IODP Expedition 359

Maldives Monsoon and Sea Level

Daily Science Report for 31 October 2015

Location: Hole U1467B (MAL-09A, 4°51.01′N, 73°17.02′E; 487 mbsl)

Science Update: We started the day deploying the MDHDS tool to the bottom of Hole U1467B after replacing the electronics module in the ERS; however, the test was aborted due to concerns about compatibility between the MDHDS and the mechanical bit release and float valve in the bottom-hole assembly. Once the tools were brought back to the rig floor at 0345 h we returned to coring operations and continued to deepen Hole U1467B using the full- and half-length APC, and XCB coring systems. By midnight we had recovered Cores U1467B-42F to 73X (351.0–578.4 mbsf; 80% recovery).

Cores U1467B-23H to 39H have been described and measured and sampled for physical properties and geochemical analyses. The cores consist of very fine grained and well sorted, partially lithified planktic foraminifera-rich wackestone. Bioturbation is common, with Thalassinoides, Chondrites, and Planolites present. The age of this interval is Late Miocene.

We held the Site U1465 science summary meeting, and scientists continue to work on and turn in their Site U1465 and U1466 reports.

Daily Science Report for 30 October 2015

Location: Hole U1467B (MAL-09A, 4°51.01′N, 73°17.02′E; 487 mbsl)

Science Update: Today we continued to deepen Hole U1467B with the full- and half-length APC coring systems. Cores U1467B-12H to 42F penetrated to 361.4 m (102% recovery). Following the recovery of Core U1467B-42F, we suspended coring operations and conducted a mud sweep to prepare the hole for testing the new Motion Decoupled Hydraulic Delivery System (MDHDS) and Electrical Release System (ERS) to deploy the Sediment Temperature Tool (SET). The initial deployment of the MDHDS was aborted after communication with the ERS module failed. The tools were brought back to the drill floor for troubleshooting. After replacing the electronics module, we began to lower the MDHDS tool back to the seafloor.

Cores U1467B-1H to 22H were measured and sampled for physical properties and described. They consist of unlithified planktonic foraminifera-rich mudstone and wackestone, inter-layered with partially lithified wackestone in the lower part of the succession. Foraminifera preservation worsens significantly with depth after Core U1467B-17H (148 mbsf). Measurements of sediment moisture and density and geochemical analyses of sediment and interstitial water samples are ongoing. Scientists started to submit the reports for Site U1465 and are finalizing revisions of the reports from Site U1466.

Daily Science Report for 29 October 2015

Location:
• Hole U1467A (MAL-09A, 4°51.0139′N, 73°17.0200′E; 487 mbsl)
• Hole U1467B (MAL-09A, 4°51.01′N, 73°17.02′E; 487 mbsl)

Science Update: We spudded Hole U1467A at 0055 h and established a seafloor depth of 487 m. Cores U1467A-1H to 4H penetrated to 32 mbsf (recovery 98%), but the next APC barrel failed to land properly; therefore, we deployed an XCB core barrel, but after experiencing excessive overpull upon retrieval, we decided to abandon the hole and bring the drill string back to the rig floor to inspect the bottom-hole assembly and the outer core barrel components. Upon inspection, we discovered that the XCB latch sleeve had been damaged, resulting in the jammed core barrels. We replaced the latch sleeve, lowered the drill string back to the seafloor, and Hole U1467B was spudded at 1430 h, establishing a seafloor depth of 487 m. Thereafter, we continuously cored with the APC system, cutting and recovering Cores U1467B-1H to 11H (0–98.5 mbsf; 100% recovery).

All cores from Hole U1467A were measured for physical properties and described. They consist of fine-grained and well-sorted unlithified mudstone to wackestone. Planktic foraminifera, pteropods, and coccoliths are the dominant components. The age at the bottom of Core U1467A-4H is estimated at ~400 k.y. Rhizon sampling for interstitial water chemistry was conducted in Cores U1467A-1H to 4H and U1467B-1H to 5H at a resolution of 1 to 2 per section. Interstitial water from squeezed IW samples (1 per core) have bee measured for alkalinity, pH, and chlorinity. Scientists submitted their reports for Site U1466 and are working on the reports for Site U1465.

