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IODP Expedition 385

Guaymas Basin Tectonics and Biosphere


Daily Science Report for 16 October 2019

Location:
• Hole U1547A (27°30.4561′N, 111°40.6980′W; water depth 1733.7 mbsl)
• Hole U1547B (27°30.4124′N, 111°40.7345′W; water depth 1732.2 mbsl)

Science Update: We continued HLAPC/XCB coring in Hole U1547A, deploying the XCB coring system whenever we had to core through hard layers. This took place on Core 20X and continuously from Core 25X onward. Cores 20X to 27X penetrated from 108.1 to 141.3 mbsf and recovered 26.5 m (80%). We made a formation temperature measurement with the SET2 tool following Core 23F. While coring and recovering Core 27X, hole conditions deteriorated and continued to worsen below 136.3 mbsf so that we decided to terminate coring at a final depth of 141.3 mbsf. We then raised the drill string ~10 m and deployed the Kuster Flow Through Sampler (FTS) tool to recover borehole fluid from 131.3 mbsf. We retrieved the tool at 1330 h and sampled 600 mL of fluid. We then started pulling the drill string out of the hole, and the bit cleared the seafloor at 1425 h, ending Hole U1547A.

After offsetting the vessel 100 m to the southwest, we positioned the bit at a water depth of 1728.9 mbsl, installed the sinker bars and APC coring system, and spudded Hole U1547B at 1545 h. Mudline Core U1547B-1H recovered 6.3 m. This determined a seafloor depth of 1732.2 mbsl. Cores 1H to 7H penetrated from the seafloor to 65.6 m (104%). We deployed the APCT-3 tool to make formation temperature measurements on Cores 4H and 6H. We pumped perfluorocarbon tracers (PFTs) downhole on all cores for monitoring drilling fluid (seawater) contamination. The pacing of coring was adjusted to the complex microbiology and biogeochemistry sampling on the core receiving platform.

Cores U1547A-14H to 27X have been split and described. Cores 14H to 24X consist of carbonate (micrite)-rich diatom clay and carbonate concretions. Starting with Core 25X, the sediment is rich in silt- and sand-size layers that show evidence of resedimentation by mass-gravity deposition. This type of lithology occurs both above and below an igneous layer recovered in Core 26X and at the top of Core 27X. We recovered ~70 cm of this sill interval from a top depth of 132.8 mbsf. The sill consists of moderately altered, pyrite-bearing basalt with a glassy margin on top. There are abundant subrounded to angular vesicles in the uppermost 25 cm of the recovered interval.

Cores U1547B-1H to 4H have been split and described. They are composed of more or less laminated olive-green clay-rich diatom ooze with several grayish silt-rich layers.

Scientists continued collecting and analyzing data from Hole U1546C.


Daily Science Report for 15 October 2019

Location: Hole U1547A (27°30.4561′N, 111°40.6980′W; water depth 1733.7 mbsl)

Science Update: We continued lowering the drill string to the seafloor to start coring with the advanced piston corer (APC) in Hole U1547A. After the drill string had reached a water depth of 1700.9 mbsl at 0300 h, we deployed the subsea camera to conduct a survey of the seafloor at this site, which is a hydrothermally active area about 30 km northwest of the northern axial graben of Guaymas Basin. The seafloor survey did not find any vent communities. At 0530 h, we picked up the top drive and positioned the drill string above the seafloor to start APC coring. We spudded Hole U1547A at 0835 h. Mudline Core 1H recovered 5.4 m. This established a seafloor depth of 1733.7 mbsl. Cores 1H to 19F penetrated from the seafloor to 108.1 mbsf and recovered 118.8 m (110%). We switched to the half-length APC coring tool after encountering a partial stroke on Core 11H. Deeper in the hole, we needed to deploy the extended core barrel (XCB) coring system to break through hard carbonate layers. This took place on Cores 12X, 14X, 16X, and 18X. We made formation temperature measurements by using the APCT-3 tool on Cores 4H, 6H, 8H, and 10H, as well as the SET2 tool following Core 16X.

