National Facility Research Vessel

Voyage Plans and Summaries

Franklin Voyage Summary No. FR03/2001

Title

Geoscience studies on the Southeast Australian continental slope and shelf: rift and drift sedimentation, and palaeo-oceanography.

Itinerary

Depart Hobart 1000, Wednesday 21 March 2001 for seismic survey

Visit Port Arthur, Tuesday 27 March for several hours to change scientific contingent, offload seismic cable, and test coring system

Visit Hobart, Tuesday 28 March for five hours during bad weather to unload compressor and seismic winch, before starting sampling program

Transfer new core catchers to vessel off Devonport at 0800 on Wednesday 4 April

Arrive Hobart 0945, Tuesday 10 April 2001.

Principal Investigators

Dr Neville Exon (Chief Scientist)
Senior Principal Research Scientist
AGSO
PO Box 378
Canberra 2601
Tel: 02-6249 9347 (wk); 02-6288 2034 (home). Fax: 02-6249 9920
Neville.Exon@agso.gov.au

Mr Peter Hill, AGSO

Professor Jock Keene, Division of Geology and Geophysics, University of Sydney

Dr Stephen Gallagher, School of Earth Science, University of Melbourne*

Dr William Howard, Antarctic Cooperative Research Centre, Hobart*

* not aboard ship

Scientific objectives

The aim of the study is to increase our knowledge of what happened to the region geologically over the last 100 million years, with especial emphasis on sedimentation and oceanographic changes during 1) Cretaceous rifting, and 2) Gondwanan drifting apart in the Cretaceous and Cainozoic. The four major activities are designed to fill important gaps in the geoscience knowledge of southeastern Australia by:

a) helping to characterise the pre-breakup Late Jurassic and Cretaceous strata (160-65 million years ago) off eastern Tasmania (Exon and Hill);

b) documenting the sedimentary history of Late Cretaceous and Early Tertiary continental breakup (95-45 m.y. ago) in deep water off eastern Tasmania and in the Otway Basin (Exon and Hill);

c) elucidating the changes through time in carbonate deposition in the eastern Otway Basin from Oligocene times to the present day (Gallagher, Leach); and

d) studying Late Quaternary palaeo-environments off eastern Tasmania and in the Bass Basin (last 500,000 years) (Keene, Howard, Harris).

Cruise objectives

The methods to be employed on what we designated as not only FR3/2001 but also AGSO Cruise 226 were seismic profiling and sea bed sampling. Coring and dredging was to be done from the trawl winch, and grab sampling from the hydrowinch. The seabed of much of the area had been mapped in detail by AGSO, largely using multibeam sonar surveying, which would allow precise definition of sampling targets. We planned to take long piston and gravity cores of soft sediments, and some short gravity cores of harder outcrops. We also intended to dredge older outcrops and grab sample surface sediments as appropriate.

Some 1320 kilometres of airgun seismic profiling were planned. We aimed to take about 45 grabs, 35 gravity and piston cores, and 15 dredge hauls during the program. The cruise time of 20 days was to include 2 purely transit days.

Cruise Track

Figure 1. Overview map showing seismic profiles (solid lines) and geological sampling program (dotted lines) off eastern Tasmania, in Bass Strait, and on the Otway margin. Only successful stations shown. Open diamonds = grabs, solid diamonds = grabs and cores, solid circles = cores, triangles = dredges

Results

The cruise was split into five parts

21-27 March, seismic survey off east Tasmania
27 March to 3 April, coring, dredging and grabs off east Tasmania
3-4 April, 8 April, grabs and coring in Bass Strait
4-7 April, coring, dredging and grabs in Otway Basin off Portland
8-10 April, transit to Hobart and core off southeast Tasmania

Seismic leg

The seismic survey off eastern Tasmania recorded 1300 km (715 nm) of seismic reflection profiling at 6 knots, and took approximately 6.5 days including transits (Figure 2, Table 1). The AGSO system used two GI airguns, a compressor requiring 1000 litres of diesel per day, and a seismic cable 600 m long with 24 channels, which were recorded digitally. The seismic profiling started 80 km southeast of Hobart and ended off St Helens. On part of the transit back to Port Arthur at 10 knots, a depressor was added to the airguns, as a test for running the seismic system at high speed on future research cruise FR9/01. This showed promise but more work is needed.

Line 1 was 180 km long, from 80 km southeast of Hobart ESE to about 50 km southwest of Cascade Seamount on the East Tasman Plateau. There are a few hundred metres of Cainozoic section visible above Cretaceous sediments on the east Tasmanian shelf, whereas Cretaceous sediments and basement have been planated and tilted and are very near the surface in the continental slope. In the 3200 m deep East Tasman Saddle to the east, about half a second of Cainozoic sediments overlies about 1 second of Cretaceous sediments above basement. A volcanic edifice halfway along the line is about 300 m high. A basement block forms the western scarp of the East Tasman Plateau, which is about 300 m high. East of this block are complex half-grabens, 1.5 seconds deep and containing Cainozoic and Cretaceous sediments.

Line 2 was shot to the north from southwest of Cascade Seamount. It crossed a volcanic rise and then ODP Site 1172 at 1355, about 40 km west of Cascade Seamount,. Volcanic intrusions are common in the sedimentary sequence, and strong diffractions appeared almost at the surface at about 2200, in a water depth of 3400 m. The 230 km long line then deepened steadily onto the abyssal plain with a thickening wedge of sediment. The line terminated in water 4400 m deep, 170 km east of Freycinet Peninsula.

Line 3 was shot to the southwest, over the East Tasman Saddle between the Tasman Basin and the L’Atalante Depression. At the start the water depth was 4350 m and basement lay about 2 seconds deep. The water shallowed slowly toward the saddle and strong diffractors occurred in the section or formed outcrops. At the culmination of the saddle at about 43°S the water depth was 3150 m and strong diffractions were only 0.2-0.3 seconds below the surface. Going down toward the L’Atalante Depression the diffractions disappeared and over 1 second of section was visible. At the end of the line the water depth was 3600 m. The 225 km long line ended about 100 km east-southeast of Port Arthur.

