Tectonic Subsidence Research Articles

Early development of carbonate platform (Xisha Islands) in the northern South China Sea

Sedimentological, paleontological, and geochemical data from core XK-1 on the Xisha Islands have allowed for a detailed documentation of the early carbonate development around the Oligocene-Miocene transition in the northern South China Sea (SCS). The deposits within the fore reef, reef, lagoon environments occurred before 23 Ma, the exposure horizon occurred around 23 Ma, and the sediments within the open lagoon setting dominated after 23 Ma. This evolution indicates a sedimentological response to water depth change, which is the combined result of eustatic sea-level fluctuations and tectonic subsidence. The tectonic subsidence during the latest Oligocene and Early Miocene (especially this period) was responsible for the obvious deepening trend. What's more, substantial physical erosion caused an increased amount of terrigenous input into the Xisha Islands area, with detrimental effects on carbonate development after the Oligocene-Miocene boundary. Over the entire South China Sea, the early carbonate systems along the northern and southern margins displayed specific evolution patterns. After comparing these patterns, we found a close relationship between the carbonate initiation and the subduction of the proto-SCS and the opening of the modern SCS. Therefore, it has been demonstrated that sea level and local tectonics as well as paleoclimatic conditions were the main controlling factors in shaping the onset of carbonate sedimentation in the SCS.

Valanginian cold/warm climatic oscillation and synsedimentary tectonic interaction for drowning the carbonate platform of Southern Tethys (Sicily)

Valanginian is a deeply investigated time interval due to the climatic, environmental and oceanographic changes that characterised it, globally recorded in sedimentary successions.During the Valanginian, an oscillation between warm and cold climatic phases is generally accepted as causing change in sedimentation, especially along the carbonate platform successions. In this context the so-called “Weissert event” occurred.The analysed stratigraphic interval consists of a Valanginian–Hauterivian package of two black metallic crusts (hardgrounds) and condensed pelagites, interbedded in the Lower Cretaceous carbonate shallow-water succession outcropping in the Palermo Mountains (NW Sicily). Integrating facies, structural, mineralogical and geochemical analysis, including analysis of δ13C and δ18O isotope records, the interaction between synsedimentary tectonics and climatic changes, as causing palaeoenvironmental and palaeoceanographic changes in the Lower Cretaceous Panormide carbonate platform, has been envisaged.A regional extensional tectonic event in the Southern Tethyan margin was detected at the Berriasian/Valanginian boundary, as responsible for the tectonic fragmentation of the Mesozoic Panormide carbonate platform in various fault-blocks. Locally, tectonic subsidence caused drowning of some of the fault-blocks. Before the recovery of the benthic carbonate factory in the Barremian, condensed pelagites and mineralised (Fe–Mn) crusts developed during the alternation of warm and cold climatic pulses.The positive–negative excursions of the Valanginian–Hauterivian δ13C pattern of the Colombrina section provide solid evidence for the chronostratigraphic assignment of the study interval to the drowning of many carbonate platforms that preludes the onset of the “Weissert event”. In detail, the drastic negative shift of δ13C in the late early Valanginian mineralised crust reveals massive release of isotopically light carbon to the atmosphere/hydrosphere reservoirs from a possible excess of volcanogenic CO2 or methane release from clathrate dissociation. Combining sedimentological data with the increase of the δ18O isotope records, two cold climate pulses are envisaged. The first one is assigned to the Berriasian/Valanginian boundary and led to the formation of the lower mineralised crust. The second and more evident positive shift of δ18O is assigned to the earliest late Valanginian, during the sedimentation of the laminated pelagites deposited immediately after the upper mineralisation event. These cold events that are comparable with the coeval cooling pulses recorded at a global scale highlight icehouse interludes during the Lower Cretaceous greenhouse mode.

