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doi:10.2204/iodp.proc.313.105.2010

Stratigraphic correlation

Seismic sequence identifications

Seismic sequence identification through the Oceanus 270 (Oc270) and Cape Hatteras 0698 (CH0698) seismic grids guided Hole M0029A site selection and the spot cores taken in the upper 250 mbsf of the hole. The drill site location lies at the crossing of dip CH0698 profile 307 common depth point (CDP) 10997 and strike CH0698 profile 310 CDP 4613 (Fig. F7 in the "Expedition 313 summary" chapter; Fig. F48). CH0698 profile 307 samples the same trend as the regional Oc270 profile 529, which is close to Hole M0029A, with CDP 3640 on Oc270 profile 529 also locating the site (Fig. F48). Time-depth correlations were based on semblance velocity data from Oc270 (see "Stratigraphic correlation" in the "Methods" chapter).

Hole M0029A is the farthest offshore of the three Expedition 313 holes and samples the thickest section of middle Miocene sediments. Seismic reflectors traced (with difficulty) from Holes M0027A and M0028A guided the selection of spot cores within the uppermost 100 mbsf of Hole M0029A. Pleistocene surfaces, including marine isotope Chron (MIC) 6/5e, MIC 4/3c, MIC 3b/3a, and MIC 2/1 (Carey et al., 2005), were penetrated during drilling, but their correlation to Expedition 313 cores will have to be done in subsequent analyses. Middle Miocene seismic sequence surfaces m1, m3, and m4 remain difficult to trace to this location because of both the hummocky to chaotic seismic facies that must be traversed and the distance between their corresponding clinoform structures and Hole M0029A.

Below surface m4, five new seismic surfaces have been identified (Figs. F47, F48; see Table T10 in the "Methods" chapter), though not all are interpreted as seismic sequence boundaries. The highest and youngest of the five reflectors, m4.1, is a high-amplitude continuous surface reflector marking the base of a seismic facies defined by low- to moderate-amplitude discontinuous subparallel reflectors. The nature of reflector m4.1 is not clearly defined within the Oc270 or CH0698 grids, though there are indications of a possible seismic sequence defining reflector terminations. The next seismic surface predicted, m4.2, is clearly tied to a clinoform structure on CH0698 profile 21 and is thought to be a seismic sequence, though a similar seismic geometry is not suggested on Oc270 profile 529. Two lower surfaces selected because of their moderate- to high-amplitude nature are m4.3 and m4.4. Neither surface can be defined as a seismic sequence boundary, but they do suggest the possibility of being flooding surfaces because of limited downlap reflector terminations. Seismic facies between these three surfaces, m4.2, m4.3, and m4.4, are similar with low to moderate amplitude and a parallel to subparallel pattern. The lowest new reflector, m4.5, is a moderate- to high-amplitude continuous reflector with onlapping reflectors. This limited information indicates the possibility that m4.5 may be a seismic sequence boundary.

Below m4.5 is a 30 ms interval of low- to moderate-amplitude parallel reflectors before reaching moderate- to strong-amplitude seismic sequence surface m5 (Fig. F47). Sequence m5.2 can be divided into two different seismic facies at 655 ms. Moderate-amplitude, discontinuous parallel reflectors that display downlapping terminations define the upper seismic facies. The lower facies is also marked by downlapping terminations, but all reflectors are noticeably weaker. High-amplitude continuous seismic sequence boundary m5.2 marks the base of this clinoform toe.

The next four seismic sequence surfaces, m5.3, m5.4, m5.45, and m5.47, are moderate-amplitude, continuous reflectors that average 15 ms separation between them (Fig. F47, F48). In Hole M0029A, there are indications of limited small-scale strata-bound faulting at this depth in both Oc270 and CH0698 data (Fig. F47). Displacement shows normal offset and probably relates to dewatering structures and compaction within fine-grained sediment (Dewhurst et al., 1999; Gay et al., 2004). Indications of these compaction structures continue down through the last three seismic sequence surfaces sampled at Hole M0029A, m5.6, m5.7, and m5.8. These deep surfaces are difficult to trace as they lose amplitude and descend into depths of decreased seismic resolution.

