Salt diapirs as an architect of Neoproterozoic stromatolite platform reefs

Halokinetic sequences in carbonate systems: An example from the Middle Albian Bakio Breccias Formation (Basque Country, Spain)

Unique outcrop exposures of two salt diapirs, a secondary salt weld, and associated syndiapiric strata in northeast Mexico offer an important perspective on salt-influenced petroleum reservoirs by allowing recognition and description of salt-related sandstone depocenters. Spectacular progressive unconformities and halokinetic sequences, coupled with laterally continuous exposures, permit accurate correlation and interpretation of syndiapiric units. Analysis of the syndiapiric Upper Cretaceous, Delgado Sandstone Member (Potrerillos Formation) delineates regional shoreline sediment dispersal locally impacted by diapiric relief and the distribution and internal character of salt diapir-proximal sandstone depocenters. Sequence-stratigraphic correlation defines striking relationships between highstand (HST) and transgressive systems tracts (TST), stratal thinning trends, and salt diapir relief. Transgressive systems tract and highstand systems tract strata show thinning and lithofacies shoaling trends toward diapirs; however, the latter is more pronounced in the HST and occurs at a greater distance from salt diapirs (within 1–2 km [0.6–1.2 mi]). Sandstone depocenters, roughly 0.5–1.0 km (0.3–0.6 mi) wide and 0.5–0.2 km (0.3–0.1 mi) thick, are present in both TST and HST strata and consist of sandier, shallower water facies. However, depocenters are better developed in TST strata as thicker stratigraphic sections on updip diapir margins. We propose that sandstone depocenters formed by preferential sediment reworking and shelf ridge development on landward diapir margins during marine transgression. Elevated diapir relief and higher subsidence rates adjacent to salt diapirs likely enhanced this process. Additionally, depocenters adjacent to El Papalote diapir are smaller and contain deeper water facies than the age-equivalent depocenters adjacent to El Gordo diapir, suggesting that it had higher, broader sea-floor relief.

Growth of a salt diapir in an anticline - A record from the Cenozoic halokinetic sequences in the Zagros Fold and Thrust Belt, Iran

Halokinetic sequences are unconformity-bound packages of thinned and folded strata adjacent to passive diapirs. Hook halokinetic sequences have narrow zones of deformation (50–200 m), >70° angular discordance, common mass-wasting deposits and abrupt facies changes. Wedge halokinetic sequences have broad zones of folding (300–1000 m), low-angle truncation and gradual facies changes. Halokinetic sequences have thicknesses and timescales equivalent to parasequence sets and stack into composite halokinetic sequences (CHS) scale-equivalent to third-order depositional cycles. Hook sequences stack into tabular CHS with sub-parallel boundaries, thin roofs and local deformation. Wedge sequences stack into tapered CHS with folded, convergent boundaries, thicker roofs and broad zones of deformation. The style is determined by the ratio of sediment-accumulation rate to diapir-rise rate: low ratios lead to tabular CHS and high ratios result in tapered CHS. Diapir-rise rate is controlled by the net differential load on deep salt and by shortening or extension. Similar styles of CHS are found in different depositional environments but the depositional response varies. CHS boundaries (unconformities) develop after prolonged periods of slow sediment accumulation and so typically fall within transgressive systems tracts in shelf settings and within highstand systems tracts in deepwater settings. Sub-aerial settings may lead to erosional unroofing of diapirs and consequent upward narrowing of halokinetic deformation zones.

