In the framework of the IDOE-SEATAR (International Decade of Ocean Exploration - Studies of East Asia Tectonics and Resources) Program, the Federal Institute for Geosciences and Natural Resources carried out a geophysical survey in the Sulu Sea during the period from March 11, 1982 to April 15, 1982 using the German research vessel R/V SONNE. The SONNE cruise no. SO-23 continued SEATAR-related studies of BGR which have been carried out during the Southeast Asian Cruise of the VALDIVIA (VA-16) in 1977. During SONNE cruise no. SO-23, multi-channel reflection measurements were carried out in parallel with magnetic, gravimetric, and sea-beam measurements on 21 lines with a total length of 3,300 km in the Sulu Sea. In the NW Sulu Basin, situated between the shelf of East Palawan in the north and the volcanic Cagayan Ridge in the south, a 50 - 100 km wide graben-like basin exists which is filled with thick Neogene and pre-Middle Miocene sediments. The basin trends east-northeast. At longitude 119°E it bends to a north-south direction. The dominating structural element within the sedimentary graben-like basin is a diapiric-chaotic zone about 25 km wide, which was only detectable west of longitude 120°E. The base of the elongated diapiric-chaotic zone, which might represent a tectonically mobilized equivalent of the Crocker Formation (Middle Miocene - Lower Oligocene) is difficult to define in the seismic monitor records. The configuration and the internal structural style of individual structures of the diapiric-chaotic zone, which can be followed over length of about 150 km, seem to resemble those of the oil-bearing province offshore western Sabah. In the eastern part of the NW-Sulu Basin east of longitude 119°E, several north-trending anticlines of presumably Middle Miocene age and locally volcanic intrusions of presumably Plio-Pleistocene age have been observed. During the second leg of the cruise SO-23 in the southeastern part of the South China Sea (April 16, 1982, to May 9, 1982) multi-channel seismic reflection measurements were carried out in parallel with magnetic, gravimetric, and sea-beam measurements on 19 lines with a total length of 3,570 km in the southeastern part of the South China Sea, including the area of the Dangerous Grounds. In addition, 2,280 km of profile was surveyed with only magnetics, gravity, and sea-beam measurements. A complex structural style was observed in the investigated part of the Dangerous Grounds, South China Sea, which is believed to be part of a microcontinental block which rifted from the continental margin of Asia in the Early Paleogene/Late Mesozoic time. There are prospective depocenters and structures trending NE-SW, E-W, and N-S in the southwestern part, i.e. the area west of longitude 117.5°E (units 2, 3, 4). Unit 4 contains a series of half-grabens with thick sedimentary infill. An imbricated melange of pre-Middle Miocene age seems to exist only off southern Palawan. The dominating structural trend in the area northeast of Reed Bank is NW-SE. Oceanic crust characterized by NW-trending magnetic lineations (anomalies 8 to 12 ?) was observed north of latitude 12°N and between longitude 118°E and the Manila Trench.
