A link density clustering algorithm based on automatically selecting density peaks for overlapping community detection

Peer reviewed

(Table 1) Age and depth of reflectors of the 3.5-kHz and airgun seismic record and their corresponding depth of ash layers, carbonate peaks, and transition zones from DSDP Hole 83-504B

DSDP cores from areas of low (Site 505) and high heat flow (Site 504 B) near the Costa Rica Rift, together with seismic profiles from the Panama Basin, have been studied to determine the relationship between: (1) carbonate content and physical and acoustic properties; and (2) carbonate content, carbonate diagenesis and acoustic stratigraphy. Except for ash and chert layers, bulk density correlates strongly and linearly with carbonate content. Velocity is uniform downcore and only small variations at a small scale are measured. Thus an abrupt change in carbonate content will cause abrupt changes in acoustic impedance and should cause reflectors that can be detected acoustically. A comparison of seismic profiler reflection records with physical properties, carbonate content and reflection coefficients indicates that the main reflectors can be identified with ash layers, diagenetic boundaries, and carbonate content variations. Diagenesis of carbonate sediments is present at Site 504B in a 260 m-thick ooze-chalk-limestone/chert sequence. These diagenetic sequences occur in areas of higher heat flow (200 mW/m**2). Seismic profiler records can be used to map the extent and depth of these diagenetic boundaries.

Milankovitch frequency peaks of ODP Site 113-693 (Table 3)

The first well logs collected below the Antarctic circle were obtained during Leg 113 at Site 693 on the Dronning Maud Land Margin (Antarctica) in the Weddell Sea. Gamma-ray, resistivity, and sonic logs were collected between 108.0 and 439.0 mbsf. The downhole logs show good agreement with the data collected from cores and provide a continuous measurement of the sedimentary record. These continuous log records show that the rather uniform Tertiary lithology seen in cores is characterized by high-frequency variability in the log data. Several thin hard streaks are identified, the largest of which coincides with a major Miocene hiatus. Associated with this hiatus is a change to lower illite content (and correspondingly lower gamma-ray counts) and to a significant increase in diatom content. Spectral analysis of the logs was performed on the lower Pliocene through upper Oligocene interval (108.0-343.0 mbsf). Between 108.0 and 245.0 mbsf, average sedimentation rates (50 and 26 m/m.y.) are high enough to show that variance is present in the orbital eccentricity (~95 k.y.) and obliquity (~41 k.y.) bands. Between 253.0 and 343.0 mbsf, the sedimentation rate (8 m/m.y.) is too low to resolve high frequency variations. The Milankovitch frequencies are best developed in the resistivity logs. Resistivity is responding to changes in porosity, which in these sediments is controlled by the abundance of biosiliceous sediments, particularly diatoms. The orbital forcing suggested by the Milankovitch frequencies may be influencing diatom productivity by inducing oscillations in upwelling, ice coverage, pack ice, and/or polynya. Although variations in diatom abundance were observed in the cores, they were not attributed to a Milankovitch signal, and therefore in this environment, downhole logs are an important contribution to the detection and understanding of orbitally influenced changes in sedimentation.

Gerald R. Ford Library Cornerstone Ceremonies

Jickling, Lyman & Powell, architects. Built 1980. On verso: Photographer's stamp; 59683

Gerald R. Ford Library Cornerstone Ceremonies

Jickling, Lyman & Powell, architects. Built 1980. On verso: Photographer's stamp; 5968-2

Gerald R. Ford Library Cornerstone Ceremonies

Jickling, Lyman & Powell, architects. Built 1980. On verso: Photographer's stamp; 5968-4