Core-seismic sequence boundary integration

The Pleistocene to upper middle Miocene section was spot-cored in Hole M0029A, and the hole bottomed in the lower Miocene. A clay/sand contact between Sections 313-M0029A-7R-2 and 8R-1 (14.63–16.05 mbsf) may mark the base of the youngest Pleistocene sequence (Fig. F49) indicated on Geopulse seismic profiles and correlated to marine isotope Chron 3 (Sheridan et al., 2000; Carey et al., 2005). A surface was encountered at Section 313-M0029A-15R-1, 8 cm (49.68 mbsf), where medium-coarse poorly sorted sands overlie clay; this may be the base of the Pleistocene (Fig. F50). This depth agrees closely with the base of the Pleistocene using Geopulse reflectors from Carey et al. (2005) and applying the time-depth conversion used in this volume.

Seismic sequence boundary m1 (predicted depth of 152–153 mbsf) may have been recovered in interval 313-M0029A-28R-3, 49–98 cm (~155.5–156 mbsf), where there is a weathered clayey silt associated with the approximate level of the reflector (Fig. F51). This clay appears to be associated with the high downhole gamma values at 156.24 mbsf.

Seismic sequence boundary m3 (predicted depth of 190–195 mbsf) could be placed at the base of Section 313-M0029A-34R-1 (193.17 mbsf). The section consists of wood over weathered silty clay with roots interpreted as a paleosol; these overlie very fine sands in Section 34R-2 (193.17 mbsf) (Fig. F52). There is a large gamma log kick (Fig. F51) in both the downhole TGR and core NGR logs and a large MSCL density increase at 192.74 mbsf (Section 313-M0029A-34R-1, 107 cm), though the significance of the latter cannot be confirmed because of spot coring.

Seismic sequence boundary m4 (predicted depth of 225–235 mbsf) may have been captured in Section 313-M0029A-40R-1, 39 cm (231.7 mbsf), where a woody clay (possible paleosol) overlies silty fine sand. This is a level of major downhole increase in both the downhole TGR and core NGR logs (Fig. F51).

Hole M0029A penetrated a 240 m thick section between seismic sequences m4 and m5 (Fig. F53). Five reflections were traced through this package (R1–R5 counting downsection; see "Seismic sequence identifications"), with two likely sequence boundaries (m4.2 and m4.4) and three other surfaces (m4.1, m4.3, and m4.5). Reflector m4.1 (predicted depth of 325–330 mbsf) appears to correlate with a contact of silty glauconite fine sand over a 10 cm thick contact zone with silty clay in interval 313-M0029A-65R-2, 80–90 cm (325.13–325.23 mbsf). Core observations (see "Lithostratigraphy") identify this as a candidate sequence boundary.

A contact that was sampled as sequence boundary but is likely a burrowed flooding surface occurs at the top of Section 313-M0029A-71R-1 (341.11 mbsf). This surface has sand-filled burrows into clay and is immediately above the predicted depth of reflector m4.2 (345–350 mbsf).

Seismic reflector m4.2 appears to be a sequence boundary in Sections 313-M0029A-72R-1, 64 cm, to 72R-1, 87 cm (343.24–343.89 mbsf). It consists of an indurated contact of clays over claystones over muddy fine sand. This likely correlation of reflector m4.2 (predicted depth = 345–350 mbsf) is associated with a very large density contrast and downhole gamma log minimum (Fig. F53). Core observations (see "Lithostratigraphy") identify this as a candidate sequence boundary.

The predicted level of reflector m4.3 (350–360 mbsf) is associated with a burrowed surface of sands over silty clay in Section 313-M0029A-74R-1, ~14 cm (350.4 mbsf). MSCL density shows a large contrast in Section 313-M0029A-75R-1 (Fig. F53), where there is a sharp contact of silty clay over fine sand at 35 cm (353.66 mbsf). The significance of this surface remains uncertain but appears to be a facies change from sands above to clays below.

The predicted level of reflector m4.4 (390–400 mbsf) appears to be a clayey zone with nodules in Section 313-M0029A-89R-1 (393–394 mbsf) in an otherwise monotonous succession. However, MSCL density data (Fig. F53) show a sharp contrast in Sections 313-M0029A-89R-2, 66 cm, 89R-2, 74 cm, 90R-1, 49 cm, and 90R-1, 106 cm. This appears to be a flooding surface because it comprises some of the finest sediments of the sequence and is sandwiched between samples with the greatest paleodepth (>100 mbsf in Sample 313-M0029A-82R-CC and 75–80 mbsf in Sample 92R-CC).