The cruise SO267 ARCHIMEDES I started on December 11th, 2018 in Suva (Fidji) and ended in Suva on January 26th, 2019. Over half of the world´s presently exploited metal deposits were formed during major episodes of crustal growth related to subduction and microplate tectonics. These processes are observed today along the entire margin of the Western Pacific, where complex microplate mosaics offer unique opportunities to study accretion and the emergence of new continental crust. The focus of SO267 was a series of crustal cross-sections at the outer edge of the Indo- Australian Plate, in the largely uncharted waters of the Kingdom of Tonga. The project, entitled “Arc Rifting, Metallogeny and Microplate Evolution – An Integrated Geodynamic, Magmatic and Hydrothermal Study of the Fonualei Rift System”, was designed to document the geological evolution of an emerging microplate mosaic in the NE Lau Basin, a region with some of the fastest growing crust on Earth, and to better understand the sequence of events that cause arc rifting and related magmatic-hydrothermal activity. Using a coordinated approach of high-resolution 2D seismics, electromagnetics and sampling, ARCHIMEDES I imaged the deep structure of the Fonualei Rift system and adjoining back-arc crust of the Niuafo’ou microplate. The goal was to address a major unsolved question concerning crustal growth in complex arc-backarc systems: at what stage in the structural and thermal evolution of the crust does arc rifting occur and seafloor spreading initiate? Planned operations included large-scale reflection and refraction seismic surveys, and a dense program of gravity, magnetics, heat flow, bathymetric mapping and sidescan imaging using the AUV ABYSS and ship-based multibeam systems. This ambitious program was made possible by a close collaboration between GEOMAR and BGR scientists, bringing together diverse expertise and state-of-the-art technologies. To understand the large-scale tectonic processes, we studied 6 different locations within an area of 300 km x 300 km: i) the southern Fonualei Rift Spreading Center (S-FRSC), ii) the region between the S-FRSC and the Eastern Lau Spreading Center (FRSC-ELSC Transfer Zone), iii) the northern tip of the Eastern Lau Spreading Center (ELSC), iv) the northern tip of the Fonualei Rift system (N-FRSC), v) the Mangatolu Triple Junction (MTJ), and vi) the southward propagating Northeast Lau Spreading centre (NELSC). The combined data represent one of the most comprehensive records of microplate formation from the modern oceans.
The cruise AL278 started on May, 10th 2006 in Kiel and ended in Kiel on May, 19th 2006. The previous BGR-cruises with RV AURELIA in 2003 and 2004 were designed to collect a grid of seismic MCS-data which should enable us to get a high-resolution overview over the upper 1 s TWT of the sediments of the German North Sea sector. During October/November 2005 a subsequent cruises with RV HEINCKE and FK SENCKENBERG was designed to tackle several special aims: - The detailed mapping of glacio-tectonic features North of Heligoland. - The shallow seismic mapping of the Holocene/Pleistocene-Boundary and topography of the Pleistocene sub-glacial valley system offshore of the East Friesian Islands. - High-resolution surveying of two areas designated for offshore wind farms in the southwestern German sector. - Detailed mapping of a wide and deep sub-glacial valley. One additional aim was to acquire a dense grid of seismic line in the area North of Weisse Bank where on several from previous cruises indications for shallow gas accumulations (e.g. “bright spots”) were found. Unfortunately, due to very bad weather conditions this aim could not be reached. Therefore this short cruise with RV ALKOR was used to acquire twelve MCS lines over this area. During the cruise a total ca. 1400 km of high quality MCS lines were surveyed and simultaneously measured by a sediment echosounder system that enabled additional profiles during transits with speeds 5 kn. Together with the previously acquired data these new data should help to extend our knowledge of the Late Tertiary and Quaternary evolution of the German North Sea Sector. The BGR high-resolution multichannel seismic reflection system consisting of a GI-Gun (0.8 l) and a 300 m streamer with 24 channels and a sediment echosounder type SES 2000 standard by Innomar, Rostock. While the BGR-seismic system was used to observe the shallow subsurface down to 2 s TWT penetration depth, the sediment echosounder with a penetration depth of several meters was primarily intended to identify sampling positions for the deployment of the BGR vibration corer during the succeeding Leg 2. Additionally, the echosounder system enables the relationship to the highest-resolution multichannel seismic measurements of the group of the University of Bremen on FK SENCKENBERG. All seismic records were processed onboard for the quality control and for a first interpretation.