Line 4, 94 km long, was shot to the west-northwest toward the Tasman Peninsula, starting about 100 km offshore. At the beginning of the profile the water is 3500 m deep, and there is up to 2 seconds of flat-lying sediment above intermittent basement. The foot of the slope is halfway along the line at a water depth of 3200 m, and an irregular but generally thick sedimentary pile covers much of the slope. At the foot of the upper slope basement appears to outcrop. The shelf break is at 150 m, about 20 km from the end of the line and the shelf sediments dip and prograde gently seaward. The line was completed about 10 km east of Tasman Peninsula.

Line 5, 137 km long, was shot to the east-northeast from 10 km east of Tasman Peninsula on the shelf in water 100 m deep. The shelf break is at 150 m, about 25 km from the end of the line, and the shelf sediments dip and prograde gently seaward. A prominent irregular unconformable surface may be karstified Miocene limestone, and this surface outcrops on the upper slope. The shelf break is underlain by a normal fault. The slope is variably sedimented and eroded by downslope movement, in part by canyons. Along much of its extent there is less than 1 second of sedimentary cover, and much of the Cainozoic is absent. The middle part of the profile runs along a bulge in the lower slope and there is about 1 second of section with continuous Cainozoic cover. Further east the surface is irregular as it crosses the northern end of the East Tasman Saddle before descending toward the Tasman Basin, and there is a major basement high and outcrop 35 km from the end. The profile stopped in water 3500 m deep with about 1 second of sediment.

Line 6, 137 km long, was shot to the west-northwest toward the southern end of Freycinet Peninsula. The profile started in water 3500 m deep with about 1 second of sediment. It is initially irregular before a pocket of flat-lying sediments more than 1 second thick onlaps basement; basement comes to outcrop at 3000 m. The slope is variably sedimented and eroded by downslope movement, and there is little Cainozoic cover. The shelf break at 120 m was 15 km southeast of Schouten Island. The shelf sediments dip gently and thicken seaward. A prominent irregular unconformity which deepens seaward from 0.1 seconds below sea bed at the inner end of the line in Great Oyster Bay, may be karstified Miocene limestone.

Line 7, 145 km long, was shot to the east-northeast from 10 km south of Schouten Island in water 80 m deep. The shelf break at 120 m was 20 km east of Schouten Island. The shelf sediments dip gently and thicken seaward. A prominent irregular unconformity, which deepens seaward from 0.1 seconds below sea bed at the inner end of the line in Great Oyster Bay, may be karstified Miocene limestone. The slope consists of three areas of basement outcrop, separated by two sedimentary basins. The upper basin is up to 1 second thick and is dominantly Cainozoic; the lower basin is somewhat thicker and is dominantly Cretaceous. Another basin, 1.5 seconds thick, underlies the abyssal plain.

Line 8, 145 km long, was shot to the west-northwest toward St Helens. Profiling started at 1155 on 26 March in water 4200 m deep. There is 1.5 seconds of sediment, Cretaceous and Cainozoic, above oceanic crust on the abyssal plain. The lower and upper slope are fairly well sedimented with more than a second of dominantly Cretaceous sediment. The mid-slope is steeper with less sediment and some slumping; it is probably overlain by shallow basement. The shelf break at 150 m was 30 km southeast of St Helens. The shelf sediments dip gently and thicken seaward.

East Tasmanian sampling

Fifteen dredge stations and 19 gravity core stations were occupied in water depths ranging from 500 to 4000 m (Figure 2, Table 2). Only seven dredge stations and eight core stations were fully successful, despite many of the targets clearly being suitable. In general the stations on the upper continental shelf were more successful than those on the lower slope and abyssal plain. The reasons for the failures varied from station to station. The dredging was clearly affected by the lightness of the gear when hard or ooze-covered outcrops were targeted. The Quaternary palaeo-oceanographic coring was probably affected adversely by a surface layer of foram sand, the result of winnowing by strong currents along the Tasmanian margin. Gravity cores have been shown not to penetrate such foram sand. Also some of the core catchers proved to have substandard spring steel and did not close fully, thus allowing any sediments penetrated to escape. Finally the flapper valve at the top of the core barrel, which stops water flushing the core out while it is pulled back up to the surface, jammed open on several occasions. This was apparently because the valve was hit by the swivel linking it to the cable.

The stations designed to sample older rocks at the sea bed were reasonably successful along the upper slope. Off Tasman Peninsula in water depths of 1180 to 1640 m, GC12 recovered Cainozoic calcarenite, DR11 recovered granite, and GC13 recovered siliceous sandstone. Further north, southeast of Freycinet Peninsula, DR4 recovered granite, arkose and pebbly mudstone in a water depths of about 2000 m. East of Freycinet Peninsula, DR2 recovered clayey sandstone and silicified sandstone nodules from water 700-800 m deep. GC2, designed to penetrate older sediments recovered muddy sand, probably of Paleogene age, from a depth of 1215 m. GC15 recovered calcareous muddy clay, also probably of Paleogene age, from a depth of 3960 m.

In the north, east of Banks Strait, DR15 recovered basalt, granite, metasediments (rounded and probably from a conglomerate), friable quartz-rich sandstone, and Cainozoic bryozoal sandstone, from water depths of 1200-1800 m. Further offshore, an east-west ridge yielded (DR13) a few chips of probable hyaloclastite, conglomerate pebbles, and Cainozoic chalk and claystone, in water depths of 2900-3100 m. On the lowermost slope DR14 yielded a little siltstone and micritic limestone from water depths of 3500-3900 m. In summary, these results show that the continental slope consists of rocks known onshore. Before much more can be said about the results the rocks need to be dated, and their distribution needs to be evaluated against information from the swath-maps and the seismic profiles along which they were taken.

Much time was spent trying to obtain Quaternary palaeo-oceanographic cores to study the history of the East Tasmanian Current. Only GC9 on the northwest East Tasman Plateau (2888 m water depth), and GC14 (2792 m) east of the Freycinet Peninsula, appear to have succeeded.