Ombilin Basin as Inverted Oblique Rift in Barisan Mountains, Sumatra: Considerations on Subsidence Mechanisms and Fault Development

Ombilin Basin is a NW-SE inverted oblique rift which is currently being part of Barisan Mountains in western Central Sumatra. Regarding its current position, Ombilin Basin can be one of the windows to see the evolution of Barisan Mountains since Paleogene. Two schools of thought, namely rift basin and pull-apart basin, have been established to explain the evolution of Ombilin Basin. This paper aims to present another perspective on the evolution of Ombilin Basin based on subsidence mechanisms and fault development. This study integrated remote sensing and subsurface interpretations. Remote sensing interpretation took the role to delineate surface fault lineaments using digital elevation model, while subsurface interpretation dealt with log and seismic interpretations, subsidence analysis, and palinspatic reconstruction. Fault lineaments derived both from remote sensing and seismic interpretations were combined to construct structural framework of the basin. Subsidence analysis generated geohistory and backstripped tectonic subsidence charts. Palinspatic reconstruction illustrated structural configurations through time. This study figured out that Ombilin Basin went through fault-controlled subsidence in Middle Eocene – Late Oligocene and thermal subsidence in Early Miocene – Late Pliocene. Each subsidence mechanism was terminated by an uplift. Subsidence mechanisms in Ombilin Basin represented the criteria of rift basin in terms of amount and rate of tectonic subsidence, duration of subsidence, and contribution of thermal subsidence. On the other hand, fault development captures extensional and strike-slip components during rifting and development of flower structures during inversion of the basin. Oblique rifting operates when dominant extensional component works together with strike-slip component. Therefore, subsidence mechanisms and fault development are in agreement to regard Ombilin Basin as inverted oblique rift.

Geochemistry, zircon U[sbnd]Pb ages and Hf isotopes of granites and pegmatites from Gubrunde region in the Eastern Nigeria Terrane: Insight into magmatism and tectonic evolution of the late Pan-African orogeny

This study reports a new dataset of whole-rock geochemistry, biotite chemistry, in situ zircon UPb geochronology and Hf isotope for a suite of granite and associated pegmatite samples from the Gubrunde region in the Eastern Nigeria Terrane (ENT), Nigeria. The Gubrunde granitic rocks are weakly ferroan, peraluminous and calc-alkalic to alkali-calcic in composition, and show I-type affinity. The zircon UPb geochronology gives an age of ~580 Ma for the rocks, although the presence of inherited zircons with early Pan-African ages of 696 ± 12, 647 ± 7 and 624–613 Ma are evident indicative of a complex history of their source rocks. The Gubrunde granite and the pegmatite yielded similar average Hf crustal model age TDM2 of 1.9 ± 0.1 Ga and εHf(t) values −6.2 ± 1.2, suggesting that they may have sourced from reworked old crustal rocks with minor contributions from the mantle. The granite and the pegmatite were likely to connect by fractional crystallization under low to moderate pressure (~2.2 to 3.0 kbar) and temperature (~717 °C), and low oxygen fugacity (<ΔNNO −1.14). The ca. 580 Ma magmatism may have been triggered by delamination of the lithospheric mantle as a consequence of crustal thinning during waning stage of the Pan-African orogeny.

Crustal structure and upper mantle anisotropy of the Afar triple junction

The Afar region is a tectonically distinct area useful for studying continental break-up and rifting. Various conflicting models have been suggested to explain the lateral variations of the anisotropy in this region. To address this issue, we investigated the tectonics of the Afar region using receiver function and shear-wave splitting measurements based on broadband seismic data from 227 stations in the region. Further, the receiver function results were inverted to obtain the crustal thickness and Vp/Vs ratio of the region. Our results reveal a thick African crust (thicker than 40 km) with typical Vp/Vs values for the continental crust, elongated down to 21 km along the rift system with very high Vp/Vs values near the fractured zones, suggesting crustal thinning near the fractured zones. Our shear-wave splitting measurements indicate a general fast axis orientation of N030E. However, substantial disparities in the fast anisotropy direction exist in the triple junction region, with some stations displaying a direction of N120E, which is perpendicular to the fast directions measured at the surrounding stations. In addition, many stations located close to the rifts and within the Arabian Plate provide mostly null measurements, indicating the presence of fluids or isotropic media. This study uses several methodologies to unravel the structure and evolution of the Afar region, providing valuable insight into the Afar, a tectonically distinct region, which will be useful for elucidating the mechanisms and characteristics of a continental break-up and the rifting process.

