Discussion of significant components of sands and sandstones from individual drill sites beginning with northern rift margin and rift sites (Sites 1115, 1109, 1118, and 1108) follows. The Moresby Seamount sites (Sites 1114, 1112, and 1116), which are more tectonically deformed, less well dated, and difficult to correlate with the regional stratigraphy, are discussed subsequently. Sand and sandstone compositions are described in ascending stratigraphic order. Point-count data were recalculated as ratios of framework to interstitial material (cement and matrix) (Table T2) and plotted against depth to illustrate the compositional characteristics and downhole variation of the sands and sandstones from each site. These data were also plotted against age to allow comparison between sites. The age constraints used are taken from shipboard biostratigraphic and magnetostratigraphic analysis (Taylor, Huchon, Klaus, et al., 1999), as modified by postcruise studies (Resig et al., in press; K. Takahashi, pers. comm., 2000) (Fig. F4). The timescale is that of Berggren et al. (1995).
The succession cored at Site 1115 on the northern rift margin consists of 802.5 m of sediments (Fig. F5), which includes the only recovered interval of Trobriand forearc sediments (middle Miocene) as well as the unconformably overlying upper Miocene-Pleistocene rift succession. Twelve lithologic units were recognized, from which 23 samples were point counted between depths of 17.47 and 698.70 meters below seafloor (mbsf) (Tables T2, T3; Fig. F6). The middle Miocene, mainly turbidite succession (Units XI and XII), accumulated at bathyal depths in the inferred forearc basin (Taylor, Huchon, Klaus, et al., 1999). A feldspathic sandstone (Unit XII; Sample 180-1115C- 44R-2, 112-113 cm) and a bioclastic sandstone (Unit XI; Sample 180-1115C-35R-1, 85-88 cm) were point counted. Detrital ferromagnesian minerals present within the feldspathic sandstone include biotite clinopyroxene and amphibole. Felsitic and colorless vitric volcanics are the only lithic fragments present. The bioclastic sandstone contains common skeletal carbonate detritus (foraminifers, shell fragments, coralline algae, and bryozoans) and sparry calcite cement. Detrital clinopyroxene and biotite are the only ferromagnesian minerals present, but the rock also contains, in decreasing order of abundance, lathwork, colorless and brown vitric, felsitic, and microlitic volcanic fragments.
Unit X, of middle Miocene age, accumulated in a neritic setting and forms the top of the forearc succession (Taylor, Huchon, Klaus, et al., 1999). Three lithic sandstones were point counted from this unit. Lathwork fragments dominate the lithic detritus. Colorless and brown vitric fragments are present with the former more dominant except in the stratigraphically highest sandstone. Rare microlitic volcanic fragments are present. Detrital clinopyroxene is common, but detrital biotite is rare or absent. Trace amounts of chloritic detritus occur throughout the sandstones of Unit X.
Unit IX, considered to be an upper Miocene succession deposited in a high-energy shallow-marine or fluvial setting, unconformably overlies Unit X, as the stratigraphically lowermost unit of the Woodlark rift basin at Site 1115 (Taylor, Huchon, Klaus, et al., 1999). A sandstone point counted from this unit is calcite cemented and dominated by lathwork detritus. Also present are rare felsitic and common, mostly brown vitric fragments. As in the stratigraphically lower sandstones of Unit X and XI, clinopyroxene is the principal detrital ferromagnesian mineral. Detrital amphibole is rarely present. A trace amount of detrital biotite was recorded. The overlying Unit VIII, of late Miocene age, is inferred to have been deposited in a lagoonal setting (Taylor, Huchon, Klaus, et al., 1999). A calcite-cemented lithic sandstone from this unit is of similar modal composition to the sandstones of Unit IX, but with brown vitric grains being the principal lithic component. Detrital ferromagnesian grains are still dominantly clinopyroxene. Rare lathwork, colorless vitric, and felsitic volcanic grains are present along with trace amounts of epidote grains.
