Calcareous nannofossil abundance and datums of sediments from ODP Leg 170 sites

Three Pleistocene, five Pliocene, and thirteen late and middle Miocene calcareous nannofossil datums have been identified in the Leg 170 cored sequences collected from a transect across the Middle America Trench off the Nicoya Peninsula. Although some nannofossil zones could not be delineated, particularly in the Pliocene and upper Miocene, there appears to be a complete or very nearly complete Pleistocene through lower Miocene section at Sites 1039 and 1040. The oldest assemblages, observed at Site 1039 and 1040, are latest early Miocene in age (nannofossil Zone NN4). These assemblages are associated with gabbro intrusions into the basal sediments (one contact metamorphic hornfels sample contains relict nannofossils), indicating an age for the intrusion event of between 15.6 and 18.2 Ma at both Sites 1039 and 1040. Reference Site 1039, located on the Cocos plate, provides the best-preserved sequence of sediments of late Pleistocene to latest early Miocene age. The sediments cored in the prism sections at Sites 1040, 1041, 1042, and 1043 all indicate that the age of nannofossil assemblages in the prism sediments, including the toe, wedge, and apron, are all Pleistocene with a considerable amount of upper Miocene reworking. A period of low sediment accumulation rates (~5.3 m/m.y.) is recorded for Pliocene and upper Miocene sediments at Sites 1039, 1040, and 1043. Pliocene calcareous nannofossil assemblages characteristic of the ~2.5- to 3.75-m.y. time interval (nannofossil Zones NN16 and equivalent nannofossil Subzones CN12b and CN12a) were not resolved at any site. Nannofossil Zones NN15, NN14, NN13, and NN12 (early late Pliocene to early Pliocene) could not be resolved at any site either because of the absence of marker species. Within the Miocene at Sites 1039 and 1040, nannofossil Zones NN10-NN6 were difficult to differentiate because of the absence of several species that define the zonal boundaries. These intervals, where the nannofossil zones have not been resolved or are partially resolved, are primarily composed of carbonate ooze deposited during an ~8.5-m.y. (2.5-11 Ma) low sediment accumulation rate time interval. The absence of many of the marker species is attributed to warmer water conditions during those periods. Many of the same marker species are absent in the sediments recovered from nearby Deep Sea Drilling Project Site 155 in the Panama Basin.

Miocene calcareous nannofossil abundance and events in sediments of ODP Leg 189 sites

During Ocean Drilling Program (ODP) Leg 189, five sites were drilled in the Tasmanian Seaway with the objective to constrain the paleoceanographic implications of the separation of Australia from Antarctica and to elucidate the paleoceanographic developments throughout the Neogene (Shipboard Scientific Party, 2001a, doi:10.2973/odp.proc.ir.189.101.2001). Sediments ranged from Cretaceous to Quaternary in age and provided the opportunity to describe the paleoenvironments in the Tasman Seaway prior to, during, and after the separation of Australia and Antarctica. This study will focus on postseparation distribution of calcareous nannofossils through the Miocene. Miocene sediments were recovered at all five Leg 189 sites, and four of these sites were studied in detail to determine the calcareous nannofossil biostratigraphy. Hole 1168A, located on the western Tasmanian margin, contains a fairly continuous Miocene record and could be easily zoned using the Okada and Bukry (1980, doi:10.1016/0377-8398(80)90016-X) zonation. Analysis of sediments from Hole 1169A, located on the western South Tasman Rise, was not included in this study, as the recovered sediments were highly disturbed and unsuitable for further analysis (Shipboard Scientific Party, 2001c, doi:10.2973/odp.proc.ir.189.104.2001). Holes 1170A, 1171A, and 1171C are located on the South Tasman Rise south of the modern Subtropical Front (STF). They revealed incomplete Miocene sequences intersected by an early Miocene and late Miocene hiatus and could only be roughly zoned using the Okada and Bukry zonation. Similarly, Hole 1172A, located on the East Tasman Plateau, contains a Miocene sequence with a hiatus in the early Miocene and in the late Miocene and could only be roughly zoned using the Okada and Bukry (1980, doi:10.1016/0377-8398(80)90016-X) zonation. This study aims to improve calcareous nannofossil biostratigraphic resolution in this sector of the mid to high southern latitudes. This paper will present abundance, preservation, and stratigraphic distribution of calcareous nannofossils through the Miocene and focus mainly on biozonal assignment.

