Papers by Cristina Broglia
Proceedings of the Ocean Drilling Program, Feb 1, 1990
The upper Miocene sedimentary sequence of Site 652, located on the lower continental margin of ea... more The upper Miocene sedimentary sequence of Site 652, located on the lower continental margin of eastern Sardinia, was cored and logged during Ocean Drilling Program (ODP) Leg 107. Geophysical and geochemical logs from the inter val 170-365 m below seafloor (mbsf), as well as various core measurements (CaC0 3 , grain size, X-ray diffraction), pro vide a mineralogical-geochemical picture that is interpreted in the framework of the climatic and tectonic evolution of the western Tyrrhenian. The results indicate the presence of short-and long-term mineralogical variations. Short-term variations are repre sented by calcium-carbonate fluctuations in which the amount of CaC0 3 is correlated to the grain size of the sediments; coarser sediments are associated with high carbonate content and abundant detrital material. Long-term variation cor responds to a gross grain-size change in the upper part of the sequence, where predominantly fine-grained sediments may indicate a gradual deepening of the lacustrine basin towards the Pliocene. Regional climatic changes and rift-re lated tectonism are possible causes of this variability in the sedimentation patterns. The clay association is characterized by chlorite, illite, and smectite as dominant minerals, as well as mixed-layers clays, kaolinite, and palygorskite. Chlorite, mixed-layers clays, and illite increase at the expense of smectite below the pebble zone (335 mbsf)-This is indicative of diagenetic processes related to the high geothermal gradient and to the chemistry of the evaporative pore waters, rather than to changes in the depositional environment.
Proceedings of the Ocean Drilling Program. Scientific results, Sep 1, 1995
Geochemical well logs were obtained through sediments at Leg 141 Sites 859 and 863. Corrections h... more Geochemical well logs were obtained through sediments at Leg 141 Sites 859 and 863. Corrections have been applied to the logs to account for variations in borehole size, drilling-fluid composition, and drill-pipe attenuation. Concentrations of Th, U, and Gd, as well as oxide weight percentages, have been calculated from the logs and compared with shipboard and shorebased X-ray-fluorescence (XRF) and carbonate bomb core measurements. The geochemical processing was performed in both open hole and cased sections of Holes 859B and 863B. Comparison of XRF core data to log data is good.
Proceedings of the Ocean Drilling Program, Oct 1, 1994
Geochemical well logs were obtained in the igneous and sedimentary sequences drilled at Sites 829... more Geochemical well logs were obtained in the igneous and sedimentary sequences drilled at Sites 829, 830, 831, and 833 of Ocean Drilling Program Leg 134. Corrections have been applied to the logs to account for variations in borehole size, borehole fluid composition, downhole temperature, and logging speed. Concentrations of the elements Th, U, and Gd, and the dry weight percentages of the oxides of Si, Ca, Al, Fe, Ti, and K have been derived. In each of the logged holes the log-derived geochemistry agrees well with shipboard carbonate-derived CaO and X-ray fluorescence core measurements.
Proceedings of the Ocean Drilling Program. Scientific results, Jun 1, 1995
Geochemical well logs were obtained through sediment and basalt at Site 504 of Leg 140. Correctio... more Geochemical well logs were obtained through sediment and basalt at Site 504 of Leg 140. Corrections have been applied to the logs to account for variations in borehole size, drilling-fluid composition, and drill-pipe attenuation. Concentrations of Th, U, and Gd, as well as oxide weight percentages, have been calculated from the logs and compared with available X-ray-fluorescence (XRF) core measurements. The geochemical processing was performed in the open hole sections of Hole 504B only. The comparison of XRF core data to log data is good.
Proceedings of the Ocean Drilling Program. Scientific results, Nov 1, 1995
Geochemical well logs were obtained in the igneous and sedimentary sequences drilled at Sites 883... more Geochemical well logs were obtained in the igneous and sedimentary sequences drilled at Sites 883 and 884 of Ocean Drilling Program Leg 145. Corrections have been applied to the logs to account for variations in borehole size, borehole fluid composition, downhole temperature, and logging speed, to derive the concentration of the elements Th and U, and the dry weight oxide percentages of the elements K and Al.
