Early Miocene Sequences Research Articles

Stratigraphy and Basin Development of the Oligocene-Early Miocene Succession, Southeastern Iraq

The study area is situated in the northern part of the Arabian Plate. The evolution of the Zagros Foreland basin is related to the compressional tectonic system at the beginning of the Tertiary Period. This study gives an adequate nomenclature for the Oligocene – Early Miocene Sequence is Missan Group. The Buzurgan Oilfield was chosen to represent the stratigraphic column corresponding to that period. These sediments were subdivided into two cycles, where each one ends by a sequence boundary, equivalent to the lowstand siliciclastic residues in the basin center. The first cycle, Paleocene-Oligocene Epoch, was deposited marly limestone with planktonic foraminifera in the basin center during the transgressive and highstand conditions. The Lower Missan Group was deposited during the latest Oligocene lowstand conditions and overlaid the deep marine Oligocene sediments. The second cycle represented the Early Miocene Epoch (Aquitanian), by which the Euphrates Formation was deposited during the transgressive and highstand conditions and ended by the lowstand conditions sediments in the basin center as an Upper Missan Sandstone Member. These two cycles are conformably bounded by Lower Miocene (Jeribe Formation) and Oligocene (Tarjil Formation).

Stuck in the middle. A geographical appraisal of the oldest insectivores – and a marsupial – from the Vallès-Penedès Basin (early Miocene, Catalonia, Spain)

The Vallès-Penedès Basin in Catalonia (NE Spain) forms a biogeographically important connection between central Europe and the Iberian Peninsula. Whereas this is well documented for the late middle and early late Miocene, the early Miocene sequence has received far less attention. New excavations yielded micromammal assemblages from the Ramblian and early Aragonian. Among the euliphotyhplans and metatherian studied, we recognize seven non-soricid species (Amphiperatherium frequens von Meyer, 1846, Galerix symeonidisi Doukas, 1986 and Galerix remmerti van den Hoek Ostende, 2003, Desmanodon daamsi van den Hoek Ostende, 1997, Heterosorex neumayrianus Schlosser, 1887, Chainodus sp., Plesiodimylus sp.) and six species of shrews (Paenelimnoecus sp., Miosorex sp., cf. Clapasorex, cf. Oligosorex, cf. Florinia sp. and Soricinae indet.). They confirm the intermediate position of the Vallès-Penedès also at the time of the older faunas, but show that differences with the Iberian inland were less pronounced. These differences can be explained by higher humidity in the coastal region, as indicated by the presence of dimylids. The differences between this coastal area and inland basin confirm the potential of coastal regions as migration corridors.

FACIES ANALYSIS AND STRATIGRAPHIC SEQUENCE ARCHITECTURE IN A BACK-ARC BASIN IN CENTRAL IRAN: A CASE STUDY FROM THE EARLY MIOCENE OF THE QOM FORMATION

Marine deposits of the Qom Formation, which is an important gas reservoir in Central Iran with the age of Early Oligocene to Early Miocene, is studied to determine facies, sedimentary paleoenvironment, and depositional sequences. The primary lithology is limestone, which is accompanied by a conglomerate, sandy marl, marl, and sandy limestone. Based on siliciclastic content, textural analysis, and the biotic constituents, ten facies have been identified. These facies belong to five depositional settings, including delta, a tidal inlet, lagoon, shoal, and open marine. According to the absence of continuous and large barrier reefs, gradual vertical variation in facies from the transitional environment (delta) to shallow open marine, the absence of oncoid, pisoid and aggregate grains that are mostly present in rimmed carbonate shelf environments, the absence of calciturbidites and slump and slide structures, the Qom Formation has been deposited in a homoclinal ramp setting (inner, middle and outer ramp). Field studies and vertical facies variation architecture in the framework of depositional system tracts led to the recognition of two 3rd order depositional sequences in the Early Miocene (Aquitanian) time. Sedimentary facies in the Qom Formation that mainly occurred in the middle ramp setting reveal a mostly aggredational stacking pattern in depositional sequences. The Early Miocene sequences stratigraphic architecture of the Qom Formation based on correlation charts are similar to the regional sequences of the Arabian plate and Zagros basin.