Crustal structure of the East African Limpopo margin, a strike-slip rifted corridor along the continental Mozambique Coastal Plain and North Natal Valley

Abstract. Coincident wide-angle and multi-channel seismic data acquired within the scope of the PAMELA Moz3-5 project allow us to reconsider the formation mechanism of East African margins offshore of southern Mozambique. This study specifically focuses on the sedimentary and deep-crustal architecture of the Limpopo margin (LM) that fringes the eastern edge of the Mozambique’s Coastal Plain (MCP) and its offshore southern prolongation the North Natal Valley (NNV). It relies primarily on the MZ3 profile that runs obliquely from the northeastern NNV towards the Mozambique basin (MB) with additional inputs from a tectonostratigraphy analysis of industrial onshore–offshore seismic lines and nearby or crossing velocity models from companion studies. Over its entire N–S extension the LM appears segmented into (1) a western domain that shows the progressive eastward crustal thinning and termination of the MCP/NNV continental crust and its overlying pre-Neocomian volcano-sedimentary basement and (2) a central corridor of anomalous crust bounded to the east by the Mozambique fracture zone (MFZ) and the oceanic crust of the MB. A prominent basement high marks the boundary between these two domains. Its development was most probably controlled by a steep and deeply rooted fault, i.e., the Limpopo fault. We infer that strike-slip or slightly transtensional rifting occurred along the LM and was accommodated along this Limpopo fault. At depth we propose that ductile shearing was responsible for the thinning of the continental crust and an oceanward flow of lower crustal material. This process was accompanied by intense magmatism that extruded to form the volcanic basement and gave the corridor its peculiar structure and mixed nature. The whole region remained at a relative high level during the rifting period and a shallow marine environment dominated the pre-Neocomian period during the early phase of continent–ocean interaction. It is only some time after break-up in the MB and the initiation of the MFZ that decoupling occurred between the MCP/NNV and the corridor, allowing for the latter to subside and become covered by deep marine sediments. A scenario for the early evolution and formation of the LM is proposed taking into account both recent kinematic and geological constraints. It implies that no or little change in extensional direction occurred between the intra-continental rifting and subsequent phase of continent–ocean interaction.

Modification of Crust and Mantle Lithosphere Beneath the Southern Part of the Eastern North American Passive Margin

AbstractThe eastern North American passive margin was modified by Mesozoic rifting. Seismic data from recent deployment of onshore and offshore stations offer a unique opportunity for studying the signature of syn‐rifting and postrifting in lithospheric structures. Using full‐wave ambient noise tomography, we construct a new seismic velocity model for the lithosphere of the southeastern United States. Our model confirms an oceanic‐continental transitional crust over a ∼70 km wide zone across the coastline. Our model reveals (a) a patch of lower‐than‐average mantle lithospheric velocities underlying this transitional crust and (b) a low‐velocity column in the mantle lithosphere beneath the Virginia volcanoes. We propose that anomaly 1 represents cooled enriched mantle that underplated the thinning crust during the initial stages of rifting around 230 Ma. Anomaly 2 likely has a more recent origin in the Eocene and may result from an asthenospheric upwelling induced by a localized lithospheric delamination.

