3D Geometry of the Chelungpu Thrust System in Central Taiwan: Its Implications for Active Tectonics

This study is aimed at constructing a 3D subsurface geometry of the Chelungpu thrust and its associated structures, as well as examining the implications of the studies results for active tectonics in the area. Nine balanced cross-sections were constructed across the foothills belt in the study area to delineate the subsurface geometry of the major thrusts in the foreland of the fold-and-thrust belt

The Tiehchanshan structure of NW Taiwan: A potential geological reservoir for CO2 sequestration

The Tiehchanshan structure is the largest gas-field in the outer foothills of northwestern Taiwan and has been regarded as the best site for CO2 sequestration. This study used a grid of seismic sections and wellbore data to establish a new 3-D geometry of subsurface structure, which was combined with lithofacies characters of the target reservoir rock, the Yutengping Sandstone, to build a geological model for CO2 sequestration. On the surface, the Tiehchanshan structure is characterized by two segmented anticlines offset by a tear fault. The subsurface geometry of the Tiehchanshan structure is, however, composed of two thrust-related anticlines with opposite vergence and laterally increasing fold symmetry toward each other. The folds are softly linked via the transfer zone in the subsurface, implying that the suspected tear fault in the surface transfer zone may not exist in the subsurface. The Yutengping Sandstone is composed of several sandstone units characterized by coarsening-upward cycles. The sandstone member can be further divided into four well-defined sandstone layers, separated by laterally continuous shale layers. In view of the structural and stratigraphic characteristics, the optimum area for CO2 injection and storage is in the structurally high in the northern part of the Tiehchanshan structure. The integrity of the closure and the overlying seal are not disrupted by the pre-orogenic high-angle faults. On the other hand, a thick continuous shale layer within the Yutengping Sandstone isolates the topmost sandy layer from the underlying ones and gives another important factor to the CO2 injection simulation

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Late Paleozoic synorogenic stratigraphy, tectonic evolution, and flexural modeling of the Permian Basin, West Texas and New Mexico

Vita.The Permian Basin of west Texas and southern New Mexico is located in the foreland of the Marathon-Ouachita orogenic belt. This complex foreland area consists of several sub-basins that are separated by intraforeland uplifts. This study focused on the kinematic history of the Central Basin Platform (CBP), subsidence and stratigraphy of the sub-basins; and the effect of tectonic load from the intraforeland uplifts on the subsidence in the sub-basins. Uplift of the CBP is best explained by clockwise rotation of these blocks. The rotation model explains: (1) the steeply dipping thrust faults at the SW and NE corners and local normal faults at NW corners of individual crustal blocks that comprise the CBP; (2) the large structural relief observed at the SW and NE corners of individual blocks; and (3) decreasing amounts of basement shortening away from thrust-faulted corners. The variable platform-to-basin relief that was produced during uplift of the CBP resulted in very different patterns of stratigraphic onlap during late Pennsylvanian to early Permian time. Patterns of intraforeland deformation could have dramatically affected basin stratigraphy during both syn- and post-orogenic stages of basin development. In this study, the CBP was treated as a topographic load that produced lithospheric flexure of the adjacent basinal areas. Results from flexural analyses compare well with reconstructed synorogenic geometries of the adjacent basins, indicating that subsidence of these basins most likely was produced by the combined topographic loads of the Marathon orogenic belt, the CBP, and probably structures associated with the uplifts surrounding the Permian Basin. Values for the flexural rigidity of lithosphere in the Permian Basin region are lowest near a prominent salient in the Marathon orogenic belt and the SW corner of the CBP, where the amount of basement shortening is greatest along the boundaries of the CBP. These low calculated rigidities reflect locally weaker lithosphere that might be related to inherent lateral strength variations in the Marathon foreland. Alternatively, high bending stresses produced in front of the prominent salient of the Marathon orogenic belt may also have weakened the lithosphere in this area

Late Paleozoic synorogenic stratigraphy, tectonic evolution, and flexural modeling of the Permian Basin, West Texas and New Mexico

Vita.The Permian Basin of west Texas and southern New Mexico is located in the foreland of the Marathon-Ouachita orogenic belt. This complex foreland area consists of several sub-basins that are separated by intraforeland uplifts. This study focused on the kinematic history of the Central Basin Platform (CBP), subsidence and stratigraphy of the sub-basins; and the effect of tectonic load from the intraforeland uplifts on the subsidence in the sub-basins. Uplift of the CBP is best explained by clockwise rotation of these blocks. The rotation model explains: (1) the steeply dipping thrust faults at the SW and NE corners and local normal faults at NW corners of individual crustal blocks that comprise the CBP; (2) the large structural relief observed at the SW and NE corners of individual blocks; and (3) decreasing amounts of basement shortening away from thrust-faulted corners. The variable platform-to-basin relief that was produced during uplift of the CBP resulted in very different patterns of stratigraphic onlap during late Pennsylvanian to early Permian time. Patterns of intraforeland deformation could have dramatically affected basin stratigraphy during both syn- and post-orogenic stages of basin development. In this study, the CBP was treated as a topographic load that produced lithospheric flexure of the adjacent basinal areas. Results from flexural analyses compare well with reconstructed synorogenic geometries of the adjacent basins, indicating that subsidence of these basins most likely was produced by the combined topographic loads of the Marathon orogenic belt, the CBP, and probably structures associated with the uplifts surrounding the Permian Basin. Values for the flexural rigidity of lithosphere in the Permian Basin region are lowest near a prominent salient in the Marathon orogenic belt and the SW corner of the CBP, where the amount of basement shortening is greatest along the boundaries of the CBP. These low calculated rigidities reflect locally weaker lithosphere that might be related to inherent lateral strength variations in the Marathon foreland. Alternatively, high bending stresses produced in front of the prominent salient of the Marathon orogenic belt may also have weakened the lithosphere in this area

