Stratal Geometries Research Articles

Mississippian (Lower Carboniferous) Facies Heterogeneity and Distribution within the Mixed Carbonate-Siliciclastic Reservoirs of the Midcontinent STACK Play, Oklahoma, USA

Summary The objective of this study is to evaluate facies heterogeneity, including both lateral and vertical distributions within the mixed carbonate and siliciclastic reservoirs of the Mississippian System (Lower Carboniferous). This research and statistical approach will aid in future investigations related to determining optimal landing zones, enhancing completion designs, and providing geologic insight into fracture driven well interference studies to increase production efficiency. This study integrates well log, petrographic, sedimentologic, and conventional core analyses along a set of transects across the Anadarko Basin and includes the development of core-based facies logs. Statistical analysis indicates that the Mississippian System in the STACK play of the Anadarko Basin is fundamentally a highly layered rhythmic succession in which a variety of carbonate rock types, siliciclastic rock types, and chert tend to form couplets with siltstone. Thickness-frequency distributions and Markov chain analysis indicate that sediment thickness and lithologic transitions were stochastically regulated and that lithologic cyclicity is not apparent. Overall lithologic trends indicate a transition from carbonate to sandstone in the midramp and from carbonate to mudstone and siltstone in the outer ramp. Stratal geometry defines a series of south-prograding clinoforms, and detailed analysis of vertical trends in the distribution of mudstone, siltstone, sandstone, chert, and carbonate facilitates identification of shoaling-upward parasequences that can be correlated regionally.

Middle Miocene renewed subduction of arabian-eurasian plates: Implications for convergent tectonic mechanisms, tectonically-induced fluid overpressures, and sediment recycling dynamics

The complex interplay between thrust wedge deformation, tectonically-induced fluid overpressures, and the complex phases of wedge-top sedimentary depositional systems in active plate convergent margins presents a formidable challenge. The offshore Makran accretionary wedge (MAW) is the world's largest, formed by the convergence of Arabian plate underneath Eurasian plate in the Early Cretaceous, followed by Middle Miocene renewed subduction. In this research, geological and geophysical constraints derived from seismic and borehole stratigraphy, seismic attributes, depth structural maps, isopach maps and 3D structural geological models reveal that Middle Miocene renewed subduction controls thrust wedge deformation. Additionally, it influences deep fluid overpressure and the deformational pattern of wedge-top sedimentary depositional systems. The seismic data analysis suggested that the basement pre-kinematic Himalayan turbidities depositional system (HTDs) have been tectonically incorporated into the accretionary wedge by Middle Miocene renewed subduction, which gave rise to complex folding and N-dipping imbricate thrusting features. These N-dipping imbricate thrust faults initiated sediment underplating and served as major structural pathways for deep fluid overpressure migration, resulting in the formation of fluid escape pipes. The fluid escape pipes exhibit conical and bifurcating geometries with inclination angles of approximately 73°, 90°, and 100°, signifying the upward migration of deep overpressured fluids. Furthermore, the Middle Miocene to Pliocene syn-kinematic piggyback and growth depositional system (PGDs) show progressive thickening (Max ∼3600 m) towards onshore MAW. It lies unconformable above the pre-kinematic HTDs and carries valuable sedimentation records, growth stratal patterns, onlap terminations, and truncations against growing structures, revealed the timing and spatial deformation of thrust faults in 3D space. In contrast, the Pleistocene to Recent post-kinematic progradational depositional system (PDs) exhibits clinoforms marked by top-lapping, on-lapping, and down-lapping reflection, which are primarily controlled by sediment recycling dynamics and sea level change since Pleistocene. It shows progressive thickening (Max ∼1800m) towards the Makran subduction zone and lies unconformably above the syn-kinematic PGDs. Abridging the analyses, the tectonic reconstruction and deformation mechanisms model shows four phases, e.g. (1) initiation of subduction and accretionary wedge formation in Eocene, (2) N-dipping imbricate thrust faults and deep fluid overpressure triggered by Middle Miocene renewed subduction, (3) development of piggyback basins and growth stratal geometries in Middle Miocene to Pliocene, (4) thrust deformation ceases and development of progradational depositional system.

