Sequence Stratigraphic Units Research Articles

Discovery of the Ordovician Millbrig K-bentonite Bed in the Trenton Group of New York State: implications for regional correlation and sequence stratigraphy in eastern North America

The Ordovician (Chatfieldian) Millbrig K-bentonite Bed is a key stratigraphic marker horizon that is regionally synchronous over much of eastern and central North America. This prominent marker is an independent source of correlation among the major chronostratigraphic and sequence stratigraphic units in this region. The general stratigraphic position of the Millbrig K-bentonite has suggested to some authors that it is identical with the Hounsfield K-bentonite at Dexter, New York (the traditional type area of the Middle Ordovician, or Mohawkian Series in North America), but previously available geochemical and biostratigraphical evidence has been insufficient to confirm this correlation. Analyses of apatites and melt inclusions in quartz phenocrysts from the Millbrig K-bentonite at eight localities in Kentucky, Missouri, Virginia, and Pennsylvania and the Hounsfield K-bentonite at its type locality at Dexter, New York, using high-precision electron microprobe analysis techniques shows that the Millbrig and the Hounsfield have identical apatite and melt inclusion chemistry indicating a geochemical correlation. This correlation is supported by conodont biostratigraphy, and δ 13C isotope chemostratigraphy. The new data demonstrate that the Millbrig K-bentonite, and therefore the base of the Chatfieldian Stage of the North American Mohawkian Series (by definition), lies very close to the base of the traditional Rocklandian Stage of New York. Furthermore, the Millbrig K-bentonite Bed lies in close proximity to the base of the Taconic supersequence over much of the Midcontinent region and in particular lies just below the M5 sequence boundary recognized in Kentucky and Tennessee. Our results permit extension of the Chatfieldian sequences into New York State and southern Ontario, and contributes to the resolution of the long-standing uncertainty about the position of the base of the Trenton Group in Ontario. Furthermore, viewed in a broad context of regional stratigraphic relations, we conclude that our results suggest that the persistent correlation difficulties reflect diachronous effects of widespread changes in oceanographic circulation patterns that emerged during Taconic Orogeny. Finally, regional differences in the timing and character of sequence bounding surfaces and facies similarities summarized here suggest that the causes of relative sea level change during the Chatfieldian may have been primarily tectonoeustatic mechanisms.

Three orders of regional sea-level changes control facies and stacking patterns of shallow platform carbonates in the Maestrat Basin (Tithonian-Berriasian, NE Spain)

Middle Tithonian-Berriasian shallow platform carbonates of the Maestrat Basin (Salzedella and Montanejos sections, NE Spain) are stacked in sequence stratigraphic units of different orders. Higher-order sequences (parasequences and subunits) have a shallowing or deepening-shallowing evolution. They have been related to the short-term eccentricity and precession cycles. Major facies changes and stacking pattern of parasequences reveal the presence of two 2nd-order sequences. The Lower Sequence is middle Tithonian-mid early Berriasian in age. The Upper Sequence extends up to the mid-late Berriasian. It is suggested that local subsidence changes along with regional sea-level changes controlled the long-term evolution of accommodation in the Maestrat Basin. Facies evolution, stacking pattern and sharp lithological changes have allowed the definition of five 3rd-order sequences in the Lower Sequence in Montanejos. The transgressive deposits are characterised by the progressive absence of the restricted lagoon facies, and the presence of deepening-upward intervals in the parasequences. The highstand deposits display an increase in siliciclastics and a progressive predominance of restricted lagoon facies. Some of the 3rd-order sequence boundaries match the sequence boundaries identified in other European basins and may be related to sea-level falls (induced by the long-term eccentricity cycle) enhanced during periods of long-term loss of accommodation.