Reconstruction on regional paleo-drainage evolution in the northern Junggar Basin, China during the last ~27 myr from provenance analyses and its implications for uplift of the Altai Mountains

Tectonic activity and climate change are regarded as two important driving forces on the evolution of large-scale drainage. The evolution of the Irtysh River and Ulungu River, two large-scale drainage systems in the northern Junggar Basin, can provide a key constraint on the uplift of the Altai Mountains and Central Asian aridification. However, we know little about the evolution of these two large-scale rivers. This study presents new detrital zircon U–Pb data from the late Oligocene to late Miocene sedimentary sequences and modern river sediments to reconstruct Cenozoic paleo-drainage evolution in the northern Junggar Basin. The detrital zircon U–Pb results show a single major population at 460-360 Ma, which is mainly derived from the Altai Mountains, for late Oligocene and early Miocene sequences, but two populations at 460-360 Ma and 340-200 Ma, which are mainly from the Altai Mountains and East Junggar terrane, for middle and late Miocene sequences. Our provenance study argues that the Irtysh River and Ulungu River in their modern extent did not exist prior ~18 Ma when the Altai Mountains allowed southward-flowing rivers to transport sediments into the inner Junggar Basin directly. The provenance shift in northern Junggar Basin at 17–18 Ma represents the progressive drainage expansion of the Ulungu River, evolving from relatively small rivers confined to the eastern Junggar Basin to a near-modern large-scale drainage system, due to the rapid uplift in the East Junggar terrane and eastern Altai Mountains in early Miocene. After ~6 Ma, the Irtysh River experienced a progressive drainage expansion, captured the southward-flowing tributaries of the Ulungu River and formed modern drainage pattern. Our study supports the initiation of exhumation before late Oligocene and a local tectonic uplift in early Miocene in Altai Mountains, which imply a complex deformation process in the Central Asia.

The Miocene Depositional Geological Evolution of Phu Khanh, Nam Con Son and Tu Chinh - Vung May Basins in Vietnam Continental Shelf

The geological development history of Miocene deposits in three sedimentary basins as Phu Khanh, Nam Con Son and Tu Chinh - Vung May is actually a depositional evolution in relation to sea level change and tectonic movement. The Miocene deposits in three basins were formed in three cycles corresponding to three depositional sequences: 1/ Early Miocene sequence: In this cycle, the tectonic setting of three basins is similar to one another, the terrain is less differentiated, the environment is mainly alluvial, coastal and shallow marine-bay. Topography of top Miocene surface was strongly deformed by the tectonic events such as compression, fault, fold that had created the rough relief and eroded unconformity surface. The product of erosion processes was supply of terrigenous depositional materials for early Miocene basins under the bay type. 2/ Middle Miocene sequence: The tectonic situation of three basins started changing. The basins were differentiated into 2 parts: The inner shelf with stable geological structure and dominated terrigenous deposits; The outer shelf was stronger subsidence the basin base topography was differentiated with the development of two sediment types: carbonate bearing terrigenous sediments and carbonate reefs. 3/ Late Miocene sequence: in this period the basins were differentiated into two distinct structural zones: the western zone with incline terrain, the dominated terrigenous sediments and the eastern zone with strong differentiated terrain, reef development they played the erosion zone role and supplied a large amount of biological clastic sediments to the shallow lagoons-bay.

Evidence for rapid faunal change in the early Miocene of East Africa based on revised biostratigraphic and radiometric dating of Bukwa, Uganda

Field expeditions to Bukwa in the late 1960s and early 1970s established that the site had a small but diverse early Miocene fauna, including the catarrhine primate Limnopithecus legetet. Initial potassium-argon radiometric dating indicated that Bukwa was 22 Ma, making it the oldest of the East African early Miocene fossil localities known at the time. In contrast, the fauna collected from Bukwa was similar to other fossil localities in the region that were several million years younger. This discrepancy was never resolved, and due to the paucity of primate remains at the site, little subsequent research took place.We have collected new fossils at Bukwa, reanalyzed the existing fossil collections, and provided new radiometric dating. 40Ar/39Ar incremental heating ages on lavas bracketing the site indicate that the Bukwa fossils were deposited ∼19 Ma, roughly 3 Ma younger than the original radiometric age. Our radiometric dating results are corroborated by a thorough reanalysis of the faunal assemblage. Bukwa shares taxa with both stratigraphically older localities (Tinderet, Napak) and with stratigraphically younger localities (Kisingiri, Turkana Basin) perfectly corresponding to our revised radiometric age.This revised age for Bukwa is important because it indicates that significant faunal turnover may have occurred in East Africa between 20 and 19 Ma. Bukwa samples immigrant taxa such as large suids, large ruminants, and ochotonids that are absent from stratigraphically older but well-sampled localities in the region, such as Tinderet (∼20 Ma) and Napak (20 Ma). Further age refinements for Bukwa and the entire East African early Miocene sequence will help to constrain the timing of this faunal turnover event, of particular importance in paleoanthropology since this temporal sequence also provides us with what is currently our best window into the early evolution of cercopithecoid and hominoid primates.