Units VII, VI, and V, spanning the upper Miocene to lower Pliocene succession and deposited at neritic water depths, contain sedimentary structures that are suggestive of reworking under the influence of traction currents (Taylor, Huchon, Klaus, et al., 1999). Two feldspathic sandstones were point counted from Unit VII. The stratigraphically lower sediments are calcite cemented and contain lithic detritus dominated by felsitic volcanic fragments, whereas the stratigraphically higher sediments are matrix supported and contain lithic detritus dominated by colorless vitric fragments. Brown vitric fragments are present in trace amounts in both sandstones, but lathwork volcanic fragments are only present in trace amounts in the stratigraphically lower sample. A single feldspathic calcite-cemented sandstone, with rare planktonic foraminifer and trace detrital carbonate grains, was studied from Unit VI. The main detrital ferromagnesian mineral present in this sandstone is biotite with lesser amounts of clinopyroxene. The lithic fragments are mainly of the colorless vitric type with traces of felsitic grains.
A feldspathic sandstone (Sample 180-1115C-19R-CC, 8-10 cm) and a bioclastic sandstone (Sample 180-1115C-15R-3, 79-83 cm) were analyzed from Unit V. The bioclastic material in the latter is dominated by planktonic foraminifer tests with minor shell debris. Both sandstones are calcite cemented and have a lithic detrital component dominated by felsitic volcanics and lesser colorless vitric fragments. Biotite and amphibole are present in both sandstones point counted from this Unit V, with clinopyroxene present only in trace amounts in the stratigraphically lower sample of the two sandstones.
Units IV, III, II, and I are thin-bedded, commonly graded sands and sandstones interpreted as having been deposited by turbidity currents followed by localized reworking by bottom currents (Taylor, Huchon, Klaus, et al., 1999). The lowermost 5 m of Unit IV accumulated at neritic depths, whereas stratigraphically higher rocks accumulated in bathyal depths (Taylor, Huchon, Klaus, et al., 1999). Two feldspathic matrix-supported sandstones were point counted from the lower to middle? Pliocene Unit IV. Colorless vitric fragments with lesser amounts of felsitic and brown vitric fragments dominate the lithic component of the sandstones. Detrital biotite and amphibole are present. The majority of the sands within Unit III (early? to middle Pliocene age), Unit II (late Pliocene-Pleistocene age), and Unit I (Pleistocene age) are matrix supported. The sands of Unit II and I are lithic, whereas sands from Unit III are feldspathic. Rare to trace amounts of skeletal carbonate and detrital carbonate aggregates are present in these sands. Colorless vitric fragments are the dominant lithic grains. Brown glass and felsitic and microlitic fragments are present in most of the samples. Detrital amphibole and biotite are present in all samples. The former is dominant in Unit III, whereas the latter is dominant in Units I and II. Clinopyroxene grains are present in trace amounts in all sandstones above 284.89 mbsf (Units III, II, and I), except Sample 180-1115B-19H-1, 65-67 cm. In addition, trace detrital muscovite plates were observed in Sample 180-1115B-24X-5, 104-105 cm; Sample 180-1115C-31X-1, 139-141 cm; and Sample 180-1115B-10R-1, 5-7 cm.
At Site 1109, on the northern margin of the Woodlark rift, 773 m of sediments and sedimentary rocks were drilled in several holes that terminated in massive dolerite (Figs. F3, F5). Thirty samples were point counted between the depths of 26.54 and 753.66 mbsf (Tables T2, T3; Fig. F7). Unit X, IX, and VIII are undated. Units X and IX were interpreted by Taylor, Huchon, Klaus, et al. (1999) to reflect terrestrial sedimentation in a marine/fluvial to swamp setting. In a single matrix-supported lithic sandstone point counted from Unit X, goethite/limonite concretions are the dominant detrital component (Pl. P2, fig. 1). Of rare volcanic fragments, felsitic types predominate, but microlitic and colorless vitric fragments are also present. Clinopyroxene is the main detrital ferromagnesian mineral, with only a single amphibole grain being point counted. Detrital chloritic grains are rarely present. The matrix is composed of smectite and chlorite (Robertson and Sharp, this volume). No sandstone was counted from the overlying Unit IX, but sandstones in this unit are of similar composition to those of Unit X. Deposition of Unit VIII probably occurred in a lagoonal setting (Taylor, Huchon, Klaus, et al., 1999). Four matrix-supported feldspathic sandstones were point counted from this unit. Amphibole and biotite are the dominant detrital ferromagnesian minerals in the majority of samples. Detrital clinopyroxene grains occur in all. Of the rare volcanic lithic detritus, felsitic and colorless vitric fragments dominate, with trace microlitic and lathwork grains being present in Sample 180-1109D-38R-2, 12-18 cm. In all samples, rare or trace amounts of carbonaceous detritus are present.