Paleozoic Paraná Basin transition from collisional retro-foreland to pericratonic syneclise: Implications on the geodynamic model of Gondwana proto-Andean margin

Providing significant advancements in the knowledge and development of the global plate tectonic theory, the Paraná Basin records a long period of sedimentary accumulation with evidence of substantial climatic and bio-stratigraphic changes throughout most all of the Phanerozoic. Two cycles of sedimentation are identified in the lowermost sequences (Rio Ivaí and Paraná groups), followed by a ~50 Ma gap until the deposition of the early Gondwanic cycle (Itararé Group). The literature suggests that some of those depositional cycles were influenced by episodes of terrane accretion during the amalgamation of the Gondwana Supercontinent. The paleo-topography generated by the Ocloyic orogeny (460-430 Ma) likely resulted in flexural subsidence in the lowermost stratigraphic cycles of the Paraná Basin. In response to dynamic topography, the forebulge probably shifted to a system dominated by long-wavelength propagation developed over a distance of more than 800 km, most likely due to the influence of the subducted oceanic lithosphere of Panthalassa. The presence of Ordovician sources in the pre-Carboniferous sequences supports a provenance of exhumed Famatinian magmatic arc and associated rocks given that Ordovician magmatic activity is not recorded anywhere else in the cratonic regions. Furthermore, important detrital zircon population yielding Cambrian ages, likely derived from Eastern Pampean Range. In additional, the gap between crystallization and depositional ages within the Paraná Basin supports a model that transitions from a collisional retro-foreland basin to a pericratonic syneclise after the deposition of the Paraná Group.

Seismic Constraint From Vp/Vs Ratios on the Structure and Composition Across the Continent‐Ocean Transition Zone, South China Sea

AbstractAt non‐volcanic passive continental margins, seismic techniques often failed to uniquely define the nature of crustal domains. Here, we overcome this problem by studying the structure and composition of the continent‐ocean transition (COT) in the Southwest Sub‐basin of the South China Sea, using P and S wave seismic tomography and Vp/Vs ratios, providing unique constraints on lithology. Throughout the image domain, we can rule out large areas of exhumed mantle as Vp/Vs ratios are always &lt;1.9 in the shallow basement layer. Instead, the COT is characterized by extended and fragmented continental crust, and possibly mafic aggregation at the bottom of the crust. In concert with observations from multichannel seismic reflection data, seismic velocities and Vp/Vs ratios suggest that the oldest oceanic crust was formed by starved magmatism, causing rugged basement, thin crust, nearly absent lower crust, and moderately serpentinized mantle below. Our results reveal that rifting occurred without un‐roofing continental mantle.

Lithospheric structure of the western Borborema Province from receiver functions and surface-wave dispersion: Implications for basin inversion

The Proterozoic Borborema province of NE Brazil was under extensional stresses during the Mesozoic, causing stretching and thinning of the lithosphere. During Cenozoic times, compression associated with the development of the South Atlantic and collision along the Andean front dominated throughout the Province. One of the main consequences of such compression might have been the formation of the Chapada de Araripe, an inverted rift basin located in the Western Province. We undertook a passive seismic experiment along a NS profile crossing the Borborema province and a short EW profile across the Chapada de Araripe, with the goal of providing constraints on the origin of the Chapada de Araripe. A variety of mechanisms can contribute to basin uplift, so understinding basin inversion is in turn important for understanding the tectonic evolution and geodynamics of NE Brazil. Through joint inversion of receiver functions and surface-wave dispersion, we show that the crust is typically 34–38 km thick under the western Province; in contrast, the crust is 43–46 km thick under the northern craton. No apparent crustal thinning is observed under the Araripe Basin, due to the presence of a relatively thick (10–14 km) high-velocity (4.1–4.3 km/s) lowermost crust. Our velocity models also image a drop in S-velocity (from 4.6 km/s to 4.3 km/s) at 135–145 km depth under the southern half of the profile, which we interpret as a mid-lithospheric discontinuity, and at 120–140 km depth under the Araripe Basin, likely representing the lithosphere-asthenosphere boundary. Our findings confirm the presence of thin lithosphere under the Araripe Basin - originally postulated by a collocated MT survey - that might have facilitated tectonic inversion of this basin through regional stress concentration and thermal buoyancy. These findings also suggest additional buoyancy contributed by a mafic lowermost crust right under the basin.