Cores U1547A-1H to 13H have been split and described. Core 1H consists of homogenous diatom clay. Starting with Core 2H, the sediments are mainly composed of alternations between laminated and homogenous diatom clay and diatom ooze. In Core 5H (from ~40 mbsf onward), authigenic carbonate precipitates (micrite and carbonate nodules) become abundant, and occasionally they are the dominant lithologic component. Up to 1.2 m thick silty beds, often with erosional bottom contacts, are also frequent in that depth range. The presence of the calcareous nannofossil Emiliania huxleyi suggests a Middle Pleistocene deposition age of <0.29 Ma. No age-diagnostic diatom species were found.


Daily Science Report for 14 October 2019

Location:
• Hole U1546C (27°37.8724′N, 111°52.7568′W; water depth 1585.6 mbsl)
• Hole U1547A (27°30.4560′N, 111°40.6980′W; water depth 1733.5 mbsl)

Science Update: We made up the triple combo logging tool string (natural gamma ray, porosity, and density sondes) to collect downhole measurements in Hole U1546C. We lowered the logging tool string into the hole to the bottom of the hole at 540.2 mbsf. After a short calibration pass, we implemented a full logging pass up to the seafloor. After the triple combo tool string returned to the rig floor at 0600 h, we rigged up the Formation MicroScanner (FMS)-sonic (resistivity imaging) logging tool string. The FMS-sonic tool string was deployed in the hole until we reached fill 15 m above the bottom of the hole. Upon implementing a single upward pass to the seafloor, the tool string returned to the rig floor at 1140 h and was disassembled by 1230 h. Next we deployed the subsea camera system to the seafloor to survey Hole U1546C and did not observe any gas release. The subsea camera system was recovered and secured by 1445 h. We then pulled the drill string out of the hole. The end of the drill string cleared the seafloor at 1500 h, ending Hole U1546C, and reached the rig floor at 1800 h. We then secured the vessel for transit and started the 13 nmi sea passage to Site U1547 (proposed Site GUAYM-12A) at 1822 h. After a 2 h transit, we arrived at the site coordinates, lowered the thrusters, and switched to dynamic positioning mode at 2047 h. We then made up the advanced piston corer (APC) bottom-hole assembly and started lowering the drill string to the seafloor, reaching a water depth of 408.9 mbsl by the end of the day.

Cores U1546C-32R to 42R have been split and described. They consist of more or less laminated, brownish gray, siliceous claystone with regular occurrence of dolostone layers. The calcareous nannofossil Pseudoemiliania lacunosa was identified in Core 42R. This suggests that the sediments at the bottom of Hole U1546C are older than 0.44 Ma, which corresponds to the Middle Pleistocene nannofossil Zone NN19. Cores 32R to 42R were barren of marine diatoms.


Daily Science Report for 13 October 2019

Location: Hole U1546C (27°37.8724′N, 111°52.7568′W; water depth 1585.6 mbsl)

Science Update: We started the day continuing RCB coring in Hole U1546C. Cores 29R to 42R penetrated from 473.6 to 540.2 mbsf and recovered 44.4 m (67%). The safety monitoring for hydrocarbon gases then obtained an anomalously low C1/C2 value from Core 42R, which led to termination of coring in Hole U1546C for safety reasons at a final depth of 540.2 mbsf at 1530 h. After circulating 50 barrels of high-viscosity mud for hole cleaning twice, we prepared the release of the RCB bit to enable downhole measurements with logging tool strings through the end of the drill pipe into the open hole. At 1830 h, we deployed the rotary shifting tool (RST) to trigger the mechanical bit release (MBR). Upon dropping the bit at the bottom of the hole, we deployed the reverse RST to shift the MBR sleeve back into the circulation position. We then raised the end of the drill string at a logging depth of 80.9 mbsf. At 2145 h, we started making up the triple combination logging tool string (triple combo: natural gamma ray, porosity, and density sondes) on the rig floor.