Proceedings of the Ocean Drilling Program, Sep 1, 1992
Geochemical well logs were obtained both in sediments and in basalts at Sites 782 and 786 during ... more Geochemical well logs were obtained both in sediments and in basalts at Sites 782 and 786 during Leg 125. Corrections have been applied to these logs to account for variations in hole size, interference of drilling fluids, and drill-pipe effects. Calcium carbonate and oxide weight percentages have been calculated from the processed logs and have been compared to the available core measurements. The log-derived carbonate curve is compared to shipboard CaCO 3 measurements in Hole 782B and in the upper portion of Hole 786B, and the two show reasonable agreement. Instrumental neutron activation analysis measurements have been compared to the natural gamma-ray measurements in Hole 786B; poor agreement exists between the log and core data for Th and U, most likely due to the very low concentration of these two elements. The numerous X-ray fluorescence measurements, performed for the basement section of Hole 786B, show excellent agreement with the logs, with the exception of MgO in the Mg-rich basalt units.
Logging data are measurements of physical properties of the formation surrounding a borehole, acq... more Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Logging data are measurements of physical properties of the formation surrounding a borehole, acq... more Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Geochemical well logs were obtained through sediment and basalt at Site 504 of Leg 140. Correctio... more Geochemical well logs were obtained through sediment and basalt at Site 504 of Leg 140. Corrections have been applied to the logs to account for variations in borehole size, drilling-fluid composition, and drill-pipe attenuation. Concentrations of Th, U, and Gd, as well as oxide weight percentages, have been calculated from the logs and compared with available X-ray-fluorescence (XRF) core measurements. The geochemical processing was performed in the open hole sections of Hole 504B only. The comparison of XRF core data to log data is good. INTRODUCTION The primary objective of Leg 140 was to deepen the previously existing Hole 504B into the sheeted dike complex (Fig. 1) (Shipboard Scientific Party, 1992). The hole was logged with the geochemical logging tool string (GLT), which measures the major elements of a formation at intervals of 0.1524 m. The GLT measurements provide continuous, in-situ chemical measurements of the rock and are not affected by incomplete core recovery or core...
On ODP Leg 102, the JOIDES Resolution returned to Hole 418A at the southern end of the Bermuda Ri... more On ODP Leg 102, the JOIDES Resolution returned to Hole 418A at the southern end of the Bermuda Rise and logged the hole with a comprehensive suite of tools to determine the geophysical properties of old oceanic crust from situ measurements. An excellent set of density, porosity, natural gamma-ray, conductivity, resistivity, full wave and multichannel sonic (P and 5), magnetic susceptibility, three-axis magnetometer, and caliper logs was obtained over varying intervals from 0 to 488 m within the basement. In addition, the sediments were logged through the pipe using the porosity and spectral gamma-ray tools, water samples were taken and temperature measurements made at selected depths in basement, and the oblique seismic experiment was successfully run with a three-component borehole seismometer clamped 41,81,230,330, and 430 m within the basement. The results demonstrate as follows: 1. Layer 2A is absent: V p increases gradually from 4.5 km/s at the sediment/basement contact to 6.9 ...
Proceedings of the Ocean Drilling Program, 1992
Geochemical well logs were obtained in sediments at Site 765 and in both sediments and basalts at... more Geochemical well logs were obtained in sediments at Site 765 and in both sediments and basalts at Site 766 of Leg 123. Corrections have been applied to the logs to account for variations in hole size, drilling fluid interference, and casing or drill pipe attenuation. Weight fractions of the major oxides and of calcium carbonate have been calculated from the reprocessed logs, and the results correlate well with shipboard CaCO 3 and X-ray fluorescence measurements. The logs show good qualitative agreement with the overall lithologic trends of Hole 765D and excellent qualitative agreement with cores from Hole 766A.
Proceedings of the Ocean Drilling Program, 1994
Geochemical well logs were obtained in the igneous and sedimentary sequences drilled at Sites 829... more Geochemical well logs were obtained in the igneous and sedimentary sequences drilled at Sites 829, 830, 831, and 833 of Ocean Drilling Program Leg 134. Corrections have been applied to the logs to account for variations in borehole size, borehole fluid composition, downhole temperature, and logging speed. Concentrations of the elements Th, U, and Gd, and the dry weight percentages of the oxides of Si, Ca, Al, Fe, Ti, and K have been derived. In each of the logged holes the log-derived geochemistry agrees well with shipboard carbonate-derived CaO and X-ray fluorescence core measurements.
