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1.
The Tale-Zang Formation in Zagros Mountains (south-west Iran) is a Lower to Middle Eocene carbonate sequence. Carbonate sequences
of the Tale-Zang Formation consist mainly of large benthic foraminifera (e.g. Nummulites and Alveolina), along with other skeletal and non-skeletal components. Water depth during deposition of the formation was determined based
on the variation and types of benthic foraminifera, and other components in different facies. Microfacies analysis led to
the recognition of ten microfacies that are related to four facies belts such as tidal flat, lagoon, shoal and open marine.
An absence of turbidite deposits, reefal facies, gradual facies changes and widespread tidal flat deposits indicate that the
Tale-Zang Formation was deposited in a carbonate ramp environment. Due to the great diversity and abundance of larger benthic
foraminifera, this carbonate ramp is referred to as a “foraminifera-dominated carbonate ramp system”. Based on the field observations,
microfacies analysis and sequence stratigraphic studies, three third-order sequences in the Langar type section and one third-order
sequence in the Kialo section were identified. These depositional sequences have been separated by both type-1 and type-2
sequence boundaries. The transgressive systems tracts of sequences show a gradual upward increase in perforate foraminifera,
whereas the highstand systems tracts of sequences contain predominantly imperforate foraminifera. 相似文献
2.
The kilometer-sized and 100-meter-thick carbonate platforms of the Escalada Fm. I and II (Middle Pennsylvanian) accumulated in the foredeep of a marine foreland basin during the transgressive phases of 3rd-order sequences and were buried by prograding siliciclastic deltaic systems in the course of the subsequent highstand. The carbonate successions show a general upward trend from grain- to mud-supported carbonates, interfingering landwards with siliciclastic deposits of a mixed siliciclastic-carbonate shelf (Fito Fm.) adjacent to deltaic systems. The spatial variability of the carbonate facies and the high-frequency (4th–5th order) cycles, from the platform margin-outer platform to the deltaic systems, has been interpreted from basin reconstruction. Carbonate facies include skeletal grainstone to packstone, ooidal grainstone, burrowed skeletal wackestone, microbial and algal boundstone to wackestone forming mounds, various algal bafflestone and coral biostromes in areas with siliciclastic input. These high-frequency transgressive–regressive cycles are interpreted to record allocyclic forcing of high-amplitude glacioeustasy because they show characteristic features of icehouse cycles: thickness >5 m, absence of peritidal facies, and in some cases, subaerial exposure surfaces capping the cycles. In the mixed cycles, siliciclastics are interpreted as late highstand to lowstand regressive deposits, whereas carbonates as transgressive-early highstand deposition. The lateral and vertical variability of the facies in the glacioeustatic cycles was a response to deposition in a rapidly subsiding, active foreland basin subjected to siliciclastic input, conditions that might be detrimental to the growth of high-relief carbonate systems. 相似文献
3.
During the Late Miocene, the marginal areas of the Mediterranean Basin were characterized by the development of mixed siliciclastic-carbonate
ramps. This paper deals with a temperate siliciclastic-carbonate ramp (late Tortonian–early Messinian in age) which crops
out in the Capo Vaticano area, Southern Apennines (Italy). Carbonate components are mainly represented by calcitic skeletal
fragments of coralline red algae, bryozoans, bivalves, and larger foraminifera, whereas corals, brachiopods, echinoderms,
and planktonic foraminifera are subordinate. In the studied ramp, the depositional geometries of the main unit, the ‘Sabbie
gialle ad Heterostegina’, show a gradual steepening from low/middle (dip about 2–5°) to steep slope settings (up to 25°). The microfacies observations,
the quantitative analyses of the main biogenic components as well as the rhodolith shapes and growth forms allowed the differentiation
between the middle and the outer ramp depositional setting and the refining of the stratigraphic framework. The middle ramp
is characterized by coralline red algal debris packstone facies often associated with larger foraminiferal floatstone/packstone
facies, while the outer ramp is characterized by rhodolith floatstone/rudstone facies. These facies pass basinward into typical
open-marine deposits (planktonic foraminiferal facies). The taxonomic composition of the coralline red algal assemblage points
to a temperate paleoclimate and emphasizes the Miocene Mediterranean phytogeographic patterns. The absence of non-skeletal
grains (ooids and green algae), the paucity of Porites patch reefs, the rare occurrence of primary marine cementation, all confirm that the studied ramp was poorly lithified within
a warm–temperate setting. The flat depositional profile of the ramp can be related to the absence or paucity of primary marine
carbonate cements. 相似文献
4.
