Ancient impact craters on Mars provide insights into the geological events and are time markers for studying global processes like colossal volcanism and fluvial activities. Among these craters, the 77 km diameter Morella Crater serves as a representative, capable of demonstrating diverse processes that acted on Martian terrain, and hence, the geological and geomorphological history of this crater is studied in detail. Despite its infilling, Morella hosts Ganges Cavus, a significant collapse structure, and Elaver Vallis, an outflow channel. We hypothesize the development of the crater through five stages, from its origin to its current denuded state, exhibiting diverse processes that determine the fate of Martian craters. Crater size-frequency distribution suggests a formation age of 3.8(-0.03)(+0.03) Ga for the plateau hosting Morella Crater and 3.6(-0.01)(+0.06) Ga for Morella Plains, the vast expansive plains within the crater. The occurrence of pyroxene and olivine in Morella Plains, identified through hyperspectral data, indicates impact-induced volcanism. The heat source associated with faulting and dike intrusion in the adjoining Ophir Catenae Structural Complex might have ruptured the confined cryosphere, resulting in the formation of Ganges Cavus and eventual filling of Morella with water, which subsequently breached to form Elaver Vallis at 3.4(-0.10)(+0.07) Ga. Hydraulic modelling reveals a floodwater volume of 3.27 x 10(12) m(3) and an estimated peak discharge of 3 x 10(7) m s(-1) associated with this event. Morella witnessed additional fluvial activity at 3.3+0.1 Ga that created the dark-toned channels. The extensive range of geological and geomorphological processes makes Morella Crater a promising location for future Mars missions.

The Cretaceous-Paleogene Boundary (KPB), the only known global impact ejecta layer, resulted from the Chicxulub Impact Event (66 Ma). KPB is well-documented across the different distal locations (paleodistances >5000 km), yet an understanding on the preservation of KPB remains evasive. Identification of the different preservation controls is thus quintessential, especially when the distal KPB maintains a constant thickness of 2-5 mm globally. We evaluate 84 distal KPB sites (as exposed on land today) through review and assessment of different parameters. The parameters include current geological provinces, nearest active tectonic boundary, geomorphic setting, lithological associations, paleoposition (at 66 Ma), paleodistance from impact point (at 66 Ma), paleoclimate and paleobathymetry. The most common geological province, closest plate boundary type and geomorphic setting are accretionary complex (43 sites), collisional boundary (53 sites) and bedrock mountain (35 sites), respectively. KPB layer manifests in different lithologies, but most commonly in clay, marl, clay limestone, and clay-marl dominant litho-units. At 66 Ma, 68 KPB deposited in marine settings, meanwhile only 16 in terrestrial conditions. Cenozoic paleobathymetry depicts the increased exposure of KPB sites to non marine settings as time progresses (Paleocene-Holocene). During Cenozoic, the warm temperate climate remains the dominant climate across majority of the distal KPB sites. Evaluation of the different parameters leads to the conclusion that the preservation of KPB is aided by deposition within sedimentary basins in marine conditions during early Paleocene, presence of thick sedimentary units overlying KPB and dominance of low-denudational climates (warm temperate/subtropical arid) during Cenozoic. Furthermore, the study weighs the Chicxulub ejecta transport mechanisms by assessing the different chemical (Ir-anomaly, boundary clay) and physical attributes (impact spherules, shocked minerals, Ni-rich spinels) at KPB. The observations support the dust cloud (non-ballistic) model of ejecta transportation and emplacement over the ballistic ejecta plume model.