Lithostratigraphy, conodont biostratigraphy and depositional environment of the Middle Devonian (Givetian) to Early Carboniferous (Tournaisian) Lipak Formation in the Pin Valley of Spiti (NW India)

Bed-by-bed lithostratigraphic sections combined with sequence stratigraphy and conodont biostratigraphy provide new information on the depositional environment and age of the Lipak Formation in the Pin Valley (Spiti). The formation comprises mixed siliciclastic and calcareous sediments at lower levels, richly fossiliferous limestones with two distinct sandstone incursions at higher levels, and dark mudstones followed by a thin siltstone interval. The upper limit of the Lipak Formation is defined by the angular unconformity below the sandstones of the Permian Gechang Formation. Lithologic correlation with sections in upper Lahaul indicates that, in the Pin Valley, the formation has been truncated just below its characteristic gypsum horizon. The lower boundary of the Lipak Formation is gradational from coastal arenites of the Muth Formation; the mappable boundary is drawn at the first appearance of dark carbonaceous, argillaceous siltstone and shale. Sedimentary structures, microfacies and conodont faunas indicate a general shallow marine depositional environment of the Lipak Formation in the Pin Valley; five sequence stratigraphic units have been distinguished. Conodont data demonstrate that the lowest 33 m of the Lipak Formation of the Pin Valley is mid to late Early varcus Subzone with characteristic species of Icriodus and Bipennatus . A previously unrecognised hiatus at c. 33 m above the base, at the boundary of sequence stratigraphic units S1 and S2, represents the interval Middle varcus Subzone to at least the end of the late Famennian Early expansa Zone. Because this hiatus does not correspond to a mappable boundary, no division of the Lipak Formation into named stratigraphic units is suggested, but we refer informally to the sediments represented by cycle S1 as Lipak A, and the sediments represented by cycles S2-S5 as Lipak B. Determination of S1 as Early varcus Subzone provides a maximum age for the gradationally underlying Muth Formation. At 75 m above the base of the composite Lipak Formation section, a 58 cm black to dark grey shale interval within late Famennian fossiliferous limestones conceivably correlates with the Hangenberg Event (end-Middle praesulcata Zone). Younger conodont faunas of the Lipak Formation -dominated by species of Clydagnathus with species of Bispathodus and Pseudopolygnathus also represented- is shown to extend to the mid-Tournaisian Early crenulata Zone.

Discussion on fault activity and sedimentation in a marine rift basin (Upper Jurassic, Wessex basin, UK)

Scientific editing by John Howell. J. K. Wright writes: I was interested to read the recent paper by ⇓Newell (2000) which incorporates a sequence stratigraphic synthesis of the Corallian of the Wessex Basin. This is an aspect of the Dorset Corallian which I investigated some years ago (⇓Wright 1986) when I subdivided the succession on a lithostratigraphic basis. Newell’s sequence stratigraphic subdivisions consist of sequences of strata bounded by major erosion surfaces. Lithostratigraphic and sequence stratigraphic units do not normally coincide, but may be coincident under special circumstances (⇓Murphy & Salvador 1999). Such circumstances occur when there is a substantial change in lithology between lithostratigraphic units that are bounded by unconformities. I would submit that this is the case in the Oxfordian of the Dorset coast, and that with some revision to the lithostratigraphy, the formation boundaries coincide with the sequence boundaries and therefore have chronostratigraphic significance. In setting up a revised stratigraphy for the Dorset Corallian Group (⇓Wright 1986), I defined formations within the group as sequences of strata bounded by erosion surfaces—in effect sequence stratigraphy. Each of these formations contained a sedimentary cycle comprising a transgressive succession followed in some cases by a regressive succession. In this way I defined six formations (sequences) although as a number of the boundaries …

Relationships between sequence stratigraphy, mineralogy and geochemistry in Cenozoic sediments of the northern North Sea

Abstract Cuttings of Cenozoic sediments from selected wells in the northern North Sea have been analysed both mineralogically and geochemically, and compared with seismic sequence stratigraphic units. Variations in the composition with respect to clay minerals, feldspars, major elements and selected trace elements have been used to establish changes in the provenance of the Cenozoic sequences. The Eocene sequence consists of a thickness of several hundreds of metres of almost exclusively smectitic clays with high Ni and Zn contents and little or no quartz. This represents a strong input from subaerial volcanism related to the rifting and initial spreading of the Norwegian-Greenland Sea. The Eocene-Oligocene smectitic mudstones have high porosity and low seismic velocity (<2km s −1 ) compared with the underlying Paleocene sediments and overlying Miocene-Pliocene sequences. The Plio cene and Pleistocene mudstones are coarse-grained clays with an immature mineralogy, which compact much more rapidly than the underlying smectitic sediments. The seismic velocity may then reach 2.5–3.0 km s −1 and thus cause a strong velocity inversion. This sequence is partly glacial and mineralogically immature, but may contain some kaolinite and smectite, which indicate reworking of lower Tertiary and Mesozoic sediments. Our obser vations indicate that sequence boundaries are closely related to tectonic movements and to changes in the sediment supply from adjacent areas. Both mineralogical and geochemical data can be used as additional tools for correlation in Cenozoic sediments in the northern North Sea. The mineralogy of these sediments also determines the rate of compaction and other factors relevant for basin modelling.