A facies analysis of the epicontinental marine Cenomanian sediments of northern Germany shows the presence of 17 facies types (FTs, including several subtypes) which can be assigned to three facies associations: 1) an inner shelf facies association (FT 1–8) with high amounts of terrigenous material and/or high-energy depositional features, 2) a middle shelf facies association (FT 9–15) of predominantly calcareous sediments with moderate amounts of generally fine siliciclastics, and 3) an outer shelf facies association (FT 16–17) of low-energy, fine-grained, pure limestones. These three facies associations roughly correspond to the well-known lithological units of the Cenomanian of northern Germany, i.e., the Essen Greensand/Cenomanian Marls complex, the Pläner Limestones, and the Poor rhotomagense Limestones. The sediments were deposited on a northward-dipping homoclinal ramp with more-or-less shoreline-parallel facies belts. The sediment composition on this ramp-like shelf was a function of the varying importance of three different sediment sources: 1) terrigenous input from the south (Rhenobohemia), generally fining/decreasing in a proximal–distal (i.e., S–N) direction; 2) production of skeletal grains, mainly by macrobenthic organisms; and 3) settling of planktic carbonate (mainly calcispheres and calcareous nannofossils). In response to decreasing water energy with increasing water depth, the seaward decreasing terrigenous influence, and increasing planktic carbonate production, increasingly finer and more calcareous sediments were deposited in a proximal–distal transect. This rather straightforward picture was slightly modified by highest carbonate accumulation rates (planktic and benthic) on the middle shelf, forming a mid-shelf depocenter (fossiliferous, calcisphere-rich Pläner Limestones). Time-transgressive, southward-directed onlap of this biosedimentary system during the Cenomanian caused a significant retreat of the coastline towards the south and a retrogradational stacking of facies belts, explaining the broadly similar facies development and lithology of Cenomanian successions across northern Germany. The boundaries of the lithological units, however, tend to be considerably diachronous in a distal–proximal transect. In the late Middle and early Late Cenomanian, a final drowning and facies levelling (“oceanization”) is indicated by the widespread deposition of uniform calcareous nannofossil mudstones (Poor rhotomagense Limestones). 相似文献
5.
Platform environments, microfacies and systems tracts of the upper Cenomanian-lower Santonian of Sinai, Egypt 总被引:1,自引:0,他引:1
Summary Factors controlling grain composition and depositional environments of upper Cenomanian—Santonian limestones of Sinai are
discussed. The mainly shallow-water, inner-platform setting investigated is subdivided into five major facies belts, each
represented by several microfacies types (MFTs). Their lateral distribution patterns and their composition underline aclear
relation between depositional environment and platform position. The facies belts include sandstones and quartzose packstones
of siliciclastic shorefaces, mudstones and bioclastic wackestones of restricted lagoons, shallow-subtidal packstones with
diverse benthic foraminifera and calcareous algae, bioclastic and/or oolitic grainstones of inner-platform shoals, and wackestones
of deep open-marine environments.
The microfacies distribution patterns of the Cenomanian-Santonian strata are evaluated with respect to local and regional
large-scale environmental changes. While protected shallow-subtidal environments with only subordinate ooids and oncoids prevail
during the late Cenomanian, high-energy oolithic shoals and carbonate sands occur locally during the middle and late Turonian.