Bass Strait sampling

The program in summarised in Figure 3 and Table 3. A grab sampling program off the eastern part of the northern Tasmanian coast began with GR02 east of Banks Strait and ended with GR07. This program was designed to resample some 1970s BMR stations, to see whether the sedimentological analyses from their pipe dredges were comparable to those from grabs. If so, the very extensive BMR pipe dredge data set can be easily amalgamated with other data sets. Four gravity cores (GC19-22) were taken on the southeastern edge of the glacial Bass Lake off Devonport. These all recovered less than 1 m of muddy shelly sand. Our first piston core (PC01) was taken with a 6 m barrel on the southern side of the lake, well north of Devonport, and recovered 4.48 m of olive grey shelly marine mud. GC23 repeated the site and recovered 5.50 m. GC24 was taken further north in worsening weather. PC02 was assembled as a 10 m piston core and deployed over the stern, but the ship could not hold station with the wind gusting to 40 knots and the station was abandoned. Later on the cruise we deployed a 10 metre corer (PC04) nearby in Bass Lake and 8.11 metres of shelly mud was recovered. The Bass Strait program met all expectations except that a new current meter was not delivered to AGSO in Hobart in time for testing during the cruise.

Otway Margin sampling

The program in summarised in Figure 4 and Tables 4 & 5. Grabs GR8-27 were taken off Port Campbell and Portland in shallow to upper slope depths (940-1200 m). These were successful in documenting the changes from nearshore quartz sand, to coarse calcareous sand, to mid-shelf hard grounds, to upper slope oozes, and to fine grained canyon mud. Two grabs came up almost empty and appear to have been on hard grounds assumed to consist of Miocene limestone. Modern living forams from the sea bed sediments were preserved in acetone and will be studied, in conjunction with forams found in underlying sediments, to determine the age of the sea floor and changes in the depositional environment through time.

Cores PC03 and GC26 came from two canyons that cut approximately 800 m into the surrounding sea bed, in water depths of 1200-1400 m. The rate of sedimentation, age of the canyon fill, and whether the canyons are cutting or being filled at present will be determined from the cores and other evidence. The cores appeared to be similar to grabs taken in the two canyons, which contained mud blocks indicating slumping or debris flows, which are an important feature of canyon formation. The magnetic susceptibilty of GC26 shows absolutely no variation from top to bottom, supporting the suggestion that it is a homogenised slump. GC25 and GC27 on the upper slope apparently contain oozes.

A deepwater program of canyon and canyon wall sampling (1800-2400 m) consisted of unsuccessful dredge DR16, and successful cores GC28-31 (Table 5). Core recovery averaged 5 m for all the Otway Basin cores. Most cores were oozes with varied but low siliciclastic content. It is not yet known whether some of these were older than Quaternary, as had been hoped.

Storm Bay Sampling

In a storm at the end of the survey, we took shelter in Storm Bay, and on our way back to Hobart attempted to take gravity cores (GC34-38) along an AGSO seismic line (Figure 2). The sediment turned out to be sandy, and hence unsuitable for gravity coring, but we did recover small amounts of sand, often shelly, at four of the stations (Table 6).

Cruise Narrative

The Franklin left Hobart at 1000 local time on 21 March for the one-week seismic profiling leg off eastern Tasmania. The threat of industrial action from the Engineers’ Guild had been averted that morning, but we had loaded both seismic and sampling gear in the belief that a port call after the seismic leg might precipitate such action. The relatively small rear deck, with sedimentological and compressor containers, plus a large seismic winch and cool trailer, was very cluttered. It would become more so when the core cradle was deployed.

Deployment of the seismic system, based on two GI airguns with total capacity of 300 cubic inches, and a hired 24-channel Stealtharray seismic cable with a tow leader of 80 m and 600 m of active sections, started at 1300 and was completed at 1700 when Line 1 commenced. A Geometrics StrataView system recorded the data. The shot interval was set at 37.5 metres and data acquisition was to be at 6 knots. The solid seismic cable proved to have two faulty channels, 4 and 14, and the first 300 m section had been wired the wrong way around, so that the channel designated 12 was actually 1 and so on. The latter problem could be overcome in the seismic processing, which Peter Hill undertook aboard on a Sun work station using the Disco/Focus system.

Line 1 was shot as planned, 180 km long in all, from 80 km southeast of Hobart east-southeastward to about 50 km southwest of Cascade Seamount on the East Tasman Plateau. It was completed at 1000 on 22 March. Strong winds from the east were combined with an easterly swell of about 2 metres, and some light rain. The digital data were processed satisfactorily.

Line 2 was shot to the north from southwest of Cascade Seamount, starting at 1100 on 22 March. Moderate easterly winds were accompanied by a 1 m swell from the east. It crossed a volcanic rise and then ODP Site 1172 at 1355, about 40 km west of Cascade Seamount. By the evening the showers had cleared, and the wind had swung around to the east-northeast with 1 m waves from the same quarter, and a 2 m swell from the southeast. After 2200, in a water depth of 3400 m, the 230 km long line deepened steadily onto the abyssal plain with a thickening wedge of sediment. The line terminated in water 4400 m deep at 0745 on 23 March, 170 km east of Freycinet Peninsula.

When an attempt was made to read and process the digital data (1700 on 23 March) it was discovered that neither tape drive had been recording normally, despite the system having indicated that all was well. On future geophysical cruises it is recommended that a PC also be connected to the system, recording the data on a hard disk so that their accumulation can be checked simply.

Line 3, 225 km long, was shot to the southwest, over the East Tasman Saddle between the Tasman Basin and the L’Atalante Depression, starting at 0840 on 23 March in sunny conditions with a low breeze and a 2 m swell from the northeast. Once it was realised that Line 2 had not been recorded normally it was decided to stop recording, turn, and check the tapes for Line 3. This was done at 1800, about 110 km down the line, and again data had not been recorded normally. The ship proceeded slowly back along the line to the northeast, while trouble shooting commenced. At 2100 it was found that the problem was in the tape drives and one was replaced. Profiling recommenced at 2130, a little north of where it had been terminated, about 110 km east of Maria Island. The line ended about 100 km east-southeast of Port Arthur at 0830 on 24 March and a relatively long transit northward to Line 4 commenced. There are problems with the data recorded along the latter part of the line.