Foraminifera from the Late Middle Eocene to Early Middle Miocene sequence of the Kachchh Offshore Basin, Western India: Paleoenvironmental Significance

Foraminifera from the Late Middle Eocene to Early Middle Miocene sequence of the Kachchh Offshore Basin, Western India: Paleoenvironmental Significance

Neogene to Quaternary extensional reactivation of a fold and thrust belt: The Agrio belt in the Southern Central Andes and its relation to the Loncopué trough (38°–39°S)

The Andean orogenic front between 38 and 39°S is formed by extensional structures delimiting the Loncopué trough. These structures are superimposed to Late Cretaceous–Late Miocene compressive structures that formed the Agrio fold and thrust belt. Gravity data, and limited borehole and seismic data complimented with previous field studies were used to construct two structural cross sections across the area of Neogene extensional deformation and remnants of the previous compressive structure. One of them was restituted for Late Cretaceous times previously to extensional relaxation of the fold and thrust belt and Late Oligocene–Early Miocene and Pliocene to Quaternary stages. Different modeling techniques and filters for gravity anomalies show that i) a series of deeper and larger depocenters, where Late Oligocene to Early Miocene sequences are buried, were located particularly at the Present trough boundaries; while ii) smaller and probably shallower depocenters were concentrated at the axial -eastern trough following structures at surface with young morphological expression. The former are interpreted as representative of the initial extensional stage when Late Cretaceous compressional basement structures were relaxated, while the latter could be the product of incipient-young extensional reactivation of the Agrio fold and thrust belt. General coincidence between both areas of extensional relaxation at the western Agrio fold and thrust belt implies that a common basement discontinuity is recurrently being reactivated through time, probably in coincidence with the eastern main Loncopué fault boundary.

Early Miocene sequence development across the New Jersey margin

ABSTRACTSequence stratigraphy provides an understanding of the interplay between eustasy, sediment supply and accommodation in the sedimentary construction of passive margins. We used this approach to follow the early to middle Miocene growth of the New Jersey margin and analyse the connection between relative changes of sea level and variable sediment supply. Eleven candidate sequence boundaries were traced in high‐resolution multi‐channel seismic profiles across the inner margin and matched to geophysical log signatures and lithologic changes in ODP Leg 150X onshore coreholes. Chronologies at these drill sites were then used to assign ages to the intervening seismic sequences. We conclude that the regional and global correlation of early Miocene sequences suggests a dominant role of global sea‐level change but margin progradation was controlled by localized sediment contribution and that local conditions played a large role in sequence formation and preservation. Lowstand deposits were regionally restricted and their locations point to both single and multiple sediment sources. The distribution of highstand deposits, by contrast, documents redistribution by along shelf currents. We find no evidence that sea level fell below the elevation of the clinoform rollover, and the existence of extensive lowstand deposits seaward of this inflection point indicates efficient cross‐shelf sediment transport mechanisms despite the apparent lack of well‐developed fluvial drainage.

Algal biostratigraphy of some Early Miocene sequences, North Eastern Desert, Egypt

Algal biostratigraphy of some Early Miocene sequences, North Eastern Desert, Egypt

Geotechnical evaluation of Turkish clay deposits: a case study in Northern Turkey

