U.S. GEOLOGICAL SURVEY 
Coastal and Marine Geology Program 
Woods Hole, MA 02543

Ship Name/Owner Operator:  R/V FARNELLA



Cruise No.:  F-90-3 and F-90-4



Project Number:



Funding Agency:  U.S. Geological Survey



Area of Operation:  Mississippi Fan and Base of the Florida Escarpment

                    in the eastern Gulf of Mexico - mostly in the area

                    26d-27d N. and 84.5d-87d W. although coring on the

                    second leg (F-90-4) of the cruise was also done in

                    the area.



Cruise Dates:  F-90-3  25 March - 8 April, 1990

                       Tampa, FL to Tampa, FL



               F-90-4  12 April - 26 April, 1990

                       Tampa, FL to Tampa, FL



Chief Scientists:  D. Twichell,  USGS - AMG - Cochief Scientist

                   W. Schwab, USGS - AMG - Cochief Scientist



Scientific Party:

         F-90-3 - D. Twichell,  USGS - AMG

                  W. Schwab, USGS - AMG

                  W. Danforth, USGS - AMG

                  B. Irwin, USGS - AMG

                  D. Lubinski, USGS - AMG

                  T. O'Brien, USGS - AMG

                  D. Mason, USGS - AMG

                  L. Bader, USGS - PMG

                  M. Hamer, USGS - PMG

                  L. Kooker, USGS - PMG

                  N. Kenyon, IOS

                  T. Crook, WHOI - DSL

                  T. Dettweiler, US Navy



                  M. Williamson, IDSS

                  K. Redman, IDSS

                  N. Lesnikowski, IDSS

                  J. McDowell, IDSS



          F-90-4 - W. Schwab,  USGS

                   D. Twichell, USGS

                   W. Danforth, USGS - AMG

                   B. Irwin, USGS - AMG

                   D. Lubinski, USGS - AMG

                   T. O'Brien, USGS - AMG

                   R. Rendigs, USGS - AMG

                   W. Winters, USGS - AMG

                   L. Bader, USGS - PMG

                   J. Barber, USGS - PMG

                   H. Lee, USGS - PMG

                   H. Nelson, USGS - PMG

                   J. Vaughan, USGS - PMG

                   N. Kenyon, IOS

                   T. Crook, WHOI - DSL

                   C. Paull, UNC

                   W. Ussler, UNC



Ship's Captain:   William Millender



Purpose of Cruise: FARNELLA cruises F-90-3 and F-90-4 were conducted

        in the Eastern Gulf of Mexico to study recent sedimentary

        processes on the Mississippi Fan and along the base of the

        Florida Escarpment.  GLORIA images in concert with 3.5 kHz

        profiles had been used to divide the fan's surface into

        several depositional lobes.  This ground-truth program

        focused on one of these depositional lobes to further our

        understanding of (1) the acoustic properties of the sediments

        that are creating the different backscatter patterns revealed

        on the GLORIA images, (2) the mechanics of transport and

        deposition of these lobes, (3) the sedimentology of these

        deposits, and (4) hopefully some insight into their timing

        of deposition.  In addition to the work on the Mississippi

        Fan, a second objective was to collect cores from plunge

        pools along the base of the Florida Escarpment to define

        the sedimentology of these deposits were sample pore water

        from the cores to measure Chloride, Sulfate, Methane, and

        Sulfide.  These chemical analyses are intended to shed light

        on the occurence of dense brines seeping out of the Florida

        Platform.



Navigation Techniques:



Scientific Equipment:

        F-90-3  SeaMARC I and 4.5-kHz profiler - IDSS

                QMIPS data acquisition system - USGS

                Masscomp sidescan sonar processing system - USGS

                3.5-kHz surface towed subbottom profiler - USGS

                Loran C and GPS navigation system - USGS

                Benthos acoustic navigation system - WHOI, DSL



        F-90-4  Piston corer - USGS

                3.5-kHz surface towed subbottom profiler - USGS

                Loran C and GPS navigation system - USGS

                Benthos acoustic navigation system - WHOI, DSL

                Gas chromatograph - UNC

                Velocimeter  - USGS



Days at Sea:  F-90-3       15

              F-90-4       14



Data Collected:

           SeaMARC 3466 km2

           4.5 kHz 950 km

           3.5 kHz 2280 km

           Cores:  Piston cores    55

                   Gravity cores   12



Remarks:       This ground-truth program was extremely successful,

          although things started a bit slowly at the beginning of

          the first leg.  A gravity line was run on the way out from

          Tampa for Bill Dillon for the Florida transect project,

          and once we were at our first survey area a brief echo

          sounder survey was conducted, and then transponders were

          deployed and surveyed in (transponder locations listed

          in Table I).  For the first several days we had problems

          with the SeaMARC I side-scan sonar system, but after the



          bugs were ironed out the system worked almost flawlessly,

          and we obtained approximately 10 days of excellent quality

          SeaMARC I imagery along the track lines shown in Figure 1.

