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doi:10.2204/iodp.proc.317.205.2014

Results

The sampling strategy for quantitative mineralogy analysis was to collect one sample from each major lithology in each 10 m long core, with as many as three samples taken per core shipboard and additional samples taken at the repository after the expedition as necessary to capture the range in lithology per core. The primary sample taken shipboard was co-located with a smear slide sample and as close as possible to samples collected for clay mineral analyses and bulk carbonate analyses, the latter of which was done shipboard. Shipboard bulk-powder XRD analyses were performed on the primary sample taken in each core and are described in the site chapters (see the “Site U1351,” “Site U1352,” “Site U1353,” and “Site U1354” chapters [Expedition 317 Scientists, 2011b, 2011c, 2011d, 2011e]). Results of postexpedition qXRD are tabulated in Table T5. The primary focus of postexpedition analyses described here was to determine the mineralogical composition of unlithified samples collected at all four locations that spanned the uppermost four seismic sequences (S16–S19), as core recovery was highest in these sequences (see the “Expedition 317 summary” chapter [Expedition 317 Scientists, 2011a]). A secondary priority was to analyze unlithified samples from depth intervals that had corresponding downhole logging data. This was done to allow for further interpretation of downhole logging data in terms of sediment mineralogy; the primary sites for accomplishing this were Sites U1351–U1354. Additional unlithified samples from Hole U1352B below the logging depth (Subunit IIA) were analyzed to validate visually observed mineralogy trends. A brief synopsis of spatial and temporal variations in mineral abundance is presented below by site and lithostratigraphic unit.

Comparison with shipboard carbonate analyses

To evaluate the accuracy of the sample preparation and data processing technique, carbonate mineral abundances determined by qXRD using the RockJock technique were compared with shipboard measurements of total carbonate based on coulometer measurements (see the “Expedition 317 summary” chapter [Expedition 317 Scientists, 2011a]). Carbonates are a common choice for evaluation of the sample preparation and data analysis techniques used here (Andrews and Eberl, 2007; Eberl, 2004). Comparison of the two methods resulted in an R² value of 0.96 (n = 194), indicating considerable correlation between the two methods (Fig. F3). The agreement between the two methods holds over the entire range of carbonate mass percentages determined with the coulometer (5%–25%; Fig. F3). The maximum offset in terms of slope is 5% (slope = 1.05) for samples <10% carbonate (coulometer), with coulometer results higher than qXRD results by ~2.5% (Fig. F3). This magnitude of difference may simply reflect lithologic/compositional heterogeneity between samples used for qXRD and coulometry.

Site U1351

The main objectives of coring at Site U1351 were to sample facies landward of but proximal to clinoformal rollovers of progradational sequence boundaries U8–U19; to sample slope facies of boundaries U4–U7 to provide age control; and to generally characterize facies, paleoenvironments, and depositional processes associated with the sequence stratigraphic model and correlate with seismic stratigraphic models (see the “Site U1351” chapter [Expedition 317 Scientists, 2011b]). Recovery was hampered by the presence of two problematic lithologies: (1) beds of presumably unlithified shell and sand in Unit I, some of which was recovered, and (2) likely high concentrations of silt in Unit II. Two lithostratigraphic units were identified that reveal downhole changes in margin sedimentation processes and paleoenvironments from an inner middle shelf setting (Unit I) to an outer shelf–upper slope setting (Unit II). The primary lithologies of Unit I are fossiliferous mud and sandy mud, very fine to medium well-sorted sand, muddy sand, mud (high clay content), and shell hash (Fig. F4A) that spans from modern to early Pliocene. Visually identified sand- and silt-size grains are dominated by quartz and feldspar, with common to rare mica (biotite and muscovite), chlorite, ferromagnesian minerals (various amphiboles), other dense minerals (zircon, clinozoisite, epidote, tourmaline, and others), and glauconite. Shipboard XRD analyses support these observations. Postexpedition analyses revealed that the most abundant minerals (median value) in Unit I are illite + muscovite (26 wt%), followed by plagioclase (albite; 24 wt%), quartz (15 wt%) and chlorite (15 wt%), total carbonates (5 wt%), and K-feldspar (4 wt%) (Table T5; Figs. F4, F5). Minerals that are occasionally observed above the 3 wt% minimum concentration include biotite. The carbonate minerals aragonite and calcite show the greatest variability within this unit (Figs. F4B, F5). Other mineral phases that could be characteristic of a Torlesse source (i.e., prehnite) were not detected above the 3 wt% threshold in this or any other lithostratigraphic unit in the expedition (Table T5). Mineralogy often changes noticeably (especially from carbonate to siliciclastics) across depths that corresponded with seismic sequence boundaries, and the greatest variability in downhole mineralogy is in the intervals corresponding to seismic sequences S16–S19 (Fig. F4).

