Eolian stratigraphic record of environmental change through geological time

The terrestrial sedimentary record provides a valuable archive of how ancient depositional systems responded to and recorded changes in Earth’s atmosphere, biosphere, and geosphere. However, the record of these environmental changes in eolian sedimentary successions is poorly constrained and largely unquantified. Our study presents the first global-scale, quantitative investigation of the architecture of eolian systems through geological time via analysis of 55 case studies of eolian successions. Eolian deposits accumulating (1) under greenhouse conditions, (2) in the presence of vascular plants and grasses, and (3) in rapidly subsiding basins associated with the rifting of supercontinents are represented by significantly thicker eolian dune-set, sand-sheet, and interdune architectural elements. Pre-vegetation eolian systems are also associated with more frequent interactions with non-eolian environments. The interplay of these forcings has resulted in dune-set thicknesses that tend to be smallest and largest in Proterozoic and Mesozoic successions, respectively. In the Proterozoic, the absence of sediment-binding plant roots rendered eolian deposits susceptible to post-depositional wind deflation and reworking by fluvial systems, whereby highly mobile channels reworked contiguous eolian deposits. During the Mesozoic, humid greenhouse conditions (associated with relatively elevated water tables) and high rates of basin subsidence (associated with the breakup of Pangea) favored the rapid transfer of eolian sediment beneath the erosional baseline. The common presence of vegetation promoted accumulation of stabilizing eolian systems. These factors acted to limit post-depositional reworking. Eolian sedimentary deposits record a fingerprint of major environmental changes in Earth history: climate, continental configuration, tectonics, and land-plant evolution.

Cretaceous and Cenozoic Basin Evolution Based on Decompacted Sediment Thickness from Petroleum Wells around New Zealand

<p>Decompacted sedimentary data from 33 New Zealand exploration wells is used to investigate basin evolution and tectonics from around New Zealand. This analysis is directed to both a comparison of basin behaviour and a search for common subsidence signatures. Common to almost all New Zealand basin subsidence curves is a sedimentary signature associated with rifting of the Gondwana super-continent (80-65 Ma). In the Great South Basin a second rifting event is inferred at 51 [plus or minus] 2 Ma, illustrated by a rapid increase in subsidence rates (with a maximum rate of 190 m.Myr-1 at Pakaha-1). Coinciding with the cessation of Tasman Sea rifting ([approximately] 53 Ma), and with the onset of rifting in the Emerald Basin ([approximately] 50 Ma), it is assumed that the event is related to the tectonic plate reorganization. An increase in sedimentation is noted at [approximately] 20 Ma in most South Island wells. Convergence on the Alpine Fault, leading to increased erosion is cited as a mechanism for this period of basin growth, consistent with the Cande and Stock (2004) model of plate motions. A second increase in sedimentation occurs at [approximately] 6 Ma in almost all wells around New Zealand. Climate-driven erosion resulting in isostatic uplift is thought to contribute to this event. Hiatuses in the sedimentary record for the Canterbury, Great South and Western Southland Basins during the late Oligocene are interpreted as the Marshall Paraconformity. It appears that the break in sedimentation located within a regional transgressional mega-sequence was caused by mid Oligocene glacio-eustatic fall and related oceanic current processes. Loading by the Northland Allochthon, in conjunction with paleobathymetry and subsidence data, is used to demonstrate the mechanical properties of the lithosphere. A lithospheric rigidity of 1.5 x [10 to the power of 22] Nm is estimated, with an elastic thickness of 12 km. Considerably lower than elastic thickness values previously calculated for the Plio-Pleistocene loading of the Taranaki Platform. It is noted that the Northland value represents a younger, hotter crust at the time of load emplacment. With the exception of the central Taranaki and Great South Basins, stretching factors ([Beta]) for the sedimentary basins surrounding New Zealand are below 2. This suggests crustal thickness prior to rifting was between 35 and 50 km, consistent with data from conjugate margins of Australia and Antarctica. An increase in water depth in the Taranaki Basin at 25 [plus or minus] 3 Ma is confirmed by this study. This coincides with a similar signature on the West Coast of the South Island at 26 [plus or minus] 2 Ma. It is suggested that a mantle flow caused by the initiation of the subduction zone at [approximately] 25 Ma extends over a broader region (>750 km) than previously thought.</p>

Cretaceous and Cenozoic Basin Evolution Based on Decompacted Sediment Thickness from Petroleum Wells around New Zealand

