Second-order Depositional Sequences Research Articles

High resolution stratigraphy of channelized deposits on a continental slope setting with sea-floor topography controlled by halokinetics, uppermost cretaceous, Espírito Santo offshore basin, Brazil

All published chronostratigraphic charts of the Espírito Santo basin, Brazil, show stratigraphic frameworks based on second-order depositional sequences. The absence of published high-resolution biostratigraphic analyses precludes the proposition of a higher order stratigraphic framework. This work breaks down the second-order depositional sequences, from Campanian to Maastrichtian succession in the drift phase of Espírito Santo offshore basin, in three third-order depositional sequences based upon seismic interpretation of a hierarchical scheme of channel on continental slope setting coupled with a correlation to a global sea-level curve. The resolution of the 2D seismic data analyzed allowed the identification of three levels of erosional surfaces and their subsequent filling, from smaller to higher: composite channels, channel complexes and channel complexes set. Channel complexes development is related to lowstand deposits on the continental slope. Also, the aspect ratio of the channel complexes analyzed are reverse to the expected for channel development on continental slope settings. Usually, the further down-dip the channels are located, the higher their aspect ratio, however, it does not happen in the study case. Most of down-dip channels show a lower aspect ratio. It is ascribed to the control of the seafloor topography by the halokinetics. The identification of the geometric pattern of the channels on seismic data allowed a proposition of an exportable depositional model to predict possible sandy deposits on the continental slope regarding the intensity of salt tectonics.

Sequence stratigraphy of the Raha Formation, Bakr Oil Field, Gulf of Suez, Egypt: Insights from electrical well log and palynological data

The current paper provides a high resolution sequence stratigraphic study of the Raha Formation from the productive Bakr Oil Field, central Gulf of Suez, Egypt. Sixty cutting rock samples spanning the Cenomanian from three wells (Bakr-114, B-115 and B-109) in the Bakr Basin, were palynologically investigated. The documented palynomorphs assemblage of either terrestrially-derived sporomorphs or marine inhabited dinocysts, allowed two palynological zones as well as their encompassing depositional palaeoenvironment to be recognized. These zones are Afropollis jardinus–Crybelosporites pannuceus Assemblage Zone (early-middle Cenomanian) and Classopollis brasiliensis-Tricolpites sagax Assemblage Zone (late Cenomanian). Detailed analysis of the particulate organic matter compositions suggested that the depositional palaeoenvironment of the Raha Formation was fluctuating between supratidal and distal-inner neritic conditions, due to successive oscillations of the Neo-Tethyan Ocean during the Cenomanian.The pronounced peaks of particulate organic matter versus gamma ray are markedly used in delineating the depositional sequences of the Raha Formation and their bounding surfaces. The Raha Formation probably corresponds to a second-order depositional sequence, which can be further subdivided into eight third-order depositional sequences, of which six are complete and two are incomplete ones. These depositional sequences are significantly synchronized based on a simple 2-D correlation model between the three wells. According to the hierarchical duration system, the Cenomanian herein was approximately attributed to 6 Myr, each of which has lower order depositional sequences that took approximately 0.9 Myr. Based on the sequence stratigraphic approach together with palynofacies analysis and gamma ray data, a condensed section was defined in the B-115.

General characteristics of quartz arenite types and their role in the recognition of sequence stratigraphic boundaries in ancient coastal and near shore sediments. A case study from Egypt and Saudi Arabia

Quartz arenites are useful in the recognition of depositional sequences and cycle boundaries in ancient coastal and near shore facies. In this study two types of quartz arenite are recognized: 1) depositional quartz arenite (calcareous, dolomitic, ferruginous and kaolinitic quartz arenites), and 2) diagenetic quartz arenite (orthoquartzite, siliceous quartz arenite, compact quartz arenite, and dedolomitic quartz arenite). Depositional quartz arenite often occurs on the tops (upper boundaries) of the depositional sequences that are bounded by sequence boundaries (with or without evidence of subaerial exposure) or correlative conformity surfaces that mark the change from forced regression to lowstand normal regression. Therefore, depositional quartz arenite can define the upper boundaries of third and fourth-order depositional sequences, cycle bases and tops (boundaries) within lowstand, transgressive and highstand systems tracts. Diagenetic quartz arenite (orthoquartzite, siliceous quartz arenite and dedolomitic quartz arenite) usually occurs at the tops (upper boundaries) of depositional sequences that have subaerial sequence boundary and have been subjected to prolonged subaerial weathering and hence is closely associated with subaerial unconformity sequence boundary surfaces and consequently indicates a sharp drop in sea level. Thus, diagenetic quartz arenite types can be used to recognize the tops (upper boundaries) of first and second-order depositional sequences. Compact quartz arenite that is considered the fourth type of diagenetic quartz arenite consists entirely of packed quartz grains, but lacking cement, occurs at the base of each fining-upward cycle (lower boundaries) in lowstand systems tracts and may define the bases of some different-order depositional sequences.

