Controls on sediment distribution in a volcanically-affected basin: insights from the Ethiopian Flood Basalt Province

This study provides a comprehensive examination of the Oligocene–Miocene Ethiopian Flood Basalt Province (EFBP) within the Blue Nile (Abay) Basin (BNB), Ethiopia. Extensive logging through 29 new sections has enabled an updated stratigraphic account of the BNB to be elucidated and reveals the significance of intravolcanic sedimentary systems within the EFBP. Five sub- and intra-volcanic surfaces were modelled using spot heights to generate isopach maps that were used to constrain the thickness variations within the stratigraphy. Additionally, lineaments, Strahler stream segments and volcanic cones were mapped out from digital elevation models (SRTM DEM) and satellite data (ASTER and LANDSAT 8 imagery). These data were used in conjunction with the isopach maps to better understand the basinal controls on the distribution of intravolcanic sedimentary systems within the BNB. The study reveals how NNE and ESE/SE structural trends have influenced the distribution of volcanoes within the basin, which has in turn disrupted the distribution and lithofacies architecture of the volcanic sequences. The presence of intrabasinal ridges parallel to the major structural trends are also revealed, which formed relatively short-lived drainage divides. The implications of these intrabasinal highs on the composition and the reservoir potential of intravolcanic sedimentary successions are discussed.

Sedimentology, petrography, and deposition of the Upper Cretaceous Codell Sandstone in the Denver Basin

We integrate new and previous stratigraphic and petrographic data for the mid-Turonian Codell Sandstone to interpret its provenance, depositional characteristics, and environments. Our focus is on sedimentologic, X-ray diffraction, and X-ray fluorescence analyses of cores and thin sections spread throughout the Denver Basin, augmented by interpretation and correlation of well logs, isopach maps, outcrops, and provenance data. Although we treat the Codell as a single mappable unit, it actually consists of two geographically disjunct sandstone packages separated by a southwest-northeast-trending gap, the NoCoZo, short for No Codell Zone. The Codell is everywhere capped by a significant unconformity and across much of the northern Denver Basin rests unconformably on the underlying shales of the Carlile Shale. In the southern Denver Basin, the Codell commonly contains two parasequences, each of which becomes less muddy upward. Biostratigraphic and geochonologic data suggest that the unit represents deposition over a relatively brief time, spanning ~0.4 Ma from ~91.7 to ~91.3 Ma. The Codell is predominantly a thin (<50 ft) sheet-like package of pervasively bioturbated coarse siltstone and very fine-grained sandstone dominated by quartz and chert grains 50 to 100 μm in diameter. The unit is more phosphatic than the underlying members of the Carlile Shale, and its grain size coarsens to medium-grained in the northern part of the basin. An unusual aspect of the Codell across our study area is the generally excellent grain sorting despite the presence of an intermixed clay matrix. This duality of well sorted grains in a detrital clay matrix is due to the bioturbation that dominates the unit. Such burrowing created a textural inversion that obscures most of the unit’s primary sedimentary structures, except for thin intervals dominated by interlaminated silty shale and very fine sandstone. A relatively widespread and unburrowed example of this bedded facies is preserved in a thin (<10 ft) interval that extends across most of the northern Denver Basin where it is informally called the middle Codell bedded to laminated lithofacies. Sparse beds with hummocky or swaley cross-stratified and ripple cross-laminated fine-grained sandstone are present locally in this bedded facies. We hypothesize that Codell sediments were derived from a major deltaic source extending into the Western Interior Seaway from northwestern Wyoming, and that the Codell was deposited and reworked southward on the relatively flat floor of the Seaway by waxing and waning shelf currents as well as storms and waves. Codell sediments were spread across an area of more than 100,000 mi2 in this epeiric shelf system that spans eastern Colorado, southeastern Wyoming, western Kansas, parts of Nebraska and beyond.

Echofacies interpretation of Pleistocene to Holocene contourites on the Demerara Plateau and abyssal plain

Off French Guiana and Suriname, North Atlantic Deep Water and Antarctic Bottom Water oceanic currents contour the Demerara marginal plateau, which promotes the formation of contourites. We have studied these contourites thanks to a new compilation of high-resolution subbottom profiles calibrated by sedimentary cores. The echofacies and isopach maps that we constructed highlight a sedimentary distribution parallel to the isobaths. The presence of moats along the slope is confirmed by the observation of parallel, elongated, sedimentary depleted zones and echofacies strongly affected by diffraction hyperbola and transparent echofacies. We interpret these features to be related to eroded slopes and mass-transport deposits. In contrast, the sedimentary drifts that we mapped are characterized by elongated and thick slope-parallel depocenters displaying bedded echofacies with wave-like bedforms. According to our interpretation, they result from interactions between the currents and the seafloor. Seismic wipeouts frequently affect those drifts, possibly resulting from high water or organic contents.