They were probably related to a change of the platform morphology and a reorganisation of the platform after a late Cenomanian
drowning. In the Coniacian-Santonian, the lack of ooids, oncoids, and the decrease of calcareous algae versus an increase
in siliciclastics indicate a shift to lower water temperature and to a more humid climate. Especially in the Turonian, the
interplay between sea-level changes, accommodation, hydrodynamics, and siliciclastic input is reflected by lithofacies and
biofacies interrelation-ships that are elaborated within individual systems tracts. In particular, increasing accommodation
intensified circulation and wave-agitation and controlled the distribution of high-energy environments of the middle and upper
Turonian trans-gressive systems tracts. During highstands protected innerplatform environments prevailed. 相似文献
6.
《Palaeoworld》2015,24(3):336-358
The Asmari Formation in Marun oilfield (south-west Iran), is about 440 m-thick marine carbonate succession with subordinate siliciclastic rocks, characterized by abundant benthic foraminifera (perforate and imperforate). Foraminiferal biostratigraphy indicates that this unit is Oligocene–Miocene in age. The distribution of benthic foraminifera and other components have led to the recognition of three siliciclastic and ten carbonate facies that were deposited in inner ramp (shoreline, tidal flat, restricted and open lagoon and shoal), middle and outer ramp sub-environments. Based on vertical facies trends, three third-order sequences in the Oligocene and three third-order sequences in the Miocene sediments have been identified. These depositional sequences are bounded by both type 1 and type 2 sequence boundaries. The transgressive systems tracts (TST) of sequences show deepening-upward facies trend with a gradual upward increase in perforate foraminifera, whereas the highstand systems tracts (HST) have a shallowing-upward facies trend and contain predominantly imperforate foraminifera. Deposition of these depositional sequences (DS) were controlled by both eustasy and tectonic subsidence. 相似文献
7.
Stefan Höntzsch Christian Scheibner Jochen Kuss Akmal M. Marzouk Michael W. Rasser 《Facies》2011,57(1):51-72
The succession of the Galala Mountains at the southern Tethyan margin (Eastern Desert, Egypt) provides new data for the evolution of an isolated carbonate platform in the Early Eocene. Since the Late Cretaceous emergence of the Galala platform, its evolution has been controlled strongly by eustatic sea-level fluctuations and the tectonic activity along the Syrian Arc-Fold-Belt. Previous studies introduced five platform stages to describe platform evolution from the Maastrichtian (stage A) to the latest Paleocene shift from a platform to ramp morphology (stage E). A first Early Eocene stage F was tentatively introduced but not described in detail. In this study, we continue the work at the Galala platform, focussing on Early Eocene platform evolution, microfacies analysis and the distribution of larger benthic foraminifera on a south-dipping inner ramp to basin transect. We redefine the tentative platform stage F and introduce two new platform stages (stage G and H) by means of the distribution of 13 facies types and syn-depositional tectonism. In the earliest Eocene (stage F, NP 9b–NP 11), facies patterns indicate mainly aggradation of the ramp system. The first occurrence of isolated sandstone beds at the mid ramp reflects a post-Paleocene-Eocene thermal maximum (PETM) reactivation of a Cretaceous fault system, yielding to the tectonic uplift of Mesozoic and Palaeozoic siliciclastics. As a consequence, the Paleocene ramp with pure carbonate deposition shifted to a mixed carbonate-siliciclastic system during stage F. The subsequent platform stage G (NP 11–NP 14a) is characterised by a deepening trend at the mid ramp, resulting in the retrogradation of the platform. The increasing deposition of quartz-rich sandstones at the mid ramp reflects the enhanced erosion of Mesozoic and Palaeozoic deposits. In contrast to the deepening trend at the mid ramp, the deposition of cyclic tidalites reflects a coeval shallowing and the temporarily subaerial exposure of inner ramp environments. This oppositional trend is related to the continuing uplift along the Syrian Arc-Fold-Belt in stage G. Platform stage H (NP 14a–?) demonstrates the termination of Syrian Arc uplift and the recovery from a mixed siliciclastic carbonate platform to pure carbonate deposition. 相似文献
8.