Line 4, 94 km long, was shot to the west-northwest toward the Tasman Peninsula, starting about 100 km offshore at 1100 on 24 March in sunny conditions with a moderate wind from the east and a 2 m swell from the west-southwest. The line was completed about 10 km east of Tasman Peninsula at 1915, and was processed without difficulty.

Line 5, 137 km long, was shot to the east-northeast from 10 km east of Tasman Peninsula on the shelf in water 100 m deep, starting at 1940 on 24 March in calm conditions with gentle easterly breezes. The profile stopped at 0630 on 25 March and the line was processed uneventfully.

Line 6, 137 km long, was shot to the west-northwest toward the southern end of Freycinet Peninsula. It started at 0730 on 25 March, but was aborted after about 150 shots because of problems with one airgun and the compressor. It started again at 1000 with a strong wind and 1 m waves from the northwest. During the day the wind and waves rose and then fell. The line ended at 2140 on 25 March, and was processed satisfactorily.

Line 7, planned to be 155 km long, was shot to the east-northeast from 10 km south of Schouten Island. When it started at 2210 on 25 March a gentle northwest wind prevailed, with associated low waves. At 0810 on 26 March, when the wind was a light gale from the northwest and waves were 2 m high, there were compressor problems and a gun started to leak. The profile was resumed at 0830, firing a single gun only. At 1054 the line was terminated 145 km from the starting point, 10 km before the planned end of line, in water 4200 m deep, and damaged seals on both guns were replaced. The vessel continued to the end of the line without a seismic profile. Despite the problems, the line processed well.

Line 8, 145 km long, was shot to the west-northwest toward St Helens in initially rapidly improving weather conditons, with wind and waves from the northwest. Profiling started at 1155 on 26 March in water 4200 m deep. By 1700, a light gale from the northwest was accompanied by 3 m waves. At 1930 the synchronisation of the two guns became a problem, and it was decided to turn one off rather than to repair the faulty gun in the bad weather conditions with departure for Port Arthur due in five hours. The profile ended off St Helens at 0030 on 27 March, the cable and guns were pulled in, and the vessel was underway for Port Arthur by 0130. The line processed well.

Between 1030 and 1130 on 27 March we tested the new gun depressor system in the lee of the east coast at 10 knots. Deploying the system from the winch wire through the top of the A-frame was not optimal, and the system yawed wildly on occasions. It was decided to try to tow it much lower on the next cruise, to put new tow points further forward, and to increase the size and length of the tail.

At 1400 on 27 March we entered Port Arthur, as decided earlier, to change scientific personnel and to unload the seismic cable for return to the United Kingdom. We then constructed the new core cradle and practised deploying cores out of the weather in the harbour. One core recovered a little sand and was labelled 226/GC01. We left Port Arthur at 2230 for a grab station on the nearby continental shelf. It was blowing a full gale with occasional gusts to 50 knots, so the Master decided against working until the weather improved and to shelter overnight. In the belief that conditions would not improve until late the next day, we took the opportunity to go to Hobart and get rid of the 20 foot compressor container, gun bundles and seismic winch, thus clearing the rear deck and making working conditions there safer and more efficient. This was now possible as the industrial threat, of keeping us in harbour if we tied up again, had been averted since we sailed.

At 1000 on 28 March we tied up in Hobart and the seismic gear was craned off onto a truck. The ship sailed again at 1500, but as we rounded Tasman Peninsula there were 30-35 knot winds from the SSW, associated with a 4 metre swell and 2 metre waves. It was decided to head for sampling sites to the north off Freycinet Peninsula, where there would be some protection from the weather.

At 0230 on 29 March grab GR01 was taken on the outer shelf. At 0240 dredge DR01 was lowered away. At 0250 the winch stopped dead with the dredge in 400 m of water. It took until 1700 to fix the winch, in calm conditions, while the cable and dredge were hauled in on the capstan. The problem proved to be sheared pins between the power pack and the winch drum. Dredge DR02 and gravity core GC02 succeeded, but gravity cores GC3-5 (at the one station) failed, probably because of a blanket of foram sand. On 30 March dredge DR03 recovered only sand, whereas dredge DR04 recovered rocks. Dredges DR05 and DR06 (at the same station) recovered only calcareous ooze from the small pipe dredges, at the first for no apparent reason and at the second because the weak link broke. Cores GC06 and GC07 (at the same station) in 3030 m of water failed, probably because of a blanket of foram sand, as did GC08 in 3250 m of water.

At 0330 on 31 March dredge DR07 started. It was aborted because of a failure in the control of the bow thruster at 0420, and work continued on the equipment until 1000, when it was decided to proceed to core station GC09 on the northwest flank of the East Tasman Plateau. This core, in water 2888 m deep, recovered 4.8 m of olive grey ooze at 1300. By then the thruster problem had been overcome, and we returned to the site of DR07. We dredged from both sides of the ridge: DR08 failed, but DR09 recovered manganese nodules and crusts.

Early on 1 April, we headed southeast to another deepwater ridge east of Tasman Peninsula but DR 10 failed, perhaps because the ridge was poorly mapped. Two nearby deepwater cores (GC10 & 11) also failed, leading to a discussion of the poor quality of the refurbished but not re-fingered core catchers. The winch could no longer be driven at full speed but we successfully dredged granite in DR11 in a full gale on the upper slope off Tasman Peninsula. Core GC12 recovered some calcarenite from the upper slope nearby, and GC13 recovered hard sandstone from the upper slope further north. The winch was running at full speed again at the second of these stations.

After a long transit to the north, GC14 recovered 2.75 m of ooze on the lower slope off Freycinet Peninsula early on 2 April. DR12 from the large triangular deepwater block further offshore came aboard at 1130 but contained no rocks. Before GC15 on the lowermost continental slope was attempted, power was transferred from the stern to the bow thruster to allow it to run at full power. Strong winds and 2.5 m sea/swell from the southwest did not affect the coring, with 3.88 m recovered. A long run northwest to the area east of Banks Strait ended with deepwater dredge DR13 which recovered some volcanic chips from an east-west ridge.

Deepwater core GC16, early on 3 April, failed, and deepwater dredge DR14 did not recover many rock fragments. DR15, on the upper slope east of Banks Strait, was full of a mixed rock assemblage. Two shallow water cores (GC17 & 18) recovered a little foram ooze and sand, and completed the initial east Tasmanian program at 1500.

