Sea-level changes from the Callovian Calabozo Formation and the distribution of dasycladacean and cyanobacteria. Mendoza Province, Neuquén Basin, Argentina

PALMA, R.M.; KIETZMANN, D.A.; PIETHÉ. R.D.

Zagreb

Simposio; 9th International Symposium on Fossil Algae; 2007

Croatian Geological Survey

Analyses of Callovian carbonate cycles from the Calabozo Formation (Neuquén Basin) in central-west Argentina high-frequency facies and accommodation changes. The succession consists of dark-gray medium-to thick bedded peloidal to bioclastic wackestones to packstones interbedded with oolitic bioclastic grainstones-packstones and coral packstone. An abundant marine biota includes, in order of abundance: bivalves, echinoderms, gastropods, corals, green algae (dasicladacean), cyanobacteria, foraminifers, calcispheres and sponges spicules. The Calabozo Formation is 35 m thick arranged in cycles typically composed of subtidal and intertidal to supratidal facies. Subtidal facies include: 1) peloidal wackestones rich in bivalves, echinoderms, forams (miliolids and rotalids) calcispheres and sponge spicules; 2) bioclastic wackestone with bivalves, echinoderms, calcispheres, ooids and green algae represented mainly by Salpingoporella annulata Carozzi; 3) coral packstone, which includes bivalves, gastropods, echinoderms and Cayeuxia (Rivularia) piae Rech Frollo; 4) bioclastic-intraclastic packstones are characterized by the occurrence of bivalves, echinoderms, gastropods, intraclasts and green algae represented by Salpingoporella annulata Carozzi, Cylindroporella Johnson; and minor cyanobacteria such as Cayeuxia (Rivularia) piae Rech Frollo; and 5) oolitic peloidal packstone-grainstone with ooids and peloids (shoals), bivalves, echinoderms, gastropods and oncoids. Cyanobacteria are represented by Cayeuxia (Rivularia) piae Rech Frollo, Cayeuxia (Rivularia) kurdistanensis Elliott, and scattered remains of Heteroporella Ott. Oncoids are characterized by a nucleus of cyanobacteria and show spherical to ovoidal morphology. Intertidal to supratidal facies consists of planar laminated stromatolite with scattered gastropods and ostracods. The interpretation of carbonate cycles and accummulation rate on Middle Callovian Calabozo Formation following the method of GOLDHAMMER et al., (1990). Thickening and thinning stacking pattern of cycles were used to identified systems tracts. The TST is characterized by a lower part of thick cycles mainly composed of subtidal facies, presumably formed during times of increased accommodation space. The HST is characterized by subtidal facies that thin upward showing progressively higher intertidal to subtidal facies. The thinning-upward cycles were generated during decrease in accommodation space, when the carbonate production exceeded it. The MFS is represent by the vertical transition from thick to successively thinner cycles as consequence of  a decrease in accommodation space. In the TST and earlier HST are very common Salpingoporella annulata Carozzi,and Cylindroporella Johnson, meanwhile in the last HST appear Cayeuxia (Rivularia) piae Rech- Frollo, Cayeuxia (Rivularia) kurdistanensis Elliott, and small fragments of Heteroporella Ott. The interbedding of  dasycladacean- cyanobacteria reveals a shallowing-upward  trend related to sea-level fluctuations. In fact, there exist a general upwards decrease in abundance of dasycladacean algae. The depositional setting of this succession comprises intertidal-supratidal facies with development of microbial mats, a quiet lagoonal subtidal  area (inner ramp) where the sedimentation was controlled by biological activity, carbonate production and fair-weather waves, and a marginal ramp  area where the lagoonal environment  was fringed  by  a shallow high-to moderate energy shoal.