Geological and Petrophysical Characterization of the Lower Senonian Matulla Formation in Southern and Central Gulf of Suez, Egypt

The Lower Senonian Matulla Formation is well developed in the southern and central Gulf of Suez. It can be subdivided into three depositional units (M1–M3). An obvious unconformity separated the middle unit (M2) from the upper unit (M3). The three units are corresponding to a second-order depositional sequence. This sequence consists of two systems tracts; the lower lowstand systems tract consists of slope fan, followed by a prograding complex. An erosion surface separated the lower from the upper transgressive systems tract. The Matulla Formation is mostly composed of sandstones and pelagic sediment intercalations. Such intercalations show obvious facies change throughout the study area, causing further subdivision of the Matulla Formation into seven rock types (RT1–RT7). The petrophysical reservoir evaluation has been achieved via determination of the effective porosity, permeability, shale content, water saturation and net-pay thickness from the environmentally corrected well log data. It indicates that the Matulla Formation can be considered as a good reservoir quality especially in its lower unit and sometimes in its middle unit as well. The available core data indicate a lithological heterogeneity of the studied Matulla Formation. Lithologically, it can be subdivided into four petrophysical and lithological facies; namely, they are sandstones, ferruginous sandstones, argillaceous sandstones and limestones. The best petrophysical properties were assigned for the ferruginous sandstones with good to excellent porosity, very good to excellent permeability, and poor to fair flow zone indicator.

Depositional environments and sequence architecture of the Raha and Abu Qada formations (Cenomanian–Turonian), west central Sinai, Egypt

Cenomanian–Turonian deposits are important reservoirs for many oil fields in the Western Desert and the Gulf of Suez region of Egypt. Study of the Raha and Abu Qada formations (Cenomanian–Turonian), from five dip-oriented outcrop locations in west central Sinai; indicates deposition of a mixed siliciclastic-carbonate system on a ramp setting. The inner ramp facies (bivalve and benthonic foraminiferal wackestone) grades northward to the mid ramp facies (echinoderm calcisphere packstone, and oyster floatstone), and outer ramp facies (planktonic foraminiferal wackestone and calcisphere wackestone).The two studied formations comprise one second-order depositional sequence (duration of approximately 10 Million years). This large scale sequence includes four third-order depositional sequences, three of which are observed in the Raha Formation, with the other one recorded in the Abu Qada Formation. Because west central Sinai was tectonically stable during the Cenomanian and Turonian, the main factor controlling the lateral and vertical distribution of facies tracts is likely due to changes in the relative sea level. The Cenomanian–Turonian boundary event is known as the largest oceanic anoxic event during the Cretaceous. This global event has been documented in three of the studied sections. The recorded δ13C excursions range from+3.04‰ to+5.24‰. These high positive excursions in δ13C are associated with highly negative values of δ18O (values range from −6.01‰ to −1.38‰).