A grab sampling program off the eastern part of the northern Tasmanian coast began east of Banks Strait with GR02 at 1600 on 3 April, and ended west of the strait with GR07 at midnight.

Four gravity cores (GC19-22) were taken in low seas on the edges of the glacial Bass Lake off Devonport early on 4 April before the ship’s boat collected a new batch of core catchers there at 0800. These all recovered less than 1 m of muddy sand. Our first piston core was taken on the southern side of the lake, well north of Devonport, at 1230. PC01 was taken with a 6 m barrel and recovered 4.48 m of olive grey shelly marine mud. GC23 repeated the site and recovered 5.50 m. GC24 was taken further north in worsening weather. PC02 was assembled as a 10 m core and deployed over the stern, but the ship could not hold station with the wind gusting to 40 knots and the station was abandoned and the corer brought back aboard. At 1930 we set out on a long transit into the weather to the Otway Basin.

At 1430 on 5 March we took the first (GR08) of a series of grabs off Port Campbell from shallow to deep water. By midnight we were recovering GR17. On 6 March we continued with grab stations south and west of Port Campbell, completing GR25 in a canyon south of Portland. With calm seas persisting, we switched to coring at 1200, and recovered PC03 from the canyon successfully. GC25 on the upper slope further west was also successful, but when we came to GC26 in a more westerly canyon, the wire jumped the block at 1730. At 1910 the situation had been remedied and the core was taken. The last two Otway grabs, GR26 and GR27, were taken late on 6 March.

On 7 March we sampled in an easterly direction in good conditions, starting with GC27 on the upper slope southwest of Portland. A deepwater program of canyon and canyon wall sampling consisted of unsuccessful dredge DR16, and successful cores GC28-31. Core recovery averaged 5 m for all the Otway Basin cores. However, those in the deepwater sites do not appear to have reached the hoped-for pre-Quaternary targets. Core GC 31, 90 km west of King Island, was completed at 2030 on 7 March in worsening conditions. Because of predictions of westerly gales, we then decided to circumnavigate Tasmania in a clockwise direction, rather than going down the west coast as planned, and headed toward Bass Strait.

On 8 March at 1115 we deployed a 10 metre piston corer in Bass Lake north of Devonport in good conditions. Half an hour later we were under way for Banks Strait with an 8.11 metre core of shelly mud aboard, the longest core ever taken from Franklin. The difficulties encountered in getting a 10 metre corer aboard with equipment designed for a shorter core can be overcome in future by some modifications. By 1500, the wind had risen to peak at 40 knots from the west. We headed for Banks Strait and then down the east coast of Tasmania.

At 1145 on 9 March we deployed GC32 on the upper slope southeast of Hobart, just as a front came through with gusts to 25 knots. The coring was successful in recovering older sediment and then we went to GC33 further southeast. Another front came through while the corer was in the water, bringing gusts to 55 knots and 5 m swells. At 1700 we decided to head west for shelter in the appropriately named Storm Bay, where some useful cores could be taken. The westerly storm kept our speed down. We attempted gravity cores from 2200 (GC34-38) in water depths of 35-70 m, along an AGSO seismic line en route to Hobart. The sediment turned out to be sandy, and hence unsuitable for gravity coring, but we did recover small amounts of sand, often shelly, at four of the five stations.

At 0945 on 10 April the ship berthed in Hobart on a calm sunny day.

Summary

Overall, the cruise met its objectives of studying rift and drift sedimentation, and palaeo-oceanography on the Southeast Australian continental slope and shelf. The east Tasmanian seismic program was completely successful and matched the cruise plan. The sampling program was somewhat curtailed by bad weather, winch and thruster failures, and other factors, but accomplished much of the cruise plan. It was least successful off east Tasmania. AGSO personnel learnt a great deal about carrying out a complex geophysical and geological cruise on the Franklin, which will stand us in good stead for the future.

Despite some problems with seismic equipment that had not been used for three years, the quality of the seismic profiles was excellent, and the planned program was generally successful, albeit with some additional time needed to cover equipment down time caused partly by rough sea conditions. The tracks are shown in Figures 1 & 2, and the results are tabulated in Table 1. The seismic survey time was increased by half a day to 5.5 days to allow completion of the program. Parts of two profiles were shot with one airgun when the other failed, rather than to stop and repair the faulty gun. One profile and half of another were recorded faultily. Fortunately these were not key lines, but in any case the data were recovered immediately post-cruise. All the data were successfully stacked and migrated, mostly aboard ship and some post-cruise. The resultant profiles are of excellent quality and penetration, given the bad weather and the limitations of the acquisition system.

Potential industrial action indicated that it might be too risky to tie up in Hobart mid-cruise, so on the geophysical leg the rear deck of the vessel was very cluttered with geophysical and geological gear. With the risk of industrial action lifted and heavy weather offshore, we in fact returned to Hobart to remove the heavy geophysical equipment, removing the clutter.

The sampling program was quite successful overall (Tables 2-6; Figures 2-4). In all, 86 stations were occupied: 38 gravity cores (21 successful), 4 piston cores (3), 16 dredges (7) and 28 grabs (28). Total core recovery was 81.4 metres from the 16 successful cores taken in soft sediments, an average recovery of about 5 metres. The fairly low success rate with the gravity core can be ascribed to problems with foram sand east of Tasmania, and shelly sand in Storm Bay. The low success rate with the dredge was related to the lightness of the gear. Looking to the future, the deployment of the heavy piston corer for the first time on Franklin was successful. However, oscillations of more than one tonne of the strain on the corer wire in water depths of more than 1800 m suggest that the piston corer might trigger prematurely in deeper water, severing the wire. Hence we did not attempt to piston core in deep water.

All samples were labelled with the prefix 226 for AGSO cruise 226, rather than FR3/01, as they are to be stored in Canberra under the AGSO system. Dredge and grab samples were examined with a hand lens aboard ship and described in some detail, sampled and packed aboard ship. Sub-samples were set aside for palaeontology and thin sectioning. The cores in their liners were cut to 1 m lengths, and they were stored undisturbed in a small hired cool facility on deck. Although no cores were split for description aboard ship, brief descriptions were made of the core catcher material, and a few cores were logged for magnetic susceptibility through the plastic liners.