The MSM67 SEGMENT research cruise was carried out between August 31st and October 4th 2017 aboard the research vessel MARIA S. MERIAN. Survey MSM67 SEGMENT it is intended to study the architecture of the rifted continental margin off East Greenland around the Jan Mayen fracture zone. Key issues to be addressed are margin segmentation and the location of the continent-ocean transition (COT). Both subjects are highly debated. Symmetric segmentation of conjugate margins has significant implications on our general understanding of continental rifting processes, and a margin-parallel COT off East Greenland would indicate an N-S opening in the Norwegian/Greenland Sea. The latter challenging most publications on the early evolution of the North Atlantic. A major open question is also the timing, duration and distribution of magmatism that resulted in the formation of the North Atlantic large igneous province. Previous suggestions of very short (~3 Myr) periods of intense magmatism have been challenged and a much longer duration and/or a post-breakup origin are under discussion. Here, we want to establish the amount of post-breakup magmatism as evident in high-velocity lower crust and test the dependence of magmatism with distance from the proposed hot-spot under Iceland and the influence of major fracture zones on volcanism.
In the scope of International Geoscientific Programs and in close cooperation with PETRONAS, Malaysia, and in agreement with the Bureau of Mineral Resources (BMR) and the Bureau of Energy Development (BED), Manila, the Federal Institute for Geosciences and Natural Resources (BGR) carried out a geophysical survey on the continental margin off Sabah during the period from 20th July to 10th August, 1986, and in the Northwestern Sulu Sea during the period from 12th August to 28th August, 1986, using the PRAKLA-SEISMOS vessel EXPLORA chartered by the BGR. The research cruise is a continuation of BGR’s marine geoscientific studies in the South China Sea and in the Sulu Sea with the German research vessels VALDIVIA (1977), SONNE (1982/83) and EXPLORA (1984). The previous investigations provided new information regarding the geological and tectonic history of the southern part of the South China Sea in the context of plate tectonics. According to the interpretation of the large amount of geophysical, geological and geochemical data collected by BGR on previous cruises the widely accepted hypotheses of the presence of an ancient subduction zone beneath the Sabah-Palawan Trough has to be revised. The main objective of the EXPLORA cruise was to search for an Oligocene-Early Miocene carbonate platform off Sabah and in the western Sulu Sea. On the continental margin off Sabah 27 lines were surveyed with gravity and multichannel reflection seismics and partly with magnetics, with a total length of 3,126 km. A strong reflector interpreted as reflector BLUE of previous BGR cruises off Palawan was recognizable beneath the Sabah Trough in depth between 4 and 7 sec (TWT). The isochrones of the reflector strike approximately 50°N. The surface of the reflector dips with 2 to 3 degree towards southeast. Toward the north-western part of the Sabah Trough the reflector is disrupted by a basement high. According to the preliminary interpretation of the gravity data, the prominent free-air anomaly associated with the Sabah Trough and adjacent areas has the same shape as the anomaly observed across the Palawan Trough. Therefore it is concluded that the Sabah Trough is underlain by a thinned continental crust.
The previous BGR-cruises with RV AURELIA in 2003 and 2004 and RV HEINCKE in 2005 and RV ALKOR in 2006 were designed to collect a grid of seismic MCS-data which should enable us to get a high-resolution overview over the upper 1-2 s TWT of the sediments of the German North Sea sector. The data format is Society of Exploration Geophysicists SEG Y. The aim of this cruise was a detailed survey in the north westernmost area of the German EEZ (exclusive economic zone), the so-called ‘Entenschnabel’ and additionally a mapping of special glacial structures off Sylt Island. The cruise was subdivided into two Legs. One outreaching additional aim was to extend the results from the previous cruises for the Late Tertiary and Quaternary sedimentary evolution into the ‘Entenschnabel’-area which was virtually unexplored by systematic shallow high-resolution seismics. During Leg 1 the BGR high-resolution multichannel seismic reflection system consisting of a GI-Gun (0.8 l) and a 500 m streamer with 36 channels and a shallow swath bathymetric system, type SIMRAD EM1200 by Kongsberg, Bergen, Norway were used. While the BGR-seismic system was used to observe the shallow subsurface down to 2 s TWT penetration depth, the swath bathymetric system was used to identify possible pockmark locations as well as sampling positions for the deployment of the BGR vibration corer during the succeeding Leg 2. All seismic records were processed onboard for the quality control and for a first interpretation loaded into GEOQUEST.