Tectono-stratigraphic evolution of salt-influenced normal fault systems: an example from the Coffee-Soil Fault, Danish North Sea

We explore how the relationships between fault activity, salt movement and sediment loading affect the stratal geometry of the hanging wall throughout the evolution of a salt-influenced normal fault system. We examine a c. 65 km long portion of the Coffee-Soil Fault System in the Danish North Sea, the hanging wall of which has been partially influenced by a pre-rift unit of mobile salt. To constrain the tectono-stratigraphic evolution of this fault system, we combine structural observations with seismic stratigraphic analysis of the hanging wall growth strata. We find that the hanging wall of the Coffee-Soil Fault System shows major depocentre shifts through time, along with marked variability in the along- and across-strike stratal geometries. We explain how the development of these characteristics is influenced by: (1) the segmentation and linkage history of the fault system; (2) the evolution of the salt-cored cover monoclines above blind basement fault segments; and (3) changes in the location and rate of accommodation generated by the load-driven withdrawal of salt up the dip-slope of the hanging wall and by fault-related subsidence. Our findings have implications for structural and stratigraphic studies in salt-influenced rift basins, as well as for understanding the potential distribution of geo-storage and hydrocarbon reservoirs in such settings.

Open fracture clustering: Integrating subsurface and outcrop analogues, Asmari Formation, SW Iran

Fracture networks play a significant role in controlling fluid flow in carbonate reservoirs. Here we have utilized a modern and rigorous technique known as normalized correlation count (NCC) to investigate the 1D spatial arrangement and size distribution of conductive opening-mode fractures in the Asmari Formation, a naturally fractured carbonate reservoir in the Zagros Fold and Thrust Belt. To overcome subsurface sampling limitations, here we integrate data from a subsurface fault-related fold called the Gachsaran anticline, and from adjacent outcrops. The Oligo-Miocene Asmari Formation is composed of three units with different lithology, thickness, and stratal geometry. Subsurface and outcrop data from the Asmari Formation have different patterns of spatial arrangements. While the fractures from outcrop anticlines show indistinguishable from random arrangements, the subsurface scanlines from the Gachsaran anticline have various clustering patterns, from self-organized regularly-spaced fracture clustering in the backlimb to externally-imposed clustering in the forelimb. The NW-SE striking fracture set in outcrops and subsurface show clustering. Aperture-size data for all fracture sets are best-fit by log-normal distributions, but sampling biases against the smallest apertures may obscure a power-law aperture-size distribution. Forcing the power-law fit to aperture-size distribution indicates steeper slopes in the backlimb and gentler slopes in the forelimb, which reflect lower and higher strain, respectively. This is consistent with higher tendency of clustering in the forelimb of the anticline which correlates with higher productivity index. Our results demonstrate the ability of NCC to identify hierarchical fracture clusters as well as to distinguish between self-organized and extrinsic organization. The results of quantitative analysis of fracture clustering and patterns in the Asmari Formation provides valuable insights that can aid in the refinement of Discrete Fracture Network (DFN) models and help make informed decisions regarding fractured reservoir development and production.

2-Dimensional joint inversion modelling of the Niger – Delta basement using potential field data

Sub-surficial models predict the occurrence and geometry of strata, geological structures, inclusions, tectonic settings and so on. Robust data including geologic information, airborne gravity, and magnetic data, with constraining drill–depth data are here integrated to model the topography of the basement that underlies the Niger Delta sedimentary sequence. The aim was to elucidate the existence of a petroleum system from the unexplored depths of the delta near the basement, hypothetically controlled by the basement structures. Airborne total magnetic intensity (TMI) and Bouguer gravity anomaly (BGA) of the Niger Delta, obtained from the Nigerian Geological Survey Agency that were noise–filtered and corrected are used. The gradient of the geomagnetic field was removed from the magnetic data and the data was reduced to the equator (RTE). As precursory operations, sub-surficial lineament structures were delineated from these grids using the Tilt Derivative filters, and the depths were determined using the Source Parameter Imaging (SPI) technique. Subsequently, basement topography models were generated across four (4) profiles in a gravity-magnetic joint inversion scheme. Consequently, the strata that constitute the Niger – Delta ‘cake’ from the Cretaceous to Recent were modeled. The results showed that the Late Cretaceous Synrift Clastics (LCSC) formation presumed to directly overlie the basement may vary in thickness from 2.15 to 2.74 km. The lineament structures were found to dominantly trend in NE – SW direction. The depth to the basement, from the 2-dimensional models, ranges approximately from 13.18 to 19.35 km. It is postulated that while the Tertiary Niger Delta is characterized by lineaments engendered by diapiric instability of the over–pressured Paleocene – Pliocene marine shales, there exist other lineament structures beneath with NE – SW as the dominant trends, offshoots of Mid – Atlantic fracture zones including Chain and Charcot. Basement undulations, which are relicts of the vast subsidence Passive margins undergo during their formation are observed. These resultant synclinal structures create accommodation for the extensive deposition of the LCSC. The juxtaposition of this reservoir facie, the lineament-laden undulating Passive basement escarpment, and, the Paleocene – Pliocene Marine Shale formation could make for another petroleum system.