Ramgarh structure in western India, with its nearly circularshaped topographic high, has captivated geologists since the nineteenth century, but with the recent studies confirming its impact origin.Ramgarh crater lies in a flat sedimentary terrain within the vast soil-covered plains of Neoproterozoic Vindhyan Supergroup.This study utilized multi-proxy approach through petrographic, and geochemical evidences to ascertain Ramgarh's impact origin and thus to provide more convincing evidence.From the petrographic study, the lithounits show multiple cracks, intense fracturing, the growth of shock-induced micro-fabrics like breccia, PFs, and PDFs, melted quartz grains, diaplectic quartz glass, and amorphous and vitrified matrix, all of which are strong indicators of an impact origin.Geochemically, the Cr, Ni, and Cu concentrations in the lithounits are high, and the chondrite normalised values that correspond to these concentrations show noticeably higher levels than the crustal average, indicates its interaction with an extra-terrestrial object.Inter-elemental ratios show positive correlation suggesting that the possible impactor is a differentiated achondrite.Furthermore, the zircon U-Pb geochronological study revealed small discrepancy in Pb isotopic ratios with large concentrations of U, which corresponds to the age between 528 and 395 Ma, and hence the impact event is postulated within this age limit.This age falls within the range of the mid-Ordovician Meteor Event (OME) (467.5 ± 0.28 Ma) and is substantially closer to the Precambrian-Cambrian Boundary Thus, the Ramgarh crater age can be further constrained to non-OME duration, as the latter event is associated with a L-Chondrite impactor, unlike the differentiated achondrite impactor at Ramgarh.

As impact cratering is regarded as the most fundamental process in the modification of planetary surfaces, it is crucial to investigate and identify terrestrial impact craters with credible evidences to learn more about the planet's evolutionary path. Consequently, terrestrial impact craters are considered as proxies for planetary explorations. However, because of the diversity of the lithologies the terrestrial craters are carved in, those in basaltic rocks, which make up the majority of planets, are thought to be the best candidates. Lonar Impact Crater in India is a well-preserved, simple bowl-shaped impact crater that is etched in tholeiitic basalt of the -65 Ma Deccan Volcanic Province (DVP). The crater has a diameter of 1.88 km and a depth of -150 m. Being a basaltic target and situated in warm temperate climatic zone, apart from the modern-day anthropogenic influence, the crater is subjected to denudation. One such study has quantified a cumulative rim erosion of 30 m and an erosion rate at 96-203 mm per kyr, indicating fast denudation of the crater.Several methods were employed to date the impact event and based on the recent in-situ cosmogenic radionuclide dating, the age is determined as 37.5 & PLUSMN; 5.0 ka. The tholeiitic flood basalt target rock at Lonar exhibits high total iron (26.25 wt%) and CaO content (9.97 wt%) with lower contents of Al2O3 (13.21 wt%) and MgO (5.96 wt%). Based on the Ni (-60 to 2500 ppm), Cr (27 to 618 ppm), and Co (38 to 196 ppm) geochemistry of sub-mm sized Lonar spherules, the most likely projectiles associated with the cratering event are the chondritic impactors. The Mesoarchean age (-3.0 to 3.1 Ga), yielded by a few zircon grains separated from an impact meltbearing breccia together with the exotic quartz grains with impact features like planar deformation feature, which is unfamiliar in a basalt-dominated impactite, proved the incorporation of the deep-seated Archean Peninsular gneiss in the impact event. This demonstrates a depth penetration of 522-570 m for the impact. However, compared to the extent of ejecta seen in comparable younger craters on the Moon and Mars, where ejecta can travel up to distances of -10R and - 15R, respectively, the expanse of spallation from the terrestrial Lonar crater is only visible in a smaller area (-3R). In the entirety, Lonar crater has been explored by many researchers, which have uncovered many aspects of the impact including ejecta particles, structural, magnetic, hydrological, and geophysical characterization. In order to better understand the cratering mechanism and characteristics of Lonar impact crater, this review paper aims to garner information from all the relevant literature and this compendium will act as a comprehensive synthesis that will reshape our understanding of not only Lonar impact crater but also the broader realms of impact cratering science.

The Luna structure of India has been rumored to be an impact crater for more than a decade without any convincing evidence. This structure (1.5-1.8 km) is prominently visible in the low-lying Banni Plains of the tectonically active Kutch Basin as a circular morphological feature with a less-prominent rim. Luna area is strewn with melt-like rocks having high specific gravity and displaying wide range of magnetic properties. It contains minerals like wustite, kirschsteinite, ulvo center dot spinel, hercynite, and fayalite. The whole rock analysis denotes PGE enrichment, with notably higher average concentrations of Ru (19.02 ppb), Rh (5.68 ppb), Pd (8.64 ppb), Os (6.03 ppb), Ir (10.63 ppb) and Pt (18.31 ppb). The target is not exposed at Luna, owing to the overlying thick sequence of Quaternary sediments. The mineralogical and geochemical signatures points to an impact into a target, which is rich in clay with elevated calcium and silica (sand/silt) content. Geochemical data suggests an iron or stony-iron meteorite as the potential projectile at Luna. The silt layer containing plant remnants, underlying the strewn layer, yielded a radiocarbon age of 6905 years, making Luna the biggest crater to result from an iron bolide within the last 10,000 years.

