Unit I sand layers fall into two compositional groups. The first group consists of volcaniclastic (ash) layers (Cores 161-974B-3H, 7H, and 9H) that are predominantly composed of colorless vitric bubble-wall and pumice fragments; these stain according to their composition and range from uniformly yellow (K-rich) or pink (Ca-rich) to a mixture of both (Ca- and K-bearing). The other samples from Unit I (Cores 974B-1H, 2H, 4H, 5H, and 6H) constitute the second group, and these are predominantly composed of monocrystalline quartz, plagioclase and potassium feldspar grains, and metamorphic lithic fragments. The latter consist of quartz-mica tectonite with lesser polycrystalline mica and quartz-feldspar-mica aggregates (Pl. 1). The youngest sample (974B-1H-3, 139-140 cm) from this second group contains more volcanic lithic fragments (brown microlitic glass and pumice with calcium and potassium stain; Pl. 1) and a wider variety of dense minerals including green amphibole, olivine(?), apatite, garnet, tourmaline, and sphene. Sedimentary lithic fragments in two samples (Cores 974B-1H-3, 139-140 cm and 2H-4, 63-65 cm) are a mix of argillite (Lsa) and limestone (Lsc) debris (Pl. 1).
Of the three samples from Unit III, one, the coarsest (161-974B-22X-CC, 28-29 cm), has a modal composition that is very similar to Unit I sand. In addition to monocrystalline and polycrystalline quartz, plagioclase and potassium feldspar grains, this sample contains fragments of granite (plagioclase + potassium feldspar + quartz + biotite), gneiss and/or coarse schist (biotite +quartz; Pl. 1), quartz-mica tectonite, siltstone, sedimentary carbonate (foraminifer calcarenite, foraminifer microsparite, and dolosiltite), and altered and devitrified felsic to intermediate to mafic volcanic debris. Many of the coarse-grained lithic fragments were included in monomineralic categories during point counting (function of Gazzi-Dickinson method). The other Unit III samples are quartzo-lithic with primarily sedimentary and lesser metamorphic lithics.
In sand from Units I, II and III at Site 976, quartz is abundant as singular grains, and as sand-sized crystals in quartz-mica tectonite fragments. It commonly exhibits undulatory extinction (Pl. 2). Grains of plagioclase, potassium feldspar, and mica flakes (biotite, muscovite, and chlorite) are also common monomineralic components. Biotite is locally altered to opaques and chlorite, and plagioclase ranges from fresh to altered. Rare grains of polycrystalline quartz are present. Within the lithic fraction, metamorphic lithic fragments are the most common. They are predominantly quartz-mica tectonite (Lmt), locally graphytic, with lesser polycrystalline mica (Lmm), serpentinite (Lmv), and phyllite (Pl. 2). Sedimentary lithic fragments include shale/argillite (Lsa) and carbonate (Lsc) lithic fragments. It is possible that some fragments counted as carbonate lithic clasts could be bioclastic debris. Both unconsolidated sand and carbonate-cemented sandstone samples were collected from Unit II; these contain a variety of carbonate components such as bioclasts, carbonate sedimentary lithic fragments, marble metamorphic lithic fragments (coarse carbonate), and incipient (coarse carbonate crystals in loose samples) to pervasive (in sandstone samples) authigenic carbonate cement. The detrital vs. authigenic (incipient cementation) origin of sand-sized carbonate was most easily determined in the cemented samples of Unit II; for that reason, mainly carbonate-cemented samples were analyzed from this unit (Pl. 2; Table 2).
Although shipboard scientists noted the unusual texture and presence of phillipsite in Unit IV sediments at Site 976 (Comas, Zahn, Klaus, et al., 1996), it was not until thin sections were prepared for this study that relict volcaniclastic textures were recognized in this unit. Unfortunately, samples from Unit IV were dried, disaggregated, and sieved; had they been first impregnated with epoxy, the extent of volcanic grain dissolution and alteration, and thus the original percentage of volcanic debris in the deposit, would have been more easily constrained. As seen in thin section, the sand-sized fraction includes clumps or "gloms" of sandy matrix that contain silt-sized fragments of volcanic glass completely altered to green clay minerals; these "gloms" also provide some textural evidence to suggest that there has been dissolution of volcanic glass and plagioclase phenocrysts (secondary porosity) and replacement/cementation by zeolites. The major sand-sized components in the three samples from Unit IV are quartz, feldspar, and authigenic zeolites. Given the propensity for feldspar and zeolite to stain, some feldspar grains may have been inadvertently counted as zeolite and visa versa. Only a few percent of sand-sized volcanic lithic debris was recognizable, including felsitic, microlitic, and vitric (pumice and shard) varieties (Pl. 2) with plagioclase phenocrysts (often partly to wholly altered). The vitric groundmass of these fragments is completely altered to green clay minerals. Euhedral to embayed biotite crystals are also present. Although no volcanic lithic fragments were identified in Sample 161-976B-72X-2, 52-54 cm, the high proportion of plagioclase feldspar crystals (phenocrysts?) and secondary zeolite in this sample suggest that it may have also had a volcaniclastic component. Metamorphic lithic fragments are also common components of Unit IV sands, but many of the coarser fragments (e.g., coarse schist; Pl. 2) were counted in monomineralic categories. Unit IV sand also contains a minor percentage of glauconite.