The sequence boundary noted in interval 313-M0029A-108R-1, 124–128 cm (449.1–449.14 mbsf) is a dramatic, burrowed, and irregular surface separating glauconitic silty sand above from siliceous silt below (Fig. F54). This sequence boundary noted in the core occurs at the depth predicted for reflector m4.5 at 445–455 mbsf. It is a general maximum in MSCL density (Fig. F55). Core observations (see "Lithostratigraphy") identify a candidate sequence boundary at 449.1 mbsf.

There is a major contact in Section 313-M0029A-118R-1, 25 cm (478.61 cm), to the top of Core 313-M0029A-20R (481.41 mbsf) (Fig. F56), which occurs at the level predicted for seismic sequence m5 (Fig. F55). A sandy silt to silty sand is intensely burrowed with clay in interval 313-M0029A-118R-1, 25–61 cm. There is an indurated zone and concretions in Sections 313-M0029A-18R-1, 61 cm (478.97), to 19R-1, 25 cm (479.75 mbsf). There is a coring gap to the top of Section 313-M0029A-20R-1, where two indurated fragments (cavings) occur above medium sand. Section 313-M0029A-19R-CC (479.82 mbsf) has sands and a deeper water (>100 m) benthic foraminifer assemblage similar to those in Core 20R and below. The main density contrasts are associated with the top of indurated zones in Sections 313-M0029A-18R-1, 61 cm (478.93 mbsf), 18R-1, 90 cm (479.25 mbsf), and 19R-1, 23 cm (479.73 mbsf), which contribute to the impedance contrast that causes reflection m5 in this corehole (predicted depth = 475–482 mbsf, with best estimate of 479 mbsf). A downhole log velocity peak occurs at 480.2 mbsf, which suggests that the reflector should be placed in the gap. Precise placement of the sequence boundary may be revealed by thin sections. Of note is the fact that this sequence boundary is seismically and paleontologically a "correlative conformity" with outer neritic shelf facies (>100 m) below and middle neritic shelf facies above. Core observations (see "Lithostratigraphy") identify a candidate sequence boundary at 478.61 mbsf.

Seismic sequence boundary m5.2 (predicted depth of 590–600 mbsf) was encountered in Section 313-M0029A-161R-2, 37 cm (602.25 mbsf) (Fig. F57), at a change from sandy silt to glauconitic sand below (Fig. F58); glauconites contain a series of six graded beds within the section. This level is a downhole change to glauconite and large increases in MCSL density and downhole TGR and spectral K logs (Fig. F57). However, core observations (see "Lithostratigraphy") place a transgressive surface at 602.25 mbsf and a candidate sequence boundary at ~621 mbsf. Further studies are needed to resolve this difference.

Seismic sequence boundary m5.3 (predicted depth of 638–642 mbsf) is best placed at Section 313-M0029A-176R-1, 13 cm (643.19 mbsf) (Fig. F57), at a change from glauconite sands to silt (Fig. F59). This is a level with a sharp MSCL density peak and is the preferred placement of the seismic sequence boundary. However, there are two other candidate placements of the sequence boundary in the cores. First, a contact in interval 313-M0029A-175R-1, 50–120 cm (640.51–641.2 mbsf), fits a model for these toe-of-slope deposits with basal glauconite sands and upper clays/silts. This level is associated with decreasing density values, but caution must be taken in interpreting these because of possible core disturbance. Core observations place a candidate sequence boundary at 640.51 mbsf (see "Lithostratigraphy"). Second, Section 313-M0029A-171R-2, 57 cm (634.43 mbsf), at a downhole change from glauconitic quartz sand to glauconite sand, is the top of a major downhole increase in gamma log values (driven by K values, indicative of glauconite in this case) and is likely a facies change. A secondary spectral K peak occurs at the level of the preferred sequence boundary at 643.19 mbsf.