Multiple Orders of Relative Sea-level Change in an Earliest Cambrian Passive-margin Succession, Mackenzie Mountains, Northwestern Canada

ABSTRACT Earliest Cambrian siliciclastic strata in the Mackenzie Mountains (Ingta, Backbone Ranges, and Vampire Formations) contain deposits of a variety of shelf, nearshore, and fluvio-deltaic depositional environments. The strata contain a hierarchical succession of sequence-stratigraphic units. Parasequences, simple depositional sequences (at least eighteen), composite sequences (three), and supersequences (one complete and part of another) have all been recognized within the succession. These units appear to record the interactions between at least five orders of relative sea-level cyclicity and formed on time frames that were broadly consistent with possible eustatic origin. Type-two sequence boundaries (generally considered rare in siliciclastic settings) appear to be common in this succ ssion, and it is suggested that location on the paleoshelf, as well as sea-level variation, can influence the character and interpretation of sequence-stratigraphic units, especially in isolated successions. While the units most easily recognized and correlated (simple and composite sequences) are the result of third- and fourth-order sea-level cycles, second-order fluctuations seem to have exerted a significant control on sequence characteristics. The general proximality/distality of the succession is apparently controlled in large part by second-order oscillations, and the nature and expression of the sequence boundaries that demarcate the simple sequences are also influenced by sea-level variations of second order. In a similar fashion, second- and third-order sea-level interactions c n influence systems-tract development within simple sequences and may determine the presence or absence of a TST within the simple sequences.

Ichnofossil Distribution in Sequence Stratigraphic Units of the Eocene Claiborne Group, U.S. Gulf Coastal Plain

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Stratigraphic correlation of the Danish onshore and offshore Tertiary successions based on sequence stratigraphy

The results of a sequence stratigraphic study of the Tertiary sedimentary succession in the Danish North Sea sector, and the adjacent parts of the Norwegian, German, and Dutch sectors are reviewed in the present paper. Lithology and thickness variations of seven major sequence stratigraphic units, comprising twentyone sequences, are shortly described. The chronostratigraphic and genetic relationships between the North Sea sequences and the Danish onshore lithostratigraphic formations are emphasized. Six major sequence stratigraphic boundaries are pointed out, being time-equivalent with regional unconformities in the onshore area. The six surfaces bound five sedimentary packages, which are isochronous in their recognized lateral extension, and comprise genetically related deposits. It is suggested to define the five units as allostratigraphic units, and thus to create a stratigraphic subdivision, which is mappable in the southeastern North Sea region, possibly in the main part of the North Sea. The five allostratigraphic units can be identified in all areas by the available data; seismic sections and logs in the offshore area, and lithology in onshore outcrops and shallow wells. The definition of an allostratigraphic scheme would create a common nomenclature across the national borders and the present coastlines, and hopefully increase the accuracy of the chro­nostratigraphic correlation between profiles in the North Sea region.

Systematic Wireline Log Predictions of Sequence Stratigraphic Units: A Case-Study from the Upper Pennsylvanian of Kansas: ABSTRACT

Systematic Wireline Log Predictions of Sequence Stratigraphic Units: A Case-Study from the Upper Pennsylvanian of Kansas: ABSTRACT

DEPOSITIONAL SEQUENCE MODEL FOR THE POST-BARROW GROUP NEOCOMIAN SUCCESSION, BARROW AND EXMOUTH SUB-BASINS, WESTERN AUSTRALIA