<p>Decompacted sedimentary data from 33 New Zealand exploration wells is used to investigate basin evolution and tectonics from around New Zealand. This analysis is directed to both a comparison of basin behaviour and a search for common subsidence signatures. Common to almost all New Zealand basin subsidence curves is a sedimentary signature associated with rifting of the Gondwana super-continent (80-65 Ma). In the Great South Basin a second rifting event is inferred at 51 [plus or minus] 2 Ma, illustrated by a rapid increase in subsidence rates (with a maximum rate of 190 m.Myr-1 at Pakaha-1). Coinciding with the cessation of Tasman Sea rifting ([approximately] 53 Ma), and with the onset of rifting in the Emerald Basin ([approximately] 50 Ma), it is assumed that the event is related to the tectonic plate reorganization. An increase in sedimentation is noted at [approximately] 20 Ma in most South Island wells. Convergence on the Alpine Fault, leading to increased erosion is cited as a mechanism for this period of basin growth, consistent with the Cande and Stock (2004) model of plate motions. A second increase in sedimentation occurs at [approximately] 6 Ma in almost all wells around New Zealand. Climate-driven erosion resulting in isostatic uplift is thought to contribute to this event. Hiatuses in the sedimentary record for the Canterbury, Great South and Western Southland Basins during the late Oligocene are interpreted as the Marshall Paraconformity. It appears that the break in sedimentation located within a regional transgressional mega-sequence was caused by mid Oligocene glacio-eustatic fall and related oceanic current processes. Loading by the Northland Allochthon, in conjunction with paleobathymetry and subsidence data, is used to demonstrate the mechanical properties of the lithosphere. A lithospheric rigidity of 1.5 x [10 to the power of 22] Nm is estimated, with an elastic thickness of 12 km. Considerably lower than elastic thickness values previously calculated for the Plio-Pleistocene loading of the Taranaki Platform. It is noted that the Northland value represents a younger, hotter crust at the time of load emplacment. With the exception of the central Taranaki and Great South Basins, stretching factors ([Beta]) for the sedimentary basins surrounding New Zealand are below 2. This suggests crustal thickness prior to rifting was between 35 and 50 km, consistent with data from conjugate margins of Australia and Antarctica. An increase in water depth in the Taranaki Basin at 25 [plus or minus] 3 Ma is confirmed by this study. This coincides with a similar signature on the West Coast of the South Island at 26 [plus or minus] 2 Ma. It is suggested that a mantle flow caused by the initiation of the subduction zone at [approximately] 25 Ma extends over a broader region (>750 km) than previously thought.</p>

The role of subsidence and accommodation generation in controlling the nature of the aeolian stratigraphic record

Despite a well-documented record of preserved aeolian successions from sedimentary basins characterised by widely variable subsidence rates, the relationship between aeolian architecture and subsidence-driven accommodation generation remains poorly constrained and largely unquantified. Basin subsidence as a control on aeolian sedimentary architecture is examined through analysis of 55 ancient case-studies categorised into settings of ‘slow’ (1–10 m/Myr), ‘moderate’ (10–100 m/Myr) and ‘rapid’ (>100 m/Myr) time-averaged subsidence rates. In rapidly subsiding basins, aeolian successions are thicker and associated with: (1) thicker and more laterally extensive dune-sets with increased foreset preservation; (2) greater proportions of wet-type interdunes and surface stabilization features; (3) more extensive interdune migration surfaces, bounding sets that climb more steeply. In slowly subsiding basins, aeolian successions are thinner, and associated with a greater proportion of (1) aeolian sandsheets; (2) supersurfaces indicative of deflation and bypass. Rapid subsidence promotes: (1) steeper bedform climb, resulting in increased preservation of the original dune foreset deposits; (2) relatively elevated water-tables, leading to sequestration of deposits beneath the erosional-baseline and encouraging development of stabilizing agents; both factors promote long-term preservation. Slow subsidence results in (1) lower angles-of-climb, associated with increased truncation of the original dune forms; (2) greater post-depositional reworking, where sediment is exposed above the erosional-baseline for protracted time. Quantitative analysis of sedimentary stratal architecture in relation to rates of basin subsidence helps demonstrate the mechanisms by which sedimentary successions are accumulated and preserved into the long-term stratigraphic record.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5515695