Tiechanshan-Tunghsiao anticline earthquake analysis: Implications for northwestern Taiwan potential carbon dioxide storage site seismic hazard

We analyze the seismicity and earthquake focal mechanisms beneath the Tiechanshan-Tunghsiao (TCS-TH) anticline over the last two decades for seismic hazard evaluation of a potential carbon dioxide storage site in northwestern Taiwan. Seismicity in the TCS-TH anticline indicates both spatial and temporal clustering at a depth range of 7 - 12 km. Thirteen 3.0 ≤ ML ≤ 5.2 earthquake focal mechanisms show a combination of thrust, strike-slip, and normal faulting mechanisms under the TCS-TH anticline. A 1992 ML 5.2 earthquake with a focal depth of ~10 km, the largest event ever recorded beneath the TCS-TH anticline during the last two decades, has a normal fault mechanism with the T-axis trending NNE-SSW and nodal planes oriented NNW-SSE, dipping either gently to the NNE or steeply to the SSW. Thrust fault mechanisms that occurred with mostly E-W or NWW-SEE striking P-axes and strike-slip faulting events indicate NWW-SEE striking P-axes and NNE-SSW trending T-axes, which are consistent with the regional plate convergence direction. For the strike-slip faulting events, if we take the N-S or NNW-SSE striking nodal planes as the fault planes, the strike-slip faults are sinistral motions and correspond to the Tapingting fault, which is a strike-slip fault reactivated from the inherited normal fault and intersects the Tiechanshan and Tunghsiao anticlines

Patterns and Sizes of Authigenic Carbonate Formation in the Pliocene Foreland in Southwestern Taiwan: Implications of an Ancient Methane Seep

Several dolomitic authigenic carbonate concretions (ACCs) are preserved in the Pliocene foreland sequence in southwestern Taiwan. Carbon isotopic signatures and the morphology of these carbonates and associated chemosymbiotic bivalve fossils reveal their methane seep origin. There are three types of ACCs: (1) massive brecciated blocks (MBBs; £_13C = -49.57 ~ -38.20‰; £_18O = 1.59 ~ 4.25‰); (2) giant chimneys (GCs; £_13C = -43.14 ~ -17.73‰; £_18O = -7.64 ~ 3.36‰); and (3) slender pipe networks (SPNs; £_13C = -43.51 ~ 5.91‰; £_18O = -6.90 ~ -3.57‰). Different shapes, sizes, stratigraphic positions, and carbon isotopic compositions are due to different flux/intensities and flow pattern of discharging methane. MBBs were derived from diffusion of methane and formed in deeper positions, whereas GCs mark the locations of feeder faults and main outlets of methane emission. SPNs formed along fractures or bedding planes; they were (1) accessories of MBBs and GCs, or (2) products of minor releases of residual geofluids. We compared ACCs of the Chiahsien Paleoseep to two previously studied cold seep carbonates within the same foredeep in southwestern Taiwan, which represent similar occurrences and stable carbon isotopic compositions. However, the older ACCs in the Chiahsien Paleoseep have undergone longer diagenesis and weathering processes and have more complicated and lower £_18O signatures. These asynchronous cold seep carbonates can indicate hydrocarbon migrations and fault activities within the orogenic belt of Taiwan

A Study of Complex Substructures in a Foothill Belt of Northwestern Taiwan Using Two-Dimensional Gravity Multiple-Source Model Inversion

The goal of this paper is to improve the capability of gravity inversion assessment of complex structures using a multiple-source model as indicated by a study of a foothill belt of north western Taiwan. In this study, a gravity inversion computer program is applied based on research developed by Tsai, which contains a Marquardt inversion algorithm for mathematical calculations and incorporates constraints on geological parameters. The computed and modified geological parameters are transformed into coordinates. The response of a proper geological model is calculated using the Talwani technique

Calcareous and agglutinated foraminifera ratio: Chemical interface tracer for Pliocene Chiahsien paleoseep, SW Taiwan

Cold-seep carbonate concretions were preserved in the Chiahsien paleoseep remnant within the Pliocene Yenshuiken Formation of southwestern Taiwan foreland sequence. Compared to the non-seep controls in the Yenshuiken Formation, muddy host rocks that were 30 cm away from such ACCs have normal marine assemblages (low agglutinated foraminifera percentages, 80 cm away from the chimneys have normal assemblages. Host rocks between pipe-shaped ACCs have similar characteristics to mudstone samples from control sites. Low percentages of calcareous foraminiferal fossils in the paleoseep remnant are due to pore water acidification within the taphonomically active zone (TAZ), which is triggered and accelerated by oxidation of sulfide [HS-, the product of anaerobic oxidation of methane (AOM)] in the methane seep environments. We suggest that foraminiferal assemblages can be influenced by methane seep activities taphonomically and that, therefore, ratios between calcareous and agglutinated foraminifera can reflect and record geochemical interface [e.g., TAZ; sulfate-methane interface (SMI) where AOM occurs] shifts on a subtler scale (only few decimeters) in paleoseep remnants