MUD DIAPIRS OF THE MEDITERRANEAN RIDGE: SEDIMENTOLOGICAL AND MICROPALEONTOLOGICAL STUDY OF THE MUD BRECCIA

Two recent sea-going expeditions showed that mud diapirism is a common feature in the accretionary wedge of the Mediterranean Ridge, but unlike in other prisms, it is well expressed exclusively in the most elevated areas of the Ridge. Three diapiric fields were discovered on the Mediterranean Ridge and informally called, from west to east, Pan di Zucchero, Prometheus 2 and Olimpi. They are located on the crestal part of the Mediterranean Ridge between Creta and the Cirenaic Promontory. Sedimentological, micropaleontological, and mineralogic investigations were performed on the mud breccia recovered in 15 cores raised during cruises BAN88 and BAN89. The sedimentological analyses allowed to recognize several sedimentary facies which are suggestive of different emplacement processes: 1) three massive facies are indicative of intrusion; 2) three organized facies are indicative of submarine extrusion and probably reworking. The micropaleontological study based on planktonic foraminifera and calcareous nannofossils provided an Oligocene age for the source sediments and/or for the sediments possibly involved in the diapiric processes of the Pan di Zucchero, and an Early Miocene age for the Olimpi and Prometheus 2 fields. No evidence was found of the typical Messinian lithologies, such as dolomite and gypsum, and microfossils ("lago-mare" biofacies). X-ray diffraction analyses allow to identify the major mineralogic component of the mud breccia and a westward decrease in the smectite content. Our investigations reveal that major differences occur between the Pan di Zuccchero and Olimpi areas, whereas minor differences are recorded between the Olimpi and Prometheus 2. Moreover, the Napoli Dome, located in the Olimpi area, differs from the other diapirs in several sedimentological, micropaleontological and mineralogic characters, and is interpreted as a mud volcano

ANOXIC VERSUS OXIC SEDIMENTATION IN THE BANNOCK BASIN AREA, 35,000 YRS B.P. TO PRESENT

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(Table 1) Description of grain size, cement, and matrix in sediment core CRP-3 sandstones

The presence of authigenic smectite in the lower Oligocene sandstones of the Cape Roberts Project core CRP-3 from the Victoria Land Basin of Antarctica is confirmed by scanning electron, scanning-transmission electron, and light microscopy. It was emplaced as a single generation of cement within the lower portion of the Oligocene section. This section has undergone no discernible compaction since cementation. Permeabilities measured on fifty core plugs show that the lower portion of the Oligocene (from 370-766 meters below sea floor) also has systematically higher values than sediment in uppermost CRP-3 and all of CRP-2 and CRP-1. Three models for smectite authigenesis are considered as multiple working hypotheses to be tested: 1) Burial diagenesis with necessary components sourced from volcanogenic materials and heavy minerals within the drilled sequence: 2) Precipitation from hydrothermal waters associated with possible igneous intrusion(s) and nearby faults; 3) Mobilization and injection of regionally compactive 'thermobaric' fluids along a nearby fault that bounds a major graben parallel to the Transantarctic Mountain Front. The preponderance of the available evidence and Occum's Razor favors the first model, although special circumstances dictated by the position of the drill site along a rapidly subsiding rift basin require that all three models be considered equally until our analyses are complete

BACTERIAL COLONIES AND MANGANESE MICRONODULES RELATED TO FLUID ESCAPE ON THE CREST OF THE MEDITERRANEAN RIDGE

A black, few centimeters thick Marker-bed of Holocene age is consistently recorded in all the deep-sea cores raised from two fields of mud diapirs recently discovered on the crest of the Mediterranean Ridge south of Crete. Detailed investigations on the ultrastructure of the Marker-bed accompained by micro-probe analysis revealed the occurrence of Mn-rich micronodules and bacterial colonies in very high number. Their occurrence is accounted to fluid escape in the accretionary prism, related to mud diapirism and tentatively associated with an important volcanic event occurred in the arc-trench system

Assessment of liquefaction potential in the central Po plain from integrated geomorphological, stratigraphic and geotechnical analysis

Large portions of the highly populated central Po Plain in northern Italy are susceptible to major liquefaction\u2013 induced ground failure and resulting damage, as illustrated by the 2012 Mw 5.6\u20135.8 earthquake sequence. Our work presents a comprehensive geomorphological, stratigraphic and geotechnical dataset from a 1012 km2 study area in the alluvial plain, analysed through the integration of different methodologies. For hazard reduction planning, we qualitatively and quantitatively assess liquefaction potential by the identification of three discrete geomorphological domains. Each geomorphological domain has variable Late Pleistocene to Holocene geological evolution, geotechnical characteristics and thus liquefaction susceptibility, as deduced from interpretation of three 25\u2013m deep continuous cores and calculation of liquefaction potential based on the geotechnical analysis of 239 cone penetration tests (CPTs). For land use planning, we present this information at various map scales consistent with inherent uncertainties of data availability. The investigation procedures and geological\u2013geotechnical interpretations may be applicable to similar liquefaction\u2013prone areas elsewhere