The POLARSTERN cruise ANTVIII/6 from 14. March to 30. April 1990 incorporated an integrated geophysical reconnaissance survey consisting of multichannel seismic measurements in parallel with gravimetric and magnetic measurements. The survey covered the plateaus Maud Rise, Astrid Ridge and Gunnerus Ridge off Queen Maud Land and the oceanic crust in their vicinity. Severe ice and weather conditions allowed seismic work only on the Gunnerus Ridge and on the oceanic crust. Together with previous BGR lines on the Astrid Ridge and the Maud Rise the new data improve considerably the understanding of the area. The main results are: 1. The oldest identified sea-floor spreading anomaly was M11 before the cruise, now it is M24. Thus spreading has begun not only 135 mill. years B.P., but at least 160 mill. years B.P. 2. The Gunnerus Ridge is strongly asymmetric. The mainly weak magnetic anomalies indicate that in contrast to the Astrid Ridge volcanism was not important during its development. 3. The magnetic anomalies are much stronger on the Astrid Ridge and west of it than east of the Astrid Ridge and on the Gunnerus Ridge. 4. The roughness of the basement surface of the oceanic crust varies in a wide range.
The expedition PS155/1 started on August 5th, 2018 in Tromsø (Norway) and ended in Longyearbyen (Spitsbergen) on September 3rd, 2018. In the course of BGR’s GREENMATE project the geological development of the European North Atlantic and the northern and north eastern Greenland shelf was analyzed using various marine geophysical methods (seismics, magnetics, gravity, heatflow measurements) and geological sampling (gravity corer, box corer, multi-corer, dredge). Sampling of marine Shelf sediments was undertaken in close correspondence with co-users from Geomar (add-on project ECHONEG), aiming to reconstruct Holocene paleo environmental and climatic evolution. Using the ship’s helicopters, marine sampling was complemented by onshore sampling operations to extract geological material at selected near coastal locations. Other scientific project groups used the cruise PS115.1 as an opportunity to quantify marine mammals and sea birds and their statistical distribution in our research area as part of the long-term project (add-on project Birds& Mammals) and to gather additional meteorological data via radiosondes (add-on Project YOPP). Against all expectations, outstanding ice conditions along the northern coast of Greenland enabled us to carry out reflection seismic surveys north of 84°N at the southern tip of Morris Jesup Rise with a 3 km long streamer. Structural data of this particular region of North Greenland is of special importance for BGR’s project GREENMATE for reconstructing the continental margin evolution. A 100 km long refraction seismic profile was measured to complement the reflection seismic data. After completing this, scientific work was concentrated on the northeastern Greenland shelf area between 76°N and 82.5°N. Over the time of the cruise a total of 2500 km of reflection seismic profiles (2250 km measured with 3km streamer length) and 100 km of refraction seismic profile (using nine ocean bottom seismometers) were measured, accompanied by gravity and magnetic surveys and seven heat flow measurement stations. Along the shelf and deep-sea area 21 geological sampling sites were chosen, with all together one dredge (around 200 kg of sample), 16 gravity cores (total core length 65 m), 12 box corers and 6 multi-corer stations. Onshore sediment sampling was done at 11 sampling sites. Beside sediment sampling hard rock from near coastal outcrops was collected in a total amount of 250 kg that will be used for age dating. The entire science program was carried out under consideration of the highest ecological standards to protect marine mammals and to meet all environmental requirements of the permitting authorities. In addition to external marine mammal observers (MMO) various acoustic monitoring systems and AWI’s on board infrared detection system AIMMS monitored any activity of marine mammals in the ships perimeter, especially during seismic operations.