Combined stratigraphic and isotopic studies of Triassic strata, Cuyo Basin, Argentine Precordillera

Research Article| September 01, 2006 Combined stratigraphic and isotopic studies of Triassic strata, Cuyo Basin, Argentine Precordillera J. N. Ávila; J. N. Ávila 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil Search for other works by this author on: GSW Google Scholar F. Chemale, Jr.; F. Chemale, Jr. 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil Search for other works by this author on: GSW Google Scholar G. Mallmann; G. Mallmann 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil Search for other works by this author on: GSW Google Scholar K. Kawashita; K. Kawashita 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil Search for other works by this author on: GSW Google Scholar R. A. Armstrong R. A. Armstrong 2Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information J. N. Ávila 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil F. Chemale, Jr. 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil G. Mallmann 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil K. Kawashita 1Laboratório de Geologia Isotópica, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501–970, Brazil R. A. Armstrong 2Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Publisher: Geological Society of America Received: 30 Aug 2005 Revision Received: 13 Feb 2006 Accepted: 03 Mar 2006 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2006) 118 (9-10): 1088–1098. https://doi.org/10.1130/B25893.1 Article history Received: 30 Aug 2005 Revision Received: 13 Feb 2006 Accepted: 03 Mar 2006 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. N. Ávila, F. Chemale, G. Mallmann, K. Kawashita, R. A. Armstrong; Combined stratigraphic and isotopic studies of Triassic strata, Cuyo Basin, Argentine Precordillera. GSA Bulletin 2006;; 118 (9-10): 1088–1098. doi: https://doi.org/10.1130/B25893.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The evolution of the Triassic–Cretaceous Cuyo Basin, located in the Andean Precordillera (NW Argentina), was mainly controlled by extensional–transtensional tectonics along NW-trending structures inherited from Paleozoic sutures. Stratigraphic and isotopic studies are herein presented in order to constrain the sedimentary infilling and source areas, as well as the age of Triassic strata related to the active faulted margin of the Cacheuta sub-basin. The whole stratigraphic package of the Cuyo Basin is interpreted as a second-order depositional sequence, comprising lowstand (alluvial fan deposits), transgressive (fluvial-deltaic and lacustrine deposits), and high-stand (oxidized lacustrine and high-sinuosity fluvial deposits) systems tracts. This stacking pattern was mainly controlled by the interplay between sedimentary influx and accommodation space, with important volcaniclastic contribution, especially during the early stages of basin development. Sm-Nd depleted-mantle model ages (TDM) for both basement and volcano-sedimentary samples range from 867 to 1345 Ma. All samples have negative ϵNd (t) values (−0.33 to −5.02). Basal deposits present older TDM model ages compared to intermediate-positioned deposits, and upper deposits present a wider range of model ages. This time-integrated factor correlates with paleo-current data, which indicate changes in the source areas through time. The Nd isotopic signature also suggests that sources of sediments for the Cacheuta sub-basin during the Triassic were restricted to units of Mesoproterozoic (Grenvillian) age, probably related to the Cuyania terrane. The U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon age of 243 ± 5 Ma, obtained in juvenile magmatic zircons from a lithoclast-free ignimbrite interlayered within the basal alluvial fan facies of the Cacheuta sub-basin, places the lowstand deposits in the Olenekian and establishes a potential chronostratigraphic horizon for future correlations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lower Cretaceous carbonate platform of the eastern Levant (Galilee and the Golan Heights): stratigraphy and second-order sea-level change

The marine succession of the late Early Cretaceous carbonate platform of the eastern Levant was located at the southern border of the Tethyan Ocean. The studied areas of Galilee and the Golan Heights represent a transect across the shallow inner platform. The investigations were focused on carbonate platform biostratigraphy and facies analysis. A precise stratigraphic interpretation of the Upper Barremian–Albian succession was compiled on the basis of the definition of larger benthic foraminifer biozones allowing subdivision of the succession into six well-dated intervals. Detailed analyses of facies and sedimentological parameters allow interpretation of platform development, in connection with platform geometry, as well as relative third-order and second-order sea-level changes. The observed facies patterns reflect a depositional geometry changing from a ramp to a flat-topped platform during Late Barremian–Middle Albian times. Three second-order depositional sequences were recorded in the studied mid-Cretaceous succession of the eastern Levant (MCEL-1 to MCEL-3). The facies analysis clearly indicates their origin in relative sea-level variations. The stratigraphic framework allows biochronostratigraphic calibration of these depositional sequences (MCEL-1: Upper Barremian–Lower Aptian, MCEL-2: uppermost Lower Aptian–middle Upper Aptian, MCEL-3: middle Upper Aptian–Middle Albian) and correlation with stratigraphic charts of local and regional sequences. The second-order sequence boundaries and maximum flooding surfaces correlate with basic sea-level variations recorded on the Arabian Plate, here interpreted as originally eustatically enhanced by subsidence. Tethyan signals are recorded around the Aptian/Albian boundary. A noticeable deepening in the upper Lower Aptian correlates with an extended platform drowning during the Selli Level (Oceanic Anoxic Event 1a: OAE 1a). Orbitolinid beds at this level suggest a deepening facies and a possible response to nutrient enhancement developing at the continental margin during OAE 1a. Eight third-order depositional sequences were observed in the Upper Barremian–Albian interval. They comprise successions of the inner ramp facies from open marine to restricted lagoons or tidal flats. The age and frequency of the Upper Barremian–Lower Aptian sequences correlate with those observed on the Pacific guyots or the Arabian Plate suggesting influence by regional sea-level cycles.

