IODP Expedition 334

Costa Rica Seismogenesis Project (CRISP)

Daily Science Report for 12 April 2011

LOCATION: Transit to Puntarenas, Costa Rica

SCIENCE UPDATE: To be able to calculate a geothermal gradient and the heat flux at Site U1381 we decided to drill Hole U1381B. Thus we plugged and abandoned Hole U1381A after retrieving the last hard rock core on deck at 0045 hr and spudded Hole U1381B at 0325 hr. We cored the first 30 m of this hole and the recovered material was dedicated to high-resolution geochemical sampling, followed by 20 m drilled down intervals. After each drilled interval a 15-minute temperature measurement was taken with the SET tool. Overall we retrieved 54.15 m of sediment and 35.69 m of basalt at this site with an average total recovery rate for sediment and basement of 42.3 and 54.8%, respectively. In the early evening we started the 94 nm long transit back to Puntarenas, Costa Rica. The rather successful Expedition 334 will end with the first line ashore at Puntarenas on 13 April 2011.

Daily Science Report for 11 April 2011

LOCATION: Site U1381 (CRIS-1A) Lat. 8°25.7150' N, Long. 84°9.4690' W

SCIENCE UPDATE: We retrieved Cores U1381A-21R to 26R (141.22–164.1 mbsf) with an average recovery rate of 65%. The material from the basement retrieved up to now consists of dark to light gray, very dense tough basalt. The basalt ranges from almost aphyric to moderately and highly phyric. The phenocryst assemblage changed with depth from one being dominated by feldspar, with pyroxene being only a minor constituent, to one being dominated by pyroxene. The basalt is mainly fresh with alteration being restricted to halos along veins and mineral boundaries.

Daily Science Report for 10 April 2011

LOCATION: Site U1381 (CRIS-1A) Lat. 8°25.7150' N, Long. 84°9.4690' W

SCIENCE UPDATE: We retrieved Cores U1381A-14R to 20R (107.64–141.22 mbsf) with an average recovery rate of 48.1%. The material from the basement retrieved up to now consists of dark gray, very dense tough basalt. The basalt mainly contains abundant feldspar and minor pyroxene. It is moderately altered. Vesicles and veins are filled with carbonate, clay and pyrite. Besides the normal work describing cores, the scientists are busy writing site reports and getting prepared for leaving the ship.

Daily Science Report for 9 April 2011

LOCATION: Site U1381 (CRIS-1A) Lat. 8°25.7150' N, Long. 84°9.4690' W

SCIENCE UPDATE: We retrieved Core U1381A-1R to 13R (0–107.64 mbsf) with an average recovery rate of 38.6% and 59.6% in sediment and basement, respectively. Basement penetrations rates slowed down to about 1.9 m per hour, because we are coring dense, very tough basalt. The sediment at this site consists mainly of greenish gray to beige silty clay to clay in the top part and of silicic ooze in the bottom part intercalated with a couple of tephra layers. Foraminifera are present throughout the entire cored sediments. The sediments are of Pleistocene age based on the observed nannofossils.

Daily Science Report for 8 April 2011

LOCATION: Site U1381 (CRIS-1A) Lat. 8°25.7147' N, Long. 84°9.4703' W

SCIENCE UPDATE: We retrieved Core U1380A-4R to 10R (412–479.75 mbsf) with an average recovery rate of 62.3% after drilling down to a depth of 397 mbsf. After retrieving the last core the hole started to behave problematically again, right around the same depth interval we had problems in Holes U1378A and U1378B. After several hours of unsuccessful attempts to clean the hole and get back to bottom we started to plug and abandon Hole 1380A at 1500 hrs and the decision was made to continue our drilling operations at Site CRIS-1A. We decided to core the sediment cover (110 m) and as much of the basement in the time window available as possible. The sediments cored from Hole U1380A consist mainly of the monotonous sequence of dark green-gray silty clay to clay observed at all the other sites already cored, intercalated with some ash layers.

Daily Science Report for 7 April 2011

LOCATION: Site U1380 (CRIS-10A) Lat. 8°35.9980' N, Long. 84°4.4037' W

SCIENCE UPDATE: In order to be able to reach and core basement in the remaining time of this expedition the decision was made to drill down the first ~400 m at this site and then start coring. According to the seismics the boundary between sediment and basement at this site is at around 550 mbsf +/- 50 m. Thus we are going to core about 150 m of the sediment coverage at this site, which should give us enough overlap for the stratigraphic correlation with the sediments drilled at Site U1378 (0.5 miles distance from this site). We spudded Hole U1380A at 0215 hrs and drilled down to a depth of 397 mbsf. At 2145 hrs we started coring, retrieving Cores U1380-2R to 3R (397–412 mbsf) with an average recovery rate of 58%.