Placement of seismic sequence boundary m5.4 (predicted depth of 658–670 mbsf) is problematic (Fig. F57). The best placement from a core-seismic perspective is in Section 313-M0029A-183R-1, 112 cm (662.48 mbsf), at a contact between clays above and glauconite-quartz sands below (Fig. F60). This is associated with a large downhole increase in both MSCL density values and sonic velocities, suggesting that this is the best placement of the seismic sequence boundary. However, there are nine core contacts encompassing the four seismic sequence boundaries, m5.3 through m5.47, in Hole M0029A, and these thin (11–19 m) sequences cannot be correlated to seismic sequences boundaries for certain considering the seismic resolution of 5 m. The successions in this toe-of-slope setting of sequence m5.3–m5.4 appear to display a pattern of basal transported glauconite sands grading up to silts/clays. Given this, it is possible to place the core sequence boundary in Section 313-M0029A-179R-1, 23 cm (648.68 mbsf), at a change from glauconite above to clay below at a modest density peak; this is where core observations place a candidate sequence boundary and interpret 662.37 mbsf as a transgressive surface (see "Lithostratigraphy").

Seismic sequence boundary m5.45 (predicted depth of 670–690 mbsf) is best placed in Section 313-M0029A-193R-2, 73 cm (673.71 mbsf), at the base of a glauconite bed on clay (Fig. F61). This is at a major downhole decrease in MSCL density values. This level is interpreted as a candidate sequence boundary based on core observations (see "Lithostratigraphy").

Seismic sequence boundary m5.47 (predicted depth of 685–690 mbsf) is in Section 313-M0029A-193R-2, 60 cm (688.0 mbsf), with glauconite sand on silt. This is the base of a density peak (Fig. F57). Two other contacts occur immediately above this: (1) Section 313-M0029A-192R-2, 11 cm (685.34 mbsf), has clay on glauconite and a density increase; and (2) Section 192R-1, 46 cm (683.16 mbsf), is the top of the glauconite and the downhole start of a density high that peaks just above 687.88 mbsf (Fig. F62). Core observations do not recognize a candidate sequence boundary near the level predicted for m5.47 but place a maximum flooding surface (MFS) near this level. Further studies are needed to resolve this difference.

Seismic sequence boundary m5.6 (predicted depth of 700–716 mbsf) occurs in a coring gap between the base of Section 313-M0029A-200R-1 (707.56 mbsf) in glauconite sand and the top of Core 201R (710.16 mbsf) in clay/claystone. The clays below are lower density than the sands above (Fig. F63). There is a major upsection TGR increase across the coring gap that is due to higher U values shown in the spectral gamma ray. Core observations place a candidate sequence boundary near this level.

Seismic sequence boundary m5.7 (predicted depth of 735–743 mbsf) occurs as a dramatic erosional surface in interval 313-M0029A-208R-1, 9–11 cm (728.56 mbsf) (Fig. F63). The surface marks a contact between glauconite sand above and tan clay below (Fig. F64). Burrowing across the contact is extensive, with burrows down to >30 cm below. There is a marked downsection decrease in MSCL density and magnetic susceptibility values associated with the contact. A TGR peak occurs above the contact (~726.3 mbsf). NGR core data show this same peak at 726.69–727.0 mbsf, suggesting a core shift of Cores 313-M0029A-207R and 208R up by ~40 cm (based on lining up the troughs because the peak is not fully sampled). The downhole spectral gamma log shows a distinct peak at 727.33 mbsf, immediately above the sequence boundary. The underlying sequence m5.8 consists of tan clays as in Hole M0028A. Core observations place a candidate sequence boundary at 728.56 mbsf (see "Lithostratigraphy").

It is not clear that Hole M0029A penetrated seismic sequence boundary m5.8 (predicted depth of 750–755 mbsf or below the corehole total depth) (Fig. F63). There are several possible placements, considering two major coring gaps. The first coring gap goes from Section 313-M0029A-213R-1, 28 cm (743.97 mbsf), to the top of Section 215R-1 (746.96 mbsf). The placement of the 53 cm of Section 313-M0029A-214R-1 is uncertain but appears to be at the top of the gap. Clays from Section 313-M0029A-212R-2, 120 cm, through Section 213R-1 are darker and have higher velocities measured on the core, suggesting that this may be the source of the impedance contrast. Large downhole TGR and K gamma peaks occur in the gap that separates glauconitic clay above from clay below. This suggests possibly placing reflector m5.8 at the base of the TGR peak (~746 mbsf). No MSCL density contrast is apparent on either side of the coring gap.