The reliability of biostratigraphic correlations in neritic carbonate platforms is often questioned because the benthic fauna on which biozonation is based are particularly sensitive to environmental change. It is crucial to know whether a population change corresponds strictly to a facies change. Conversely, there arise the questions of determining how populations are renewed over time and how new species appear even if facies associations remain unchanged. This is the case with the Gavrovo-Tripolitza zone of Greece, an isolated shallow carbonate platform surrounded by two oceanic domains (Pindos-Olonos Zone and Ionian Zone). The absence or scarcity of faunas generally used in Upper Cretaceous biostratigraphy has led to the use of local biozonation instead, based on faunas endemic to Adriatico-Aegean platforms. The final two biozones based on Rhapydioninidae foraminifera are: - CsB6 (Upper Campanian-Lower Maastrichtian): the "Murciella biozone" is the total range zone of all Rhaphydionininae except for Rhapydionina liburnica; - CsB7 (Upper Maastrichtian): the total range zone of R. Liburnica. The purpose of this paper is to test the biostratigraphic value of the benthic foraminifera by comparing the distribution of the biostratigraphic limits with the distribution of time-surfaces. These time-surfaces are established from sedimentological analysis and sequences stratigraphy. The Upper Cretaceous of the Gavrovo platform is formed by stacked shallowing-upward parasequences which are usually capped by an exposure surface. Most of them were exposed in supratidal environments and dolomitized to a greater or lesser extent. Some underwent continental diagenesis as recorded by karsts, microkarsts and karstic fillings (fig. 5), root traces, alveolar-septal structures, microcodiums, pseudomicrocodiums, pedogenetic pseudomicrokarsts and continental stromatolithic laminations. Although outcrops are great distances apart and located on different structural blocks, they record a major discontinuity within the Maastrichtian. It is characterized by continental exposure, a change in the main type of parasequences, and disruption of the parasequence stacking pattern as evidenced on Fischer plots. In each outcrop, limestones exhibiting continental diagenesis are cut by an erosional surface. This surface is proposed as a local maximum of regression and a transgressive surface. On a peculiar outcrop, the surface marks the inflection point between thinning-upward and thickening-upward parasequence trends on the Fischer plot. In proximal platforms, such a point can be interpreted as corresponding to a local maximum of regression and this surface is also a transgressive surface. The same features occurred in many other outcrops and show that the entire platform was subaerially exposed. Similar episodes of exposure associated with continental diagenesis are reported for Maastrichtian deposits of other Adriatico-Aegean platforms. Continental exposure and associated erosion is currently interpreted as a result of a fall in relative sea level caused either by uplift or by eustatic sea level fall. Successive shallowing up parasequences showing final exposure and continental diagenesis would imply an impossible yo-yo type subsidence. Accordingly, the proposed maximum of regression is thought to be eustatically controlled. Moreover, the maximum of regression caps CsB6 parasequences controlled by allocyclic mechanisms as indicated by similar stacking patterns in different and remote outcrops. This strongly suggests CsB6 sedimentation was eustatically controlled and the relevant maximum of regression is proposed as a time-surface. The distribution of foraminifer populations in the outcrops studied here indicates that the Rhapydionininae of biozone CsB6 do not occur above the maximum of regression. The regressive maximum clearly coincides with the disappearance of foraminifer species whereas the subsequent transgressive episode is characterized by the emergence of just one species. And yet, population renewal is not related to a fundamental change in the platform environment: very shallow water facies association below and above the maximum regression surface are identical. This supports the hypothesis that sea level variations were the cause of faunal extinction and renewal. It is evidenced too that the boundary between the two populations can be used as a time marker. In this case study, the biostratigraphy based on the use of benthic and shallow-water dependent foraminifera is genuinely chronostratigraphic.

This study delves into the microfacies analysis and facies associations of the Khasib Formation by examining four wells in the Ad'Dimah, Gharraf, Amara, and Majnoon oilfields. All these locations are within the Mesopotamian Zone in southern Iraq. Four facies associations including six microfacies, from the deepest to the shallowest, in the studied succession were identified as, Basin Facies Association which includes the planktonic foraminiferal and calcisphere mudstone-wackest one microfacies RMF 2, Outer Ramp Facies Association is consisting of planktonic foraminiferal wackest one microfacies RMF 5 and Oligosteginal pack stone-wackest one microfacies RMF 3, Middle Ramp Facies Association is including ooidsgrainstone with densely packed concentric ooids microfacies RMF 29 and bioclasticgrainstone and packstonemicrofacies RMF 27, and finallyInner Ramp Facies Association which consists of bioclastic and foraminiferal wackestone to packstone microfacies RMF 7. Two stratigraphic sequences have significantly influenced the development of the stratigraphic column of the Khasib Formation, based on microfacies characteristics and the succession of their facies associations. The first stratigraphic sequence commenced with a transgressive phase overlying an unconformity surface SB1 with the Mishrif Formation. This phase was marked by a succession of facies associations from a restricted inner ramp environment, followed by shoal and basinal association facies (deepening upward) in the Ad'Dimah and Majnoon oil fields. However, in the Garraf and Amara oil fields, the shoal facies did not deposit during this cycle. The transgressive phase terminated with the maximum flooding surface at the end of the deep basin facies association and the onset of shoal facies deposition in all studied wells. This shoal facies was deposited during the highstand system tract (shallowing upward), marking the final stage of the first cycle. The second sequencewas began with a transgressive surface which characterized by the deposition of the outer ramp facies association, followed by the deep basin facies association (deepening upward) during the second marine transgression phase The deposition of the Khasib sequence was terminatedwith the deep basin facies and the maximum flooding surface with the Tanuma Formation, which overlies Khasib Formation in all studied oilfields.