The Kaladgi Basin is one of the several Proterozoic sedimentary basins of India. This basin has a binary evolutionary history with an angular unconformity separating the older deformed and younger undeformed rock sequences of the Kaladgi Supergroup, named the Bagalkot and Badami Groups, respectively. The Bagalkot Group is known to be of late Paleoproterozoic-Mesoproterozoic age. However, the timings of deposition of the Badami Group sediments and the closure of the basin have been speculative. We carried out C-O-Sr isotope studies of the marine carbonate successions of this basin namely Chitrabhanukot, Chikshellikeri, Lakshanhatti (Bagalkot Group), and Konkankoppa (Badami Group). Our results indicate that δ13C of all the carbonate formations have preserved the primary marine signature. Restricted variation of δ13C in the carbonates of the Bagalkot Group (0 ± 2 ‰) suggests a steady state organic carbon burial; whereas, much wider range of variation of δ13C in the Konkankoppa Limestone of Badami Group (-2.2 to + 3.5 ‰) hints at a dynamic organic carbon burial scenario. These signatures are consistent with the C-isotope stratigraphy of the Meso-Neoproterozoic times. The 206Pb-207Pb dating of the youngest unit of the Kaladgi Supergroup, the Konkankoppa Limestone yielded a depositional age of 604 ± 25 Ma. This age, considered together with the primary 87Sr/86Sr ratio of 0.70781, extends the active sedimentation of the Badami Group well into the Ediacaran Period. These data confirm the existence of a long duration depositional hiatus, of >500 million years, between the Bagalkot and the Badami Groups. Results of this study also refutes the claim that the sedimentation in most of the Proterozoic basins of peninsular India ended by 1000 Ma.

•Ancient impact-generated subsystem of Valles Marineris on Mars.•Evidence of fluvial and aeolian processes on the wall of this impact structure.•The catastrophic inundation and aeolian processes eroded the inselbergs.•An evolutionary model is proposed.

The surface of the earth is continuously modified by the action of various active geological agents, and one of the resultant is erosion. Climate, lithology, slope, precipitation, temperature, vegetation and anthropogenic activities are the chief controlling factors of erosional processes. The rate of erosion associated with various geomorphological features has been estimated using several different methods. Meteorite impact craters being a positive relief feature, formed by an impetuous process, thus, is an ideal candidate for quantifying the rate of erosion. Several authors have attempted to quantify the erosion rate with the availability of scanty number of terrestrial impact craters. In this study, apart from taking into account other factors, paleoclimatic parameters have been incorporated to estimate the erosion rate of simple impact craters. The rate of erosion has been quantified in selected terrestrial simple impact craters considering the influence of various climatic zones traversed by the crater in relation to its topographical parameters and the geological province where the crater is located. The temporal range of each crater in distinct paleoclimatic zoneshave been derived to better constrain the influence of climate on erosion. The rate of erosion of the region hosting the impact craters and the individual crater are estimated separately using different methods. In the first method, the relief of the geological province where the crater is located is considered and in the second method, the initial relief of the transient impact crater is calculated using a set of crater morphological parameters. The estimated values of erosion rates of craters are correlated with the published works. The values are found to be similar except for the older craters, which we believe due to the large uncertainties associated with paleoclimatic data. Difference in the erosion rates of older craters can also be attributed to dynamic evolutionary trends of terrestrial simple impact craters pertaining to the influence of various regional elements in the vicinity of the crater including the drainage, tectonic activities, precipitation, temperature and lithology.

WITH THE AID OF PALAEOCLIMATE DATA. Saranya R. Chandran, Devika Padmakumar, Shania James, Varsha M. Nair, Subhami Mohan, K.S.Sajinkumar, Department of Geology, University of Kerala, Thiruvananthapuram 695581, Kerala, India (saranyarchandran.geo@keralauniversity.ac.in); Physical Research Laboratory, Navrangpura, Ahmedabad 380009, Gujarat, India; Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI 49931, USA.

