Evidence of the Cretaceous-Paleogene (K-Pg) extinction can be seen across the Mississippi Embayment, however research examining the K-Pg boundary in the state of Mississippi is lacking. The objective of this study addresses how macrofauna changed across the K-Pg boundary in Oktibbeha County, Mississippi and subsequent comparison to other Early Paleogene and Late Cretaceous benthic marine macrofaunal localities. Comparison included previously collected material as well as specimens collected during this study in order to reconstruct the biological community living on the seafloor in the earliest Paleocene Mississippi Embayment. The primary fauna present after the K-Pg extinction was mainly composed of small suspension and deposit feeding oysters and clams as well as carnivorous gastropods. New Paleocene fauna and survivor species exhibited drastically smaller body sizes than organisms in the Cretaceous; postulated to be due to a relative decrease in primary producers and environmental nutrients.

Most major Phanerozoic mass extinctions induced permanent or transient changes in ecological and anatomical characteristics of surviving benthic communities. Many infaunal marine organisms produced distinct suites of biogenic structures in a variety of depositional settings, thereby leaving an ichnological record preceding and following each extinction. This study documents a decrease in burrow size in Thalassinoides-dominated ichnoassemblages across the Cretaceous-Paleogene (K-Pg) boundary in shallow-marine sections along the Atlantic Coastal Plain (Walnridge Farm, Rancocas Creek, and Inversand Quarry, New Jersey) and the Gulf Coastal Plain (Braggs, Alabama and Brazos River and Cottonmouth Creek, Texas). At New Jersey sites, within a regionally extensive ichnoassemblage, Thalassinoides ichnospecies (isp.) burrow diameters (DTh) decrease abruptly by 26-29% (mean K=15.2 mm, mean Pg=11.2 mm; n=1767) at the base of the Main Fossiliferous Layer (MFL) or laterally equivalent horizons. The MFL has been previously interpreted as the K-Pg boundary based on last occurrence of Cretaceous marine reptiles, birds, and ammonites, as well as iridium anomalies and associated shocked quartz. Across the same event boundary at Braggs, Alabama, DTh of simple maze Thalassinoides structures from recurring depositional facies decrease sharply by 22% (mean K=13.1 mm, mean Pg=10.2 mm; n=26). Similarly, at the Cottonmouth Creek site, Texas, Thalassinoides isp. occurring above the previously reported negative £_13C shift and the first occurrence of Danian planktonic foraminifera are 17% smaller in diameter (mean K=21.5 mm, mean Pg=17.9 mm; n=53) than those excavated and filled prior to deposition of a cross-bedded, ejecta-bearing sandstone complex commonly interpreted as the Chicxulub ¡¥event deposit¡¦. At both of these impact-proximal regions, the Cretaceous and Paleogene burrows were preserved in similar lithologies, suggesting that a reduction in size cannot be attributed to sedimentological factors. At all localities, up-section trends in DTh are statistically significant (fÑfnf¬0.05; non-parametric Kruskal-Wallis test). Using the burrow diameter as a proxy for tracemaker body size, a reduction in DTh above the K-Pg boundary likely reflects dwarfing within the post-extinction community of decapod crustaceans. Dwarfing during the early recovery stages of the end-Cretaceous mass extinction, as recorded by ichnofossils, occurred within glauconite-producing (New Jersey), carbonate (Alabama), and siliciclastic (Texas) depositional environments and appears to be widespread. Because this ichnological signal appears to be a general phenomenon across the crisis interval, trace-fossil analysis provides a potential in-situ field method for constraining and correlating the stratigraphic position of the K-Pg and other extinction events, particularly in the absence of other macroscopic, microscopic, and geochemical indicators. Whereas overprinting of the original marine ichnofabric by morphologically similar continental traces is not a concern in lithified sections of Alabama and Texas, such an occurrence must be considered within unconsolidated sections. Within the Hornerstown Formation of New Jersey, a pervasive Thalassinoides framework contains traces of burrowing bees and wasps. Due to their penetration of up to 1 m, excavations just beyond the weathering front are insufficient for exposing the original marine ichnofabric. Insect burrow diameters (7-25 mm) are within the range of Thalassinoides traces (4-31 mm), exhibit occasional branching, and lack of ornamentation (bioglyphs) on the burrow walls. Therefore neither size nor gross morphology are adequate for distinguishing these widely diachronous and unrelated ichnites, especially when the insect burrows have been filled. However, the presence of backfill menisci and a beige clay halo help distinguish the ancient marine burrows, whereas highly oxidized fill and the occurrence of a terminal brooding chamber are diagnostic of modern insect burrows. / Geology

