CRETACEOUS ANOXIC EVENTS

Micropaleontology in Multi-disciplinary research: Applications to OAE2 and KTB

TitleMicropaleontology in Multi-disciplinary research: Applications to OAE2 and KTB
Publication TypeBook Chapter
Year of Publication2013
AuthorsKeller, G
Book TitleProceedings of XXIII Indian Colloquium on Micropaloentology and Stratigraphy and International Symposium on Global Bioevents in Earth's History
Volume1
ChapterPart I, Pp. 1
EditionSpecial Publication
PublisherGeological Society of India
CityBangalore
ISBN978-93-80998-08-04
Keywordsapplications
URLhttp://www.geosocindia.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=227&category_id=20&option=com_virtuemart&Itemid=6

Stratigraphy of the Cenomanian–Turonian Oceanic Anoxic Event OAE2 in shallow shelf sequences of NE Egypt

TitleStratigraphy of the Cenomanian–Turonian Oceanic Anoxic Event OAE2 in shallow shelf sequences of NE Egypt
Publication TypeJournal Article
Year of Publication2011
AuthorsEl-Sabbagh, A, Tantawy, AAAM, Keller, G, Khozyem, H, Spangenberg, J, Adatte, T, Gertsch, B
JournalCretaceous Research
Volume32
Issue6
Pagination705 - 722
Date PublishedJan-12-2011
ISSN01956671
Abstract

Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated to evaluate the response to OAE2. Age control based on calcareous nannoplankton, planktic foraminifera and ammonite biostratigraphies integrated with δ13C stratigraphy is relatively good despite low diversity and sporadic occurrences. Planktic and benthic foraminiferal faunas are characterized by dysoxic, brackish and mesotrophic conditions, as indicated by low species diversity, low oxygen and low salinity tolerant planktic and benthic species, along with oyster-rich limestone layers. In these subtidal to inner neritic environments the OAE2 δ13C excursion appears comparable and coeval to that of open marine environments. However, in contrast to open marine environments where anoxic conditions begin after the first δ13C peak and end at or near the Cenomanian–Turonian boundary, in shallow coastal environments anoxic conditions do not appear until the early Turonian. This delay in anoxia appears to be related to the sea-level transgression that reached its maximum in the early Turonian, as observed in shallow water sections from Egypt to Morocco.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0195667111000474
DOI10.1016/j.cretres.2011.04.006
Short TitleCretaceous Research

Middle and late Cenomanian oceanic anoxic events in shallow and deeper shelf environments of western Morocco

TitleMiddle and late Cenomanian oceanic anoxic events in shallow and deeper shelf environments of western Morocco
Publication TypeJournal Article
Year of Publication2010
AuthorsGertsch, B, Adatte, T, Keller, G, Tantawy, AAAM, Berner, Z, Mort, HP, Fleitmann, D
JournalSedimentology
Volume57
Issue6
Pagination1430 - 1462
Date PublishedJan-10-2010
KeywordsMiddle Cenomanian event, Morocco, oceanic anoxic event 2, palaeoclimate, shallow shelf environments
Abstract

The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ13Corg for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ13C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.  PDF

URLhttp://doi.wiley.com/10.1111/j.1365-3091.2010.01151.x
DOI10.1111/sed.2010.57.issue-610.1111/j.1365-3091.2010.01151.x

Cenomanian–Turonian transition in a shallow water sequence of the Sinai, Egypt

TitleCenomanian–Turonian transition in a shallow water sequence of the Sinai, Egypt
Publication TypeJournal Article
Year of Publication2008
AuthorsGertsch, B, Keller, G, Adatte, T, Berner, Z, Kassab, AS, Tantawy, AAAM, El-Sabbagh, AM, Stüben, D
JournalInternational Journal of Earth Sciences
Volume99
Issue1
Pagination165 - 182
Date PublishedJan-01-2010
ISSN1437-3254
Abstract

Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, δ13C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanian–early Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, low-oxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak δ13C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the δ13C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the δ13C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first δ13C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous δ13C shift, but delayed effects of OAE2 dependent on water depth.  PDF

URLhttp://link.springer.com/article/10.1007%2Fs00531-008-0374-4
DOI10.1007/s00531-008-0374-4
Short TitleInt J Earth Sci (Geol Rundsch)

Oceanic events and biotic effects of the Cenomanian-Turonian anoxic event, Tarfaya Basin, Morocco