Preliminiary results and documentation of sediment core CRP-3 from the Ross Sea off Cape Roberts, Antarctica

The site for CRP-3, 12 km east of Cape Roberts (77.006°S; 103.719°E)was selecte to overlap the lower Oligocene strata cored in nearby CRP-2/2A, and to sample the oldest strata in the Victoria Land Basin (VLB) for Paleogene climatic and tectonic history. As it transpired there was underlap of the order of 10s of metres. CRP-3 was cored from 3 to 939 mbsf (metres below the sea floor), with a core recovery of 97%. Coring took place from October 9 to November 19, 1999, on 2.0 to 2.2 m of sea ice and through 295 in of water. The Cenozoic strata cored were mostly g1acially influenced marine sediments of early Oligocene age, though they may be earliest Eocene near the base, where at 823 mbsf Devonian Beacon sandstone was encountered. Following CRP-1 and CRP-2/2A, CRP-3 completes the coring of 1500 m of strata on the western margin of the VLB. Core fractures and other physical properties, such as sonic velocity, density and magnetic susceptibility, were measured throughout the core. Down-hole logs for these and other properties were taken from 20 down to 900-919 mbsf. Also, vertical seismic profile data were gathered from shots offset both along strike and up dip from the hole. Sonic velocities in CRP-3 are close to 2.0 km/s in the upper 80 m, but become significantly faster below 95 mbsf, averaging 3.2+0.6 km/s to the bottom of the hole. An exception to this is an interval of dolerite conglomerate from 790 to c. 820 mbsf with a velocity of c. 4.5 km/s. Dip of the strata also increases down-hole from 10° in the upper 100 m to around 22° at the bottom. Over 3000 fractures were logged through the hole, and borehole televiewer imagery was obtained for most of the hole for orienting core and future stress field analysis. Two high-angle crush zones, interpreted as faults, were encountered at c. 260 and c. 540 mbsf, but no stratigraphic displacement could be recognised. A third fault zone is inferred from a low angle shear zone in the upper part of a coarse dolerite conglomerate from 790 to 805 mbsf. Temperature gradient was found to be 28.5°.km-1. Basement strata cored from 823 mbsf to the bottom of the hole are largely light-reddish brown medium-grained sandstone (quartz-cemented quartzarenite) with abundant well-defined parallel lamination. These features are comparable with the middle Devonian part of the Beacon Supergroup, possibly the Arena Sandstone. This interval also includes a body of intrusive rock from 901 to 920 mbsf. It has brecciated contacts and is highly altered but some tholeiitic affinity can be recognised in the trace element chemistry. Its age is unknown. Post-Beacon sedimentation began on deeply eroded quartzarenite with the deposition of a thin sandstone breccia and conglomerate, probably as terrestrial talus, followed by dolerite conglomerate and minor sandstone of probable fluvial origin to 790 mbsf. Sedimentation continued in a marine setting, initially sandstone and conglomerate, but above c. 330 mbsf the strata include mudstone and diamictite also. The older sandstone and conglomerate beds are seen as the products of rapid episodic sedimentation. They are interpreted by some as the product of glaciofluvial discharge into shallow coastal waters, and others as a result of sediment gravity flows, perhaps glacially sourced, into deeper water. The core above c. 330 mbsf has facies that allow the recognition of cyclic sequences similar to those in CRP-2A. Fourteen unconformity-bounded sequences have been recognised from 330 mbsf to the sea floor, and are interpreted in terms of glacial advance and retreat, and sea level fall and rise. Detailed lithological descriptions on a scale of 1 :20 are presented for the full length of the core, along with core box images, as a 300 page supplement to this issue. The strata cored by CRP-3 are for the most part poorly fossiliferous, perhaps as a consequence of high sedimentation rates. Nevertheless the upper 200 m includes several siliceous microfossil- and calcareous nannoplankton-bearing intervals. Siliceous microfossils, including diatoms, ebrideans, chrysophycean cysts and silicoflagellates are abundant and well-preserved in the upper 67 m - below this level samples are barren or poorly preserved, but contain residual floras that indicate assemblages were once rich. No siliceous microfossils were found below 193 mbsf. Calcareous nannofossil have a similar distribution but are generally well preserved. Foraminifera, marine and terrestrial palynomorphs, and marine macrofossils were found consistentlsy down to c. 330 mbsf and sporadically to 525 mbsf. The taxa suggest marine deposition in water depth of c. 50 to 120 m. Below 525 mbsf no microfossils were found, apart from mudstone with similar marine and terrestrial palynomorphs at 781 mbsf, and rare miospores in the conglomerate below 790 mbsf. The terrestrial miospore record, which include several species of Nothofagus and podocarpaceous conifers, suggest low diversity woody vegetation, implying