An integrated micropaleontological, mineralogical and sequence stratigraphical investigation was carried out across the Cretaceous/Paleogene (K/P) boundary in the Haymana basin, Turkey. A 29.41 m thick boundary section consisting of limestones and marls was measured and 90 samples were analyzed. Biostratigraphic and chronostratigraphic works are based on the planktonic foraminifera. 64 planktonic species were identified and 5 biozones were established. The biozones are, in ascending order, Planoglobulina acervulinoides zone, Racemiguembelina fructicosa zone, Pseudoguembelina hariaensis zone for the Late Maastrichtian / Guembelitria cretacea (P0) zone and Parvulorugoglobigerina eugubina (P1a) zone for the Early Danian. In order to detect the mineralogical changes across the boundary bulk and clay minerals were analyzed using X-ray diffractometry (XRD). Calcite, quartz,feldspar and the clay minerals composed of smectite (montmorillonite) and chlorite are the main components of the rocks. A decrease in calcite and an increase in the detrital minerals (quartz, feldspar) and the clay minerals were detected in the boundary beds. In order to find out the depositional history of the area a detailed microfacies study was performed and 10 microfacies type were determined. The microfacies types defined correspond to slope to basin environment. Based on microfacies analyses, the sequence stratigraphic framework of the boundary beds was constructed. K/P boundary beds were recorded in the transition of transgressive systems tract to highstand systems tract, coinciding with a maximum flooding surface. These beds show a similar pattern with many other K/P boundary beds in different locations of the world indicating eustatic sealevel variations overprint the tectonic control in the basin.

Aus Patagonien lagen bisher wenige Daten zu paläoökologischen Veränderungen und zur Paläobiodiversität an der Kreide-Paläogen (K/Pg)-Grenze vor. Um diese Lücke zu schließen, wurden in den argentinischen Provinzen Neuquén und Chubut zahlreiche Profile im Bereich der K/Pg-Grenze detailliert beprobt. Während einer Planktonkrise, wie sie für die K/Pg-Grenze angenommen wird, werden für benthische Mollusken folgende Entwicklungen erwartet: 1. eine Abnahme der Individuenzahlen der Benthosorganismen, 2. eine Abnahme der vom Plankton als Nahrungsquelle direkt abhängigen Organismen, 3. eine Abnahme der Benthonten mit planktotrophen Larvalstadien, 4. eine Abnahme der mittleren Körpergröße der Individuen benthischer Faunengemeinschaften und 5. eine Abnahme der Organismen mit hoher Stoffwechselrate bzw. aktiver, mobiler Lebensweise. Tatsächlich waren die hungerresistenten Gruppen der Nuculoida (flach-infaunale Depositfresser) und der Lucinidae (Chemosymbionten) im Danium signifikant häufiger als im Maastrichtium, während der Faunenanteil der Suspensionsfresser im Danium im Vergleich zum Maastrichtium signifikant niedriger ist. In den Faunengemeinschaften des Daniums von Bajo de Añelo konnten Abnahmen der Individuenzahlen, der mittleren Mobilität und der mittleren Größe festgestellt werden. Die beobachteten paläoökologischen Veränderungen zeigen somit eine Selektivität, die sich auch in der Paläobiodiversitätsdynamik widerspiegelt. Auch hier sind Suspensionsfresser, die direkt vom Planktonangebot abhängig sind, stärker betroffen als Chemosymbionten und flach-infaunale Depositfresser. Die Aussterberaten für Bivalven sind mit 28% moderat. Insgesamt sind die festgestellten Selektivitätsmuster konsistent mit den zu erwartenden Folgen einer Planktonkrise. Trotz einiger regionaler Unterschiede handelte es sich um ein globales Ereignis an der K/Pg-Grenze, das Nord- und Südhalbkugel gleichermaßen betroffen hat. / From Patagonia only a few data on palaeoecological changes and on palaeobiodiversity at the Cretaceous/Paleogene (K/Pg)-boundary are available so far. Therefore detailed samples in different K/Pg-sections in the Argentinian provinces of Neuquén and Chubut were taken to increase the data set for this region. The following trends are expected from a crisis of primary productivity in the aftermath of the K/Pg-boundary: 1. a reduction in the number of individuals of benthic organisms, 2. a decrease in the relative abundance of organisms which rely directly on photosynthesis, 3. a lower proportion of individuals with planktotrophic larval stages, 4. a reduction in the average body size of individuals within palaeocommunities and 5. an increased abundance of organisms with low metabolic rates or inactive lifestyles. In fact the proportion of the starvation-resistant groups of the Nuculoida (shallow-infaunal deposit feeders) and Lucinidae (chemosymbionts) were significantly higher in the Danian compared to the Maastrichtian. In contrast to this, the proportion of suspension feeders in the palaeocommunities was significantly lower in the Danian in comparison with the Maastrichtian. In the Danian benthic assemblages of the Bajo de Añelo area, a decrease in number of individuals, mean mobility and mean size was recognised after the K/Pg-boundary. Thus the palaeoecological changes display a selectivity, which is also reflected in the palaeobiodiversity. Suspension feeders, which depend directly on plankton particles from the water column, show higher extinction rates than chemosymbionts and shallow-infaunal deposit feeders. The extinction rates of Patagonian bivalves are moderate (28%). Overall, the recognized selectivity patterns are consistent with the expected aftermath of a crisis in primary productivity. Despite some local differences, the results argue for a global event at the K/Pg-boundary during which the northern and southern hemispheres were similarly affected.