A paleoecological and sedimentological study was carried out on shallow-water carbonates of the Kras Plateau (SW Slovenia)
with the goal of reconstructing paleoenvironmental conditions and evolution of foraminiferal communities on the northwestern
Adriatic Carbonate Platform (AdCP) during the Late Paleocene–earliest Eocene. Three facies have been recognized and summarized
in a carbonate ramp model. Within these facies, six foraminiferal assemblages, representing different ramp sub-environments,
have been defined: during the Late Paleocene sedimentation took place in a protected innermost ramp with (1) smaller miliolids-
and (2) small benthic foraminifera-dominated assemblages thriving on partly vegetated, soft substrates. In the Uppermost Paleocene,
sedimentation primarily occurred along a mid ramp. The upper mid-ramp was sporadically influenced by storms/currents and occupied
by (3) Assilina-dominated assemblage occurring on a soft sandy substrate. The deeper mid-ramp was characterized by (4) ‘bioconstructors’-
and (5) orthophragminids-dominated assemblages, colonizing biotopes with substrates of different nature. During the earliest
Eocene, deposition occurred in an inner-ramp setting with (6) alveolinids-nummulitids assemblage thriving on muddy and sandy
substrate, partly covered or close to seagrass beds. The Late Paleocene–earliest Eocene environmental conditions, coupled
with the long-term evolution of larger benthic foraminifera (LBF), seem to have favored this low-light dependent group as
common sediment contributors. By comparing the evolution of the shallow-water biota from the Adriatic area with data from
the Pyrenees and Egypt, a general latitudinal trend can be recognized. However, on a smaller geographical scale, local conditions
are likely to have played a pivotal role in promoting the evolution of biota characterized by suites of unique features. 相似文献
9.
The Jahrum Formation was deposited in the foreland basin in southwest Iran (Zagros Basin). The Zagros mountain belt of Iran, a part of the Alpine–Himalayan system, extends from the NW Iranian border through to SW Iran, up to the strait of Hormuz. The various facies of the Jahrum Formation were deposited in four main genetically related depositional environments, including: tidal flat, lagoon, shoal and open marine. These are represented by 14 microfacies. The Jahrum Formation represents sedimentation on a carbonate ramp. Tidal flat facies are represented by fenestral fabric, stromatolitic boundstone and thin-bedded planes. Carbonate deposition in a shallow marine lagoon was characterised by wacke–packstone, dominated by various taxa of imperforate foraminifer. The shoals are made up of medium- to coarse-grained skeletal and peloidal grainstone. This facies was deposited predominantly in an active high energy wave and current regime, and grades basinward into middle ramps facies are represented by wackestones–packstones with a diverse assemblage of echinoderm and large benthic foraminifers with perforate wall. Outer ramp facies consist of alternating marl and limestones rich in pelagic foraminifera. There is no evidence for resedimentation processes in this facies belt. The sequence stratigraphy study has led to recognition of three third-order depositional sequences. 相似文献
10.
Facies models of a shallow-water carbonate ramp based on distribution of non-skeletal grains (Kimmeridgian,Spain) 总被引:2,自引:0,他引:2
The internal facies and sequence architecture of a Late Jurassic (Late Kimmeridgian) shallow carbonate ramp was reconstructed
after the analysis and correlation of 17 logs located south of Teruel (northeast Spain). The studied rocks are arranged in
five high-frequency sequences A–E (5–26 m thick) bounded by discontinuities traceable across the entire study area (20 × 25 km).
Facies analysis across these sequences resulted in the reconstruction of three sedimentary models showing the transition from
interior ramp environments (i.e., lagoon, backshoal, and shoal) to the progressively deeper foreshoal and offshore areas.
Coral-microbial reefs (meter-sized patch and pinnacle reefs) have a variable development throughout the sequences, mostly
in the foreshoal and offshore-proximal environments. The preferential occurrence and down-dip gradation of non-skeletal carbonate
grains has been evaluated across the three models: low-energy peloidal-dominated, intermittent high-energy oolitic-dominated
and high-energy oolitic–oncolitic dominated. The predominance of these non-skeletal grains in the shoal facies was mainly
controlled by the hydrodynamic conditions and spatial heterogeneity of terrigenous input. The models illustrate particular
cases of down-dip size-decrease of the resedimented grains (ooids, peloids, oncoids) due to storm-induced density flows. Offshore
coarsening of certain particles (intraclasts, oncoids) is locally observed in the mid-ramp areas favorable for microbial activity,
involving coral-microbial reef and oncoid development. The observed facies variations can be applicable to carbonate platforms
including similar non-skeletal components, where outcrop conditions make the recognition of their three-dimensional distribution
difficult. 相似文献
11.