Clay deposits in Oltu-Narman basins (Erzurum, northern Turkey) have been studied to determine their engineering properties and to evaluate their uses for geotechnical applications. These deposits are concentrated in two different stratigraphic horizons namely the Late Oligocene and the Early Miocene sequences. Clay-rich fine-grained sedimentary units are deposited in shallow marine and lagoonar mixed environments. Their clay minerals originated by the alteration of Eocene calc-alkaline island-arc volcanics, preferably from pyroclastics (trachite and andesite flow), which form the basement for the Oltu depression. Smectite group clay minerals are found abundant in clay deposits. The experimental results show that the clay soils have high plasticity behaviors and low hydraulic conductivity properties. The optimum water content, the free swell, and the swelling pressure of clay samples decreased and the maximum dry unit weight of clay samples increased under high temperature. Consequently, it is concluded that the expanding of clay soils is an important soil problem that cannot be avoided in the significant parts of Oltu city and its villages. However, the soils of clay-rich layers in the outcrops-section of clay deposits can be successfully used to build compacted clay liners for landfill systems and to construct vertical and horizontal barriers for protection of ground water and for preventing soil pollution in geotechnical applications.

Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States

Research Article| May 01, 2006 Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States James V. Browning; James V. Browning 1Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar Kenneth G. Miller; Kenneth G. Miller 1Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar Peter P. McLaughlin; Peter P. McLaughlin 2Delaware Geological Survey, DGS Building, University of Delaware, Newark, Delaware 19716, USA Search for other works by this author on: GSW Google Scholar Michelle A. Kominz; Michelle A. Kominz 3Department of Geosciences, Western Michigan University, Kalamazoo, Michigan 49008-5150, USA Search for other works by this author on: GSW Google Scholar Peter J. Sugarman; Peter J. Sugarman 4New Jersey Geological Survey, P.O. Box 427, Trenton, New Jersey 08625, USA Search for other works by this author on: GSW Google Scholar Donald Monteverde; Donald Monteverde 4New Jersey Geological Survey, P.O. Box 427, Trenton, New Jersey 08625, USA Search for other works by this author on: GSW Google Scholar Mark D. Feigenson; Mark D. Feigenson 5Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar John C. Hernández John C. Hernández 5Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2006) 118 (5-6): 567–588. https://doi.org/10.1130/B25551.1 Article history received: 19 Dec 2003 rev-recd: 07 Mar 2005 accepted: 10 Apr 2005 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation James V. Browning, Kenneth G. Miller, Peter P. McLaughlin, Michelle A. Kominz, Peter J. Sugarman, Donald Monteverde, Mark D. Feigenson, John C. Hernández; Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States. GSA Bulletin 2006;; 118 (5-6): 567–588. doi: https://doi.org/10.1130/B25551.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We use backstripping to quantify the roles of variations in global sea level (eustasy), subsidence, and sediment supply on the development of the Miocene stratigraphic record of the mid-Atlantic continental margin of the United States (New Jersey, Delaware, and Maryland). Eustasy is a primary influence on sequence patterns, determining the global template of sequences (i.e., times when sequences can be preserved) and explaining similarities in Miocene sequence architecture on margins throughout the world. Sequences canbecorrelatedthroughoutthemid-Atlantic region with Sr-isotopic chronology (±0.6 m.y. to ±1.2 m.y.). Eight Miocene sequences correlate regionally and can be correlated to global δ18O increases, indicating glacioeustatic control. This margin is dominated by passive subsidence with little evidence for active tectonic overprints, except possibly in Maryland during the early Miocene. However, early Miocene sequences in New Jersey and Delaware display a patchwork distribution that is attributable to minor (tens of meters) intervals of excess subsidence. Backstripping quantifies that excess subsidence began in Delaware at ca. 21 Ma and continued until 12 Ma, with maximum rates from ca. 21–16 Ma. We attribute this enhanced subsidence to local flexural response to the progradation of thick sequences offshore and adjacent to this area. Removing this excess subsidence in Delaware yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude that sea-level rise and fall is a first-order control on accommodation providing similar timing on all margins to the sequence record. Tectonic changes due to movement of the crust can overprint the record, resulting in large gaps in the stratigraphic record. Smaller differences in sequences can be attributed to local flexural loading effects, particularly in regions experiencing large-scale progradation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Quantification of the Effects of Eustasy, Subsidence, and Sediment Supply on Miocene Sequences, U.S. Mid-Atlantic Margin