Another coring gap separates Core 313-M0029A-215R from Core 217R (750–752.86 msbf). It is possible that the sequence boundary is in the coring gap. The third possibility is that a sequence boundary occurs associated with an increase in downhole TGR values at 753.8 mbsf, though NGR values place it in the core at 753.22 mbsf (Section 313-M0029A-217R-1, 36 cm; note 44 m uphole shift in core). Section 313-M0029A-217R-1, ~36 cm, and below contains thin wisps of glauconite sand. Again, there is no major density contrast associated with the cores recovered in either at 753.22 mbsf or across the coring gap.

An acoustic impedance log was computed for Hole M0029A following the Onshore Science Party to aid in core-seismic integration. The impedance log was constructed in two ways using MSCL bulk densities; velocities were taken both from MSCL velocity logs and downhole sonic logs. The resultant acoustic impedance logs are complementary because no sonic logs were available for the upper part of the hole and MSCL sonic quality was poor and the data were spotty for the middle part; only the lower part of the hole had overlapping sonic and MSCL acoustic impedance records. Impedance records shown on the synthesis figures (Figs. F49, F51, F53, F55, F57, F63) allow evaluation of seismic-core correlation made by other means: (1) we first predicted depth based on the velocity-depth function (Table T13), and (2) we then slightly adjusted our predicted depths based on core surfaces, downhole log, and MSCL changes. Adding the acoustic impedance logs as we did after the fact provides a reasonably independent means of testing our core-seismic integration.

The impedance log in the top 330 m (Figs. F49, F51, F53) and core-log-seismic integration is hampered by spot coring. Below this, acoustic logs are very helpful. Reflector m4.2 is associated with a large impedance contrast at 343 mbsf and seismic evidence for a clinoform rollover (see "Seismic sequence identifications"); core observations suggest that it is a candidate sequence boundary. Reflector m4.3 was placed slightly (~2 m) above a decrease in acoustic impedance. This reflector has been interpreted as flooding surface because of downlap (see "Seismic sequence identifications") and an NGR peak (see "Core-seismic-log synthesis") but was not identified as such by core observations (see "Lithostratigraphy"). Similarly, reflector m4.4 occurs directly on a downhole decrease in impedance and is associated with seismic downlap and interpreted as a flooding surface but was not identified as such by core observations. Further study of both surfaces is needed.

Both reflectors m4.5 and m5 have major acoustic impedance peaks precisely at the levels predicted (449.1 and 478.61 mbsf, respectively) and have been interpreted as candidate sequence boundaries based on core observations (see "Lithostratigraphy") and seismic criteria. Similarly, reflectors m5.2 (602.25 mbsf), m5.3 (641.2 mbsf), m5.4 (662.37 mbsf), and m5.45 (673.71 mbsf) are associated with large acoustic impedance contrasts within <1 m of where they are predicted, though core observations interpret the surfaces associated with m5.2 and m5.4 as transgressive surfaces. Interestingly, the impedance log does not identify a clear placement of reflector m5.47 because both possible locations (683.66 and 687.87 mbsf) are associated with impedance contrasts. The upper level is a downhole increase in acoustic impedance (as are most sequence boundaries at Site M0029), whereas the lower level is a downhole decrease in impedance. We favor placing the sequence boundary at the lower surface (687.87 mbsf) where deeper water glauconite sands lie on offshore silts. Core observations do not identify either as a candidate sequence boundary but place a transgressive surface in between at ~685 mbsf (see "Lithostratigraphy"). Further study of the interval from 683 to 690 mbsf is needed.

The placement of reflector m6 (707.86–710.16 mbsf) is associated with the largest decrease in acoustic impedance noted at this site, though the impedance record cannot place the precise location of the source of the reflector within 3 m. The acoustic impedance record associated with reflector m5.8 suffers from poor recovery and the lack of a sonic record, but there is a strong hint of a contrast at ~753 mbsf.

Core-seismic-log synthesis

Figures F49, F51, F53, F55, F57, and F63 summarize the ties between sequence boundaries, sediment facies, and chronostratigraphy developed in Hole M0029A. (These figures are combined in Fig. F65.) The figures illustrate the same information as those for Holes M0027A and M0028A and are discussed below, emphasizing the relations among core sequences, logs, and seismic facies within the lithostratigraphic framework.