Unit II is early Pliocene to late Miocene in age and is composed of mud and very fine sandy mud, both occasionally shell bearing, with minor amounts of very fine muddy sand (Fig. F4). Incipient to well-developed authigenic carbonate cementation is observed as cemented intervals (nodules and concretions). Recovery in this unit was poor, so lithologic trends with depth are ambiguous, but the lowermost part of Unit II contains slightly more calcareous sandy mud. The composition and mineralogy of Unit II is similar to that of Unit I, but the visually described carbonate content is less variable in Unit II; glauconite is less concentrated in this unit; and quartz, feldspar, and illite + muscovite as seen in shipboard XRD analyses are less variable. Postexpedition qXRD analyses support these observations (Table T5; Figs. F4, F6). The most abundant mineral (median value) in Unit II is quartz (26 wt%), followed by plagioclase (25 wt%), illite + muscovite (20 wt%), chlorite (11 wt%), and total carbonates (8 wt%). Minerals that are occasionally observed above the 3 wt% minimum concentration include K-feldspar, epidote, and biotite. Quartz shows the greatest variability within this unit (Figs. F4, F6).

The boundary between Units I and II is a transitional interval between 247 and 300 meters below seafloor (mbsf) in lithofacies, biofacies, and downhole logging data. Postcruise qXRD results cannot definitively place a single transition point, although quartz concentrations are higher below this transition (Fig. F4A).

Site U1352

The main objectives of coring at Site U1352 were to sample slope sediments basinward of clinoform breaks of progradational seismic sequence boundaries that can provide sequence boundary ages; to penetrate the Marshall Paraconformity and the top of the underlying Amuri limestone; and to describe sedimentary processes in an slope-basin setting where contour currents are active but where obvious sediment drift geometries observed in seismic data are absent (see the “Site U1352” chapter [Expedition 317 Scientists, 2011c]). Recovery at the site varied between holes, with a reduction in intervals that represented a transition between lithified and unlithified lithologies. The site contained three lithostratigraphic units. Unit I spans the Holocene to middle Pliocene and is composed of three subunits. Subunit IA is primarily muddy facies composed of calcareous sandy mud; interbedded sand, mud, and clay; massive sand; mottled sandy mud; homogeneous mud; shelly mud; and marl (Fig. F7A). Visually identified sand- and silt-size grains are quartz, feldspar, rock fragments, mica (mostly muscovite), ferromagnesian minerals (hornblende), and dense minerals (epidote and zircon). Authigenic minerals include pyrite in the upper part of the subunit and microcrystalline carbonate in the lower part of the subunit and in cemented zones. Shipboard XRD data support these observations with the exception of a lack of the minor authigenic phases such as pyrite. From postexpedition qXRD analyses, the most abundant mineral (median value) in Subunit IA is illite + muscovite (28 wt%), followed by plagioclase (27 wt%), quartz (20 wt%), chlorite (14 wt%), and K-feldspar (4 wt%). (Table T5; Figs. F7A, F8). Minerals that are occasionally observed above the 3 wt% minimum concentration include total carbonates and show the greatest variability within this unit (Figs. F7B, F8). In contrast to the shelf site, mineralogy does not change noticeably across depths that corresponded with seismic sequence boundaries, and no downhole trends in mineralogy are observed within the intervals corresponding to seismic sequences (Fig. F7).