The AGSO program east of Tasmania attempted 19 gravity cores with 8 successful, and 15 dredges with 7 successful. Deepwater dredging and coring proved to be surprisingly unsuccessful. The poor dredging results were probably due to the lightness of the gear. The poor deepwater gravity coring results east of Tasmania probably could be blamed largely on current-swept foram sands unsuitable for gravity coring, and to some extent on poor-quality AGSO core catchers. The stations designed to sample older rocks at the sea bed were reasonably successful along the upper slope. Among the rocks recovered were granite, arkose, fine grained metamorphic rocks, siliceous and clayey sandstone, pebbly mudstone, basalt and calcarenite. Two deepwater cores recovered sediments of probable Paleogene age: muddy sand and calcareous muddy clay.

The Sydney University and AGSO programs in Bass Strait went well, with four successful grab stations, four short cores east of Devonport, and four longer cores in the region of the ancient Bass Lake north of Devonport. The longest, an 8 metre long piston core, was the longest ever taken in Bass Lake and from Franklin. New core catchers were collected in Devonport and worked well for the rest of the cruise.

The Melbourne University program in the Otway Basin also went well, with 27 grabs of surface sediments, two Quaternary cores on the upper slope, and two Quaternary cores in the base of two canyons on the upper slope, followed by a deep water AGSO sampling program. This latter program of canyon and canyon wall sampling consisted of an unsuccessful dredge and four cores. All cores were technically successful and recovery averaged 5 m.

An opportunistic attempt to take gravity cores in Storm Bay on the way back to Hobart was unsuccessful, because the sediments were too sandy.

Franklin was sometimes at the limit of its capabilities on the geological leg. Considerable time was lost unavoidably to bad weather, but breakdowns of the deep sea winch and associated gear, and various problems with the thrusters, are a cause for concern. The engineering group led by Gordon Gore worked long and hard to overcome recurring problems, which cost a day’s ship time altogether. Because a winch solenoid failed and there was no replacement on the ship, for much of the cruise switching from one winch to another meant moving the solenoid. Clearly, the aging equipment on Franklin needs a major refurbishment if the ship is to continue as a National Facility.

Scientific Personnel Llist

Geophysical leg (first 6 days)

Neville Exon, AGSO, Chief Scientist, Geology
Peter Hill, AGSO, Geophysics
Steve Thomas?, AGSO, Electronics technician
Ken Elphick, AGSO, Mechanical technician
Craig Wintle, AGSO, Mechanical technician
Jon Stratton, AGSO, Geological technician
Lyndon O’Grady, AGSO, Geological technician
Rick Smith, AGSO, GIS expert
Ron Plaschke, CMR, Cruise Manager
Bernadette Heaney, CMR, Computing
Lindsay MacDonald, CMR, Electronics

Geological leg (last 14 days)

Neville Exon, AGSO, Chief Scientist, Geology
Jock Keene, Sydney University, Sedimentologist
Peter Hill, AGSO, Geophysics
Peter Harris, AGSO, Sedimentologist
Andrew Heap, AGSO, Sedimentologist
Andrea Leach , Melbourne University, Foraminiferal micropalaeontologist
Jon Stratton, AGSO, Geological technician
Lyndon O’Grady, AGSO, Geological technician
Dave Mitchell, Sydney University, Geological technician
Ron Plaschke, CMR, Cruise Manager
Bernadette Heaney, CMR, Computing
Lindsay MacDonald, CMR, Electronics

Crew members

Ian Taylor, Master
Arthur Staron, Chief Officer
John Boyes, Second Officer
Gordon Gore, Chief Engineer
Simon Gould, First Engineer
Hugh McCormick, Second Engineer
Terry Ganim, Bosun
Tony Hearne, AB
Norman Irvine, AB
Malcolm McDougall, AB
Phil French, Greaser
Aung Zin, Chief Cook
Denis Taylor, Second Cook
David Willcox, Chief Steward

We are very grateful to the Master, Ian Taylor, and his maritime crew for their wholehearted support and professional seamanship throughout the cruise, and to the engineering group led by Gordon Gore for fixing various equipment breakdowns. The deck crew led by bosun Terry Ganim were helpful under sometimes difficult conditions. We thank the CMR staff of Ron Plaschke, Bernadette Heaney and Lindsay MacDonald for ensuring that all the necessary scientific support was provided. The excellent food kept spirits high. The AGSO technical group did an excellent job, and was led well by Steve Thomas on the first leg and Jon Stratton on the second. Sydney University technician David Mitchell did an excellent job on the second leg in teaching us how to deploy the piston corer.

Figures

Figure 2. Detailed map showing seismic profiles (solid lines) and geological sampling program off eastern Tasmania. Only successful stations shown. Open diamonds = grabs, solid circles = cores, triangles = dredges

Figure 3. Detailed map showing geological sampling program in Bass Strait. Open diamonds = grabs, solid circles = cores, triangles = dredges

Figure 4. Detailed map showing geological sampling program on the Otway margin. Open diamonds = grabs, solid diamonds = grabs and cores, solid circles = cores, triangles = dredges

Tables

Table 1. Seismic lines off east Tasmania

Line	Start	End	Length km/nm	Bearing (nearest deg.)
FR3/01-1	43° 27.468’ 147° 50.00’	44° 12.993’ 149° 52.598’	185/100	117°
FR3/01-2	44° 12.658’ 149° 50.730’	42° 05.260’ 150° 33.409’	243.0/131.1	014°
FR3/01-3	42° 05.260’ 150° 33.409’	43° 38.034’ 148° 45.956’	225.7/121.8	221°
FR3/01-4	43° 29.867’ 148° 59.729’	43° 01.786’ 148° 03.038’	94/51	304°
FR3/01-5	43° 01.992’ 148° 03.309’	42° 49.604’ 149° 42.704’	137/74	081°
FR3/01-6	42° 49.657’ 149° 42.332’	42° 24.427’ 148° 12.028’	137/74	291°
FR3/01-7	42° 26.109’ 148° 13.526’	41° 56.744’ 149° 51.325’	155.4/83.8	068°
FR3/01-8	41° 54.444’ 149° 57.518’	41° 22.819’ 148° 22.539’	145.2/78.4	294°

