The trace fossil assemblages from the shallow marine Turonian-Campanian chalky limestones are described for the rst time from Kopet-Dagh, Iran, enhancing the record of this fossil group in the Cretaceous of the Middle East. Shelf-sea chalky limestones of the Abderaz Formation are highly bioturbated and allow relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high-resolution sequence stratigraphic framework. Based on their lithological and ichnological characteristics, as well as stratal geometries, the Abderaz Formation exhibits 11 facies representing three depositional zones: basinal, outer shelf, and middle shelf. Six ichnocoenoses could be differentiated in the studied section: (i) stable habitats, represented by a suite of soft substrates, including mottled-Thalassinoides ichnocoenosis; (ii) unstable, physically controlled habitats, represented by a suite of soft substrates of low-to-high energy with Thalassinoides-Planolites- Ophiomorpha and Ophiomorpha-Planolites ichnocoenoses; (iii) dysoxic to anoxic habitats, represented by a suite of soft substrates of low energy including Thalassinoides-Chondrites ichnocoenosis; and (iv) substrate-controlled suite, represented by a suite of rm to hard substrates, including Thalassinoides suevicus and Thalassinoides- Spongeliomorpha suites. With the identi cation of mfs and SB/TS as bounding surfaces of the stratal units, the Glossifungites-demarcated erosional discontinuities (TS and FS) and the positions of the ichnocoenoses within genetically related stratal units (genetically related ichnocoenoses), three third-order depositional sequences are recognized in a sequence stratigraphic framework. This study reveals important sedimentological and ichnological features of shelf-sea chalky limestones and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical signi cance of trace fossil assemblages that can be readily translated to analogous depositional systems.
SEQUENCE STRATIGRAPHIC AND SEDIMENTOLOGIC SIGNIFICANCE OF BIOGENIC STRUCTURES FROM CHALKY LIMESTONES OF THE TURONIAN-CAMPANIAN ABDERAZ FORMATION, KOPET-DAGH, IRAN
MONACO, Paolo;
2016
Abstract
The trace fossil assemblages from the shallow marine Turonian-Campanian chalky limestones are described for the rst time from Kopet-Dagh, Iran, enhancing the record of this fossil group in the Cretaceous of the Middle East. Shelf-sea chalky limestones of the Abderaz Formation are highly bioturbated and allow relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high-resolution sequence stratigraphic framework. Based on their lithological and ichnological characteristics, as well as stratal geometries, the Abderaz Formation exhibits 11 facies representing three depositional zones: basinal, outer shelf, and middle shelf. Six ichnocoenoses could be differentiated in the studied section: (i) stable habitats, represented by a suite of soft substrates, including mottled-Thalassinoides ichnocoenosis; (ii) unstable, physically controlled habitats, represented by a suite of soft substrates of low-to-high energy with Thalassinoides-Planolites- Ophiomorpha and Ophiomorpha-Planolites ichnocoenoses; (iii) dysoxic to anoxic habitats, represented by a suite of soft substrates of low energy including Thalassinoides-Chondrites ichnocoenosis; and (iv) substrate-controlled suite, represented by a suite of rm to hard substrates, including Thalassinoides suevicus and Thalassinoides- Spongeliomorpha suites. With the identi cation of mfs and SB/TS as bounding surfaces of the stratal units, the Glossifungites-demarcated erosional discontinuities (TS and FS) and the positions of the ichnocoenoses within genetically related stratal units (genetically related ichnocoenoses), three third-order depositional sequences are recognized in a sequence stratigraphic framework. This study reveals important sedimentological and ichnological features of shelf-sea chalky limestones and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical signi cance of trace fossil assemblages that can be readily translated to analogous depositional systems.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