Proceedings of the Ocean Drilling Program, 1992
Geochemical well logs were obtained in the sedimentary sequences drilled at Sites 798 and 799 in ... more Geochemical well logs were obtained in the sedimentary sequences drilled at Sites 798 and 799 in the Sea of Japan. The recorded data have been corrected for variations in borehole size, borehole fluid composition, downhole temperature, and logging speed and were processed to derive the concentration of the elements Th, U, and Gd and the dry weight percentages of oxides of the elements Si, Ca, Al, Fe, Ti, and K at 0.1524-m intervals (6 in.). The log-derived geochemistry shows fair agreement with XRF core measurements for Hole 798B.
Proceedings of the Ocean Drilling Program, 1991
Velocity, density, resistivity, and neutron-porosity logs were recorded in virtually the entire 2... more Velocity, density, resistivity, and neutron-porosity logs were recorded in virtually the entire 222-m-thick section of basaltic back-arc crust drilled at Site 768 and through the 106-m section of MORB crust at Site 770. Our analysis of these logs and comparison with measurements on discrete cores permit determination of interlog relationships and evaluation of the reliability of each log. Crustal porosity (Φ) at the two sites is most accurately determinable from transit time (At) and the inverse of velocity: Φ = 0.0054 At-0.259. Porosity is also closely related to resistivity (R o), according to the Archie equation: R o-Rwd<f" 1 where /? w is resistivity of the formation fluid, and a and m are empirically determined "constants." Both logs and cores indicate that a and m range from 2 to 6.5 and 1.2 to 1.6, respectively. Density values estimated from sonic porosity are broadly similar to, but more reliable than, density logs. Neutron-porosity logs yield values 10%-20% higher than actual porosities; this error is caused primarily by lack of proper tool eccentralization and secondarily by the presence of hydrous alteration minerals in the rocks. These in-situ geophysical properties of oceanic crust 18 Ma and 42 Ma help to bridge the in-situ measurement gap between 6 Ma and 110 Ma at other sites. Observed velocities, densities, and porosities are generally similar to predictions from crustal aging models. We infer that this correspondence is largely coincidental; observed properties here are related more to style of volcanism than to crustal aging, and crustal heterogeneity is so high that a 100-200-m-interval is not representative of larger scale geophysical properties.
Marine Slides and Other Mass Movements, 1982
The more than 3000 m high Malta Escarpment forms the western boundary of the eastern Mediterranea... more The more than 3000 m high Malta Escarpment forms the western boundary of the eastern Mediterranean. The escarpment has an average dip of about 20°, however the lower part of the escarpment is steeper and has a slope of approximately 60° (Figure 1). Extensive exposures of late Triassic-lower Liassic shallow water limestone occurs along this lower part of the escarpment (Chayes et al, 1980; Scandone et al, in press; Cita et al, in press).
Geochemical well logs were obtained at Sites 761, 762, and 764 of Leg 122 on the Exmouth Plateau.... more Geochemical well logs were obtained at Sites 761, 762, and 764 of Leg 122 on the Exmouth Plateau. The preliminary log measurements which were presented in the Initial Reports have been corrected for borehole size, borehole fluids, and logging speed variations. The corrected logs are used to calculate percentages of the naturally radioactive elements and oxides of the formation. The CaCO3 logs agree well with core-derived carbonate measurements from Holes 762C and 764B, and agree less with measurements from Hole 761C. The geochemical logs are found to be useful in refining major lithologic changes in each of the three wells.
www-odp.tamu.edu
Geochemical well logs were obtained both in sediments and in basalts at Sites 782 and 786 during ... more Geochemical well logs were obtained both in sediments and in basalts at Sites 782 and 786 during Leg 125. Corrections have been applied to these logs to account for variations in hole size, interference of drilling fluids, and drill-pipe effects. Calcium carbonate and oxide weight percentages have been calculated from the processed logs and have been compared to the available core measurements. The log-derived carbonate curve is compared to shipboard CaCO 3 measurements in Hole 782B and in the upper portion of Hole 786B, and the two show reasonable agreement. Instrumental neutron activation analysis measurements have been compared to the natural gamma-ray measurements in Hole 786B; poor agreement exists between the log and core data for Th and U, most likely due to the very low concentration of these two elements. The numerous X-ray fluorescence measurements, performed for the basement section of Hole 786B, show excellent agreement with the logs, with the exception of MgO in the Mg-rich basalt units.