Sequence stratigraphy of the Lower Cenomanian Bahariya Formation, Bahariya Oasis, Western Desert, Egypt

The Lower Cenomanian Bahariya Formation corresponds to a second-order depositional sequence that formed within a continental shelf setting under relatively low-rate conditions of positive accommodation (< 200 m during 3–6 My). This overall trend of base-level rise was interrupted by three episodes of base-level fall that resulted in the formation of third-order sequence boundaries. These boundaries are represented by subaerial unconformities (replaced or not by younger transgressive wave ravinement surfaces), and subdivide the Bahariya Formation into four third-order depositional sequences. The construction of the sequence stratigraphic framework of the Bahariya Formation is based on the lateral and vertical changes between shelf, subtidal, coastal and fluvial facies, as well as on the nature of contacts that separate them. The internal (third-order) sequence boundaries are associated with incised valleys, which explain (1) significant lateral changes in the thickness of incised valley fill deposits, (2) the absence of third-order highstand and even transgressive systems tracts in particular areas, and (3) the abrupt facies shifts that may occur laterally over relatively short distances. Within each sequence, the concepts of lowstand, transgressive and highstand systems tracts are used to explain the observed lateral and vertical facies variability. This case study demonstrates the usefulness of sequence stratigraphic analysis in understanding the architecture and stacking patterns of the preserved rock record, and helps to identify 13 stages in the history of base-level changes that marked the evolution of the Bahariya Oasis region during the Early Cenomanian.

Devonian Jauf Formation, Saudi Arabia: Orbital Second-order Depositional Sequence 28

ABSTRACTThe Devonian Jauf Formation (Huj Group) froms part of a regional transgressive-regressive depositional sequence that extends more than 1,500 km across the Arabian Platform from the Al Jawf outcrops in northwest Saudi Arabia, to the subsurface of eastern Saudi Arabia and Oman (Misfar Group). The formation ranges in thickness from 200–335 m in eastern Saudi Arabia to about 300–330 m in northwest Saudi Arabia. It disconformably (?unconformably) overlies the continental to shallow-marine Tawil Formation, and is unconformably overlain by the continental Jubah Formation. The Jauf Formation consists of five members that are apparently conformable; from base-up: Sha’iba Shale, Qasr Limestone, Subbat Shale, Hammamiyat Limestone and Murayr. In the Al-Qalibah reference section, it is divided into 21 informal units. The Early Devonian Emsian Hammamiyat Member represents the main marine flooding event; it consists of Hammamiyat units 1–6 each characterized by a clastic section that is capped by limestone.The Jauf Formation is interpreted as an orbital second-order depositional sequence (denoted DS2 28), which is bounded by two second-order sequence boundaries: SB2 28 = Jauf/Tawil (c. 407.6 Ma) and SB2 27 = Jubah/Jauf (c. 393.0 Ma). The Jauf Formation appears to consist of six third-order depositional sequences (DS3 28.1 to 28.6) that were deposited in the Early Devonian, ?Pragian and Emsian stages The Hammamiyat Member (DS3 28.4) is interpreted to consist of six fourth-order orbital cycles (DS4 28.4.1 to 28.4.6) each deposited in 0.405 million years.