Daily Science Report for 28 October 2015

Location:
• Hole U1465C (MAL-01A; 4°55.9865′N, 73°0.7002′E; 510 mbsl)
• Transit to Site U1467
• Hole U1467A (MAL-09A, 4°51.01′N, 73°17.02′E; 488 mbsl)

Science Update: We cut and recovered Cores U1465C-15F through 26X to a depth of 233.2 mbsf using the APC and XCB systems interchangeably. After experiencing increased pump pressures and excessive drill string torque, we made the decision to abandon Hole U1465C at approximately the same depth at which we ran into hole problems in Hole U1465B (~230 mbsf). By 1430 h, we had cleared the seafloor and continued to pull the drill string back to the drill floor, thus ending operations at Site U1465. Total recovery in Hole U1465C was just 3%. By 1818 h, we had recovered the positioning beacon, secured the rig floor, and raised the thrusters to begin our transit to Site U1467 (MAL-09A). The 17 nmi distance to the new site was completed in 2 h. By midnight we were lowering the drill string to the sea bottom to spud Hole U1467A.

All cores from Hole U1465C have been measured for physical properties and described. The cored interval in Hole U1465C consists of unlithified grainstone dominated by skeletal grains planktic foraminifera in the upper ~65 m, underlaid by floatstone, and medium- to coarse-grained, well-sorted packstone with interlayered coarse-grained rudstone and grainstone at the bottom. Benthic foraminifera are the main skeletal component, with solitary corals, bryozoan, echinoid spines, bivalves, planktic foraminifera, and otoliths as minor components. We held the Site U1466 science summary meeting at noon. Later in the afternoon, scientists began to turn in their Site U1466 reports for review and started to work on the reports for Site U1465.

Daily Science Report for 27 October 2015

Location: Hole U1465C (MAL-01A; 4°55.99′N, 73°0.69′E; 510 mbsl)

Science Update: We started the day cutting and recovering Core U1465B-23R from 221.3 mbsf before running into trouble with the hole due to loss of circulation, probably because of the high porosity of the formation. As a result, we decided to stop coring Hole U1465B, pull out of the hole, and start a new hole with the APC/XCB coring systems. We cleared the seafloor at 0610 h, and offset the ship 20 m east of Hole U1465B. After pulling the drill string back to the rig floor, we made up the APC/XCB bottom-hole assembly and lowered it to the seafloor, tagging the seafloor at 510 m. Coring in Hole U1465C started at 1330 h, and we cored continuously to 123.7 mbsf, cutting and recovering Cores U1465C-2F to 14X. Recovery over this interval was 28%. Our plan is to continue coring Hole U1465C until APC/XCB refusal.

Cores U1465C-2F to 4F were measured for physical properties and described. They consist of medium- to coarse-grained, well-sorted packstone with interlayered coarse-grained rudstone and grainstone. Benthic foraminifera are the main skeletal component, with solitary corals, bryozoan, echinoid spines, bivalves, planktic foraminifera, and otoliths as minor components.

Daily Science Report for 26 October 2015

Location: Hole U1465B (MAL-01A; 4°55.9862′N, 73°0.6897′E; 512.5 m)

Science Update: We started the day pulling out of Hole U1466B and ending coring operations at Site U1466. After clearing the seafloor, the ship was moved west ~1800 m to the coordinates of Site U1465 where we planned to rotary core a second hole. At 0655 h, after tagging the seafloor at 512.5 m, we spudded Hole U1465B and started to drill ahead to 65.9 mbsf. From that depth down we began RCB coring, cutting and recovering Cores U1465B-2R to 22R (65.9 to 211.6 mbsf) with a combination of full- and half-length RCB cores in an attempt to improve recovery of the ancient carbonate platform rocks. Despite our efforts, the overall recovery for the cored interval was just 6%.

The sedimentary sequence recovered from Hole U1465B consists of medium- to very-coarse, poorly-sorted dolomitic grainstone and rudstone with abundant skeletal components, which include branching corals with encrusting red algae, red algae nodules and molds of bivalves and gastropods, and benthic foraminifera. Highly fragmented and recrystalized bioclastic grains were abundant. Geochemists completed ICP analyses and continue CHNS analyses on sediment samples.

Daily Science Report for 25 October 2015

Location: Hole U1466B (MAL-02A; 4°55.9880′N, 73°1.6894′E; 518 m)

Science Update: We started the day continuing to RCB core Hole U1466B. Cores U1466B-48R through 57R were cut and recovered, extending the hole from 712 to 809.7 m, and reaching the revised total target depth of 800 m for Hole U1466B at 1200 h. Core recovery for Hole U1466B averaged 18%. We then began to condition the hole for downhole logging by circulating a heavy mud sweep. After dropping the bit, we pulled the pipe up to logging depth (80 mbsf) and began to rig up for wireline logging. The first logging run consisted of the triple combo tool string without the source, but the tool string was not able to pass 366 mbsf. We collected log data upward from that depth, recovered the logging tools, and decided to abandon further logging. By midnight, we had rigged down from wireline logging and were continuing to pull the drill string back to the drill floor. Our plan is to return to Site U1465 to RCB core Hole U1465B to ~720 m.