Evidence of current reworking in the sandstones within Unit VII (lower Pliocene) and paleontological evidence indicate deposition of this unit in a shallow-marine environment (Taylor, Huchon, Klaus, et al., 1999). Four calcite-cemented sandstones were studied from this unit. All are feldspathic except for the stratigraphically lowest sandstone, which is bioclastic. Detrital ferromagnesian minerals are mainly amphibole and biotite but with trace amounts of clinopyroxene present throughout. The main lithic detritus is felsitic and colorless vitric fragments, which occur in varying proportions. Trace amounts of microlitic fragments are present in some sandstones. Detrital skeletal carbonate (foraminifer, shell fragments, coralline algae, and bryozoans) predominates within the bioclastic sandstone and is common in most of the other sandstones.
Unit VI, of middle Miocene to early Pliocene age, is interpreted to show an apparently abrupt change from an inferred shallow-water environment to a bathyal quiet setting interrupted by rare, mainly high-density turbidity currents (Taylor, Huchon, Klaus, et al., 1999). Eight matrix-supported sandstones were point counted from this unit, ranging in composition from feldspathic to lithic. Colorless vitric fragments are the dominant lithic components in the majority of sandstones. Felsitic volcanic fragments are present in rare to trace amounts in all, whereas trace amounts of microlitic and lathwork volcanic fragments are present in several. Amphibole and biotite are the dominant detrital ferromagnesian minerals, with trace amounts of clinopyroxene present in Samples 180-1109D-10R-4, 95-98 cm, and 17R-7, 34-46 cm.
All the sandstones in Unit V to Unit I were probably deposited by turbidity currents at bathyal depths (Taylor, Huchon, Klaus, et al., 1999). Two feldspathic and three lithic matrix-supported sandstones were point counted from Unit V (middle Pliocene age). In all, colorless vitric fragments are the dominant volcanic detritus. Trace amounts of microlitic, felsitic, and lathwork volcanic lithic fragments are present in some sandstones. Clinopyroxene is absent from Unit V, with amphibole and biotite the dominant detrital ferromagnesian minerals.
Three sands were point counted from the middle to upper Pliocene Unit IV, two feldspathic sands (Samples 180-1109C-28X-2, 0-3 cm, and 37X-5, 106-108 cm) and a lithic sand (Sample 34X-5, 106-108 cm). This unit records the first appearance of serpentinite detritus at this site, with trace serpentinite grains in Samples 180-1109C-34X-5, 106-108 cm, and 28X-2, 0-3 cm. Common colorless vitric fragments dominate the lithic sand, but trace amounts of microlitic and felsitic volcanics are present. Rare to trace amounts of volcanic lithic grains are present in the feldspathic sands (brown vitric, colorless vitric, and felsitic types). Biotite is the predominant detrital ferromagnesian mineral toward the top of the unit, whereas amphibole is more common toward the base. Detrital clinopyroxene grains occur in trace amounts in the stratigraphically highest sand.
Within Unit III (upper Pliocene to Pleistocene), a feldspathic (Sample 180-1109C-22X-CC, 23-23.5 cm) and a lithic (Sample 24X-CC, 18-20 cm) sand were point counted. The sands are dominated by framework components, principally feldspar and volcanic fragments. Colorless vitric fragments and lesser brown vitric fragments are the main volcanic detritus in Sample 180-1109C-22X-CC, 23-23.5 cm. Lathwork and felsitic and microlitic volcanic fragments are dominant in the other, stratigraphically lower sandstone. Also present in the latter are rare serpentinite, rare olivine, trace schist, and rare carbonaceous detritus. Trace detrital serpentinite grains are present in Sample 180-1109C-24X-CC, 18-20 cm.