Lonar Impact Crater is a simple meteorite impact crater carved out on the 65 Ma old Deccan tholeiitic flood basalts. The crater, though scoured in a basaltic terrain, is still preserved in its most pristine form, with a central crater lake. The geomorphology, geochemistry, geochronology, hydrology, geophysical parameters, and structural aspects of Lonar Crater have been explored in detail, but still continue to contribute valid scientific insights into the geology of terrestrial impact craters. Lonar serves as a potential analog site for studying impact cratering on planetary surfaces with basaltic terrains such as the Moon and Mars. Besides being a highly recognizable impact crater in India, the Lonar crater and its hinterland stand out with its archeological relevance and spiritual influence among the people. The numerous temples in and around the crater premises uphold the cultural significance of the region. The crater and adjacent areas are rich in flora and fauna representing a diverse ecosystem in the vastness of the arid Deccan Flood Basalts. Hence, the astrobleme and its surrounding is declared a Ramsar site and is also a protected wildlife sanctuary. The Indian Government has also declared the crater a National Geological Monument as well as an archaeological monument. Furthermore, the astrobleme is a unique site with socio-cultural and economic significance. With these plethoras of importance, combined with the geological and socio-cultural aspects in its hinterland, together with the most acclaimed UNESCO world heritage centers Ajantha and Ellora caves in the neighborhood, it stands as the right candidate for a UNESCO Global Geopark. However, the crater and its ecosystem are not preserved well enough, and the uniqueness of the crater is diminishing. But after selection as a Ramsar site, the area shows increased vegetation growth. The SWOT analysis conducted in this study accounts for Lonar Crater and its adjoining areas as a potential global geopark. Thus, through this study, we try to propagate the vivid and myriad importance of the Lonar crater and the necessity of protecting this geological monument from both anthropogenic and natural processes and to appraise the necessity for nominating this area as a UNESCO Global Geopark.

The impact origin of Ramgarh crater in India has been a topic of debate for several decades due to its conspicuous morphology, with recent studies confirming the structure as a complex impact crater. In this work, we present the results from an integrated petrographic and geochemical study to evaluate the impact origin of the crater, in conjunction with introduction of a new geochronological data for the crater through zircon U-Pb systematics. Petrographic studies of the target Vindhyan sedimentary rocks show the presence of shock fabrics such as planar fractures, decorated planar deformation features, brecciation, melted grain boundaries, diaplectic glass, and vitrified matrix. Geochemically, the lithounits have high concentrations of Cr, Ni, Cu, and the corresponding chondrite normalized values show notably elevated levels than crustal average. The elevated levels of Cr, Ni and Cu in the target rocks indicate its interaction with an extra-terrestrial object. The positive correlation between Ni and Co, higher concentration of Cr (9-623.35 ppm), and more importantly the average Ni/Cr (-0.006- - 1.3), Ni/Co (-1.8 to -22) and Cr/Co (-57--368) ratios in the target lithounits of Ramgarh, point to a differentiated achondrite being the possible impactor. The zircon U-Pb geochronological data from two samples in this study do not show significant Pb-loss and U enrichment. However, the relatively younger age of 528-395 Ma, depicted by quartzite sample (AN-4), along with the discordance and distinguishable Pb-loss, might hint that the impact event at Ramgarh have occurred between this timeframe. This age is considerably closer to the PrecambrianCambrian Boundary (543 Ma) and, it also encompasses the age corresponding to the mid-Ordovician Meteor Event (OME) (467.5 +/- 0.28 Ma). As this study infers that the potential impactor at Ramgarh is a differentiated achondrite and not a L-chondrite, the OME age can be ignored, further narrowing the age of Ramgarh impact structure. Our study also confirms the Ramgarh structure as an impact crater, and constrains the possible timing of the impact.