Repeating fast radio bursts from collapses of the crust of a strange star

SummaryStrange stars (SSs) are compact objects made of deconfined quarks. It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS. Here we suggest that the intriguing repeating fast radio bursts (FRBs) are produced by the intermittent fractional collapses of the crust of an SS induced by refilling of materials accreted from its low-mass companion. The periodic/sporadic/clustered temporal behaviors of FRBs could be well understood in our scenario. Especially, the periodicity is attributed to the modulation of accretion rate through the disk instabilities. To account for a ~16-day periodicity of the repeating FRB source of 180916.J0158+65, a Shakura-Sunyaev disk with a viscosity parameter of 0.004 and an accretion rate of 3 × 1016 g s−1 is invoked. Our scenario, if favored by future observations, will serve as indirect evidence for the strange quark matter hypothesis.

Depositional evolution of a tectonically‐confined proximal‐foredeep deep‐marine system: Miocene Serra Palazzo Formation (Southern Apennines, Italy)

The Miocene Serra Palazzo Formation (SPF) was deposited in a foredeep basin in front of the growing Southern Apennines orogenic wedge. A new detailed facies analysis, based on high‐resolution physical stratigraphy, for a 570 m‐thick interval, has been undertaken in order to reconstruct the depositional history. Two phases of development can be recognized. The older one was characterized by the sedimentation of sandy channel‐lobe transition zone (cltz) deposits with various degrees of amalgamation; roughly in the middle, a 26 m‐thick sandy megaturbidite was deposited. At this time, basin topography, including the inbound slope base and topography due to the orogen‐related flexural subsidence, caused significant flow confinement illustrated by a number of sedimentary features, such as syn‐sedimentary deformation structures, hummocky laminations, and differences in the palaeocurrent directions recorded in the same event bed. The younger phase was characterized by the sedimentation of more‐proximal amalgamated sandy channel deposits, followed upwards by an even more‐proximal sequence of thick levees with thin‐bedded and fine‐grained facies. Tectonics was one of the main controls on the stacking patterns of the submarine fans of the SPF basin. Particularly, the outward thrust migration governed the evolution from the cltz deposits to the levee deposits and it might have caused the repeated waxing‐waning flow cycles recorded in the channel deposits and the changes in bed dip angles in the levee deposits.

Geodynamic significance of a buried transient Carboniferous landscape

Abstract It is increasingly clear that present-day dynamic topography on Earth, which is generated and maintained by mantle convective processes, varies on timescales and length scales on the order of 1–10 m.y. and 103 km, respectively. A significant implication of this behavior is that Phanerozoic stratigraphic records should contain indirect evidence of these processes. Here, we describe and analyze a well-exposed example of an ancient landscape from the Grand Canyon region of western North America that appears to preserve a transient response to mantle processes. The Surprise Canyon Formation lies close to the Mississippian-Pennsylvanian boundary and crops out as a series of discontinuous lenses and patches that are interpreted as remnants of a westward-draining network of paleovalleys and paleochannels within a coastal embayment. This drainage network is incised into the marine Redwall Limestone whose irregular and karstified upper surface contains many caves and collapse structures. The Surprise Canyon Formation itself consists of coarse imbricated conglomerates, terrestrial plant impressions including Lepidodendron, and marine invertebrate fossils. It is overlain by marine, fluvial, and aeolian deposits of the Supai Group. These stratal relationships are indicative of a transient base-level fall whose amplitude and regional extent are recognized as being inconsistent with glacio-eustatic sea-level variation. We propose that this transient event is caused by emplacement and decay of a temperature anomaly within an asthenospheric channel located beneath the lithospheric plate. An analytical model is developed that accounts for the average regional uplift associated with landscape development and its rapid tectonic subsidence. This model suggests that emplacement and decay of a ~50 °C temperature anomaly within a channel that is 150 ± 50 km thick can account for the observed vertical displacements. Our results are corroborated by detrital zircon studies that support wholesale drainage reorganization at this time and by stratigraphic evidence for spatially variable regional epeirogeny. They are also consistent with an emerging understanding of the temporal and spatial evolution of the lithosphere-asthenosphere boundary.