A total of three sands were point counted from Units II and I (Pleistocene). The stratigraphically lowermost sand sampled from Unit II is feldspathic and framework dominated, whereas the higher sands are matrix dominated and, although containing common feldspar, are of overall lithic composition. Colorless and brown vitric fragments are the principal lithic components present. In Sample 180-1109C-10H-3, 43-45 cm, lathwork volcanic fragments are common, with microlitic and felsitic fragments rarely present. Rare microlitc, lathwork, and felsitic volcanic fragments are present in the sand of Unit I, but only trace amounts of lathwork and felsitic fragments are present in the stratigraphically lowest sand of Unit II. All sandstones contain trace amounts of detrital serpentinite grains. Detrital biotite, clinopyroxene, amphibole, and chlorite are present in all samples. Detrital muscovite grains are present in both sandstones of Unit II. Detrital skeletal material (mostly planktonic foraminifers) and carbonate aggregates are present throughout the sandstones counted within Unit I and II.
Site 1118 is located ~9 km due south of Site 1109, toward the northern margin of the Woodlark rift basin (Figs. F3, F5). From 0 to 205.0 mbsf, the site was drilled without coring. Of eight lithostratigraphic units recognized from Hole 1118A between 205.0 and 926.6 mbsf, only sandstones from Units I to V were point counted (Tables T2, T3; Fig. F8).
Sandstones from Unit V (lower Pliocene to middle Pliocene) and Unit IV (middle Pliocene) are of similar composition. They show clear evidence of deposition from turbidity currents and later reworking in bathyal depths (Taylor, Huchon, Klaus, et al., 1999). The sandstones are lithic and feldspathic and dominantly matrix supported. Lithic detritus is dominated by colorless vitric grains. Felsitic fragments are present in rare to trace amounts. Trace amounts of microlitic, lathwork, and brown vitric fragments are present in some sandstones. Amphibole and biotite are the dominant and, in most cases, only detrital ferromagnesian minerals present, although trace amounts of detrital clinopyroxene are present in three samples.
Units I-III are interpreted as turbidity-current deposits that accumulated at bathyal depths. They lack the evidence of reworking noted in the underlying unit (Taylor, Huchon, Klaus, et al., 1999). Eight feldspathic and lithic sandstones were sampled from Unit III (middle to upper Pliocene) between 632.49 and 493.40 mbsf. The majority of the sandstones are framework supported and contain detrital carbonate (skeletal and aggregate). Detrital biotite, clinopyroxene, and amphibole are present in all the sandstones. Clinopyroxene decreases in abundance downsection. Lathwork fragments are the principal lithic detritus in the sandstones of the stratigraphically higher part of the unit but also decrease in overall abundance downhole as do microlitic fragments, present in common to trace amounts, in the upper part of the unit but absent in some of the stratigraphically lowest sandstones. Colorless vitric fragments are present in all the sandstones but become more abundant in the stratigraphically lower part of the unit. Felsitic and vitric fragments are present in all sandstones. Brown vitric fragments were counted only in the stratigraphically higher sandstones.
Two sandstones were point counted from Unit II (middle to upper Pliocene), Sample 180-1118A-20R-3, 112-124 cm, a feldspathic matrix-supported sandstone, and Sample 180-1118A-24R-5, 105-107 cm, a lithic framework-supported sandstone. The volcanic lithic detritus in the former is composed of, in decreasing order of abundance, colorless vitric, lathwork, brown vitric, and felsitic grains. The stratigraphically lower sandstone shows an increase in volcanic fragments and the appearance of microlitic detritus. Detrital biotite, clinopyroxene, and amphibole are present in both sandstones, with trace amounts of muscovite only in the stratigraphically higher sample.
Three matrix-dominated sands were point counted from Unit I (middle-late Pliocene to Pleistocene age). They are feldspathic or lithic and contain rare skeletal (planktonic foraminifer) and aggregate carbonate detritus. Rare to trace amounts of carbonaceous detritus are present in the two stratigraphically higher samples. The dominant lithic detritus in all samples is volcanic, but serpentinite is also present in Samples 180-1118A-4R-CC, 17-19 cm, and 9R-1, 35-38 cm. Colorless and brown vitric, felsitic, lathwork, and microlitic grains are present, with colorless vitric types dominant in Samples 180-1118A-4R-CC, 17-19 cm, and 9R-1, 35-38 cm. Lathwork fragments are the most common volcanic detritus in Sample 180-1118A-15R-5, 141-142 cm. Muscovite is present in the two stratigraphically highest sands. Detrital biotite, clinopyroxene, and amphibole are present in varying amounts in all samples.
