Integrated brachiopod-based bioevents and sequence-stratigraphic framework for a Late Ordovician subpolar platform, eastern Anti-Atlas, Morocco

2014 ◽  
Vol 152 (4) ◽  
pp. 603-620 ◽  
Author(s):  
JORGE COLMENAR ◽  
J. JAVIER ÁLVARO
Keyword(s):  
High Energy ◽  
Late Ordovician ◽  
Low Energy ◽  
Upper Ordovician ◽  
Third Order ◽  
Sequence Stratigraphic ◽  
Faunal Change ◽  
Stratigraphic Framework ◽  
Distinct Event ◽  
Continuous Record

AbstractThe Upper Ordovician (Katian–Hirnantian) brachiopods of Tafilalt, eastern Anti-Atlas, are locally abundant, diverse and well preserved, providing a near-continuous record of faunal change on a high-latitude siliciclastic-dominated platform. A chronostratigraphic framework, based on brachiopod distribution and preservation in shell accumulation events and integrated with sequence stratigraphy, has been generated for the Katian interval, which has allowed correlation with the chitinozoan-based chronostratigraphic and sequence-stratigraphic framework erected for the central Anti-Atlas. In Tafilalt, two Katian (transgressive–regressive) composite depositional sequences, c. 60 and 170 m thick and related to third-order fluctuations in sea level, were unaffected by Hirnantian glaciogenic erosion. They were deposited on a mixed platform with a bryonoderm association dominated by brachiopods, bryozoans and echinoderms. Brachiopods developed in high-energy inner shelf areas, whereas bryozoans (mainly trepostomates and fenestrates) and pelmatozoans (cystoids and crinoids) dominated in low-energy outer shelf areas. Brachiopod accumulations mark distinct event surfaces, such as lag and event concentrations, hydraulic simple and composite concentrations related to transgressive surfaces, and hiatal condensed concentrations marking maximum flooding surfaces. The taphonomic condensation displayed by the Hirnantian Alnif Member, which onlaps the erosive base of glaciogenic tunnel channels, is explained as reworking and resedimentation of allochthonous, robust, biogenic hard parts sourced from the underlying (Katian) Ktaoua Group.

Distribution Regularity of the Ordovician Reef-Bank Reservoir inside Sequence Stratigraphic Framework in Central Tarim Basin

2014 ◽  
Vol 484-485 ◽  
pp. 612-615
Author(s):  
Feng Zhu
Keyword(s):  
Tarim Basin ◽  
Carbonate Platform ◽  
Late Ordovician ◽  
Third Order ◽  
Sequence Stratigraphic ◽  
Stratigraphic Framework ◽  
Platform Margin ◽  
Carbonate Platform Margin ◽  
Organic Reef ◽  
Integrated Study

Based on the integrated study of the outcrops, the seismic, drilling and logging data of Lianglitage formation in central Tarim Basin, the sequence stratigraphic framework of the platform margin is built, and the Lianglitage formation is divided into 3 third-order sequences. The vertical pattern and lateral distribution for carbonate reef-bank reservoir in sequence stratigraphic framework are analyzed. The reef-bank reservoir mainly developed in highstand system tract of sequence Ssq2, and distributed along the carbonate platform margin of the Middle-Late Ordovician in central Tarim Basin. The mudstone mound, organic reef, granule bank are vertically stacked. Laterally, the area of well shun3-shun4-shun2-shun6 are characterized by multiphase bank reservoir overlapping, and the area of well TZ82-TZ44 - TZ161-TZ24 - TZ26 are characterized by multiphase organic reef and bank overlapping. The reef-bank complexes in sequence Ssq2 are the main targets of exploration in central Tarim Basin.

