Mineral lithotype identification on the andrill AND-2A drillcore, antarctica by using ternary mineral rock physics templates built from a self-consistent approach

Abstract

In this work, wet bulk density ?WBD and compressional wave velocity VP core log data obtained along the AND-2A drillcore are plotted on density-velocity ternary mineral Rock Physics Templates (RPTs) built from a Self-Consistent (SC) micromechanics modelling with the purpose to deter- mine data trends that allow us to assist in identifying mineral lithotypes and lithological features throughout the 1138 m length of the drillcore. The elastic properties of the three dominant miner- als present in the drillcore (mixed clays, quartz, and calcite) and the pore-filling fluid (brine) were used as input data for the SC model. The interpreted lithology is then compared to that obtained from the analysis of the AND-2A drillcore ?WBD and VP log data using Gardner type density-velocity cross plots. Results from both the SC and Gardner methods are in good agreement with the main lithologies present in the AND-2A drillcore already reported in the scientific literature. Our findings also agree well when compared to the lithological description of six selected rock samples obtained at different depths on the AND-2A drillcore. These results suggest that the proposed SC approach could be helpful to assist to identify lithology in scientific drill holes where downhole elastic proper- ties may exist over intervals where portions of the drillcore were not recovered. Furthermore, even when elastic property data sets come from measurements on cores, the SC approach is likewise useful because, from visual analysis alone, lithology can sometimes be difficult to determine, and additional information from the analysis of the elastic properties may provide more insight.

Identification of lithological characteristics on glacial sediments using a micromechanics approach

“…Conversely, our interpretation of Gardner's relationship is supported by the distribution of mineral lithotypes shown by the RPTs over the AND-2A drillcore. Additionally, these findings are in line with the primary lithological characteristics listed by Fielding et al [8]. Also, exist a direct relationship between the lithological features of the six chosen samples and the predicted mineral lithotypes.…”

“…The qualitative X-ray diffraction (XRD) study (see Table 4) performed on these samples reveals that the feldspars, mica, carbonates, calcium minerals, clay minerals, and carbonates are their primary constituent minerals. We can see from Tables 2 and 3 that the six chosen samples and the described lithology in Fielding et al [8] are in agreement with the lithology identified by the Gardner and SC approaches. As a result, LSU 2, LSU 3, and LSU 4 are all composed primarily of siliceous rocks rich in clay.…”

“…On the other hand, the siliceous lithotype is connected to siliceous rocks, primarily conglomerate, sandstone, and diamictite. Results in Figure 3 are displayed in Table 2 along with the primary lithological features that match the LSUs described by Fielding et al [8]. Note that, these LSUs span over fourteen different depth intervals [mbsf] on the AND-2A.…”

“…Six chosen samples recovered from the AND-2A are shown in thin slices and pictures in Figures 4 and 5. These samples were selected as being typical of the fine to coarse grain sizes identified through the three geological stages of the AND-2A Drillcore: the lower Miocene (1138.54 to 800 mbsf), the middle Miocene (800 to 223 mbsf), and the upper Miocene (223 to 0.0 mbsf) [8]. They are branded according to the depth [mbsf] at which are situated.…”

“…The Southern McMurdo Sound Project (SMS), an Antarctic drilling project, collected the AND-2A drillcore [5]. The drilling began over an 8.5-meter-thick sea ice podium while submerged in a 380-meter seawater pillar, and it was completed 1138 meters below the sea bottom [8][mbsf] .…”