scholarly journals Vertical changes of depositional environments of the Lower to Middle Miocene Kadonosawa Formation based on analyses of fossil ostracode faunas

1994 ◽  
Vol 100 (2) ◽  
pp. 136-149_2 ◽  
Author(s):  
Toshiaki Irizuki ◽  
Takashi Matsubara
Keyword(s):  
Middle Miocene ◽  
Depositional Environments ◽  
Vertical Changes

Biostratigraphically constrained Neogene palaeoenvironments of the Red Sea rift

2021 ◽  
Author(s):  
Geraint Hughes ◽  
Osman Varol
Keyword(s):  
Sea Level ◽  
Red Sea ◽  
Debris Flows ◽  
Middle Miocene ◽  
Depositional Environments ◽  
Early Miocene ◽  
Arabian Plate ◽  
Tectonic Activity ◽  
Gulf Of Suez ◽  
Gulf Of Aden

<p>Marine sediments deposited in response to the Neogene opening of the Red Sea during divergence of the African-Arabian plate margin provide micropalaeontological chronological evidence to calibrate synchronous palaeoenvironmental events from the Gulf of Suez to the Gulf of Aden. This facility provides insights to the timing and relative rates of tectonic subsidence associated with the rifting episodes of the region. Biostratigraphic index forms include planktonic and benthonic foraminifera and calcareous nannofossils. These, combined with various associated microfossils and macrofossil fragments, permit interpretation of a range of depositional environments that span intertidal to bathyal regimes. Onset and recovery from various hypersaline events are similarly interpreted by integrating microfossils and lithology. Following an episode of emergence and sporadic volcanicity, subsidence and the first Neogene marine transgression created brackish to shallow marine lagoons during the Early Miocene (Foraminiferal Letter Stage Upper Te). Rapid subsidence and accumulation of deep marine mudstones, of local hydrocarbon source-rock quality, with thinly interbedded siliciclastic and calciclastic debris flows commenced in the Early Miocene (Planktonic foraminiferal zones N5-N8; Nannofossil zones NN3-NN5). The debris flows increased in abundance and provide good hydrocarbon reservoirs. The Gulf of Suez and Red Sea experienced episodic isolation from the Indian Ocean during the latest Early Miocene and earliest Middle Miocene (Planktonic foraminiferal zones N8-N9; Nannofossil zone NN5 Foraminiferal Letter Stage Middle-Upper Tf1), resulting in hypersaline events with precipitation of submarine gypsum and halite. The isolation is attributed to constriction of the southern Red Sea, in the vicinity of the Bab El Mandab Straits, by eustatic sea level fall as well as probable tectonic activity; the synchronous Gulf of Aden succession does not display evidence for such hypersaline events. A prolonged hypersaline phase extended over most of the Middle Miocene, for which absence of biostratigraphic data precludes age control. During the latest Middle Miocene to Late Miocene, rejuvenation of the hinterland cause rapid deposition of terrestrial and fluviatile coarse and fine siliciclastics, with similar biostratigraphic paucity except for rare diatoms and palynomorphs. Renewed subsidence, associated with opening of the Aqaba Fault, combined with eustatic sea level rise caused marine deposition to recommence in the Pliocene.</p>

THE INFLUENCE OF DEPOSITIONAL ENVIRONMENT AND BASIN HISTORY ON THE TAPHONOMY OF MAMMALIAN ASSEMBLAGES FROM THE BARSTOW FORMATION (MIDDLE MIOCENE), CALIFORNIA

Palaios ◽  
2020 ◽  
Vol 35 (4) ◽  
pp. 175-190
Author(s):  
KATHARINE M. LOUGHNEY ◽  
CATHERINE BADGLEY
Keyword(s):  
Middle Miocene ◽  
Element Composition ◽  
Depositional Environments ◽  
Skeletal Element ◽  
Ephemeral Wetland ◽  
Facies Associations ◽  
History Of ◽  
Fossil Assemblages ◽  
Depositional Setting ◽  
Barstow Formation