Summary The marine Paleogene of the Tremp Basin in the Central Southern Pyrenees corresponds to four depositional sequences which
are related to global eustatic third order cycles (Tejas A 2.3–2.6). Associated transgressive and downlap surfaces coincide
with boundaries of biozones. Lowstand systems tracts consist of estuarine and braid delta systems. Transgressive and highstand
systems tracts are composed of carbonate banks and reefs.
Slow thrust-induced changes of the basin topography conditioned the basic type and the areal distribution of carbonate highstand
and clastic lowstand systems. Rapid relative sea level changes controlled the activity and internal dynamic of the depositional
systems. E-W directed blind thrust anticlines are covered during highstand periods by carbonate fringing banks withNummulites bars. N-S orientation of thrust anticlines leads to the evolution of reef-dominated barrier banks and shelf lagoonal homoclinal
ramps. On-bank transport of carbonate sands dominates during transgressions, off-bank transport during highstand periods.
Continuous thrusting during the Ilerdian caused angular unconformities only in combination with relative sea level fall. Sequence-internal
onlap configurations result from contemporaneous tectonic tilting. Fourth order carbonate bank margin cycles contain well
developed lowstand tracts due to increased subsidence rates. Fourth order flooding surfaces are marked by paleosoil horizons
at their landward continuation. 相似文献
12.
Pierre Moissette Jean-Jacques Cornée Beya Mannaï-Tayech Mohsen Rabhi Jean-Pierre André Efterpi Koskeridou Henriette Méon 《Palaeogeography, Palaeoclimatology, Palaeoecology》2010,285(1-2):85-103
The marine Messinian deposits of Tunisia cover a narrow littoral strip some 300 km long between the northern Bizerte and Cap Bon areas and the central–eastern Sahel region. Litho- and biofacies analysis of six stratigraphic sections reveals the distinctive features of these deposits.The lower Messinian deposits are characterized by ubiquitous siliciclastics and abundant oolitic/bioclastic limestones organized in an eastward facing ramp. Westward (landward), this ramp changes into coastal lagoons, sometimes containing evaporites. Eastward, the ramp passes to the reefal Pelagian Platform extending as far as Lampedusa.Two main sedimentary cycles are distinguished: 1) an early Messinian siliciclastic retrogradational then oolitic/bioclastic progradational cycle (Beni Khiar Formation and lower Oued bel Khedim Formation); 2) a late Messinian brackish to continental cycle that probably accumulated in rapidly subsiding lagoons (Oued el Bir Formation and upper Oued bel Khedim Formation). The Tunisian early Messinian cycle is partly eustatically controlled, but the late Messinian cycle cannot be confidently correlated to other well-known Messinian series because of tectonic movements.The lower Messinian deposits of Tunisia are also characterized by abundant suspension-feeding organisms (molluscs and bryozoans) and rare corals, calcareous algae, echinoids, and larger benthic foraminifers. The proposed palaeoenvironmental model shows that the lower Messinian ramp of Tunisia was located on a current-protected margin and subjected to continent-derived sediment and nutrient supply. Eastward, nutrient influx diminished and a shallow-water isolated carbonate platform with coralgal facies developed between the western and the eastern Mediterranean basins. The main hydrological connection between these two basins occurred through a narrow seaway situated to the northeast of the Pelagian Platform, south of Sicily and Malta. 相似文献
13.