Sequence stratigraphy and architecture of a late Early–Middle Aptian carbonate platform succession from the western Maestrat Basin (Iberian Chain, Spain)

Syn- and post sedimentation activities of the salt diapirs have dramatically affected the surrounding sedimentary successions in the SE Zagros. These episodic movements could be mainly documented by various spatial geometries and huge lateral and vertical variations in sedimentary features. The Handun diapir in the north of Bandar-Abbas as a classic example has been investigated in this study. Due to three dimensional geometry of halokinetic sequences, good evidence of rising salt and sedimentation style adjacent in the Handun diapir reveals the salt-sediment interaction. We report the growth evolution of the diapir based on field data in four domain of Handun diapir. Halokinetic growth strata (hook and wedge) developed in the Paleocene-Eocene time interval (Pabdeh and Jahrum Formations) in S domain. Passive diapirism resulted in lateral extrusion of Hormoz salt to form an allochthonous salt sheet toward SW flank and the Middle Eocene carbonate platform displays overturned flap with SW domain. In contrast, carbonate and siliciclastic form hook halokinetic sequences in NW domain. After; the Eocene- Oligocene Unconformity, halokinesis and the Neogene shortening of the Zagros led to a secondary salt weld and squeezed diapir which appeared in hook halokinetic sequences in the Oligocene to Lower Miocene Razak siliciclastic Formation and the Lower-Middle Miocene Guri carbonate member. So, our results provide new insights into using halokinetic sequences in diapiric growth analysis of the Zagros diapirs.

In this study, progradation and the subsequent retrogradation of a late Paleocene isolated carbonate platform (Galala Mountains, Eastern Desert, Egypt) is demonstrated by variations of distinct facies associations from the platform margin in the north to the hemipelagic basin in the south. A combination of a sea-level drop and tectonic uplift at around 59 Ma (calcareous nannofossil biozone NP5) favored the initiation of the carbonate platform. From this time onwards, the facies distribution along the platform–basin transect can be subdivided into five facies belts comprising nine different facies associations. Their internal relationships and specific depositional settings are strongly coupled with the Maastrichtian–Paleocene seafloor topography, which resulted from local tectonic movements. Patch reefs and reef debris were deposited at the platform margin and the horizontally bedded limestones on the upper slope. Slumps and debris flows were stored on the lower slope. In the subhorizontal toe-of-slope facies belt, mass-flow deposits pass into calciturbidites. Further southwards in the basin, only hemipelagic marls were deposited. Between 59 and 56.2 Ma (NP5–NP8), the overall carbonate platform system prograded in several pulses. Distinct changes in facies associations from 56.2 to 55.5 Ma (NP9) resulted from rotational block movements. They led to increased subsidence at the platform margin and a coeval uplift in the toe-of-slope areas. This resulted in the retrogradation of the carbonate platform. Furthermore the patch-reef and reef-debris facies associations were substituted by the larger foraminifera shoal association. The retrogradation is also documented by a significant decrease in slump and debris-flow deposits on the slope and calciturbidites at the toe of slope.

Sequence organization and growth patterns of late Mesoproterozoic stromatolite reefs: an example from the Burovaya Formation, Turukhansk Uplift, Siberia

The stratigraphy adjacent to the El Papalote diapir in the La Popa basin, northeastern Mexico, displays depositional thinning, abrupt lateral facies changes, and intense local deformation near the diapir. The strata comprise a series of halokinetic sequences that provide a means of local correlation of stratal packages in an otherwise complex patchwork of seemingly disparate facies. Halokinetic sequences are relatively conformable successions of growth strata genetically influenced by near-surface or extrusive salt movement and are locally bounded at the top and base by angular unconformities that become disconformable to conformable with increasing distance from the diapir. Halokinetic sequences differ from traditional depositional sequences in scale and mechanism of formation. Halokinetic sequences at El Papalote diapir could not be traced farther than 1 km from the diapir, whereas depositional sequences are typically basin wide. Halokinetic sequences form as the rate of net vertical diapiric rise varies relative to the local sediment-accumulation rate, whereas depositional sequences form as the accommodation rate varies relative to the regional sediment-accumulation rate. Angular unconformities form when the net diapiric-rise rate exceeds the local sediment-accumulation rate, allowing diapiric inflation at the surface to generate steep, unstable slopes along which subjacent growth strata are either truncated by attendant slope failure or by current or shoreface erosion. In the case of slope failure, the sequence-bounding unconformity is typically overlain by mass-transport deposits derived from gravitational failure of the domed salt body. Increasing the local sediment-accumulation rate relative to the net diapiric-rise rate results in diapir onlap and overlap, which suppress diapiric surface topography and erosion. Halokinetic sequences are previously unrecognized but probably common features around near-surface or extrusive salt bodies in salt basins found elsewhere in the world. Their understanding may be used to predict the geometry, distribution, and quality of reservoir facies directly adjacent to salt bodies and provide critical data to determine the complex evolution of migrating passive salt bodies.

