(Table 1) Distribution of larger benthic and planktonic foraminifers in ODP Hole 135-841B

Larger foraminifers were recovered from three levels within Hole 841B, located on the Tongan Platform. The lowest faunas are from Eocene beds (Unit V) in fault contact with an older rhyolitic volcanic sequence. These Eocene faunas are typified by two assemblages: one with Amphistegina waiareka, Astewcyclina matanzensis, Discocyclina omphala, Operculina pacifica, together with rare Heterostegina saipanensis and Sherbornina carteri; the second assemblage contains these species and, in addition, Spiroclypeus vermicularis. The lowest assemblage is associated with a middle Eocene planktonic foraminifer fauna (Acarinina, Morozovella), and the upper faunas with a late Eocene assemblage. This Eocene unit is disconformably overlain by a middle Miocene sequence (Unit IV) containing assemblages dominated by planktonic foraminifers. Two samples were found to contain shallow-water benthic foraminifers: one contained Amphistegina radiata, Cycloclypeus sp., Lepidocyclina (Nephrolepidina) ?howchini, and Sphaerogypsina globula; a second sample from this section contained only Amphistegina radiata. The third level at which larger foraminifers were found was in the lower part of the late Miocene section (Unit III), where late Eocene larger foraminifers (Asterocyclina matanzensis, Discocyclina omphala, Nummulites pengaronensis, and Pellatispira madaraszi) are present in a conglomeratic sequence with late Miocene planktonic foraminifers present in the matrix. The two larger foraminifer assemblages of Unit V are typical of the Ta3 and Tb Letter Stages, which are distinguished by the presence of Spiroclypeus vermicularis. The Ta3 Letter Stage assemblage is associated with a Zone P14 planktonic fauna, and the Tb Letter Stage assemblage with Zones PI5 to PI6 fauna. The larger foraminifers associated with middle and late Eocene planktonic foraminifers are almost certainly in situ, and indicate water depths from between 50 and 100 m in the middle Eocene, shallowing to 100 m by the end of the Eocene. The middle Miocene faunas have been derived from shallow-water environments adjacent to the sites of deposition (which would have been in excess of 100 m), and may have been contemporaneous or reworked from rocks no older than the Ta5 Letter Stage. Late Eocene larger foraminifers (Tb Letter Stage) were reworked into the deep-water, late Miocene environments as products of erosion from adjacent exposures of Eocene carbonates. A hiatus is probably present in the lower part of the Eocene section, separating the middle and late Eocene (Ta3 and Tb Letter Stages-Zones P14 and P15). This is probably the result of eustatic changes. Unit V almost certainly contains the Eocene/Oligocene boundary, based on the planktonic foraminifer evidence, but larger foraminifers disappear some distance below this boundary, within Zones P15 or P16. The larger foraminifer faunas from Units III and V provide evidence that water depths at this part of the Tongan Platform have increased from approximately 50 m during the late middle Eocene to below the calcium carbonate compensation depth by the late Miocene, respectively

Miocene to Pleistocene planktonic foraminifer biostratigraphy of ODP Leg 135 sites