Early Ilerdian (Early Eocene, Shallow Benthic Zones 5 and 6) carbonate systems of the Pyrenees shelf were deposited after a time of severe climatic (‘Paleocene–Eocene Thermal Maximum, PETM’) and phylogenetic (‘Larger Foraminifer Turnover’) changes. They reflect the radiation of nummulitid, alveolinid, and orbitolitid larger foraminifera after remarkable biotic changes at the end of the Paleocene, and announce their subsequent flourishing in the Middle Eocene.A paleoenvironmental model for tropical carbonate environments of this particular time interval is provided herein. During the Early Ilerdian, the inner and middle ramp deposits from Minerve, Campo and Serraduy revealed the end-member of a tropical carbonate factory with carbonate production dominated by the end-members of biotically (photo-autotrophic skeletal) controlled and biotically induced carbonate precipitation. Inner platform environments are dominated by alveolinids and in part by orbitolitids, middle platform environments are dominated by nummulitids. Corals are present, but they do not form reefs, which is a typical feature for the Eocene. Nummulite shoal complexes, which are well-known from the Middle Eocene are also absent during the studied Early Ilerdian interval, which may reflect the early evolutionary stage of this group. 相似文献
14.
The Tortonian carbonate ramp of Menorca was previously studied on the basis of outcrops along sea-cliff outcrops. These sea
cliffs, in combination with inland water wells, are the basis for a facies model for the reconstruction of the internal architecture
and for characterizing the internal heterogeneities of this carbonate platform. However, any such three-dimensional reconstruction
is generally limited by the given geometrical arrangement of the two-dimensional outcrops and the uncertainties of correlation
with the one-dimensional wells. Here, ground-penetrating radar (GPR) has been employed in order to test and refine the depositional
model. Although GPR is well known for being an excellent tool for high-resolution underground studies of sedimentary systems,
the application for studying carbonate rocks is still far from routine. The reason for this discrepancy is two-fold: the minor
mineralogical contrast between lithologies in carbonate rocks results in subtle reflections, and, even more important, the
porosity structure in carbonates is thoroughly and repeatedly changed during diagenesis, commonly across the different facies,
leading to problems in predictability of the petrophysical properties. The study of the Menorcan carbonate ramp with large
distance–deep penetration GPR sections demonstrates that in spite of these difficulties, GPR is a valuable tool for extrapolating
information from outcrops and wells. It is useful for characterizing heterogeneities larger than outcrop scale. 相似文献
15.
Summary Peritidal dolostones (Trigonodus-Dolomite) characterize the back-bank environment of the Upper Muschelkalk (Middle Triassic)
carbonate ramp of SW-Germany. These deposits represent the Late Highstand Systems Tract (HST) of the ‘Third-Order’ Middle
to Upper Muschelkalk depositional sequence. The HST forms an overall shallowing-upward trend and is build by a progradational
stack of 1–2 m thick shallowing-upward cycles. The latter vary from subtidal-to-intertidal cycles at the base of the investigated
section to intertidal-to-supratidal cycles at the top of the section.
Six major facies types can be recognized: subtidal associations are characterized by oolithic grainstones, lagoonal oncolithic
wackestones and peloidal mudstones.
Intertidal associations are characterized by ostracod wackestones and laminated mudstones, supratidal facies consist of laminated
mudstones with tepee horizons and flat pebble conglomerates as well as paleosol horizons.
Thin section petrography, cathodoluminescence-microscopy and stable isotope geochemistry reveal a complex dolomitization history
(evaporative dolomitization; burial dolomitization). The strong negative oxygen isotope signatures(−3.28 to−5.85‰) point out
burial dolomitization as the dominant stage.
The Trigonodus-Dolomite shows intercrystalline porosity and some vuggy porosity. Subtidal dolo-grainstones with idiotopic
texture at the base of the investigated section have fair permeabilities (5–30 mD) and high porosities (14–32%). Inter-to
supratidal dolo-wackestones and dolo-mudstones with xenotopic texture at the top of the section have very low permeabilities
(0.3–1.0 mD) and lower porosities (11–16%). The reservoir characteristics with lateral continuity of porous and permeable
zones at the base of the section and less porous and impermeable zones at the top again reflect the stacking pattern of shallowing-upward
cycles within the overall shallowing-upward trend of the HST. Primary facies and dolomitization processes thus control the
distribution of porosity and permeability. 相似文献
16.