Research Article| May 01, 2006 Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States James V. Browning; James V. Browning 1Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar Kenneth G. Miller; Kenneth G. Miller 1Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar Peter P. McLaughlin; Peter P. McLaughlin 2Delaware Geological Survey, DGS Building, University of Delaware, Newark, Delaware 19716, USA Search for other works by this author on: GSW Google Scholar Michelle A. Kominz; Michelle A. Kominz 3Department of Geosciences, Western Michigan University, Kalamazoo, Michigan 49008-5150, USA Search for other works by this author on: GSW Google Scholar Peter J. Sugarman; Peter J. Sugarman 4New Jersey Geological Survey, P.O. Box 427, Trenton, New Jersey 08625, USA Search for other works by this author on: GSW Google Scholar Donald Monteverde; Donald Monteverde 4New Jersey Geological Survey, P.O. Box 427, Trenton, New Jersey 08625, USA Search for other works by this author on: GSW Google Scholar Mark D. Feigenson; Mark D. Feigenson 5Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar John C. Hernández John C. Hernández 5Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2006) 118 (5-6): 567–588. https://doi.org/10.1130/B25551.1 Article history received: 19 Dec 2003 rev-recd: 07 Mar 2005 accepted: 10 Apr 2005 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation James V. Browning, Kenneth G. Miller, Peter P. McLaughlin, Michelle A. Kominz, Peter J. Sugarman, Donald Monteverde, Mark D. Feigenson, John C. Hernández; Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States. GSA Bulletin 2006;; 118 (5-6): 567–588. doi: https://doi.org/10.1130/B25551.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We use backstripping to quantify the roles of variations in global sea level (eustasy), subsidence, and sediment supply on the development of the Miocene stratigraphic record of the mid-Atlantic continental margin of the United States (New Jersey, Delaware, and Maryland). Eustasy is a primary influence on sequence patterns, determining the global template of sequences (i.e., times when sequences can be preserved) and explaining similarities in Miocene sequence architecture on margins throughout the world. Sequences canbecorrelatedthroughoutthemid-Atlantic region with Sr-isotopic chronology (±0.6 m.y. to ±1.2 m.y.). Eight Miocene sequences correlate regionally and can be correlated to global δ18O increases, indicating glacioeustatic control. This margin is dominated by passive subsidence with little evidence for active tectonic overprints, except possibly in Maryland during the early Miocene. However, early Miocene sequences in New Jersey and Delaware display a patchwork distribution that is attributable to minor (tens of meters) intervals of excess subsidence. Backstripping quantifies that excess subsidence began in Delaware at ca. 21 Ma and continued until 12 Ma, with maximum rates from ca. 21–16 Ma. We attribute this enhanced subsidence to local flexural response to the progradation of thick sequences offshore and adjacent to this area. Removing this excess subsidence in Delaware yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude that sea-level rise and fall is a first-order control on accommodation providing similar timing on all margins to the sequence record. Tectonic changes due to movement of the crust can overprint the record, resulting in large gaps in the stratigraphic record. Smaller differences in sequences can be attributed to local flexural loading effects, particularly in regions experiencing large-scale progradation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Middle to late Miocene sequence stratigraphy of the Transylvanian Basin (Romania)

The history of Middle to Late Miocene evolution of the Transylvanian Basin was determined by the bordering Carpathian orogen evolution, the tectonic events being well recorded by the sedimentary history. The basin evolved in a back-arc setting, under a regional, compressional stress field. The major tectonic events produced during the Late Sarmatian and Post-Pannonian were related to the reactivation of the pre-Badenian fault systems. The Transylvanian Basin got uplifted after the Late Pannonian (? during the Pliocene), and at least 500 m of sedimentary cover was eroded. Based on seismic and well-log interpretation, core and outcrop sedimentology, and microfauna, eight sequences were defined. The early Middle Miocene sequences are roughly synchronous to five 3rd order global sea-level cycles. Most of the recognized sequence boundaries are enhanced by regional tectonic events. The sedimentary evolution was also strongly influenced by salt-tectonics, active starting with the Late Sarmatian. Two sequences were identified in the Lower Badenian deposits. The third sequence (late Early Badenian to early Mid Badenian) preserves information about deeper shelf settings. The lowstand of the following sequence was responsible for the deposition of the salt formation (late Mid Badenian), an important lithostratigraphic marker in the sedimentary record of the basin. In general, the Upper Badenian deposits (parts of the 4th and 5th sequences) belong to deep marine submarine fan systems. The Sarmatian (partially 5th, 6th and partially 7th sequences) was characterized by diverse salinity conditions, stretching from brackish to hypersaline, and by high tectonic instability, which induced several significant relative sea-level falls. During that time, deltaic (north) and fandeltaic (east) systems fed submarine fans, stacked between salt-related submarine heights (“channeled” deep-marine depocenters). Most of the Pannonian deposits (partially 7th and 8th sequences) belong to submarine fan systems, but shallower facies were also found in the western and eastern part of the basin.