Subunit IB is primarily mud, sometimes rich in shell. Secondary lithologies include calcareous very fine to fine sand, sandy mud, and muddy sand intercalated with the mud. Visually identified minerals are similar to Subunit IA but with a greater concentration of carbonates, and shipboard XRD analyses support these observations and include a noticeable decrease in quartz deeper in this subunit. From postexpedition qXRD analyses, the most abundant mineral (median value) in Subunit IB is illite + muscovite (29 wt%), followed by plagioclase (25 wt%), quartz (16 wt%), chlorite (16 wt%), K-feldspar (4 wt%), and total carbonates (4 wt%) (Table T5; Figs. F7, F9). Minerals that are occasionally observed above the 3 wt% minimum concentration include amphibole. Total carbonates show the greatest variability within this unit (Figs. F7, F9). As in Subunit IA, mineralogy does not change noticeably across depths that corresponded with seismic sequence boundaries, although the boundaries tend to be relatively enriched in carbonates and deficient in siliciclastics. As in Subunit IA, no downhole trends in mineralogy are observed within the intervals corresponding to seismic sequences (Fig. F7).

Subunit IC is comprised of homogeneous mud, calcareous sandy mud and sandy marl, and sandy marlstone (Fig. F7), and mineralogy observed visually and in shipboard XRD is similar to the two other subunits but has an obvious higher degree of variability within the subunit. From postexpedition qXRD analyses, the most abundant mineral (median value) in Subunit IC is illite + muscovite (29 wt%), followed by plagioclase (23 wt%), quartz (17 wt%), chlorite (14 wt%), total carbonates (8 wt%), and K-feldspar (4 wt%) (Table T5; Figs. F7, F10). Minerals that are occasionally observed above the 3 wt% minimum concentration include epidote and amphibole. Total carbonates show the greatest variability within this unit (Figs. F7, F10). As in Subunits IA and IB, mineralogy does not change noticeably across depths that corresponded with seismic sequence boundaries, although the boundaries tend to be relatively enriched in carbonates and deficient in siliciclastics. As in Subunits IA and IB, no downhole trends in mineralogy are observed within the intervals corresponding to seismic sequences (Fig. F7).

The lithologic transition between Units I and II is indistinct, reflecting a gradual transition to deeper slope depositional environments. Postexpedition qXRD analyses supports this observation, with no remarkable changes in composition at this break, although chlorite and illite + muscovite concentrations increase and total carbonates decrease upsection across this transition (Fig. F7). Unit II spans the middle Pliocene through early Miocene and is comprised of hemipelagic to pelagic lithologies of calcareous sandy mud, sandy marls, chalk, sandy marlstone, and sandy limestone, with minor amounts of calcareous mudstone and sandstone. A noticeable trend in Unit II is a gradual downhole progression from uncemented bioturbated calcareous sandy mud and marl (Subunit IIA) to lithified marlstone and limestone (Subunit IIB) with a greater abundance of glauconite and dark muddy intervals, current-generated structures, and laminated sandstone beds in Subunit IIC. Within Unit II, mineralogy that was visually identified and from shipboard XRD minerals is similar to Unit I, but with a reduction in ferromagnesian minerals and quartz deeper in the section. From postexpedition qXRD analyses, the most abundant mineral (median value) in Subunit IIA is total carbonates (24 wt%), followed by plagioclase (21 wt%), quartz (20 wt%), illite + muscovite (16 wt%), and chlorite (10 wt%) (Table T5; Figs. F7, F11). Minerals that are occasionally observed above the 3 wt% minimum concentration include K-feldspar. Total carbonates show the greatest variability within this unit.