Eustatic versus tectonic control on the development of Neoproterozoic and Cambrian stratigraphic sequences of the Lublin-Podlasie Basin (SW margin of Baltica)

A sequence stratigraphy is applied for the Neoproterozoic to Cambrian sedimentary fill of the Lublin-Podlasie Basin (LPB). The main goal of the study is to discriminate between eustatic and tectonic control on the development of sedimentary sequences. The Neoproterozoic and Cambrian sedimentary succession is subdivided into two second-order depositional sequences, separated by a major regional unconformity. The lower sequence A is poorly recognised. It is presumably of the early Neoproterozoic age and is characterized by continental to coastal shallow marine deposition. Sequence B comprises a time span of the (?late Neoproterozoic) to Middle Cambrian. The lowermost part of the sequence B is composed of a lowstand system tract (LST). A low relative sea-level (RSL), associated to the LST development, was controlled by regional thermal doming, followed by a rapid clastic and volcanogenic deposition, exceeding rate of subsidence of extensional grabens. The terminal Ediacaran was a time of a transgressive system tract I (TST I) development. Increase of the RSL was induced by a transition from syn-rift to post-rift subsidence. During the development of a following highstand system tract I (HST I) the RSL remained high. Significant local supply of sediments, exceeding in rate the basement subsidence, caused progradation of shoreline. The higher up-section TST II is characterized by gradual increase of the RSL and represents continuing thermal sag phase of the LPB. It was coeval with a global transgression and controlled mainly by eustatic sea level rise. The beginning of the Middle Cambrian corresponds to development of a HST II, controlled by decelerating rate of RSL rise, even though it coincides with the Hawke Bay regression. The HST II is therefore interpreted as controlled by local tectonic processes, superimposed on continued post-rift thermal subsidence of the passive margin.

Tectono-Stratigraphic Note: Time calibration of late Carboniferous, Permian and Early Triassic Arabian stratigraphy to orbital-forcing predictions

The recent publication of GTS 2004 (Gradstein et al., 2004) provides an opportunity to recalibrate in time the late Carboniferous, Permian and Early Traissic Arabian Stratigraphy (GeoArabia Special Publication 3, Edited by Al-Husseini, 2004) as represented by the rock units in subsurface Interior Oman (Osterloff et al., 2004a, b) and the Haushi-Huqf Uplift region (Angiolini et al., 2004) (Figure). Additionally, sequence stratigraphic models of orbital forcing (Matthews and Frohlich, 2002; Immenhauser and Matthews, 2004) provide new insights in regards to the time calibration of depositional sequences: the “Rosetta Stone” approach. The Rosetta Stone approach predicts that the period of a third-order depositional sequence is 2.430 ± 0.405 my (denoted DS3 and here adjusted to increase the fourth-order ‘geological tuning fork’ from 0.404 to 0.405 my based on Laskar et al., 2004). The present calibration is also tied to the orbital-forcing model developed by R.K. Matthews (in Al-Husseini and Matthews, 2005; this issue of GeoArabia) that predicts that a second-order depositional sequence (denoted DS2) consists of six DS3s that were deposited in a period of about 14.58 my (6 x 2.430 my); the DS2 being bounded by two regional second-order sequence boundaries (SB2) corresponding to sea-level maximum regression surfaces.

Arabian Orbital Stratigraphy: Periodic Second-Order Sequence Boundaries?

ABSTRACTA simplified model of orbital-forcing suggests that the Phanerozoic Eon may be represented by 38 periodic second-order depositional sequences (DS2) each lasting about 14.58 million years (my). The DS2s are separated by second-order sequence boundaries (SB2, maximum regression surface) that should be manifested as regional stratigraphic discontinuities (unconformity, disconformity, time hiatus). To test this simple model, the Arabian succession was reviewed to identify candidate regional stratigraphic discontinuities that might be periodic at 14.58 my. Of the 38 predicted SB2s, 34 regional stratigraphic discontinuities were identified within the uncertainty of biostratigraphic-radiometric age dating, or by stratigraphic position. One SB2 could not be positioned in the succession because of ambiguous biostratigraphic dating. One was predicted within a long-lasting hiatus, and another two were predicted within an undifferentiated formation. The four unidentified SB2s reflect on the limitations of the data sample, rather than on the viability of the model.Because the stratigraphic discontinuities represent age spans with bounding ages that are at best believed to have accuracies of about ± 3.0 my, the model-data correlation was considered inconclusive. The resulting analysis, however, demonstrates that the ages in million years before present (Ma) of interpreted Arabian (and possibly global) sequence stratigraphic surfaces and depositional sequences, as estimated by biostratigraphic-radiometric dating techniques, are highly inaccurate (± 5–10 my). This conclusion suggests that presently used chronostratigraphic correlations across the Arabian Platform should be treated with great caution. The correlation of model SB2s to regional stratigraphic discontinuities, affords an alternative time scale that may eventually assist in the calibration of the biostratigraphic-radiometric time scale. An orbital-forcing time scale has a decided advantage in that it comes with precise third- and fourth-order stratigraphic predictions imbedded as sea-level fluctuations. The next level of testing is whether these orbital-forcing predictions hold up to precise correlation to stratigraphy.