Thomas Wotte 《Facies》2009,55(3):473-487
Detailed litho- and biofacies investigations of the Lower–Middle Cambrian carbonate Láncara Formation resulted in its subdivision
into nine lithofacies types: (1) claystone, (2) recrystallized mudstone, (3) laminated mudstone with laminoid-fenestral fabrics,
(4) stromatolite, (5) laminated aggregate grainstone, (6) non-laminated aggregate grainstone, (7) oolitic-bioclastic floatstone,
(8) echinodermal packstone, and (9) bioclastic grainstone. The thicknesses of lithofacies 1–7 (lower member of the Láncara
Formation) decrease from south to north. Lithofacies types 8–9 (upper member of the Láncara Formation) are characterized by
similar thicknesses and low facies and faunal gradients and are thus indicative of deposition on a carbonate ramp. From palaeoecological,
palaeo(bio)geographical, palaeomagnetic, and tectonic considerations, the depositional environment of the Láncara Formation
is re-interpreted as an eastward/north-eastward sloping, low morphology carbonate ramp. The Cantabrian Zone, with a primary
lateral extension of about 300 km, is further construed to be an element of a widespread and connected, discontinuous drowned
Perigondwanan depositional system. 相似文献
17.
The Kuwait example studied here may serve as a model for ancient carbonate ramp systems just as the classical—but markedly different—southern Arabian-Persian Gulf ramp of the Trucial Coast (United Arab Emirates). Five sedimentary facies may be distinguished on the modern southern Kuwait carbonate ramp based on quantitative sedimentological, mineralogical, and geochemical analyses of 130 surface sediment samples and by using multivariate statistics. These facies include (1) inner ramp ooid-skeletal grainstone with common aggregate grains, peloids, and molluscs, (2) limited occurrences of nearshore quartz-ooid sand, (3) mid ramp mollusk packstone to grainstone, (4) outer ramp mollusk-marl wackestone with abundant siliciclastic fines, and (5) coralgal grainstone that is found on small nearshore patch reefs and outer ramp pinnacle and platform reefs. In addition to facies (1), an aggregate grain packstone to grainstone sub-facies is mapped out where abundances of this grain type exceed 20%. Ooid-skeletal grainstone, mollusk packstone to grainstone, and coralgal grainstone are predominantly aragonitic with 5–10% insoluble residue on average. Mollusk-marl wackestone has 55% insoluble residue on average with aragonite and low-magnesium calcite predominating in the carbonate fraction. Dolomite in this facies is interpreted to be of eolian origin derived from the upwind deserts of Syria and Iraq. Facies distribution is correlated with water depth, and hence controlled by depositional energy, primarily wavebase. This correlation is seen in the results of statistical analyses and in the fact that facies boundaries are more or less parallel to depth contours. Ooid-skeletal grainstones are found in depths from 0 to <10 m. The boundary between the mollusk packstone to grainstone and the mollusk-marl wackestone, which also marks the transition from grain-supported to mud-supported textures, is situated between 15–20 m depth and is much sharper than the boundary between the ooid-skeletal and the mollusk packstone to grainstone facies. Carbonate-dominated facies may also be distinguished geochemically as indicated by significantly different carbon and oxygen isotope compositions. The latter should be kept in mind when using bulk isotope values for chemostratigraphy or for paleo-environmental reconstructions in fossil carbonate ramps and platforms.An erratum to this article can be found at . 相似文献
18.