Sedimentary evolution of distributive fluvial systems within intraplate tectonic active basins: Case study of the Early Cretaceous Araripina Formation (Araripe Basin, NE Brazil)

The Lower Cretaceous Araripina Formation records deposition in a distributive fluvial system that is a part of the post-rift sequence of the Araripe Basin, NE Brazil. Following the opening of the Brazilian Equatorial Margin, the reactivation of regional faults of the Paleoproterozoic basement resulted in tectonic subsidence and formation of a regional-scale DFS. The Araripina Formation is an up to 40-m-thick succession of rhythmically interbedded sandstone and mudstone, organized in two depositional sequences separated by a regional disconformity. We recognized and grouped nine sedimentary facies into six facies associations that we interpreted as deposits of meandering channels, ribbon channels, minor channels, floodplain, lateral and terminal splays, and distal floodplain. The lower sequence facies associations suggest deposition in the medial to distal part of a distributive fluvial system in a tectonically active, interior basin subjected to episodic flooding. The periodic inundations were responsible for activating ephemeral channels and producing sheetfloods, followed by deposition of lateral and terminal splays in distal flooded areas. Syn-sedimentary deformation structures are present in rhythmite facies (truncating surfaces, load structures, injectite and convoluted folds) in the upper part of the lower sequence. The upper sequence was formed after a period of intense tectonic activity in a large distal floodbasin dominated by suspension. The deposition culminates in an interval with pedogenetic deposits cross-cut by a regional disconformity with the upper Exu Formation. Paleocurrent data from both depositional sequences indicate paleodepositional slope towards southeast and east with source-areas located to the northwest and west. This pattern is similar to that observed in the lower Santana Group and opposite to the westward direction of sedimentary transport in the overlying Exu Formation implying significant change of source region, basin topography and continental paleodrainage in the Araripe Basin after the Albian.

Imaging Early Oceanic Crust spreading in the Equatorial Atlantic Ocean: Insights from the MAGIC wide-angle experiment

During the MAGIC (Margins of brAzil, Ghana, and Ivory Coast) experiment, five combined wide-angle, and reflection seismic profiles were acquired in the Pará-Maranhão/Barreirinhas/Ceará basins northern Brazil. This is a pull-apart passive margin, with two strike-slip borders. The equipment deployed includes 143 sea-bottom seismometers (OBS), a 4.5-km seismic streamer, and a 7587-in3 airgun array. In this paper, we focus on the distal parts of three profiles, and one entire transverse NW-SE profile, located on the presumed Cretaceous oceanic crust.Forward modelling of these wide-angle data sets reveals an E-W lateral evolution of the oceanic crust spreading initiation with: 1) just after the so-called intermediate domain, 60 km-wide domain that consists of a 5-km-thick crystalline crust. The basement presents two layers characterized by high acoustic velocity. This domain is bounded to the NW by a NW-SE volcanic line (Volcano Alignment), and 2) a 5-km-thick oceanic crust consisting of two layers characterized by “normal velocities” spanning between the two main fracture zones that fringe the Pará-Maranhão-Barreirinhas-Ceará segment. Despite a similar thickness, these two sub-domains present different velocity distribution in their two layers. They are both overlain by 5.5 km of sedimentary deposits. Forward wide-angle modelling confirms that the seafloor spreading process was progressive, with firstly the emplacement of a proto-oceanic crust, and then a thin oceanic crust. The “proto-oceanic” crust presents a similar seismic velocity with the intermediate domain interpreted as exhumed lower continental crust except for the lower part where the intruded lower crust gives place to a very sharp Moho at the base of the proto-oceanic domain. By contrast, the thin oceanic crust domain has a lower velocity structure in its upper layer, that is interpreted as basalt and is absent in the proto-oceanic crust. This eastward evolution, as also observed in the Provençal Basin, and the Santos Basin, suggests the involvement of the lower continental crust in the first steps of seafloor spreading.