Cores U1546C-17R to 31R have been split and described. Cores 17R to 20R mainly consist of medium-grained mafic igneous rock representing the lower part of the intersected sill. This moderately to highly phyric dolerite contains phenocrysts of mainly plagioclase and subordinate pyroxene. A slight alteration is present. Sericite, chlorite, and epidote are the predominant alteration minerals. No vesicles or veins have been observed. Core 20R shows a transition from slightly altered dolerite to highly altered basalt that appears to be mingled with some sediment, making up the lowermost 0.4 m of the recovered sill, with contact to the underlying sediment at 431.7 mbsf. Core 21R recovered sediment from the contact zone with the sill, consisting of altered fine-grained silty clay with chert. Cores 22R to 31R contain well-laminated brownish black siliceous claystone with variable amounts of nannofossils and benthic foraminifers. No new age-diagnostic species have been observed through Core 31R, so the examined interval is still within nannofossil Zone NN20 (>0.29 Ma).


Daily Science Report for 12 October 2019

Location: Hole U1546C (27°37.8724′N, 111°52.7568′W; water depth 1585.6 mbsl)

Science Update: We continued RCB coring in Hole U1546C. Cores 15R to 28R penetrated from 405.5 to 473.6 mbsf and recovered 47.5 m (70%). Core 20R intersected the bottom sill/sediment contact at 431.7 mbsf. We pumped perfluorocarbon tracers (PFTs) for drilling fluid (seawater) contamination monitoring on Cores 21R and 22R, the first two sediment cores below the sill.

Cores U1546C-9R to 16R have been split and described. They consist of slightly to moderately altered, medium- to coarse-grained mafic igneous rocks. From Sections 9R-2 through 10R-6, the recovered sill material shows a change in texture from porphyritic dolerite to equigranular gabbro. The gabbroic layer is ~15 m thick. At the bottom of Core 10R, the doleritic texture resumes. Plagioclase phenocrysts are present throughout the doleritic intervals, while pyroxene is a minor phenocryst phase below the gabbro layer only. Occasionally occurring veins are mainly filled with zeolite minerals.


Daily Science Report for 11 October 2019

Location: Hole U1546C (27°37.8724′N, 111°52.7568′W; water depth 1585.6 mbsl)

Science Update: We continued RCB coring in Hole U1546C. Cores 8R to 14R penetrated from 360.4 to 405.5 mbsf and recovered 37.6 m (83%). Deployment of perfluorocarbon tracers (PFTs) for drilling fluid (seawater) contamination monitoring was stopped after Core 8R at a depth of 366.6 mbsf.

Cores U1546C-6R to 8R have been split and described. Section 6R-1 recovered the sediment/sill contact at ~348 mbsf. Black to dark gray claystone and brown dolomite are present above the contact with the sill. The top margin of the sill consists of highly altered, plagioclase-phyric subvolcanic rock mingled with some sediment. Core 7R consists of sparsely to highly vesicular, sparsely plagioclase phyric dolerite. Core 8R consists of sparsely vesicular to nonvesicular, highly plagioclase phyric dolerite. The material in both cores is moderately altered, occasionally showing veins filled with calcite and zeolite. Generally, these minerals also fill the observed vesicles.

The absence of E. huxleyi from Cores U1546C-1R to 6R suggests that the sediments above the sill are younger than 0.29 Ma. This would place the examined interval within nannofossil Zone NN20. No age-diagnostic diatoms were observed.


Daily Science Report for 10 October 2019

Location: Hole U1546C (27°37.8724′N, 111°52.7568′W; water depth 1585.6 mbsl)

Science Update: We continued lowering the drill string to the seafloor. After the bit had reached a water depth of 1564 mbsl, we picked up the top drive, deployed the center bit, and positioned the end of the drill string for spudding Hole U1546C. At 0305 h, we spudded Hole U1546C (40 m south and 20 m east of Hole U1546B). We then drilled without core recovery from the seafloor to 308.2 mbsf, while pumping 20 barrels of high-viscosity mud in total. Upon recovering the center bit at 1330 h, we began coring with the rotary core barrel (RCB) system. Cores U1546C-2R to 7R penetrated from 308.2 to 360.4 mbsf and recovered 10.4 m (20%). The recovery increased substantially after a formation change from the sedimentary overburden (16%) to the underlying sill (69%) at the bottom of Core 6R at ~357 mbsf.