Sequence stratigraphy of continental Triassic strata of Southernmost Brazil: a contribution to Southwestern Gondwana palaeogeography and palaeoclimate

The continental Triassic succession of southernmost Brazil comprises two second-order depositional sequences—the Sanga do Cabral (Early Triassic) and the Santa Maria (Middle to Late Triassic) supersequences. The first one includes ephemeral, low-sinuosity fluvial deposits developed on a low gradient plain. Based on fossil tetrapods, especially procolophonids, an Upper Induan age is estimated for this sequence. Facies association of the Santa Maria Supersequence indicates low-sinuosity fluvial rivers, deltas and lakes. This supersequence can be further subdivided into three third-order sequences (age provided by palaeovertebrate biostratigraphic data) as follows: Santa Maria 1 (Ladinian), Santa Maria 2 (Carnian to Early Norian) and Santa Maria 3 (probably Raethian or Early Jurassic) sequences. The Gondwanides paroxysms I and II in the Sierra de la Ventana–Cape Fold Belt are directly related to the development of both supersequences. The source area of the Sanga do Cabral Supersequence was located to the south. It consisted of an uplifted peripheral bulge situated landward of the retro-foreland system, from where older sedimentary rocks were eroded. The source area of the Santa Maria Supersequence was also positioned southwards and related to the uplifted Sul-Rio-Grandense and Uruguayan shields. The Santa Maria Supersequence stratigraphic architecture is comparable to the Triassic rift basins of Western Argentina. Diagenesis, facies and palaeontology of the studied succession suggest a dominantly semiarid climate during the Triassic.

Paleoproterozoic basin development and sedimentation in the Lake Superior region, North America

Abstract The peneplaned Archean craton in the Lake Superior region was the platform upon which a continental margin assemblage was deposited. Extension resulted in localized rifts that received thicker accumulations of sediments and volcanic rocks than did adjacent parts of the platform. Seas transgressed onto the continent several times and an ocean basin opened south of the present-day Lake Superior. Island arcs that formed during subduction collided with the craton margin as the ocean basin closed; oceanic crust is poorly preserved as a dismembered ophiolite sequence. The arc volcanics are preserved as the Wisconsin magmatic terranes. The collision resulted in a fold-and-thrust belt known as the Penokean orogen. To the north of the fold-and-thrust belt, a northward-migrating foreland basin — the Animikie basin — developed. Thick turbidite successions were deposited along the basin axis, and terrigenous clastics and Lake Superior-type iron-formation were deposited on the shelf along the northern margin of the basin. The primary paleoclimatic indicators are: (1) glaciogenic rocks at the base of the Paleoproterozoic succession in Michigan indicating ice-house conditions; (2) remnants of a paleosol on the glaciogenic rocks indicative of deep weathering, probably under subtropical conditions and therefore of greenhouse conditions; and (3) carbonate minerals after gypsum, halite, and anhydrite in stromatolitic dolomite, indicative of aridity. Three second-order depositional sequences are bounded by major unconformities, and can be correlated throughout the Lake Superior region.

