To Chicxulub KT Impact Crater
To preliminary data from the Chicxulub Crater cruise
Principal Investigators: Richard T. Buffler,
Gail Christeson, and Yosio Nakamura
Funded by: the National Science Foundation
This cruise was part of a collaborative effort between the British Institutions
Reflection Profiling Syndicate (BIRPS)
(UK), the Canadian Geological Survey,
Imperial College (UK), the Lunar and Planetary Institute, the
Universidad Nacional Autónoma de México (UNAM), and The University of Texas Institute for Geophysics (UTIG). The
purpose of this joint project is to image in detail the internal crustal structure and
morphology of the Chicxulub impact crater and to quantify its dimensions.
Dick Buffler, Yosio Nakamura and Ben Yates represented UTIG onboard the RV Longhorn.
The other members of the shipboard scientific party were John Brittan (Imperial College),
Roy Cooper (Canadian Geological Survey), Adilce Flores (UNAM), and Carlos Ruiz (PEMEX
observer).
Cruise Reports
Thursday, September 26, 1996
From Gail Christeson
"The Longhorn left Port Aransas on schedule Sunday, and cleared Mexican customs Wednesday. Unfortunately en route the magnetometer was lost at sea (no details yet). The Longhorn is currently deploying OBSs along the main seismic line that traverses the crater. The GECO Sigma has also cleared customs and is currently deploying the streamer - streamer testing is estimated to be completed tonight or early tomorrow. So far everything is on schedule."
Friday, September 27, 1996
From Dick Buffler (onboard the Longhorn)
We have deployed 25 OBS along Line A, a 310km east-west trending line across the crater, and 1 OBS along Line C, a near-shore line that trends northeast. The GECO Sigma began shooting at 4:30 a.m. this morning along Line A. The Longhorn will make a gravity survey for a few days until we go back to pick up the first eight OBSs from Line A and deploy them along Line B, a northwest trending line.
The weather has been good, the seas calm. The crew of the Longhorn has been outstanding, working hard with the scientific crew. The scientific crew has been outstanding. Yosio has earned the nickname, "Iron Man," for staying up all night, watching as each OBS was deployed.
Everything is going smoothly.
Gail adds:
"All OBSs have now been deployed along the first shooting line for the Chicxulub experiment. The GECO Sigma started shooting at 4:30 this morning, and as of noon had fired 2100 shots (56 km). One large gun is down and the ship had just passed through a small fleet (50 boats) using fishing poles to get octopi. Other than that all has gone very smoothly.
"The magnetometer was lost at the connection to the cable. The speculation on board the ship was that perhaps it was attacked by a shark, one fin was damaged, and it rotated out of control and snapped the connection (honest - I wouldn't make this up!)"
Saturday, September 28, 1996
From Dave Snyder aboard the GECO Sigma, 9:30 Saturday morning:
We continue shooting line CHIX-A, having restarted at 14:02 GMT after fixing an airleak on one gun subarray. We acquired 181.45 km of data in this first sequence. We had stopped shooting at 10.48 GMT, so this adds 3 hours to the projected endtime of the line. We have just passed the location of OBS 16. Our bottom speed is 4.0 knots at present. I now estimate EOL at about 11.00 GMT on Sunday provided no more circles are required. The LONGHORN cruised past us at 23.30 GMT last evening (18.30 Local time), collecting gravity data as it sailed westward. Dick Buffler and I had a good chat and it was a nice photo opportunity before the LONGHORN disappered into the sunset.From Mike Warner, Land Party, Saturday evening:
We have just retrieved the first of the land data. We can see the Sigma start shooting on time. Beautiful records, signal to noise at least 10:1. Both the land and OBS data should be excellent. We are trying to find more info about locations of octopus boats, but no useful info yet. The local paper has published our track and likely times of passage today, so that may help a bit.
Sunday, September 29, 1996
From Dave Snyder aboard the GECO Sigma, 9:00 Sunday morning:
We completed the shooting of line CHIX-A at 10.49 GMT (5.49 local time). We acquired 344.4 km of data total for the line. This was almost exactly the time that OBS 1 stopped recording. We are now in transit to line CHIX-C and estimate arrival at the start of the line at 02.00 GMT on Monday (21.00 Sunday local time).
Monday, September 30, 1996
From Dave Snyder aboard the GECO Sigma, 9:30 Monday morning:
We began the shooting of line CHIX-C at 4.19 GMT (23.19 local time). We have now acquired 90 km of data, about 2/3 of the line. We estimate finishing CHIX-C about 16.00 local time today. We will attempt to keep the airguns firing and record as much as possible between lines CHIX-C and CHIX-B. When we get into shallow water, we will shallow the streamer. Aim points for EOL and SOL are OBSs 34 and 35. We will not record for about 2 hours in the shallowest water in order to reset the recording system and do QC during the line change, but we hope to keep the guns firing. Start of line CHIX-B is estimated for between 22.00 and 24.00 if no equipment problems occur and we do not run aground or run down octopi fishers just outside Progreso!Glad to hear land records are of good quality and the shot times are readable. So far we can not produce any good quality stacks of any sort, so I cannot comment on any "preliminary results". I can state that noise levels are excellent and shallow reflectors are definitely there.
Wednesday, October 2, 1996
From Dave Snyder: We finished shooting the survey yesterday at 19.30 GMT (14.30 local time). We acquired 647.5 km of data during the survey. We have just docked at Progreso. Suman will go ashore then and will carry hard copy and discs with absolute shot times for the land party. Mike and I will meet at the pier if possible, and I may try to go ashore. It is uncertain yet whether I will likely stay on SIGMA for a few more days to supervise navigation tape processing. I just spoke with Dick Buffler on the ship's radio. Apparently the port authority thinks we shot a little too close to shore yesterday, but Geraldo Basurto thinks that should be no real problem once things are discussed.
Additional news: Weather and equipment cooperated during the experiment, allowing each of the three lines to be extended 18-35 km, for a total of 84 extra km. The Longhorn will continue collecting gravity data through Sunday morning, when it will begin retrieving the 26 OBSs still on the bottom. Recovery operations are planned through sunrise Tuesday morning, followed by a final fueling/customs port call in Progresso. At this time Roy Cooper from the Canadian Geological Survey, Adilce Flores from UNAM, and Carlos Ruiz from PEMEX will disembark; Roy Cooper and Alan Hildebrand will collect additional nearshore gravity data from another vessel for a few days. The Longhorn expects to dock at Port Aransas the morning of Friday, October 11.
Monday, October 7, 1996
From Gail Christeson:
The Longhorn is currently busy recovering OBSs - recovery operations started yesterday and will continue into tomorrow morning. Unfortunately one OBS was lost today. Two people initially sighted the OBS, but the beacon did not go on, and visual contact was subsequently lost. Feelings on board the ship are that it sank. Of the recovered OBSs all recorded fine.
Friday, October 11, 1996
From Gail Christeson:
The Longhorn is currently off Port Aransas waiting for a 1:00 customs clearance. Tropical Storm Josephine, which passed over the Yucatan, initially caused no problems. Unfortunately, by the time it was in the northwest Gulf and downgraded it was creating rough seas off the Yucatan. Because of this situation the OBS furthest from port had to be abandoned in order to head in and recover the last 2 OBSs. However on the way in the OBS previously lost was sighted and recovered! Notices have been put out to the fishing community, so hopefully the one lost OBS will be recovered in the near future. Dick, Yosio, and Ben should be back in Austin tonight or tomorrow.