Lower Eocene carbonate ramp clinoforms of the southern Tethys; Zagros Foreland Basin, SW Iran: Sequence stratigraphy architecture, basin physiography and carbonate factory controlling parameters

AbstractExcellent cliff exposures in the Khush‐Ab and Chenareh anticlines (Zagros Foreland Basin, SW Iran) offer a good opportunity to document stratal geometries, paleofacies heterogeneity, depositional architecture and depositional cycles of the Lower Eocene sedimentary basin system. These unique outcrops containing six logged sections have been studied across a large‐scale transect, covering ca. 10 km of continental (Kashkan Formation), carbonate‐dominated platforms (Taleh‐Zang Formation) and submarine fan to basin‐floor settings (Amiran and Pabdeh formations). Field observations of the bedding geometries revealed a set of NE–SW oriented carbonate ramp clinoforms (clinoformal units 1–4) with sigmoidal cross‐sectional shapes and an internal fore‐stepping architecture. Based on detailed facies analysis, six facies associations (FA) were identified (FA.I to FA.VI), which are interpreted to have been deposited laterally in the continental, proximal to distal and deep‐water settings of a distally steepened carbonate ramp. According to the stratal stacking pattern, bounding surface, facies architecture and internal makeup of carbonate clinoforms, four H‐F‐cycles (cycle I–IV) corresponding to a lower hierarchical rank (fourth‐order cycle) were recognized and nested within the regressive stacking pattern (HST) of a higher hierarchical rank (third‐order sequence). These H‐F‐cycles are arranged in three segments (bottomset, foreset and topset) of each clinoformal unit. Higher rank transgressive blocks (TST) discriminated each clinoformal unit by up‐deepening sets of the H‐F‐cycle V. In total, five third‐order depositional sequences were identified. The sequence, stratigraphic framework and internal makeup of this carbonate platform indicate that these carbonate sloping successions are the type of accretionary carbonate ramp clinoforms that display an ascending ramp‐slope break trajectory. Evolutionary episodes of biogenic communities, climatic change, local tectonic movements, physical processes (e.g. waves and storms) and water depth gradient are major forcing parameters that controlled the carbonate factory and depositional geometry of this Lower Eocene succession; however, carbonate‐producing organisms and eustatic sea‐level fluctuations played the first role, and local tectonic movements in response to tectonic activities of the Zagros Foreland Basin played the second role. As a result, Taleh‐Zang carbonate platforms are rich in diverse assemblages of LBFs without fragments of coral and red algae, which appear to be a consequence of a hothouse state that diminishes the global thermal gradient, weakens pycnoclines and thereby limits the turbulence.

UNLOCKING THE ARCHITECTURE OF THE COLONIZATION WINDOW: ICHNOFABRICS FROM UPPER CRETACEOUS TIDE-INFLUENCED MEANDER-LOOP DEPOSITS

ABSTRACT Studies dealing with the colonization window typically emphasize two major features: duration (short term vs. long term) and frequency of colonization (episodic vs. continuous). However, our understanding of tide-influenced meander loops requires consideration of an additional feature, the architecture of the colonization window, which comprises not only the spatial dimension and geometry of the colonization surface, but also its evolution through time. Tide-influenced meander-loop systems show a heterogeneous trace-fossil distribution that reflects the variety of processes operating along the point-bar and overbank colonization surfaces. Ichnofabric analysis of tide-influenced meander-loop deposits from the Upper Cretaceous Tremp Formation (Pyrenees, Spain) provides valuable insights into the sedimentary and ichnological dynamics of these marginal-marine systems and allows the importance of stratal geometry controlling the colonization window to be evaluated. Six ichnofabrics are identified in point bars and associated overbank deposits. These ichnofabrics differ in bioturbation index (e.g., higher in the upper part than the lower-middle parts of point bars), preservation of primary sedimentary fabric (typically preserved in the lower-middle parts of point bars), inferred behavior and trophic types (e.g., dominance of dwelling or feeding structures in the lower-middle and upper parts of point bars, respectively), and other features such as depth of penetration, ichnotaxonomic composition, presence or absence of root trace fossils and/or mottling, or number of superimposed suites. The key environmental factor controlling the nature and distribution of ichnofabrics is the morphology of the point-bar lateral-accretion surfaces and their evolution through time. The architecture of the colonization window is here linked to the helicoidal flow and discharge changes in meandering channels, and the successive development of lateral accretion units with time.