Lithostratigraphic Unit I (3.85–325.12 mbsf)

The upper ~50 mbsf of Hole M0029A is Pleistocene, according to the biostratigraphic information at this site and estimates based on previous study of the New Jersey shelf (Carey et al., 2005). It belongs to the upper part of lithostratigraphic Subunit IA (see "Lithostratigraphy"), but it is sedimentologically poorly constrained because of the discontinuous and low recovery.

A gamma ray peak at ~10 mbsf correlates with a fine-grained interval in Cores 313-M0029A-6R and 7R. Otherwise, both above this depth and below, the log character is consistent with a moderately uniform deposit of coarse-grained sediment. Pleistocene deposits (from fluvial to shoreface environment) (Fig. F49) overlie a discontinuity tentatively placed at 46.68 mbsf (Section 313-M0029A-15R-1, 8 cm) and correspond to a significant time hiatus (Pleistocene–Pliocene).

Only spot cores were obtained from the base of the Pleistocene to the top of Subunit IE at 261.81 mbsf. Several peaks in TGR values (>150 cps) are observed at 50–53, 58, 68–69, 126, and 135–138 mbsf. Cores at 50–53 and 68–69 mbsf were nonmarine silty clays thought to be paleosols. This suggests that several other sharp gamma spikes of similar character but lacking cores could be paleosols as well. In general, sediments of Unit I were deposited in a range of shelf settings (shoreface to foreshore, coastal plain, and estuarine).

The boundaries between lithostratigraphic Subunits IB, IC, and ID cannot be clearly established (see "Lithostratigraphy"), and the succession was only spot cored (Fig. F51). Nonetheless, Subunit IB was assigned to a fluvial–deltaic–shoreface environment (high content of organic matter and wood debris, or seen also in the high concentration of U and Th), and Subunit IC (lower delta plain sediments) contains paleosols at 193.17 mbsf that correspond to reflector m3. There is no time constraint for this unconformity in Hole M0029A. Similarly, reflector m4 is poorly constrained in age (Serravalian–Tortonian according to dinocyst biostratigraphy). By contrast, the predicted depth to reflectors m1, m3, and m4 occur near or close to (within 5 m) the tops of fine-grained intervals within the overall sand-prone Unit I indicated by gamma log values (Fig. F51).

This thick interval (Subunits IB, IC, and ID) is seismically characterized by a homogeneous facies with discontinuous reflectors. The oscillations of gamma ray values within Subunit IE correlate with lithology, but the enrichment in U concentration between 293 and 304 mbsf can be attributed to an increase in organic matter (see "Downhole measurements").

Lithostratigraphic Unit II (325.12–641.21 mbsf)

Lithostratigraphic Unit II is almost fully recovered, as illustrated in Figure F53. The contact between lithostratigraphic Units I and II is placed at 325.13 mbsf within the predicted depth interval for seismic reflector m4.1 (325–330 mbsf). The associated lithological boundary occurs in interval 313-M0029A-65R-2, 80–90 cm (see "Core-seismic sequence boundary integration"). This surface is a candidate sequence boundary based on core observations (see "Lithostratigraphy").

The seismic prediction for reflector m4.2 is between 341 and 350 mbsf. The sequence boundary associated with this reflector is described at 343.24–343.89 mbsf (Sections 313-M0029A-71R-R, 64 cm, to 72R-1, 57 cm) and corresponds to a major kick in bulk density and a minimum in gamma ray values. This sequence boundary is placed within the predicted depth interval based on velocity function, and it marks the transition between lithostratigraphic Subunits IIA₁ and IIA₂ (offshore clay and silt). The associated MFS is placed at 341.11 mbsf (top of Section 313-M0029A-71R-1), corresponding to a burrowed surface (see "Core-seismic sequence boundary integration") immediately above the predicted depth for reflector m4.2 (Fig. F53). Middle Miocene age has been assigned to this surface based on nannoplankton (NN6–NN7) and dinocyst (DN6–DN8) biostratigraphy. It marks the passage from a seismic facies characterized by discontinuous reflectors (Subunits IE and IIA₁) to a facies characterized by semitransparent reflectors downhole (Fig. F53). It is possibly related to gradual lithological change between lithostratigraphic Units I and II.