High Resolution Sequence Stratigraphy of Silurian Strata in Tazhong Area

2013 ◽  
Vol 734-737 ◽  
pp. 111-116
Author(s):  
Lei Zhang ◽  
Lun Wei Zhu ◽  
Xue Juan Zhang
Keyword(s):  
High Resolution ◽  
Sequence Stratigraphy ◽  
Third Order ◽  
Sequence Stratigraphic ◽  
Stratigraphic Framework ◽  
Tazhong Area ◽  
Sequence Boundaries ◽  
High Resolution Sequence Stratigraphy ◽  
Comprehensive Study

According to the fundamental principles of high resolution sequence stratigraphy, this paper focused on the application of high resolution sequence stratigraphy to Silurian strata in Tazhong area. Based on the comprehensive study of logging, drilling and seismic information, the high resolution sequence boundaries of Silurian strata and two scales of datum level cycles (long-term and intermediate-term) can be recognized in Tazhong area. Seven chronstratigraphic boundaries can be recognized in Silurian strata, including four sequence boundaries, which were the transformation from datum level falling to datum level rising, and three flooding surfaces, which the transformation from datum level rising to datum level falling. The Silurian strata in Tazhong area can be divided into three third-order sequences which correspond to three long-term datum level cycles, and 11 fourth-order sequences (parasequence sets) relating to 11 intermediate-term datum level cycles. The classification aforementioned can much better solved the corresponding problem between the six lithological sections of Silurian strata and sequence formations, finally establishes the high resolution sequence stratigraphic framework of Silurian strata in Tazhong area.

scholarly journals Paleoecology of Cyclocrinites darwini (Miller) - a cyclocrinitid alga from the Cincinnatian series (Upper Ordovician)

1992 ◽  
Vol 6 ◽  
pp. 177-177
Author(s):  
Peter B. Lask
Keyword(s):  
Structural Similarity ◽  
High Energy ◽  
Energy Conditions ◽  
Upper Ordovician ◽  
Third Order ◽  
Coral Rubble ◽  
Lake Formation ◽  
Lateral Branches ◽  
Key Largo ◽  
Cincinnatian Series

Cyclocrinitids are considered to be calcareous green algae closely related to, or members of, the dasycladacean algae. Cyclocrinitids are characterized by a globular thallus 1-5 cm in diameter consisting of whorls of calcified meromes borne from a tubular or spherical central axis. The species Cyclocrinites darwini is distinguished from other cyclocrinitids by the presence of lateral branches arranged in a stellate pattern at the distal end of each merome.C. darwini is restricted to strata of the Cincinnatian Series. Specimens are commonly found in shale-filled channels cutting through nodular, irregularly-bedded limestones within the Mt. Auburn Formation and the lower Sunset Member of the Arnheim Formation. Numerous specimens are also known from the Bellevue Member of the Grant Lake Formation at Maysville, Kentucky. Each of these units has been interpreted to be the top of separate shoaling-upward, third-order cycles. These facies are abundantly fossiliferous, often consisting of broken, abraded, and reworked material.The modern dasyclad Neomeris is cited for its structural similarity to the cyclocrinitids and ecological parallels have been postulated as well. Neomeris and a similar dasyclad Batophora, thrive while attached to pieces of coral rubble at depths of less than 3 m in the high-energy conditions associated with a reef crest environment at Key Largo, Florida.It is likely that C. darwini lived under similar conditions, attached to rubble in shoaling areas. Preservation only occurred in instances when thalli were broken off from their holdfasts and swept into ripple troughs or downslope channels cutting across the shoals. It has been suggested that the presence of cyclocrinitids is indicative of relatively quiet environments below wave base. For Cyclocrinites darwini, the opposite would appear to be the case.

