无鲕粒滩的碳酸盐岩台地逐渐向发育厚层鲕粒滩的碳酸盐岩台地演化;沉积环境从潮下低能深水演变为开阔台地,并逐渐变浅形成鲕粒滩、局限台地;沉积岩类型从叠层石、凝块石灰岩等微生物岩逐渐变化为生物碎屑灰岩、生物扰动灰岩和含生物扰动鲕粒灰岩。     

Biostratigraphy,microfacies and depositional environments of upper Viséan limestones from the Burren region,County Clare,Ireland

The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian–Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. (1) An Holkerian to lower Asbian unit of skeletal peloidal and bryozoan bedded limestone. (2) Lower Asbian unit of massive light grey Koninckopora‐rich limestone, representing a shallower marine facies. (3) Upper Asbian terraced limestone unit with minor shallowing‐upward cycles of poorly bedded Kamaenella‐rich limestone with shell bands and palaeokarst features. This unit is very similar to other cyclic sequences of late Asbian age in southern Ireland and western Europe, suggesting a glacio‐eustatic origin for this fourth‐order cyclicity. (4) Lower Brigantian unit with cyclic alternations of crinoidal/bryozoan limestone and peloidal limestone with coral thickets. These cycles lack evidence of subaerial exposure. (5) Lower Brigantian bedded cherty dark grey limestone unit, deposited during the maximum transgressive phase of the Brigantian. (6) Lower to upper Brigantian unit mostly comprising cyclic bryozoan/crinoidal cherty limestone. In most areas this youngest unit is truncated and unconformably overlain by Serpukhovian siliciclastic rocks. Deepening enhanced by platform‐wide subsidence strongly influenced later Brigantian cycle development in Ireland, but localized rapid shallowing led to emergence at the end of the Brigantian. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian–Brigantian formation boundary is recognized by the presence of upper Asbian Cf6γ Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6δ Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age. Copyright © 2006 John Wiley & Sons, Ltd.     

西秦岭早三叠世沉积特征及其构造控制作用

西秦岭早三叠世沉积由深水浊积岩、角砾岩、砾岩、滑塌堆积、深水灰岩和钙质泥岩六个岩相组成，在垂向上表现为受构造控制而形成的四个沉积旋回。浊积岩及滑塌堆积的指向表明，大陆边缘的斜坡倾向西南，古水流方向２００-２６０°、说明沿碌曲－成县以北的北方板块边缘在早三叠世存在一引张构造背景，这与扬子板块向北俯冲引起的拖拉滚动有关。     

柴北缘托莫尔日特滩间山群碎屑岩组的沉积环境与构造背景分析SCIEI北大核心CSCD

柴北缘构造带断续出露的寒武-奥陶纪滩间山群火山-沉积岩系是早古生代时期原特提斯洋俯冲造山作用的产物,也是中国西部块状硫化物和造山型金矿床的重要含矿岩系。前人已对滩间山群火山岩组开展了大量的地球化学和同位素年代学研究,而碎屑岩组的沉积序列和沉积相研究相对薄弱。我们在柴北缘托莫尔日特地区地质填图过程中,对该地区的滩间山群碎屑岩组开展了系统的沉积组合序列和沉积相研究。托莫尔日特地区滩间山群碎屑岩组是由富含火山碎屑物质的含砾砂岩、砂岩、粉砂岩、泥岩、沉凝灰岩、硅质凝灰岩、硅质岩及少量砾岩共同组成。可分为下岩性段和上岩性段,其中下岩性段为一套形成于海底扇外扇环境以沉凝灰岩为主的沉积组合;上岩性段包含海底扇内扇、中扇和外扇沉积,且以中扇环境的沉积为主。垂向上,它们呈现出粒度向上逐渐变细特征;空间上,具有向北西方向火山物质成分逐渐增多、砾岩和砂岩厚度变薄且砾岩消失的变化特征。砂岩主要为岩屑长石杂砂岩,其中岩屑主要是安山岩和少量玄武岩、英安岩、凝灰岩;长石主要为斜长石;石英碎屑相对缺失。砾岩中砾石以安山岩和硅质岩为主,并含有少量灰岩和凝灰岩砾石。底冲刷面、正粒序、平行层理和波纹层理等沉积构造普遍发育,呈现出典型的浊流沉积特征;同时在局部露头见有滑塌构造和波痕。区域上,这套沉积组合序列位于寒武-奥陶纪岛弧火山岩的南侧;古水流分析显示,它们的碎屑物质主要来自于其北东方向。这些结果表明,柴北缘构造带东段的滩间山群碎屑岩组是一套成熟度极低且与寒武-奥陶纪岛弧火山活动密切相关的沉积组合。     

广西百色盆地东部古近系那读组湖相灰岩

百色盆地东部田东坳陷那坤地区古近系那读组三段下部发育一套数米至数十米厚的湖相灰岩,岩石以浅灰色-灰色、含大量的螺蚌化石和具核形石结构为特征,间夹有薄层的泥岩、钙质泥质粉砂岩。本文在实测地表剖面和详细观察岩心的基础上,仔细研究了此套灰岩的岩石学特征。依据丰富的原生沉积构造、古生物化石标志以及沉积地球化学、测井相特征将湖相灰岩的沉积相划分为滨湖、颗粒滩、浅湖三个亚相以及灰泥坪、沼泽、颗粒坪、滩缘、滩核、滩间水道、灰泥浅湖、泥质浅湖等八个微相,并详细地研究了各微相的沉积特征。结合该灰岩的区域分布和沉积相的平面展布格局指出沉积相主体属于浅湖的颗粒滩,并提出了相应的沉积相模式。