Nannofossil biostratigraphy of ODP Hole 206-1256B sediments

Site 1256 of Ocean Drilling Program Leg 206 to the Guatemala Basin on the eastern flank of the East Pacific Rise yielded a near-complete, middle Miocene-Quaternary carbonate-rich section that provides an opportunity to study low-latitude biostratigraphic and paleoceanographic events. The sedimentary sequence in Hole 1256B has been zoned using calcareous nannofossils according to the biostratigraphic schemes by Martini of 1971 (modified by Martini and Müller in 1986) and Okada and Bukry of 1980. The nannofossil assemblage is characteristic of the low latitudes, with abundant Gephyrocapsa, Discoaster, and Sphenolithus, and is in general moderately to well preserved, depending on nannofossil abundance and the presence of diatoms. Age estimates for the first occurrence and last occurrence of Reticulofenestra rotaria were derived from biostratigraphy and magnetostratigraphy independently and assigned to 7.18 and 6.32 Ma, respectively. Linear sedimentation rates, calculated using 28 nannofossil datums and age estimates, are high in the middle Miocene, decrease from the late Miocene to the Pliocene, then increase upsection. The abrupt drop in carbonate mass accumulation rates during the early late Miocene is referred to as the "carbonate crash." This pattern reflects (1) the long-trend decrease of productivity as the site moves away from the upwelling system at the equatorial divergence as well as (2) fluctuation in the chemistry of the bottom waters associated with production of the North Atlantic Bottom Water and ventilation via the Panama Gateway. A basement age of 14.5 Ma was obtained by extrapolating the 39.1-m/m.y. rate in the middle Miocene to the basement at 250.7 meters below seafloor, and is consistent with the ~15-Ma age of the oceanic crust estimated from marine magnetic anomalies. Reworked nannofossils and lithologic changes were used to unravel postdepositional history, and three episodes were recognized, one of which in the latest Miocene can be widely correlated.

Late Miocene to Holocene calcareous nannofossils from ODP sites of Leg 125

During Leg 125 of the Ocean Drilling Program, nine sites were drilled in the Mariana and Izu-Bonin areas. The sediments recovered range in age from early Pliocene to late Pleistocene in the Mariana Region and from middle Eocene to late Pleistocene in the Izu-Bonin region. This contribution concerns the biostratigraphic study of the latest Miocene (CN9b Subzone) to late Pleistocene interval. Aquantitative analysis of all calcareous nannofossil associations was conducted for the interval encompassing late Miocene to the top of the early Pliocene. Moreover, the genera Discoaster, Amaurolithus, and Ceratolithus were quantitatively investigated from the late Miocene to late Pliocene interval. Some bioevents were identified, and variations in the composition of assemblages were linked to climatic changes.

Cenozoic calcareous nannofossils from the Lesser Antilles Forearc Region

During Leg 110 of the Ocean Drilling Program, sediment was recovered from six sites in the vicinity of the Lesser Antilles Forearc. Hole 671B, drilled near the toe of the Barbados deformation front, was the first-ever penetration of the decollement between the underthrusting Atlantic Plate and the off scraped Barbados accretionary prism. Stratigraphic repetitions in sequence associated with tectonic movement along the decollement zone, first observed on DSDP Leg 78A, were further documented at four ODP Leg 110 sites. A significant biostratigraphic inversion is present at Site 671 at 128 mbsf in which upper Miocene sediments rest atop lower Pleistocene strata. Smaller repetitions in sequence are recorded at Sites 671, 673, 674, and 676. Leg 110 sediments range from middle Eocene to early Pleistocene in age. Pliocene/Pleistocene assemblages are generally well preserved; however, Miocene assemblages have undergone extensive dissolution at all Leg 110 sites. Paleogene sediments are sometimes recrystallized and the nannofossils contained within exhibit a range in preservation from poor to good.

