Joseph E. Hazel

Age and correlation of emerged pliocene and pleistocene deposits, U.S. Atlantic Coastal Plain

Abstract Paleontologic and paleomagnetic investigations were conducted on several hundred Pliocene and Pleistocene marine samples from five regions of the emerged Atlantic Coastal Plain: (1) the Delmarva Peninsula, (2) eastern Virginia, (3) central and northern North Carolina, (4) southern North Carolina and northeastern South Carolina, and (5) the Charleston area, South Carolina. Molluscan and ostracode interval and assemblage zonations, which are the primary means of regional correlation, have been calibrated using planktic biochronologic, paleomagnetic, radiometric and amino-acid recemization data. These multiple dating criteria were used to determine the age and, where possible, the duration of marine transgressive/regressive sequences. A correlation chart illustrates the age relationships of 27 formations from five regions. One important conclusion is some of the Yorktown Formation of Virginia and North Carolina (including the “Duplin” Formation), and some of the Raysor of South Carolina are late Pliocene in age. The late Pliocene Chowan River Formation of North Carolina is older than the early Pleistocene Waccamaw Formation of South Carolina, which in turn may be older than the James City Formation of North Carolina. During the last 1.0 million years, multiple marine transgressions occurred in each region, but the age of these middle and late Pleistocene formations often may differ from one area to the next. A significant result of the study is the evidence for the lack of time equivalence of formations in the five different regions; that is, the sequence of marine transgressions in one region does not necessarily correspond to that in another. This appears to be the result of differing subsidence and uplift histories, the patchiness of the depositional record, and the limitations of the dating techniques in light of the rapidity and frequency of sea-level fluctuations.

Ostracodes and chronostratigraphic position of the Upper Cretaceous Arkadelphia Formation of Arkansas

ABsTRACr-The ostracode assemblage of the Arkadelphia Formation, upper Maastrichtian, of southwestern Arkansas is characterized by a well-preserved, relatively diverse, and abundant fauna representing 36 podocopid species and an undetermined number of species of the platycopid genus Cytherella. Thirteen of these account for 85 percent of the fauna. The dominant forms are Cytherella spp., Brachycythere rhomboidalis (Berry, 1925), Haplocytheridea renfroensis Crane, 1965, Haplocytheridea bruceclarki (Israelsky, 1929), and Brachycythere ovata (Berry, 1925), which account for about 57 percent of the specimens found. Other species that are less common, but are characteristic of the Arkadelphia, are Antibythocypris macropora (Alexander, 1929), Ascetoleberis hazardi (Israelsky, 1929), Aversovalva fossata (Skinner, 1956), Brachycythere ledaforma (Israelsky, 1929), Curfsina communis (Israelsky, 1929), Cytheromorpha arbenzi (Skinner, 1956), Escharacytheridea micropunctata (Alexander, 1929), and Veenia arachoides (Berry, 1925). The ostracode assemblage indicates that the Arkadelphia was deposited in the inner sublittoral zone. The species Veenia parallelopora (Alexander, 1929) and Brachycythere foraminosa Alexander, 1934, are restricted to the Arkadelphia Formation and allow correlation with other Gulf Coastal Plain Upper Cretaceous units. A new ostracode interval zone, the Veenia parallelopora Zone, is proposed. This zone divides the Platycosta lixula Zone. Calcareous planktic microfossils reported from the Arkadelphia and its correlatives in the Veenia parallelopora Zone indicate that these deposits are late Maastrichtian in age, not middle Maastrichtian as some authors have thought.

Shared versus derived characters in the pore-system of Loxoconcha (Ostracoda, Crustacea)

Ontogenetic development of the pore-systems of two species of Loxoconcha, phytal L. japonica and bottom-dwelling L. uranouchiensis, were examined. Adult pore-systems differ between the two species in number and distribution of “smooth”-type bristles, the basal structure of “twisted”-type bristles and the existence of microhairs. These specific features start to differentiate after the A-2 or A-3 juvenile stage, a fairly late moulting stage, and continue to differentiate until the adult stage. These characters are identified as lower phylogenetic ones based on the ontogeny-phylogeny relationship. The result is consistent with the estimate that the characters were regarded as adaptive and specialized through the consideration of their function to the respective habitats. The mode of increase of the two types of pore-systems was revealed. The “twisted”-type bristle, whose number is common between the two species at all stages, reaches the final number, except for one, at the A-3 juvenile stage. In contrast, the “smooth”-type bristle continues to increase in number until adult stage, and, as mentioned above, the specific differences become more obvious as the moulting stages advance. This type of pore-system is valuable for specific differentiation. Two types of pore-system that differ from each other in the pattern of increase were recognized in other ostracod taxa. The two types of pore-systems have different significance in ostracod taxonomy and the recognition of the type is indispensable for future taxonomy.