a cold temperate to periglacial climate for the hinterland throughout the period recorded by CRP-3. Important components of the warmer Eocene flora, known from erratics in southern McMurdo Sound, are missing, through the dominance of smectite in clay from strata below 650 mbsf suggests that the landscape prior to the timne of deposition had experienced a more temperate weathering regime. Biostratigraphy for ihe upper part of CRP-3 is provided by diatoms and calcareous nannofossils. The first appearance of Cavitatus jouseanus at 48 mbsf suggests an age of arround 31 Ma for this horizon. The last appearance of Transverspontis pulcheroides at 114 mbsf in an interval of relatively high abundance indicates a reasonably sound age for this horizon at 32.5 ± 0.5 Ma. The absence of particular resistant diatoms that are older than 33 Ma supports an age that is younger than this for the upper 200 m of CRP-3. Marine palynomorphs, which occur sporadically down to 525 mbsf and in a single occurrence at 781 inbsf, have biostratigraphical potential once the many new species in this and other CRP cores are described, and F0 and LO datums established. The mudstone at 781 mbsf has a new clinocyst species, rare Lejeunecysta cysts and a variety of acritarchs and prasinophytes, a varied marine assemblage that is quite different from and presumably younger than the well known Transantarctic Flora of mid to late Eocene age. On this basis and for the moment we conclude that the oldest strata in CRP-3 are earliest Oligocene (or possibly latest Eocene) in age - c. 34 Ma. Over 1l00 samples were taken for magnetic studies. Four magnetozones were recognisd on the basis of NRM intensity and magnetic susceptibility, reflecting the change in sediment composition between quartz sand-dominated and dolerite-dominated. For this report there was time only to produce a magnetostratigraphy for the upper 350 m. This interval is largely of reversed polarity (5 normal intervals total 50 of the 350 m), in contrast to the dominantly normal polarities of CRP-2/2A, and is inferred to be Chron C12R. This extends from 30.9 to 33 Ma. consistent with the biostratigraphic datums from the upper part of CRP-3. The lower limit of reversed polarity has yet to be established. The short period normal events are of interest as they may represent cryptochrons or even polarity changes not recognised in the Geomagnetic Polarity Time Scale. Erosion of the adjacent Transantarctic Mountains through the Kirkpatrick Basalt (Jurassic tholeiitic flows) and dolerite-intruded Beacon Supergroup (Devonian-Triassic sandstone) into granitic basement beneath is recorded by petrographical studies of clast and sand grain assemblages from CRP-3. The clasts in the lower 30 m of the Cenozoic section are almost entirely dolerite apart from a few blocks from the Beacon Supergroup beneath. Above this, however, both dolerite and granitoids are ubiquitous, the latter indicating that erosion had reached down to granitic basement even as the first sediment was accumulating in the VLB. No clasts or sand grains of the McMurdo Volcanic Group were found, but rare silt-size brown volcanic glass occurs in smear slides through most of CRP-3, and is interpreted as distal air fall from alkaline volcanism in northern Victoria Land. Jurassic basalt occurs as clasts sporadically throughout the sequence: in the sand fraction they decline upwards in abundance. The influence of the Devonian Beacon Supergroup is most striking for the interval from 600 to 200 mbsf, where quartz grains, from 10 to 50% of them rounded, dominate the sand fraction. Laminae of coal granules from the overlying Permian coal measures in all but the upper 150 in of the CRP-3 sequence show that these also were being eroded actively at this time. CRP-3 core completed the stratigraphical sampling of the western margin of the VLB by not only coring the oldest strata (Seismic Unit V5) but also the basin floor beneath. This has several important tectonic implications: - most of the Kirkpatrick Basalt and the Beacon Supergroup with the sills of Ferrar Dolerite have been eroded by the time down-faulting displaced the Beacon to form the basin floor. - matching the Beacon strata at the bottom of CRP-3 with the equivalent strata in the adjacent mountains suggests c. 3000 m of down-to-the-east displacement across the Transantarctic Mountain Front as a consequence of rifting and subsequent tectonic activity. - the age of the oldest Cenozoic strata in CRP-3 (c. 34 Ma), which are also the oldest strata in this section of the VLB, most likely represents the initiation of the rift subsidence of this part of the West Antarctic Rift System. This age for the oldest VLB fill is much younger than previously supposed by several tens of millions of years, but is consistent with newly documented sea floor spreading data immediately north of the northern Victoria Land continental margin. These new data sets will drive a re-evaluation of the relationship between initiation of uplift of the Transantarctic Mountains (currently c.55 Ma) and VLB subsidence