Calcareous nannofossil biostratigraphy of ODP Leg 108 sediments

Calcareous nannofossils were examined from the 400 cores recovered at 12 sites during Ocean Drilling Program Leg 108 in the eastern equatorial Atlantic Ocean and along the northwest African margin, representing a transect spanning 24° of latitude. Thirty calcareous nannofossil biohorizons were recognized in the Neogene and Quaternary sequences; only Site 661, located in water depths of 3500 m, contains a fossiliferous record older than the Oligocene. At Site 661, a 200-m-thick sequence of Upper Cretaceous sediments yielded Maestrichtian and uppermost Campanian nannofossils, yet a continuous Cretaceous/Tertiary boundary was not recovered. Widespread sediment slumps and turbidites deposited at many sites interrupted the pelagic sedimentation. A careful study of calcareous nannofossil and foraminifer assemblages correlated to paleomagnetic records suggests that "slumped" units at most sites were added as extra sediments to rapidly deposited pelagic sediments, with minor disturbance of the surrounding layers. Nannofossils are generally common to abundant and moderately preserved at all sites except for those located in two upwelling areas, where placoliths are etched and discoasters overgrown. Typical low-latitudinal zonal markers were used during this study, yet some of them were considered to be of little biostratigraphic value because of their inconsistent stratigraphic ranges and low abundances. This is especially apparent for the intervals representing the Miocene/Pliocene and Oligocene/Miocene boundaries. Characteristic nannofossils of cool-water conditions and low discoaster abundances occur at the coastal African upwelling and along the south equatorial divergence sites, signifying a stronger advection of cold waters toward the equator within the Canary and Benguela eastern boundary currents.

Tertiary and Quaternary calcareous nannoplankton biostratigraphy of ODP Leg 112 holes

Positions of all cores recovered during Ocean Drilling Program (ODP) Leg 112 off Peru are shown in the standard calcareous nannoplankton zonation. Stratigraphic and regional occurrences and preservation of calcareous nannoplankton are discussed for all sites, and fossil lists are presented for selected samples. Late Miocene to Holocene nannoplankton assemblages in the upwelling systems off Peru and scattered blooms, especially of Gephyrocapsa species and Helicosphaera carteri, are described. Scyphosphaera assemblages found in late Miocene Zone NN9 {Discoaster hamatus Zone) at Site 684 are compared with similar assemblages from Gabon on the west coast of Africa. Remarkable subsidence is indicated by early and middle Eocene nearshore and shallow-water nannoplankton assemblages for Sites 682, 683, and 688. Besides several local hiatuses, major regional hiatuses were noted at Site 682 (upper Eocene, uppermost middle Eocene, and part of the lower and middle Oligocene missing), Site 683 (uppermost middle Eocene to lower part of the middle Miocene missing), and Site 688 (part of the middle Eocene, uppermost middle Eocene to upper Oligocene, and parts of the lower and middle Miocene missing).

Neogene calcareous nannofossils in ODP Leg 116 holes

The three sites (717, 718, and 719) drilled on the distal Bengal Fan during ODP Leg 116 cored turbidite sediments almost exclusively. Calcareous nannofossils were recovered sporadically and, although all of them probably have been redeposited, it is possible to date the sediments at all three sites with reasonable confidence. Site 717 penetrated the uppermost middle Miocene Catinaster coalitus highest occurrence datum and represents the most nearly continuous succession of turbidites. Site 718 penetrated the lower Miocene, well below the Helicosphaera ampliaperta highest occurrence datum, but this site contains a major late Pliocene to mid-Pleistocene hiatus. Site 719, the shallowest hole, penetrated only into the upper Miocene. Identification of several critical lowest occurrence datums allows using the poorly constrained but more numerous highest occurrence datums for comparison with the model succession (zonal markers) and thereby to derive a reasonably accurate time framework for the sediments.