Site 1108 is located near the base of the northern slope of the Moresby Seamount (Figs. F3, F5) and was positioned with the aim of penetrating the major extensional detachment fault defining the southern margin of the Woodlark rift. Four units were recognized within the succession recovered from Site 1108, which consists of 485.2 m of sediments and sedimentary rocks of middle Pliocene to late Pleistocene age (Fig. F5). Unit IV, of middle Pliocene to Pleistocene age, is well lithified. It shows sufficient variation in the relative abundances of different sedimentary rocks to allow recognition of three subunits: Subunit IVA, dominated by medium- to coarse-grained sediments, Subunit IVB, mostly fine grained with rare medium- to coarse-grained sediments, and Subunit IVC, mainly composed of conglomerate. Sandstones from Unit IV are considered to have been deposited by turbidity currents in bathyal depths (Taylor, Huchon, Klaus, et al., 1999). There is some suggestion that reworking by bottom currents has taken place. The three coarser-grained intervals of conglomerate that form Subunit IVC are interpreted as high-density turbidity-current or debris-flow deposits. The stratigraphically higher part of the succession at this site (Units I-III) comprises calcareous hemipelagic sediments and lower breccias composed of heterogeneous clasts inferred to have been derived from upslope on the Moresby Seamount (Robertson et al., 2001).
A total of 19 sandstones were point counted from this site (Tables T2, T3; Fig. F9), the majority (17) from Unit IV. The remaining samples are two sandstone pebbles from Unit II. Sandstones from Unit IV are calcite cemented, of lithic or feldspathic composition, and mostly framework supported. They all display a similar composition, except for the appearance of metamorphic and/or serpentinite detritus in all samples from 333.94 mbsf and higher. The sandstones contain felsitic, colorless vitric, brown vitric, and microlitic volcanic lithic fragments in a range of relative abundances. Muscovite, biotite, clinopyroxene, and amphibole are present in all except Sample 180-1108A-49R-CC, 5-6 cm, from close to the base of the unit, in which only biotite and clinopyroxene are present.
Two sandstone pebbles from Unit II are a lithic sandstone (Sample 180-1108B-3R-CC, 0-4 cm) and a feldspathic sandstone (Sample 180-1108B-5R-CC, 6-8 cm). Both are cemented by calcite, framework supported, and have a similar composition to the sandstones within the stratigraphically higher part of Unit IV (<380.84 mbsf).
The sands and sandstones from the northern rift sites range from feldspathic to lithic sandstones and include both framework- and matrix-supported varieties (Fig. F10). Most lower Pliocene samples counted from Sites 1115, 1109, and 1118 are cemented by calcite and contain detrital carbonate. Upper to middle Miocene sandstones from Site 1115 are mostly calcite cemented, in contrast to the upper Miocene sandstones from Site 1109. Compared to the other northern sites of the Woodlark rift, the middle to upper Pliocene sandstones sampled from Site 1108 are unusually cemented by calcite. A common feature of Sites 1108, 1118, and 1109 is the appearance of metamorphic and serpentinite lithic detritus in sandstones of middle to late Pliocene age (Fig. F11). The earliest recorded serpentinite detritus within the sandstones is estimated to have occurred at 2.98 Ma at Site 1108 and 2.91 Ma at Site 1109. Serpentinite detritus was not observed from Site 1118 until 1.93 Ma, and neither metamorphic nor serpentinite lithic detritus was recorded from Site 1115. Detrital schist and gneiss grains occur in greatest abundance at Site 1108, where they appear at the same level as does serpentinite detritus. The only other northern site where schist and gneiss were observed is Site 1109 (Sample 180-1109C-24X-CC, 18-20 cm [217.88 mbsf; 1.78 Ma]). The distribution of detrital muscovite flakes parallels the distribution of metamorphic and serpentinite, with an increasing abundance in the progressively younger upper Pliocene to Pleistocene samples from Sites 1108, 1118, and 1109. However muscovite is also present within upper Miocene sandstones at Site 1115.