Structural traps at the top 'Barrow Group' are the most successful oil exploration targets in the Barrow/Exmouth Sub-basins. However, a reinterpretation of recent exploration activities undertaken by BHP Petroleum Pty Ltd, combined with regional investigations on the Exmouth Plateau, has cast doubt on the validity of accepted stratigraphic nomenclature for the Neocomian succession. A more geologically rational subdivision of the upper part of the Neocomian succession into two discrete sequence stratigraphic units is proposed.Key seismic data from the Exmouth Plateau, tied into wells with good age control, have enabled precise recognition of the Intra-Valanginian Unconformity within the currently-defined Barrow Group. The Barrow Group (sensu stricto) is redefined in this paper as the Barrow Megasequence (restricted to a Berriasian age succession), comprising a rapid progradational phase, which was abruptly terminated by the Intra-Valanginian event.Local erosion of the Barrow Megasequence along the Novara Arch through an Early Valanginian uplift, during the ensuing Valanginian regional transgression, contributed to the development of a parasitic clastic wedge, previously referred to as the Upper Barrow Delta on the Exmouth Plateau and here named the Zeepaard Sequence, with a nominated section in Zeepaard-1. The Zeepaard sequence is terminated by a Top Valanginian unconformity, upon which a final deltaic clastic pulse was deposited as the Birdrong Sequence. Each successive clastic wedge had a more limited development, with the basinward progradation terminating well short of the underlying stratigraphic unit. The Birdrong Sequence was terminated by an Intra-Hauterivian unconformity upon which the highly glauconitic, thin, Mardie Greensand Member of the Muderong Sequence was developed.The Zeepaard Sequence and overlying Birdrong Sequence can be characterised using both seismic and well log character. Well data in particular has enabled detailed stratigraphic mapping of the Birdrong Sequence which is thin and generally not seismically resolvable across the Barrow Sub-basin. This paper presents a detailed sequence stratigraphic analysis of the Birdrong Sequence using well log data.

A Modern Regional Geological Analysis of Venezuela: Lessons from a Major New World Oil Province on Exploration in Mature Areas

Venezuela has produced some 44 billion bbl of oil since the early part of the century. As such, it represents one of the world's major oil producers and a mature petroleum province. However, major tracts of Venezuela's sedimentary basins remain underexplored and large discoveries are still being made in new and old reservoir systems. A regional geological analysis of Venezuela, focusing on basin evolution and sequence stratigraphy and incorporating data from the three national oil companies, is presented. The analysis presents a regionally consistent tectonostratigraphic model capable of explaining the evolution of the Mesozoic and Cenozoic basins of Venezuela and placing the major reservoir facies in their regional tectonic and sequence stratigraphic context. Four regional cross sections describe the stratigraphic and structural model. The model recognizes a Jurassic rifting event and inversion, succeeded by an Early Cretaceous passive margin. In western Venezuela, the Early Cretaceous passive subsidence is enhanced locally by extension related to the Colombian active margin. Venezuela experienced a major change in the Campanian with the initial collision of the Caribbean arc, recorded by foreland structuring and widespread stratigraphic changes. From the Campanian onward, the tectonostratigraphic evolution can be modeled in terms of a progressive southeast-directed arc-continent collisionmore » and the migration of the associated foredeep and rift basins. Within the tectonic framework, the major sequence stratigraphic units are identified and the reservoir distribution interpreted. This model provides a strong predictive tool to extrapolate reservoir systems into Venezuela's underexplored areas and to readdress its traditional areas.« less

Cretaceous Sequence Stratigraphy of the Northern South American Passive Margin: Implications for Tectonic Evolution

The passive margin of northern South America, from Colombia to northeastern Venezuela, was relatively stable through the Cretaceous and only broadly affected by the entry of the Caribbean Plate into the Protocaribbean Basin. This region offers a unique opportunity to test the relative effects of global sealevel change, autocyclic sedimentologic processed, and regional tectonics in shaping the stratigraphic record of Cretaceous passive margins. High-resolution stratigraphic studies of Colombia and Venezuela have established a precise system of regional chronology and correlation with resolution <1 Ma (50-500 ka for the middle Cretaceous). This allows precise separation of allocyclic and autocyclic controls on facies development. This new chronology integrates assemblage zone biostratigraphy with event/cycle chronostratigraphy. Newly measured Cretaceous sections in Venezuela and throughout Colombia are calibrated to this new chronology, and sequence stratigraphic units independently defined to the third-order of resolution. Graphic correlation of all sections is used to identify sequences with regional stratigraphic expression, and those which correlate to sequence stratigraphic standards of North America, Europe and the global cycles of Hag et al. (1988). 50-60 percent of the stratigraphic sequences across the South American passive margin correlate to other continents and to the global sequence stratigraphic standard, reflecting strong eustatic influencemore » on Cretaceous sedimentation across northern South America. The remaining sequences in this region reflect tectonic modification of the passive margin and autocyclic sedimentary processes.« less