Initiation of Clockwise Rotation and Eastward Transport of Southeastern Tibet Inferred from Deflected Fault Traces and GPS Observations

AbstractEastward transport and clockwise rotation of crust around the southeastern margin of the Tibetan Plateau dominates active deformation east of the Eastern Himalayan Syntaxis. Current crustal movement inferred from GPS measurements indicates ongoing distortion of the traces of the active Red River fault and the Mesozoic Yalong-Yulong-Longmen Shan thrust belt. By extrapolating current rates back in time, we infer that this pattern of deformation developed since 10.1 ± 1.5 Ma. This date of initiation is approximately synchronous with a suite of tectonic phenomena, both near and far, within the wide Eurasia/Indian collision zone, including the initiation of slip on the Ganzi-Yushu-Xianshuihe fault and crustal thinning and E-W extension by normal faulting on N-S–trending rifts in the plateau interior. Accordingly, the eastward movement of eastern Tibet and the clockwise rotation of that material seem to be local manifestations of a larger geodynamic event at ca. 10–15 Ma that changed the kinematic style and reorganized deformation not only on the plateau-wide scale, but across the entire region affected by the India/Eurasia collision. Convective removal of some or all of Tibet's mantle lithosphere seems to offer the simplest mechanism for these approximately simultaneous changes.

High-resolution late Paleozoic cyclostratigraphy and tectonic evolution of the Keeler Basin, California, southwest Laurentia

Abstract Cyclic strata exposed in the Inyo Mountains of eastern California contain a continuous 6 m.y. record of deep marine deposition that spans the Pennsylvanian–Permian boundary. To better understand the geologic evolution of southwest Laurentia and the role of glacially driven eustasy in upper Paleozoic stratigraphy, we measured two detailed ∼600 m composite stratigraphic sections of the Keeler Canyon Formation and collected a handheld spectral gamma ray log. Post-depositional deformation complicates field relationships, but 1:5000 scale mapping of faults and folds permits assembly of two continuous sections. Measured strata alternate at the 5–20 m scale between intervals of fine-grained laminated marlstone and intervals of mixed carbonate and siliciclastic turbidites and debrites. Based on facies characteristics and a prominent marker horizon, we reassign the Pennsylvanian-Permian age upper Salt Tram unit of the upper Keeler Canyon Formation to a new Estelle Member. We estimate sediment accumulation rates within the Keeler Canyon Formation using published conodont biostratigraphy and correlative U-Pb geochronology from Eastern Europe combined with spectral analysis and timescale optimization using the Astrochron R package. Evolutive harmonic analysis of gamma ray-derived element concentrations reveals prominent bundled periodicities that are consistent with both long and short eccentricity cycles. Average sediment accumulation rates calculated using the time scale optimization function of Astrochron suggest a gradual increase from 40–60 m/m.y. to ∼120 m/m.y. during the late Pennsylvanian and then a minima of ∼50 m/m.y. near the Pennsylvanian–Permian boundary, which is followed by an increase to ∼175 m/m.y. into the Early Permian. This trend in sediment accumulation rates and subsequent Permian contractile deformation are compatible with flexural subsidence in a SW-migrating foreland basin related to the southern part of the late Antler orogenic system.

Archaeological and Natural Indicators of Sea-Level and Coastal Changes: The Case Study of the Caesarea Roman Harbor

Archaeological and geomorphological features, as well as traces left by tsunamis, earthquakes, and vertical earth-crust displacements, are used to identify sea-level and coastal changes. Such features may be displaced, submerged or eroded by natural processes and human activities. Thus, identifying ancient sea levels and coastal changes associated with such processes may be controversial and often leads to misinterpretations. We exemplify the use of sediment deposits and sea-level and coastline indicators by discussing the enigmatic demise of the Roman harbor of Caesarea, one of the greatest marine constructions built in antiquity, which is still debated and not fully understood. It was suggested that the harbor destruction was mainly the result of either tectonic subsidence associated with a local, active fault line, or as a result of an earthquake/tsunami that struck the harbor. Here we examine and reassess the deterioration of the harbor in light of historical records, and geological, geomorphological and archaeological studies of natural and man-made features associated with the harbor. We show that the alleged evidence of an earthquakes or tsunami-driven damage to the outer breakwaters is equivocal. There is no supporting evidence for the assumed tectonic, active fault, nor is there a reliable historic account of such a catastrophic destruction. It is suggested that geo-technic failure of the breakwater’s foundations caused by a series of annual winter storms was the main reason for the destruction and ultimate collapse of the western basin of the harbor. The breakwaters were constructed on unconsolidated sand that was later washed away by storm waves and sea currents that frequently hit the Israeli coast and undercut the breakwaters. The pounding effect of the waves could have contributed to the destruction by scouring and liquefying the sandy seabed underlying the foundations. Tsunamis that may have hit Caesarea could have added to the deterioration of the breakwaters, but did not constitute the main cause of its destruction.