Detrital ferromagnesian minerals show several systematic changes at the northern sites (Fig. F12). The oldest (lower Miocene) sandstone from Unit XII at Site 1115 contains minor amounts of biotite, amphibole, and clinopyroxene, but in the upper middle Miocene and lower upper Miocene sandstones, clinopyroxene dominates and, in some samples, is the only ferromagnesian mineral present. A parallel trend is shown by the volcanic fragments at Site 1115, with felsitic and colorless vitric volcanic fragments dominating the oldest sandstone and lathwork fragments increasing rapidly in abundance in overlying sandstones (Fig. F13). The abundance of clinopyroxene grains begins to decrease in the upper upper Miocene as the quantity of detrital biotite and amphibole grains increase. The change is accompanied by an increase in felsitic and a decrease in lathwork detritus. By the middle Pliocene, clinopyroxene has nearly disappeared from all the sandstones within the northern rift sites but clinopyroxene reappears in the upper middle Pliocene sediments and becomes more abundant in the Pleistocene, especially in sandstones of Site 1109 (Fig. F12). Colorless vitric and felsitic fragments dominate the volcanic detritus within sands and sandstones of the upper upper Miocene and younger in the northern sites (Fig. F13). Lathwork and microlitic fragments increase from the upper middle Miocene upward, which correlates with an increase in detrital clinopyroxene grains.
At Site 1114, located near the northeastern edge of Moresby Seamount, almost 286 m of sediments and sedimentary rocks was recorded, separated by a low-angle extensional fault from metamorphic basement rocks (metadolerite) (Figs. F3, F14). Twelve samples were point counted from four of the seven lithostratigraphic units recognized (Units V, IV, III, and II) (Tables T2, T3; Fig. F15). These units were inferred to have been deposited by turbidity currents in bathyal depths (Taylor, Huchon, Klaus, et al., 1999). A framework-supported lithic sandstone from Unit V (middle Pliocene), which lies directly above a tectonic breccia (Unit VI), contains predominantly lathwork grains, although microlitic, felsitic, brown vitric, and colorless vitric volcanic fragments are also present. Clinopyroxene is the dominant detrital ferromagnesian mineral along with minor detrital biotite and chloritic grains. Two lithic sandstone samples from Unit IV (middle Pliocene) have a similar composition but also show trace amounts of detrital muscovite.
Seven sandstones sampled from Unit III (middle to upper Pliocene) include both feldspathic and lithic sandstones, which range from framework to matrix supported. Sandstones from Subunit IIIA (Samples 180-1114A-14R-1, 106-108 cm, and 15R-1, 46-48 cm) contain abundant detrital skeletal carbonate (foraminifer, algae, and shell fragments) and detrital carbonate aggregates. Sandstones counted from Unit III show a similar composition to underlying sandstones, save for an increase in detrital biotite and colorless vitric or brown vitric volcanic fragments toward the top of the unit. Serpentinite detritus occurs in one of these sandstones (Sample 180-1114A-9R-2, 15-17 cm [76.03 mbsf]). Two framework-supported feldspathic sandstones from Unit II (upper Pliocene) differ from the majority of the underlying sandstone in that colorless vitric grains make up the majority of the lithic fragments and there is an accompanying increase in the abundance of detrital biotite. Carbonaceous detritus is present within the sandstones of Unit II and the stratigraphically highest sandstone of Unit III.