The predicted depth of reflector m4.3 is between 350 and 360 mbsf. This interval contains a surface described at 350.4 mbsf (Section 313-M0029A-74R-1, 14 cm) and is interpreted as a facies change at the top of a flooding interval. Paleodepth indications are consistent with the interpretation (see "Paleontology"), and it is positioned at the top of the gamma ray kick, within Subunit IIA₂.

The contact between lithostratigraphic Subunits IIA₂ and IIA₃ falls into the interval bounded by m4.3 and m4.4, an interval with remarkably uniform gamma log character despite changes in lithology (Fig. F53). There are clear changes in density that may be responsible for the weak and discontinuous reflectors that onlap a clinoform front and correspond to generally silty clay with occasional graded intervals in an offshore setting. The predicted depth for seismic reflector m4.4 is between 390 and 400 mbsf (Fig. F53), and it matches well with an associated surface described in Section 313-M0029A-89R-1 (393–394 mbsf). This surface is associated with a flooding surface (likely the MFS, given benthic foraminifer paleodepth estimates), and it falls in an interval containing carbonate nodules (see "Core-seismic sequence boundary integration").

Seismic reflectors m4.5 and m5 bracket lithostratigraphic Subunit IIB₁ (Fig. F55) and are positioned at 445–455 and 475–482 mbsf, respectively, according to the prediction based on the velocity function used during Expedition 313. Both predictions are in accordance with the sedimentological facies (see "Lithostratigraphy"). The sequence boundary m4.5 transition between lithostratigraphic Subunits IIA₃ (offshore clay/silt) and IIB₁ (clinoform slope apron) is described at 449.1 mbsf (Section 313-M0029A-108R-1, 124 cm) as a surface separating glauconitic silt from siliceous silt (see "Lithostratigraphy"). No particular expression in the well log data is observed, whereas a peak in bulk sediment density is found at this level.

Sequence boundary m5 is placed at 478.61 mbsf (Section 313-M0029A-118R-1, 25 cm), corresponding to an indurated silt bed (Fig. F55). A change of seismic facies occurs at this surface. Reflectors above m5 commonly onlap the m5 clinoform; those below m5 downlap deeper surfaces, building seaward as toe-of-clinoform deposits. The seismic reflection is most likely caused by a high impedance contrast related to high density values in the cemented zone.

The predicted depth range for seismic reflector m5.2 is between 590 and 600 mbsf, slightly shallower than a surface described in the core (Section 313-M0029A-161R-2, 37 cm; 602.25 mbsf) and interpreted as an MFS (see "Lithostratigraphy") and a major density contrast. Further studies are needed to resolve the interpretation of sequence boundaries versus MFSs. This reflector is at the contact between lithostratigraphic Subunits IIC and IID (offshore silt overlying partially cemented glauconite sand, toe-of-slope apron of Subunits IID₁ and IID₂).

Lithostratigraphic Unit III (640.51–650.13 mbsf)

The predicted depth interval for sequence boundary m5.3 is at 638–642 mbsf. Three possible surfaces (640.5, 643.4, and 649.7 mbsf) in the core could be associated with this seismic reflector (see "Core-seismic sequence boundary integration"). The best tie is at 643.19 mbsf, relying on the sediment physical properties (significant density peak and an increase in the gamma ray values, associated with K that reveal the presence of glauconite). Several boundaries in physical properties were recognized between 634 and 643 mbsf that will help to better define the placement of reflector m5.3, which is poorly constrained in age. Seismic reflectors m5.3 and m5.4 delineate lithostratigraphic Unit III, which was poorly recovered and interpreted as deposited in a deep offshore environment, as indicated by paleodepth indication (75–100 m) given by benthic foraminifers (see "Paleontology").

Lithostratigraphic Unit IV (650.13–663.88 mbsf)

The best placement for sequence boundary m5.4 is at 662.37 mbsf (Section 313-M0029A-183R-1, 102 cm) (Fig. F57). This position matches the predicted depth range (658–670 mbsf). Nonetheless, other surfaces are observed in the cores and large variations in density are present and could be associated with the seismic reflector (see "Core-seismic sequence boundary integration"). Refinement of core-seismic-log correlation will possibly clarify the position of reflector m5.4 in the sedimentary record. Nonetheless, the two surfaces described in cores (649.68 and 622.37 mbsf) bound the lithostratigraphic Unit IV, characterized by fine-grained, indurated sediments of offshore environments (75–100 mbsf, as shown by benthic foraminifers).