Integrated stratigraphy of the lower Altonian (Early Miocene) sequence at Tangakaka Stream, East Cape, New Zealand

The biostratigraphy of a rapidly deposited, deep bathyal, lower Altonian (Early Miocene) sequence through Whakai Formation, East Cape, is presented. We interpret the depositional milieu, identify and describe foraminiferal and nannofossil bioevents potentially useful in biostratigraphy, and relate these to the magnetostratigraphy, 40Ar/39Ar ages, and ages using the Sr isotope sea‐water curve. Although lower and upper contacts of the 623 m section through Whakai Formation are obscured, a high (c. 0.9 m/ka) flux of muddy sediment has produced an amplified record of most of the lower Altonian Globorotalia incognita Zone and the base of the overlying Globorotalia zealandica Zone. No significant breaks were identified. Benthic foraminiferal paleodepth proxies suggest that the site was on the lower slope (>1000 m) throughout, but the moderate abundance of planktonic taxa shows that it was not in fully oceanic water. Planktonic assemblages identify warm‐temperate water masses. Abundance data for both nannofossils and planktonic foraminifera are cyclic, and temperature oscillations in the Milankovitch band are inferred. Nannofossil proxies indicate that sea temperatures were warmest in the upper Globorotalia incognita Zone. There is a prominent “crash” in populations of warm‐water taxa at 457 m, at the base of the middle Altonian zone. Among the benthic foraminifera, Bolivina punctato‐striata occurs at the base of the section, and its first appearance datum (FAD) may be a useful proxy in the vicinity of the base of Altonian; the FAD of Sigmoilopsis compressa occurs near the base of the middle Altonian Globorotalia zealandica Zone. Globorotalia praescitula (planktonic foraminifera) is persistent in very low numbers through the sequence; individuals are small and easily overlooked, but they are distinctive and considered to identify strata above the base of Altonian reliably. The FAD of Paragloborotalia bella is near the base of the section in the Globorotalia incognita Zone and may be a useful supplementary criterion for basal Altonian. Qualitative criteria for recognition of the FAD of Globorotalia zealandica are cited. The species arises by relatively rapid phyletic transformation from Globorotalia incognita and defines the boundary between the lower and middle Altonian zones. Transitional populations occur over 50 m. The lower Altonian Globorotalia incognita Zone appears to be missing at the Altonian stratotype. Apaleomagnetic, 40Ar/ 39Ar, and 87Sr/86Sr composite age model for the Tangakaka Stream section indicates that much of the lower Altonian Globorotalia incognita Zone lies in Chrons C5En and C5Er. The lower Altonian/middle Altonian (Globorotalia zealandica Zone) boundary occurs within Chron C5En. The Otaian/Altonian boundary occurs below the base of the Tangakaka Stream section, but above the top of the nearby Hoia section, in the vicinity of the Chron C6n/ C5Er boundary (c. 19.0 Ma).

Seismic stratigraphy and structural history of the Reinga Basin and its margins, southern Norfolk Ridge system