Site U1353

The main objectives of coring at Site U1353 were to sample facies landward of clinoformal rollovers of seismic sequence boundaries U5–U19 to estimate paleowater depths in order to evaluate eustatic amplitudes and to investigate the facies, paleoenvironments, and depositional processes at the most landward shelf setting occupied during Expedition 317 (see the “Site U1353” chapter [Expedition 317 Scientists, 2011d]). Core recovery varied at Site U1353 as a function of drilling technique (higher recovery with the advanced piston corer [APC], and very low with the extended core barrel [XCB]) and lithology (coarser lithologies were more difficult to recover with considerable downhole contamination by cave-in). The site contained two lithostratigraphic units that transition from a heterolithic upper section with abrupt contacts (Unit I) to a more sedimentary featureless mud–dominated section with depth (Unit II), suggesting a gradual transition in depositional environments during the Pliocene–modern period represented in these cores. Unit I is Holocene to early Pliocene in age, and the primary lithologies are heterolithic facies dominated by a homogeneous mud with trace amounts of very fine sand (Fig. F12A). Secondary lithologies include beds of sandy shelly mud, shell layers to shell hash mixed with abundant bioclastic and siliciclastic materials; well-sorted, very fine, highly micaceous sand; and micaceous, homogeneous sandy marl. The visually determined sediment composition of Unit I is quartz and feldspar, with lesser dense minerals (epidote, amphibole, and zircon), sheet silicates (biotite, muscovite, and chlorite), and rock fragments. Authigenic components include pyrite and other opaque minerals. Mineralogy determined from shipboard XRD analyses is in general agreement with the visually determined composition. From postexpedition qXRD analyses, the most abundant mineral (median value) in Unit I is plagioclase (24 wt%), followed by illite + muscovite (23 wt%), quartz (18 wt%), chlorite (13 wt%), total carbonates (6 wt%), and K-feldspar (5 wt%) (Table T5; Figs. F12, F13). Minerals that are occasionally observed above the 3 wt% minimum concentration include epidote and amphibole. Total carbonates show the greatest variability within this unit, although illite + muscovite and quartz also have large (~30 wt%) variability (Figs. F12A, F13). As at Sites U1351 and U1354, mineralogy often changes noticeably (especially from carbonate to siliciclastics) across depths that corresponded with seismic sequence boundaries. The greatest variability in downhole mineralogy is within the intervals corresponding to seismic sequences S16–S19, and there is a trend of high carbonate mineral concentration just above seismic sequence boundaries and enrichment in siliciclastics upsection with the sequences (Fig. F12).

The Unit I/II boundary is noted by a transition from heterolithic facies to more homogeneous lithologies below the transition at 151 mbsf, and no distinct changes in mineralogy from postexpedition qXRD analyses are apparent (Fig. F12). Unit II is early Pliocene–middle to early Miocene in age and is characterized by its general lithologic uniformity, lacking the clay-rich and marl-rich beds seen in Unit I. The primary lithology of Unit II consists of homogeneous mud with varying amounts of micaceous very fine sand (Fig. F12). The visually documented sediment composition of Unit II is similar to Unit I, with comparable mineralogy, but with noticeably less amounts of hornblende and green ferromagnesian mineral concentrations in the uppermost part of Unit II, which are not observed below 365 mbsf in XRD data. From postexpedition qXRD analyses, the most abundant mineral (median value) in Unit II is quartz (27 wt%), followed by plagioclase (26 wt%), illite + muscovite (23 wt%), chlorite (12 wt%), and K-feldspar (4 wt%) (Table T5; Figs. F12, F14). Minerals that are occasionally observed above the 3 wt% minimum concentration include total carbonates and epidote (Fig. F14). Total carbonates show the greatest variability within this unit, although as in Unit I, illite + muscovite and quartz also have large (~30 wt%) variability (Figs. F12, F13). Core recovery was reduced in this unit, so it is difficult to discern any obvious compositional changes within or at seismic sequences and boundaries, although coarser sediment at the boundaries are enriched in quartz and carbonates.