Sequence stratigraphy from core and wireline log data: the Viking Formation, Albian, south central Alberta, Canada

The plateau of Jbel Bou Dahar (High Atlas, Morocco) represents an outstanding example of a well-preserved early Mesozoic carbonate platform. Field observations of the large-scale sedimentary structures and the arrangement of lithofacies associations within the mid- and lower slope were combined with detailed microfacies analyses and gamma-ray measurements. The investigations were carried out in order to (1) resolve the sequence stratigraphic architecture of the slope, and (2) reconstruct the sediment export patterns and depositional processes related to high-frequency sea-level variations. The slope strata are arranged into two different types of lithofacies associations that are bounded by characteristic discontinuities and show a specific occurrence along the investigated slope section. The steep (8-18°) mid-slope is dominated by thick- to medium-bedded limestone successions that were able to maintain a high angle of repose due to their detrital composition. The sediment packages are bounded by basal low-angle unconformities and wedge out within the lower slope or thin into the adjacent basin as single carbonate layers. The sediments are characterized by coarse-grained and poorly sorted floatstones to rudstones, which show low gamma-ray values and contain components derived mainly from the platform edge. The facies associations were interpreted as debris-flow deposits that were exported during sea-level lowstands when the flattened platform top and extended parts of the margin were exposed and sediment production was restricted mainly to the outer margin and upper slope section. In contrast, the gently dipping lower slope (4-18°) is characterized by rhythmic limestone-marl alternations that show increasing thicknesses with increasing distance from the platform. From the lower part of the mid-slope down, the successions onlap the debris-flow deposits, forming a characteristic interfingering pattern of different lithofacies associations. The medium- to thin-bedded carbonates of the limestone-marl alternations comprise two different microfacies types: (1) mudstones to wackestones with high gamma-ray values and a mixed shallow-marine to deep-marine microfacies, overlain by (2) well-sorted, arenitic packstones to grainstones with low gamma-ray values and a shallow-marine component composition. The latter points to the platform interior and margin as primary source areas. The shallow-marine material was exported during sea-level highstands when the carbonate factory included the entire platform margin and the flooded lagoons of the platform top. During these periods, the exported fine-grained sediments could maintain only low angles of repose. Thus they bypassed the steep upper and mid-slope sections, developed into turbidites during downslope transport, and were finally redeposited on the gently dipping lower slope and in the adjacent basin. The architecture of the investigated slope area shows a characteristic interfingering of different facies associations that can be interpreted as genetic highstand and lowstand stratigraphic sequences. The arrangement of these sequences along the slope, as well as their composition, were controlled by high-frequency sea-level fluctuations, affecting the primary sediment production (source area), export patterns, and sedimentary processes, resulting in a shift of the depositional centers during different sea-level stands.

Correlation and sequence stratigraphic interpretation of the lithostratigraphic Snake Cave Interval: Implications for hydrocarbon reservoir prospectivity between the southeast Blantyre and northwestern Neckarboo Sub-basins, Darling Basin, southeastern Australia

The Lower Cretaceous Cupido and Coahuila platforms of northeastern Mexico form part of the extensive carbonate platform system that surrounded the ancestral Gulf of Mexico. A sequence-stratigraphic model for these Barremian to Albian platforms was constructed from regional correlations of vertical cycle stacking patterns constrained by newly acquired biostratigraphic data and C and Sr isotope stratigraphy. The Cupido shelf lagoon (Barremian-Aptian) is composed of up to 150 peritidal cycles, which stack into high-frequency sequences that are correlated across the shelf. Cupido high-frequency sequences build into a lower partial composite sequence (Cu1), an overlying full composite sequence (Cu2), and the transgressive base of a third composite sequence (Cu-Co3) related to backstepping of the Cupido platform. The highstand part of Cu-Co3 is recorded in evaporite and carbonate facies of the Coahuila platform (Aptian-Albian). More than 80 meter-scale evaporite-to-carbonate cycles characterize the restricted interior of the Coahuila platform and stack into two full composite sequences (Co4, Co5). The Coahuila platform was drowned in the latest Albian or earliest Cenomanian, terminating shallow-water carbonate sedimentation in the region. Regional correlations of the depositional sequences in northeast Mexico with coeval platforms in Texas and the northern Gulf coast indicate that the lower two composite sequences of the Cupido shelf correlate with the lower part of the Sligo-Hosston platform in Texas. The transgressive systems tract of the third composite sequence of the Cupido-La Pena is recorded in Texas by the upper Sligo and Pearsall formations. The highstand systems tract and the disconformable top of the third composite sequence (Coahuila platform) is likely coeval with the upper Glen Rose platform in Texas. The fourth and fifth composite sequences are correlative with the Fredericksburg platform and the Washita-Devils River platforms of Texas, respectively. We conservatively correlated our sequence-stratigraphic framework with composite global sequences and eustatic curves derived from several other basins. Given the available time resolution, results are variable, but sequence boundaries at the top of Cu-Co3 and Co5 appear to have clear interbasinal equivalents.