George A. Seiglie

The Quebradillas Limestone (Miocene-Pliocene), northern Puerto Rico, and tectonics of the northeastern Caribbean margin

The uppermost formation of the limestone belt of northern Puerto Rico is herein redesignated the “Quebradillas Limestone.” A type section is established within the original type locality north of the town of Quebradillas. As here redefined, the Quebradillas Limestone consists of a limestone sequence overlying the uppermost Amphistegina -algal limestone of the “Aymamon limestone” along Highway 2 north of the town of Quebradillas. The formation consists of three types of limestone biomicrite which form the basis for subdividing the formation into three members. The lower member consists of globigerine biomicrite and is 16 m thick. In many areas, the lower member contains thin beds of oyster shells and shell fragments inter-bedded within marl. Both the matrix of the oyster-bearing beds and the marl are rich in planktonic foraminifers. The middle member is essentially Operculinoides biomicrite and is slightly Amphistegina -algal biomicrite, and its thickness is estimated to be 44 ± 4 m. The threefold subdivision has been recognized throughout the outcrop belt of the formation from the west coast of the island eastward to Barceloneta; it probably applies to the easternmost outcrops as well. The Quebradillas-“Aymamon” boundary is an erosional unconformity between the two formations. The globigerine limestone of the lower member of the Quebradillas fills solution cavities in the uppermost “Aymamon,” and in places, the upper “Aymamon” shows marked relief. Most of the Quebradillas is Pliocene in age, although part of the lower member may be latest Miocene. The Quebradillas Limestone is a regressive sequence. The lower member represents a lower neritic to upper bathyal environment; the middle member, an outer shelf environment; and the upper member, a forereef, subtidal, and intertidal beach environment. The upper member is veneered by what appears to be a paleosol which in turn, is overlain by Quaternary eolianite, marginal marine, and marine deposits. The Quebradillas is not limited to only the onshore coastal area of the island but extends northward into the Puerto Rico Trench. Above a water depth of 5,000 m, the Quebradillas covers an area of at least 4,000 km 2 on the southern slope of the trench, and the total area could be as much as 9,000 km 2 . Seismic and dredge-sample data suggest that the Quebradillas consists of the same facies offshore as in both outcrop and one well onshore. The presence of widespread Quebradillas in the Puerto Rico Trench has important tectonic implications for regional studies of both the Puerto Rico Trench and the northern Caribbean region.

Some West African Cenozoic Agglutinated Foraminifers with Inner Structures: Taxonomy, Age and Evolution

Compressed agglutinated foraminifers with characteristic inner structures are included in the family Tawitawiidae. They have a fanlike arrangement of incomplete inner partitions and triserial, biserial, uniserial, or combined series of chambers. The genera have an evolutive history that is in agreement with their biostratigraphic distribution. Pavopsammia, n. gen., with a triserial-biserial trending to uniserial arrangement of chambers is described in this family. Spiropsammiinae, n. subfam. is erected to include agglutinated foraminifers with fan-arranged, bulboid alveoles in planispiral or planispiral-uniserial chambers. Spiropsammia, n. gen. is described with two species: S. uhligi (Schubert) which has planispiral-uniserial chambers, and S. primula, n. sp. with only uniserial chambers. Two other species of agglutinated planispiral foraminifers with inner structures are also abundant in the Tertiary of West Africa: Reticulophragmium cf. venezuelanum and Hemicyclammina plana?. Some West African Cenozoic agglutinated foraminifers with inner structures: taxonomy, age and evolution

Alveovalvulinidae, n. fam., and Neogene diversification of agglutinated foraminifers with inner structures

Alveovalvulinidae, n. fam., is described for foraminifers with inner structures consisting of alveoli conjoined through tubiform connections. This family ranges from Early Miocene to Holocene, and includes the genera Alveovalvulina and Guppyella (= Alveovalvulinella). The family Liebusellidae is redescribed. Four groups of agglutinated foraminifers with inner structures reached their maximum diversification during the Early and Middle Miocene: Alveovalvulinidae, Pavonitinidae, Spiropsammia and the Cyclamminidae (Cenozoic). They occur chiefly in bathyal to abyssal sediments of tropical waters. Other minor groups of agglutinated foraminifers with inner structures, mainly relict Cretaceous genera, do not appear to follow the Early-Middle Miocene diversification. The geographic distribtltion of the Neogene agglutinated foraminifers is as follows: 1) Alveovalvulinidae occur only in the Caribbean and the Gulf of Mexico; 2) Pavonitinidae and Spiropsammia occur chiefly in West Africa and central Europe; and 3) Liebusella has been reported only from along the eastern sides of the continents.

Stratigraphy and Petroleum Possibilities of Middle Tertiary Rocks in Puerto Rico: DISCUSSION

Interpretation, stratigraphic nomenclature, age of rocks (biostratigraphy, foraminifera); separate discussions by Moussa and Seiglie, and by Meyerhoff; for reference to paper by Monroe, W. H., see Am. Assoc. Pet. Geol., Bull., Vol. 57, No. 6, 1973

Duquepsammiidae, a new family, and Duquepsammia, a new genus of agglutinated foraminifers

Duquepsammiidae, n. fam., includes only one genus, Duquepsammia, n. gen., of which Spiroplectoides cubensis is the type species. Duquepsammia is characterized by an inner structure in the biserial chambers and in the microspheric form by a relatively large number of chambers and whorls in the spiral stage. The megalospheric form is a homeomorph of Spiro- plectammina Cushman.

A comment on the foraminiferal genera Asterellina and Eoeponidella

Geographic distribution from Antarctica to England and Bering Sea, Asterellina junior synonym of Eoeponidella

Foraminifers and Continental Drift

The global distribution of Orbitolina along the tropical and subtropical belts of the world during the Early Cretaceous is interpreted as an ecological chance caused by absence of competition. Distribution and diversification of Late Cretaceous larger foraminifers in the Caribbean appear more closely related to ecology than to continental drift. No species of Discocyclinidae or Nummulites has been reported as common to the Eastern and Western Hemispheres during the Paleogene. In contrast to this, many species of Lepidocyclina are common to the Eastern and Western Hemispheres during the Oligocene and Miocene.