Cores U1546B-44F to 59X have been split and described. Cores 44F to 56X consist of greenish brown diatom clay. Starting with Core 57X, an increase in sediment stiffness and a decrease in diatom preservation was observed. Dolostone layers occur regularly once per core on average, and laminated intervals are present, although the majority of the sediment is homogeneous.

Cores U1546C-2R to 5R have been split and described. They consist of brown siliceous claystone that contains several dolostone layers.


Daily Science Report for 9 October 2019

Location:
• Hole U1546B (27°37.8840′N, 111°52.7809′W; water depth 1585.6 mbsl)
• Underway to Guaymas, Mexico
• Guaymas pilot station
• Underway to Site U1546
• Hole U1546C (27°37.8732′N, 111°52.7575′W; water depth 1585.6 mbsl)

Science Update: We started the day continuing XCB coring in Hole U1546B. Core 59X penetrated from 331.3 to 333.8 mbsf and recovered 2.5 m (77%). We then terminated coring at 0045 h and pulled the drill string out of the hole to prepare for transit to Guaymas, Mexico, to conduct a medical repatriation of a crew member. The bit cleared the seafloor at 0215 h, ending Hole U1546B at a final depth of 333.8 mbsf. After the bit had arrived on the rig floor at 0530 h, we secured the vessel for transit. At 0600 h, we began our transit to Guaymas. We arrived at the pilot station at 1215 h, and the patient disembarked the vessel at 1225 h. After the pilot boat had left, we began the sea passage for returning to Site U1546. We arrived on site at 1730 h and switched to dynamic positioning mode. At 1815 h, we started preparing to spud Hole U1546C. We assembled the rotary core barrel (RCB) coring tool and made up the RCB bottom-hole assembly. We then began lowering the drill string to the seafloor, reaching a water depth of 590 mbsl by the end of the day.

Cores U1546B-7H to 43F have been split and described. They consist of diatom ooze and clay, showing overall decreasing lamination and increasing bioturbation with predominance of diatom clay from Core 20H onwards. Carbonate-rich indurated intervals and dolostones occur regularly.


Daily Science Report for 8 October 2019

Location: Hole U1546B (27°37.8840′N, 111°52.7809′W; water depth 1585.6 mbsl)

Science Update: We continued HLAPC/XCB coring in Hole U1546B throughout the day. Cores 24X to 58X penetrated from 202.5 to 331.3 mbsf and recovered 136.3 m (106%). We mainly deployed the HLAPC coring tool to a depth of 293.3 mbsf (Core 54F) and switched to the XCB coring tool whenever we had to core through hard carbonate layers. This happened at several depths, corresponding to Cores 24X, 27X, 31X, 34X, 36X, 40X, 42X, 46X, 48X, 53X. Starting with Core 55X, we deployed the XCB system permanently. We pumped perfluorocarbon tracers (PFTs) down the hole on all cores for monitoring drilling fluid (seawater) contamination.

The last cores of Hole U1546A, i.e., Cores U1546A-63X and 64X, have been split. They consist of medium-grained dolerite that will be described in detail once processing and description of Hole U1546B sediment cores have been completed. Biostratigraphic analysis of sediment cores from Hole U1546A has been completed through the bottom of the sediment succession in Core 62X. No older age-diagnostic flora has been observed in either calcareous nannofossils or marine diatoms. The bottom of Hole U1546A thus remains in nannofossil Zone NN20 with an age between 290 and 440 ka.

Cores U1546B-1H to 6H have been split and described. They consist of alternating finely laminated and homogenous diatom clay and diatom ooze. Soft sediment deformation has occasionally been observed. There are no samples taken for micropaleontology in Hole U1546B.