Pseudomorphs of impact spherules from a Cretaceous-Tertiary boundary section at Shell Creek, Alabama

Abstract During a biostratigraphic investigation of a Cretaceous-Tertiary boundary section at Shell Creek, Alabama dark green spherules with distinctive morphologies were serendipitously found in the lower Danian basal Clayton sand. With the exception of in the upper 30 cm, they were found throughout the sand, upwards from an erosional contact separating the sand from the underlying upper Maastrichtian Prairie Bluff Chalk. Additional studies revealed that the spherules exhibit the morphologies of splash-form tektites and that their original composition has been altered to a smectite external layer with a calcite core. The presence of spherules with similar morphologies and size distribution in K-T boundary sections at Beloc (Haiti) and in Arroyo El Mimbral (northeastern Mexico) leads to the deduction that the Shell Creek spherules represent altered impact ejecta. Impact glasses, Ni spinels and shocked mineral grains were searched for extensively, but intense alteration and dilution by detrital quartz sand have made it unlikely that such supporting evidence of an impact origin will be found at this site. Nonetheless, the large sizes of the microtektite pseudomorphs, which are well over 1 mm in diameter, and abundance (the total fluence is about 2 g/cm2), makes this location an important corroboration of a proximal site for the K-T impact.

Revised Sequence Stratigraphic Interpretation of the Eocene-Oligocene Boundary Interval, Mississippi and Alabama, Gulf Coast Basin, U.S.A.

ABSTRACT Examination of regional stratigraphic relationships and graphic correlation of biostratigraphic data from two important localities has resulted in a new interpretation of the sequence stratigraphy of the Eocene-Oligocene boundary interval in Mississippi and Alabama. The much-studied section at St. Stephens Quarry in southwestern Alabama does not contain all of the components of the depositional sequence. At St. Stephens, the highstand systems tract is missing and is represented by a marine hiatus (condensed section) at the top of the Upper Eocene Shubuta Clay. As a consequence, the surface of maximum starvation and the overlying sequence boundary are merged. Lowermost Oligocene sediments, which were deposited in the lowstand systems tract, rest on this maximum flooding surface / seque ce boundary. These findings agree with those from other parts of the Gulf Coast where the Eocene-Oligocene boundary has been recognized as a sequence boundary associated with a subaerial unconformity and a downward shift in coastal onlap. Revision of the sequence stratigraphic interpretation at St. Stephens Quarry alleviates much of the confusion concerning the relationship between the Eocene-Oligocene boundary and the sequence boundary. This new interpretation shows that not all sections contain all components of a particular depositional sequence and that caution is warranted when sequence stratigraphic interpretations are used to evaluate observations. The sequence stratigraphic interpretation of the section at St. Stephens has undergone revision as new observations have become available.

The North American Genus Climacoidea Puri, 1956, and the Tribe Campylocytherini (Neogene and Quaternary)

The genera Reticulocythereis Puri, 1960, and Climacoidea Puri, 1956, which occur in Pliocene to Holocene marine deposits of the Atlantic and Gulf Coastal Plain, have been examined and found to possess a vertical row of four adductor muscle scars and two frontal scars, a carapace that is subovate in lateral view and widest behind the middle, and an amphidont hinge having a conical anterior tooth in the right valve. These and other characteristics indicate placement in the North American ostracode tribe Campylocytherini. Climacoidea and Reticulocythereis differ from one another and from the campylocytherine genus Proteoconcha Plusquellec and Sandberg, 1969, only in details of carapace ornament. We propose that Proteoconcha and Reticulocythereis be relegated to subgenera of the genus Climacoidea. As do other genera of the tribe, species of Climacoidea inhabit inner sublittoral to brackish environments in mild-temperate to subtropical waters. Two new species C. (Reticulocythereis) foresteri , and C. (Reticulocythereis) reticulata are diagnosed.