Total length = 1321 km (713 nm)

Table 2. East Tasmanian Sampling Stations

No	Planned Station	Actual Station	Co-ordinates (single location for cores and grabs, start and end points for dredges)		Water depth (m)	Description
0		GC01	43°10.11’ 147°53.12		34	Sand
1	ET-G3	GR01	42°10’ 148°34.7’		350	Calcareous sand
2	ET22-D	DR01	42º 07.7’ 148º 38.0’		840	Aborted. Winch failure on way down
3	ET22-D	DR02	42° 07.7’ 148° 38.1’	42° 07.4’ 148° 37.7’	800-700	Clayey sst, silicified sst nodules, clayey sand
4	ET21-Cs	GC02	42° 09.78’ 148° 40.36’		1215	346 cm greenish olive muddy sand
5	L7Cl	GC03	42°14.27’	148°52.88’	1844	Catcher broken, no recovery
6	L7Cl	GC04	42°14.27’	148°53.05’	1844	No penetration, no recovery
7	L7Cl	GC05	42°14.26’	148°53.06’	1845	No penetration, no recovery
8	L7DR	DR03	42°18.3’ 148°39.8’	42°18.5’ 148°39.4’	1350-1250	Sand only
9	ET18-D	DR04	42° 29.4’ 148° 52.3’	42° 29.2’ 148° 52.3’	2000-1950	Granite, arkose, gritty mudstone, sand
10	ET17-D	DR05	42° 37.7’ 149° 04.2’	42° 37.8’ 149° 03.5’	2900-2800	Calcareous ooze
11	ET17-D	DR06	42° 37.8’ 149° 04.1’	42° 38.2’ 149° 03.9’	3000-2790	No recovery, 3 tonne shear pin broke
12	ET16-Cl	GC06	42° 40.0’ 149° 13.1’		3071	No recovery, flapper valve open
13	ET16-Cl	GC07	42° 40.1’ 149° 13.2’		3070	Little penetration. Greenish ooze trace
14	ET15-Cs	GC08	42° 46.4’ 149° 20.4’		3250	Little penetration. Greenish ooze trace sample
15	ET14-D	DR07	43° 07.10’ 149° 40.00’	43° 07.65’ 149° 40.58’	2973-2559	Aborted by thruster control failure
16	ET13-Cl	GC09	43° 21.97’ 150° 03.02’		2888	480 cm olive grey nanno ooze
17	ET14-D	DR08	43° 08.10’ 149° 41.32’	43° 07.62’ 149° 40.57’	2750-2640	No recovery. Distorted pin, so on bottom
18	ET-14D	DR09	43° 07.1’ 149° 40.0’	43° 07.3’ 149° 40.24’	3000-2800	Manganese nodules and crusts, ooze
19	ET11-D	DR10	43° 32.0’ 149° 10.9’	43° 32.1’ 149° 11.2’	3400	Foram nanno ooze
20	ET12Cl	GC10	43° 31.94’ 149° 09.10’		3407	No recovery
21	ET12-Cl	GC11	43° 31.93’ 149° 09.08’		3408	No recovery. Trace of ooze
22	L4Dr	DR11	43°08.9’ 148°17.4’	43°08.9’ 148°17.1’	1600-1300	Granite, foram nanno ooze, corals
23	L4Cs	GC12	43°08.64’ 148°16.75’		1180	? Miocene calcarenite, ooze, corals in catcher
24	L5Cs	GC13	42°58.75’ 148°26.92’		1640	Brown siliceous sst and sand in catcher
25	ET23-Cl	GC14	41° 56.36’ 149° 09.90’		2792	275 cm of grey calcareous ooze
26	ET24-D	DR12	41° 51.3’ 149° 27.1’	41° 51.5’ 149° 26.5’	3450-3100	Yellowish grey nanno ooze
27	ET25-Cl	GC15	41° 49.48’ 149° 34.08’		3960	388 cm olive gray calcareous muddy clay
28	ET29-D	DR13	40° 52.9’ 149° 03.5’	40° 55.6’ 149° 03.7’	3100-2900	Small haul. Volcanics, conglomerate pebbles, chalk, clay, ooze
29	ET30-Cl	GC16	40° 48.85’ 149° 25.24’		4038	Ooze trace
30	ET31-D	DR14	40° 42.4’ 149° 13.9’	40° 41.9’ 149° 13.1’	3900-3500	Small haul. Siltstone, micritic limestone, ooze
31	ET28-D	DR15	40° 41.8’ 148° 54.2’	40° 42.2’ 148° 54.2’	1800-1200	Full dredge. Basalt, granite, rounded metasediment cobbles, quartz sandstone, bryozoal sandstone. Corals
32		GC17	40° 50.25’ 148° 49.95’		809	Minor foram ooze in core catcher
33		GC18	40° 50.36’ 148° 46.83’		487	Minor foram sand in core catcher
79	ET1-Cs	GC32	43° 30.98’ 148° 09.67’		65	Foram ooze over weathered sandston
80	ET3-Cl	GC33	43° 37.00’ 148° 16.30’		2150	Aborted by storm