Daily Science Report for 7 October 2019

Location: Hole U1546B (27°37.8840′N, 111°52.7809′W; water depth 1585.6 mbsl)

Science Update: The day started with preparing for coring operations in Hole U1546B. We installed the sinker bars and lowered the bit to the seafloor to spud Hole U1546B. We then started APC coring in Hole U1546B at 0050 h. Mudline Core U1546B-1H recovered 4.3 m. This established a seafloor depth of 1585.6 mbsl. Cores 1H to 23H penetrated from the seafloor to 202.5 mbsf and recovered 213.0 m (105%). We switched to the XCB coring tool to core through a hard layer at 134.8 mbsf (Core 16X). We pumped perfluorocarbon tracers (PFTs) down the hole on all cores for monitoring drilling fluid (seawater) contamination. As at the previous site, Hole U1546B is dedicated to extensive collection of whole-round cores for microbiology and biogeochemistry research. The pacing of coring was adjusted to the complex microbial sampling program conducted on the core-receiving platform.

Cores U1546A-44F to 62X have been split and described. Cores 44F to 56X consist of greenish brown diatom clay. A change in color from olive to dusky yellowish brown, starting with Core 57X, corresponds to an increase in sediment stiffness and a decrease in diatom preservation. This siliceous claystone continues until the bottom of the sedimentary overburden in Core 62X, above the contact with the sill. In Core 62X, darker siliceous claystone is present. Dolostone layers occur regularly once per core on average and laminated intervals are present, although the majority of the sediment is homogeneous. At the bottom of Section 62X-CC we recovered the top chilled margin of the underlying basalt sill in a ~20 cm thick interval. Biostratigraphic examination through Core 60X has not yielded any new age-diagnostic taxa for either calcareous nannoplankton or marine diatoms. Thus, a Late to Middle Pleistonce biostratigraphic age (<290 ka) remains through Core 39F based on the NN21 nannofossil biozone, which is the base of identified species E. huxleyi.


Daily Science Report for 6 October 2019

Location:
• Hole U1546A (27°37.8851′N, 111°52.7939′W; water depth 1586.1 mbsl)
• Hole U1546B (27°37.8840′N, 111°52.7818′W; water depth 1585.6 mbsl)

Science Update: We started the day continuing HLAPC/XCB coring in Hole U1546A. Cores 51F to 64X penetrated from 283.0 to 361.2 mbsf and recovered 61.5 m (79%). Formation temperature measurements were made through deployment of the SET-2 tool after Cores 51F and 57X. We switched to XCB coring to penetrate through a hard carbonate layer on Core 53X. After Core U1546A-54F, we permanently deployed the XCB coring tool in stiffer sediment formation. Our goal was to deepen the hole to the top contact of a seismically imaged sill at around 350 mbsf. We eventually intersected the sill contact on Core U1546A-63X at ~358.5 mbsf. Upon recovering another interval of the same sill in Core 64X at 2120 h, we started pulling the drill string out of Hole U1546A from a final depth of 361.2 mbsf. The bit cleared the seafloor at 2320 h, ending Hole U1546A. We then moved the vessel 20 m to the east to position the bit for spudding Hole U1546B.

Cores U1546A-19H to 43H have been split and described. They mainly consist of diatom clay. At the bottom of Core 22F, the micrite component that was significant in shallower cores becomes less abundant. However, carbonate-rich indurated intervals and dolostones continue to occur regularly. Unlike the shallower part of the hole, the majority of the sediments are bioturbated and lamination is rare. Biostratigraphic examination through Core U1546A-35F has not yielded any new age-diagnostic taxa for either calcareous nannoplankton or marine diatoms, so a Late to Middle Pleistonce biostratigraphic age (<290 ka) remains.

Scientists continued to collect and analyze Hole U1545B data and submitted the first draft of their Site U1545 reports. We held the second science summary meeting for Site U1545, with the other half of the laboratory groups presenting their Site U1545 results to the entire science party.