Crustal architecture, heat transfer modes and geothermal energy potentials of the Algerian Triassic provinces

The Triassic province is located within the Eastern Algerian Sahara, towards the Eastern edge of the M'zab Dorsal. Several hydrothermal reservoirs have been identified within this area along the Oued Righ valley and Rehabi-Berriane structural axis, forming an area of high temperature geothermal activity. The genetic mechanism of this geothermal system is currently unclear and needs urgent scientific reaction. In this work, we present a new conceptual model of the geothermal system in the Triassic provinces, using the structural model obtained through integrated study of recent edge detection techniques and the calculation of thermal proprieties of the middle and the lower crust. This multidisciplinary approach proposes a novel heat transfer mechanism and reservoir architecture within the province. We used spectral analysis on aeromagnetic data to determine the Curie point depth, geothermal gradient, heat flow, and radiogenic heat production. The results outlined the major structural trends within the Eastern Algerian Sahara. Deep heat flow sources were observed between 12.5 to 23 km depths and the geothermal gradient within the lower crust reaches 35 °C/km. The measurement of the thermal properties in petroleum wells indicates different thermal distributions. The delineated geothermal pattern is linked to the deformation of the Moho and the presence of deep-seated faults along the middle and lower crustal boundary. The shallow Curie point depth can be interpreted to be a result of the crustal thinning giving the high heat flow values. These results provide a physical representation of the heat transfer modes in the Oued Righ and constitute a unique continuous geothermal system within the eastern Algerian Sahara.

Permian geothermal units in the Sichuan Basin: Implications for the thermal effect of the Emeishan mantle plume

The Emeishan mantle plume is supposed to play an important role in the Permian thermal regime and source rock hydrocarbon generation evolution in the Sichuan Basin, Southwest China. In this paper, we provide new valuable insights into the spatial thermal effect of the Emeishan mantle plume to the Sichuan basin and maturity evolution of the Paleozoic source rocks. Cambrian core samples from four wells were selected for zircon fission track and zircon (U–Th)/He analysis in order to determine their thermal histories. Then the thermal histories of typical wells throughout the basin were obtained based on the above result and previous studies. According to the peak heat flow value (q), four Permian geothermal units were classified: a stratospheric heat flow unit (q ≥ 90 mW/m2), a high heat flow unit (80 ≤ q < 90 mW/m2), a medium heat flow unit (70 ≤ q < 80 mW/m2), and a normal heat flow unit (q < 70 mW/m2). The interpretation of the abnormal Permian heat flow indicates that the enormous heat flow anomalies with values of >20 mW/m2 occurred in the stratospheric and high heat flow units was mainly caused by the mantle plume, while the weak Permian thermal perturbation with heat flow anomalies of <15 mW/m2 in other two units was more likely associated with crustal thinning. The thermal effect of the Emeishan mantle plume may be contained within the stratospheric and high heat flow units. By comparing the maturation histories of the Paleozoic source rock, we identified the thermal effect on the maturity evolution. The thermal perturbation had no obvious impact on the maturity evolution of the Lower Permian and Lower Silurian Longmaxi Formation. Only the Lower Cambrian Qiongzhusi Formation within high geothermal unit suffered significant thermal effect of the mantle plume and matured rapidly during the end of the Early Permian.