Barform deposits of the Carolyn Shoemaker formation, Gale crater, Mars

ABSTRACT The early environmental history of Mars is encoded in the planet's record of sedimentary rocks. Since 2012, the Curiosity rover has been ascending Mount Sharp, Gale crater's central mound, making detailed observations of sedimentary strata exposed there. The primary depositional setting represented by the rocks examined thus far has been a perennial lake, represented by the mudstones and sandstone lenses of the Murray formation. Here, we report on the sedimentology of outcrops examined in the Carolyn Shoemaker formation, which sits stratigraphically above the Murray formation. We interpret strata exposed in the Glasgow and Mercou members of the Carolyn Shoemaker formation to represent river bars in ancient alluvial and shoreline settings based on sedimentary structures, stratal geometries measured from photogrammetric data, and erosional morphology. The transition from a lacustrine to a fluvial depositional setting records the aggradation and progradation of coastal rivers into what was previously the extent of the Gale lake system. This may have occurred due to the shrinking of the lake over time due to climate-driven changes in the basin water balance, or local three-dimensionality in shoreline evolution, such as the formation of a new sedimentary lobe following a channel switch.

Identification of Quaternary alluvial-fan deposits (Rügen, SW Baltic Sea): Significance for recognition of syn-kinematic sedimentation in glacitectonic complexes

We present a detailed study of an alluvial fan accumulated in a piggyback basin syn-kinematically to the emergence of a Weichselian glacitectonic complex (Jasmund peninsula, SW Baltic Sea). Although sediments formed contemporaneously with glacitectonic events have already been documented, a systematic approach is missing so far. Facies, architecture and distribution of alluvial-fan deposits are identified here as key features for analyzing glacitectonic complexes.The deposition of those syn-kinematic deposits was controlled by the progradation of thrust-faults and the resulting morphologic changes of both the thrust-bounded ridges and the adjacent piggyback basins. Another controlling factor is the episodic high runoff of meltwater discharge (glacial lake outburst flood, jökulhlaup) from lakes near the ice front. Sheetflood and debris-flow processes dominated the sedimentation and gave way to alluvial-fan, fan-delta and glacifluvial deposits. A stepwise rotation of the depositional plain within the piggyback basin is indicated by internal unconformities and the distinct converging stratal geometry. Based on three luminescence ages the development of the syn-kinematic alluvial-fan sequence and consequently of the glacitectonic complex took place between 21 and 19 ka during a late Weichselian readvance of the Scandinavian Ice Sheet. The overall results are summarized in a seven-stage genetic model, beginning with the initial glacitectonic phase and ending with the overfilled piggyback basin and subsequent overriding of the structure by the glacier front. With the presented criteria, the successive growth of the alluvial-fan deposits can be linked directly with the emergence of a glacitectonic complex formed during an ice advance.

Two-dimensional model of flow and transport in porous media: Linking heterogeneous anisotropy with stratal patterns in meandering tidal channel deposits of the Venice Lagoon (Italy)

Understanding the internal structure of permeable and impermeable sediments (e.g. point-bars and tidal-flat deposits) generated by the evolution of meandering tidal channels is essential for accurate modeling of groundwater flow and contaminant transport in coastal areas. The detailed reconstruction of stratal geometry and hydraulic properties from measurements must be accompanied by depositional history information. In this work, we use high resolution reconstructions of ancient tidal channels of the Venice Lagoon (Italy) to drive 2D simulations of groundwater flow and transport, showing the importance of incorporating information on the sediment accumulation processes into the hydraulic characteristics and how horizontal anisotropy emerging from these processes significantly influences transport. Effective hydraulic conductivity is modeled with a heterogeneous 2D anisotropic tensor with principal directions aligned with observed sedimentation sequences. Comparison of flow and solute dynamics simulated using reconstructed and theoretical hydraulic properties show drastically different pathways of solute propagation.