Diverse and well-preserved planktonic foraminifers were recovered from six sites (834-839) drilled in the Lau Basin. Planktonic faunas from the Tongan Platform sites varied from those of the Lau Basin sites by being less well preserved (Site 840) to being very poorly preserved and very sparse (Site 841); at Site 841 most samples were barren. All sites penetrated a volcaniclastic sequence in which thick ash beds were encountered; foraminifer populations within the ash beds were often very small, making it difficult to obtain biostratigraphic data. No hiatuses were encountered in the upper Miocene to Pleistocene sections of the Lau Basin, but a possible break occurs at Site 840 on the Tongan Platform. Site 834 penetrated through a Quaternary-Pliocene sequence overlying basaltic basement, and topmost Miocene (Zone N17B) sediments interbedded within the volcanic sequence. Site 835 penetrated into the lower Pliocene (Zones N19 to N19-20). Site 836 penetrated the shortest section, with Zone N22 {Globorotalia (Truncorotalia) crassaformis hessi Subzone) directly overlying basalts. Site 837 penetrated into the basal part of Zone N22 (Globigerinoides quadrilobatus fistulosus Subzone) overlying basalt. Site 838 failed to encounter basalts, with the oldest sediment being from Zone N22 (Globigerinoides quadrilobatus fistulosus Subzone). Site 839, within the same basin as Site 838, located Zone N22 (Globigerinoides quadrilobatus fistulosus Subzone) sediments directly overlying igneous basement. Site 840 penetrated into the upper Miocene Zone N17A without encountering any major unconformity. Site 841, studied mainly from core-catcher samples, penetrated a Quaternary to questionable upper Miocene sequence that was in fault contact with middle Miocene (Zones N8 to N9) sediments. For the Lau Basin sites, reworking was encountered only in Sites 834 and 835. Site 834 was drilled adjacent to the Lau Ridge, on which are developed numerous reef al and shallow-water environments, where erosional conditions could have been expected during sea-level lowstands. Site 835 was drilled in a narrow basin that has been remote from these erosional influences; slumping and erosion of material from the adjacent basin slopes appears to have been the source of the reworking. For the Tongan Platform sites, reworking was observed only in the lower part of the upper Miocene section at Site 841, where late Eocene larger foraminifers are present in conglomerates and grits. The presence of Globorotalia (Globorotalia) multicamerata and small specimens of Sphaeroidinellopsis spp. in the Pleistocene of Site 840 may indicate reworking, but this is not clear. Unit I, which marks a reduction in volcanic activity in the Lau Basin, ranges in age from the lower part of Zone N22 (Globigerinoides quadrilobatus fistulosus Subzone) at Sites 834 and 835, to within Zone N22 (Globorotalia crassaformis hessi Subzone) at Sites 836 to 838, and within the upper part of Zone N22 (Bolliella praeadamsi Subzone) at Site 839. Units II and III are generally represented by thick to very thick ash beds, which generally contain low-diversity and often poorly preserved assemblages. Igneous sources seem to have remained important contributors of sediment up to the present day

Paleogene and Neogene larger foraminifera of ODP Leg 133 holes

At several sites drilled during Ocean Drilling Program (ODP) Leg 133 on the Queensland Plateau, larger shallow-water benthic foraminifers have been recovered from neritic carbonates and from turbidites that consist of shallow-water-derived material. Within neritic sediments, the occurrence of different faunal associations provides a tool for biostratigraphic subdivision. Three main phases of neritic deposition occurred on the Queensland Plateau. An Eocene episode is characterized by subtropical to temperate associations (Operculina—Nummulites Facies). It is unconformably followed by a late Oligocene to middle Miocene episode that contains tropical to subtropical associations (Spiroclypeus Facies, Larger Foraminifer-Coral Facies, Austrotrillina Facies, Flosculinella-Amphistegina Facies, Marginopora Facies, and Miogypsina Facies). After the middle Miocene, most of the Queensland Plateau carbonate platform was drowned. The post-middle Miocene to Holocene reefs, which are characterized by a geographically more restricted distribution, shed neritic material including larger benthic foraminifers into adjacent basinal areas. This process is associated with a partial reworking of middle Miocene deposits containing Lepidocyclina (Nephrolepidina)

Eocene-Oligocene planktonic foraminifera of ODP Hole 135-841B

A middle Eocene to lower Oligocene sedimentary sequence was drilled at Site 841 in the Tonga forearc region during Ocean Drilling Program Leg 135. A 56-m-thick sequence of volcanic sandstone, spanning from Cores 135-841B-4IR to -47R (549.1 to 605 mbsf), unconformably overlies rhyolitic volcanic basement. The middle Eocene planktonic foraminifer assemblages (P Zone?), which occur in association with larger benthic foraminifers, include spinose species of Acarinina, Morozovella, and Truncorotaloides, but their abundance is low. Late Eocene and early Oligocene faunas are abundant and show the highest diversity of the Paleogene sequence drilled at this site. They have been assigned to Zones P15-16 and P18, respectively. The Eocene/Oligocene boundary was not recognized because of a hiatus in which Zone P17 (37.2-36.6 Ma) was missing. Another hiatus is recorded in the interval between the middle and late Eocene, spanning at least 1.8 Ma. Paleogene assemblages of Site 841 contain equal numbers of warm- and cool-water species, an attribute of the warm middle-latitude Paleogene fauna of the Atlantic Ocean. In particular, common to high abundances of cool-water taxa, such as Globorotaloides, Catapsydrax, Tenuitella, and small globigerinids, may be related to the opening of a shallow seaway south of Tasmania permitting the influx of cool Indian Ocean waters into the South Pacific before the late Eocene (approximately 37 Ma)