Patrick I. McLaughlin Carlton E. Brett Susannah L. Taha McLaughlin Sean R. Cornell 《Palaeogeography, Palaeoclimatology, Palaeoecology》2004,210(2-4):267-294
Detailed facies analysis and event stratigraphy of an Upper Ordovician (Rocklandian–Edenian) cratonic ramp succession in eastern North America yields insights into eustatically driven sequence architecture and localized tectonic instability. Seven, predominantly subtidal, mixed carbonate-siliciclastic depositional sequences (3rd order) are identified and correlated across the length of a 275-km ramp–to–basin profile. Within the larger depositional sequences (3rd order) at least two smaller orders (4th and 5th) of cyclicity are recognizable. Three systems tracts occur within each sequence (transgressive, TST; highstand, HST; regressive, RST) and are considered in terms of their component parasequences (5th order). Generally, TSTs are composed of skeletal grainstone–rudstone facies, HSTs are dominated by shaly nodular wacke-packstone facies, and RSTs are mostly calcarenite facies. Systems tracts, sequence boundaries and their correlative conformities, maximum flooding surfaces, and forced regression surfaces were traced from shallow shelf to basinal settings. This high-resolution framework also provides insight into the timing of tectonic fluctuations on this cratonic ramp during the Taconic Orogeny and documents the relative influence of tectonism on lateral facies distributions and eustatically derived cyclicity. 相似文献
19.
Ivan Martin-Rojas Roberta Somma Francisco Delgado Antonio Estévez Alessandro Iannace Valeria Zamparelli 《Facies》2012,58(2):297-323
A litho-biostratigraphic analysis has been carried out in the Gador-Turon unit of the Sierra de Gador (Alpujarride complex,
Betic Cordillera, SE Spain). The Triassic succession of this unit is composed of a lower meta-detrital formation overlain
by an upper meta-carbonate formation divided in six members. In the latter, a Ladinian–Carnian-rich fossil association has
been found (foraminifers, algae, bivalves, microproblematica, trace fossils). Facies analysis has enabled the recognition
of 22 facies of platform origin. This succession accumulated as a subsiding margin-type carbonate platform with homoclinal
ramp geometry (Anisian?–Ladinian) evolving into a fault-block-type platform with a steeper-margined geometry (Ladinian–Carnian).
Slope deposits of this latter platform show a prism-like geometry with progradational patterns and include syn-sedimentary
structures associated with normal faults capped by younger beds. The results of the present research indicate that the architecture
of the platform studied has been controlled mainly by climate and oceanic factors during the development of the ramp, and
by syn-sedimentary extensional tectonics during the development of the steeper-margined platform. The Ladinian–Carnian tectonic
activity was probably also responsible for the siliciclastic input and the shift to a mixed terrigenous-carbonate platform. 相似文献
20.
Within the Gavrovo–Tripolitza area (southern continental Greece), marine carbonate platforms existed from the Late Triassic
to the Late Eocene. The Middle–Upper Eocene marine shallow-water carbonates of the Klokova Mountain represent remnants of
the large volumes of sediment that were produced on a middle ramp sedimentary system which culminated in the Lower Oligocene
terrigenous deposits. Facies analysis of Bartonian–Priabonian shallow-water carbonate successions and the integration with
palaeoecological analysis are used to produce a detailed palaeoenvironmental model. In the proximal middle ramp, porcelaneous
foraminiferal packstone facies is characterised by larger foraminifera such as Praturlonella and Spirolina. These forms thrived in a shallow-water setting with low turbidity, high-light intensity and low-substrate stability. The
foraminiferal packstone facies, the thin coralline wacke–packstone facies and the rhodolith packstone facies deposited approximately
in the same depth range adjacent to one another in the middle-ramp. Nummulitids (Nummulites, Assilina, Pellatispira, Heterostegina and Spiroclypeus) increase in abundance in the middle to distal mid-ramp together with the orthophragminids. Coralline algae, represented
by six genera, are present in all facies. Rhodoliths occur in all facies but they show different shapes and growth forms.
They develop laminar sub-ellipsoidal shapes in higher turbulence conditions on mobile sand substrates (foraminiferal packstones
and rhodolith rudstones), whilst sub-discoidal shapes often bound by thin encrusting coralline plants in lower hydrodynamic
settings. The distinctive characteristics of the palaeoecological middle-ramp gradient are an increase in dominance of melobesioids,
a thinning of the encrusting coralline plants and a flattening of the larger benthic foraminiferal shells. 相似文献