Stratigraphic relationships of the Eocene Duchesne River Formation and Oligocene Bishop Conglomerate, northeastern Utah—pulsed sedimentary response to rollback of the subducted Farallon slab

The Uinta Mountains are an east-west-trending, reverse fault-bounded, basement-cored Laramide uplift. The Eocene Duchesne River Formation and Oligocene Bishop Conglomerate represent late stage, intermontane basin fill of the Uinta Basin in northeastern Utah. Detailed mapping (1:24,000 scale), clast counts in conglomerate beds, description of lithology and stratigraphic contacts, and radiometric dating of pyroclastic fall beds of the Duchesne River Formation and Bishop Conglomerate in the Vernal NW quadrangle in northeastern Utah reveal stratal geometries of middle Cenozoic depositional units, the uplift and unroofing history of the eastern Uinta Mountains, and give evidence for the pulsed termination of Laramide uplift related to rollback of the Farallon slab and lithospheric delamination. These relationships show the continuation of Laramide uplift in this region until after 37.9 Ma and before 34 Ma, an age younger than the previously reported 45 to 40 Ma. The Duchesne River Formation consists of four members: the Brennan Basin, Dry Gulch Creek, Lapoint, and the Starr Flat. A normal unroofing signal is found within the formation with a downward increase in Paleozoic clasts and an upward increase in Proterozoic clasts. The oldest member, the Brennan Basin Member contains 80% to 90% Paleozoic clasts and less than 20% Proterozoic clasts. Conglomerate beds in the progressively younger Dry Gulch Creek, Lapoint, and Starr Flat Members of the Duchesne River Formation show significant increases in Proterozoic clasts (34% to 73%) and a decrease in Paleozoic clasts (27% to 66%). The Bishop Conglomerate overlies the Duchesne River Formation, but shows no clear change in clast composition. In the Duchesne River Formation, the proportion of beds containing fine gravel to boulder-sized clasts decreases significantly with distance from the Uinta uplift, from almost 100% near the source (<0.5 km) to 50% to 20% to the south (10 km). The lower part of the Duchesne River Formation exhibits a fining upward sequence that may represent a lull in tectonic uplift. The fine-grained lithofacies of the Dry Gulch Creek and Lapoint Members of the Duchesne River Formation pinch out within about 1 to 2 km from the Uinta uplift. In this proximal region conglomerates equivalent in age to the Lapoint Member cannot be separated from the younger conglomerates of the Starr Flat Member and are mapped together as one unit. Where the fine-grained lithologies appear farther from the uplift, the Starr Flat Member conglomerates deposited above Lapoint Member siltstones represent a southward progradation of alluvial fans away from the uplifting mountain front. The Starr Flat Member is overlain by the Bishop Conglomerate. These units are similar in sedimentary structure and clast composition and are distinguished by an angular unconformity that developed after 37.9 Ma. Stratigraphic and structural relationships between the Duchesne River Formation and Bishop Conglomerate reveal evidence of at least three episodes of Laramide-age uplift of the Uinta Mountains during the deposition of these formations: (1) deposition of fining upward sequences beginning with a basal coarse-grained unit within the Brennan Basin, Dry Gulch Creek, and Lapoint Members; (2) progradation of alluvial fans to the south form the younger Starr Flat Member resulted from an increase in sediment supply likely associated with renewed uplift; and (3) tilting and truncation of Duchesne River Formation to form the Gilbert Peak erosional surface, and prograding alluvial fans of the Bishop Conglomerate. These episodes of pulsed uplift are possibly the result of dripping lithosphere that occurred during Farallon slab rollback. New 40Ar/39Ar ages of 39.4 Ma from ash beds in the Dry Gulch Creek and Lapoint Members emplaced from Farallon rollback volcanism help to constrain the timing of deposition and uplift. These new ages and other existing radiometric and faunal ages suggest a significant unconformity of as much as 4 m.y. between the Duchesne River Formation and the overlying Bishop Conglomerate, which rangesfrom 34 to 30 Ma in age and show that Laramide uplift continued after 40 Ma in this region.

The sedimentology and depositional environments of the Bastians Dal and Muslingebjerg formations: evidence for the earliest phases of Jurassic rifting in North-East Greenland