Site U1354

The main objectives of coring at Site U1354 were similar to those at Site U1353: to sample facies landward of clinoformal rollovers of seismic sequence boundaries U5–U19 but at an intermediate position in the shelf portion of the transect to estimate paleowater depths in order to evaluate eustatic amplitudes, and to investigate the facies, paleoenvironments, and depositional processes at the most landward shelf setting occupied during Expedition 317 (see the “Site U1354” chapter [Expedition 317 Scientists, 2011e]). As at Site U1353, core recovery varied as a function of drilling technique (higher recovery with APC and very low with XCB) and lithology (coarser lithologies were more difficult to recover). The site contains two lithostratigraphic units, with Unit I being further divided into two subunits. Postexpedition qXRD analyses at this site focused on the S16–S19 sequences as sampled primarily in Hole U1354B (Fig. F15). Unit I spans the Holocene to early Pliocene and is distinguished by a very heterogeneous assemblage of muddy facies. Subunit IA is mostly calcareous mud and calcareous sandy mud, shelly marl, and sandy marl (Fig. F15A). Minor lithologies include very fine to fine sand, calcareous silty very fine to fine sand, and clay-rich mud. The visually determined composition is largely quartz and feldspar, micas (including chlorite, muscovite, and occasionally biotite), rock fragments, ferromagnesian minerals (hornblende), and dense minerals (zircon and epidote). Authigenic components include varying amounts of opaque minerals, carbonate, and glauconite. From postexpedition qXRD analyses, the most abundant mineral (median value) in Subunit IA is plagioclase (23 wt%), followed by illite + muscovite (22 wt%), quartz (15 wt%), chlorite (13 wt%), total carbonates (12%), and K-feldspar (4 wt%) (Table T5; Figs. F15, F16). Minerals that are occasionally observed above the 3 wt% minimum concentration include epidote (Fig. F16). Total carbonates show the greatest variability within this unit, although illite + muscovite and quartz also have large (~30 wt%) variability (Figs. F15, F16). As at Sites U1351 and U1353, the mineralogy often changes noticeably (especially from carbonate to siliciclastics) across depths that corresponded with seismic sequence boundaries. Boundary U17 was not observed in Hole U1354B, but a change in composition at ~51 mbsf is similar to other sequence boundaries and could represent the depth of boundary U17 in this hole (Fig. F15B). The greatest variability in downhole mineralogy is within the intervals corresponding to seismic sequences S16–S19, and there is a trend of high carbonate mineral concentration just above seismic sequence boundaries and enrichment in siliciclastics upsection with the sequences (Fig. F15).

Hole U1354C is offset 20 m from Hole U1354B and was drilled to advance the hole after severe weather precluded drilling in Hole U1354B. From postexpedition qXRD analyses, the most abundant mineral (median value) in Subunit IA is illite + muscovite (25 wt%), followed by plagioclase (23 wt%), quartz (15 wt%), chlorite (15 wt%), total carbonates (11 wt%), and K-feldspar (4 wt%) (Table T5; Figs. F17, F18). Minerals that are occasionally observed above the 3 wt% minimum concentration include amphibole (Fig. F18). Total carbonates show the greatest variability within this unit, although illite + muscovite and chlorite also have large (~20–30 wt%) variability (Figs. F17, F18).

Subunit IB lithology is less varied than in Subunit IA and is characterized by a more repetitive succession of facies including homogeneous greenish gray mud and greenish gray to gray calcareous sandy mud to sandy marl. Smear slide observations suggest that composition of this unit is similar to Subunit IA but with decreased concentration of ferromagnesian minerals and glauconite. From postexpedition qXRD analyses, the most abundant mineral (median value) in Subunit IB is illite + muscovite (33 wt%), followed by chlorite (25 wt%), plagioclase (22 wt%), quartz (16 wt%), and K-feldspar (4 wt%) (Table T5; Figs. F17, F19). Minerals that are occasionally observed above the 3 wt% minimum concentration include total carbonates (Fig. F19). Total carbonates show the greatest variability within this unit, followed by illite + muscovite, although quartz and chlorite also have large (20 wt%) variability (Figs. F17, F19).

The Unit I/II boundary is noted by a transition from heterolithic facies to more homogeneous lithologies below 250 mbsf, and no distinct changes in mineralogy from postexpedition qXRD analyses are apparent (Fig. F17) except for decreased variability in total carbonates. Unit II is early Pliocene in age and is characterized by its general lithologic uniformity, dominated by gray, homogeneous silty mud with rare scattered shells. Unit II contains fewer calcareous beds than Unit I (Fig. F17). The visually documented sediment composition of Unit II is similar to Unit I, with comparable mineralogy, but with noticeably less amounts of carbonate. From postexpedition qXRD analyses, the most abundant mineral (median value) in Unit II is plagioclase (26 wt%), followed by quartz (25 wt%), illite + muscovite (23%), chlorite (14%), and total carbonates (4 wt%) (Table T5; Figs. F17, F20). Minerals that are occasionally observed above the 3 wt% minimum concentration include K-feldspar and epidote (Fig. F20). Illite + muscovite show the greatest variability within this unit although quartz also has large (~20 wt%) variability (Figs. F17, F20).

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