Plio-Pleistocene benthic foraminifera of the Tyrrhenian Sea

Benthic foraminifers from Site 652, Site 653 (Hole 653A), and Site 654 of Leg 107 (Tyrrhenian Sea, Western Mediterranean), which penetrated with more or less good recovery the Plio-Pleistocene stratigraphic interval, were studied in a total of 699 close-spaced samples. A total number of 269 species have been classified and their quantitative distribution in each sample is reported. The benthic foraminifers assemblage is more diversified in Site 654, less diversified in Site 652. Less than a half of the benthic foraminifers species listed from Plio-Pleistocene Italian land sections are present in the coeval deep-sea Tyrrhenian record, in which shallow water species are missing and Nodosarids are poorly represented. A very few species have comparable stratigraphic distribution in the three deep-sea sequences and in Italian land sections when compared against calcareous plankton biostratigraphy. In the same three sites, the first appearance levels of several species are younger and younger, and last appearance levels are earlier and earlier from Site 654 to Site 653 and Site 652. Five biostratigraphic events, biochronologically evaluated and occurring at the same level in the deepsea Tyrrhenian record and in several land sections, have been selected as zonal boundaries of the proposed benthic foraminifers biostratigraphic scheme. The Plio-Pleistocene interval has been subdivided into four biozones and one subzone, recognizable both in the deep-sea and land-based sequences. The Cibicidoides (?) italicus assemblage zone stretches from the base of the Pliocene to the extinction level of the zonal marker, biochronologically evaluated at 2.9 Ma. The Cibicidoides robertsonianus interval zone stretches from the Cibicidoides (?) italicus extinction level to the Pliocene Mediterranean FO of Gyroidinoides altiformis, evaluated at 2.4 Ma. The Gyroidinoides altiformis interval zone stretches from the Mediterranean Pliocene FO of the zonal marker to the appearance level of Articulina tubulosa, evaluated at 1.62 Ma. The Articulina tubulosa assemblage zone stretches from the appearance level of the zonal marker to the Recent. In the Articulina tubulosa biozone, the Hyalinea baltica subzone is proposed. The appearance level of Hyalinea baltica is evaluated at 1.35 Ma, well above the Plio-Pleistocene boundary as defined in the Vrica stratotype section.

Sediment geochemistry, foraminiferal fauna parameter, census counts and Varimax PC-factor loadings and scores of foraminiferal assemblages of sediment core GeoB12615-4

Analogous to West- and North Africa, East Africa experienced more humid conditions between approximately 12 to 5 kyr BP, relative to today. While timing and extension of wet phases in the North and West are well constrained, this is not the case for the East African Humid Period. Here we present a record of benthic foraminiferal assemblages and sediment elemental compositions of a sediment core from the East African continental slope, in order to provide insight into the regional shallow Indian Ocean paleoceanography and East African climate history of the last 40 kyr. During glacial times, the dominance of a benthic foraminiferal assemblage characterized by Bulimina aculeata, suggests enhanced surface productivity and sustained flux of organic carbon to the sea floor. During Heinrich Stadial 1 (H1), the Nuttallides rugosus Assemblage indicates oligotrophic bottom water conditions and therefore implies a stronger flow of southern-sourced AAIW to the study site. During the East African Humid Period, the Saidovina karreriana Assemblage in combination with sedimentary C/N and Fe/Ca ratios suggest higher river runoff to the Indian Ocean, and hence more humid conditions in East Africa. Between 8.5 and 8.1 kyr, contemporaneous to the globally documented 8.2 kyr Event, a severe reduction in river deposits implies more arid conditions on the continent. Comparison of our marine data with terrestrial studies suggests that additional moisture from the Atlantic Ocean, delivered by an eastward migration of the Congo Air Boundary during that time period, could have contributed to East African rainfall. Since approximately 9 kyr, the gaining influence of the Millettiana millettii Assemblage indicates a redevelopment of the East African fringe reefs.

Pliocene-Pleistocene calcareous nannofossils from the Iberian Abyssal Plain

During Ocean Drilling Program Leg 149, five sites were drilled on the Iberia Abyssal Plain, west of the Iberian Peninsula. Five holes (Holes 897A, 897C, 898A, 899A, and 900A) yielded Pliocene-Pleistocene sediments, which consist mainly of turbidites. Among these, Holes 897C and 898A yielded significant Pliocene-Pleistocene sediments that provided a high-resolution nannofossil biostratigraphy essential for locating paleomagnetic polarity events and for interpreting the age and frequency of turbidite sedimentation in the Iberia Abyssal Plain. Pliocene-Pleistocene nannofossils recovered during Leg 149 are generally abundant and well to moderately preserved. Although reworking is evident in most samples, the Pliocene-Pleistocene nannofossils proved quite reliable for dating the sediments. Most Pleistocene zonal boundaries proposed by S. Gartner in 1977 and the Pliocene standard zonal boundaries proposed by E. Martini in 1971 were easily recognized. In addition, several other nannofossil events proposed by D. Rio et al. in 1990 and by T. Sato and T. Takayama in 1992 were recognized and proved valuable for improving the resolution of Pliocene-Pleistocene nannofossil biostratigraphy. The Pliocene-Pleistocene nannofossil biostratigraphic results of Holes 897C and 900A coincide rather well with the discerned paleomagnetic polarity events. As a result, the combination of nannofossil biostratigraphic and paleomagnetic studies provides important information for fulfilling the second objective of this leg: to determine the history of turbidite sedimentation in the Iberia Abyssal Plain. The general trend of sedimentation rates inferred by nannofossil biostratigraphy indicates that sedimentation rates increase from the continental margin to the deep sea along with increasing water depth.