ABSTRACT The Barstow Formation in the Mojave region of California was deposited in an extensional-basin setting of the Basin and Range province and preserves diverse middle Miocene mammalian assemblages. Six facies associations represent the dominant depositional environments in the basin, which changed through time from alluvial-fan and playa-dominated settings to floodplains and spring-fed wetlands. The majority of fossil localities and specimens occur in later-forming facies associations. We analyzed the taphonomic characteristics of fossil assemblages to test whether basin-scale facies associations or locality-scale facies exert more control on the preservational features of mammalian assemblages through the formation. We documented the facies settings of 47 vertebrate localities in the field in order to interpret depositional setting and the mode of accumulation for fossil assemblages. We evaluated skeletal material in museum collections for taphonomic indicators, including weathering stage, original bone-damage patterns, hydraulic equivalence, and skeletal-element composition. We evaluated four alternative modes of accumulation, including attritional accumulation on the land surface, accumulation by fluvial processes, carnivore or scavenger accumulations, and mass-death events. The majority of localities represent attritional accumulations at sites of long-term mortality in channel-margin, abandoned-channel, poorly drained floodplain, and ephemeral-wetland settings. Skeletal-element composition and taphonomic characteristics varied among facies, indicating an important role for depositional setting and landscape position on fossil-assemblage preservation. We find that locality-scale facies have a greater influence on the taphonomic characteristics of fossil assemblages; the taphonomy of each facies association is influenced by the facies that compose it. The facies composition and distribution within facies associations change through the formation, with a greater variety of depositional settings forming later in the history of the basin. Heterogeneous landscapes present more settings for fossil accumulation, contributing to the increase in fossil occurrence through the depositional history of the formation.

scholarly journals Depositional environment, organic matter characterization and hydrocarbon potential of Middle Miocene sediments from northeastern Bulgaria (Varna-Balchik Depression)

2015 ◽  
Vol 66 (5) ◽  
pp. 409-426 ◽  
Author(s):  
Alexander Zdravkov ◽  
Achim Bechtel ◽  
Stjepan Ćorić ◽  
Reinhard F. Sachsenhofer
Keyword(s):  
Organic Matter ◽  
Middle Miocene ◽  
Depositional Environments ◽  
Hydrocarbon Potential ◽  
Carbonate Sediments ◽  
Terrestrial Organic Matter ◽  
Anoxic Environments ◽  
Moesian Platform ◽  
Rock Eval ◽  
Resistivity Log

Abstract The depositional environments and hydrocarbon potential of the siliciclastic, clayey and carbonate sediments from the Middle Miocene succession in the Varna-Balchik Depression, located in the south-eastern parts of the Moesian Platform, were studied using core and outcrop samples. Based on the lithology and resistivity log the succession is subdivided from base to top into five units. Siliciclastic sedimentation prevailed in the lower parts of units I and II, whereas their upper parts are dominated by carbonate rocks. Unit III is represented by laminated clays and biodetritic limestone. Units IV and V are represented by aragonitic sediments and biomicritic limestones, correlated with the Upper Miocene Topola and Karvuna Formations, respectively. Biogenic silica in the form of diatom frustules and sponge spicules correlates subunit IIa and unit III to the lower and upper parts of the Middle Miocene Euxinograd Formation. Both (sub)units contain organic carbon contents in the order of 1 to 2 wt. % (median: 0.8 for subunit IIa; 1.3 for unit III), locally up to 4 wt. %. Based on Hydrogen Index values (HI) and alkane distribution pattern, the kerogen is mainly type II in subunit IIa (average HI= 324 mg HC/g TOC) and type III in unit III (average HI ~200 mg HC/g TOC). TOC and Rock Eval data show that subunit IIa holds a fair (to good) hydrocarbon generative potential for oil, whereas the upper 5 m of unit III holds a good (to fair) potential with the possibility to generate gas and minor oil. The rocks of both units are immature in the study area. Generally low sulphur contents are probably due to deposition in environments with reduced salinity. Normal marine conditions are suggested for unit III. Biomarker composition is typical for mixed marine and terrestrial organic matter and suggests deposition in dysoxic to anoxic environments.