Basin evolution of the Paleoproterozoic Karelian Supergroup of the Fennoscandian (Baltic) Shield

Abstract The peneplaned Archean craton of the Fennoscandian Shield served as a platform upon which a continental margin assemblage, the Karelian Supergroup, was deposited between ∼2.45 and ∼1.9 Ga. Major subaerial unconformities separate five sedimentary-volcanic groups of the supergroup — the Sumian, Sariolian, Jatulian (Lower and Upper), Ludicovian, and Kalevian. Second-order depositional sequences are implied. Early extension (∼2.45 Ga) resulted in localized rifts that were likely areas of later subsidence as well; they received thicker accumulations of sediments and volcanic rocks than did the adjacent platform. It is in these rifts and perhaps other downwarped areas that the sediments that were once more widespread were preserved, leading to interpretations of separate depositional basins by some workers. Seas transgressed onto the craton at least three times — in Sariolian time as evidenced by interpreted glaciomarine deposits, in Jatulian time as evidenced by widespread orthoquartzites (including tidalites) and stromatolitic carbonates, and in Ludicovian time as evidenced by organic-rich shales and turbidites. The tectonic-magmatic history is complex. Three episodes of mafic volcanism were widespread at 2.45, 2.2, and 2.1 Ga. Island arcs formed to the south of the craton and collided at ∼1.9–1.85 Ga (the Svecofennian orogeny). This collision resulted in northeastward thrusting (e.g. the Outokumpu nappe) and folding and metamorphism of the Karelian Supergroup. The primary paleoclimatic indicators are (1) glaciogenic rocks near the base of the Paleoproterozoic succession indicating ice-house conditions; (2) remnants of a major paleosol on the glaciogenic rocks, indicative of deep weathering under greenhouse conditions (subtropical or tropical?); and (3) carbonate pseudomorphs after evaporite minerals in stromatolitic dolomites, perhaps indicative of aridity. Similarities in magmatism, tectonics, sedimentary rock types and sequences, and paleoclimatic indicators have led to hypotheses that the Fennoscandian Shield and North America may have been part of the same supercontinent during Neoarchean and Paleoproterozoic time.

Basin analysis and mineral endowment of the Proterozoic Itajaí Basin, south‐east Brazil

A basin evolution synthesis and an integration of geological and geophysical data, relevant as guides to the exploration of gold and lead–zinc deposits in the Itajaí Basin, are presented in this paper. The Itajaí Basin is interpreted as a collision‐related foreland basin consisting of weakly metamorphosed sediments deposited between the structural front of the Dom Feliciano fold and thrust belt and the proximal flank of the cratonic forebulge. Its sediments represent a second‐order depositional sequence deposited during a foreland transgression–regression cycle related to flexural subsidence. After deposition, the basin underwent a main late‐collisional compressional deformation phase followed by an extensional post‐orogenic relaxation. Known gold and lead–zinc deposits are associated with late‐orogenic faulting of the Itajaí Basin sediments. The gold‐bearing quartz veins are of filonean hydrothermal affiliation, while the lead–zinc deposits were formed by solution‐remobilization in a meteoric–connate–magmatic mineralizing fluid. Major trends of favourability for such deposits are recognized. The most favourable sites for lead–zinc deposits are near known mineralized areas and also along a NE‐orientated fault at the margin adjacent to the Dom Feliciano metamorphic belt. The higher favourability for gold deposits is assigned to an area along the same NE trend, and also around a small known deposit near the cratonic margin.

Insights into the Origins of First- and Second-Order Depositional Sequences in the North Slope of Alaska: ABSTRACT

Insights into the Origins of First- and Second-Order Depositional Sequences in the North Slope of Alaska: ABSTRACT

The effect of rift shoulder erosion on stratal patterns at passive margins: Implications for sequence stratigraphy

Numerical modelling indicates that the erosion of uplifted rift flanks at passive margins has a profound effect on offshore stratigraphic patterns. Flexural uplift, due to isostatic rebound in response to erosion, extends far into the basin and causes uplift of the shelf. As a result, the contemporaneously deposited sedimentary wedge displays a characteristic offlap pattern. When the rift shoulder is largely eroded, onlap-promoting mechanisms related to cooling of the lithosphere enable sediments to onlap onto the basin margin. The initial offlapping and subsequent onlapping strata form one complete second-order depositional sequence comprising a shelf-margin-, transgressive-and highstand-systems tract. The modelling inferences are in broad agreement with stratal patterns and basin geometries observed on the U.S. east coast, the southeastern Brazilian and southeastern Australian passive margins and the Transantarctic Mountains-Ross Sea Shelf system. The initial offlaps caused by erosion of rift shoulders have important implications for the deriviation of eustatic signals from coastal onlap patterns.