Recognition of a Santonian Submarine Canyon, Great Valley Group, Sacramento Basin, California: Implications for Petroleum Exploration and Sequence Stratigraphy of Deep-Marine Strata

Sequence biostratigraphy is a relatively new discipline that has rapidly expanded in parallel with the development of sequence stratigraphy. Sequence bios- tratigraphic concepts have resulted in significant improvements in our ability to calibrate biozones, correlate and determine ages of sedimentary units, and to estimate environments of deposition. Significant advances in the development of integrated biostratigraphic methods and knowledge during the past 20 years are now being rapidly integrated into the physical framework provided by depositional sequences. Sequence stratigraphy provides a physical framework consisting of a predictable hierarchy of correlation surfaces, ranging from sequence boundaries to parasequence boundaries, within which biostratigraphic observations may be placed. These correlation surfaces define chronostratigraphic units with varying degrees of lateral extent that can be used to assess, using time-distance grids, the relative position of biozone 'tops' or 'bases'. They also provide a physical link between the open-ocean planktonic microfossil chronozones and chronozones developed in paralic and non-marine strata. In addition, the delineation of large, apparently sudden, water depth changes across downlap surfaces, associated with condensed sections, has resulted in more accurate and precise paleobathymetric estimation in exploration wells. Recognition and biostratigraphic 'fingerprinting' of major water depth changes are essential for correlation through intensely faulted areas.The rate of return from biostratigraphic and geochemi- cal sampling is generally poor primarily because of the lack of emphasis on the importance of developing and maintaining well planned sampling strategies and programs throughout an exploration drilling program. The design of biostratigraphic and geochemical sampling strategies has been improved by sequence stratigraphic concepts. Biostratigraphic sample quality (high) is inversely proportional to sedimentation rate (low). Sequence biostratigraphy provides a consistent, predictable, method of recognising low sedimentation rate units in the subsurface using a variety of tools, ranging from seismic to well log facies analysis.Some of the basic principles of sequence biostratigraphy are illustrated using an example from the Carnarvon Basin. The Barremian A. cinctum andM. australis dinocyst Acme and Oppel zones respectively, appear to be strongly associated with distinct environments. Consequently, it is difficult to calibrate them to the AGSO timescale and to use them regionally as reliable zones to subdivide the Barremian. Abundant numbers of A. cinctum appear to be restricted to specific regions of the Carnarvon dominated by shallower marine conditions and associated with the infilling of major incised river systems. Further biostratigraphic subdivisions within the Early Cretaceous and specifically the M. australis - A. cinctum interval are warranted, especially in light of the number of plays and prospects defined and discoveries made within this interval of the Carnarvon Basin. More detailed biostratigraphic work coupled with regional sequence stratigraphy and a more focussed sampling strategy should produce a high quality age-model for this prospective interval that had not received significant attention until recently.

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The birth of a forearc: The basal Great Valley Group, California, USA: REPLY

Geology ◽

10.1130/g47050y.1 ◽

2019 ◽

Vol 47 (12) ◽

pp. e494-e494

Author(s):

Devon A. Orme ◽

Kathleen D. Surpless

Keyword(s):

Great Valley Group ◽

Great Valley

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Occurrence of Zoophycos in the Ruteh Formation, Middle Permian (Guadalupian), Central Alborz, Iran: palaeoenvironmental and sequence stratigraphy implications

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen ◽

10.1127/njgpa/2020/0949 ◽

2020 ◽

Vol 298 (3) ◽

pp. 285-309

Author(s):

Forough Abasaghi ◽

Asadollah Mahboubi ◽

Mohammad Hosein Mahmoudi Gharaie ◽

Mohammad Khanehbad

Keyword(s):

Sea Level ◽

Sequence Stratigraphy ◽

Middle Permian ◽

Hydrodynamic Condition ◽

Anal Ysis ◽

Sea Level Fluctuations ◽

Marine Strata ◽

System Tracts ◽

Environmental Sequences ◽

Homoclinal Ramp

Zoophycos is widely distributed in the marine strata of the Middle Permian Ruteh For- mation in the Alborz Mountain, Iran. The investigation of the Zoophycos, along with environmental variables is a useful tool for interpretation of the palaeoenvironmental and sequence stratigraphy anal- ysis. The petrographic observations led to the identification of ten facies in four facies belts including tidal flat, lagoon, shoal, and open marine, deposited on a homoclinal ramp. Moreover, two third- order depositional sequences were recognized in response to the sea- level fluctuations within the Ruteh For - mation. Detailed studies of the sequence stratigraphy revealed a relationship between the occurrences of Zoophycos and changes in the hydrodynamic condition in the basin. It appears that Zoophycos has been influenced by the ecological and palaeoenvironmental parameters, such as sedimentation rate, nutrient supply, oxygen, wave base, and substrate in the shallow to deep environments. Based on the sedimentological and ichnological analysis, Zoophycos has been formed with various dimensions, morphology, fillings, and densities together with rising and falling in the sea-level. The trace- maker has followed an opportunistic strategy in the unstable conditions of shallow environments, whereas it has chosen a k-selected strategy in more stable deep environments. Additionally, variability in Zoophycos illustrates, how the trace- maker adopted itself with environmental sequences. This reason, owing to optimal conditions, has caused that the abundance of Zoophycos was high in the Transgres- sive System Tracts (TST). Evidence shows that the response of Zoophycos to the ecological properties of the environment usually has deposit- feeder and chemosymbiosis behaviours.

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The birth of a forearc: The basal Great Valley Group, California, USA

Geology ◽

10.1130/g46283.1 ◽

2019 ◽

Vol 47 (8) ◽

pp. 757-761 ◽

Cited By ~ 4

Author(s):

Devon A. Orme ◽

Kathleen D. Surpless

Keyword(s):

North America ◽

Detrital Zircon ◽

Forearc Basin ◽

Early Stages ◽

Structural Style ◽

Basin Development ◽

Great Valley Group ◽

Extensional Model ◽

Great Valley

AbstractThe Great Valley basin of California (USA) is an archetypal forearc basin, yet the timing, structural style, and location of basin development remain controversial. Eighteen of 20 detrital zircon samples (3711 new U-Pb ages) from basal strata of the Great Valley forearc basin contain Cretaceous grains, with nine samples yielding statistically robust Cretaceous maximum depositional ages (MDAs), two with MDAs that overlap the Jurassic-Cretaceous boundary, suggesting earliest Cretaceous deposition, and nine with Jurassic MDAs consistent with latest Jurassic deposition. In addition, the pre-Mesozoic age populations of our samples are consistent with central North America sources and do not require a southern provenance. We interpret that diachronous initiation of sedimentation reflects the growth of isolated depocenters, consistent with an extensional model for the early stages of forearc basin development.

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