Lithostratigraphic Unit V (663.88–728.55 mbsf)

Sequence boundary m5.45 is predicted at 670–680 mbsf (Fig. F57). The associated sedimentary surface (contact between Subunits VA [offshore setting] and VB [debrite apron]) is placed within this interval (Section 313-M0029A-193R-2, 73 cm; 673.71 mbsf) at the base of the increasing bulk sediment density based on MSCL measurements.

Sequence boundary m5.47 falls within lithostratigraphic Subunit VB in the depth range predicted from the velocity function (685–690 mbsf). The surface that correlates with this seismic reflector is tentatively positioned in Section 313-M0029A-193R-2, 60 cm, at ~688 mbsf, corresponding to a density peak (Fig. F57). Several peaks in density and in gamma ray values are observed below the position of m5.47, mainly occurring at glauconite-rich horizons. Seismic facies belonging to lithostratigraphic Units II, III, IV, and V are characterized by strong parallel reflectors (Fig. F57).

Sequence boundary m5.6, predicted between 700 and 716 mbsf, is placed in a core gap between 707.56 and 710.16 mbsf (Fig. F63). This correlates with a significant peak in gamma ray values (>250 cps) due to high K concentration. It indicates the presence of glauconite-rich sand found at the top of Core 313-M0029A-201R (710.16 mbsf; lithostratigraphic Subunit VC, composed of silty glauconitic sand deposited as a series of debrites). Surface m5.6 as detected in the core encompasses the depth interval calculated on function velocity. Surface m5.6 has reasonably good age constraints because it falls within the interval where nannofossil Zone NN3 was identified for the first time.

Lithostratigraphic Unit VI (728.55–747.27 mbsf)

The surface corresponding to sequence boundary m5.7 is positioned at 728.56 mbsf, considerably higher (~7–15 m) than the predicted depths (735–743 mbsf) (Fig. F63). However, the sedimentological expression of this discontinuity appears spectacular on the sedimentary record (burrowed contact between glauconite sand and clay; see "Core-seismic sequence boundary integration"). This surface marks the transition between lithostratigraphic Units V and VI (see "Lithostratigraphy"). Sediments below this surface consist of banded clays and claystones, reflecting a river-influenced offshore delta environment (see "Lithostratigraphy") barren of microfossil content. Banded clays lie in sequence m5.8 as they do in Hole M0028A.

Lithostratigraphic Unit VII (747.27–756.33 mbsf)

The contact between lithostratigraphic Units VI and VII is possibly marked by seismic reflector m5.8. The predicted depth for sequence boundary m5.8 is placed between 750 and 755 mbsf, near the bottom of Hole M0029A (Fig. F63). Several sedimentary surfaces observed in the cores can be associated with this reflection. The upper one is higher than the predicted depth at 746 mbsf (between Sections 313-M0029A-213R-1 and 215R-1) at the peak of gamma ray values corresponding to glauconitic clays. The interval between 750 and 752.86 mbsf across the coring gap, or at 753.22 mbsf at the top of a horizon showing a significant decrease in gamma ray values (possibly the base of a coarse-grained interval), might encompass sequence boundary m5.8. These two horizons match well the predicted depths; nonetheless, only the refinement of biostratigraphic, core, and seismic correlations can clarify the position and the age of this surface.

In summary, lithostratigraphic Unit I from 0 to 280 mbsf is poorly recovered, resulting in difficult correlation between seismic reflections and sedimentary surfaces.

Prominent peaks in NGR/TGR values and concentrations of K, U, and Th allowed placing the base of the Pleistocene and reflectors m1, m3, and m4, whereas density contrast was used to define reflectors m4.1, m4.3, and m4.4 within lithostratigraphic Unit II. These reflectors are interpreted as MFSs (burrowed surfaces, indurated, or with nodules). The correlation between seismic reflectors and core observation for the interval between reflectors m4.1 and m4.4 is problematic (Fig. F53); further revision in interpretation will be needed.

Reflectors m4.5 and m5 (lithostratigraphic Unit II) coincide perfectly with surfaces observed in the core, and they are well defined by density contrasts.

Correlation of seismic reflectors m5.3, m5.4, and m5.8 is still under discussion; additional bio- and chronostratigraphic data are necessary to clarify the position of these surfaces.

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