TitleOceanic events and biotic effects of the Cenomanian-Turonian anoxic event, Tarfaya Basin, Morocco
Publication TypeJournal Article
Year of Publication2008
AuthorsKeller, G, Adatte, T, Berner, Z, Chellai, EH, Stüben, D
JournalCretaceous Research
Volume29
Issue5-6
Pagination976 - 994
Date PublishedJan-10-2008
ISSN01956671
Abstract

Profound biotic changes accompanied the late Cenomanian δ13C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover, though no mass extinction, beginning with the rapid δ13C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding δ13C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in diversity to just two species, the dominant (80–90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0195667108000773
DOI10.1016/j.cretres.2008.05.020
Short TitleCretaceous Research

Organic carbon deposition and phosphorus accumulation during Oceanic Anoxic Event 2 in Tarfaya, Morocco

TitleOrganic carbon deposition and phosphorus accumulation during Oceanic Anoxic Event 2 in Tarfaya, Morocco
Publication TypeJournal Article
Year of Publication2008
AuthorsHaydon, MP, Adatte, T, Keller, G, Bartels, D, Föllmi, KB, Steinmann, P, Berner, Z, Chellai, EH
JournalCretaceous Research
Volume29
Issue5-6
Pagination1008 - 1023
Date PublishedJan-10-2008
ISSN01956671
Abstract

With a multi-proxy approach, an attempt was made to constrain productivity and bottom-water redox conditions and their effects on the phosphorus accumulation rate at the Mohammed Plage section on the Tarfaya coast, Morocco, during the Cenomanian-Turonian Anoxic Event (OAE 2). A distinct δ13Corg isotope excursion of +2.5‰ occurs close to the top of the section. The unusually abrupt shift of the isotope excursion and disappearance of several planktonic foraminiferal species (e.g. Rotalipora cushmani and Rotalipora greenhornensis) in this level suggests a hiatus of between 40–60 kyrs at the excursion onset. Nevertheless, it was possible to determine both the long-term environmental history as well as the processes that took place immediately prior to and during OAE 2. TOC% values increase gradually from the base of the section to the top (from ∼2.5% to ∼10%). This is interpreted as the consequence of a long-term eustatic sea-level rise and subsidence causing the encroachment of less oxic waters into the Tarfaya Basin. Similarly a reduction in the mineralogically constructed ‘detrital index’ can be explained by the decrease in the continental flux of terrigenous material due to a relative sea-level rise. A speciation of phosphorus in the upper part of the section, which spans the start and mid-stages of OAE 2, shows overall higher abundances of Preactive mass accumulation rates before the isotope excursion onset and lower values during the plateau. Due to the probable short hiatus, the onset of the decrease in phosphorus content relative to the isotope excursion is uncertain, although the excursion plateau already contains lower concentrations. The Corg/Ptotal and V/Al ratios suggest that this reduction was mostly likely caused by a decrease in the available bottom oxygen content (probably as a result of higher productivity) and a corresponding fall in the phosphorus retention ability of the sediment. Productivity appears to have remained high during the isotope plateau possibly due to a combination of ocean-surface fertilisation via increased aridity (increased K/Al and Ti/Al ratios) and/or higher dissolved inorganic phosphorus content in the water column as a result of the decrease in sediment P retention. The evidence for decreased P-burial has been observed in many other palaeoenvironments during OAE 2. Tarfaya's unique upwelling paleosituation provides strong evidence that the nutrient recycling was a global phenomenon and therefore a critical factor in starting and sustaining OAE 2.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0195667108000761
DOI10.1016/j.cretres.2008.05.026
Short TitleCretaceous Research

Phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2

TitlePhosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2
Publication TypeJournal Article
Year of Publication2007
AuthorsHaydon, MP, Adatte, T, Föllmi, KB, Keller, G, Steinmann, P, Matera, V, Berner, Z, Stüben, D
JournalGeology
Volume35
Issue6
Pagination483
Date PublishedJan-01-2007
ISSN0091-7613
Abstract