The aim of this study is to elucidate the character of the earliest phases of Jurassic rifting in North-East Greenland. To achieve this, detailed sedimentological analysis and geological mapping were undertaken on the outcrops of central Kuhn Ø (74°53’55’’N,20°20’56”W). In this region the basement is overlain by the fluvial Bastians Dal Formation (Middle Jurassic) which is, in turn, overlain by the coal-bearing Muslingebjerg Formation. A maximum thickness of 140 m is calculated for the Bastians Dal Formation and mapping of stratal geometries demonstrates thinning to both the north and south, confirming that these deposits infill a palaeovalley. Predominantly south-westward palaeocurrent orientations are observed and likely reflect the orientation of the palaeovalley (NE–SW). The overlying Muslingebjerg Formation displays significant lateral variations in thickness as well as facies, thickening from a 5-m-thick coal seam in the north to 50 m in the south. Southern outcrops include two intervals of fine-grained sandstones displaying low-angle and trough cross-bedding some of which contain suggestions of tidal bundling. The arrangement of facies suggests that coal formation occurred in both fluvial- and shallow-marine (tidal?) environments. Coals are similar to those described elsewhere from the Muslingebjerg Formation and display subtle differences consistent with variable degrees of marine influence. Mapping demonstrates the presence of an NE–SW-oriented bounding fault in the south of the region into which the Muslingebjerg Formation thickens. This likely also controlled the orientation of the underlying NE–SW-aligned palaeovalley and is oblique to the proposed overall N–S orientation of faulting related to rifting through the Mid to Late Jurassic. Instead, these alignments resemble those that define pre-Jurassic phases of rifting and may therefore indicate a transitional phase of tectonism. Faulting on a similar alignment can be traced SW, cutting Lindeman Fjord and following the valleys east of the A. P. Olsen Land plateau.

Burial and Exhumation of Sedimentary Rocks Revealed by the Base Stimson Erosional Unconformity, Gale Crater, Mars

AbstractSedimentary rocks record the ancient climate of Mars through changes between subaqueous and eolian depositional environments, recognized by their stratal geometries and suites of sedimentary structures. Orbiter‐ and rover‐image‐based geologic mapping show a dynamic evolution of the 5‐km‐thick sedimentary sequence exposed along the flanks of Aeolis Mons (informally, Mt. Sharp) in Gale crater, Mars, by deposition of subaqueous strata followed by exhumation via eolian erosion and then deposition of overlying, onlapping strata of inferred eolian origin. This interpretation suggests that a significant unconformity should occur at the base of the onlapping strata, thus predicting lateral variations in elevation along the contact between the underlying Mt. Sharp group and overlying Stimson formation. Curiosity rover and high‐resolution orbital image data quantify paleotopographic variability associated with the contact; ∼140 m of net elevation change and a slope closely aligned with the modern topography is expressed along the regional contact. These results support the interpretation of an erosional unconformity between these strata and that it was likely formed as a result of eolian erosion within the crater, indicative of a transition from wet to dry climate and providing insight into the stratigraphic context, geologic history, and habitability within Gale crater.

Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System

Abstract The Keweenaw fault system along Lake Superior’s south shore in Michigan, USA is one of the most significant fault systems associated with North America’s Midcontinent Rift System. Reverse slip has thrust Portage Lake Volcanics (ca. 1.1 Ga) southeastward over Jacobsville Sandstone (ca. 1.0 Ga). Growing consensus in the 1970s about a major rift beneath Lake Superior led to the idea that reverse movement on the Keweenaw fault involved inversion of a rift-bounding normal fault. To test this idea, we integrated bedrock geology maps, subsurface mining data, and geophysical data to build a wellconstrained cross-section from the Minnesota, USA-Ontario, Canada border to central Upper Michigan. The cross-section shows the Keweenaw and Hancock faults to be parts of a reverse, listric system detached deep within the layered volcanic section. Correlation of offshore seismic units with onshore stratigraphic units defines a gradual change in stratal dip from 55° NW near the faults to horizontal near the center of Lake Superior. This stratal geometry implies that onshore listric fault geometry continues offshore and that the fault system soles into a basal detachment at 12–15 km depth. Absence of second-order folds northwest of the peninsula indicates that the fault system does not ramp downward from the basal detachment through the lower crust. The observations and model preclude ideas that the Keweenaw fault was a rift-bounding normal fault inverted by post-rift crustal shortening, or that it formed by upward propagation of a deeper normal fault undergoing inversion. Instead, our results imply that the fault initiated as a detached thrust in relatively brittle upper crust and that shortening of relatively ductile lower crust occurred on other structures.