Main target of the project GIGICS (Cooperative German-Indonesian Geoscientific Investigations in the Celebes Sea) is the investigation of the internal crustal structure and the plate tectonic evolution of the Celebes Sea and its active continental margins off Mindanao and Northern Sulawesi. These investigations were carried out during the cruise SO98 of RV SONNE by the Federal Institute for Geosciences and Natural Resources (BGR), Hannover; the German Research Centre for Geosciences (GFZ), Potsdam; the GEOMAR, Kiel; the Institute of Oceanography (IfM), Hamburg; the Mines and Geoscience Bureau, Manila; the Agency for the Assessment and Application of Technology, Jakarta, and the Institute of Oceanography, Wormley. The cruise SO98 consisted of three legs of two weeks duration and one leg of four weeks duration. The total amount of data acquired during the cruise were: - 3,300 km of multichannel reflection seismics, - over 6,800 km of gravimetric and magnetic data and approximately 10.000 km of swath bathymetric and sediment echosounder data, - 3 wideangle-/refractionseismic profiles, each of 120 - 150 km length, - geological, geochemical sampling and oceanographical measurements at a total of 37 stations. During the cruise SO98 a widespaced but regular grid of magnetic and gravimetric profiles were acquired in the eastern part of the Celebes Sea from which up to then reliable data were very sparse. WEISSEL (1980) recognized in the western Celebes Sea WSW-ENE striking magnetic lineations, which he interpreted as chrons 18 - 20 (39 - 43 Ma according to the timescale of HARLAND et al. (1990)). The data from cruise SO98 show that there is no continuation of these anomalies to the east. In the eastern part the magnetic field of the Celebes Sea is less clear and much more disturbed. Nevertheless, E-W-striking anomalies are recognizable. Because amplitudes of local magnetic anomalies are higher than the lineations, the correlation of these lineations with the magnetic reversal scale is still somewhat ambiguous. The gravity map compiled from the measured gravimetric data shows elongated positive anomalies in the eastern part of the Celebes Sea. Exceptions occur at the deep sea trenches off North Sulawesi (North Sulawesi Trench) and Mindanao (Cotabatu Trench) and at the Sulu Archipelago where strong negative gravity anomalies were found. A remarkable NW-striking gravity high of up to 60 mgal was found in the central eastern part of the Celebes Sea. Gravimetric modelling suggests that this high can be correlated with the gravimetric effect of the Molucca Sea Plate subducting from the east under the Sangihe Arc. The reflection seismic data from the northern part of the Celebes Sea show indications for a juvenile subduction of oceanic Celebes Sea crust under the Sulu Archipelago. The oceanic crust bends down towards the Sulu Arc with angles between 2° and 5° and the sedimentary sequence above is deformed indicating a compressional stress regime. With the exception of two linear arranged seamount-like basement highs the Celebes Sea is dominated by two different oceanic crustal types showing distinct differences in the topography. The first one is showing a very similar reflection seismic pattern as it is found for oceanic crust of the Atlantic (HINZ et al., 1994). This type is characterized by a small-scale block-faulted relief of the top basement and a low reflectivity in lower crustal levels typically related as to be accreted at slow to intermediate spreading ridges. This type is found in the western, northern and southern part of the investigated area. In the eastern and especially in the southeastern part the igneous crust shows a very different image. The reflection of the top of the basement is less distinct and of lower frequency. The relief is very much smoother than in the previous type. This reflection seismic image indicates a volcanic/magmatic overprinting of the oceanic crust in this part of the Celebes Sea. Another target of cruise SO98 was the area of the active continental margin off North Sulawesi and its accretionary complex. The internal structure of the accretionary complex should be investigated to decide