Daily Science Report for 5 October 2019

Location: Hole U1546A (27°37.8851′N, 111°52.7939′W; water depth 1586.1 mbsl)

Science Update: We continued coring in Hole U1546A throughout the day, using the APC, HLAPC, and XCB coring tools. Cores 18H to 50F penetrated from 155.8 to 283.0 mbsf and recovered 139.1 m (109%). We recorded strong overpull force upon retrieval of Core U1546A-21H, so we switched to HLAPC. While using the HLAPC coring tool, we occasionally switched to the XCB coring tool to penetrate through hard layers. This happened on Cores 26X, 31X, 34X, 37X, 41X, 45X, and 47X. All APC cores were oriented. At several depths, we made formation temperature measurements using both the APCT-3 tool (on Cores 19H, 22F, and 28F) and the SET-2 tool (after Cores 28F, 35F, and 43F).

Cores U1546A-7H to 18H have been split and described. Cores 7H to 10H mainly represent alternations between laminated and homogenous diatom clay and diatom ooze. ​From Cores 11H to 18H, tilting and folding of laminae and beds occur regularly, and diatom ooze and clay are mixed with micrite. On average, two carbonate layers/nodules with different levels of induration are present in each core. Biostratigraphic analysis through Core U1546A-16H has not yielded any new age-diagnostic taxa for either calcareous nannoplankton or marine diatoms, so a Late to Middle Pleistonce biostratigraphic age (<290 ka) remains.

Scientists continued to collect and analyze Hole U1545B data and prepare their Site U1545 reports. We held the first science summary meeting for Site U1545, with half of the laboratory groups presenting their Site U1545 results to the entire science party.


Daily Science Report for 4 October 2019

Location:
• Hole U1545B (27°38.2301′N, 111°53.3295′W; water depth 1594.2 mbsl)
• Hole U1546A (27°37.8851′N, 111°52.7939′W; water depth 1586.1 mbsl)

Science Update: We started the day continuing to XCB core in Hole U1545B. Cores 63X to 67X penetrated from 347.9 to 387.3 mbsf and recovered 7.0 m (18%). We made a formation temperature measurement following Core 63X using the SET2 tool. After the XCB bit was destroyed with Core 66X and we advanced only 0.5 m in 45 min of coring Core 67X, we decided to terminate coring in Hole U1545B. At 0815 h we started pulling the drill string out of the hole, and the bit cleared the seafloor at 0945 h, ending Hole U1545B and Site U1545. At 1005 h, we started moving the vessel to Site U1546 (proposed primary Site GUAYM-02B). We arrived on the site coordinates at 1045 h and prepared for APC coring operations in Hole U1546A. We lowered the drill string to a water depth of 1558 mbsl and picked up the top drive. The bit was then positioned at 1581.4 mbsl—5 m above the seafloor depth obtained from the precision depth recorder—for taking the first core. At 1230 h, we spudded Hole U1546A. Mudline Core U1546A-1H arrived on deck at 1250 h, recovering 3.8 m. This established a seafloor depth of 1586.1 mbsl. APC Cores 1H to 17H advanced from the seafloor to 155.8 mbsf and recovered 165.2 m (106%). We made temperatures measurements on every third core with the APCT-3 tool, starting with Core 4H.

Cores U1545B-46F to 67X, the last from Hole U1545B, have been split and described. They consist of diatom clay and silty clay. We also confirmed a basaltic modal composition for the microcrystalline hard rock layer recovered in Core U1545A-71X.

Cores U1546A-1H to 6H have been split and described. They consist of alternations between finely laminated and homogenous diatom clay and diatom ooze. Cores 2H and 3H show evidence of soft sediment deformation. Calcareous biostratigraphic markers indicate a Late to Middle Pleistocene age (<290 ka) at the base of Core 3H. No age diagnostic diatoms have been observed.

Scientists continued to collect and analyze Hole U1545B data, and prepare their Site U1545 reports and presentations for the science summary meeting.