Daily Science Report for 6 April 2011

LOCATION: Site U1378 (CRIS-3B) Lat. 8°35.5408' N, Long. 84°4.6415' W

SCIENCE UPDATE: Drilling proceeded smoothly until after Core U1378B-63X was on deck at 0035 hrs when hole problems were encountered. After over 12 hrs of unsuccessful attempts to clean the hole, we decided to plug and abandon Hole U1378B. The total depth reached at this site is 523.9 mbsf. The observed material (Cores U1378B-43X to 59X) still consists mainly of the monotonous sequence of dark green gray silty clay to clay. Intercalated in this material are tephra layers (becoming less frequent with depth) as well as unconsolidated, coarse sand layers (middle part of the sequence) and again sequences of intense brecciation denoting fault zones. Distributed throughout the entire observed material are abundant foraminifera.

Daily Science Report for 5 April 2011

LOCATION: Site U1378 (CRIS-3B) Lat. 8°35.5415' N, Long. 84°4.6313' W

SCIENCE UPDATE: Drilling proceeded smoothly in the last 24 hrs; retrieving Cores U1378B-49X to 63X (388.64–523.9 mbsf) without any problems, with an average recovery rate of 99.2%. We are still observing (Cores U1378B-31X to 42X) the monotonous sequence of mainly dark green-gray silty clay to clay that becomes a little coarser with depth and more lithified. Superimposed on this main background sedimentation are frequent tephra layers and some fault zones as indicated by sequences showing intense brecciation.

Daily Science Report for 4 April 2011

LOCATION: Site U1378 (CRIS-3B) Lat. 8°35.5415' N, Long. 84°4.6313' W

SCIENCE UPDATE: We retrieved Cores U1378B-31X to 48X (246.9–388.64 mbsf) with an average recovery rate of 96.5%. The sediments observed up to now (Cores U1378B-18H to 30X) still consist of the monotonous sequence of mainly dark gray silty clay to clay that is, compared to the other site, interrupted by more abundant ash layers. In the deeper parts of the described cores several tempestite layers, consisting of coarse-grained sand with abundant shells, are intercalated in the normal background sediments. Abundant foraminifera are dispersed throughout the entire cored sediments, which are of Pleistocene age.

Daily Science Report for 3 April 2011

LOCATION: Site U1378 (CRIS-3B) Lat. 8°35.5415' N, Long. 84°4.6313' W

SCIENCE UPDATE: We retrieved Cores U1378B-12H to 30X (99.6–245.24 mbsf) with an average recovery rate of 109%. The sediments (Cores U1378B-7H to 17H) consist of olive-green silty clay that are frequently interrupted by up to 5 cm thick graded sand sequences and by several tephra layers. In Core U1378B-13H a gradational change back to the monotonous sequence of mainly silty clay to clay that frequently alternates with sandy layers we have already cored at Hole U1379C. Abundant foraminifera and nannofossils are dispersed throughout the entire cored material and indicate a Pleistocene age.

Daily Science Report for 2 April 2011

LOCATION: Site U1378 (CRIS-3B) Lat. 8°35.5415' N, Long. 84°4.6313' W

SCIENCE UPDATE: After retrieving the last core, Hole U1379C was plugged and abandoned and we started our 45 minute transit back to Site U1378 at 0945 hrs. At 1100 hrs we started to pick up the bottom hole assembly and spudded Hole U1378B at 1315 hrs. We retrieved Cores U1378B-1H to 11H (0 – 99.6 mbsf) with an average recovery rate of 101%. The material consists of olive green silty clay that is frequently interrupted by fining upward sands and by four tephra layers. The sediments are quite soft down to ~15 mbsf, below which the silty clay is more consolidated. In contrast to Site U1379, the sediment contains abundant foraminifera and nannofossils dispersed throughout the entire recovered cores. Based on the observed nannofossil community the sediments were deposited in the late Pleistocene.

Daily Science Report for 1 April 2011

LOCATION: Site U1379 (CRIS-4A) Lat. 8°40.8496' N, Long. 84°2.0169' W

SCIENCE UPDATE: Cores U1379C-105X to 118X (899–949 mbsf) were retrieved with an average recovery rate of 33%. The core recently described (720–851 mbsf) is mainly composed of dark greenish gray fining upward units ranging from sandy clayey silt to silty clay. However, the majority of the unit is clayey silt. There are a few areas where the sediment becomes slightly coarser than the background sedimentation rate. Foraminifera are present throughout; shell fragments are only rarely present. Generally, this sequence is interrupted by some rare 2 to 5 cm thick fine sand layers and frequent hardened tephra layers, which show normal grading within the normal bedding inclination but show reworking within the soft stage at the top. In the lower part of this interval, the sequence is also interrupted by carbonate concretions. According to the observed nannofossil community the transition from Pleistocene to Pliocene must be somewhere within this 720–851 mbsf depth range.