Paleocommunity and evolutionary ecology of Paleozoic crinoids

1997 ◽  
Vol 3 ◽  
pp. 69-106 ◽  
Author(s):  
Peter F. Holterhoff
Keyword(s):  
Beta Diversity ◽  
Fossil Record ◽  
Evolutionary Ecology ◽  
Alpha Diversity ◽  
High Energy ◽  
Late Ordovician ◽  
Low Energy ◽  
Late Paleozoic ◽  
Common Component ◽  
Early Diversification

Crinoids were a common component of Paleozoic benthic paleocommunities, yet they have been under-utilized in paleoecological analyses. Recent efforts to incorporate disarticulated ossicles into these analyses have greatly increased the robustness of paleoecological patterns noted for the Crinoidea. Analyses of crinoid functional morphology, particularly filtration dynamics, have provided testable hypotheses concerning the distribution of crinoids among benthic environments. These models predict that crinoids with dense-mesh filtration fans should be most common in high energy, shoreward paleoenvironments, whereas open-fan crinoids should be most common in low-energy, offshore paleoenvironments. Review of the Paleozoic fossil record appears to support these general predictions—from the Late Ordovician to the end of the Paleozoic, dense-fan crinoids are most abundant in nearshore paleoenvironments, whereas open-fan crinoids are most abundant offshore.The partitioning of crinoid diversity through the Paleozoic shifted through time. Beta diversity was highest in the Ordovician, implying that the early diversification of crinoids was focused on partitioning the benthic landscape among taxa. Beta diversity was quite low by the late Paleozoic, however, local and within-habitat alpha diversity was much greater than during the Ordovician. This resulted in generally higher levels of eurytopy in the late Paleozoic compared to the Ordovician. Patterns of faunal disassembly associated with regional extinctions in North America during the Ordovician and Permian underscore the differences in the paleoecology of these crinoid faunas.

scholarly journals Facies, sequence stratigraphy and reservoir/seal potential of a Jilh Formation outcrop equivalent (Wadi Sahtan, Triassic, Upper Mahil Member, Sultanate of Oman)

GeoArabia ◽  
2012 ◽  
Vol 17 (3) ◽  
pp. 85-128 ◽  
Author(s):  
Michael Obermaier ◽  
Thomas Aigner ◽  
Holger C. Forke
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Second Order ◽  
Late Triassic ◽  
Small Scale ◽  
Third Order ◽  
Sequence Stratigraphic ◽  
Oman Mountains ◽  
Sequence Boundaries ◽  
Reservoir Potential

ABSTRACT The investigated Middle to Upper Triassic Upper Mahil Member, representing a Jilh outcrop equivalent in the Northern Oman Mountains, illustrates the proximal portion of a flat epeiric carbonate ramp. A sedimentological study of well-exposed outcrops in Wadi Sahtan may serve as a reference section for a sequence-stratigraphic framework and detailed facies description of the Upper Mahil Member. It also provides an insight into the seal and reservoir potential of carbonates in a low-accommodation inner ramp setting. Outcrop observations and thin section analyses yielded 14 different lithofacies types ranging from a supratidal marsh to high-energy subtidal shoal environment. Vertical facies stacking patterns show three basic small-scale cycle motifs (fifth-order). While mud-rich backshoal cycles with claystone intercalations and rooted/bioturbated mud-/wackestones illustrate potential baffles and seal units around the center of the Upper Mahil, potential reservoir units occur stratigraphically in the upper part of the formation. There, a few meter-thick trough cross-bedded oolitic-/peloidal-rich grainstone depicts maximum accommodation within backshoal to shoal cycle types below the erosional base-Jurassic unconformity. The investigated outcrop section in Wadi Sahtan was subdivided into nine almost complete third-order sequences. Two to four of these sequences are further stacked into three second-order super-sequences which are well reflected in the gamma-ray pattern. The highest reservoir potential occurs around second-order maximum floodings. Internal seals can be observed at third-order sequence boundaries where shales and muddy carbonates are up to 20 m thick. A regional correlation with subsurface data from Yibal and Lekhwair in Oman shows that the apparent thickness changes in the Upper Mahil (Jilh) are mainly determined by the Late Triassic/Early Jurassic erosional truncation. The occurrence of thick anhydrite units in the subsurface indicates a more proximal setting towards the southwest.

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