whether this active margin is also of the 'splinter-type' or not. During former geophysical cruises with RV SONNE oceanic crustal splinters were discovered in the accretionary wedges of the Sulu Sea and off Costa Rica (e.g. HINZ et al., 1991). From our reflection seismic measurements this active continental margin is morphologically subdivided into three units and consists of two accretionary complexes of different internal structural style: the lower and middle continental slope is underlain by an intensively thrusted, sedimentary accretionary wedge. This wedge was most probably formed during the last 5 Ma. Landward of this wedge an older and seismically very complex accretionary unit is present which is overlain at its landward termination by a sedimentary fore-arc basin. Within this older accretionary complex, units with a strong, low frequency reflection pattern were found which are interpreted to represent crustal splinters of igneous oceanic or ophiolitic nature. This interpretation is supported by our gravity and magnetic data. The magnetic profiles show an increase of the magnetic field towards the north arm of Sulawesi across the continental margin. This increase of the magnetic field suggests an increase of magnetized material within the older accretionary wedge towards the northern arm of Sulawesi where ophiolites are emplaced. During the interpretation of the reflection seismic data of the project GIGICS BSR's (bottom simulating reflectors) were discovered for the first time along the active continental margin of North-Sulawesi. BSR's are the seismic expression of a velocity decrease at the bottom of a gas hydrate zone. The distribution and depth of the BSR's correlates with the geochemical and geothermal results. Radiometric age dating and geochemical analyses from pillow basalts of a seamount from the southeastern Celebes Sea indicate hot-spot activity in this part of the Celebes Sea during or shortly after the formation of the oceanic crust approximately at 43 Ma ago. Three NW-striking ridges or seamount-chains in the northeastern Celebes Sea were mapped and investigated in detail. They are thought to represent a wrench fault system extending through the northeastern Celebes Sea. At the flank of one of these ridges a strongly alterated plagioclase-olivine basalt sample was dredged which was overlain by non-fossiliferous clay stone. A similar lithostratigraphic sequence was drilled during ODP leg 124 (RANGIN et al., 1990). The geochemical composition of these basalts is different from typical MORB. The existence of a large crustal splinter within the accretionary wedge off southwestern Mindanao obviously is responsible for a high thermal conductivity which in turn could have enhanced heat flow (108.1 mW/m2) and methanogenesis (405 ppb). The heat flow of 103.0 mW/m2 at the deformation front of the Mindanao wedge and the high methane concentration of 5.555 ppb suggests tectonically induced fluid transport within the wedge. High methane concentrations between 8.044 and 49.006 ppb at the lower slope off Sulawesi and in the North Sulawesi Trench are accompanied by high heat flow values of up to 100.5 mW/m2. Heat flow is significantly lower upslope (31.3 mW/m2). This general heat flow distribution pattern is seen over a large portion of the accretionary wedge. The elevated heat flow values and high methane concentrations near the deformation front most likely result from heat transport by fluids squeezed out from vertically and laterally compacting sediments. The reduced heat flow towards the coast is compatible either with a cooling effect of slow subduction of the oceanic crust, or stacking of cool slabs of compacted sediments. A subduction of oceanic crust with a heat flow around 60 mW/m2 over a period of more than 3 million years would have produced the low heat flow values of the upper slope if the wedge consists of claystone with a low thermal conductivity (1.2 - 1.7 W/mK). Even in the low-heat flow area isolated fluid venting is possible. Lateral variations in the heat flow pattern (e.g. broadening of the anomalies in the west) may be due to different thermal regimes within the subducted crust.