The paleo-positions of terrestrial meteorite impact craters along with distance and displacement registered since formation due to plate tectonics were deciphered using GPlates, an interactive GIS-based plate tectonic recon-struction and modeling software. The results of the study are intriguing as several craters have traversed across the globe, both from the Eastern to Western hemisphere and from the Southern to Northern hemisphere, and vice versa. The oldest crater studied was Foelsche, which traversed from the Southern to Northern hemisphere and from the Western to Eastern hemisphere while covering a distance of 39080 km in the past 981 million years and recording a relatively shorter displacement of 10470 km. On the other hand, Ja euro nisja euro rvi and Suvasvesi South have traveled longer distances (27781 and 29050 km, respectively) and are among the most displaced craters (17400 and 16988 km, respectively). Similarly, the paleo-position, distance, and displacement for all craters, with ages <1100 Ma, were computed in the study. Based on the derived paleo-position, we have accessed the possibility of any selective distribution of craters across different latitudinal segments. As Earth is a planet that recorded dynamic variations in the terrestrial surface area across different geological ages, calculating the same was an arduous task. The land area within each of the three latitudinal segments, viz. 0-30 degrees, 30-60 degrees, and 60-90 degrees, in which a crater formed was calculated for the geological time corresponding to an impact cratering event. This calculated land area within the respective lat-itudinal zone at each instance of a crater's formation was then compared with the total land area on Earth. The results showed that 0-30 degrees and 30-60 degrees segments have equal crater frequencies whereas the 60-90 degrees segment has a lesser frequency. The latitudinal crater distribution on Earth was then compared with Moon and Mars. The results revealed that there is a non-selective distribution of terrestrial impact craters across different latitudinal segments, indicating a non-perceivable latitudinal dependency for impact events.

The paradigm of plate tectonics has aided in the identification of the journey of continents on the globe, their assembly into supercontinents, disruption, and re‐assembly. Here, we use meteorite impact craters as proxies for tracking the voyage of lithospheric plates. Employing the provisions in GPlates, an interactive geographic information system‐based plate tectonic reconstruction model, we were able to identify the palaeo‐position, and velocity of the 174 terrestrial impact craters, formed after 1,100 Ma, across the globe. These parameters of craters were evaluated for independent tectonic plates and were correlated with global tectonic events. For example, the similarity in the velocity of Beaverhead (900 Ma) and Holleford (550 Ma) craters since 550 Ma is traced to the connection between the Eastern Basin and North America Craton commencing 1,100 Ma, and through the South Basin and Range. Likewise, the drastic reduction in the velocity of Spider Crater (700 Ma) in Australia after 600 Ma can be attributed to the subduction between east and west Gondwana. The accelerated motion of the Indian Plate at 63 Ma, when the lithosphere was hovering over the Réunion hotspot, is also explained. With the advent of more improved plate tectonic models and the discovery of more impact craters, improvised interpretations will be possible.

Context and Design: The speciality of periodontology has been evolved with leaps and bounds in all aspects ranging from advances in diagnostic aids to use of growth factors and periodontal regeneration techniques in treatment, thus making speciality per se reach new heights. Moreover, with development of technology, periodontal treatment is freely accessible to general dental practitioners. However, knowledge of periodontal diagnosis and treatment is usually limited to undergraduate level and most of times private practice deals only with chief complaint of patient. Aim: Evaluate the knowledge and perception of general dentists towards periodontal treatment. Materials and Methods: The study involved a survey for 50 practicing general dentists having their clinics in Hubli-Dharwad city with qualification of Bachelor of Dental Surgery only. A pre-tested close ended questionnaire was distributed comprising of 20 questions and knowledge, perception levels were assessed. Statistical Analysis used: Percentage-wise distribution of responses to various questions was used. Results: Although 90.4% of general dentists did believe in the success of periodontal treatment and did recommend their patients to undergo various periodontal treatment procedures, 88.5% of the dentists performed most of periodontal surgeries and phase I therapy on their own. 78% of dentists referred cases to specialist only for grafting, ridge augmentation and dental implant procedures. About 71.2% of dentists considered gingival health for prosthetic considerations and 94.2% of them did evaluate periodontal condition before referring case for orthodontic treatment. It was noted that 84.6% of dentists followed up periodontal cases as a part of maintenance phase and 57.7% of them did attend CDE program regarding consequences periodontal disease progression and its treatment outcomes in past 1 year. Conclusions: In this study, dentists reported rendering nonsurgical and surgical periodontal therapy on a wi