scholarly journals Stratigraphy and depositional evolution of the uppermost Oligocene –Miocene succession in western Denmark

2004 ◽  
Vol 51 ◽  
pp. 89-109 ◽  
Author(s):  
Erik Skovbjerg Rasmussen
Keyword(s):  
Sea Level ◽  
Middle Miocene ◽  
Depositional Environments ◽  
Sediment Supply ◽  
Coarse Grained ◽  
Sea Level Changes ◽  
Fluvial Systems ◽  
North East ◽  
The North ◽  
Tectonic Movements

The uppermost Oligocene – Miocene succession in Denmark is subdivided into six depositional sequences. The development of the succession was controlled both by tectonic movements and eustatic sea-level changes. Tectonic movements generated a topography, which influenced the depositional pattern especially during low sea level. This resulted in sediment by-pass on elevated areas and the confinement of fluvial systems to structural lows. Structural highs further created restricted depositional environments behind the highs during low sea level. The structural highs were also the locus for sandy spit deposits during transgression and high sea level. Initially sediment supply was from the north and north-east but shifted within the Middle Miocene to an easterly direction indicating a significant basin reorganisation at this time. Eustatic sea-level changes mainly controlledthe timing of sequence boundary development and the overall architecture of the sequences.Consequently, the most coarse-grained sediments were deposited within the forced regressive wedge systems tract, the lowstand systems tract and the early transgressive systems tract. The most distinct progradation occurred in the Aquitanian (Lower Miocene) and was associated with a cold period in central Europe.The subsequent rise of sea level until the Serravallian (Middle Miocene) resulted in an overall back-stepping stacking pattern of the sequences and in decreasing incision.

scholarly journals The middle Miocene palynofloras of the Salihpaşalar lignite mine (Yatağan Basin, southwest Anatolia): environmental characterisation and comparison with palynofloras from adjacent basins

2018 ◽  
Vol 99 (4) ◽  
pp. 591-636 ◽  
Author(s):  
Johannes M. Bouchal
Keyword(s):  
Shallow Water ◽  
Middle Miocene ◽  
Depositional Environments ◽  
Temporary Ponds ◽  
Woody Vegetation ◽  
Lake Shore ◽  
The Third ◽  
Lignite Mine ◽  
Angiosperm Pollen ◽  
Algal Spores

Abstract As the third part of an ongoing investigation of middle Miocene palynofloras in the Yatağan Basin (YB), southwestern Anatolia, the palynofloras of the Salihpaşalar lignite mine in the main YB were studied. Seven types of algal spores, aplanospores/zygospores or cysts, six types of lycophyte and fern spores, 12 types of gymnosperm pollen and 90 types of angiosperm pollen were identified. Of a total of ca. 140 plant taxa described from the YB, over 10% are confined to the Salihpaşalar assemblage. Differences between coeval palynofloras of the Sekköy Member might reflect changing or prograding depositional environments. A number of rare accessorial taxa reflect these local differences: Pilularia, Valeriana, Drosera and Persicaria aff. amphibia only occur at Salihpaşalar and are typical of shallow water or temporary ponds associated with a lake shore. Apart from this, all the palynofloras, originating from the lignite seams and overlying limnic limestones (uppermost Turgut and Sekköy Member), of the YB are strongly indicative of extensive woody vegetation with a dominance of diverse Fagaceae and Pinaceae. In addition, a list comparing the well-documented YB palynomorphs to morphologically similar palynomorphs of published late early to middle Miocene plant assemblages of western Anatolian was compiled. Such a comparison reveals that in many instances different taxon names have been used to denote the same taxa. Hence, resolving these synonymies is a prerequisite of any meaningful comparison of palynofloras in the region.

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