Four sections documenting the impact of the late Cenomanian oceanic anoxic event (OAE 2) were studied in basins with different paleoenvironmental regimes. Accumulation rates of phosphorus (P) bound to iron, organic matter, and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of OAE 2, with an associated increase in δ13C values. Accumulation rates of P return to pre-excursion values in the interval where the δ13C record reaches its first maximum. An offset in time between the maximum in P accumulation and peaks in organic carbon burial, hydrogen indices, and Corg/Preact molar ratios is explained by the evolution of OAE 2 in the following steps. (1) An increase in productivity increased the flux of organic matter and P into the sediments; the preservation of organic matter was low and its oxidation released P, which was predominantly mineralized. (2) Enhanced productivity and oxidation of organic matter created dysoxic bottom waters; the preservation potential for organic matter increased, whereas the sediment retention potential for P decreased. (3) The latter effect sustained high primary productivity, which led to an increase in the abundance of free oxygen in the ocean and atmosphere system. After the sequestration of CO2 in the form of black shales, this oxygen helped push the ocean back into equilibrium, terminating black shale deposition and removing bioavailable P from the water column.  PDF

URLhttp://geology.geoscienceworld.org/cgi/doi/10.1130/G23475A.1
DOI10.1130/G23475A.1

Cenomanian–Turonian and δ13C, and δ18O, sea level and salinity variations at Pueblo, Colorado

TitleCenomanian–Turonian and δ13C, and δ18O, sea level and salinity variations at Pueblo, Colorado
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G, BERNER, ZSOLT, Adatte, T, Stüben, D
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume211
Issue1-2
Pagination19 - 43
Date PublishedJan-08-2004
ISSN00310182
Abstract

Stable isotopes of the surface dwelling planktic foraminifera Hedbergella planispira, its abundance variations, and mineralogical analysis of the Cenomanian–Turonian at Pueblo, CO, reveal cyclic variations in surface salinity due to changes in precipitation, freshwater influx, marine incursions and long-term sea-level fluctuations. Hedbergella planispira is a proxy for salinity variations, as indicated by 2–4x more negative δ18O values in intervals of peak abundances as compared to intervals with reduced populations. Negative δ18O values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods, accompanied by increased clastic transport. More positive δ18O values reflect more normal marine salinities as a result of arid periods and/or marine incursions and correlate with intervals of increased biogenic carbonate deposition. The magnitude of salinity variations during the low sea-level of the Hartland Shale is twice that during the sea-level transgression of the Bridge Creek Limestone. The rapid positive δ13C shift that marks the onset of Oceanic Anoxic Event 2 (OAE 2) at Pueblo occurred over a period of about 100 ky (93.90–94.00 Ma), and coincided with the major sea level transgression that culminated in the deposition of the basal Bridge Creek Limestone. A positive δ13C shift also occurred in the Rotalipora cushmani zone prior to OAE 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter. The likely cause for OAE 2 is depletion of 12C in the water column as a result of high primary productivity, whereas an earlier R. cushmani zone event was primarily caused by increased input of terrigenous organic matter. Both δ13C events are associated with enhanced organic matter preservation and anoxic or dysoxic bottom waters.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0031018204002007
DOI10.1016/j.palaeo.2004.04.003
Short TitlePalaeogeography, Palaeoclimatology, Palaeoecology

Age and paleoenvironment of the Cenomanian–Turonian global stratotype section and point at Pueblo, Colorado

TitleAge and paleoenvironment of the Cenomanian–Turonian global stratotype section and point at Pueblo, Colorado
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G, Pardo, A
JournalMarine Micropaleontology
Volume51
Issue1-2
Pagination95 - 128
Date PublishedJan-04-2004
ISSN03778398
Abstract

Biostratigraphy and stable isotopes indicate that the global stratotype section and point (GSSP) at Pueblo contains an essentially complete sedimentary record across the global ocean anoxic event (OAE 2) and the Cenomanian–Turonian boundary. The OAE 2 δ13C shift occurred over a period of about 90 ky and was accompanied by a major sea level transgression, which at its peak was marked by an incursion of oxygen-rich waters creating a benthic oxic zone that lasted about 100 ky. A mid-Cenomanian δ13C shift, sea level transgression and faunal turnover occurred about 2 my before OAE 2. δ18O values of the planktic foraminifer Hedbergella planispira and its relative abundance changes reveal cyclic variations in surface salinity due to alternating freshwater influx and marine incursions, whereas dominance by the low oxygen tolerant Heterohelix species indicates a well-developed oxygen minimum zone (OMZ) for most of the middle to late Cenomanian and early Turonian.