Three-dimensional geometry and growth of salt-detached strike-slip faults, Outer Kwanza Basin, offshore Angola

&lt;p&gt;Strike slip faults are a prominent tectonic feature in Earth to accommodate horizontal and/or oblique slip that trend parallel to fault strike. These faults are commonly formed on plate boundaries setting, where they are basement-involved and driven by elastic crustal loading at seismogenic depths. Still, we also observe the strike slip faults on salt-bearing slopes, where the faults are typically thin-skinned and accommodate spatial variability in the rate of seaward flow of salt and its overburden. In both cases, relatively little is still known of their three-dimensional geometry and growth in comparison to both normal and reverse fault, that have been extensively studied.&lt;/p&gt;&lt;p&gt;We use a high-quality, depth-migrated 3D seismic dataset to investigate salt-detached strike-slip faults in the mid-slope translational domain of the Outer Kwanza Basin, offshore Angola. We show that NE-SW-striking faults are presently located above elongate, margin-parallel, NE-trending ramps, more amorphous, dome-like structural highs, and areas of relatively subdued relief. The faults are broadly planar, display normal and/or reverse offsets, and may locally bound negative flower structures. These faults offset a range of salt and overburden structures, including salt walls and anticlines, and salt -detached thrusts and normal faults, defining six major structural compartments. Our displacement-distance (Tx) analysis of several faults reveal they are characterized by complex throw distributions that define 3-to-10, now hard-linked segments. In vertical profiles, these segments are characterized by symmetric-to-asymmetric throw distributions (Tz) that record throw maxima at the top of the Albian, Eocene and/or Early Miocene. Expansion indices (EI) and isopach maps demonstrate the presence of fault-related growth strata, with complex thickness patterns also reflecting the combined effect of vertical (i.e. diapirism) and horizontal (i.e. translation) salt tectonics. &amp;#160;Taken together, our observations suggest the salt detached strike-slip faults evolved during three key phases: (i) Albian &amp;#8211; nucleation and local linkage of individual segments; (ii) Eocene-to-Oligocene &amp;#8211; reactivation, propagation, and death of many now-linked segments; and (iii) Miocene &amp;#8211; local fault reactivation due to salt diapirism. &amp;#160;&lt;/p&gt;&lt;p&gt;We show that salt detached strike-slip faults in the translational domain of the Outer Kwanza Basin grew above either rugose or relatively flat base-salt surface. More specifically, salt detached strike-slip faults, like normal and reverse faults documented elsewhere, grew in response to the propagation and eventual linkage of initially isolated segments. We also highlight that the coeval growth of salt walls can play a role in controlling the three-dimensional geometry and kinematics of salt detached strike-slip faults.&lt;/p&gt;

2D Seismic Interpretation of the Meyal Area, Northern Potwar Deform Zone, Potwar Basin, Pakistan

Meyal Field is considered as one of the chief hydrocarbon producing fields in the Potwar Basin, Pakistan. The present research emphasize on the subsurface structures affecting the Mesozoic-Cenozoic successions exclusively foremost reservoir units comprising the Eocene Chor Gali and Sakesar formations. Data from six seismic lines and three wells (aligned with those lines) have been deliberated comprehensively with remarkable and tremendous calibration. Five prominent and imperative reflectors specifically the Permian, Triassic, Jurassic, Paleocene and Eocene successions were interpreted through seismic tactics. Time structure maps were equipped on the basis of two-way travel time (TWT) of the seismic line. Likewise, four isopach maps portrayed the thickness discrepancy of prospective hydrocarbon strata. Structurally, analytical section reveals that the Meyal anticline is a plunging and faulted anticline. The pop-up structure is constrained by back-thrust from the north and fore-thrust from the south, on the dip lines. These maps depicted potential reservoir, demarcate promising site for future hydrocarbon exploration.

GEOLOGY AND PETROLEUM POTENTIAL OF NOVY PORT FIELD ON THE RESULTS OF THE INTERPRETATION OF 2D SEISMIC AND DEEP DRILLING

The objective of this study was to build a set of structural and isopach maps of seismic sequences, seismic-geological sections, paleo-sections and correlation schemes; structural-tectonic and paleotectonic analysis of Novy Port shaft; to study the influence of tectonic processes and lithological factors on the oil and gas content of Jurassic and Cretaceous sedimentary sequences. It was concluded that the formation of the structural trap of Novy Port field began in Berrias-Aptian, the most intensive growth of the structure occurs in the post-Turonian time due to the upward movement of the basement block.

Low Net: Gross Reservoirs of the Transgressive Shelf Systems in the Upper Mancos Shale, El Vado Sandstone, San Juan Basin, New Mexico

The El Vado (EV) Sandstone Member (upper Coniacian) of the Mancos Shale has been considered both a conventional and unconventional hydrocarbon resource target (Ridgley, 2001) in the San Juan Basin (SJB) of northwestern New Mexico. Sandstones of the EV were deposited on the marine intracontinental shelf along the west margin of the Cretaceous Seaway. The EV is part of a transgressive-regressive wedge of rock that overlies a large, older transgressive wedge that contains the Tocito Sandstone. The EV is examined in outcrops in the northeast and the southeast parts of the SJB. In northern outcrops, the EV consists of five parasequences of interbedded sands and shales of similar thickness (∼4 m each) separated by marine-shale units that become progressively sandier upward. To the south, the EV Sandstone transitions from a shelf-deposited into a lower-shoreface sandstone. Well logs and core are used to map the subsurface distribution of the EV Sandstone in the SJB. It is reflected in logs as a thick (∼36.6 m; 120 ft) interval of low gamma ray and high resistivity, associated with highly laminated sand to silt interbedded with shales. A total of 13 cross sections are correlated and used to construct total-interval isopach and parasequence-scale isopach maps for the EV. Regional net-sand and net:gross maps, determined from 104 digitized well logs, highlight the regional distribution of sand in the formation. Thicks are oriented north to south and show compensated deposition suggesting that individual parasequences are not in communication across the basin, but opportunity exists to penetrate stacked parasequences with single vertical wells.