Calcareous nannofossils in ODP Hole 131-808C

ODP Leg 131 recovered nannofossil-bearing sediments from Site 808 in the Nankai Trough, western Pacific Ocean. Three holes were examined for nannofossils, 808A, 808B, and 808C. A total of 22 nannofossil events were recognized, of which 10 are used as zonal markers. The sediments recovered from Hole 808A (0-111.4 mbsf) contain Pleistocene nannofossil assemblages that are mostly well preserved. All samples from this hole were assigned to nannofossil Zone NN21. The nannofossil assemblages observed in Hole 808B (111.0-358.8 mbsf) are poorly to well preserved and were all assigned to the Pleistocene. The NN21/NN20 Boundary is placed at 230.7 ± 4.4 mbsf. Hole 808C was cored from 298.5 to 1327 mbsf and basalt was reached at 1289.9 mbsf. The sediments recovered range in age from the upper part of Zone NN20 of the Pleistocene to Zone NN5 of the middle Miocene and contain poorly to well-preserved nannofossil assemblages. The Pliocene/Pleistocene Boundary, marked by the FO Gephyrocapsa caribbeanica, was placed at 776.3 ±1.6 mbsf, and the Miocene/Pliocene Boundary is tentatively placed at 955.9 ±1.5 mbsf. The lowermost sediments above basement as well as a sediment sample intercalated between basalt flows are assigned to Zone NN5, with an age of approximately 15 Ma. Age estimates provided by nannofossils show that the sedimentation rate in the trench-fill deposits of the Nankai Trough was very high, 800-1350 m/m.y (0-0.46 Ma), whereas in the Shikoku Basin deposits (> 0.46 Ma), the sedimentation rate was much lower (24-200 m/m.y). These age estimates also provide an extrapolated age of approximately 15 Ma for the basaltic basement at Site 808.

Cenozoic calcareous nannofossils in DSDP Leg 77 holes

Three of the six DSDP Leg 77 sites drilled in the western approaches to the Straits of Florida yielded thick sequences of Cenozoic sediment rich in calcareous nannofossils. Hiatuses are prominent in each of these continuously cored intervals. A prominent upper Oligocene hiatus, observed at each of these three sites, can be correlated to a large-scale "global" regression event. Other disconformable horizons present in the study area cannot be positively related to sealevel fluctuations and may be caused by a number of factors including local tectonic activity. Paleogene sections are generally marked by thick accumulations within the upper Oligocene Sphenolithus ciperoensis Zone and by a pronounced braarudosphaerid-holococcolith bloom recorded in the lower Oligocene and upper Eocene. This bloom is particularly well developed at Site 540. All samples examined contain abundant nannofossils. Preservation fluctuates throughout the sections from good to poor.

Occurrence of nannoplankton observed in Early Pliocene samples from Zanclean stratotype of Capo Rossello, Sicily (Table I)

Calcareous nannoplankton biostratigraphy has been worked out in the eastern Mediterranean utilizing deep-sea sediments recovered from DSDP Leg 42A Sites 375 and 376. These two drill sites were located approximately 55 km west of Cyprus on the Florence Rise. Sediments, ranging in age from early Miocene (Helicosphaera ampliaperta Zone) through Holocene, contain sufficient age-diagnostic species to recognize essentially all of the lowlatitude nannoplankton zones described by Bukry, although regional, secondary marker species are needed to define some zonal boundaries. Reworked Cretaceous and Paleogene nannoplankton occur throughout the stratigraphic interval studied, but not in quantities large enough to mask indigenous species. Sedimentation rates at Sites 375 and 376 were highest in the late Miocene and late Pleistocene. Open-marine, warm-water species of discoasters are present in significant numbers throughout the Miocene and Pliocene. Earliest Pliocene assemblages contain numerous specimens of ceratoliths. Nannoplankton in post-Messinian sediments at the drill sites and the Zanclean stratotype at Capo Rossello, Sicily, indicate that the base of the Amaurolithus tricorniculatus Zone (base of Triquetrorhabdulus rugosus Subzone) corresponds with the Miocene-Pliocene boundary.