          Our main problem, once the bugs were out of the system,

          was the Loop Current which was highly variable in direction

          and had speeds reaching 3.5 knots.  This current made

          towing the SeaMARC vehicle at 2-3 knots within 500 m of

          the bottom extremly challenging for much of the cruise.



               The first, and westernmost area focused on where

          the depositional lobe breached the levee of the main

          channel.  This survey covered approximately 925 km2 and

          covered the transition from the main channel to the

          beginning of the distributary channel that extends off

          to the east.  The distributary channel could only be

          traced to within about 5 km of the main channel, and a

          mottled area separates the two channels.  Mass wasting

          seemed to be common on the flanks of the levees of the

          main channel, and we think that the complicated transition

          from the main channel to the distributary channel was due

          to this area being masked by mass wasting deposits. The

          distributary channel was followed eastward to the second

          survey area which was at the distal end of this channel

          system and covered an area of approximately 2200 km2.

          The distributary channel did not bifurcate until within a

          few 10s of kilometers of its end.  Several bifurcations

          were observed, and at the end of each were areas of high

          acoustic backscatter that had abrupt edges with the

          surrounding acoustically low backscatter sea floor.

          The area that was surveyed north of the distal part of

          the distributary channel shows that this channel shifted

          laterally during its development.  Other channel segments

          with high backscatter areas at their distal ends were

          observed that are now isolated from the most recently

          active channel.



               During the second leg of the cruise 67 cores were

          collected; 20 in the western area, 9 along the base of

          the Florida Escarpment, and 38 in the area of the eastern

          SeaMARC survey.  A listing of core locations, lengths,

          and intended uses is given in  Table II.  Cores were

          split, described, and sampled at sea except for those

          that were stored for future geotechnical analyses.  Many

          of the cores were not very long (see Table II), and in

          many cases the reason for this was the unexpected sandy

          nature of the bottom sediments.  Some of the short cores,

          particularly at the beginning of the cruise, were the

          result of not having the trip wire or free-fall length

          set correctly.



               Cores from the western study area recovered mostly

          muddy sediments (although there were occasional silt beds

          interspersed in the mud) from the channel floors and

          levees of both the main  and distributary channels.

          The cores visually were homogeneous for the most part

          although some evidence of mass wasting was seen and a

          few turbidite beds were present. 



               In the western area, the high backscatter areas at

          the ends of the distributary channels and the channel

          floors had layers of poorly sorted fine sand in them

          while the low backacatter regions consistently recovered

          muds with organic-rich bands in them.  In general, the

          stratigraphy in the cores from the high-backscatter

          areas revealed a basal unit comprising a single layer

          or several sand layers that were several 10s of cm to

          at least 1 m in thickness.  In a few instances, though,

          the cores penetrated through the sand unit and recovered

          mud similar to that found in the surrounding low-backscatter

          areas.  Overlying the sand layers often was a mud unit

          with different colored mud clasts in it, and at the top

          of all cores was a muddy to foram sand rich layer that

          was about 30 cm thick.  The origin of these deposits

          is unclear.  Some of the sand units were graded and

          appeared to be turbidites, but others were massive

          suggesting perhaps a different mechanism of deposition.

          The presence of clasts in some of the muddy units

          suggests that they may be of debris flow origin.



               The nine cores collected along the base of the

          Florida Escarpment were collected to look at the

          interplay of carbonate sediments shed off the Florida

          Platform and the Mississippi Fan sediments, and also to

          look at the pore water chemistry of these sediments.

          Carbonate debris flows were cored that were interbedded

          with fan muds.  Water samples were taken for chemical

          analyses to be completed back at the University of

          North Carolina.



PAGE-SIZE TRACK CHART:  Overview of survey area

                        Figure 1B

                        Figure 1C