Samples from Unit I at Site 977 and Unit I at Site 978 are compositionally similar with quartz as the most common monocrystalline component. Many of these quartz grains (individual grains and grains within quartz-mica tectonite lithic fragments) are inclusion rich and display undulatory extinction. Some polycrystalline quartz is present. Mica is common in both monocrystalline and polycrystalline (lithic) forms. Muscovite, biotite, and chlorite (included in mica category) are present, but muscovite is the most common. Biotite is typically altered to clay minerals. Lithic fragments are predominantly metamorphic: quartz-mica tectonite and locally polycrystalline-mica fragments are common (Pl. 2).
The only sample from Unit II at Site 977 that was examined in this study (Sample 161-977A-57X-CC, 33-34 cm) comes from a 1-cm-thick, granule-rich sand lamina recovered at the contact between Units I and II. The 40 cm of gravel recovered below this contact is comprised of volcanic and sedimentary rock fragments: common rhyodacite (phenocrysts of quartz, biotite, and plagioclase), limestone/dolomite, and quartz arenite, and minor andesite and basalt. The sand at the top of Unit II also consists predominantly of sedimentary and volcanic clasts with a lesser metamorphic component. Mineralogically mature sandstone/siltstone lithic fragments are common; they are composed of well-rounded to angular quartz grains, but locally contain trace amounts of feldspar grains, matrix, and carbonate cement. A range of other sedimentary lithic types is present including shale, foraminifer biocalcarenite, microsparite, cherty micrite, radiolarian chert, micrite, and foraminifer biomicrite (Pls. 2, 3). Volcanic clasts are rare to common in this sample and include rhyodacitic (phenocrysts of quartz, biotite, and plagioclase) and altered intermediate to mafic volcanic rocks with plagioclase microlites. A few clasts of granite (quartz + plagioclase + K-feldspar + biotite), quartz-mica tectonite (schist), and felsic tuff are present (Pl. 3). Using the Gazzi-Dickinson method, many of these lithic clasts are counted in monomineralic categories because they contain sand-sized feldspar and quartz grains/crystals.
The main component of sand samples from Unit I at Site 979 is quartz (Table 2), both as individual grains and crystals within metamorphic lithic fragments. This quartz exhibits undulatory to straight extinction. Bioclastic debris is so abundant in Site 979 sand that it was counted only in a few samples and skipped in the remainder (Table 2). Other calcareous debris was counted as detrital sedimentary lithic fragments (Lsc) or coarse carbonate grains (Carb). Muscovite and biotite flakes are common, particularly biotite, which ranges from altered to pristine. Feldspar grains are typically fresh and consist predominantly of plagioclase, with lesser potassium feldspar. Glauconite is common in every sample, particularly as fecal pellets and foraminifer steinkerns (infillings). Metamorphic lithic fragments are mostly quartz-mica tectonite and polycrystalline mica. In addition to calcareous varieties, the sedimentary lithic fraction includes fragments of shale/argillite and siltstone. Volcanic lithic debris is for the most part concentrated in the uppermost (161-979A-2H-2, 96-97 cm) and lowermost (979A-55X-4, 140-142 cm and 58X-1, 80-82 cm) samples. It consists of fresh, altered, and devitrified colorless (felsic) to brown (intermediate to mafic) glassy fragments with predominantly vitric and lesser lathwork textures. Some felsitic volcanic lithic fragments are also present. The pristine glass fragments take a stain indicating both calcium- and potassium-rich varieties are present.
The beach samples collected along the southern Spanish coast generally consist of coarse, subangular to rounded, medium- to well-sorted sand. A similar range of grain types is found in all the samples, except one volcaniclastic sample (Table 2). Quartz is a major component both as individual grains and crystals within metamorphic lithic fragments. Grains of plagioclase are common, whereas polycrystalline quartz, potassium feldspar, coarse carbonate, zeolite, biotite, and muscovite are minor constituents. Lithic fragments are predominantly metamorphic (Pl. 3), with common quartz-mica tectonite, serpentinite, and lesser quantities of polycrystalline mica. Locally, carbonate and argillite are the most common sedimentary lithic fragments (Pl. 3). Volcanic lithic fragments are limited to Sample #2 (see Table 2 for sample location) and consist of roughly equal proportions of orange/brown, altered and potassium-rich (yellow stained) colorless glass.