All cores from Hole U1466B have been measured for physical properties and described. Cores U1466B-48R to 53R are predominantly lithified to partially lithified, bioturbated fine- to medium-grained dolomitic packstone and wackestone. Core U1466B-54R consisted of graded sequences and convolute laminae consistent with turbiditic deposits. The lowermost part of the record consisted of thin to thick beds of alternating bioturbated white nannofossil chalk and dark brown organic-rich sediment. The age at the base of the cored section is lowermost Miocene. In the Geochemistry Laboratory, sediment samples were prepared for CHNS and ICP analyses.

Daily Science Report for 24 October 2015

Location: Hole U1466B (MAL-02A; 4°55.9880′N, 73°1.6894′E; 518 m)

Science Update: We continued to RCB core Hole U1466B. Cores U1466B-18R through 47R extended the hole from 469.4 to 712 m CSF-A. Core recovery over this interval averaged 14%. The cores are predominantly lithified to partially lithified, heavily bioturbated fine- to medium-grained dolomitic packstone and wackestone. Biogenic components mainly include skeletal grains of planktic foraminifera, although benthic foraminifera are the primary components in Core U1466B-34R (at ~590 m CSF-A). The age of the cored section is early to middle Miocene. All interstitial water (IW) samples have been measured for major cation and anion concentrations, therefore completing the IW geochemistry program for Holes U1465A and U1466A. Geochemical analyses of sediment samples are ongoing.

Daily Science Report for 23 October 2015

Location: Hole U1466B (MAL-02A; 4°55.9880′N, 73°1.6894′E; 518 m)

Science Update: We started the day RCB drilling Hole U1466B to 314 mbsf. At ~0800 h we deployed a wash core barrel and drilled through to the bottom of the hole, pumped a mud sweep, and then recovered the wash barrel in preparation for rotary coring. Cores U1466B-2R through 17R (314–469.4 m) were cut and recovered by the end of the day. Core recovery over this interval averaged 16%.

Cores U1466B-2R through 12R were measured for physical properties, split, and described. The cores are predominantly lithified to partially lithified, fine- to medium-grained dolomitic grainstone and packstone with abundant bioturbation. The age of this section is middle Miocene. All interstitial water samples (IW and Rhizons) from Holes U1465A and U1466A have been measured for minor elements by ICP. XRD data derived from squeezed whole-round sediment samples were processed to obtain carbonate mineral abundances.

Daily Science Report for 22 October 2015

Location: Hole U1466B (MAL-02A; 4°55.9894′N, 73°1.6898′E; 528.0 mbrf)

Science Update: Hole U1466A was completed today after cutting Cores U1466A-47F through 50X, from 306.3 m to 326.2 m CSF, and reaching APC/XCB refusal. Total core recovered in Hole U1466A is 243.8 m (75%). The drill string and the XCB bit were pulled out of the hole and retrieved back to the drill floor at 1000 h, ending Hole U1466A. Following, we assembled the rotary core barrel (RCB) bit and the RCB bottom-hole assembly. The drill string was lowered to the seafloor and we spudded Hole U1466B at 1620 h, establishing a seafloor depth of 528 mbrf with the drill string tag. The plan for Hole U1466B is first to drill down without recovery to ~314 m and then to RCB core to the ~1010 m target depth.

The sedimentary interval recovered in Cores U1466A-40X to 50X consists of partially lithified to lithified, very fine- to medium-grained dolomitic packstone and wackestone. The age of this interval is early to middle Miocene. The geochemistry team continues to process interstitial water samples (Rhizons) and completed headspace analyses for Holes U1465A and U1466A. Sediment samples are being prepared for carbonate analyses.

Daily Science Report for 21 October 2015

Location: Hole U1466A (MAL-02A; 4°55.9888′N, 73°1.6785′E; 528.9 mbrf)

Science Update: Today we continued to deepen Hole U1466A with the full-length and half-length APC and the XCB coring systems. Cores U1466A-18X to 46X penetrated from 138.8 m CSF to 306.3 m CSF (62% recovery). Because of high drill string torque and pump pressures after cutting Core U1466A-20F, a decision was made to conduct a second wiper trip to clean and stabilize the hole. We resumed APC coring ~2 h later at 0400 h.

The major lithologies in Cores U1466A-13H (100.5 m CSF) to 22H (171.5 m CSF) are very pale brown to yellow and white unlithified grainstone and packstone. Skeletal grains of planktic foraminifera are the dominant components in Cores U1466A-13H to 15H, whereas benthic foraminifera dominate the composition of Cores U1466A-16H to 22H. Ages of the cores have reached middle Miocene (Core U1466A-34F).