Terrace Morpho-Sedimentary Sequences on the Sibari Plain (Calabria, Southern Italy): Implication for Sea Level and Tectonic Controls

The Sibari Plain (northeastern Calabria) shows a well-developed stair of late Quaternary marine/coastal terraces resulting from the interaction between sea level fluctuations and tectonic uplift. This paper (i) provides a stratigraphic description of terraced deposits between the Raganello and Coscile rivers, (ii) assesses the relative controls of eustacy and uplift on the staircase formation, and (iii) unravels the Quaternary morphosedimentary evolution of the study area. A geomorphological approach was coupled with stratigraphic field surveys. Photo interpretation, topographic map analyses, and field surveys allowed us to map ten orders of terraces forming telescopically incised valley-fills. Based on the uppermost position of foreshore deposits on inner margins and an average uplift rate of ~1 mm/y, inferred from the Marine Isotope Stage (MIS) 5.5, terraces were correlated with highstands. Sedimentological and stratigraphic analyses allowed us to recognize four assemblages of genetically associated sedimentary facies related to superimposed and juxtaposed coastal and alluvial systems, showing a seaward-stepping architecture. Based on stratal geometry and facies association, we argue that alluvial/fluvial sediments and coastal depositional systems formed contemporaneously along the same terrace. Terrace arrangement resulted from repeated cycles of valley incision (sea level fall) and aggradational to progradational stacking pattern (sea level rise and highstands) in a framework of sustained uplift.

Stratigraphic variability of Upper Holocene marginal marine sediments along the Al Qahmah Coast of Red Sea, Saudi Arabia

The stratigraphic architecture of Upper Holocene sediments along the coast of Al Qahmah in southern Red Sea, Saudi Arabia, provides a high-resolution analog of marginal marine carbonate and siliciclastic sedimentation under variable climatic, tectonic, and sea-level conditions. The sediments include a basal shallow marine limestone and overlying beach, deltaic, fluvial, eolian, and sabkha siliciclastic deposits, comprising four stratigraphic units ranging from 10s to 100 s cm thick. A lithostratigraphy is established using subsurface stratigraphic and petrographic data from 64 trenches and three shallow refraction seismic sections. A chronostratigraphy is established using four age points and sedimentation rates. The entire interval has been deposited in the last ~4000 years. Significant stratigraphic variability is reflected by vertical and lateral changes in the thickness, type, and stratal geometry of the four units. Five major geological events are interpreted: Initial shallow marine carbonate deposition during a relative sea-level highstand was terminated by seaward progradation of deltaic-beach sediments during a slow shoreline regression. This is followed by a major stream channel incision during the maximum regression and a relative sea-level fall. The ensuing fluvial channel filling, transgressive ravinement, and deposition of beach sediments signify a relative sea-level rise. Finally, eolian, sabkha, and beach sediments have been deposited in a stabilized and diversified environmental setting under an arid climate. The lacuna associated with stream erosion and transgressive ravinement is up to ~400 years long, resulting in a stratigraphic completeness of ~88%. The sedimentation rate of the siliciclastic sediments is ~0.1 cm/year estimated at a scale of 1000s of years. Episodic syn-depositional faulting in the source area and depositional site, relative seal-level change, autogenic environmental shift, and/or climatic changes between humid and arid conditions have collectively played variable roles in the formation of the stratigraphic variability. The interpreted tectonic, relative sea-level, and climatic trends offer an important data point for future studies in the Red Sea region and beyond for the Late Holocene.

Early deformation structures connected to the progradation of a carbonate platform: The case of the Nuvolau Cassian platform (Dolomites - Italy)

Among the several Triassic carbonate platforms of the Dolomites, the high and vertical cliff of the Gusela del Nuvolau Cassian carbonate platform provides one of the best exposures of a platform - basin transition. However, its analysis using traditional filed surveys can often be limited and distorted due to the difficult and often impossible accessibility of its walls and the lack of optimal observation points. For this reason, in this study an analysis based on the Digital Outcrop Model (DOM) developed by Uncrafted Aerial Vehicle (UAV) digital photogrammetry technique was used. The 3D DOM analysis allowed to properly determine the stratal geometry and the fracture network of the carbonate platform and underlying basinal deposits (San Cassiano Formation) and to identify the presence of early deformation structures. These structures were probably driven by the differential compaction of the basinal facies that is due the differential load of the carbonate platform as confirmed by the numerical 2D models. These structures are generally orthogonal to the NE progradation direction of the carbonate platform, as in the nearby Lastoni di Formin platform.