Profound faunal changes accompanied these oceanographic events, including the extinction of 30% of the species assemblage and an equal gain in evolutionary diversification, though the overall combined relative abundances of outgoing and incoming species were less than 2% and 4%, respectively, of the total assemblages. The faunal turnover began with the sea level transgression and rapid increase in δ13C values, and accelerated with the influx of oxygen-rich deep water, increased water mass stratification and competition during the benthic oxic zone. The incursion of oxygen-rich deep waters at this time was also observed in Morocco and may represent a global event of a still unknown source.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0377839803001051
DOI10.1016/j.marmicro.2003.08.004
Short TitleMarine Micropaleontology

Planktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A

TitlePlanktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A
Publication TypeJournal Article
Year of Publication2003
AuthorsAbramovich, S, Keller, G
JournalMarine Micropaleontology
Volume48
Issue3-4
Pagination225 - 249
Date PublishedJan-07-2003
ISSN03778398
Abstract

An abrupt global warming of 3-4°C occurred near the end of the Maastrichtian at 65.45-65.10 Ma. The environmental effects of this warm event are here documented based on stable isotopes and quantitative analysis of planktonic foraminifera at the South Atlantic DSDP Site 525A. Stable isotopes of individual species mark a rapid increase in temperature and a reduction in the vertical water mass stratification that is accompanied by a decrease in niche habitats, reduced species diversity and/or abundance, smaller species morphologies or dwarfing, and reduced photosymbiotic activity. During the warm event, the relative abundance of a large number of species decreased, including tropical^subtropical affiliated species, whereas typical mid-latitude species retained high abundances. This indicates that climate warming did not create favorable conditions for all tropical^subtropical species at mid-latitudes and did not cause a massive retreat in the local mid-latitude population. A noticeable exception is the ecological generalist Heterohelix dentata Stenestad that dominated during the cool intervals, but significantly decreased during the warm event. However, dwarfing is the most striking response to the abrupt warming and occurred in various species of different morphologies and lineages (e.g. biserial, trochospiral, keeled globotruncanids). Dwarfing is a typical reaction to environmental stress conditions and was likely the result of increased reproduction rates. Similarly, photosymbiotic activity appears to have been reduced significantly during the maximum warming, as indicated by decreased δ13C values. The foraminiferal response to climate change is thus multifaceted resulting in decreased species diversity, decreased species populations, increased competition due to reduced niche habitats, dwarfing and reduced photosymbiotic activity.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0377839803000215
DOI10.1016/S0377-8398(03)00021-5
Short TitleMarine Micropaleontology

Age and paleoenvironment of the Maastrichtian to Paleocene of the Mahajanga Basin, Madagascar: a multidisciplinary approach

TitleAge and paleoenvironment of the Maastrichtian to Paleocene of the Mahajanga Basin, Madagascar: a multidisciplinary approach
Publication TypeJournal Article
Year of Publication2003
AuthorsAbramovich, S, Keller, G, Adatte, T, Stinnesbeck, W, Hottinger, L, Stüben, D, Berner, Z, Ramanivosoa, B, Randriamanantenasoa, A
JournalMarine Micropaleontology
Volume47
Issue1-2
Pagination17 - 70
Date PublishedJan-01-2003
ISSN03778398
KeywordsMadagascar; Maastrichtian; Paleocene; age; paleoclimate; paleoenvironment
Abstract

Lithology, geochemistry, stable isotopes and integrated high-resolution biostratigraphy of the Berivotra and Amboanio sections provide new insights into the age, faunal turnovers, climate, sea level and environmental changes of the Maastrichtian to early Paleocene of the Mahajanga Basin of Madagascar. In the Berivotra type area, the dinosaur-rich fluvial lowland sediments of the Anembalemba Member prevailed into the earliest Maastrichtian. These are overlain by marginal marine and near-shore clastics that deepen upwards to hemipelagic middle neritic marls by 69.6 Ma, accompanied by arid to seasonally cool temperate climates through the early and late Maastrichtian. An unconformity between the Berivotra Formation and Betsiboka limestone marks the K–T boundary, and juxtaposes early Danian (zone Plc? or Pld) and latest Maastrichtian (zones CF2–CF1, Micula prinsii) sediments. Seasonally humid warm climates began near the end of the Maastrichtian and prevailed into the early Danian, accompanied by increased volcanic activity. During the late Danian (zones P1d–P2), a change to seasonally arid climates was accompanied by deepening from middle to outer neritic depths.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0377839802000944
DOI10.1016/S0377-8398(02)00094-4
Short TitleMarine Micropaleontology