Tectonic Evolution of Southern part of the Mesopotamian Foredeep Basin

This study investigated the tectonic evolution of the southern part of the MesopotamianForedeep basin. Subsidence and sedimentation rates were calculated for six oil wellsdistributed on the tectonic subzones of the sedimentary basin through the use of restoredthickness rates according to Backstripping Method for Cretaceous and Tertiary sequences. Theconsequence of this study indicates the subsidence and sedimentation rates changing verticallyand laterally through geologic time. As shown, the sequences of Albain subcycle are widesubsidence and sedimentation rates especially for the Mauddud Formation at the Am-1wellwhich located in the eastern part of the sedimentary basin (Tigris subzone), as well as for thesequences of Cenomanian-Early Turonian subcycle especially for the Ahmadi and Mishrifformations were increase in subsidence and sedimentation rate toward (Am-2 and Mj-3) wells.Both wells located within the Tigris and the eastern part of Zubair subzone. This is inaccordance with the closure of the South Tethys Sea because of the influences of the Austrianand Subhersynian orogenies. Three unconformity surfaces determine clearly in the depositinalbasin of incompatibility during the Early Turonian, Danian and Oligocene epochs. Thoseunconformities affects all tectonic subzones except for the Am-1well where it was notinfluences by the unconformity during the Oligocene epoch. The subsidence and sedimentationprocess continued at high rates, reflecting the large thickness of the eastern part of the basin inthe Tigris subzone area. Sedimentation rates augment significantly at the well (AG-19), whichindicates the effect of faults on the Tigris subzone. This affects the degree of maturation andthe source of hydrocarbons in the sedimentary basin.

Middle and Late Devonian paleogeography of the eastern Anti-Atlas (Morocco)

The eastern Anti-Atlas of Morocco represents one of the most completely exposed and perfectly documented biostratigraphic records of the entire Devonian worldwide. Paleogeographically it is clearly differentiated into shallow basins, pelagic platforms, and land areas which are newly defined and illustrated, one from the top of the Middle Devonian, the other from the middle Famennian as two of the most characteristic intervals. The dominant paleogeographic feature is the T-shaped Tafilalt Platform which, in spite of common unconformities and hiatuses, provides the best-documented biostratigraphic record through the entire Devonian. The westernmost termination of this platform was emerged during most of the Devonian (and locally even earlier) and became only flooded again by the Tournaisian transgression. In contrast to previous interpretations, this area is considered as autochthonous. In the Mader Basin subsidence was up to one hundred times higher with respect to the adjacent platforms, but water depth during the Middle Devonian to middle Famennian interval generally remained above storm-wave base. Devonian rocks are only patchily and incompletely preserved on the Mader Platform, which can be considered as an intermittently flooded peninsula connected to the Lower Paleozoic farther west. The major paleotectonic element of the entire area is the Great Anti-Atlas Fault, a sinistral strike-slip fault, which sharply confines the above-mentioned realms in the south.

Numerical Modelling to Evaluate Sedimentation Effects on Heat Flow and Subsidence during Continental Rifting

Sedimentation impacts thermal and subsidence evolution in continental rifting. Estimating the blanketing effect of sediments is crucial to reconstructing the heat flow during rifting. The sedimentary load affects the basin subsidence rate. Numerical investigation of these effects requires active and complex simulations of the thermal structure, lithospheric stretching, and sedimentation. In this paper, we introduce a numerical model to quantify these effects, which was developed using the COMSOL Multiphysics® simulation software. Our numerical setting for the analytical and numerical solutions of thermal structure and subsidence is based on previous continental rifting studies. In our model, we accumulate a column of 5 m thick sediment layers with varied stretching factors and sedimentation rates, spanning the syn-rift to early post-rift phases over a period of 12 myr. Our results provide intuitive models to understand these sedimentation effects. The models show that an increase in sedimentation thickness significantly decreases surface heat flow, leading to lower geothermal temperature, and amplifies the subsidence magnitude. The findings also demonstrate that increases in the stretching factor and sedimentation rate enhance the blanketing effect and subsidence rate. Based on these results, we discuss key outcomes for geological applications and the possible limitations of our approach.

Microfaulting by early diagenesis of micritic continental carbonates - dilatant and compactive shear localization (Montpellier area, France)

&lt;p&gt;Microfaults formed in continental carbonates reveal poorly known mechanisms of shear localization induced by early diagenesis during compaction. These faults are characterized by sinuous shape, bed-controlled, pervasive distribution, no calcite precipitation, and mainly disaggregation processes. Two main sets were described: (1) The first set is composed by normal-sense, high-angle microfaults affecting the top of carbonate beds showing undulating pedogenic bed surface. They show porosity increase and are sometimes organized in polygonal patterns. Their occurrence seems related to overconsolidation of pedogenic surface and density inversion &amp;#8211; phreatic loading &amp;#8211; fluid expulsion processes in the surficial carbonate bed. (2) The second set is composed by low-angle compactive microfaults with large slickenlines and incipient shear-offset. Their organization within two conjugate systems (normal-sense set and strike-slip set) almost contemporaneous is consistent with a NS extension following the slope induced by the basin subsidence to the south. Their occurrence seems related to vertical loading below few meters depth and occurred by shear-enhanced compaction and incipient pressure-solution process. The presence of such structures gives news information concerning dilatant or compactive shear processes and rheological properties of micritic carbonates during early diagenesis.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;