Sequence stratigraphic reconstruction of the late Middle Devonian Geneseo Formation of NY, USA: Developing a genetic model for “Upper Devonian” unconventional targets in the Northern Appalachian Basin

The late Middle Devonian Geneseo Formation and its lateral equivalents in the northern Appalachian Basin are significant secondary targets to the extensively explored Marcellus Sub-group. Surface to sub-surface characterization of the mudstone-dominated Geneseo Formation combines detailed observations of facies, facies associations, stratal architecture, stratal geometry, and stratal terminations, in combination with geochemical proxies to assess proximal to distal trends and enable prediction of hydrocarbon play element quality and distribution. Correlations within this mudstone-rich succession are conducted at the parasequence-scale, and incorporate detailed descriptions of four drill cores, >100 outcrops, and mapping of >500 wireline logs.The Geneseo Formation herein has been subdivided into two depositional sequences comprising three lithostratigraphic units (i.e., Lower Geneseo, Fir Tree, and Upper Geneseo members respectively). The Lower and Upper Geneseo members show systematic aggradational to progradational parasequence stacking patterns, as well as downlap‒onlap stratal terminations with underlying strata; these members represent highstand systems tracts. The Fir Tree Member occurs between the Lower and Upper Geneseo members, truncates the underlying Lower Geneseo, shows progradational‒aggradational‒retrogradational parasequence stacking patterns, and spans two systems tracts: lowstand and transgressive.Isopach maps were constructed within the high-resolution sequence-stratigraphic framework to better understand thickness trends at the landing-zone scale. Thickness variation across the basin suggests reactivation of basement structures and syndepositional faulting strongly influenced accommodation. Specifically, the N–S trending Clarendon-Linden Fault System appears to have been a western sediment barrier during Geneseo time and the primary depocenter of fine-grained clastics occurs in south-central NY in a structural low. As the Geneseo system advanced, the succession sequentially filled topographic lows from east to west (proximal to distal). Understanding the controls on reservoir quality and distribution of secondary and tertiary targets to the Marcellus can facilitate ranking and prioritization of landing-zones, as well as optimization of well placement for completion design.

Changes in Coral Skeleton Growth Recorded by Density Band Stratigraphy, Crystalline Structure, and Hiatuses

Next-generation high resolution brightfield microscopy, x-radiography, and microcomputed tomography (microCT) analyses indicate that coral skeleton high density band (HDB) and low density band (LDB) stratigraphic sequences record dynamic changes in coral growth history. HDB-LDB sequences were studied within three small heads of Orbicella annularis, an ecological keystone species in the Caribbean Sea, collected from the leeward fringing reefs on Curaçao. Results indicate that HDB layers are formed by the thickening of exothecal and endothecal dissepiments, costae, and theca located at the margin and external to individual skeletal cups (corallites). Conversely, septa and columellas located inside individual corallites do not change in thickness. HDB-LDB stratigraphic sequences were laterally traced from the center to the margins of individual coral heads, demonstrating that shifts took place in the trajectory of coral skeleton growth. Normal HDB layers in the center of individual coral heads are formed at the same time (age-equivalent) as surfaces of erosion and no skeleton growth (hiatuses) on the margins of the heads. These hiatus surfaces within HDB-LDB stratal geometries indicate that multiple marine ecological and environmental processes affect the orientation, size, shape, and geometry of coral skeletons during coral growth history. The presence of these hiatus surfaces in other large coral heads would strongly impact sclerochronology and the interpretation of multiple environmental factors including sea surface temperature (SST).

Forward Modelling for Structural Stratigraphic Analysis, Offshore Sureste Basin, Mexico

The stratal architecture of deep-water minibasins is dominantly controlled by the interplay of two factors, structure growth and sediment supply. In this paper we explore the utility of a reduced-complexity, fast computational method (Onlapse-2D) to simulate stratal geometry, using a process of iteration to match the model output to available subsurface control (well logs and 3D seismic data). This approach was used to model the Miocene sediments in two intersecting lines of section in a complex mini-basin in the deep-water Campeche Basin, offshore Mexico. A good first-pass match between model output and geological observations was obtained, allowing us to identify and separate the effects of two distinct phases of compressional folding and a longer-lasting episode of salt withdrawal/diapirism, and to determine the timing of these events. This modelling provides an indication of the relative contribution of background sedimentation (pelagic and hemipelagic) vs. sediment-gravity-flow deposition (e.g. turbidites) within each layer of the model. The inferred timing of the compressional events derived from the model is consistent with other geological observations within the basin. The process of iteration towards a best-fit model leaves significant but local residual mismatches at several levels in the stratigraphy; these correspond to surfaces with anomalous negative (erosional) or positive (constructive depositional) palaeotopography. We label these mismatch surfaces “informative discrepancies” because the magnitude of the mismatch allows us to estimate the geometry and magnitude of the local seafloor topography. Reduced-complexity simulation is shown to be a useful and effective approach, which, when combined with an existing seismic interpretation, provides insight into the geometry and timing of controlling processes, indicates the nature of the sediments (background vs. sediment-gravity-flow) and aids in the identification of key erosional or constructional surfaces within the stratigraphy.