Palaeoenvironment of the Cenomanian–Turonian transition at Eastbourne, England

TitlePalaeoenvironment of the Cenomanian–Turonian transition at Eastbourne, England
Publication TypeJournal Article
Year of Publication2001
AuthorsKeller, G, Han, Q, Adatte, T, Burns, SJ
JournalCretaceous Research
Volume22
Issue4
Pagination391 - 422
Date PublishedJan-08-2001
ISSN01956671
KeywordsCenomanian–Turonian; Eastbourne; planktic foraminifera; stable isotopes; sea-level changes
Abstract

Lithology, stable isotopes and planktic foraminiferal analyses of the Eastbourne section at Gun Gardens (southeast England) reflect sea-level fluctuations and changing climatic and oceanographic conditions across the Cenomanian–Turonian transition. The δ13C excursion began with a 1.8‰ positive shift in Plenus Marls Beds 1–3 (R. cushmani Zone), a trough in Bed 4, a second δ13C shift of 0.8‰ in Bed 7 and a gradually decreasing plateau during deposition of the Ballard Cliff Member. Lithological variations, sharp erosion surfaces, bioturbation and increased detrital influx indicate that sea-level fluctuations, cooling and a marine regression accompanied the δ13C excursion within the Plenus Marls, followed by warming and a major marine transgression in the upper part of the Plenus Marls and Ballard Cliff Member. Two faunal turnover phases coincided with the two-phased δ13C excursion. Phase I in Bed 3 is marked by the extinction of the deeper dwelling planktic foraminifer Rotalipora, the origination of the thermocline dweller Dicarinella, dominance of the low oxygen tolerant Heterohelix species, and common surface dwellers Guembelitria and Whiteinella. This faunal turnover reflects a lower sea level, enhanced productivity and temporary expansion of the oxygen minimum zone associated with climate cooling and increased upwelling. Phase II near the top of the Plenus Marls (Beds 7–8) is marked by the temporary disappearance of about 50% of the species, increased abundance of surface dwellers and a shift to dominance of low-oxygen tolerant Heterohelix species globally. This faunal turnover may reflect increased primary productivity and a long-term expansion of the oxygen minimum zone associated with climate warming and a marine transgression. Faunal turnover phase II stratigraphically correlates with the global oceanic anoxic event in Italy (Bonarelli Level) and Tunisia (Bahloul Formation), whereas phase I correlates with the onset of organic-rich facies in the upper R. cushmani Zone of these regions. High resolution biostratigraphic correlation is based on planktic foraminifera and the subdivision of Whiteinella archeocretacea Zone into three subzones.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0195667101902642
DOI10.1006/cres.2001.0264
Short TitleCretaceous Research

A multiple microfossil biochronology for the Miocene

TitleA multiple microfossil biochronology for the Miocene
Publication TypeBook Chapter
Year of Publication1985
AuthorsBARRON, JOHNA, Keller, G, Dunn, DA
Book TitleGeological Society of America Memoirs
Pagination21–36
PublisherGeological Society of America
Abstract

A multiple microfossil biochronology is presented for the Miocene which allows resolution of time approaching 100,000 years. Carbonate stratigraphy is integrated to greatly enhance this resolution. Graphical correlation techniques were applied to over 20 DSDP (Deep Sea Drilling Project) sections to identify 175 planktonic foraminiferal, calcareous nannofossil, radiolarian, and diatom datum levels between 24.0 and 4.3 Ma which show the most consistent (isochronous) correlations. Ages are estimated for these datum levels through 72 direct correlations to paleomagnetic stratigraphy and extrapolation between the correlation points. The resulting Miocene time scale resembles previously published time scales except for the early Miocene, where recent paleomagnetic correlations result in changes.

The three CENOP (Cenozoic Paleoceanography Project) time slices (~21, 16, and 8 Ma) are characterized biostratigraphically (planktonic foraminifers, calcareous nannofossils, radiolarians, and diatoms) and in terms of carbonate stratigraphy. The ages of the time slices are estimated as follows: the early Miocene time slice (21.2–20.1 Ma; given as 22 Ma in this volume), the late early Miocene time slice (16.4–15.2 Ma), and the late Miocene time slice (8.9–8.2 Ma).

An alternate time scale utilizing a paleomagnetic Anomaly 5-paleomagnetic Chron 11 correlation is also presented. Estimated ages for microfossil zones and datum levels in the late middle and early late Miocene (14–7 Ma) utilizing the alternate time scale are generally younger than those for the more traditional time scale. The late Miocene time slice has an estimated age of 8.0–7.0 Ma.  PDF

URLhttps://doi.org/10.1130/mem163-p21
DOI10.1130/mem163-p21