Site 1116 is located on the southern flank of the Moresby Seamount, 8 km south of Site 1114 (Figs. F2, F3). Three lithostratigraphic units were recognized at this site, which was drilled to 158.90 mbsf (Fig. F14). Unit III accumulated during the Pliocene at middle bathyal depths (Taylor, Huchon, Klaus, et al., 1999). Within this unit, thick-bedded sandstones that commonly show a basal inverse-graded interval were interpreted as deposits from high-density turbidity currents, whereas other sandstones in the unit were interpreted as deposits from lower-density "classical" turbidites (Taylor, Huchon, Klaus, et al., 1999). Seven lithic and feldspathic sandstones from between 152.38 and 81.96 mbsf were point counted from this unit (Tables T2, T3; Fig. F16). All are framework supported except for Sample 180-1116A-17R-2, 53-55 cm, and all are calcite cemented. In the lower part of the unit, the lithic detritus is dominated by lathwork and brown vitric fragments, whereas felsitic fragments become more dominant in stratigraphically higher sandstones. Microlitic and colorless vitric fragments are present in rare and trace amounts throughout Unit III. Clinopyroxene is the principal detrital ferromagnesian mineral throughout Unit III, except for Sample 180-1116A-13R-4, 51-54 cm, in which biotite is more abundant. Grains of serpentinite are recorded in two sandstones from Unit III (Samples 180-1116A-11R-1, 16-19 cm [81.96 mbsf], and 16R-1, 103-107 cm [131.03 mbsf]).
Unit II, of Pliocene age, contains paraconglomerate intercalated with sandstone. These rocks are considered to be deepwater debris-flow and turbidity-current deposits (Taylor, Huchon, Klaus, et al., 1999). A single matrix-supported lithic sandstone point counted from this unit contains rare detrital serpentinite and schist grains. The latter contain epidote and chlorite veins, together with prehnite and pumpellyite (Sample 180-1116A-6R-1, 9-11 cm [42.49 mbsf]) (Pl. P3, fig. 3). Detrital prehnite and pumpellyite grains occur in the sandstone. Lathwork fragments are the most abundant lithic detritus, which also includes, in order of decreasing abundance, felsitic, microlitic, colorless, and brown vitric grains. Clinopyroxene is the most abundant detrital ferromagnesian mineral, with subordinate biotite. A single detrital muscovite plate was noted.
A lithic and a feldspathic sandstone from Unit I (upper Pliocene) are both framework supported and cemented by calcite. They contain similar lithic detritus to the sandstones in Unit II with lathwork and felsitic detritus predominating. Clinopyroxene is the principal detrital ferromagnesian mineral, with subordinate biotite, rare clinopyroxene, and trace amphibole. The stratigraphically higher of the sandstones contains rare detrital muscovite, serpentinite, and schist grains.
The Pleistocene deposits of Site 1112, as far as can be determined from the minimal recovery, probably comprise a talus deposit on the northern side of Moresby Seamount (Taylor, Huchon, Klaus, et al., 1999). Two sandstone pebbles from this site were point counted, a lithic framework-supported sandstone (Sample 180-1112A-3R-1, 2-5 cm [20.52 mbsf]) and a feldspathic framework-supported sandstone (Sample 180-1112A-9R-CC, 25-27 cm [78.15 mbsf]). Lathwork grains are the principal lithic component in both pebbles. Other volcanic detritus includes colorless vitric, brown vitric, microlitic, and felsitic types. Clinopyroxene is the most common detrital ferromagnesian mineral, and trace amphibole is also present. Detrital biotite is common in the stratigraphically higher pebble.
The upper Pliocene to Pleistocene sandstones from Sites 1116 and 1114 are feldspathic, whereas the older sandstones are dominated by lithic volcanic detritus (Fig. F17). The majority of sandstones from these sites are partially to well cemented by calcite. Carbonaceous material is only observed in the upper Pliocene to Pleistocene sandstones of Site 1114. For the Pliocene and Pleistocene time interval, either felsitic or lathwork grains alternate as the principal lithic component. Microlitic, colorless vitric, and brown vitric volcanic grains occur in most of the sandstones. The first occurrence of serpentinite at Site 1116 is estimated to have occurred at ~3.05 Ma, but at Site 1114, it is only observed in a single sandstone of ~2.01-Ma age (Fig. F17). Schist and gneiss grains are only present at Site 1116 in sandstones estimated at ~2.40 and ~2.00 Ma in age. Clinopyroxene is the dominant detrital ferromagnesian mineral at these sites, except within sandstones estimated as ~3.17 Ma (Site 1116) and ~2.00 Ma (Site 1114) age, in which biotite is dominant. Chloritic detritus is more abundant within upper Pliocene to Pleistocene sandstones. Sandstone pebbles recovered from Site 1112 are of similar composition to those sandstones of Sites 1114 and 1116, which have a detrital lithic component dominated by lathwork grains (Fig. F17).