Are seismic/depositional sequences chronostratigraphic units?

Sequence Stratigraphic Analysis is claimed to be a “new globally valid system of stratigraphy … a precise methodology to subdivide, correlate and map sedimentary rocks” (Vail et al., 1991, p. 622). Sequence stratigraphic units, such as depositional sequences, depositional systems tracts, and parasequences, are time-equivalent rocks of specific durations controlled by cyclical changes in sediment supply related to eustasy. These units are bounded by regionally extensive unconformities with erosion beneath and onlapping strata above, or by physical surfaces separating either different patterns of stratal geometry or shoaling-up facies units. According to this school, precise correlations are based upon inferred time relations within depositional models.Several key concepts of sequence stratigraphy have their origins in early geological studies. For many years geologists have separated time-equivalent strata by regional unconformities related to changes in climate or sea level, e.g., J. Woodward, 1695 and T. C. Chamberline, 1909. Stratal surfaces, such as bentonites and limestone markers, have been used in place of fossils for time correlations since the first wells were drilled. Stratigraphic models have strongly influenced how we correlate strata since the time of William Smith.Two developments are, indeed, new and have sparked the current resurgence in stratigraphic research. One is the seismic technology to test the physical continuity of strata on a regional scale (50-100 km), and to test the stratal geometry of genetically related depositional packages. The second is the chart of global coastal onlap events and eustasy (Haq et al., 1988).Some key research problems are: (1) how to identify unique, time-significant stratal surfaces; (2) how to test their physical continuity; (3) how to test the time relations within depositional models; and (4) how to identify the unique, time-significant global events recorded in the stratigraphic record. These stratigraphic concepts can be tested by graphic correlation, which is a powerful technique of high precision, quantitative stratigraphy. Its application in Cretaceous sections of the Gulf Coast and Oman, and in the Plio-Pliestocene of the Gulf Coast aids the distinction between synchronous surfaces and diachronous boundaries.

Biothems: sequence stratigraphic units and their implications for regional tectono-stratigraphic interpretations

Biothems are regional wedge- or lens-shaped bodies of strata that are: bounded shelfward or cratonward by paleontologically recognizable unconformities; generally thicken on marine shelves, where they are typically conformable with underlying and overlying biothems; are commonly thinner or represent “starved” sequences further basinward; and in their most basinward extent, are either bounded by biostratigraphically recognizable unconformities or are conformable with underlying and overlying biothems. Biothems are practical units whose definition and degree of refinement are dependent on the quality and availability of biostratigraphic control. As recognized to date, biothems have a logical distribution of faunal and floral components, as well as facies groupings that represent internally consistent and logical sequences of depositional environments. The use of biothems as primary sequence stratigraphic units places the emphasis on relative time in a stratigraphic framework.A west-to-east transect within the North American Mississippian System, which extends from the Basin and Range Province, across the Transcontinental Arch (TA) and into the Anadarko Basin, was constructed to demonstrate the regional distribution and tectono-stratigraphic significance of biothems relative to the axis of the TA. The relationships portrayed on the transect, tied to an understanding of North American Mississippian paleogeography, imply that biothems deposited during relative highstand events on one flank of the TA are time-equivalent to biothems deposited during relative lowstand events on the opposite flank of the TA. This distribution is interpreted to have been controlled by intraplate tectonic events that formed “piano-key” basins along the flanks of the TA. The spatial patterns of these basins are not consistent with published models of basin evolution. A further conclusion is that the lack of transgressive or regressive coincident Mississippian biothems on either flank of the TA suggests that it is inadvisable to impose the Mississippi Valley-derived eustasy curve on western flank depositional sequences.