Daily Science Report for 3 October 2019

Location: Hole U1545B (27°38.2301′N, 111°53.3295′W; water depth 1594.2 mbsl)

Science Update: We continued coring in Hole U1545B, alternating between the HLAPC and XCB coring tools. Cores 40F to 62X penetrated from 245.8 to 347.9 mbsf and recovered 84.8 m (83%). We mainly used HLAPC coring to a depth of 328.5 mbsf (Core 60F) and switched to XCB coring on Cores 48X, 54X, and 57X after we recorded partial strokes due to encountering hard carbonate layers. Starting with Core 61X, we deployed the XCB coring tool permanently after we had to drill over the core barrel on Core 60F. For formation temperature measurements, we deployed the APCT-3 tool on Cores 45F and 49F, and the SET-2 tool following Cores 45F, 49F, and 60F. We continuously deployed perfluorocarbon tracers (PFTs) on all cores for monitoring drilling fluid (seawater) contamination.

Cores U1545B-21F to 45F have been split and described. They consist of light olive to olive gray micrite-rich diatom clay, revealing a decrease in both authigenic micrite content and abundance of carbonate concretions compared to shallower cores.


Daily Science Report for 2 October 2019

Location: Hole U1545B (27°38.2301′N, 111°53.3295′W; water depth 1594.2 mbsl)

Science Update: We continued coring in Hole U1545B, starting the day with switching from APC to HLAPC coring. Cores 18F to 39F penetrated from 147.6 to 245.8 mbsf and recovered 94.6 m (96%). For formation temperature measurements, we deployed the APCT-3 tool on Cores 20F, 27F, 33F, and 39F, and the SET2 tool following Cores 27F, 33F, and 39F. Partial strokes were recorded on Cores 18F, 23F, 24F, 26F, 27F, 35F, and 36F. We pumped perfluorocarbon tracers (PFTs) downhole on all cores for monitoring drilling fluid (seawater) contamination. The pacing of coring continued to be adjusted to the microbial sampling program implemented on the catwalk.

Cores U1545B-8H to 20F have been split and described. They mainly consist of light olive-gray diatom ooze with laminated and homogenous textures. Subordinate intercalated carbonate layers and nodules are common.


Daily Science Report for 1 October 2019

Location: Hole U1545B (27°38.2301′N, 111°53.3295′W; water depth 1594.2 mbsl)

Science Update: We started the day deploying the subsea camera system to the seafloor to survey Hole U1545A. We did not observe any gas release from the subseafloor through the hole. The subsea camera system was recovered by 0200 h. We then started pulling the drill string out of the hole and the bit cleared the seafloor at 0225 h, ending Hole U1545A. After the drill string was raised to a water depth of 1567.1 mbsl, we picked up the top drive, and lowered the bit to the seafloor to spud Hole U1545B. We then installed the sinker bars and started APC coring Hole U1545B at 0410 h. Mudline Core U1545A-1H recovered 3.7 m. This established a seafloor depth of 1594.2 mbsl. Cores 1H to 17H penetrated from the seafloor to 147.6 mbsf and recovered 154 m (104%). We made formation temperature measurements (APCT-3 tool) on every third core starting with Core 4H. A partial stroke was encountered on Core U1545B-16H. We pumped perfluorocarbon tracers (PFTs) down the hole on all cores for monitoring drilling fluid (seawater) contamination. The pacing of coring was adjusted to the complex microbial sampling program conducted on the core-receiving platform.

Hole U1545B is dedicated to extensive collection of whole-round cores for microbiology and biogeochemistry research. The selected core sections are processed on board for (1) few shipboard microbial analyses (e.g., cell counting, microbial rate measurement) and (2) shipboard sampling for personal postexpedition research. This approach implies that the majority of the recovered material from each core is not subjected to Core Laboratory analyses and description. Hole U1545B core description is thus based on observations obtained from the top and bottom section of each core. There are no core catcher samples taken for micropaleontology in this hole.

Cores U1545B-1H to 7H have been split and described. They consist of olive-gray laminated diatom ooze with variable proportions of clay, silt, authigenic carbonate, and other biosiliceous and calcareous microfossils.