DR = dredge
GC = gravity corer = 15.49 m total
GR = grab

Table 3. Bass Strait sampling stations

No	Station	Lat/Long	Depth	Recovery	Description
34	GR02	40° 49.60’S 148°39.84’E	92 m	Good	Quartz-rich m-c bryozoal sand
35	GR03	40° 39.55’S 148° 07.10’E	38 m	Poor	Hard ground with sponges and shells
36	GR04	40° 45.03’S 147° 49.05’E	33.5 m	Good	Quartz-rich m sand with shells
37	GR05	40° 40.72’S 147° 35.53’E	43.5 m	Good	Gravelly calcareous sand
38	GR06	40° 40.60’S 147° 21.02’E	53.5 m	Good	Medium calcareous sand
39	GR07	40° 40.69’S 147° 08.63’E	66.5 m	Good	Muddy calcareous sand
40	GC19	40° 38.02’S 146° 49.99’E	70.5 m	74 cm	Muddy calcareous sand
41	GC20	40° 38.12’S 146° 49.94’E	70.5 m	64 cm	Gravelly muddy calcareous sand
42	GC21	40° 47.03’S 147° 00.01’E	67 m	59 cm	Gravelly muddy calcareous sand
43	GC22	40° 57.00’S 146° 34.94’E	67 m	63 cm	Gravelly muddy calcareous/terrigenous sand
44	PC01	40° 34.99’S 146° 10.06’E	75 m	448 cm	Olive grey shelly mud
45	GC23	40° 35.03’S 146° 10.02’E	75 m	550 cm	Olive grey shelly mud
46	GC24	40° 15.04’S 146° 10.08’S	82.5 m	480 cm	Greenish grey shelly mud
47	PC02	40° 15.0’S 146° 10.0’S	82.5 m		10 metre corer aborted late in deployment because of bad weather
78	PC04	40° 25.06’S 146° 20.10’S	81 m	811 cm	Bluish grey firm shelly mud

GR = grab
GC = gravity core
PC = piston core
Total core recovery = 25.49 m

Table 4. Otway Margin Quaternary Sampling Stations

No	Plan	Station	Lat/Long	Depth	Recovery	Description
48	OT33	GR08	38° 39.59’ 142° 59.80’	50.5 m	Good	Quartz-rich medium sand
49	OT32	GR09	38° 44.00’ 142° 55.55’	64.5 m	Good	Coarse calcareous sand with terrigenous debris
50	OT31	GR10	38° 48.40’ 142° 51.33’	66 m	Good	Coarse calcareous sand with minor terrigenous debris
51	OT30	GR11	38° 52.88’ 142° 47.07’	72 m	Poor	Hard ground with calcareous sand and sponges
52	OT29	GR12	38° 57.33’ 142° 42.73’	88 m	Poor	Hard ground with calcareous sand
53	OT28	GR13	39° 01.81’ 142° 38.75’	100.5 m	Good	Coarse calcareous sand with no terrigenous debris
54	OT27	GR14	39° 06.31’ 142° 34.43’	160.5 m	Good	Medium grained muddy calcareous sand
55	OT25	GR15	39° 15.83’ 142° 38.82’	1009 m	Good	Clayey nanno ooze with some forams
56	OT24	GR16	39° 11.00’ 142° 29.97’	1179 m	Good	Clayey nanno ooze with some forams
57	OT23	GR17	39° 07.64’ 142° 25.74’	1124 m	Good	Clayey nanno ooze with some forams
58	OT22	GR18	39° 01.64’ 142° 15.71’	1168 m	Good	Clayey nanno ooze with some forams
59	OT21	GR19	38° 56.23’ 142° 07.23’	892 m	Good	Clayey nanno ooze with some forams
60	OT20	GR20	38° 50.93’ 141° 54.42’	517 m	Good	Clayey nanno ooze with some forams
61	OT19	GR21	38° 49.66’ 141° 45.52’	527 m	Good	Clayey nanno ooze with some forams
62	OT18	GR22	38° 47.82’ 141° 32.79’	471 m	Good	Clayey nanno ooze with some forams
63	OT17	GR23	38° 44.07’ 141° 21.53’	431 m	Good	Clayey nanno ooze with some forams
64	OT16	GR24	38° 41.49’ 141° 15.66’	453 m	Good	Clayey nanno ooze with some forams
65	OT15	GR25	38° 37.99’ 141° 08.33’	1400 m	Good	Clayey nanno ooze with some forams
66	OT14	PC03	38° 38.05’ 141° 08.40’	1410 m	460 cm	Calcareous silty mud with some terrigenous sand
67	OT14	GC25	38° 34.30’ 140° 59.49’	636 m	550 cm	Calcareous silty mud with some terrigenous sand
68	OT13	GC26	38° 30.65’ 140° 51.45’	1166 m	577 cm	Calcareous silty mud with some terrigenous sand
69	OT13	GR26	38° 30.63’ 140° 51.44’	1178 m	Good	Calcareous silty mud containing small mud blocks
70	OT12	GR27	38° 27.74’ 140° 55.60’	208 m	Good	Calcareous muddy sand with some terrigenous grains
71	OT14	GR28	38° 34.33’ 140° 59.46’	647 m	Good	Calcareous silty mud with some terrigenous sand
72	OT16	GC27	38° 41.52’ 141° 15.67’	461 m	445 cm	Clayey nanno ooze with some forams

GR = Grab
PC = Piston core
GC = Gravity core
Total core recovery = 20.32 m

Table 5. Otway Margin Deep-water Sampling Stations

No	Plan	Station	Co-ordinates (single location for cores, start and end points for dredges)		Water depth (m)	Recovery	Description
73	OT1-D	DR16	38° 50.5’ 141° 06.8’	38° 50.9’ 141° 07.7’	2400-2000	Poor. No real bites	Calcareous ooze
74	OT2-Cs	GC28	39° 15.21’ 141° 58.14’		2397	435 cm	Nanno ooze with forams
75	OT4-Cl	GC29	39° 25.72’ 142° 18.48’		2240	544 cm	Nanno ooze with forams
76	OT5-Cs	GC30	39° 35.73’ 142° 11.04’		2508	530 cm	Foram nanno ooze
77	OT7-Cs	GC31	39° 51.28’ 142° 53.77’		1840	500 cm	Sticky foram nanno ooze

DR = dredge
GC = gravity core
Total core recovery = 20.09 m

Table 6. Storm Bay Sampling Stations

No	Planned Station	Actual Station	Co-ordinates	Water depth (m)	Description
81	SB-Cl	GC34	43° 28.01’ 147° 24.06’	67	No recovery
82	SB-Cl	GC35	43° 27.96’ 147° 24.18’	68	Minor shell grit
83	SB-C2	GC36	43° 20.09’ 147° 27.65’	67	Minor olive fine sand
84	SB-C3	GC37	43° 13.98’ 147° 32.55’	60	Minor coarse shelly sand
85	SB-C4	GC38	43° 08.87’ 147° 26.07’	35	Minor gravelly shelly sand

GC = gravity corer

Updated: 31/01/03