During RV SONNE cruise 137 from 21st November to 28th December 1998 Geoscientific Investigations on the active Convergence Zone between the east Eurasian and Indo-Australian Plate (GINCO I) were carried out along the Sunda Arc, off Sumatra, Java and the Sunda Strait. The studies were headed by the BGR in close cooperation with German and Indonesian research institutions. A total amount of 5,500 km of magnetic, gravity and swath bathymetric profiles were recorded of which multi-channel seismic data exceeded 4,100 km. The scientific objectives were: (1) investigation of the structure and age of the accretionary wedges, outer arc highs and fore-arc basins off Sumatra and Java with special emphasis on the evolution of the Sunda Strait and the Krakatau area (2) differences in tectonic deformation between oblique (Sumatra) versus frontal (Java) subduction (3) search for oceanic crustal splinters in the accretionary wedges (4) definition of seismic sequences, thicknesses and ages of the fore-arc basin sediments as a pre-requisite for later on hydrocarbon assessments (5) identification and regional occurrence of bottom simulating reflectors (BSR) indicating gas hydrates. From the GINCO I project there is evidence for the existence of two accretionary wedges along the Sunda Arc: wedge I is of assumed Paleogene age and wedge II of Neogene to Recent age. The first inner wedge I is composed of tectonic flakes which are correlated from SE Sumatra across the southern Sunda Strait to NW Java. This implies a very similar plate tectonic regime at the time of the flake development during the Upper Oligocene to Lower Miocene and without marked differences in plate convergence direction from Java to Sumatra. Wedge I shows backthrusting along the northern transition toward the fore-arc basin. Today, wedge I forms the outer arc high and the backstop for the younger, outer wedge II. Magnetic, gravity and seismic results show, that within both wedges, there are no indications for an oceanic crustal splinter as hitherto postulated. Both wedges are underlain by oceanic crust of the subducting Indo-Australian slab which could be correlated from the trench off Sumatra up to 135 km to the northeast and up to 65 km from the trench off Java. Since the top of the oceanic crust differs considerably in reflectivity and surface relief we distinguished two types in the seismic records. One type is characterized by strong top reflections and a smooth surface and underlies accretionary wedge II and the southwest part of the wedge I (outer arc high) off Sumatra and Java. The second type has a low reflectivity and a rougher relief and underlies the tectonic flakes of accretionary wedge I (outer arc high) between the southwestern tip of Sumatra, the SundaStrait and NW Java. The missing outer arc high off the southern entrance of the Sunda Strait is explained by Neogene transtension in combination with arc-parallel strike-slip movements. The NW-SE running, transpressional Mentawai strike-slip fault zone (MFZ) was correlated from the SE Sumatra fore-arc basin to the NW Java fore-arc basin. Off the Sunda Strait northward bending branches of the MFZ are connected with the Sumatra Fault zone (SFZ). It is speculated that the SFZ originally was attached to the Cimandiri-Pelabuhan-Ratu strike-slip faults and shifted from the volcanic arc position into the fore-arc basin area due to clockwise rotation of Sumatra with respect to Java as well as due to increasingly oblique plate convergence since the late Lower Miocene. We explain the transtension of the western Sunda Strait (Semangka graben) and the transpression with inversion of the eastern Sunda Strait, along the newly detected Krakatau Basin, by this rotation. Seismostratigraphic interpretation revealed 5 main sequences (A - E), tentatively dated as Paleogene to Recent in age. The oldest seismic sequence A of assumed Eocene to Oligocene age is bounded at the top by a major erosional unconformity that was identified on all GINCO seismic profiles. The seaward diverging seismic pattern of sequence A is interpreted as a correlative sequence to the prograding Paleogene deltaic sediments encountered by wells offshore central and northern Sumatra. This is opposed to previous interpretation which assumed seaward dipping reflector sequences of basaltic origin erupted along the former Mesozoic passive margin of Sumatra. According to constructed time structure maps, the main NW-SE running depocentres of the post-Paleogene sediments are arc-parallel off Sumatra and Java with thicknesses of 3 s (TWT) and 5 s (TWT), respectively. The main depocentres of the Semangka graben and of the Krakatau Basin of the Sunda Strait strike north-south and have infills of 2 s - 5 s (TWT). Bottom simulating reflectors (BSR) occur within the upper sequences C - D along the flanks of the fore-arc basins and along doming structures but could not be detected in basin centres. Empiric relations of heat flow values and depths of BSR were determined indicating that with increasing waterdepth and decreasing heat flow the depths of the BSR increase.
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