Proceedings of the Ocean Drilling Program, 102 Scientific Results, 1988
DSDP Hole 418A, drilled through 324 m of sediments and 544 m of basalts during DSDP Legs 51-53 at... more DSDP Hole 418A, drilled through 324 m of sediments and 544 m of basalts during DSDP Legs 51-53 at the southern end of the Bermuda Rise, was reoccupied during ODP Leg 102 for the purpose of obtaining a comprehensive suite of geophysical logs. Although a hole restriction at 469 m below seafloor (145 m into basement) prevented the recording of the complete log suite throughout the open-hole interval, two passes of the first Schlumberger tool combination, consisting of resistivity-sonic-gamma-ray-caliper, were recorded from just below the sediment/basalt interface at 324 to 788 mbsf. The remaining 80 m was not logged owing to the suspected presence of a logging tool and cable lost during DSDP Leg 53. The second Schlumberger lowering, consisting of compensated neutron porosity, natural gamma spectroscopy, and lithodensity, and the third lowering, dual resistivity laterolog and gamma ray, were both recorded in open hole from 464 to 788 mbsf. The second combination was also recorded through the pipe to the mud line. Careful calibration of these measurements in fresh flow basalts, corrections for known borehole effects, and comparison of gamma-ray results to core mineralogy result in an excellent set of physical-property measurements throughout the logged interval. Differences in gamma-ray activity, mostly due to the potassium-40 decay series, separate the basement interval into three zones on the basis of smectite content. The uppermost zone 1 consists of a series of relatively unaltered, low-porosity (<15%), high \ p (>5 km/s) massive basalts and more porous lower velocity pillows capped by a 9-m-thick, more highly altered pillow unit, the total extending from 324 to 388 mbsf (log lithologic Units 1 to 4). In zone 2, from 388 to 514 mbsf (log lithologic Unit 5 and Subunit 6A), the pillow basalts contain large amounts of smectite within fractures and voids; porosities generally range from 15% to 25%, and velocities vary inversely with smectite content and porosity from 3.5 to 5 km/s. The bottom of the Subunit 6A breccia at 514 mbsf marks a geophysical boundary separating these altered pillows from the much fresher pillows and flows of Subunit 6B to Subunit 13C in the remainder of the logged interval, which we refer to as zone 3. In this zone velocities are generally above 4 km/s and reach 6 km/s in the massive flows. Porosities are generally below 20%; smectite is generally less than 5%. The density log is more sensitive to well-bore rugosity than the other logs, but aside from this effect, density ranges from 2.4 to 2.95 g/cm 3. After correction for the presence of smectite, density is generally inversely proportional to porosity, as expected in a two-phase (seawater-basalt) system. Although velocities within the altered section (zone 2) are somewhat lower than in the remainder of the hole, nowhere are they as low as in seismic Layer 2A. In the uppermost 190 m of the basement where smectite is replaced by void space, the average velocity can be reduced to less than 3.5 km/s. Thus, alteration and smectite infilling over the 110 Ma since the formation of these rocks can raise in-situ velocities and eliminate Layer 2A as part of the crustal aging process.
Geochemical well logs were obtained in sediments at Site 791 and in both sediments and basalts at... more Geochemical well logs were obtained in sediments at Site 791 and in both sediments and basalts at Sites 792 and 793 of Leg 126. Corrections have been applied to the logs from the latter two sites to account for variations in hole size, drilling fluid interference, and drill-pipe attenuation. Oxide and calcium carbonate weight percentages have been calculated from the processed logs and are compared to the available core measurements. Log-derived CaCO 3 measurements correlate well with shipboard CaCO 3 core measurements from Hole 79IB. In Holes 792E and 793B the log-derived oxides, with the exception of SiO 2 , agree extremely well with the X-ray fluorescence measurements.
OCEANS '85 - Ocean Engineering and the Environment, 1985
All wells drilled by the Ocean Drilling Program which penetrate more than 4 0 0 meters of sedimen... more All wells drilled by the Ocean Drilling Program which penetrate more than 4 0 0 meters of sediment, and any wells with significant basement penetration, are now logged as part of routine operations on the J O I D E S Resolution. Standard logs include resistivity, sonic velocity, neutron porosity, density, and both natural and induced gamma-ray spectrometry. Specialty logs include an acoustic borehole televiewer and a
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Papers by Cristina Broglia