The Reinga Basin northwest of the North Island of New Zealand was initially formed by crustal extension in Cretaceous time. Gravity models suggest up to 35—40% crustal thinning. The seismic stratigraphy of the basin is continuous with that of the offshore western North Island, where reflectors are well constrained by oil exploration data. In the Reinga Basin, there are two Cretaceous sequences above an older Mesozoic basement. The lower sequence is apparently terrestrial and may include both pre‐rift and syn‐rift subsequences; the upper is a rift‐filling marine sequence. These are overlain by Paleocene and Eocene blanket sequences that were laid down during a period of relative tectonic quiescence consistent with cooling subsidence, continued submergence, a northeast‐facing continental shelf, and absence of a significant active plate boundary. A strong regional reflector, caused by a combined unconformity and Oligocene condensed sequence, separates the Paleogene and Neogene sequences. The Neogene sequences record sedimentary infill from several source directions, not only from the New Zealand landmass, but from the north and west as well. Near the Northland coast, sediment accumulated in clastic wedges and ponded sub‐basins from the Miocene to the present day. Along the flanking ridges to the northwest, similar deposition occurred in the Early and Middle Miocene but changed in the Late Miocene to sedimentation in drifts flanked by scours. This change reflects the end of tectonism, a diminishing clastic sediment supply, and the establishment of a throughgoing oceanic current regime as the marginal ridges submerged. This pattern of sedimentation persists today. Post‐Cretaceous volcanism occurred in two parts of the basin. In the central southeastern part, volcanic bodies in the ?Oligocene to Early Miocene sequences could be a northwestern extension of the Northland volcanic arc. In the western part, small intrusive and extrusive bodies appear to be of Pliocene intraplate origin. Compression (or transpression) had an important role in developing the basin's present form. Miocene compressional structures—asymmetric anticlines, reverse faults, everted basins, and pop‐ups—are present everywhere but at the southeastern end. The present marginal ridges have structurally complex origins. The Reinga Ridge which forms the northeastern margin is a transform boundary with the Norfolk backarc basin. Deformation thought to be caused by the action of the transform is recorded in folded and faulted Cretaceous‐Paleogene sequences and syntectonic Early and Middle Miocene sequences along its length. The southwestern margin of the basin is a double ridge comprising the Wanganella Ridge, an early Middle to early Late Miocene, compressional uplift, and the older, eroded West Norfolk Ridge, which contains Cretaceous half‐grabens. The northern half of the Wanganella Ridge is an everted ?Oligocene to Early Miocene aulacogen in which slivers of basement rock were thrust up along with the sedimentary fill, whereas the southern half is an uplifted block of folded sedimentary rocks of probable Cretaceous or older age. Paleogeographic reconstructions show that Oligocene uplift of the Norfolk Ridge and Miocene uplift of the Reinga Ridge could have provided a means for terrestrial biota of New Caledonian affinities to spread into New Zealand. The total sediment thickness in the Reinga Basin is estimated to be 3.5–5.5 km. Potential source, seal and reservoir rocks are present, and there is an abundance of suitable structures. The potential for petroleum occurrences in the basin is good.

Fluvial palaeoenvironments in the intracratonic Amazonas Basin (Early Miocene-early Middle Miocene, Colombia)

Based on a detailed study of Early Miocene to early Middle Miocene sediments in the Caquetá River area (Amazonas Basin, Colombia), a reconstruction of the palaeoenvironmental and palaeogeographical history is made. Sediment composition, sedimentary sequences and transport directions indicate that the succession was deposited by a low sinuosity fluvial system with an anastomosing character that originated from the Guyana Shield. Basin subsidence, Precambrian and Palaeozoic palaeorelief, and a changing base level controlled deposition in this fluvial system. Sedimentary environments such as channels, abandoned channels, crevasse splays, backswamps and palaeosoils characterized this system where fluvial flooding was common. The Early Miocene to early Middle Miocene sequences have been truncated by a more recent fluvial system, probably of Pliocene to Pleistocene age, representing the precursor of the present Caquetá River. Palynological analysis suggest that the sediments are part of the Retitricolporites and the Psiladiporites-Crototricolpites pollen zones. Fifteen new species are described which belong to the genera: Psilatricolpites, Retitricolpites, Retitricolporites, Bombacacidites, Syncolporites and Psilastephanocolporites. The palynological assemblages indicate that the area was characterized by palm swamps, riparian vegetation and a rather diverse tropical forest. Intervals rich in marine palynomorphs accompanied by high concentrations of mangrove pollen grains ( Zonocostites) suggest periods of marine influences and mangrove development. It is thought that the marine intervals are related to the Late Burdigalian transgression.