In the Geochemistry Laboratory, all the squeezed water samples from Hole U1465A (9 samples) and 29 from Hole U1466A have been analyzed for alkalinity and chlorinity. We are in the process of analyzing the Rhizon samples from the first five cores in Hole U1466A for alkalinity and chlorinity. Samples from Holes U1465A and U1466A have been prepared for ion chromatography analysis. All samples supplied by Physical Properties have been weighed in preparation for the determination of percent carbonate. In addition, samples have been selected for total organic carbon analysis. A portion of all the squeeze cake samples as well as samples selected by the sedimentologists will be analyzed by X-ray diffraction; the first batch of data was produced last night.

Daily Science Report for 20 October 2015

Location:
• Hole U1465A (MAL-01A; 4°55.98′N, 73°0.68′E; 515 mbsl)
• Transit to Site U1466
• Hole U1466A (MAL-02A; 4°55.99′N, 73°1.68′E; 528.9 mbrf)

Science Update: We started the day recovering Core U1465A-11X from a depth of 76.6 m CSF and reaching the initial objective in Hole U1465A, which was to core down until we could sample and date the top of the ancient platform edge. We then pulled out of the hole and cleared the seafloor, ending Hole U1465A. The ship was moved ~1 nmi to the east in dynamic positioning (DP) mode to the coordinates of Site U1466. After establishing a precision depth recorder (PDR) depth at 529 mbrf, we spudded Hole U1466A at 0625 h, and recovered Core U1466A-1H with 5 m of recovery. A combination of full-length and half-length APC cores were required to extend the hole to a depth of 138.8 m CSF (Cores U1466A-1H to 17H). In the process, Core U1466A-10F failed when the core barrel did not penetrate very far into the formation, and sand in the upper portion of the hole created coring and hole cleaning problems. Due to the unstable hole conditions, we conducted a wiper trip to clean up and stabilize the hole and later continued coring operations. By midnight we switched to XCB coring and partially cut Core U1466A-18X to 145.3 m CSF. Successful temperature measurements were taken on Cores U1465-3H and 4H (26.1 m and 35.6 m, respectively) in Hole U1465A, and in Core U1466A-8H (71.5 m) in Hole U1466A.

The major lithologies in Cores U1465A-3H to 11X (Hole U1465A) are unlithified grainstone with thick to medium intercalated rudstone, dominated by skeletal grains of planktic foraminifera, with pteropods, echinoderms, bryozoans, Halimeda, and benthic foraminifera as minor components, and medium to coarse grained, lithified floatstone. Similarly, the major lithology in Cores U1466A-1H to 4H (Hole U1466A) is unlithified grainstone and packstone, dominated by skeletal grains of planktic foraminifera, with pteropods, otoliths, echinoderms, bryozoans, Halimeda, and benthic foraminifera as minor components.

Rhizon sampling for interstitial water chemistry was conducted in Cores U1466A-1H to 5H at a resolution of one sample per section. In the Geochemistry Laboratory, interstitial water from squeezed IW and Rhizon samples are being measured for alkalinity, pH, and chlorinity.

Daily Science Report for 19 October 2015

Location: Hole U1465A (MAL-01A; 4°55.98′N, 73°0.68′E; 515 mbsl)

Science Update: We arrived at Site U1465 (MAL-01A) at 0418 h. The thrusters and hydrophones were lowered and the ship was switched to dynamic positioning (DP) mode at 0453 h. At 0611 h we deployed the positioning beacon and continued to assemble the bit and bottom-hole assembly including verifying the correct space-out of the core barrel. After establishing a PDR depth of 514.4 m below the rig floor, the first APC core barrel was deployed, recovering just a water core. The bit was lowered 9 m and a second APC core barrel was deployed, recovering another water core, with just a small sample of sandy material in the cutting shoe. On the third attempt, we first lowered the drill string to tag the seafloor, encountering resistance at ~524.4 m and 528 m below the rig floor. Then with the bit positioned at 523.4 mbrf, we spudded Hole U1465A at 1405 h with 7.43 m of recovery in Core U1465A-1H. Thereafter, we had to use the full-length and half-length advanced piston coring (APC) systems to extend the hole to a depth of 69.1 m CSF (Cores U1465A-1H to 10H). By midnight, the total core recovered was 52.8 m (76.4%). Cores U1465A-1H to 2H consisted of poorly to well sorted unlithified grainstone to rudstone, dominated by skeletal grains planktic foraminifera, with pteropods, echinoderms, bryozoans, Halimeda, and benthic foraminifera as minor components. Planktic foraminifera biostratigraphy revealed an estimated age of 3.59–3.85 Ma at the base of Core U1465A-10H.