New evidence and model on the evolution of the southeast Anatolian orogen

Research Article| February 01, 1993 New evidence and model on the evolution of the southeast Anatolian orogen YÜCEL YILMAZ YÜCEL YILMAZ 1Istanbul Teknik Üniversitesi, Maden Fakültesi, Jeoloji Mühendisligi Bölümü. Maslak Istanbul 80628 Turkey Search for other works by this author on: GSW Google Scholar GSA Bulletin (1993) 105 (2): 251–271. https://doi.org/10.1130/0016-7606(1993)105<0251:NEAMOT>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation YÜCEL YILMAZ; New evidence and model on the evolution of the southeast Anatolian orogen. GSA Bulletin 1993;; 105 (2): 251–271. doi: https://doi.org/10.1130/0016-7606(1993)105<0251:NEAMOT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract This paper describes the orogenic evolution of the southeast Anatolian orogenic belt based mostly on new geologic data collected from its constituent tectonic units in the course of new mapping programs of the past decade.The southeast Anatolian orogenic segment of the Alpides may be divided into three approximately east-west-trending zones. From south to north, they are the Arabian Platform, followed by a zone of imbrication, and then a zone of nappes. The Arabian Platform includes a mostly marine, sedimentary succession deposited from early Cambrian to middle Miocene time. The zone of imbrication is a narrow belt sandwiched between the Arabian Platform and the zone of nappes. It consists of imbricated thrust slices emplaced onto a Late Cretaceous to early Miocene sequence. The zone of nappes is the highest tectonic unit, consisting of two stacks of nappes simply designated the lower and upper nappes. The lower nappe is represented by the slices of a polyphase metamorpbic ophiolitic assemblage and the Maden Group. The upper nappe rests on the lower nappe and is represented by the Bitlis and Pötürge metamorphic massifs.Southeastern Anatolia underwent two major episodes of Alpide deformation. The first occurred during the Late Cretaceous period, when ophiolite was emplaced on the Arabian Platform. This event was not the consequence of a continental collision. The ophiolite obduction onto the Arabian Platform was followed by a regionwide extension and a new marine transgression over the platform immediately after the ophiolite obduction. The second episode of deformation occurred during middle Eocene-Miocene time in two distinct stages as a result of the progressive elimination and complete closure of the ocean(s) which led to the collision between the zone of nappes located to the north (being a part of Eurasia) and the Arabian plate. The Maden marginal basin formed north of the subduction zone that eliminated the ocean between Eurasia and Arabia, along the southern margin of the Taurus belt, and abutted the Arabian Plate much later, during the final collision.The second episode of deformation formed the present orogenic segment leading to the amalgamation of different tectonic units. These amalgamated nappes collided with the Arabian plate and welded onto it at the latest stage of the orogenic evolution during the Miocene epoch. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Miocene biofacies development and geological history of the Gulf of Suez, Egypt

Miocene sediments of the Gulf of Suez were deposited in a rapidly subsiding rift which became active during Late Oligocene and Early Pliocene tectonic episodes. Complex lithological variations associated with the variable submarine structure commonly preclude detailed correlation of drilled subsurface successions. Thick Middle to Late Miocene evaporites and their geometry obscure seismic interpretation of prospective sub-evaporitic Early and Middle Miocene sequences. The thick Miocene sediments are believed to have significantly furnished the source, as well as the reservoirs and seals for the oil discovered in the Gulf of Suez. Over four billion barrels of oil have been established as recoverable reserves in Miocene reservoirs. A new Gulf-wide detailed correlation scheme is established based upon a series of newly defined microfaunal assemblage zones. These zones are based on holistic analysis of microfauna utilizing planktonic and benthonic foraminifera, diatoms, otoliths and pteropods. Dating by planktonic foraminifera and calcareous nannofossils indicates the zones are isochronous. Vertical and lateral variations in assemblage characteristics have been identified, mapped and are concluded to be the results of vertical and lateral differences in salinity, water depth, water clarity, lithological variation and oxygen availability. The correlative applicability of this scheme within the Gulf of Suez provides potential for it to serve as a reference for drilled sequences in the Red Sea, where thicker evaporite sequences make sub-evaporitic stratigraphic correlation even more difficult owing to the greater seismic attenuation. Isochronous palaeoenvironmental variations are detected, utilizing the zonation scheme, both within the Gulf of Suez and the Red Sea region, which will assist in the correlation and mapping of stratigraphic sequences of hydrocabon potential. Detection, confirmation and the degree of displacement of faults is also improved by the application of the scheme.

Early to Middle Miocene Planktonic Foraminiferal Datum Levels of the Equatorial and Subtropical Pacific

Early to Middle Miocene Planktonic Foraminiferal Datum Levels of the Equatorial and Subtropical Pacific